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The sedimentology of Middle Holocene tsunami facies in northern Sutherland, Scotland, UK
Abstract
Lagoonal sediments attributed to the main Holocene marine transgression in Strath Halladale, northern Sutherland, contain a complex coarser layer believed to have been deposited during the tsunami associated with the Second Storegga Slide off South West Norway. The coarser sequence is dated at between 7590±50 and 7290±50 radiocarbon years BP (6507–6260 cal BC and 6228–6029 cal BC). Detailed stratigraphical analysis has determined a distinctive suite of sedimentary sub-units within the coarser layer in marked contrast to the sediments, which occur above, and below. A pronounced erosional unconformity with the underlying sediments is recorded with the base of the tsunami layer characterised by eroded material from the underlying peat. The presence of a mixed diatom assemblage, although fragmentary, indicates a chaotic accumulation of the deposit with all habitats represented. Variations in particle size within the sequence disclose striking similarities with those from contemporary tsunami deposits. The run-up of the tsunami sediments is calculated at a minimum of 4.6 m. This is the first occasion on which a deposit of the Second Storegga Slide tsunami has been found outside the North Sea basin and indicates that the area affected by the tsunami may have been larger than has been previously described.
... The characteristics of this tsunami sand layer are its content of planctonic microfossils in contrary to littoral deposits that would have a bentic, shallow-water micro fauna and flora. We use this technique (Dawson, 1999;Dawson & Smith, 2000) in the analyses of the Swedish tsunami beds. ...
... The diatom content of the tsunami sand contains planctonic deep-water species from the open Lake Ancylus basin (Aulacosira islandica, Aulacosira ambigua, Alacosira italica, Aulacosira arenaria, Gyrosigma attenuatum, Fragilaria construens, etc.). This implies the same tsunami bed characteristics as recorded in Scotland (Dawson, 1999;Dawson & Smith, 2000). We believe that this is a good methodology of identifying tsunami beds, and discriminate them from littoral beds. ...
... In Scotland, there are excellent records of the Storegga tsunami. The identification of planctonic deep-water species (not shallow-water bentic or lagoonal species) in the tsunami sand layers offers means of discriminating its origin as to a tsunami wave deposit and not a shallow sea deposit (Dawson, 1999;Dawson et al, 2000). In Sweden, we have identified a very high number -17 -of past tsunami events. ...
... In contrast, storm deposits are usually composed of many thin laterally extensive near-horizontal bedforms Increase in marine diatoms. (Hemphill-Haley, 1996; The presence of marine diatoms or mixed assemblages is indicative of a marine origin for Dawson and Smith, 2000;Sawai, 2002; the deposit. Both storms and tsunami are capable of transporting marine diatoms during Bondevik et al., 2005;Dawson, 2007) washover events. ...
... Unfortunately when considered alone many of the characteristics are equivocal. In fact most of the signatures presented in Table 1, including the presence of marine diatoms (Hemphill-Haley, 1996;Dawson and Smith, 2000) or increases in particular elemental concentrations (Chague- Goff and Goff, 1999;Goff and Chague-Goff, 1999;Chague-Goff et al., 2000;Goff et al., 2001) only indicate the marine origin of the sediments and inundation by ocean water. Hence storm surges, sea-level change or regional subsidence may show similar sedimentological characteristics (Witter et al., 2001). ...
... Deposits from this tsunami have been detected across the North Atlantic: in the Faroe Islands (Grauert et al., 2001), along the coast of Norway (Bondevik et al., 1997) and Greenland (Wagner et al., 2007). However, most of the deposits have been studied in the United Kingdom: in Scotland mainland (Dawson et al., 1988;Dawson and Smith, 2000;Dawson et al., 1996;Tooley and Smith, 2005), in the Shetland Islands (Bondevik et al., 2005;Bondevik et al., 2003) and in NE England (Horton et al., 1999;Shennan et al., 2000;Smith et al., 2004) (Figure 1). ...
... In Inverness, excavations revealed a Mesolithic horizon covered by a layer of marine sand that was ascribed to the Storegga tsunami (Dawson et al., 1990). In northern Sutherland (North Scotland), a coarser layer in marked contrast with the under and overlying sediments has been described and associated with the Storegga tsunami (Dawson and Smith, 2000;Dawson et al., 1996). These authors identified a mixed diatom assemblage, with all coastal and some offshore habitats represented. ...
... Deposits from this tsunami have been detected across the North Atlantic: in the Faroe Islands (Grauert et al., 2001), along the coast of Norway (Bondevik et al., 1997) and Greenland (Wagner et al., 2007). However, most of the deposits have been studied in the United Kingdom: in Scotland mainland (Dawson et al., 1988;Dawson and Smith, 2000;Dawson et al., 1996;Tooley and Smith, 2005), in the Shetland Islands (Bondevik et al., 2005;Bondevik et al., 2003) and in NE England (Horton et al., 1999;Shennan et al., 2000;Smith et al., 2004) (Figure 1). ...
... In Inverness, excavations revealed a Mesolithic horizon covered by a layer of marine sand that was ascribed to the Storegga tsunami (Dawson et al., 1990). In northern Sutherland (North Scotland), a coarser layer in marked contrast with the under and overlying sediments has been described and associated with the Storegga tsunami (Dawson and Smith, 2000;Dawson et al., 1996). These authors identified a mixed diatom assemblage, with all coastal and some offshore habitats represented. ...
This study applies heavy mineral analysis to the Storegga tsunami deposit across a range of locations (Whale Firth, Maggie's Kettle Loch and Scatsta Voe) in Shetland (Scotland). The usefulness of this proxy is tested in the identification and characterization of these palaeotsunami units. Furthermore, provenance relationships are established based on the mineralogical content of tsunami deposits and their potential source. Finally, the capability of identifying different phases of tsunami inundation in an 8200 years old tsunami deposit is attempted.
... In the latter case, dating moss still containing chlorophyll provides good evidence for an age of material alive when the tsunami struck (Bondevik, 2002). Examination of entrained material has even suggested the season of the event (Dawson and Smith, 2000;Bondevik et al., 1997). Deposits of the Lisbon tsunami in the Scilly Isles have been dated by OSL methods supporting the historic age of the deposit (Banergee et al., 2001). ...
... Examination of clasts within the tsunami deposit can also indicate the season of the event as well as provide material for dating. The stage in the development of buds (Bondevik et al., 1997), fruit (Dawson and Smith, 2000) and moss (Rydgren and Bondevik, 2015) and also the size of fish bones (Bondevik et al., 1997) at sites in Norway and Scotland entrapped within the tsunami deposits suggest that the Storegga tsunami struck in late autumn. However sedimentological evidence from Finmark in northern Norway implies that it occurred when the ground was not frozen (Romundset and Bondevik, 2011) suggesting a time between April and October. ...
Over the years many events around the coasts of the UK have been described as tsunamis or tidal waves. Evaluation of the data indicates only a few of these events are definitely tsunamis. The data types vary from sedimentary deposits, primarily of pre-historic events, through recorded observations, particularly reports in 19th and 20th century newspapers, to tide gauge records mainly from the latter half of the 20th century.
The major tsunami events within the UK include the Storegga tsunami which struck coasts in the northern half of the country about 8150BP, and the tsunami triggered by the 1755 Lisbon earthquake. Lesser events are primarily associated with earthquakes with epicentres offshore Portugal, but others are local events triggered by coastal cliff falls. These lesser events are often only noted on tide gauge records.
Most reported events are probably not tsunamis. Many are likely to have been weather related events known as meteotsunamis. These are large amplitude, long wavelength seiches caused by rapid changes in air pressure. They occur predominantly along on the south coast of England and have over the years caused fatalities and damage to structures. Some are uncertain events where the triggering mechanism is not clear. These include sediment layers found in Shetland resembling tsunami deposits but it is uncertain if the sediment is deposited by waves or are aeolian or through downslope processes.
... The Storegga deposits are generally a medium to fine sand layer, often pale in colour (e.g. Smith et al. 1999, Dawson & Smith 2000, but coarse sand to gravel in some locations , found within peat layers (Smith et al. 2004). The deposits often contain peat rip-up clasts embedded within the sand deposit, indicating erosion (Dawson & Smith 2000). ...
... Smith et al. 1999, Dawson & Smith 2000, but coarse sand to gravel in some locations , found within peat layers (Smith et al. 2004). The deposits often contain peat rip-up clasts embedded within the sand deposit, indicating erosion (Dawson & Smith 2000). The sediment found in the tsunami deposits is clearly dependent on the local sediment characteristics, but also on the wave and local geomorphological characteristics (Takashimizu et al. 2012). ...
Myths and legends across the world contain many stories of deluges and floods. Some of these have been attributed to tsunami events. Doggerland in the southern North Sea is a submerged landscape thought to have been heavily affected by a tsunami such that it was abandoned by Mesolithic human populations at the time of the event. The tsunami was generated by the Storegga submarine landslide off the Norwegian coast which failed around 8150 years ago. At this time there were also rapid changes in sea level associated with deglaciation of the Laurentide ice sheet and drainage of its large proglacial lakes, with the largest sea level jumps occurring just prior to the Storegga event. The tsunami affected a large area of the North Atlantic leaving sedimentary deposits across the region, from Greenland, through the Faroes, the UK, Norway and Denmark. From these sediments, run-up heights of up to 20 metres have been estimated in the Shetland Isles and several metres on mainland Scotland. However, sediments are not preserved everywhere and so reconstructing how the tsunami propagated across the North Atlantic before inundating the landscape must be performed using numerical models. These models can also be used to recreate the tsunami interactions with now submerged landscapes, such as Doggerland. Here, the Storegga submarine slide is simulated, generating a tsunami which is then propagated across the North Atlantic and used to reconstruct the inundation on the Shetlands, Moray Firth and Doggerland. The uncertainty in reconstructing palaeobathymetry and the Storegga slide itself results in lower inundation levels than the sediment deposits suggest. Despite these uncertainties, these results suggest Doggerland was not as severely affected as previous studies implied. It is suggested therefore that the abandonment of Doggerland was primarily caused by rapid sea level rise prior to the tsunami event.
... The bottom sediments of lakes are good geological archives, which preserve information about past natural-climatic environments, including strong catastrophic events (earthquakes, tsunamis, landslides). Numerous traces of strong catastrophic events were studied in the various geological and tectonic settings in different parts of the world (Bondevik et al. 1997;Dawson, Smith 2000;Mörner 2005;Agnon et al. 2006;Guyard et al. 2007;Morey et al. 2013, etc.). In lake sequences catastrophic events are represented by stratigraphic non-conformities, changes in diatom flora and mixed sand, silt, gravel, plant macrofossils in organic matrix. ...
... The giant catastrophic event, the Storegga Slide, triggered a widespread tsunami in the North Atlantic ca 8200-8000 cal yr BP (Bondevik et al. 1997(Bondevik et al. , 2003Dawson, Smith 2000;Romundset, Bondevik 2011). Tsunami deposits have been discovered at numerous sites (the Norwegian coast, Shetland, Scotland, Faroe Islands and Finnmark area of the Barents Sea). ...
Nikolaeva, S., Tolstobrov, D., Tolstobrova, A. 2019. Disturbances in the primary stratigraphy of lake sediments on the Murmansk coast (Russia): their identification and relationship with catastrophic events. Baltica, 32 (2), 156-169. Vilnius. Abstract. The results of lithological, diatom analyses and radiocarbon dating of bottom sediments of small coastal lake basins along the Murmansk coast of the Barents Sea (the Kola Region, Russia) are presented. Sedi-mentary successions of two lakes reveal the presence of distinctive deposits, very different from the sediment above and below. These deposits are represented by erosional unconformity beds, gyttja and sand mixed with plant macrofossils, and characterized by changes in diatom flora and sand in a matrix of organic material. The sediments were deposited due to different catastrophic events: paleo-tsunami and paleo-earthquakes. According to radiocarbon analysis data, a tsunami occurred between 10,400-8200 cal yr BP and a paleo-earthquake occurred between 8200-7200 cal yr BP. We discuss various causes and mechanisms for the formation of disturbances in lake sediments, including the Storrega tsunami and paleo-earthquakes, which during and after deglaciation were strong and frequent.
... Deposits from the Storegga tsunami are widespread and have been found across the northern North Atlantic coastal margin: in NE England (e.g. Horton et al., 1999;Shennan et al., 2000;Smith et al., 2004;Boomer et al., 2007), N Scotland (Dawson and Smith, 2000;Dawson et al., 1996a), NE Scotland (e.g. Dawson et al., 1988;Long et al., 1989;Tooley and Smith, 2005), NW Scotland (e.g. ...
... horizon covered by a layer of marine sand that was ascribed to the Storegga tsunami (Dawson et al., 1990). In northern Sutherland (North Scotland), Dawson et al. (1996a) and Dawson and Smith (2000) described a coarser layer up to 75 cm thick markedly contrasting with the vertically confining sediments. A pronounced erosional unconformity with the underlying sediments was observed. ...
This paper reviews the evidence for onshore sedimentary imprints of tsunami inundation known from the geological record of the Atlantic basin. The central aim of the paper is to offer a broad overview on the main deposits and key localities that have been documented along the Atlantic coastlines, and which attest to the local or regional impact of tsunamis during historical, pre-historical and recent geological times. Considerable detail is devoted to summarising key diagnostic criteria used to identify the deposits as tsunami-derived, and to set each deposit in its own unique geomorphological setting and context, always referring to the latest scientific knowledge of the events that generated them. The paper also discusses the relationships between the different tsunamigenic sources that concurred to the formation of the deposits, as well as critical information on magnitude and frequency, as inferred from the sedimentary responses preserved in the sediment archives. Documented case studies range from the well-studied landslide-triggered and earthquake-triggered Storegga and 1755 Lisbon tsunamis, respectively, to collapse- and eruption-triggered tsunamis in the Atlantic archipelagos, to other less well-known events in the south Atlantic, Caribbean and Arctic. Despite its less frequent tsunami recurrence, the Atlantic coastal stratigraphy presents some world-class case studies and outstanding outcrops, from which critical knowledge can be gained with respect to some of the most enigmatic aspects of tsunami science.
... In the inner areas of these protected coastal systems the arrival of the tsunami wave takes place after dispersion of the initial energy, which occurs through friction with the bottom when the wave crosses a shallow tidal system. The innermost limit of the tsunamigenic layer is simply evidenced as a fine but continuous level of plant fragments that may also contain a variable amount of small soft boulders (Bondevik et al., 1997;Dawson and Smith, 2000). In the most open areas of these systems, other surface deposits characteristic of high-energy events and linked to geomorphological features characteristic of storms, such as cheniers or washover fans, develop. ...
From a depositional point of view, tsunami deposits can be defined as high-energy event
sequences, generated by highly energetic dynamic processes involving a high degree of
erosion and transport of sediments. Tsunamis are waves induced either by plate tectonics or
by the impact of meteorites or large underwater landslides. They are characterized by a
wavelength of dozens of kilometers and by their high speed. Interest in the study of
tsunamigenic deposits has increased in recent times, with numerous works published in the
last few years on tsunamites generated by documented events, such as the Hokkaido-
Nansei-Oki earthquake in 1993 (Nanayama et al., 2000; Sawai, 2002), the Okoropunga
tsunami in New Zealand in the 15th century (Goff et al., 2004) or the one associated with the
famous volcanic eruption of the Krakatoa in 1883 (Van den Bergh et al., 2003).
In coastlines protected from swell, such as bays, estuaries or coastal lagoons, tsunamis
usually generate complex but easily recognizable deposits (tsunamites) clearly differentiated
from storm deposits, as storms cannot reach these environments. In the inner areas of these
protected coastal systems the arrival of the tsunami wave takes place after dispersion of the
initial energy, which occurs through friction with the bottom when the wave crosses a
shallow tidal system. The innermost limit of the tsunamigenic layer is simply evidenced as a
fine but continuous level of plant fragments that may also contain a variable amount of
small soft boulders (Bondevik et al., 1997; Dawson and Smith, 2000). In the most open areas
of these systems, other surface deposits characteristic of high-energy events and linked to
geomorphological features characteristic of storms, such as cheniers or washover fans,
develop. These features can also be generated during tsunamis, and in this case it is difficult
to distinguish the depositional mechanisms of both phenomena.
Criteria in favor of the action of tsunamis in this coastal sector are
... The criteria and proxies to distinguish between the tsunami and storm deposits are being developed, a clear discrimination between these deposits is still difficult (Fujiwara and Kamataki, 2007;Goff et al., 2012;Morton et al., 2007;Shimazaki et al., 2011). Several studies describe the characteristics of tsunami deposits in terms of their occurrence, preservation, grain sizes and sedimentary structures (e.g., Bahlburg and Spiske, 2012;Dawson and Smith, 2000;Fujiwara, 2007;Fujiwara and Kamataki, 2007;Goff et al., 2012;Morton et al., 2007;Switzer and Jones, 2008). Tsunami deposits are usually comprised of sediments with the clast size ranging from clay to boulders, and can occur as single-bed or multiple bed deposits and have characteristic depositional structures developed by wave action resulting from inflow and backwash (Bahlburg and Spiske, 2012;Fujiwara and Kamataki, 2007). ...
... Examination of clasts within the deposit can also indicate the season of the event as well as providing suitable material for dating. The stage in the development of buds (Bondevik et al. 1997), mosses (Rydgren & Bondevik 2015) and fruit (Dawson & Smith 2000), and also the size of fish bones (Bondevik et al. 1997) entrapped within the tsunami deposits at sites in Norway and Scotland, suggest that the tsunami struck in late autumn. ...
Tsunamicataloguesprovideimportantdatasetsinassessingtheriskfrominfrequentbut potentially high-impact events. Although the UK is located away from subduction zones (the most common origin of tsunamis), tsunamis have struck its shores, most notably those triggered by the prehistoric Storegga submarine landslide and the 1755 Lisbon earthquake. Since the major events of 2004 (Indian Ocean) and 2011 (Japan) tsunamis are in the public psyche, even if the risks to UK coasts are not. Due to this heightened awareness, many reported events are claimed to be tsunamis and the potential for tsunamis is increasingly included in risk planning; understanding the true fre- quency of tsunamis is therefore important. Within the UK, the evidence for tsunamis includes tide gauge readings, reported visual observations and interpretation of sedimentological features. Cata- logues need to consider whether the event is a true tsunami in order to avoid a plethora of claims that confound risk assessments; for example, recent well-documented events generated by weather sys- tems (meteotsunamis) provide a possible explanation for some historical events. A detailed exam- ination of the impact of tsunamis upon the UK coast is provided, including examples of events triggered by the three primary causes of tsunamis: seismicity, submarine landslides and coastal landslides.
... These high-energy events cause the deposition of sedimentary layers with characteristic textural and mineralogical features (Clague et al., 2000;Singarasubramanian et al., 2006;Babu et al., 2007). In most cases, these investigations are concentrated on a single event (Dawson and Smith, 2000;Wagner et al., 2007), although even six tsunamis have been recognized in a single section (e.g., Cisternas et al., 2005). ...
A multidisciplinary study of sediment cores from Doñana National Park (SW Spain), a broad region of wetlands in SW Spain, provides the base for the reconstruction of the main palaeoenvironmental changes that occurred in the Guadalquivir estuary since OIS 3. The facies analysis differentiates six main facies, deposited in freshwater pond and marsh (FA-1: laminated silt), brackish marsh or the periphery of a brackish lagoon (FA-2: greyish silt), a shallow lagoon (FA-3: green silt and clay), the marine connection of this lagoon (FA-4: yellow silt) or sandy spit (FA-6: yellow sand), whereas FA-5 includes bioclastic silt and sand with a tsunamigenic origin.The vertical arrangement of these facies, their dates and a detailed comparison with previous works permit to delimitate ten phases in the Late Pleistocene to Holocene evolution of this lowland. In the oldest phase (OIS 3), this area was occupied by freshwater marshes. Phase 2 (OIS 2) was characterized by the alternation of freshwater and brackish marshes, partly enclosed by aeolian units. During the third phase (Early Holocene), the brackish marshes constituted the northern limit of a broad lagoon that extended along the present-day inner shelf. The sea-level highstand of the Present Interglacial (Flandrian transgression, phase 4: ̃6.5 cal BP) caused the inundation of this area, occupied by an open lagoon. Between 6.5 and 4.6 cal ka (phase 5), incipient brackish marshes emerged along the margins of this lagoon and a first tsunamigenic event (5100-4800 cal BP) eroded partially the Doñana spit. The following phase (4.6-3.7 cal ka) was relatively quiet, with predominance of infilling processes. This calm scenario was interrupted by a new period of instability (phase 7: 3.7-3 cal ka), with two new high-energy events. The progressive infilling is the main feature of phase 8 (3-2.2 cal ka), with the emersion of new brackish marshes and a decreasing depth in the adjacent lagoon. The first historical tsunamis (phase 9: 2.2-1.9 cal ka) induced the creation of washover fans and bioclastic ridges overlying the previous marshes. Since 1.9 cal ka (phase 10), the growing of the Doñana spit and the fluvial-tidal sediment inputs caused an important filling of the Guadalquivir estuary (Doñana National Park), only interrupted by new tsunami records (̃1.8-1.5 cal ka).
... e.g. Dawson et al., 1996;Dawson and Smith, 2000;Bondevik et al., 2005;Razzhigaeva et al., 2007;Sawai et al., 2009). Breakage of diatom valves within tsunami deposits has also been observed (e.g. ...
Introduction The significance of relative sea level during the late Quaternary is recognized by disciplines across the Earth sciences. Sea-level histories are important for calibrating and constraining geophysical models of Earth’s rheology and glacio-isostatic adjustment (e.g. Peltier, 2004). Sea level is crucial to any study of coastal evolution as it serves as the ultimate baseline for continental denudation (Summerfield, 1991). For human populations, sea levels during the late Quaternary have been an important factor in sustaining coastal communities and may have profoundly influenced the very initiation of human civilization (e.g. Turney and Brown, 2007). Publication of reports from the Intergovernmental Panel on Climate Change (IPCC, 2007) re-emphasized the importance of sea level as a barometer of climate and drew attention to the potentially devastating consequences of future climate-related sea-level change (e.g. Rahmstorf, 2007). However, the IPCC also highlighted the uncertainty with which the driving mechanisms of sea-level change are understood and the disconnection between long-term geological and recent observational trends. Predictions of sea level for the twenty-first century rely on models, and the veracity of model output is based on verification against observations. Interpretation of these observations requires great care in light of the large spatial and temporal variability in relative sea-level change (Milne et al., 2009). Sea level is far from a constant, planar surface and exhibits spatial and temporal changes at a multitude of scales. To the observer, these changes are manifestations of relative sea level, a term which reflects the uncertainty in separating the often simultaneous contributions from movements of the ocean surface and land (Shennan, 2007).
... The nine most extensive probable tsunami deposits (uppercase letter labels in Table 2; Fig. 8) have characteristics similar to those of tsunami deposits described from peat or soil sequences landward of sandy beaches (e.g., Dawson and Smith, 2000;Gelfenbaum and Jaffe, 2003;Bourgeois et al., 2006;Jankaew et al., 2008;MacInnes et al., 2009;Sawai et al., 2012;Szczuciński et al., 2012), where sheets of clean sand less than a few centimeters thick can be mapped for hundreds of meters inland. Beds D, H, I, and N rise 7-8 m along the 265 m length of the core transect; even the deepest beds of this group, found only in a few cores, extend at least 100 m (Fig. 5). ...
Despite the Alaska-Aleutian megathrust's role as the source of some of the largest earthquakes and tsunamis, the history of its pre-20th-century tsunamis is largely unknown west of the rupture zone of the great (M9.2) 1964 earthquake. Stratigraphy in core transects at two boggy lowland sites on Chirikof Island’s southwest coast preserves tsunami deposits dating from the postglacial to the 20th century. In a 500-m-long basin 13-15 m above sea level and 400 m from the sea, 4 of 10 sandy to silty beds in a 3- to 5-m-thick sequence of freshwater peat were probably deposited by tsunamis. The freshwater peat sequence beneath a gently sloping alluvial fan 2 km to the east, 5-15 m above sea level and 550 m from the sea, contains 20 sandy to silty beds deposited since 3.5 ka; at least 13 were probably deposited by tsunamis. Although most of the sandy beds have the consistent thicknesses (over distances of 10-265 m), sharp lower contacts, good sorting, and(or) upward fining typical of tsunami deposits, the beds contain abundant freshwater, very few brackish, and no marine diatoms. Apparently, tsunamis traveling inland over low dunes and boggy lowland entrained largely freshwater diatoms. Abundant fragmented diatoms, and lake species in some sandy beds not found in host peat, were probably transported by tsunamis to >10 m at the eastern site. Single-aliquot regeneration OSL dating of the third youngest bed is consistent with its having been deposited by the tsunami recorded at Russian hunting outposts in 1788, and with the second youngest bed being deposited by a tsunami during an upper-plate earthquake in 1880. We infer from stratigraphy, 14C-dated peat deposition rates, and unpublished analyses of the island’s history that the 1938 tsunami may locally have reached >10 m. As this is the first record of Aleutian tsunamis extending throughout the Holocene, we cannot estimate source earthquake locations or magnitude for most tsunami-deposited beds. We infer that no more than 3 of the 23 potential tsunamis beds at both sites were deposited following upper-plate faulting or submarine landslides independent of megathrust earthquakes. If so, the Semidi segment of the Alaska-Aleutian megathrust near Chirikof Island probably sent high tsunamis southward every 180-270 yr for at least the past 3500 yr.
... There are common characteristic features, which have been described by numerous researchers (e.g. Dawson and Smith 2000;Goff et al. 2001;Tuttle et al. 2004;Morton et al. 2007): (i) Laterally extensive and thicklybedded sand sheets (often structureless) showing landward thinning; (ii) normal or inverse grading; (iii) presence of marine microfossils and macrofauna. In contrast, storm deposits typically are produced through bedload transport and display extensive planar laminae, foresets, troughs, and climbing ripples with a maximum bed thickness close to shore thinning abruptly landward (Morton et al. 2007). ...
Analysis of the CARLA-11 core drilled along the lower Loukkos valley near Larache in northern Morocco shows a thin level of shelly sand at 465 to 482 cm depth, whose sedimentological features are those of a high-energy, certainly a tsunami deposit. The level can be subdivided into 3 subunits: Subunit 1 (6 cm) shows a sharp erosive base and comprises basal medium to coarse sands containing numerous marine shell fragments of bivalves, plant fragments and rip-up clasts of organic matter. Subunit 2 (7 cm) is a flame structure consisting of coarse sand containing a layer of organic matter and another one of greyish clay. Subunit 3 (4 cm) is similar to subunit 1 and consists of coarse sands containing numerous complete or broken shells of bivalves, plant fragments and dark organic matter. The deposit is mostly composed of subangular to subrounded quartz grains derived from nearby Miocene sandstones. Benthic and planctonic foraminifera are common within the samples. Magnetic susceptibility measurements show two major lows at ~350 cm, and especially at 477 cm within the high-energy deposit. Subunit 1 can be interpreted as the result of the first wave uprush of a tsunami, Vol. 34, No. 2, page 83 (2015) the fine mud level of subunit 2 capping subunit 1 can be interpreted as emplaced during a decantation phase, and subunit 2 probably corresponds to a second wave uprush, Subunit 3 might be interpreted as the result of the backwash (outflow phase). The age of this event can be roughly dated between 5 and 3 ky BP according to recent dating of nearby levels.
... The pseudo sand-sheet geometry of the tsunami deposit extends over an area of 35 km², and shows evidence for the transport of highly concentrated suspended sediments driven by wave-dominated sedimentary processes (turbidity flow) over relatively short periods of time (hours or minutes) and rapid accumulations of sediment under high-energy conditions (Dawson and Smith, 2000;Sugawara et al., 2014). A comparison of the sand distribution in the studied tsunami deposit with sand distributions in other tsunami deposits worldwide indicates that such sand-sheet deposits are relatively horizontally homogeneous (Clague et al., 1994;Nanayama and Shigeno, 2006;Jankaew et al., 2008;Prendergast et al., 2012), and that vertical heterogeneity is expressed by graded sequences of 'fine-to coarse-grained sand (Cantalamessa and Di Celma, 2005;Dawson and Stewart, 2007;Jankaew et al., 2008;Prendergast et al., 2012). ...
Geological and reservoir modelling are mandatory in studies that regard the geological storage of CO2. The aim of this study was to investigate the intra‐unit heterogeneity of the two sandstone deposits observed in the Aliaga outcrop at metre scales, and to examine how heterogeneity can impact the behaviour of CO2 in the zone close to the injector well during injection and post‐injection processes in a deep saline aquifer scenario.
The Aliaga outcrop, is an 8400‐m² 2D vertical face in the upper part of the Camarillas Fm. (Early Cretaceous, Galve sub‐basin). The studied sandstone deposits correspond to a tsunami and a barrier island – tidal inlet, which were described in macroscale (centimetre to metric) and microscale (micron); further cores were drilled along outcrop to collect samples for porosity and permeability measurements. The two sandstone deposits were generated by distinct sedimentary processes under the same sedimentary system, and showed distinct petrophysical characteristics.
The modelling process was different for each deposit, and honoured the petrophysical characteristics that were used to build the reservoir model post‐hoc. The petrophysics models reflected the sandy variability, which was represented by the facies distribution. The facies were defined as a function of the sand sorting at the petrographic scale. The tsunami facies and porosity distributions are homogeneous, whereas the barrier island‐tidal inlet facies and porosity distributions are heterogeneous. Porosity and permeability are strongly correlated in both deposits; thus, the permeability modelling was carried out as a function of the porosity model by applying a regression equation.
Although the permeability is usually low (tens of mD), the two deposits behaved as a reservoir. At a short‐time scale (7 years), both reservoirs stored at least of 60% injected CO2, with the 20‐40% dissolved in the brine. At the sub‐metric scale, under the same reservoir conditions and fluid model parameters, the thickness of reservoir has the major impact in the amount of CO2 dissolution rather than the permeability contrast.
... Over longer Holocene timescales, the preservation of a tsunami deposit for 8000 years will clearly be assisted if it was deposited on and buried by peat [e.g. at Wick River Valley (Dawson and Smith, 1997) and Sullum Voe, Shetland (Bondevik et al., 2003)], in fine-grained cohesive sediments that are resistant to erosion [e.g. at Maryton, Montrose (Smith et al., 2004)], in subtidal lagoons where it is buried by marine clastic deposits [e.g. Strath Halladale (Dawson and Smith, 2000)] or in lakes that lie above and beyond the reach of tidal processes [e.g. on Norway's west coast (Bondevik et al., 1997)]. ...
We reconstruct one of the longest relative sea-level (RSL) records in north-west Europe from the north coast of mainland Scotland, using data collected from three sites in Loch Eriboll (Sutherland) that we combine with other studies from the region. Following deglaciation, RSL fell from a Lateglacial highstand of +6-8m OD (Ordnance Datum=ca. mean sea level) at ca. 15k cal a BP to below present, then rose to an early Holocene highstand and remained at ca. +1m OD between ca. 7 and 3k cal a BP, before falling to present. We find no evidence for significant differential Holocene glacio-isostatic adjustment between sites on the north-west (Lochinver, Loch Laxford), north (Loch Eriboll) and north-east (Wick) coast of mainland Scotland. This suggests that the region was rapidly deglaciated and there was little difference in ice loads across the region. From one site at the head of Loch Eriboll we report the most westerly sedimentary evidence for the early Holocene Storegga tsunami on the Scottish mainland. The presence of the Storegga tsunami in Loch Eriboll is predicted by a tsunami wave model, which suggests that the tsunami impacted the entire north coast of Scotland and probably also the Atlantic coastline of north-west Scotland.
... The mixed freshwater, brackish, and marine diatom assemblages found in Sands 1-5 are typical of tsunami deposits because tsunamis erode, transport, and deposit marine, brackish, and freshwater sediments as they inundate coastal and inland areas (e.g. Dawson et al., 1996;Dawson and Smith, 2000;Sawai et al., 2008;Szczuiński et al., 2012). Within the mixed assemblages of Sands 1, 2, and 5, we observed a significant (>30%) increase in marine and brackish estuarine taxa (common in modern river channel samples and found in low abundances throughout sections of sediment in Pit 13 and Exposure 9) compared to underlying sediments. ...
The stratigraphy within coastal river valleys in south-central Chile clarifies and extends the region’s history of large, earthquakes and accompanying tsunamis. Our site at Quidico (38.1°S, 73.3°W) is located in an overlap zone between ruptures of magnitude 8–9 earthquakes in 1960 and 2010, and, therefore, records tsunamis originating from subduction-zone ruptures north and south of the city of Concepción. Hand-dug pits and cores in a 3-m-thick sequence of freshwater peat in an abandoned meander (a little-examined depositional environment for tsunami deposits) and exposures along the Quidico River show five sand beds that extend as much as 1.2 km inland. Evidence for deposition of the beds by tsunamis includes tabular sand beds that
are laterally extensive (>100 m), well sorted, fine upward, have sharp lower contacts, and contain diatom assemblages dominated by brackish and marine taxa. Using eyewitness accounts of tsunami inundation, 137Cs analyses, and 14C dating, we matched the upper four sand beds with historical tsunamis in 2010, 1960, 1835, and 1751. The oldest prehistoric bed dates to 1445–1490 CE and correlates with lacustrine and coastal records of similar-aged earthquakes and tsunamis in south-central Chile.
... Because of the high sensitivity of the tsunami depositions to inundation distance, run-up, and flow height (Abe et al., 2012;Dawson and Smith, 2000;Nakamura et al., 2012;Nanayama et al., 2007;Nanayama and Shigeno, 2006), we attempted to reconstruct the two marine inundations on the Jinshan plain based on the distributions of the quartzose event layers (Fig. 3A). The two inundations were likely comparable, because they have similar event layer distributions, except for the lack of the lower layer in the Yuantanchi River system (Figs. ...
... There are common characteristic features, which have been described by numerous researchers (e.g. Dawson and Smith 2000;Goff et al. 2001;Tuttle et al. 2004;Morton et al. 2007): (i) Laterally extensive and thicklybedded sand sheets (often structureless) showing landward thinning; (ii) normal or inverse grading; (iii) presence of marine microfossils and macrofauna. In contrast, storm deposits typically are produced through bedload transport and display extensive planar laminae, foresets, troughs, and climbing ripples with a maximum bed thickness close to shore thinning abruptly landward (Morton et al. 2007). ...
Analysis of the CARLA-11 core drilled along the lower Loukkos valley near Larache in northern Morocco shows a thin level of shelly sand at 465 to 482 cm depth, whose sedimentological features are those of a high-energy, certainly a tsunami deposit. The level can be subdivided into 3 subunits: Subunit 1 (6 cm) shows a sharp erosive base and comprises basal medium to coarse sands containing numerous marine shell fragments of bivalves, plant fragments and rip-up clasts of organic matter. Subunit 2 (7 cm) is a flame structure consisting of coarse sand containing a layer of organic matter and another one of greyish clay. Subunit 3 (4 cm) is similar to subunit 1 and consists of coarse sands containing numerous complete or broken shells of bivalves, plant fragments and dark organic matter. The deposit is mostly composed of subangular to subrounded quartz grains derived from nearby Miocene sandstones. Benthic and planctonic foraminifera are common within the samples. Magnetic susceptibility measurements show two major lows at ~350 cm, and especially at 477 cm within the high-energy deposit. Subunit 1 can be interpreted as the result of the first wave uprush of a tsunami, the fine mud level of subunit 2 capping subunit 1 can be interpreted as emplaced during a decantation phase, and subunit 2 probably corresponds to a second wave uprush, Subunit 3 might be interpreted as the result of the backwash (outflow phase). The age of this event can be roughly dated between 5 and 3 ky BP according to recent dating of nearby levels.
... Over the last three decades, the number of paleotsunami studies has increased significantly, providing new perspectives on tsunami inundation dynamics. These new perceptions were achieved through the application of diverse multiproxy analysis that allowed robust reconstruction of tsunami inundation and backwash phases [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. ...
The CE 1755 Lisbon tsunami was the largest historical tsunami to affect the Atlantic coasts of Europe and North Africa. This study presents the results obtained from the application of different sedimentological techniques (e.g., grain size, morphoscopy, microtextural analysis, geochemistry, radiocarbon dating) on sediments retrieved from the Alcabrichel River alluvial plain (of about 500 m far away from its mouth and approximatively 50 km northwest of Lisbon, Portugal). The results allowed the identification of a sandy layer that was associated with the CE 1755 tsunami. Furthermore, a new microtextural semi-quantitative classification was applied to enhance the identification of extreme marine inundation deposits. Based on sedimentological data, three different tsunami inundation phases were identified, including two inundations and a likely backwash. This innovative work offers physical evidence of the spatial presence of the CE 1755 tsunami event on the western coast of Europe. It also enables a reconstruction of tsunami inundation dynamics, with two flooding waves and an interspersed backwash.
... A1,A4). Within the mixed freshwater, brackish, and marine diatom assemblages that typically characterize tsunami deposits (e.g., Dawson et al., 1996;Dawson and Smith, 2000;Smith et al., 2004;Bondevik et al., 2005;Sawai et al., 2008Sawai et al., , 2009Horton et al., 2011;Nelson et al., 2015), sand beds 1 and 2 display high relative abundances of marine planktonic (e.g., Paralia sulcata, Thalassiosira angulata), tychoplanktonic (Delphineis kippae and D. surirella), and epipsammic (Opephora pacifica) diatoms common in the Quidico coastal littoral zone (Hong et al., 2017). Similar increases in marine planktonic, tychoplaktonic, and epipsammic diatoms are observed in sand beds 3, 5, and 7, supporting an offshore source rather than a fluvial source for the sand beds. ...
The Arauco Peninsula (37°-38°S) in south-central Chile has been proposed as a possible barrier to the along-strike propagation of megathrust ruptures, separating historical earthquakes to the south (1960 AD 1837, 1737, and 1575) and north (2010 AD, 1835, 1751, 1657, and 1570) of the peninsula. However, the 2010 (Mw 8.8) earthquake propagated into the Arauco Peninsula, re-rupturing part of the megathrust that had ruptured only 50 years earlier during the largest subduction zone earthquake in the instrumental record (Mw 9.5). To better understand long-term slip variability in the Arauco Peninsula region, we analyzed four coastal sedimentary sections from two sites (Tirúa, 38.3°S and Quidico, 38.1°S) located within the overlap of the 2010 and 1960 ruptures to reconstruct a ∼600-year record of coseismic land-level change and tsunami inundation. Stratigraphic, lithologic, and diatom results show variable coseismic land-level change coincident with tsunami inundation of the Tirúa and Quidico marshes that is consistent with regional historical accounts of coseismic subsidence during earthquakes along the Valdivia portion of the subduction zone (1960 AD and 1575) and coseismic uplift during earthquakes along the Maule portion of the subduction zone (2010 AD, 1835, 1751). In addition, we document variable coseismic land-level change associated with three new prehistoric earthquakes and accompanying tsunamis in 1470–1570 AD, 1425–1455, and 270–410. The mixed record of coseismic subsidence and uplift that we document illustrates the variability of down-dip and lateral slip distribution at the overlap of the 2010 and 1960 ruptures, showing that ruptures have repeatedly propagated into, but not through the Arauco Peninsula and suggesting the area has persisted as a long-term impediment to slip through at least seven of the last megathrust earthquakes (∼600 years).
... Tsunamis are waves of large wavelength caused by eventual disturbances of the sea floor during seisms, volcanic eruptions or submarine landslides (Dawson and Smith 2000). From a human point of view, a tsunami is a low frequency high-magnitude event, but within a geological timescale is a frequent phenomenon. ...
Spain is definitely a coastal country. The Spanish coast extends along more than 9000 Km and 22 of the 50 Spanish provinces have coastal edges over the Atlantic Ocean or the Mediterranean Sea (Fig. 1.1). In general terms it is a low altitude coast, but is too diverse displaying different littoral environments. The beaches are the most valuable environment in economic terms by the tourism, nevertheless, dunes, rias, estuaries, deltas, fan-deltas, lagoons, rocky coasts and cliffs with different geologic and dynamic controls are distributed along the coastal extension. In the last six decades the entire coast of Spain has experienced a deep human modification and is actually under an extreme urban pressure. In this chapter, the reader will find the keys to understand the importance of the Spanish Coastal Systems which are described in the subsequent chapters of this book.
... No evidence has so far been reported for this event on either mainland Scotland or Orkney. However, when searching for evidence for the larger 8150-year BP Storegga tsunami, Dawson and Smith (2000) noted the sheltering effect of the Orkney and Shetland Islands located immediately in the path of an incoming tsunami from the continental slope. This suggests that geological evidence for the 5500 BP event may exist on the Orkney Islands, although nothing has been reported to date (Fig. 5). ...
Recent large tsunamis in the twenty-first century have provided graphic reminders of the catastrophic impacts such natural hazards can have upon coastal communities. Death tolls in the thousands give rise to the rapid adoption of coastal mass burials for the interment of the dead. While recognised as a necessary practice in the aftermath of such contemporary tragedies, the paucity of coastal mass burial sites related to earlier tsunamis reported in the archaeological record is unusual. We establish a suite of criteria for identifying the geological and archaeological evidence of inundation by past tsunamis and review case studies from two well-documented prehistoric coastal mass burial sites in the Southern Hemisphere (Solomon Islands and Vanuatu). To varying degrees, both sites possess numerous characteristics that suggest direct correlation with previously reported catastrophic palaeotsunamis. In the Northern Hemisphere, we investigate palaeotsunami inundation as an alternative hypothesis for mass burial sites in Orkney and Shetland, a relatively tectonically inactive region where such an association is unlikely to have ever been considered. The nature, chronology and location of these mass burial sites fit well with the proposed archaeological evidence for palaeotsunami inundation, and they also appear to be contemporaneous with the as-yet poorly documented Garth tsunami (~ 5500 years BP). We suggest that a potentially key diagnostic criterion for determining a palaeotsunami linkage is the use of diatom testing on skeletal remains to establish whether death was caused by drowning in saltwater, a test which has never been applied in this context.
... (2004) vermeldenbovendien, dat de kusten van Groot-Brittannië door de tsunami over een lengte van minstens 600 km overstroomd werden. Dawson & Smith (2000) vonden tsunami-afzettingen lot 4,6 meter boven het toenmalige zeeniveau in Noord-Schotland ten westen van de Orkney-Eilanden, dus buiten het Noordzeebekken. Maar de tsunami reikte nog verder. ...
... Para além dessas características, os depósitos tsunamigénicos podem apresentar indícios de deformação sedimentar de origem sismogénica referenciada como soft-sediment deformation (Ribeiro e Terrinha, 2007) ou sismito (Ramos-Pereira et al., 2009;Araújo-Gomes, 2013 De acordo com Scheffers e Kelletat (2003), 45% da literatura sobre o tema incide sobre a análise dos sedimentos finos e inclui inúmeros trabalhos que estão focados sobretudo na análise destes sedimentos: Dawson et al., 1988;Long et al., 1989Long et al., , 1995Long et al., , 1996Darienzo e Peterson,1990;Minoura e Nakaya, 1991;Andrade, 1992;Atwater, 1992;Bourgeois, 1993;Yeh et al., 1993;Clague et al., 1994;Minoura et al., 1994;Sato et al.,1995;Shi et al., 1995;Bondevik, 1996;Hindson et al., 1996;Clague, 1997;Moya, 1999;Hindson e Andrade, 1999;Clague et al., 2000;Dawson e Smith, 2000). ...
... (2004) vermeldenbovendien, dat de kusten van Groot-Brittannië door de tsunami over een lengte van minstens 600 km overstroomd werden. Dawson & Smith (2000) vonden tsunami-afzettingen lot 4,6 meter boven het toenmalige zeeniveau in Noord-Schotland ten westen van de Orkney-Eilanden, dus buiten het Noordzeebekken. Maar de tsunami reikte nog verder. ...
In this article a summary is given of the extensive geological literature about tsunamis in Northwestern Europe. These tsunamis all have their origin in massive slidings of parts of the continental shelf off Norway into the deep Norwegian Sea.
Literature study on tsunamis that have occurred in NW-Europe during the Holocene.
This thesis presents a study of tsunami deposits created by the 2004 Indian Ocean tsunami at the Thai Andaman coast. The outcomes of a study are the characteristics of tsunami deposit for paleo-tsunami database, the identification of major sediment layers in tsunami deposit and the reconstructing tsunami run-ups from the characteristics of tsunami deposit for a coastal development program. rnThe investigations of tsunami deposit are made almost 3 years after the event. Field investigations characterize the tsunami deposit as a distinct sediment layer variable in thickness of gray sand deposited with an erosional basis on a pre-existing soil. The best location for the observation of recent tsunami deposit is the area located about 50-200 m inland from the coastline. In most cases, the deposit layer is normally graded. In some cases, the deposit contains rip-up clasts of muddy soils and/or organic matters. The tsunami deposits are compared with three deposits from coastal sub-environments. The mean grain-size and standard deviation of deposits show that the shoreface deposits are fine to very fine sand, poorly to moderately well sorted; the swash zone deposits are coarse to fine sand, poorly to well sorted; the berm/dune deposits are medium to fine sand, poorly to well sorted; and the tsunami deposits are coarse to very fine sand, poorly to moderately well sorted. The plots of deposit mean grain-size versus sorting indicate that the tsunami deposits are composed of shoreface deposits, swash zone deposits and berm/dune deposits as well. rnThe vertical variation of the texture of tsunami deposit shows that the mean grain-size fines upward and fining landward. The analysis and interpretation of the run-up numbers from the characteristics of tsunami deposits get three run-ups for the 2004 Indian Ocean tsunami at the Thai Andaman coast. It corresponds to field observations from the eye-witness reports and local people’s affirmations. The total deposition is a major transportation pattern of onshore tsunami sediments. The sediments must fine in the direction of transport. In general, the major origins of the sediment are the swash zone and berm/dune zone where coarse to medium sand is a significant material, the minor origin of tsunami sediment is a shoreface where a significant material is fine to very fine sand. Only at an area with flat slope shorface, the major origin of tsunami sediment is the shoreface.rn The thicknesses, the mean grain-sizes, and the standard deviations of tsunami deposits are used to evaluate the influences of coastal morphology on the sediment characteristics. The evaluations show that the tsunami affected areas were attacked by the variable energy waves. Wave energies at the direct tsunami wave affected areas are higher than at the indirect tsunami wave affected areas. Tsunami wave energy is highly dissipated at an area with steep slope shoreface. In the same way, tsunami run-up energy is highly dissipated at an area with steep slope onshore. A channel paralleled to the coastline decreases the run-up velocity, slightly dissipates run-up energy. The road and pond highly influence the characteristics of tsunami deposit and tsunami run-up. A road obstructs the run-up velocity, dissipates run-up energy. A pond decreases run-up velocity, dissipates run-up energy.rn The characteristics of tsunami deposit can be interpreted for reconstructing the characteristics of tsunami run-up such as a run-up height and a flow velocity. Soulsby et al.(2007)’s model is applied for reconstructing tsunami run-up at the study areas. The input parameters are sediment grain-size and sediment inundation distance. Ao Kheuy beach and Khuk Khak beach, Phang Nga province, Thailand are the areas listed for reconstructing tsunami run-up. The evaluated run-up heights are 4.2-4.9 m at Ao Kheuy beach, and 5.4-9.4 m at Khuk Khak beach. The evaluated run-up velocities are 12.8-19.2 m/s (maximum) and 0.2-1.9 m/s (mean) at the coastline and onshore, respectively. Hence, a reasonably good agreement between the evaluated and observed run-up is found. Tsunami run-up height and velocity can be used for coastal development and risk management in the tsunami affected areas. The case studies from the Thai Andaman coast suggest that in the area from coastline to about 70-140 m inland was flooded by the high velocity (high energy) run-ups, and those run-up energies were dissipated there. That area ought to be a non-residential area or a physical protection construction area (flood barrier, forest planting, etc.).rn
Earthquake and tsunami records on centennial and millennial temporal scales are necessary to understanding long-term subduction zone behavior and the occurrences of large, but infrequent events. Microfossils, such as diatoms, incorporated into coastal stratigraphy provide some of the most detailed reconstructions of the history of earthquakes and tsunamis. We explore qualitative and quantitative techniques that employ the relation between diatoms and salinity, tidal elevation, and life form to: (1) reconstruct records of vertical land-level change associated with large earthquakes; and (2) identify anomalous sand and silt beds deposited by tsunamis. A global database shows diatoms have been successfully employed in the reconstruction of earthquake and tsunami histories in Chile, the Indian Ocean, Japan, New Zealand, the North Sea, the Pacific Northwest of North America, and the South Pacific. We use case studies from some of these locations to highlight advancements in the field and new capabilities that diatoms have enabled. Examples from the Pacific Northwest of North America illustrate the evolution of quantitative diatom-based reconstructions of earthquake related land-level change. In Alaska and Japan, diatoms have documented land-level changes throughout the earthquake deformation cycle, including possible preseismic land-level change signals and postseismic deformation. Diatoms helped identify coseismic uplift along the central Chile subduction zone coast, and uplift and subsidence along the Alaska-Aleutian megathrust, expanding our knowledge of the variability of slip in megathrust ruptures. In tsunami studies, diatoms help determine the provenance of anomalous sands and silts found in low-energy coastal stratigraphic sequences. In Japan, allochthonous marine and brackish diatoms within sand deposits signaled repeated marine incursions into a coastal lake, helping identify a possible predecessor to the 2011 Tohoku tsunami. In the Pacific Northwest of North America and Chile, diatoms were used to estimate tsunami run-up beyond the landward limit of tsunami sedimentation. Examples from the North Sea, Thailand, and Japan show the fragmentation and sorting of diatom valves may provide evidence of high-energy transport during the rapid, turbulent flow of a tsunami. To conclude, we emphasize the importance of studying the modern diatom response to changes in land level and/or tsunami inundation to improve diatom-based records of prehistoric earthquakes and tsunamis.
The potential impact of the abrupt 8.2 ka cold event and the Storegga Slide tsunami on human demography, settlement patterns and culture in the North Sea Basin and its hinterlands has emerged as a key question and research theme. Following on from a paper that evaluated the impact of the 8.2 ka event on the Mesolithic population of western Scotland that employed a Bayesian analysis of the radiocarbon record to identify ‘activity events’ as a proxy for the human population size (Wicks and Mithen, 2014), we have employed a similar approach to assess the impact on the northeast British population. We find evidence for a significant population decline similar to the results from western Scotland, especially in coastal locations, although there is evidence for subtle differences in the data. We interpret this as reflecting significant and rapid population reductions amongst both low density inland populations and higher density coastal populations. The geographical location and topography of the northeast British littoral in relation to the Storegga tsunami meant that populations living along this coastline were likely to be some of the most vulnerable to, and heavily affected by, the impacts of this catastrophic environmental event. In combination with the western Scotland study this research supports the probability that there was significant population collapse resulting from abrupt and profound climatic and vegetation change augmented by the Storegga megaslide tsunami.
The number of tsunami-related scientific publications increased within the last years due to numerous extensive and destructive tsunami events worldwide. The research on tsunami deposits is needed to improve hazard assessment in coastal areas worldwide. While the state of knowledge is rising, the discipline is still relatively young and there are presently a high number of unsolved questions and processes. In the field of palaeotsunami research new insights gained from the most recent events, such as sedimentary characteristics, morphologic features, as well as the recently used methods or so called proxy toolkit, are not yet widely tested on historical events.
In this thesis I try to shed light on diverse problems by means of three case studies carried out in coastal regions of the western Peloponnese (Greece), the Sultanate of Oman and along the eastern Gulf of Cádiz (Spain).
There are open questions as to how the clear identification of tsunami deposits can be carried out and how the preservation of historical event deposits varies in specific archives. Furthermore, the proxy toolkit on palaeotsunami deposits differs from recent deposit investigations. The deposit characteristics, the way of detecting and proving them, the several types of archives, the deposit preservation potential and the challenges of the proxy toolkit are all discussed.
The first case study from Greece uses an approach to detect palaeotsunami deposits by different classical investigation methods, such as sedimentological, palaeontological and geochemical investigations, in different environments/archives. Sedimentary evidence includes the existence of rip-up clasts in multiple sandy fining upward sequences with an erosive base as well as a mixture of foraminifera species from different habitats. Radiocarbon dating proves a minimum of one tsunami landfall in the study area between AD 540 and minimum AD 1274.
The second case study from Oman demonstrates the extensive use of ground penetrating radar (GPR) as well as its potential and limitations concerning tsunami deposit investigations. This investigation method is tested on an inferred tsunami deposit which was identified in previous studies by huge blocks and boulders, most probably transported by tsunami wave action along the coast close to Fins (Oman). The investigated GPR facies reveals wedging out structures, channels, scours and erosion mounds, as well as landward directed foresets. Sedimentary evidence by trenching and age calibration is also presented.
The third case study carried out along the south-eastern Gulf of Cádiz shows an integrative multi-method approach on palaeotsunami deposits. In this study several classical and new investigation tools/techniques were tested and compared to the most recently discovered tsunami characteristics. Furthermore, new tsunami features were found within the sedimentary record of high-energy event deposits. In the presented study a combination of different dating techniques (radiocarbon and optically stimulated luminescence) was also tested to yield possible event ages of the palaeotsunami.
Based on the conclusions achieved from the presented studies I try to answer some of the main questions which arose at the start of this research, regarding the incomplete state of knowledge on tsunami features and characteristics. This thesis also comprises a summary of event ages in the different study areas. The event ages yielded by different dating results are compared to the recent tsunami catalogue of each region, and recurrence intervals which are necessary for an improved hazard assessment are discussed.
Diatoms found within widespread sand beds deposited by tsunamis provide the framework for some of the most detailed historical and long-term (centuries to millennia) earthquake and tsunami reconstructions. In this chapter, we explore how the salinity preferences, life forms, and valve structures of diatoms are particularly useful for identifying tsunami sands within a variety of low-energy coastal environments around the world. We discuss the highly variable "signature" of diatoms within tsunami deposits and describe instances where clearly anomalous, allochthonous marine and brackish diatoms within tsunami deposits help support a marine incursion. We highlight how the fragmentation and sorting of diatom valves may provide evidence of high-energy transport during the rapid, turbulent flow of a tsunami; the potential use of diatoms to estimate tsunami runup beyond the landward limit of sedimentation; and the challenges in differentiating tsunami from storm deposits using diatoms.
The catalog of tsunami deposits in the western Mediterranean, with the exception of the Balearic Islands, is not very large. In total there are 82 localities, of which 65 correspond to the Balearic archipelago. From chose two sites have tsunamites while the rest correspond to large blocks on cliffs. This work is the result of a bibliographic scan of all the articles related to this type of event with the aim of facilitating an adequate weighing of the risks in this half of the Mediterranean. Tsunami frequency is highest in the central Mediterranean and high in the eastern Mediterranean where the vast majority of research work is found. The work describes the general characteristics of the western Mediterranean deposits and their relation with the mathematical models of propagation towards the coast. Resumen: El catálogo de depósitos de tsunami en el Mediterráneo occidental, a excepción de las Baleares, no es muy numeroso. En total son 82 localidades, de las que 65 corresponden al archipiélago Balear. De este conjunto tan solo dos localidades presentan tsunamitas, mientras que el resto corresponde a bloques de gran tamaño sobre acantilados. Este trabajo es el resultado de un revisión bibliográfica de artículos relacionados con este tipo de depósitos sedimentarios asociados a eventos de tsunami, con el objetivo de facilitar una adecuada ponderación de los riesgos en este tercio del Mediterráneo. La frecuencia de tsunamis es más alta en el Mediterráneo central y sobretodo en el oriental donde se encuentra la gran mayoría de los trabajos de investigación. El trabajo describe las características generales de los depósitos del Mediterráneo occidental y su relación con los modelos matemáticos de propagación hacia las costas. Palabras clave: Mediterráneo occidental, tsunami históricos, bloques, tsunamitas. REVISIÓN DE LOS DEPÓSITOS DE TSUNAMIS, BLOQUES Y TSUNAMITAS, EN LAS COSTAS DEL MEDITERRÁNEO OCCIDENTAL Review of tsunami deposits, blocks and tsunamites on the coasts of the western Mediterranean
This report is the published product of a study by the British Geological Survey (BGS) produced as a contribution to EU Framework 6 STREP project TRANSFER Work Package 1. TRANSFER (Tsunami Risk and Strategies for the European Region) is a project examining the tsunami processes in the European area to assess the tsunami hazard, vulnerability and risk assessment, and to identifying how the best strategies to reduce tsunami risk can be delivered to local communities and civil defence agencies. This catalogue attempts to list tsunami events and events previously reported as possible tsunamis detected around the coast of the UK during the Holocene. It includes events detected by their geological evidence, human observations or by measurements recorded by tidal gauges.
Les blocs supratidaux de tempête que l’on trouve au sommet des falaises vont à l’encontre du schéma classique qui décrit l’érosion des falaises. Généralement, le recul des escarpements rocheux se fait au rythme des écroulements gravitaires dont les éléments s’accumulent en pied de falaise, la mer intervenant surtout dans le déblaiement des matériaux accumulés à la base des versants. Dans le cadre de cette thèse, nous étudions les processus d’érosion qui se traduisent par l’accumulation de dépôts grossiers en sommet de falaise. Nous montrons qu’au cours des événements météo-océaniques extrêmes, les effets combinés d’un niveau d’eau à la côte particulièrement élevé et du déferlement de vagues de haute énergie peuvent se manifester localement par l’arrachement et le transport de blocs littoraux supratidaux. Leur masse peut dépasser plusieurs dizaines de tonnes, et leur remaniement peut se faire à plusieurs mètres au-dessus du niveau des hautes mers. De même, leur déplacement peut atteindre plusieurs dizaines à centaines de mètres à l’intérieur des terres. A l’heure où l’on s’interroge sur une possible intensification et/ou augmentation de la fréquence des événements météoocéaniques extrêmes, la dynamique morphosédimentaire de ces blocs littoraux apparait comme un indicateur géomorphologique pertinent pour l’évaluation de ces changements. Un suivi topo-morphologique, sédimentaire et hydrodynamique pluriannuel a été réalisé sur plusieurs sites bretons (Finistère) et islandais (presqu’île de Reykjanes). Les résultats de ce suivi ont montré des schémas de circulation hydro-sédimentaire bien distincts suivant le contexte morphodynamique. Si dans certains cas, les processus transversaux prédominent dans l’édification et le remaniement de ces accumulations, dans d’autres cas, la composante longitudinale contrôle une partie des transferts à la côte. Les processus d’arrachement et de transport de blocs sont concomitants, et peuvent se produire à plusieurs reprises au cours d’un même événement et/ou hiver, y compris pendant les tempêtes d’intensité modérée. L’étude rétrospective des conditions météo-océaniques favorables au déclenchement de ces processus sur les 70 dernières années montre une forte variabilité interannuelle, sans périodicité ni tendance particulière. Cette variabilité est commandée par la dynamique atmosphérique WEPA aux latitudes tempérées de la Bretagne, et par l’ONA aux latitudes sub-polaires de l’Islande.
Turbidity current and coastal storm deposits are commonly characterized by a basal sandy massive (structureless) unit overlying an erosional surface and underlying a parallel or cross‐laminated unit. Similar sequences have been recently identified in fluvial settings as well. Notwithstanding field, laboratory and numerical studies, the mechanisms for emplacement of these massive basal units are still under debate. It is well accepted that the sequence considered here can be deposited by waning‐energy flows, and that the parallel‐laminated units are deposited under transport conditions corresponding to upper plane bed at the dune–antidune transition. Thus, transport conditions that are more intense than those at the dune–antidune transition should deposit massive units. This study presents experimental, open‐channel flow results showing that sandy massive units can be the result of gradual deposition from a thick bedload layer of colliding grains called sheet flow layer. When this layer forms with relatively coarse sand, the non‐dimensional bed shear stress associated with skin friction, the Shields number, is larger than a threshold value approximately equal to 0·4. For values of the Shields number smaller than 0·4 the sheet flow layer disappeared, sediment was transported by a standard bedload layer one or two grain diameters thick, and the bed configuration was characterized by downstream migrating antidunes and washed out dunes. Parallel laminae were found in deposits emplaced with standard bedload transport demonstrating that the same dilute flow can gradually deposit the basal and the parallel‐laminated unit in presence of traction at the depositional boundary. Further, the experiments suggested that two different types of upper plane bed conditions can be defined, one associated with standard bedload transport at the dune–antidune transition, and the other associated with bedload transport in sheet flow mode at the transition between upstream and downstream migrating antidunes.
IntroductionSlope Stability ConsiderationsLandslide TypesImpactFrequency—Magnitude IssuesVulnerability with Respect to Landslide TypesConclusion
Diatoms commonly live in aquatic, naturally illuminated environments from hot-springs to wet soils, intertidal mudflats to the open ocean. As different species of diatoms tend to occupy different niches of the environment, changes in diatom assemblages have been used to infer changes in the coastal environment from freshwater to marine water conditions or vice versa. For sea-level studies, diatoms have been an important proxy for the evaluation and estimation of the indicative meaning of sea-level index points. Sea-level change is an important driving force for changes in coastal environments. There are several ways by which diatoms can help in reconstructing the amount of land-level change relative to sea level and the extent of tsunami or flood water. Despite the fact that diatoms are a useful proxy for sea-level reconstructions, there are some intrinsic problems. This situation occurs when environmental conditions have changed significantly over time in a locality.
The Holocene is the geological epoch, in which the most important human civilizations appear. From that times, the environmental phenomena and the hazards associated with them become very relevant for their wide impact on historical events: They will mingle with the human vicissitudes, influencing the development and decline of the same civilizations. Taking into account the hypothesis formulated by Felice Vinci about the migration of Baltic populations towards the Mediterranean area as a result of the end of the "optimum climate" in the Bronze Age, data on the geological and climatic conditions of the North Europe and Mediterranean are summarized. In particular, information on the glacio-eustatic changes, on the phenomena of isostatic uplift, on tsunamis, earthquakes and other natural events that affected the two examined areas are reported. This study aims to contribute to frame in geological and palaeogeographic terms the hypothesis supported by Vinci, through the analysis the geological and climatic conditions that could have favoured the settlement of peoples from the North in the Mediterranean, also because of a demographic and socio-economic weakening of indigenous populations as a result of catastrophic phenomena. The reconstruction of the paleogeographic conditions of the two areas and the natural events occurred can provide useful information to better identify the places that were the scene of the Trojan War.
We provide a short report on the final year of the INQUA Shorelines Subcommission on Western Europe (2002-3). This includes a review of activities under four themes: sea-level changes in the next century; sea-level changes along a north-south transect from the uplifting coasts of Fennoscandanvia to the subsiding coasts of the North Sea and the Baltic, and the meta stable areas such as Portugal and France; comparisons between modeled and empirical observations of relative sea-level (RSL) change, and palaeo-tsunami and storm records. We conclude by providing a report on the final 2002 Annual Meeting including its field meeting at Greifswald and Mecklenburg - West Pomerania and provide a list of some recent publications by members of the INQUA Shorelines Subcommission.
http://link.springer.com/referenceworkentry/10.1007%2F978-3-642-27737-5_646-1
This paper summarises developments in understanding sea level change during the Quaternary in Scotland since the publication of the Quaternary of Scotland Geological Conservation Review volume in 1993. We present a review of progress in methodology, particularly in the study of sediments in isolation basins and estuaries as well as in techniques in the field and laboratory, which have together disclosed greater detail in the record of relative sea level (RSL) change than was available in 1993. However, progress in determining the record of RSL change varies in different areas. Studies of sediments and stratigraphy offshore on the continental shelf have increased greatly, but the record of RSL change there remains patchy. Studies onshore have resulted in improvements in the knowledge of rock shorelines, including the processes by which they are formed, but much remains to be understood. Studies of Late Devensian and Holocene RSLs around present coasts have improved knowledge of both the extent and age range of the evidence. The record of RSL change on the W and NW coasts has disclosed a much longer dated RSL record than was available before 1993, possibly with evidence of Meltwater Pulse 1A, while studies in estuaries on the E and SW coasts have disclosed widespread and consistent fluctuations in Holocene RSLs. Evidence for the meltwater pulse associated with the Early Holocene discharge of Lakes Agassiz–Ojibway in N America has been found on both E and W coasts. The effects of the impact of storminess, in particular in cliff-top storm deposits, have been widely identified. Further information on the Holocene Storegga Slide tsunami has enabled a better understanding of the event, but evidence for other tsunami events on Scottish coasts remains uncertain. Methodological developments have led to new reconstructions of RSL change for the last 2000 years, utilising state-of-the-art GIA models and alongside coastal biostratigraphy to determine trends to compare with modern tide gauge and documentary evidence. Developments in GIA modelling have provided valuable information on patterns of land uplift during and following deglaciation. The studies undertaken raise a number of research questions which will require addressing in future work.
This is the third and final (and a little late!) Newsletter of the INQUA Subcommission on Shorelines of Northern and Western Europe for the Intercongress period 1995-1999. For Intercongress period 1999-2003 the subcommission has a new committee, a new direction and a new name: Sea Level Changes and Coastal Evolution of Northern and Western Europe.
The Subcommission has been very active during the 1995-1999 Intercongress period. Two field meetings have taken place, the first to the Aquitaine coast of France (April, 1997) and the second to the Baltic coast of Poland (May, 1998).
I am pleased to announce that the first field meeting of the 1999-2003 period will take place in September-October, 2000 along the south-western and southern Portugese coast and is being organised by Delminda Moura at the University of Algarve. Initial information is included in this newsletter and first circulars will be distributed as soon as possible. If you would like to organise the second (or third) field meeting for the 1999-2003 period please come forward. This newsletter also provides a variety of reports on present research in member countries. Thankyou to all those who have contributed to this newsletter and any suggestions on how it can be improved would be welcome.
Finally, the outgoing committee, Jean-Pierre Tastet (President), Kaj Strand Petersen (Vice-President) and myself would like to express our thanks to all members of the subcommission who have contributed to its success during 1995-1999.
The timespan of instrumental and historical records of earthquakes and tsunamis limit our understanding of long-term subduction zone behavior. Coastal stratigraphy, incorporating diatom sea-level indicators, has provided some of the most detailed geological reconstructions of earthquake induced land-level change and tsunami inundation, often over multiple seismic cycles.
In central Chile, I extended the seismic history through a study of a lowland stratigraphic sequence at Quintero (32.5°S). I documented six laterally continuous sand beds dated to 6200, 5600, 5000, 4400, 3800, and 3700 cal yr BP, probably deposited by high tsunamis. Sediment properties and diatom assemblages of the sand beds--anomalous marine planktonic diatoms and upward fining of silt-sized diatom valves and sediments--point to a marine sediment source and high-energy deposition. I inferred coseismic uplift concurrent with the deposition of the sand beds based on an increase in freshwater siliceous microfossils in units overlying the beds. Our record indicates the recurrence interval of large tsunamigenic earthquakes in central Chile is ~500 years, implying that the frequency of historical earthquakes (~80 year recurrence) in central Chile is not representative of the greatest earthquakes the subduction zone can produce.
My study sites in south-central Chile are located in the overlap of the 1960 (Mw 9.5) Valdivia segment and the 2010 (Mw 8.8) Maule segment ruptures. My paleoseismic investigations from the Tirúa (38.3° S) and Quidico (38.1°S) rivers were consistent with eyewitness accounts of tsunami inundation (AD 2010 and 1960) and historical accounts of coseismic land-level change (AD 2010, 1960, 1835, 1751, and 1575). The vertical deformation inferred from diatom analysis suggests that Maule segment earthquakes result in uplift at our sites (e.g., 2010, 1835, and 1751), and Valdivia segment earthquakes result in no deformation (e.g., 1960) or subsidence (e.g., 1575). I identified four prehistoric tsunami deposits dated to AD 1457-1575, 1443-1547, 256-461, and 176-336. Diatoms indicate uplift coincident with sand deposition in AD 1457-1575 and AD 256-461, which we attribute to the Maule segment. Subsidence coincident with sand deposition in AD 1443-1547, and no change in elevation in AD 176-336, is attributed to the Valdivia segment.
Giant submarine landslides in the Storegga area on the continental slope west of Norway took place on at least three occassions during the Late Quaternary. This paper provides a summary of present knowledge regarding tsunamis generated as a result of the Storegga Slides. Most attention, however, is given to the tsunami generated by the Second Storegga Slide that took place circa 7,000 years ago. The tsunami generated by this landslide is believed to have struck most coastlines bordering the eastern North Atlantic. The paper summarises the geological evidence for the former occurrence of this tsunami. These results are compared with the results of recent mathematical modelling of the landslide and tsunami. Remarkably, there is relatively good agreement between estimates of tsunami run-up derived from the sedimentary evidence and run-up values obtained from the modelling experiments.
At a number of locations on the east coast of Scotland, raised Holocene estuarine deposits belonging to the Main Postglacial Transgression contain a distinctive layer predominantly of grey micaceous silty fine sand. Diatom analyses indicate that it is of marine origin; pollen analyses indicate that it is associated with early to middle Flandrian assemblages; and 14C analyses of peat at the upper and lower contacts indicate an event of relatively short duration around 7000 BP. It is thought at present that the layer resulted from either an increase in the rate of rise of relative sea level or a storm surge of unusual magnitude. -from Authors
A description is given of a distinctive marine deposit at Boca do Rio on the Algarve coast of Portugal. It is proposed here that the sediment accumulation was deposited by the tsunami generated by the Lisbon earthquake of 1 November, AD 1755. The deposit exhibits sedimentary characteristics quite unlike other coastal sediment accumulations that are deposited by more moderate wave régimes. These include laterally continuous sand layers, chaotic pebble horizons, large amounts of gravel-sized shell debris and distinctive assemblages of marine microfossils. A preliminary attempt is made here to use the empirical field and laboratory data to define more clearly the processes of coastal sedimentation that characterize tsunami runup. The use of tsunami sediments as time synchronous marker horizons is also discussed.
The Dornoch Firth area contains widespread evidence of Holocene relative sea-level changes. In this study, one and possibly three raised shorelines have been identified on the basis of morphological evidence and have been found to slope downwards towards the north. The highest of these raised shorelines, which reaches up to +7.2 m OD, is correlated with the Main Postglacial Shoreline in Scotland. Stratigraphical and palaeoecological studies of coastal sediment sequences, including radiocarbon dating, disclose a sequence of relative sea-level changes. This began with a fall in relative sea-level from a buried estuarine surface lying at c. −2.0 m OD shortly before c. 9600 bp. Subsequently, a rapid rise of about 7 m took place between c. 7900 and c. 7000 bp, following which, relative sea-level reached the highest raised shoreline. Shortly before the rise in relative sea-level culminated, at c. 7000 bp, a high-energy marine flood occurred. This flood is correlated with a tsunami thought to have occurred about this time in the Northern North Sea. The subsequent fall in relative sea-level to the present may not have been continuous.
Diatoms (Bacillariophyta) help identify the onshore deposits of tsunamis from earthquakes on the Cascadia subduction zone along the Pacific coast of Oregon, Washington, and British Columbia, and on faults high in the North American plate in the Puget Sound area of Washington. At the Copalis River, Washington, diatom analyses suggest that a tsunami deposit about 300 calendric years old (300 yr BP) originated from sandy shoals of the lower estuary rather than nearby beaches or coastal dunes. At Cultus Bay and West Point, Washington, well-preserved benthic estuarine diatoms in sand sheets overlying tidal-marsh peat indicate that the deposits came from intertidal or nearshore areas of Puget Sound. On an abruptly uplifted mudflat at the landward end of Hood Canal at Lynch Cove, Washington, tidal-flat diatoms refute the possibility of a terrestrial source for the sand. Diatoms in 300-yr-BP tsunami deposits on the Niawiakum River, Washington, confirm that the sand in these deposits had a marine source, and help to identify the landward extent of tsunami inundation. Diatom assemblages in deposits of the 300 yr BP and AD 1964 tsunamis at Port Alberni, British Columbia, consist of different dominant taxa, but both indicate that the sand units originated from Alberni Inlet. Diatoms add to stratigraphic evidence that tsunamis flooded Bradley Lake, a freshwater lake on the south-central Oregon coast, three times during the past 1700 years. Planktonic marine diatoms only found above 1-70-cm-thick sand layers in otherwise clayey lacustrine sediment imply tsunami inundation.
On December 12, 1992, at 5:30 A.M. GMT, an earthquake of magnitude Ms
7.5 struck the eastern region of Flores Island, Indonesia (Figure 1), a
volcanic island located just at the transition between the Sunda and
Banda Island arc systems. The local newspaper reported that 25-m high
tsunamis struck the town of Maumere, causing substantial casualties and
property damage. On December 16, television reports broadcast in Japan
via satellite reported that 1000 people had been killed in Maumere and
twothirds of the population of Babi Island had been swept away by the
tsunamis.The current toll of the Flores earthquake is 2080 deaths and
2144 injuries, approximately 50% of which are attributed to the
tsunamis. A tsunami survey plan was initiated within 3 days of the
earthquake, and a cooperative international survey team was formed with
four scientists from Indonesia, nine from Japan, three from the United
States, one from the United Kingdom, and one from Korea.
Flandrian (Holocene) relative sea level changes in the lower Ythan valley, NE Scotland, U.K., are inferred from detailed stratigraphical evidence including microfossil analysis and radiocarbon assay. The principal event recorded is the Main Postglacial Transgression, which was under way in the area by c. 8300 and had culminated before c. 4000 radiocarbon years BP. It is concluded that the rise in relative sea levels during the transgression in the area exceeded 12 m; that the mean rate of rise there was 8·05 mm a−1 between c. 8300 and c. 7100 radiocarbon years BP, or 7·09 mm a−1 based upon calibrated dates for the same period, before declining markedly to 1·75 mm a−1 (radiocarbon) or 1·86 mm a−1 (calibrated) to the culmination of the event. By comparison with other sites, the culmination appears to have been time-transgressive in eastern Scotland. Deposits of the Second Storegga Slide tsunami, which occurred during the Main Postglacial Transgression, are present in the Ythan valley, where the sediment run-up of the event at the sites studied is estimated to have been within the range 2·99–5·19 m.
Sedimentary successions in small coastal lakes situated from 0 to 11 m above the 7000 year BP shoreline along the western coast of Norway, contain a distinctive deposit, very different from the sediments above and below. The deposit is interpreted to be the result of a tsunami inundating the coastal lakes. An erosional unconformity underlies the tsunami facies and is traced throughout the basins, with most erosion found at the seaward portion of the lakes. The lowermost tsunami facies is a graded or massive sand that locally contains marine fossils. The sand thins and decreases in grain size in a landward direction. Above follows coarse organic detritus with rip-up clasts, here termed ‘organic conglomerate’, and finer organic detritus. The tsunami unit generally fines and thins upwards. The higher basins (6–11 m above the 7000 year shoreline) show one sand bed, whereas basins closer to the sea level 7000 years ago, may show several sand beds separated by organic detritus. These alternations in the lower basins may reflect repeated waves of sea water entering the lakes. In basins that were some few metres below sea level at 7000 years BP, the tsunami deposit is more minerogenic and commonly present as graded sand beds, but also in some of these shallow marine basins organic-rich facies occur between the sand beds. The total thickness of the tsunami deposit is 20–100 cm in most studied sites. An erosional and depositional model of the tsunami facies is developed.
The Second Storegga Slide on the continental slope off western Norway has been dated at between 8000 and 5000 yrs B.P. A prominent sand layer in Flandrian (Holocene) deposits along the coast of eastern Scotland, and dated at approximately 7000 yrs B.P. may have been deposited by a tsunami generated by the slide. The altitude and stratigraphy of the layer allow estimates to be made of the magnitude of the earthquake which initiated the slide.
Geological processes associated with tsunamis are poorly understood. In recent years, descriptions of sediments inferred to have been deposited by former tsunamis range from those associated with the KTimpact at ca. 65Myr to those related to the Great Alaska earthquake of 1964. Most earth science textbooks do not consider the geology and geomorphology of tsunamis. Tsunamis produce unique coastal landforms that are characterised by the effects of high-magnitude erosion and deposition. Tsunamis frequently deposit boulder accumulations in many coastal areas; runup processes often also result in the deposition of continuous and discontinuous sediment sheets. Many earthquake-generated tsunamis are also associated with the flooding of coastlines caused by coseismic subsidence. On the seabed, tsunamis may also result in the remobilisation of sediments and the formation of distinctive strata. Most published interpretations of the stratigraphic data that forms the basis for most of the world's Holocene sea-level curves do not consider palaeotsunamis as agents of coastal sedimentation. Biostratigraphic investigations of modern tsunami sediments are crucial in this regard because they assist greatly in the identification of particular microfossil assemblages that can be used to distinguish coastal sediments deposited by palaeotsunamis from storm surges and also from those sediments that have resulted from much longer-term changes in relative sea level.
The Age Calibration Program, CALIB, published in 1986 and amended in 1987 is here amended anew. The program is available on a floppy disk in this publication. The new calibration data set covers nearly 22 000 Cal yr (approx 18 400 14C yr) and represents a 6 yr timescale calibration effort by several laboratories. The data are described and the program outlined. -K.Clayton
Evidence is presented for Holocene relative sea-level changes on the margin of a glacio-isostatically uplifted area: the lower Wick River valley, northern Caithness, Scotland. Lithostratigraphic, biostratigraphic and chronostratigraphic analyses of intercalated clastic and organic sediments disclose evidence for a rapid rise of relative sea level from at least as low as -3.6 m to +1.5 m O.D. during the mid-Holocene, culminating between c. 6900 and c. 5900 BP. This is correlated with the Main Postglacial Transgression, identified widely in eastern Scotland. Following a subsequent regression, the sediments record two further marine transgressions beginning at c. 4400 and c. 1200 BP. The presence of late-Holocene estuarine deposits as the highest Holocene marine sediments is a situation only recorded to date at one other site in mainland Scotland. The coastal sediment sequence also indicates evidence for a palaeotsunami that occurred at between c. 7300 and c. 7000 BP and was associated with the Second Storegga Slide, one of the world's largest submarine sediment slides, located on the continental slope west of Norway.
The Japan Sea Earthquake of May 26, 1983 triggered a large-scale tsunami that surged over the coast of NE Japan and caused considerable damage. The tsunami resulted in peculiar sedimentary processes on the coast. Depending on the hydraulic scale of the tsunami, three kinds of sedimentary processes were recognized, each of which left unique deposits. Such deposits are expected to remain in sedimentary sequences, preserving remarkable sedimentary facies. Borehole samples drilled at different localities in coastal regions have been examined to detect traces of ancient tsunamis. Sedimentological and geochemical studies of the samples reveal that layered deposits, similar to those developed by the Tsunami of the Japan Sea Earthquake, are common in the drilled cores. Estimated ages of these deposits are exactly equivalent to the dates of ancient tsunamis documented in historical records. These results show that the invasion of tsunamis is recorded in coastal depositional sequences. From analyses of long borehole cores we conclude that large-scale tsunamis produced by submarine earthquakes have invaded the coastal regions of the Tsugaru and Sendai Plains at intervals of 250 to 400 yr and about 800 yr, respectively.
The interpretation of diatom biostratigraphy is a little used technique in the study of onshore tsunami sedimentation. Evidence is presented from examples from three tsunamis in which sediments were either observed to have been deposited; documentary evidence attests to the presence of sediment sheets, or finally, in the case of palaeo tsunamis, morphological and stratigraphical evidence permits the interpretation of tsunami inundation and the subsequent deposition of sediment. Examples from Scotland and Canada, and preliminary results from Indonesia, illustrate distinctive diatom assemblages that are associated with tsunami sedimentation. These assemblages contrast with the sediments immediately underlying and overlying the tsunami sediment. Data is presented showing an often chaotic assemblage, attributable to the tsunami waves crossing many distinctive diatom habitats, from fully marine planktonic and benthic species, through the varied intertidal zone and finally over the onshore terrestrial environments.The deposits attributable to tsunami inundation, particularly in Scotland, disclose a high proportion (often in excess of 65%) of broken diatom valves, and an over-representation of centric species due to their greater resistance to erosion. Together the information derived from known historical tsunamis and from palaeo tsunamis with good stratigraphical and dating control provide a good basis for the study of the diatom characteristics of modern tsunamis.
article size, organic content, loss on ignition (LOI), geochemistry, radiocarbon and 137Cs analyses were carried out on paired cores taken from Wainui, Totaranui and Awaroa Inlets, Abel Tasman National Park. A 1700 year record of long- and short-term environmental changes was produced representing a sedimentary and geochemical sequence from tidal flat to mature salt marsh. The sequence is punctuated by a series of short-term environmental changes, namely tsunami, establishment of salt marsh, and European settlement. Long-term environmental changes include fluctuating accretion rates and relative sea level rise. Tsunami “signatures” include: (i) a peak in fines, (ii) contemporaneous or “delayed” peak in organic content and/or LOI, (iii) contemporaneous peaks in Fe and/or S, (iv) dilution of anthropogenic contaminants, and (v) visible change in the sediments. Ruptures of the Wellington and West Wairarapa Faults are considered to be the tsunamigenic sources. Pre-European sediment accretion rates in Abel Tasman National Park range from 0.5 to 1.7mm/a, with post-European settlement rates increasing to 1.6–2.7mm/a. In the past 30 years, rates have increased to 2.3–3.3mm/a. The component of relative sea level rise is estimated to be about 1.3–2.2mm/a which compares favourably with the nearest tidal records from Wellington.
Lacustrine deposits of the Pacific coast of northeast Japan, consisting mostly of black organic mud, contain intercalated thin beds of well-sorted medium sand. Examination of the deposits from a coastal site of Sanriku has revealed that sand grains are of marine origin and are fractions of deposits in marshy ponds, transported from the littoral environment by a great flooding of seawater. The mode of sedimentation shown in the thin beds of sand implies that they were deposited by tsunamis, each with a maximum rise of 1 m or more above sea level.
The Japan Sea Earthquake of May 26, 1983 triggered a large-scale tsunami that surged over the coast of NE Japan and caused considerable damage. The tsunami resulted in peculiar sedimentary processes on the coast. Depending on the hydraulic scale of the tsunami, three kinds of sedimentary processes were recognized, each of which left unique deposits. Such deposits are expected to remain in sedimentary sequences, preserving remarkable sedimentary facies. -from Authors
Relict shore features and deposits of Flandrian age in the Montrose Basin area are examined. The main features are the former estuarine mudflats of the carselands surrounding the Basin and a complex of sand and shingle ridges lying to seaward. These features are thought to have accumulated as a result of the Main Postglacial Transgression in the area. During the transgression, a storm surge which took place at about 7000 years B.P. resulted in the deposition of a widespread layer of grey micaceous silty fine sand in the carse deposits. The culmination of the transgression is marked by an extensive carseland surface, which attains circa + 6.0m to + 7.0m, O.D. and by continued accumulation of the sand and shingle ridge complex, which reaches + 10.0m, O.D. As relative sea level fell subsequently, a second surface was produced, attaining circa + 4.0m to + 5.0m, O.D. in the carselands and up to + 5.8m, O.D. in the sand and shingle ridge complex. The wide extent of this feature in the latter area is probably due to the fortuitous location of a surface of Late Devensian deposits beneath.
Relict Flandrian estuarine deposits in the Ythan valley are confined to an area in the lower valley around the present estuary. They rest upon a discontinuous layer of peat over an irregular surface of sand and gravel, and consist for the most part of a grey silty clay, or carse deposit, which forms terraces or small areas of carseland. At the seaward end of the estuary the grey silty clay contains a layer of grey, micaceous, silty fine sand, which tapers into the basal peat, whilst in places the surface of the grey silty clay is covered by peat and/or blown sand. The vegetational context and age of these deposits have been determined at Waterside, near the mouth of the present estuary. Here, the grey silty clay accumulated as the result of a marine transgression which began in the early Flandrian, and culminated between about 6189·95 and some time prior to 4000·80 radiocarbon years B.P. The carseland surface produced by this phase of accumulation is the highest Flandrian estuarine surface in the valley, at about 4·5 m O.D., and is correlated with the Main Postglacial Shoreline elsewhere in eastern Scotland. Withdrawal of the sea from this level may have been interrupted by the formation of a lower carseland surface before present levels were reached, though this is far from certain. The grey, micaceous, silty fine sand layer is dated at approximately 6850·140 radiocarbon years B.P., and is correlated with similar layers that may have been deposited following a storm surge. The paper concludes with some considerations on the age and distribution of the Main Postglacial Shoreline in eastern Scotland.
The statigraphy in 25 coastal lakes shows that most of the Norwegian coastline was impacted by a large tsunami about 7200 14C BP. The methodology has been to core a staircase of lake basins above the contemporary sea level in several areas and to map the tsunami deposit to its maximum elevation. The tsunami was identified in the sedimentary record as an erosional unconformity overlain by graded or massive sand with shell fragments, followed by redeposited organic detritus. The greatest recorded runup along the coast (10–11 m above high tide) is found in areas most proximal to the Storegga slide scar on the Norwegian continental slope (Sunnmøre). To the north and south, runup is less, about 6–7 m at Bjugn (250 km north of Sunnmøre) and about 3–5 m in Austrheim (200 km to the south of Sunnmerre). This runup pattern supports the suggestion that the tsunami was generated by the Second Storegga Slide. The recorded runup heights are consistent within and between the investigated areas, and imply that the tsunami wave was not significantly influenced by the local topography, suggesting a very long wave length. The mapped runup estimates are in good agreement with a numerical model of the tsunami generated by the Second Storegga slide, and indicate that the slide was a single major event rather than a set of smaller slides.
Onshore tsunami deposits resulting from the 1993 Southwest Hokkaido and 1983 Japan Sea earthquakes were described to evaluate the feasibility of tsunami deposits for inferring paleoseismic events along submarine faults. Tsunami deposits were divided into three types, based on their composition and aerial distribution: (A) deposits consisting only of floating materials, (B) locally distributed siliclastic deposits, and (C) widespread siliclastic deposits. The most widely distributed tsunami deposits consist of the first two types. Type C deposits are mostly limited to areas where the higher tsunami runup was observed. The scale of tsunami represented by vertical tsunami runup is an important factor controlling the volume of tsunami deposits. The thickest deposits, about 10 cm, occur behind coastal dunes. To produce thick siliclastic tsunami deposits, a suitable source area, such as sand bar or dune, must be available in addition to sufficient vertical tsunami runup. Estimation of the amounts of erosion and deposition indicates that tsunami deposits were derived from both onshore and shoreface regions. The composition and grain size of the tsunami deposits strongly reflect the nature of the sedimentary materials of their source area. Sedimentary structures of the tsunami deposits suggest both low and high flow rgimes. Consequently, it seems very difficult to identify tsunami deposits based only on grain size distribution or sedimentary structure of a single site in ancient successions.
This paper presents a method for reconstructing sedimentary environments on the basis of diatoms in clastic deposits of coastal wetlands. The method includes improvements and updates of previously described approaches of coding ecological data on diatom species for computer utilization and of combining diatom species into ecological groups, which are related to specific environments.
The assessment of autochthonous and allochthonous diatoms is the major problem in the palaeoenvironmental diatom research in tide-influenced coastal areas, because the allochthonous influx by tidal currents (mainly marine planktonic and tychoplanktonic diatoms) is significant. In tidal deposits, the allochthonous diatoms often outnumber the autochthonous assemblage. Criteria for the assessment regarding which diatoms are ‘in or out of place’ are discussed.
Geomorphological processes associated with tsunami run-up and backwash are highly complex. To date, most studies have considered the sedimentology of palaeo-tsunamis while almost no detailed studies have been undertaken in areas known to have been affected by tsunamis in recent times. Research on contemporary tsunamis show that coastal landscapes may be greatly altered not only by direct tsunami run-up orthogonal to the shoreline, but also by episodes of vigorous backwash and by water flow sub-parallel to the coastline. The combined effect of these processes produces hitherto unrecognised coastal landforms that are dominated by the effects of high-magnitude erosion and deposition. Deposition of large boulders is also associated with severe tsunamis, while in adjacent areas run-up processes often result in the deposition of continuous and discontinuous sediment sheets. In many instances the upper limit of sediment deposition lies well below the upper limit of wave run-up which is frequently marked by a well-defined zone of stripped vegetation and soil. The processes described have considerable implications for models of coastal evolution. It may even be the case that the evolution of particular stretches of coastline are dominated by such high-magnitude low-frequency events.
A mathematical model based on the hydrodynamic shallow water equations is developed for numerical simulation of water waves generated by the submarine Storegga Slides on the Norwegian continental slope. The equations are solved numerically by a finite difference technique. Computations of wave amplification effects reveal run-up heights for the Second Storegga Slide between 3 and 5 m in exposed areas along the eastern coast of Greenland, Iceland and Scotland and the western coast of Norway. The calculated run-up heights agree remarkably well with possible tsunami wave heights deduced from geological evidences along the eastern coast of Scotland. The generated wave heights are strongly dependent on the acceleration of the slide. The effects of shear stress at the interface between the water and the slide body, has turned out to be important.
Thesis (doctoral)--University of Bergen, 1996. Includes bibliographical references.
At sites near the Brazos River, Texas, an iridium anomaly and the paleontologic Cretaceous-Tertiary boundary directly overlie
a sandstone bed in which coarse-grained sandstone with large clasts of mudstone and reworked carbonate nodules grades upward
to wave ripple-laminated, very fine grained sandstone. This bed is the only sandstone bed in a sequence of uppermost Cretaceous
to lowermost Paleocene mudstone that records about 1 million years of quiet water deposition in midshelf to outer shelf depths.
Conditions for depositing such a sandstone layer at these depths are most consistent with the occurrence of a tsunami about
50 to 100 meters high. The most likely source for such a tsunami at the Cretaceous-Tertiary boundary is a bolidewater impact.
Tsunami favoured over storm or seiche for sand deposits overlying buried Holocene peat Onshore tsunami deposits caused by the SW Hokkaido and 1993 Japan Sea earthquakes Observational and theoretical aspects of tsunami sedi-mentation Flandrian relative sea level changes in the Montrose Basin area
- M A Reinhardt
- J Bourgeois
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- T Shimamoto
- A Tsutsumi
- K Kawamoto
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- ±
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European waters including the Medi-terranean Sea Admiralty Hydrographic Department A guide to the morphology of the diatom Frustule, with a key to the British freshwater genera
- Admiralty Tide
- Tables Barber
- H G Haworth
Admiralty Tide Tables, 1996. European waters including the Medi-terranean Sea, vol. 1. Hydrographer of the Navy, Admiralty Hydrographic Department. Barber, H.G., Haworth, E.Y., 1981. A guide to the morphology of the diatom Frustule, with a key to the British freshwater genera, Freshwater Biological Association, Ambleside (109pp.).
The Storegga tsunami deposits in western Norway and Postglacial sea level margin on Svalbard Tsunami sedi-mentary facies deposited by the Storegga tsunami in shallow marine basins and coastal lakes, western Norway. Sedimentol-ogy 44, The Storegga tsunami along the Norwegian coast, its age and runup
- S S Bondevik
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- J Mangerud
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Model simulations of tsunamis generated by the Storegga slide Diatoms as an aid in identifying late Holocene tsunami deposits. The Holocene Traces of tsunami preserved in inter-tidal lacustrine and marsh deposits:some examples from Northeast Japan
- C B Harbitz
- E Hemphill-Haley
Harbitz, C.B., 1991. Model simulations of tsunamis generated by the Storegga slide. Institute of Mathematics, University of Oslo, series 5, 30pp. Hemphill-Haley, E., 1996. Diatoms as an aid in identifying late Holocene tsunami deposits. The Holocene 6 (4), 439±448. Minoura, K., Nakaya, S., 1991. Traces of tsunami preserved in inter-tidal lacustrine and marsh deposits:some examples from Northeast Japan. J. Geol. 99, 265±287. Minoura, K., Nakaya, S., Uchida, M., 1994. Tsunami deposits in a lacustrine sequence of the Sanriku coast, northern Japan. Sediment. Geol. 89, 25±31.
Reconnaissance of the Late Holocene Evolution of Okupe Lagoon, Kapiti Island, New Zealand
- Goff
Tsunami favoured over storm or seiche for sand deposits overlying buried Holocene peat, Willapa Bay, Washington
- Reinhardt
Flandrian relative sea level changes in northern Scotland. Unpublished PhD dissertation
- S Dawson
Observational and theoretical aspects of tsunami sedimentation. Unpublished PhD dissertation
- S Shi