This is the working title for a paper my advisor and I are submitting to Marine Geology. The paper comes from my MSc thesis, which focuses on reconstructing intense flooding events due to hurricanes in the northern GoM.
Four LiDAR data sets are used here to investigate both subaerial and subaqueous sediment volume changes during the most recent intense storm impact, Katrina, and the fair-weather period following. This investigation will provide the most high-resolution geomorphological and sedimentological analysis of the Ship Island system to date and will tackle questions of island sustainability in the light of a possible artificial restoration of the island to its original form using dredged materials. A study funded by MsCIP https://gom.usgs.gov/web/Projects/View/4
Research Item (40)
Barrier systems around the world are experiencing accelerated sea-level rise, reduced sediment supply, and frequent hurricane impacts. However, detailed quantitative field-based studies concerning the response to these external forcing mechanisms are scarce, particularly on the scale of entire islands. The Mississippi – Alabama barrier island chain, located along the U.S. Gulf of Mexico coastline has lost land on the order of hectares per year since records began in the 1840s, putting mainland coastal communities and important ecosystems at risk. Here we present an analysis of Light Detection and Ranging (LiDAR) digital elevation models, revealing erosional/depositional patterns and geomorphologic changes around the most vulnerable of these islands, Ship Island. Four LiDAR datasets (2004, 2007, 2010, and 2012), capturing the complete topography of the island and some bathymetry in the inlet and surrounding shallows to depths of up to 8 meters, are used to investigate subaerial and subaqueous sediment volume changes between these years. The impact of Hurricane Katrina, which produced the highest storm surge ever recorded in the United States, is captured in the 2004-2007 data set. During this time, sediment comparable to 1.5 times the 2004 subaerial island volume was lost from the area included in the topographic/bathymetric dataset. Only 1/5 of this volume was recovered to this area between 2007 and 2010. The island returned to a state of sediment loss between 2010 and 2012, albeit within the error bounds, while the aerial extent of the islands continued to increase. This study examines the impact severe storm events can have on vulnerable barrier islands. It highlights the importance of utilizing 3D datasets that include both topographic and bathymetric data for morphodynamic analyses of barrier island systems.
Follets Island, a transgressive island located on the upper Texas coast, is an ideal location to study barrier island transition from a rollover subaerial barrier to subaqueous shoals. This system also allows for an examination of coastal response to accelerated sea-level rise, storms, and sediment supply. The landward shoreline retreat rate during historical time is similar to the landward retreat rate of the bay shoreline, hence its current classification as a rollover barrier. However, the island has a limited and diminishing sand supply, which makes it even more vulnerable to erosion during storms and relative sea-level rise. Four core transects that extend from the upper shoreface to the back barrier bay are used to constrain the thickness of washover, barrier and upper shoreface deposits and to estimate sediment fluxes in the context of the overall sand budget for the island over centennial timescales. Stratigraphic architecture reveals two prominent transgressive surfaces. A lower flooding surface separates red fluvial-deltaic clay from overlying bay mud and an upper erosional surface separates back-barrier deposits from overlying shoreface and foreshore deposits. Radiocarbon ages are used to constrain the evolution of the barrier and its long-term rate of island migration whereas 210Pb dates are used to constrain the modern sand overwash flux. Results show that significant washover sands are deposited in the bay and about twice this volume is deposited as subaerial washover deposits. The total sand washover volume shows that overwash processes account for about half of the sand produced by shoreline erosion in historical time. Our results also indicate that the historical rate of shoreline retreat is about an order of magnitude faster than the geologic rate. We estimate back-barrier accommodation space to be about three times greater than the volume of the barrier. Hence, given the current shoreline erosion and overwash flux rate, Follets Island will eventually transition from a subaerial rollover barrier to subaqueous shoals. The frequency of severe storms along the Texas coast is not believed to have varied significantly in recent time, but the rate of sea-level rise has increased approximately five-fold and sand supply to the island is minimal. This leads us to suggest that accelerated sea-level rise and diminished sand supply are the main causes of this unprecedented change.
The northern Gulf of Mexico has been devastated by recent intense storms. Camille (1969) and Katrina (2005) are two notable hurricanes that made landfall in nearly the same location in Mississippi. Fully understanding the risks and processes associated with hurricane impacts are impeded by a short and fragmented instrumental record, however. Paleotempestology has the potential to employ modern analogues from intense storms in this region to extend the hurricane record beyond pre-observational time. Existing empirically-based models can back-calculate surge heights over coastal systems as a function of transport distance, particle settling velocity, and gravitational acceleration. We collected sediment cores in a pond (3) and adjacent beach (1) in Hancock County, Mississippi. Grain-size, loss-on-ignition, and microfossil analyses were conducted on cores in the context of a Bayesian statistical age model using 137Cs and 14C dating. Using Hurricane Camille to calibrate the archive, similar coarse-grained deposits were identified, and inverse sediment transport models calculated paleosurge intensities similar in magnitude to Camille over the 2500-yr record. Our multi-millennial annual average landfall probability (0.48%) closely matches previously published studies from the Gulf of Mexico, indicating that intense hurricanes have not varied over these timescales. Over centennial timescales, active intervals occurred between 900 to 600 and 2200 to 1900 yr BP, with relative quiescence between 1900 to 900 yr BP. Comparisons with other published sites support the notion that southerly shifts in the Loop Current may be responsible for the decline in activity around 600 yr BP.
The interpretation of sediments deposited by prehistoric tropical cyclones (TC's) is limited by a lack of modern analogues, particularly in the South Pacific. On 13 March 2015, TC Pam made landfall on Vanuatu, reaching Category 5 intensity with 10-minute sustained wind speeds as high as 270 km/h. Three months after landfall, we measured flow height (terrain elevation plus storm flow depth) and inland extent of TC Pam's maximum coastal inundation (composed of astronomical tides, storm surge, and superimposed storm waves), and described the sedimentological characteristics of the TC Pam overwash sediments from trenches and transects at two sites (Manuro and Port Resolution Bay).
- Apr 2017
- AAPG Annual Convention and Exhibition
This paper reviews the recent work of John B. Anderson through the lense of the presenting author and former student. This includes coastal geology, sedimentology, paleotempestology, and global change based primarily on field-based data and observations. Specifically, this talk reviews several Texas coastal studies on mechanisms of erosion, coastal sediment budgets, hurricane impacts over centennial and millennial timescales, and source to sink evolution in response to eustatic changes. This work is critical towards furthering our understanding of the dynamics associated with sedimentary systems. Along the upper Texas coast, both natural and anthropogenic mechanisms of erosion were quantified, in an effort to determine whether current erosion rates are unprecedented over historic time. River damming has had a minimal impact on sediment delivery to the coast, while engineering structures designed to slow down beach erosion have starved downdrift areas of sand deposition. This work paved the way for a study, which determined the volumetric sand flux over geologic and historic timescales into a tidal delta along the upper Texas coast. The majority of this sand was derived from erosion of Galveston Island, and revealed that erosion of this barrier island has been significantly enhanced due to a combination of accelerated sea-level rise coupled with hurricanes over centennial relative to millennial timescales. Bays along the northwestern Gulf of Mexico also responded to episodes of Holocene sea-level rise by rapidly flooding, and bayhead deltas backstepped landward at high rates. Furthermore, the millennial scale rate of hurricane impacts along the upper Texas coast was quantified. Over the past ~5,000 years, the annual intense hurricane landfall probability for south Texas is ~0.46%. Similar long-term annual probabilities across the Gulf of Mexico suggest that intense hurricane activity over multimillennial periods has not varied significantly. The evolution of late Quaternary depositional systems along the Texas margin was examined over the last 125,000 years. This work demonstrated the complex response of coastal systems from sea-level and sediment supply variations.
- Aug 2016
A tsunami generated by the C.E. 1707 Hōei earthquake is largely thought to be the flood event of record for southwestern Japan, yet historical documentation of the event is scarce. This is particularly true within the Bungo Channel, where significant inconsistencies exist between historical records and model-derived tsunami heights. To independently assess flooding from the Hōei tsunami in this region, we present complementary reconstructions of extreme coastal inundation from three back-barrier lakes in the northern Bungo Channel: Lake Ryuuoo, Lake Amida, and Lake Kamega. At all sites, the age of the most recent prominent marine overwash deposit is consistent with the timing of the 1707 tsunami. When combined with historical documentation of the event, these sedimentological records provide strong evidence that the 1707 tsunami is the most significant flood of recent centuries and one of the most significant floods over the last millennium in the region. At Lake Ryuuoo, modern barrier beach elevations and grain sizes in the tsunami’s resultant deposit provide ~4 m as the first physically based height constraint for the 1707 tsunami in the northern Bungo Channel. A concurrent transition in lithology that is consistent with regional geomorphic change is also observed at all three sites around 1000 years ago, although the precise timing and nature of the transition remain unclear.
Level 1 Moderate Resolution Imaging Spectroradiometer (MODIS) data is processed to extract the remote sensing reflectance at the wavelength of 645 nm and binned into an 8-day composite at a resolution of 500 m. The study uses a regional ocean color algorithm to compute suspended particulate matter (SPM) concentration based on these 8-day composite images. Multivariate analysis is applied between the SPM and time series of tides, wind, turbidity and river discharge measured at federal and academic institutions’ stations and moorings.
Due to relatively short instrumental observations, paleohurricane records can be useful for extending our knowledge of hurricane response to known variable climatic and oceanographic conditions in the past. By carefully selecting new sites from around the world, additional insights can be gained towards a more complete understanding of basin-wide hurricane trends. Here we highlight a paleotempestological study from Mangrove Lake (ML), Bermuda. Due to the unique offshore location of Bermuda in the western Atlantic, this site contains information about northeastwardly recurving Atlantic storms. ML currently has a flooding height threshold of 7 meters above sea-level, being separated from the ocean by stable Pleistocene-age eolianites. Therefore, it is likely that storms preserved in this setting represent large inundation events. Based on nearly 30 rapid turn-around gas ion source AMS radiocarbon dates, four conventional AMS ages, and short-lived isotopic accumulation rates, a Bayesian statistical age model is constructed. We will discuss the multiproxy paleotempestological approach consisting of X-radiographs, X-ray fluorescence, micropaleontology, and grain size measurements in the context of the ~2,000 year age model to estimate the frequency, intensity, and timing of storms. Preliminary data from the lake show numerous coarse-grained deposits containing the offshore forminifer Homotrema rubrum, interpreted as storm-induced transport. The timing of these deposits suggests elevated periods of hurricane activity occurred between ~500 and ~1,000 yr BP using the standard marine reservoir radiocarbon correction. ML could provide valuable insight concerning Atlantic hurricane variations due to changing North Atlantic Oscillation-like conditions and regional oceanographic changes. Furthermore, this site could shed light on regional storm trends through a comparison with established records.
Do storms have the competency to move boulders? This topic has been a polarizing question in coastal settings around the world. Some researchers have shown boulders emplaced during storms, while others invoke tsunamis as the only appropriate mechanism. Here we present a unique dataset of boulders being transported during relatively minor storms at Spittal Pond, Bermuda. The exposed limestone rock barrier at this site is quickly colonized by a cyanobacterium, Scytonema hofmanni, but this does not occur beneath boulders blocking sunlight. However, when boulders are transported, the fresh, white limestone surface is exposed leaving an outline of the former location. Photographic evidence of large boulders near the site was taken in 2013. During reconnaissance work in 2014, some of the largest boulders were documented to have moved several meters. Numerous smaller boulders were inferred to have moved based on unweathered limestone outlines matching nearby boulders. The only inundation events during this time interval were Hurricanes Fay (category 1) and Gonzalo (category 2) that both made landfall in October 2014. The largest boulders transported were between ~1 and 8 tonnes, and simple numerical modeling suggests that flow velocities would have to exceed ~4 and 6 m/s, respectively. This work suggests that even modest storms have the competency to move boulders.
The northwestern Gulf of Mexico Basin is an ideal natural laboratory to study and understand source-to-sink systems. An extensive grid of high-resolution seismic data, hundreds of sediment cores and borings and a robust chronostratigraphic framework were used to examine the evolution of late Quaternary depositional systems of the northwestern Gulf of Mexico throughout the last eustatic cycle (~ 125 ka to Present). The study area includes fluvial systems with a wide range of drainage basin sizes, climate settings and water and sediment discharges. Detailed paleogeographic reconstructions are used to derive volumetric estimates of sediment fluxes (Volume Accumulation Rates). The results show that the response of rivers to sea-level rise and fall varied across the region. Larger rivers, including the former Mississippi, Western Louisiana (presumably the ancestral Red River), Brazos, Colorado and Rio Grande rivers, constructed deltas that advanced across the shelf in step-wise fashion during Marine Isotope Stages (MIS) 5–2. Sediment delivery to these deltas increased during the overall sea-level fall due to increases in drainage basin area and erosion of sediment on the inner shelf, where subsidence is minimal, and transport of that sediment to the more rapidly subsiding outer shelf. The sediment supply from the Brazos River to its delta increased at least 3-fold and the supply of the Colorado River increased at least 6-fold by the late stages of sea-level fall through the lowstand. Repeated filling and purging of fluvial valleys from ~ 119–22 ka contributed to the episodic growth of falling-stage deltas. During the MIS 2 lowstand (~ 22–17 ka), the Mississippi River abandoned its falling-stage fluvial–deltaic complex on the western Louisiana shelf and drained to the Mississippi Canyon. Likewise, the Western Louisiana delta was abandoned, presumably due to merger of the Red River with the Mississippi River, terminating growth of the Western Louisiana delta. The Brazos River abandoned its MIS 3 shelf margin delta to merge with the Trinity, Sabine and Calcasieu rivers and together these rivers nourished a lowstand delta and slope fan complex. The Colorado and Rio Grande rivers behaved more as point sources of sediment to thick lowstand delta–fan complexes. Lowstand incised valleys exhibit variable morphologies that mainly reflect differences in onshore and offshore relief and the time intervals these valleys were occupied. They are deeper and wider than falling stage channel belts and are associated with a shelf-wide surface of erosion (sequence boundary). During the early MIS 1 (~ 17 ka to ~ 10 ka) sea-level rise, the offshore incised valleys of the Calcasieu, Sabine, Trinity, Brazos, Colorado, and Rio Grande rivers were filled with sediment. The offshore valleys of smaller rivers of central Texas would not be filled until the late Holocene, mainly by highstand mud. The lower, onshore portions of east Texas incised valleys were filled with sediment mainly during the Holocene, with rates of aggradation in the larger Brazos and Colorado valleys being in step with sea-level rise. Smaller rivers filled their valleys with back-stepping fluvial, estuarine and tidal delta deposits that were offset by flooding surfaces. In general, the sediment trapping capacity of bays increased as evolving barrier islands and peninsulas slowly restricted tidal exchange with the Gulf and valley filling led to more shallow, wider bays. A widespread period of increased riverine sediment flux and delta growth is attributed to climate change during MIS 1, between ~ 11.5 and 8.0 ka, and occurred mainly under cool-wet climate conditions. Relatively small sea-level oscillations during the MIS 1 transgression (~ 17 ka to ~ 4.0 ka) profoundly influenced coastal evolution, as manifested by landward stepping shorelines, on the order of tens of kilometers within a few thousand years. The current barriers, strand plains and chenier plains of the study area formed at different times over the past ~ 8 ka, due mainly to differences in sand supply and the highly variable relief on the MIS 2 surface on which these systems formed. Modern highstand deposition on the continental shelf formed the Texas Mud Blanket, which occurs on the central Texas shelf and records a remarkable increase in fine-grained sediment supply. This increase is attributed to greater delivery of sediments from the Colorado and Brazos rivers, which had filled their lower valleys and abandoned their transgressive deltas by late Holocene time, and to an increase in westward directed winds and surface currents that delivered suspended sediments from the Mississippi River to the Texas shelf. Collectively, our results demonstrate that source-to-sink analyses in low gradient basin settings requires a long-term perspective, ideally a complete eustatic cycle, because most of the sediment that was delivered to the basin by rivers underwent more than one cycle of erosion, transport and sedimentation that was regulated by sea-level rise and fall. Climate was a secondary control. The export of sediments from the hinterland to the continental shelf was not directly in step with temperature change, but rather varied between different fluvial–deltaic systems.
- Dec 2014
- American Geophysical Union
Is a small quantity of high-precision ages more robust than a higher quantity of lower-precision ages for sediment core chronologies? AMS Radiocarbon ages have been available to researchers for several decades now, and precision of the technique has continued to improve. Analysis and time cost is high, though, and projects are often limited in terms of the number of dates that can be used to develop a chronology. The Gas Ion Source at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS), while providing lower-precision (uncertainty of order 100 14C y for a sample), is significantly less expensive and far less time consuming than conventional age dating and offers the unique opportunity for large amounts of ages. Here we couple two approaches, one analytical and one statistical, to investigate the utility of an age model comprised of these lower-precision ages for paleotempestology. We use a gas ion source interfaced to a gas-bench type device to generate radiocarbon dates approximately every 5 minutes while determining the order of sample analysis using the published Bayesian accumulation histories for deposits (Bacon). During two day-long sessions, several dates were obtained from carbonate shells in living position in a sediment core comprised of sapropel gel from Mangrove Lake, Bermuda. Samples were prepared where large shells were available, and the order of analysis was determined by the depth with the highest uncertainty according to Bacon. We present the results of these analyses as well as a prognosis for a future where such age models can be constructed from many dates that are quickly obtained relative to conventional radiocarbon dates. This technique currently is limited to carbonates, but development of a system for organic material dating is underway. We will demonstrate the extent to which sacrificing some analytical precision in favor of more dates improves age models.
- Oct 2014
- Geological Society of America
Paleohurricane archives can elucidate current and future hurricane impacts by establishing a geologic and climatic context from numerous sites across the Earth. Due to relatively short instrumental observations in most regions, these records have been useful for interpreting long-term coastal environment evolution and hurricane response to variable climatic and oceanographic conditions in the past. By comparing existing and carefully selected new sites, additional insights can be gained towards a deeper understanding of basin-wide Holocene Atlantic trends. Here we highlight an ongoing paleotempestological project from Mangrove Lake (ML) and Spittal Pond (SP), Bermuda. Due to the unique location of Bermuda in the western Atlantic, these ponds could yield one of the only coastal records of northeastwardly recurving Atlantic storms. These sites have different flooding heights required for inundation and storm deposition, with minimum thresholds of 7 meters (ML) and 3 meters (SP). ML appears to contain a ~4,000 yr B.P. record of intense hurricanes, while Spittal Pond contains a similar ~3,000 yr B.P. record of less intense storms. We will discuss a multiproxy paleotempestological approach consisting of X-radiographs, X-ray fluorescence, and grain size measurements in the context of a short-lived isotope and radiocarbon-derived age model. These sites will provide valuable insight concerning Holocene Atlantic hurricane variability due to North Atlantic Oscillation-like conditions, in addition to quantifying regional trends and responses of storms to oceanographic changes.
Hurricanes annually threaten the Atlantic Ocean margins. Historical hurricane records are relatively short and palaeohurricane sedimentary archives provide a geological and climatic context that sheds light on future hurricane activity. Here we review palaeo-trends in hurricane activity elucidated from sedimentary archives. We discuss dating methods, site selection and statistics associated with previously published records. These archives have been useful for understanding the long-term evolution of coastal systems and the response of intense hurricane activity to climatic changes. Regional shifts in hurricane overwash on centennial to millennial timescales have been linked to various climatic modes of variability, including El Niño/Southern Oscillation and the North Atlantic Oscillation, but could also reflect regional-scale controls on hurricane activity.
The results from nearly three decades of marine geological research in the northwestern Gulf of Mexico are compiled in an effort to understand those factors (e.g., sea-level rise, sediment supply, subsidence, antecedent topography) that influenced coastal evolution during the last eustatic cycle (~ 120 ka to Present). Armed with this information, we evaluate coastal response to variable sea-level rise of the Holocene and accelerated rise during historical time to gain a better understanding of how the coast is likely to respond to future changes.
Incorporating technology into courses is becoming a common practice in universities. However, in the geosciences, it is difficult to find technology that can easily be transferred between classroom- and field-based settings. The iPad is ideally suited to bridge this gap. Here, we fully integrate the iPad as an educational tool into two graduate-level K-12 in-service teacher outreach classes, one classroom-based course and one field-based course. We describe our field and classroom course objectives, and the integration of iPads into both settings. We assess the impact of the iPad in these courses through the use of pre- and posttests and surveys. Most participants enthusiastically use iPads once the initial learning curve is overcome. They tend to spend roughly the same amount of time using technology, but they substitute iPad use for laptop use once they become proficient with the iPad. Additionally, when equipped with an iPad, there is a possible increase in overall productivity as the participants spend more time preparing both for their university outreach classes and the classes they teach. However, they do spend more time on certain noneducational activities (i.e., picture/music/movies), but they appear to be more efficient and spend less time browsing the internet and conducting research for their classes. Interestingly, having participants work with iPads appears to increase confidence in general technology use, including laptops, as well as increasing confidence in the iPad as a teaching tool for their own classrooms. Pre- and posttest data suggest that there is no link to increased content knowledge by integrating iPads versus traditional teaching methods.
The upper Texas coast is an ideal location to examine coastal response to global change over geologic and historic time. Here we quantify the long-term sequestration for sand eroded from an island into two main sinks, offshore Galveston Island and San Luis Pass Tidal Delta, in order to compare long-term and short-term erosion. We determine the average storm-related offshore sand flux for the middle part of the Holocene (ca. 5240-5040 [2σ] cal yr B.P. to present) to be ~4200-4400 ± 670 m3/yr, with a decrease in the offshore sand flux to ~920-970 ± 270 m3/yr during the latter part of the Holocene (ca. 2730-2610 [2σ] cal yr B.P. to present). The tidal delta initially formed ca. 2100 (1σ median) cal yr B.P., when the rate of sea level rise slowed from 2.0 mm/yr to 0.60 mm/yr. We calculate the sand flux from Galveston Island into San Luis Pass from ca. 2100 (1σ median) cal yr B.P. to 200 yr ago to be ~4700 m3/yr. Evidence from navigational charts and sediment cores suggests this flux has increased to ~10,000 m3/yr over the past ~200 yr. Coupling these data with recently published long-term sand fluxes to the shore face of Galveston Island yields a total of only ~130,000 ± 28,000 m3/yr, i.e., significantly less than the ~240,000 ± 49,000 m3/yr estimated to have been eroded during historic time using the measured erosion rates. While some of this increased erosion can be attributed to anthropogenic influences, the magnitude of change requires additional forcing, specifically, the recent acceleration in relative sea-level rise punctuated by storm impacts during historic time.
- Apr 2013
- Joint Penrose/Chapman Conference
Hurricanes annually threaten the Western Atlantic margins. Due to a relatively short instrumental record, paleohurricane archives can shed light on current and future hurricane impacts by providing a geologic and climatic context. We introduce existing archives and discuss dating methods, site selection criteria, and statistical applications. These records have been useful for interpreting long-term coastal evolution and hurricane response to changing climatic and oceanographic conditions. However, carefully selected new sites can provide valuable insights towards a deeper understanding of Holocene Atlantic basin-wide trends. Here we highlight ongoing paleotempestological projects from two locales: Bermuda and central Texas. Mangrove Lake, Bermuda appears to contain a ~4000 yr B.P. record of northeastwardly recurving intense hurricanes potentially only impacting Bermuda. This site will provide valuable data concerning the influence of the Holocene North Atlantic Oscillation-like conditions on intense hurricanes, in addition to understanding regional trends and variations of storms in response to oceanographic changes. A record from offshore Matagorda Island, central Texas utilizes the inner shelf environment to interpret intense hurricane impacts in relation to Gulf of Mexico sea-surface temperature and El Niño/Southern Oscillation-like variations over the last ~1500 yr B.P.
- Mar 2013
- Treatise on Geomorphology, Vol 10, Coastal Geomorphology.
The morphodynamics of open-ocean barrier systems (barrier islands, barrier spits, and mainland or headland beaches), synthesizing classic studies, current scientific knowledge, and future research directions regarding a number of barrier systems globally are reviewed. Within a coastal tectonic framework, the authors address: (1) Amero-trailing-edge coasts (USA’s New England coast, mid-Atlantic Bight coast, North Carolina Outer Banks, Georgia Bight coast, and Florida Atlantic coast; Brazil’s Santa Catarina coast; German Bight coast; and southern and western Australian coasts); (2) marginal-sea coasts (USA’s Florida Gulf Coast; Gulf Coast of Alabama, Mississippi, and Louisiana; Texas Gulf Coast; and eastern Australian coast); and (3) collision coasts (USA’s Alaskan Pacific coast and New Zealand). Moreover, the chapter includes a glossary and robust current set of references.
There is now evidence that suggests that the effects of anthropogenic global change will increase hurricane frequency and magnitude in the near future. Major factors influencing hurricane activity include changing sea surface temperatures (SST) and the El Nino/Southern Oscillation (ENSO) dynamics in the North Atlantic and surrounding basins. However, statistical trends observed from the historic record have come into question, as technological advances through time have provided more reliable data regarding storm frequency and magnitude. Field-based geologic studies can bridge this gap by providing hurricane activity over centennial to millennial timescales that significantly expand the historic record. From these types of analyses, more robust statistical conclusions can be drawn. Here we show that intense hurricane landfalls in the western Gulf of Mexico appear to correlate with higher SST and decreased El Niño activity in the past. A carefully selected sediment core from the inner shelf offshore Matagorda Island, Texas yields a ~4,500 yr B.P. record that correlates well with the long-term hurricane frequency previously established from published sites around the Gulf of Mexico. Between ~1,000 and ~1,500 yr B.P., intense hurricane strikes were frequent, and coincide with a time where a nearby Gulf of Mexico SST record suggests similar or possibly slightly higher SST than modern. This same time interval also coincides with decreased El Niño activity based on a published proxy from Ecuador. Between ~1,000 yr B.P. to modern times (i.e. ~150 years ago), as SST become cooler in addition to El Niño activity decreasing, intense hurricane impacts are reduced. The last ~150 years shows frequent intense hurricane strikes again coinciding with high SST and lower El Niño activity. Analysis of the geologic record therefore suggests that if SST increases and El Niño events decrease, Gulf of Mexico intense hurricane activity becomes elevated.
The 2011 Tohoku earthquake and consequent tsunami along with frequent typhoon strikes serve as stark reminders that natural hazards present a significant threat to the Pacific coast side of Japan. This region has a very long historic record of frequent typhoon strikes and devastating tsunamis, making Japan an ideal location to study and characterize sedimentological and geochemical signatures associated with typhoon and tsunami-derived deposits. Presently, instrumental records for natural hazards of these type extend only back to ~1945 AD. Geologic records retrieved from this region can be used to extend existing historic records even further, which, in turn, allows the risk associated with the frequency of these events in the region to be better established. Here we discuss records of typhoon and tsunami events recovered from terrestrial coastal ponds from three sites in Ehime Prefecture, southwestern Japan. A multi proxy approach consisting of loss on ignition, X-Ray fluorescence, density, X-radiograph, grain size, and magnetic susceptibility is used to characterize dense layers as marine-sourced material in sediment cores. Radiocarbon and short-lived isotopic analyses provide chronological age constraints. Characterized events consistently show spikes in strontium, magnetic susceptibility, and percent inorganic values. Events that correlate chronologically with this multi proxy approach across multiple sites are considered to be tsunami derived, whereas non-correlative events having localized event signals are likely associated with typhoons. This methodology is a powerful tool for distinguishing between typhoons and tsunamis, and for better assessing the return periods of natural disasters along the Pacific Japan coast.
Coastlines are some of the most populated and rapidly expanding areas of the United States. Here, people seek employment, build residences and facilitate urban growth. However, most people do not fully realize all of the risks associated with living along a coast. Relative sea-level rise, erosion, and severe storms continuously alter the landscape. Anthropogenic interventions designed to slow these natural processes often foster decline at a greater rate. Building residences and other permanent structures further exacerbates the problem. Along the Upper Texas coast, public policy intended to protect and make life more viable is actually creating “moral hazards” and escalating the financial burdens on government. This article identifies several public policies at the local, state and federal levels of government that are working at cross purposes by allowing risky investment decisions that put people’s livelihoods in jeopardy. The authors conclude that a different, more sustainable set of policy options is required and offer several recommendations for consideration.
The Gulf of Mexico coast is especially vulnerable to rapid coastal changes. The recent acceleration in the rate of sea-level rise and continued steady rate of hurricane impacts is expected to elicit dramatic effects on barrier islands. Galveston Island (GI), located along the upper Texas coast, is ideally suited to quantify the relative influence of sea-level rise and hurricane impacts on the erosion of a barrier island through time due to its low elevation, dense core coverage and radiocarbon constraints on barrier evolution, and more than four decades of shoreline change monitoring. GI formed ~5,500 yr B.P., and has been eroding naturally for the past ~1,800 yr B.P. Sand eroded from GI is transported via longshore currents and deposited directly into the San Luis Pass Tidal Delta complex (SLPTDC). No other known sand sources exist for the SLPTDC, and very little sediment bypass occurs to the west. Therefore, we can examine the erosional history of GI through time by quantifying sediment fluxes into the SLPTDC, in addition to quantifying offshore and backshore sand fluxes due to cyclone impacts. Although many tidal inlets along the Gulf of Mexico have been anthropogenically modified, the SLPTDC has remained natural, thereby allowing a unique opportunity to conduct this study. The SLPTDC formed ~2,100 yr B.P., roughly the same time when erosion along GI began, and corresponds to the time when the rate of sea-level rise decelerated from ~2.0 mm/yr to ~0.60 mm/yr. It has been sequestering sediment relatively continuously throughout its history. In the last 200 years, the sand flux into the SLPTDC has more than doubled relative to the first two millennia. As this material is sourced from GI, this suggests that erosion of the barrier has accelerated in the last ~200 years. Additionally, GI's offshore (seaward of the shoreface) and backshore sand flux due to hurricane impacts have been minor contributors to the erosion of GI. This analysis suggests that the recent acceleration in the rate of sea-level rise, punctuated by hurricane delivery of sand to the longshore transport system, has increased the erosion of GI during the last ~200 years.
In July 2011, a Rice University Summer course consisting of 21 in-service K-12 science teachers conducted fieldwork on Galveston Island, Texas. The goal of this class was to better prepare local teachers to teach the Texas state standards (TEKS) in addition to gaining valuable research, fieldwork, and technology experience. Participant groups developed independent research projects aimed at investigating hurricane impacts, barrier island erosion, nearshore oceanographic conditions, coastal environments, and natural versus anthropogenic dunes. These projects were carried out through the collection and use of ArcGIS, stratigraphical, sedimentological, and geophysical data comprised of satellite/aerial photography, elevation data, sediment push cores, and Ground Penetrating Radar (GPR). Participants analyzed Light Detection and Ranging (LIDAR) elevation data and several years of Galveston Island imagery, in order to locate appropriate areas to collect cores and GPR lines. Sediment push cores up to ~2 meters in length were collected, and they provided a valuable stratigraphic framework. Participants analyzed core sections for grain size and color variations, mollusc shells, and organic material to make environmental interpretations. These cores revealed hurricane washover beds, dune stratigraphy, and shoreline facies. GPR profiles were collected along the central part of Galveston Island, and the teachers interpreted and characterized the subsurface to ~2 meters depth. Several coastal geologic features, such as beach ridges, swales, and barrier island seaward dipping reflectors, were imaged clearly. Furthermore, sediment cores were collected along many GPR lines in order to verify subsurface interpretations. To seamlessly record and share data in the field, 3G enabled iPads were incorporated into the course. Participants used these devices to take field notes, pictures, and videos, in addition to having access to LIDAR and satellite imagery processed on campus. Merging several types of technology and data for this field course allowed these in-service K-12 teachers to gain valuable independent research experience.
- Mar 2011
- GSA South-Central Section Annual Meeting
With the well-documented acceleration of sea-level rise and the potential increasing frequency of hurricane strikes over historical time, erosion along the Gulf of Mexico is expected to be dramatic. However, there is a lack of quantitative field-based studies to document how coastal evolution in the geologic past compares to the historic record. Here, we relate changes in the sand flux of a tidal delta to barrier island erosion. Tidal inlets sequester sand from longshore currents, and can record changes on adjacent barrier islands. Most tidal inlets and deltas along the Gulf of Mexico coast have been anthropogenically modified, therefore making it difficult to directly compare natural versus man-induced changes. However, San Luis Pass along the upper Texas coast has remained entirely natural, therefore presenting the unique opportunity to study the response of Galveston Island to global change over both geologic and historic time. By constraining relative sea-level rise (subsidence and eustasy), sediment supply variations, and hurricane impacts, we assess the influence of these forcing mechanisms on coastal change. We determine that the tidal inlet and delta did not form until ~2,100 yr B.P., coinciding with a sea-level rise deceleration from 2.0 mm/yr to 0.60 mm/yr. Over the past ~200 years, the sand flux into San Luis Pass has more than doubled relative to the geologic past. This sand is derived from erosion of Galveston Island, meaning that erosion of this barrier has increased in recent time. These changes are associated with the recent relative sea-level rise acceleration and/or increased hurricane frequency, and are expected to represent the response of similar barriers along the Gulf of Mexico coast.
The upper Texas coast is one of the most populated areas along the Gulf of Mexico. Three dynamic barriers along this section of coastline (Bolivar Peninsula, Galveston Island, and Follets Island) have a well-documented history of shoreline change. Numerous engineering studies incorporating both sedimentological data and numerical models have been established for this system to understand sediment fluxes. However, rarely have previous studies examined sediment fluxes for the upper Texas coast in light of certain fundamental concepts of coastal geology. Here, we discuss the current theory and understanding of barrier island dynamics from a geologic standpoint as they relate to sediment budgets for the upper Texas coast. From sediment cores, we quantify both shoreface and washover sand fluxes, which previously were not incorporated as sand sinks into sediment budgets for this system. Shoreface sand fluxes represent a sizable portion of the total budget, whereas modern washover sand fluxes are minimal. Until now, a depth of closure (beyond which sediment transport is negligible) of 4 m has typically been used; however, our data suggest a depth of at least 8 m would be more appropriate. We show that the combined upper and lower shoreface has the potential to sequester ~160,000 ± 39,000 m3/y of sand, equaling ~17% of the entire calculated sediment flux and ~37% of the total longshore transport flux for the upper Texas coast, based on previous studies. Therefore, we recommend revised approaches to future sediment budget studies in order to establish more robust analyses. Ultimately, it will be crucial to use both engineering principles and geologic concepts to construct an accurate and realistic scenario for coastal restoration projects.
Extending some 600 kilometers, the Texas coast is one of the most vulnerable coastlines to rising sea-level because of its low elevation and gradient. The current rate of sea-level rise (~3-4 mm/yr) for this part of the Gulf of Mexico is roughly six times the average rate (~0.6 mm/yr) over the past 4,000 years. This rate will likely continue to increase, and the impact on coastal systems is expected to be dramatic. During the middle Holocene, the rate of sea-level rise in the northwestern Gulf of Mexico was ~5 mm/yr, which coincides with the low-end of rate projections for the coming century. Along the Texas coast, this was a time of rapid coastal change, as rates of shoreline retreat were up to ~20 m/yr. Several barrier islands were drowned to form sand banks that currently exist ~ 50 kilometers offshore (Sabine and Heald Bank). Additionally, bays along the upper Texas coast experienced flooding events when bay-head deltas rapidly migrated landward. However, several central Texas barriers remained relatively stable throughout the rapid rise of the middle Holocene (e.g. Mustang and Matagorda Islands) due to higher rates of sediment supply (due to longshore current convergence). Elsewhere, barrier islands did not begin to stabilize until the rate of sea-level rise decreased to < 2.0 mm/yr (which occurred ~5,000 yrs B.P.). An examination of sediment cores from the upper Texas coast revealed that net sand transport from erosion of Galveston Island into San Luis Pass, a tidal delta at the west end of the island, is more than double the average flux for the past several millennia. This suggests that erosion of Galveston Island has increased over historic time relative to geologic time. This change is mainly attributed to accelerated sea-level rise. Other barriers show evidence for accelerated retreat in historical time, some of which is due to direct anthropogenic influence and other cases are likely due to accelerated sea-level rise.
For three years, a Rice University graduate summer course has worked in Wyatt Chapel Cemetery, an abandoned site located on the campus of Prairie View A&M University. The course participants consist of in service K-12 science teachers, most of whom have participated in this course since its inception. Wyatt Chapel Cemetery is the ideal field course location for several reasons. First, decades of abandonment have raised several questions about the extent of the cemetery, the number of graves, and those known to be buried there. Secondly, the soil and environmental factors are ideally suited for geophysical and sedimentological fieldwork and data collection. Lastly, the local community has expressed significant interest in answering longstanding questions regarding the history of the cemetery. Ultimately, the results of the work will be aimed toward designating this area as a historic site. This past summer (2010), course participants returned to Wyatt Chapel Cemetery to continue the investigation consisting of Ground Penetrating Radar (GPR), sediment trenching, and environmental observations, in conjunction with historical archive examinations. GPR is a non-intrusive geophysical method to image the subsurface to a depth of approximately 3 meters in this area. These data were used to interpret stratigraphy, and identify any associated man-made subsurface anomalies (i.e. interpreted graves, pathways, debris, etc.). Trenching provided valuable subsurface data that were used to calibrate the GPR, observe stratigraphic architecture and structures, and determine the depth of a regional clay layer that likely serves as the burial depth limit. Additionally, all points of interest (i.e. headstones, anomalies, and graves) were measured using a total station, which offers centimeter-scale precision. Data were consolidated and displayed using Geographic Information Software (GIS), so as to provide an interactive map. During the course, all efforts were documented using digital video cameras. The course approach of integrating field and lab work provided valuable research experience for the K-12 teachers, and allowed for formulation and completion of independent research projects. Additionally, the incorporation of technology in the course serves to motivate participants to do the same in their own classroom.
A primary effect of global warming is accelerated sea level rise, which will eventually drown low-lying coastal areas, including some of the world's most populated cities. Predictions from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) suggest that sea level may rise by as much as 0.6 meter by 2100 [Solomon et al., 2007]. However, uncertainty remains about how projected melting of the Greenland and Antarctic ice sheets will contribute to sea level rise. Further, considerable variability is introduced to these calculations due to coastal subsidence, especially along the northern Gulf of Mexico (see http://tidesandcurrents.noaa.gov/sltrends/sltrends.shtml).
Hurricane magnitude and frequency have been linked to numerous mechanisms, including the steady rise in annual sea-surface temperatures, El Nino-Southern Oscillation (ENSO) variations, and atmospheric changes. In order to better understand those factors that control hurricane magnitude and frequency, a long-term record spanning the entire Gulf of Mexico coast is needed. Here we present a detailed record from ca. 5300-900 yr B.P. of past intense hurricane impacts for cores collected from Laguna Madre, Texas, United States. Relative storm intensities were calculated for each event, and the average intense storm impact probability for south Texas was determined to be similar to 0.46% (annual landfall probability). Previous field studies in Western Lake, Florida, and Lake Shelby, Alabama, reveal similar probability intense hurricane strikes of similar to 0.39%. Although high-frequency oscillations between warm and dry and cool and wet climate conditions have occurred in Texas through the late Holocene, there has been no notable variation in intense storm impacts across the northwestern Gulf of Mexico coast during this time interval, implying no direct link between these changing climate conditions and annual hurricane impact probability. In addition, there have been no significant differences in the landfall probabilities of storms between the eastern and western Gulf of Mexico during the late Holocene, suggesting that storm steering mechanisms have not varied during this time.
The response of coastal systems to global change is currently not well understood. To understand current patterns and predict future trends, we establish a geologic record of coastal change along the Gulf of Mexico coast. A study examining the natural versus anthropogenic mechanisms of erosion reveals several sand sources and sinks along the upper Texas coast. It appears that hurricane washover and offshore sand deposits are minimal sand sinks, while flood-tidal deltas are areas of significant sand sequestration. Additionally, it appears that damming of rivers has had only a minimal effect on sedimentation along the upper Texas coast. However, hard engineering structures placed on the beach have exacerbated erosion due to trapping sand of that would otherwise be in the longshore transport system. Coastal sand budgets are derived to put geologic events (such as hurricanes and erosion) into context. Sand budgets often use engineering assumptions to establish sand transport within a coastal system. However, a disconnect typically exists between engineering principles and geologic concepts when quantifying these budgets. Geologic principles are relied upon to calculate a sand budget and evaluate published sediment budgets. This reveals that assuming too shallow a depth of closure can result in ∼17% error in the total calculated sediment flux and an error of ∼40% of the total longshore transport flux for the upper Texas coast. This suggests that revised approaches are necessary to accurately represent sand transport within the coastal zone. The long-term probability of hurricane impacts in the western Gulf of Mexico is constructed. For south Texas, an intense hurricane landfall probability of ∼.46% is established for the past ∼5,000 years. Based on published studies, this is similar to the intense hurricane impact probability of ∼.39% for the eastern Gulf of Mexico. Studying the evolution of San Luis Pass provides a unique opportunity to study the response of accelerated sea-level rise and hurricane impacts on the evolution of a natural tidal delta system and adjacent Galveston Island. This study reveals an increased sand flux into San Luis pass tidal delta, and suggests that the erosion along Galveston Island has more than doubled over historic time relative to geologic time.
- Oct 2009
- Geological Society of America
The anthropogenic contribution to hurricane formation, intensity, and track have been heavily debated in recent years. Hurricane magnitude and frequency has been linked to numerous mechanisms, including the steady rise in annual sea surface temperatures, ENSO variations, and atmospheric changes. In order to better understand and predict future hurricane activity for the entire Gulf coast, a robust sampling strategy spanning the geologic past must be achieved. Here, we present a detailed record from ~4,000-900 yr BP of past intense hurricane impacts for 4 cores collected from Laguna Madre, South Padre Island, TX. From sediment dynamics equations, we calculate storm surges associated with these deposits to be between ~2 and 3.8m. We determine an approximate landfall probability of ~.45% for storms of these intensities over this time interval. Comparison of our data to previous studies in Western Lake, FL and Lake Shelby, AL reveals similar hurricane frequency trends and suggests relatively constant intense hurricane strikes for the Gulf of Mexico from ~4,000-500 yr BP. Western Lake, FL shows probabilities of intense storm strikes of .36%, while Lake Shelby, AL shows .34%. Intense hurricane impacts in the Gulf were likely regulated by shifting warm, dry air masses in southwestern North America. The intervals of intense hurricane strikes presented in this study all coincide with centennial length periods of warm, dry air masses centered over Texas. During warmer, drier periods, hurricanes are less likely to impact the Gulf Coast than during cooler, wetter periods. For the past 500 yrs, a cool, wet climate regime has prevailed.
- Dec 2008
- American Geophysical Union
Hurricanes act as one of the primary controls on barrier island migration through wave and wind energy, and their frequency has been suggested to indicate changes in climate (El Niño) cycles. Texas has an extensive coastline containing barriers in various stages of evolution. Through a detailed sedimentological examination and radiocarbon age constraints of offshore storm sands, beach ridge breaching events, storm surge channels, and washovers, we offer a geologic record of severe storm impacts along the Texas Coast. From offshore core data, we ascertain that sand storage along the upper and lower shoreface (the profile of which is controlled by catastrophic storm impacts) is minimal over geologic timescales (i.e. 100-1000 years). Hence, an offshore record of storm impact is lacking. Using high resolution LIDAR data, we map breaching events of prominent beach ridges. Storm surge channels on the bayside of barriers (which are cut by water flowing towards the Gulf of Mexico when storm surge recedes) are also being dated, although they likely record lower magnitude storms. This study reveals that hurricane washover formation is only a minor contributor to sand transport within the system, as accumulation rates in back-barriers range from .095 - .4m/C. By examining the sedimentological components of hurricane impacts, we establish a hurricane impact chronology and conclude that the frequency of major storms along the Texas Coast is actually quite minimal.
- Oct 2008
- Geological Society of America
The Texas coast stretches some 590 kilometers, and includes a wide variety of shoreline types. Although there can be a dynamic range of response temporally and spatially, most of the Texas Coast has a well-documented history of shoreline and bayline erosion. But, how do current erosion rates compare to those of the past few millennia? Recently collected field data, including offshore to backbarrier core transects, are used to study facies assemblages and measure long-term erosion rates for three transgressive barrier islands: Follet's (FI), Matagorda (MI), and South Padre Island (SPI). FI and SPI are thin barriers (2m and 3m thick, respectively) experiencing rapid erosion (averaging 3 to 4 m per year), while MI (11m thick) has been a relatively stable long-term sand sink. All three barriers rest on Holocene lowstand fluvial deposits where subsidence due to compaction is negligible (ranging from .4 - 2mm/yr). Radiometricaly-constrained sediment budgets for these barriers are used to determine the long-term shoreline retreat and to examine the contributions of different erosion mechanisms (i.e. littoral drift, fluvial sediment input, subsidence, hurricane washover, and offshore sand transport). The late Holocene backbarrier sedimentary architecture of these systems is similar: thin amalgamated washover deposits overlaying bay mud. Over longer timescales (i.e. centuries to millennia), hurricane washover has been minor. Instead, sand eroded from these barriers is mainly sequestered within the shoreface and tidal deltas. The development of numerical models to predict coastal response to accelerated sea level rise and climate controlled variations in sediment supply hinges on developing a better understanding of how and where sand is sequestered.
Coastal subsidence causes sea-level rise, shoreline erosion and wetland loss, which poses a threat to coastal populations. This is especially evident in the Mississippi Delta in the southern United States, which was devastated by Hurricane Katrina in 2005. The loss of protective wetlands is considered a critical factor in the extensive flood damage. The causes of subsidence in coastal Louisiana, attributed to factors as diverse as shallow compaction and deep crustal processes, remain controversial. Current estimates of subsidence rates vary by several orders of magnitude. Here, we use a series of radiocarbon-dated sediment cores from the Mississippi Delta to analyse late Holocene deposits and assess compaction rates. We find that millennial-scale compaction rates primarily associated with peat can reach 5 mm per year, values that exceed recent model predictions. Locally and on timescales of decades to centuries, rates are likely to be 10 mm or more per year. We conclude that compaction of Holocene strata contributes significantly to the exceptionally high rates of relative sea-level rise and coastal wetland loss in the Mississippi Delta, and is likely to cause subsidence in other organic-rich and often densely populated coastal plains.