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The Pink and White Terraces of Lake Rotomahana: What was their fate after the 1886 Tarawera eruption?
Abstract
The Pink and White Terraces that once stood regally on the shores of old Lake Rotomahana, and which were unique in their beauty as a natural wonder of the world, were regarded by the local Maori as a taonga, or treasure, because of the therapeutic qualities of the waters and their majestic appearance. The eruption of Mt. Tarawera on June 10 1886 is commonly cited as the cause of their demise, with the lake rapidly rising soon thereafter to drown the large, newly formed Rotomahana crater and other volcanic edifices shaped during the excavation of the old lake. Thus, the effects of the eruption have been masked from onlookers for more than 125 years. However, application of state-of-the-art survey techniques usually applied in the marine realm to modern Lake Rotomahana, including AUV surveys with numerous sensors, seismic profiling, water column surveys and deployment of deepsea cameras, has provided a wealth of new information about the state of hydrothermal systems in the lake and the probable fortunes of the Pink and White Terraces.
... Despite nineteenth century narratives that included primary geological descriptions with early photographs, the 1859 survey of Lake Rotomahana by Ferdinand von Hochstetter was essentially undertaken in cartographic isolation. As such, improved context for that pioneering survey and better definition of how former geothermal features at Rotomahana were arranged, including the whereabouts of The Terraces, can help connect the past landscape to modern lake-bottom geological surveys (e.g., de Ronde et al., 2016a). In addition, refining Lake Rotomahana's former sinter terrace configurations before and after the 1886 eruption can enrich the regional Quaternary volcanic history of New Zealand (Keam, 2016), and add value to TVZ contemporary volcanogenic processes (see references in de Ronde et al., 2016aRonde et al., , 2018 by offering new insights about how magma plumbing systems operate. ...
... As such, improved context for that pioneering survey and better definition of how former geothermal features at Rotomahana were arranged, including the whereabouts of The Terraces, can help connect the past landscape to modern lake-bottom geological surveys (e.g., de Ronde et al., 2016a). In addition, refining Lake Rotomahana's former sinter terrace configurations before and after the 1886 eruption can enrich the regional Quaternary volcanic history of New Zealand (Keam, 2016), and add value to TVZ contemporary volcanogenic processes (see references in de Ronde et al., 2016aRonde et al., , 2018 by offering new insights about how magma plumbing systems operate. ...
... The location and orientation of the Pink Terrace we have ascribed nests that former site within a subtly reduced region of heat flux relative to elevated values in the Pink Terrace hydrothermal system. Both the Pink and White Terrace former site locations we identified, via orientating and scaling the 1863 map, are very close to remains of sinter terrace seen in underwater camera footage (de Ronde et al., 2016a). The White Terrace location is situated west of "Pinnacle Ridge" on the 1863 map. ...
Te Otukapuarangi (the Pink Terrace), Te Tarata (the White Terrace) and Te Ngāwhā a Te Tuhi (the Black Terrace) were massive siliceous sinter formations at Lake Rotomahana, New Zealand, that were ostensibly lost in the catastrophic 1886 Tarawera eruption. Previous work using an unpublished watercolor map and notes by Ferdinand von Hochstetter (b. 1829–d. 1884) has recently supported claims that the former Pink and White Terraces survived the 1886 eruption, and that they may be located under tephra adjacent to the modern lake margin. Divergent perspectives about the fate of Lake Rotomahana's former sinter terraces suggest the reconstruction of New Zealand's largest historic volcanic eruption is incomplete. The undervalued approach of pairing modern geomorphic techniques with extant historic resources and geophysical data can help resolve this controversy. We harnessed a wider amount of unique historic data recorded during Hochstetter's (1859) survey than previously reported to locate the sites of Lake Rotomahana's former sinter terraces. Volcanic landforms, the physical geography of the countryside, and former settlements are tied together via common sightings between sequential survey datums. Light detection and ranging (LIDAR) data supported the reconstruction of Hochstetter's (1859) survey. Of significance, shared landmarks between the survey stations increased the confidence for resecting the 1859 datum position on the southern margin of former Lake Rotomahana. Hochstetter's survey watercolor maps are part of a series drafted prior to a final version being professionally printed, and they do not portray a spatially accurate depiction of how sinter terraces and geothermal features around former Lake Rotomahana were arranged. As such, assertions of their superior cartographic nature are not well-founded, and application of them to provide former Terrace locations is compromised. The published pre-eruption map of Lake Rotomahana validates well against Hochstetter's field diary measurements. When Hochstetter's published map is orientated using reconstructed survey datum positions at Lake Rotomahana, the former locations of the White and Pink Terraces lie entirely within the modern boundaries of the lake and not on land. The Black Terrace may have been destroyed and/or converted to an eruption crater, but may still exist on land (intact or in-part) west of Lake Rotomahana's modern shoreline. This study demonstrates the value of historic cartography to improve understanding of volcanic processes, and the potential to apply similar approaches to volcanic environments elsewhere that hold a range of pre-instrumental observations.
... Indeed, Cornel de Ronde coincidentally offers a similar possibility in one of his 2016 papers in press: "with considerable upheaval of the landscape post-eruption, it is entirely conceivable that slumping may have occurred locally, transporting competent structures like the terraces downslope." 20 The Hochstetter Survey appears to validate the GNS 2011-2012 Pink Terrace fragment claim. However, in the 2016 GNS papers the revised Pink Terrace site is not as consistent with the Hochstetter Survey, for given the latest bathymetry it is hard to see how a huge terrace fragment could reach the reported 2016 position. ...
The Pink and White Terraces were New Zealand’s eighth wonder of the world, until the Tarawera eruption on 10 June 1886 engulfed them. Without pre-eruption survey data, scientific and government teams failed to relocate the terraces, which were assumed lost. Over 2011-
2012 GNS Science announced the rediscovery of parts of both terraces in Lake Rotomahana: however, by 2016 they resiled these claims, concluding the majority of both terraces destroyed.
This paper maps their original locations based on reverse engineering unpublished 1859 survey data from Ferdinand von Hochstetter. Evidence suggests the locations may have survived the eruption, with the terraces buried in ash, crossing the shoreline on land not subject
to local volcanic cratering. Excavation is conceivable. The Pink and White Terraces may again delight visitors in Rotorua via the Terraces Track, complementing the world-class New Zealand walking tracks.
Note this paper was freely available for years and can be downloaded from: https://citationsy.com/archives/q?doi=10.26686/jnzs.v0i23.3988
... Their claims were published in institutional journals (Winner, 2012). In 2016, the team published articles describing the rediscovery (De Ronde et al., 2016a, b [DR-2016a and Keam, 2016Keam, [K-2016). ...
This week in Surveying+Spatial journal; conflicting survey research of the Pink and White Terraces by an international oceanographic team and by local researchers is reviewed and reconciled.
After replicating the marine team survey mapping, and examining photo-interpretation, sonar and georeferencing; the reconciliation uncovered mistakes. These help explain differences between the two surveys.
The reconciliation integrated both approaches to make striking new findings about the Pink and White Terraces. It locates pre-eruption features, thought lost but now seen to have likely survived the 1886 Tarawera eruption.
Surveying+Spatial is the professional journal of Survey and Spatial New Zealand (formerly New Zealand Institute of Surveyors).
Surveying+Spatial article conclusions:
The north-south lake axis analysis offers a Pareto optimal solution, incorporating Keam and marine team geoscience, with Hochstetter’s survey location of the Pink and White Terraces.
Hochstetter’s remains the only primary, pre-eruption survey evidence of the Pink, Black and White Terrace locations.
The survival of the northern Steaming Ranges and Rangipakaru; increase the likelihood the White Terrace location may also survive.
... This paroxysmal stage of the eruption was over by 6.00 am when most activity ceased. See also recent papers by de Ronde et al. (2016aRonde et al. ( , 2016b, Keam (2016), and Lorrey and Woolley (2018). ...
This tour guide describes the origin of tephras and tephra-derived soils in North Island, New Zealand, including via upbuilding pedogenesis, and their mineralogical and other properties relevant to farming and orcharding in the Waikato-Bay of Plenty regions.
... This paroxysmal stage of the eruption was over by 6.00 am when most activity ceased. See also recent papers by de Ronde et al. (2016aRonde et al. ( , 2016b, Keam (2016), ...
Itinerary
DAY 1 Wednesday 21 December: Mamaku Plateau-Rerewhakaaitu-Lake Tarawera:
1 Goodwin Farm, Tapapa Rd, Tapapa: welded ignimbrite, tephras, loess, buried soils (Tirau soil)
- stratigraphy of sequence (230 ka and younger) and upbuilding pedogenesis
- Tirau silt loam
2 Brett Rd, Rerewhakaaitu: Holocene tephras and buried soisl (Rotomahana soil)
- Volcanic landscape, historical importance of area for NZ soil survey
- Stratigraphy of sequence (~9.5 cal ka to 10 June 1886 Tarawera eruption) and upbuilding pedogenesis
- Rotomahana sandy loam,
3 Ash Pit Rd, Rerewhakaaitu: tephras and buried soils (Matahina soil [only if time])
- Matahina gravel
- buried spodic/podzol soil features,
4 Okareka Loop Rd tephra section with proximal Rotorua Tephra and buried soils, loess,
Buried Village Museum, Te Wairoa,
Lake Tarawera (Stoney Point).
DAY 2 Thursday 22 December: Otorohanga-Waitomo Caves -Pirongia Mountain:
1 Raynes Road section: Ultisol in composite tephra sequence (Kainui soil),
2 Otorohanga Kiwi House,
3 Waitomo Caves,,
4 Pirongia Mountain: Mangakara forest walk,
5 Evening meal on an Andisol.
DAY 3 Friday 23 December: Hobbiton, Hamilton gardens including Te Parapara (ancient Maori garden):
1. Hobbiton tour 10.15 am (2 hrs),
2. Hamilton Gardens incl. Te Parapara Garden and human-modified soils (Tamahere soil).
The cultural and naturalNaturalheritageheritageHot springheritage of hot springs is closely linked with many intersecting margins, and it can be challenging to separate some of their individual characteristicsCharacteristics. While the main objective of this book is to explore and examine the wide-reaching geoheritageGeoheritage of hot springsHot springgeoheritage in different settings, this chapter is looking primarily at aspects of the naturalNaturalheritage heritage related to hydrothermal areasHydrothermalarea.
We investigate the geological and hydrothermal setting at Lake Rotomahana, using recently collected potential-field data, integrated with pre-existing regional gravity and aeromagnetic compilations. The lake is located on the southwest margin of the Okataina Volcanic Center (Haroharo caldera) and had well-known, pre-1886 Tarawera eruption hydrothermal manifestations (the famous Pink and White Terraces). Its present physiography was set by the caldera collapse during the 1886 eruption, together with the appearance of surface activities at the Waimangu Valley. Gravity models suggest subsidence associated with the Haroharo caldera is wider than the previously mapped extent of the caldera margins. Magnetic anomalies closely correlate with heat-flux data and surface hydrothermal manifestations and indicate that the west and northwestern shore of Lake Rotomahana are characterized by a large, well-developed hydrothermal field. The field extends beyond the lake area with deep connections to the Waimangu area to the south. On the south, the contact between hydrothermally demagnetized and magnetized rocks strikes along a structural lineament with high heat-flux and bubble plumes which suggest hydrothermal activity occurring west of Patiti Island. The absence of a well-defined demagnetization anomaly at this location suggests a very young age for the underlying geothermal system which was likely generated by the 1886 Tarawera eruption. Locally confined intense magnetic anomalies on the north shore of Lake Rotomahana are interpreted as basalts dikes with high magnetization. Some appear to have been emplaced before the 1886 Tarawera eruption. A dike located in proximity of the southwest lake shore may be related to the structural lineament controlling the development of the Patiti geothermal system, and could have been originated from the 1886 Tarawera eruption.
We investigate the geological and hydrothermal setting at Lake Rotomahana, using recently collected potential-field data, integrated with pre-existing regional gravity and aeromagnetic compilations. The lake is located on the southwest margin of the Okataina Volcanic Center (Haroharo caldera) and had well-known, pre-1886 Tarawera eruption hydrothermal manifestations (the famous Pink and White Terraces). Its present physiography was set by the caldera collapse during the 1886 eruption, together with the appearance of surface activities at the Waimangu Valley. Gravity models suggest subsidence associated with the Haroharo caldera is wider than the previously mapped extent of the caldera margins. Magnetic anomalies closely correlate with heat-flux data and surface hydrothermal manifestations and indicate that the west and northwestern shore of Lake Rotomahana are characterized by a large, well-developed hydrothermal field. The field extends beyond the lake area with deep connections to the Waimangu area to the south. On the south, the contact between hydrothermally demagnetized and magnetized rocks strikes along a structural lineament with high heat-flux and bubble plumes which suggest hydrothermal activity occurring west of Patiti Island. The absence of a well-defined demagnetization anomaly at this location suggests a very young age for the underlying geothermal system which was likely generated by the 1886 Tarawera eruption. Locally confined intense magnetic anomalies on the north shore of Lake Rotomahana are interpreted as basalts dikes with high magnetization. Some appear to have been emplaced before the 1886 Tarawera eruption. A dike located in proximity of the southwest lake shore may be related to the structural lineament controlling the development of the Patiti geothermal system, and could have been originated from the 1886 Tarawera eruption.
In 2018, Bunn and Nolden published a paper purporting to have established the true position of the Pink and White Terraces of Lake Rotomahana using forensic cartography, ‘reverse engineering’ an 1859 compass survey of Ferdinand von Hochstetter. Their results suggest that the terraces are buried partly on land, near the present-day lake shore.
Sightlines constructed using an 1881 Charles Spencer photograph overlooking the White Terraces towards distant Maungaongaonga and Maungakakaramea, and replicated by us, show the location of the White Terraces by Bunn and Nolden to be untenable. Fitting the pre-1886 eruption outline map of Lake Rotomahana of Keam (2016. The Tarawera eruption, Lake Rotomahana, and the origin of the Pink and White Terraces. Journal of Volcanology and Geothermal Research 314:10–38.) to our high-resolution bathymetry shows a remarkable fit of the shoreline around the Pink Terraces area to distinct bathymetric features. Side-scan sonar images of inferred tiers of Pink Terraces (de Ronde CEJ, Scott BJ, Leonard GS, Calvert AT. 2016a. Evolution of the sublacustrine geothermal system of Lake Rotomahana, New Zealand: effects of the 1886 Mt. Tarawera eruption—an introduction. Journal of Volcanology and Geothermal Research 314:1–9.) show they sit where the map of Keam would have them lie.
The 1859 field diaries of Ferdinand von Hochstetter (1829–1884) include raw data from a compass survey of Lake Rotomahana. The azimuth array is reverse engineered to identify Hochstetter’s survey baseline. Survey iterations are performed to reconstruct the historic Lake Rotomahana over today’s topographic map. Hochstetter’s papers include a method-of-squares survey map of Lake Rotomahana, providing scale and orientation to the reverse engineered projection. The forensic cartography delivers control points which enabled the authors to georeference Hochstetter’s survey map over the new Lake Rotomahana map. Black Terrace Crater and Te Ariki datum are derived. Validation by waterways, valleys and vegetation lines is undertaken, a biological bathymetry completed and three-point resection performed on the key survey station. The cartography shows the Pink, Black and White Terrace spring locations, Te Otukapuarangi, Te Ngāwhā a Te Tuhi and Te Tarata lie buried on land. From novel lake altimetry the plotted terrace spring locations lie buried 10–15 m. A full archaeological site investigation including imaging and core drilling is indicated to examine the three terrace locations. Excavation on one or more of the Pink, Black and White Terrace sites may then be determined.
Note this paper was freely available from the Royal Society and can now be downloaded from: https://citationsy.com/archives/q?doi=10.26686/jnzs.v0i23.3988
The locations of the lost Pink and White Terraces of Lake Rotomahana, New Zealand are plotted on today’s map by using sightlines in photographs of the terraces before they vanished in the volcanic eruption of 10 June 1886. Evidence is presented that the terraces could not have survived the eruption unmodified, in their original positions, at these locations. These photo sightlines and map plots add valid independent evidence to the debate about the fate of the terraces, and corroborate the finding of the 2011–2014 survey of Lake Rotomahana by GNS Science New Zealand scientists and their collaborators from Woods Hole Oceanographic Institution, USA, that the terraces did not survive the eruption intact. Evidence is presented that Dr Ferdinand von Hochstetter’s 1860s’ maps of Lake Rotomahana cannot be relied upon for accurate bearings and distances between ground features around the lake and terraces, and that, consequently, A. R. Bunn’s locations of the terraces derived from the maps are not reliable enough to support his conclusion that at least some of the terraces survived unmodified in their original position, and may be uncovered by excavation.
The geochemistry of hot springs is fundamental to explain the composition of hydrothermal fluids and includes references to their most common mineral content. Different sections of the chapter are looking at various hydrothermal processes as well as unusual thermo-tolerant life forms such as thermophiles and hyper-thermophiles. The chemical composition of hydrothermal solutions is further explored in the context of mineral deposits and hydrothermal alteration.
This visual presentation represented current (2016) applications of side-scan sonar in shallow water environments.
A review of some current (as of 2016) applications of sonar in shallow water environments including lakes, rivers and estuaries using simple side-scan sonar tools.
Scientific drilling programmes yield game-changing datasets to improve knowledge of Earth processes, and are pushing the limits of conventional geothermal uses. The Taupō Volcanic Zone (TVZ) in Aotearoa New Zealand is the ideal place to study the interactions between tectonic, magmatic, volcanic, geothermal and microbiological processes in a rapidly rifting young volcanic arc that hosts numerous rhyolite calderas, andesite and dacite cones. Unravelling the heat and mass transport mechanisms in the TVZ has direct implications for understanding the entire "subduction factories", better assess associated earthquake and volcanic hazards, and sustainably use geothermal resources which, in New Zealand, are of great significance to Māori. Since the 1950s, extensive geophysical, geological and geochemical datasets have been collected throughout the TVZ. Geothermal drilling up to 3.2 km depth and 340°C into near-neutral pH reservoirs has provided a window into the sub-surface TVZ. This lead to discoveries on geothermal, continental rift and arc systems. To expand the exploration of TVZ's subsurface with in-situ data outside conventional geothermal reservoirs, we propose the establishment of a scientific drilling programme. Scientific drilling will advance our understanding of: (1) feedbacks between the volcanic arc and an active rift; (2) controls on the timing and rates of volcanic and seismic events; (3) large-scale hydrology and magma systems; and (4) the microbiological diversity and function of the deep biosphere. We present the Okataina Volcanic Center, an accessible rhyolitic caldera where extensive surface data is already available, as one of the candidate areas with exciting potential to answer these research themes. At these very early stages, we seek to build strong relationships with Māori groups, and a multidisciplinary national and international team, to develop the idea of a TVZ scientific drilling. This programme will aim to test fundamental geoscientific and geothermal concepts within the TVZ's exceptional geological setting, and strengthen linkages with other ongoing geothermal scientific drilling programmes.
Raw Soils have minimal evidence of soil development, usually because of a short time since the parent materials were deposited or exposed at the land surface. The Raw Soils are associated with some of New Zealand’s most spectacular scenic landscapes. Raw Soils are scattered throughout New Zealand, particularly in association with high mountains (eroding alpine rock areas and active screes), braided rivers, beaches and tidal estuaries, non-stabilised sand dunes, recently emplaced lavas or tephras, and active geothermal areas. They cover about 3% of New Zealand (about 700,000 ha). Raw Soils lack a distinct topsoil or the topsoil is very thin (<5 cm) and they have no B horizon. The soil profile properties, therefore, correspond largely with those of the parent materials.
All hot springs, regardless of their temperature and flow rateFlowrate, their size and location, or their economic usage, face threats to their sustainabilitySustainability. These threats are to a large degree based on human activitiesActivityhuman, which have led to the contaminationContaminationandOver-exploitationover-exploitationExploitation of a vast number of natural water resourcesWaterresource on a global scale. This applies to groundwaterGroundwaterreservoirsReservoirs (Groundwater) as well as hydrothermal systemsHydrothermalsystem. Researchers have analysed satellite observations spanning 14 years and were able to directly associate undesirable changes in freshwaterFreshwater storage areas with several key factors: human impact, climate changeClimate change and natural variability (NASA. (NASA (2018) NASA satellites reveal major shifts in global freshwater. Retrieved from https://www.nasa.gov/press-release/nasa-satellites-reveal-major-shifts-in-global-freshwater). NASA Satellites Reveal Major Shifts in Global Freshwater. Retrieved from https://www.nasa.gov/press-release/nasa-satellites-reveal-major-shifts-in-global-freshwater.). While perhaps not much can be done about natural variability such as changing rainfall patterns influenced by climatic phenomena like the El NiñoEl NiñoSouthern Oscillation (ENSO)El Niño Southern Oscillation (ENSO), the threat of climate changeClimate change however should be taken more seriously and counteracted in every possible way; especially, where human interference might accelerate a looming water crisis.
A new technique for measuring conductive heat flux in a lake was adapted from the marine environment to allow for multiple measurements to be made in areas where bottom sediment cover is sparse, or even absent. This thermal blanket technique, pioneered in the deep ocean for use in volcanic mid-ocean rift environments, was recently used in the geothermally active Lake Rotomahana, New Zealand. Heat flow from the lake floor propagates into the 0.5 m diameter blanket and establishes a thermal gradient across the known blanket thickness and thereby provides an estimate of the conductive heat flux of the underlying terrain. This approach allows conductive heat flux to be measured over a spatially dense set of stations in a relatively short period of time. We used 10 blankets and deployed them for 1 day each to complete 110 stations over an 11-day program in the 6 x 3 km lake. Results show that Lake Rotomahana has a total conductive heat flux of about 47 MW averaging 6 W/m2 over the geothermally active lake. The western half of the lake has two main areas of high heat flux; 1) a high heat flux area averaging 21.3 W/m2 along the western shoreline, which is likely the location of the pre-existing geothermal system that fed the famous Pink Terraces, mostly destroyed during the 1886 eruption 2) a region southwest of Patiti Island with a heat flux averaging 13.1 W/m2 that appears to be related to the explosive rift that formed the lake in the 1886 Tarawera eruption. A small rise in bottom water temperature over the survey period of 0.01 °C/day suggests the total thermal output of the lake is ~ 112-132 MW and when compared to the conductive heat output suggests that 18-42% of the total thermal energy is by conductive heat transfer.
We investigate the geological and hydrothermal setting at Lake Rotomahana, using recently collected potential-field data, integrated with pre-existing regional gravity and aeromagnetic compilations. The lake is located on the southwest margin of the Okataina Volcanic Center (Haroharo caldera) and had well-known, pre-1886 Tarawera eruption hydrothermal manifestations (the famous Pink and White Terraces). Its present physiography was set by the caldera collapse during the 1886 eruption, together with the appearance of surface activities at the Waimangu Valley. Gravity models suggest subsidence associated with the Haroharo caldera is wider than the previously mapped extent of the caldera margins. Magnetic anomalies closely correlate with heat-flux data and surface hydrothermal manifestations and indicate that the west and northwestern shore of Lake Rotomahana are characterized by a large, well-developed hydrothermal field. The field extends beyond the lake area with deep connections to the Waimangu area to the south. On the south, the contact between hydrothermally demagnetized and magnetized rocks strikes along a structural lineament with high heat-flux and bubble plumes which suggest hydrothermal activity occurring west of Patiti Island. The absence of a well-defined demagnetization anomaly at this location suggests a very young age for the underlying geothermal system which was likely generated by the 1886 Tarawera eruption. Locally confined intense magnetic anomalies on the north shore of Lake Rotomahana are interpreted as basalts dikes with high magnetization. Some appear to have been emplaced before the 1886 Tarawera eruption. A dike located in proximity of the southwest lake shore may be related to the structural lineament controlling the development of the Patiti geothermal system, and could have been originated from the 1886 Tarawera eruption.
Domal masses of geyserite, which surround many geyser vents in the Whakarewarewa geothermal area, are formed largely of spicules, spicule columns, and shrub columns. The non-branching spicules and the branches of branching spicules, individually up to 3 cm high and 1 mm diameter, have a laminated core encased by siliceous cortex. Silicified microbes are rare in the core but common in the cortex. Silicified microbial mats and pseudodendrites are found in the crevices between neighbouring spicules. Shrub columns, up to 5 cm high and 1.5 cm in diameter, are formed of opal-A that was precipitated around a three-dimensional, branching, shrub-like microbial (?) structure. The shrub branches, which are hollow with scalloped walls, do not contain any evidence of the original microbes or minerals that formed them. Silicified microbial mats are present between the columns. Microbial boring and etching by acidic steam led to local diagenetic degradation of these columns. In the geyserite mounds at Whakarewarewa, spicules and spicule columns are common, whereas shrub columns are rare. Interbedding and intercalation of spicular geyserite with shrub columnar geyserite indicate, however, that these different morphologic entities probably formed under similar environmental conditions on the mounds around the geyser vents. Petrographic evidence shows that the spicules, spicule columns, and shrub columns grew through a combination of biotic and abiotic processes.
Young volcanic lakes undergo a transition from rapid, post-eruptive accumulation of volcaniclastic sediment to slower pelagic settling under stable lake conditions, and may also be influenced by sublacustrine hydrothermal systems. Lake Rotomahana is a young (129 year-old), hydrothermally-active, volcanic lake formed after the 1886 Tarawera eruption, and provides a unique insight into the early evolution of volcanic lake systems. Lake-bottom sediment cores, 20–46 cm in length, were taken along a transect across the lake and characterised with respect to stratigraphy, facies characteristics (i.e., grain size, componentry) and pore water silica concentrations. The sediments generally comprise two widespread facies: (i) a lower facies of light grey to grey, very fine lacustrine silt derived from the unconsolidated pyroclastic deposits that mantled the catchment area immediately after the eruption, which were rapidly reworked and redeposited into the lake basin; and (ii) an upper facies of dark, fine-sandy diatomaceous silt, that settled from the pelagic zone of the physically stable lake. Adjacent to sublacustrine hydrothermal vents, the upper dark facies is absent, and the upper part of the light grey to grey silt is replaced by a third localised facies comprised of hydrothermally altered pale yellow to yellowish brown, laminated silt with surface iron-rich encrustations. Microspheres, which are thought to be composed of amorphous silica, although some may be halloysite, have precipitated from pore water onto sediment grains, and are associated with a decrease in pore water silicon concentration. Lake Rotomahana is an example of a recently-stabilised volcanic lake, with respect to sedimentation, that shows signs of early sediment silicification in the presence of hydrothermal activity.
This chapter introduces the historical and geographical background for the scientific studies at Tarawera and Lake Rotomahana in the Taupo Volcanic Zone of New Zealand as detailed in this Special Issue of the Journal of Volcanology and Geothermal Research. It also presents the results of some original investigations. These are based partly on the large body of historical information that exists about the 1886 Tarawera eruption and the geothermal system at Rotomahana, and partly on the results of dedicated geological studies by other researchers within the Okataina Volcanic Centre where the historical events took place. Specifically the new material here presented includes a detailed analysis of a previously almost neglected narrative by the only observer to witness the 1886 eruption from the southeast of the erupting craters and leave an account of his observations. The importance of a co-operative interplay between pre-existing tectonic deformation and its responses to strong seismic activity induced by magmatic intrusion is emphasised as being a major determinant in the course of the eruption and as the main trigger of the eruption explosions that were audible throughout half of the land area of New Zealand. The chapter then concentrates on showing how the recent geological studies, in conjunction with ideas on the architecture of geysers, permit an explanation to be given as to how the unique Pink and White Terraces came to be formed.
The craters associated with the 1886 AD phreatomagmatic Rotomahana eruption, Okataina Volcanic Centre, New Zealand, and the near-vent geology are now hidden beneath Lake Rotomahana and its post-eruptive sediment fill. Lithic clasts from the near-vent lithic lapilli ash deposits of the Rotomahana Pyroclastics are used in this study to trace geological and geothermal conditions before the eruption, as well as vent excavation dynamics. Near-vent deposit characteristics were described in the field, representative lithic clasts were documented petrographically, and unaltered clasts were analysed for major and trace element compositions. The majority of the lithic clasts were rhyolites with subordinate ignimbrites and hydrothermally altered clasts, and trace siltstone and silicified clasts. The rhyolites were classified into four petrographic groups according to phenocryst content and assemblage and were more diverse with respect to geochemical compositions. Most of the rhyolite lithics in the Rotomahana Pyroclastics did not match the rhyolite domes exposed subaerially around the lake, but did have affinities with the pre-Matahina caldera Wairua Rhyolite, and potentially other older non-exposed domes. Ignimbrites most likely correlated either to the Matahina ignimbrite or older non-exposed units. Hydrothermally altered rhyolite and ignimbrite lithic clasts are common and suggest that there has been a long-lived hydrothermal system in this sector, possibly dating back to early activity of the Okataina Volcanic Centre. The diversity in lithic types indicate a spatial variation in country rock lithology and strength, which probably contributed to the vent position and morphology along the Rotomahana fissure.
Lake Rotomahana is a crater lake in the Okataina Volcanic Centre (New Zealand) that was significantly modified by the 1886 Tarawera Rift eruption. The lake is host to numerous sublacustrine hydrothermal vents. Water column studies were conducted in 2011 and 2014 along with sampling of lake shore hot springs and crater lakes in Waimangu Valley to complement magnetic, seismic, bathymetric and heat flux surveys. Helium concentrations below 50 m depth are higher in 2014 compared to 2011 and represent some of the highest concentrations measured, at 6 × 10− 7 ccSTP/g, with an end-member 3He/4He value of 7.1 RA. The high concentrations of helium, when coupled with pH anomalies due to high dissolved CO2 content, suggest the dominant chemical input to the lake is derived from magmatic degassing of an underlying magma. The lake shore hot spring waters show differences in source temperatures using a Na–K geothermometer, with inferred reservoir temperatures ranging between 197 and 232 °C. Water δ18O and δD values show isotopic enrichment due to evaporation of a steam heated pool with samples from nearby Waimangu Valley having the greatest enrichment. Results from this study confirm both pre-1886 eruption hydrothermal sites and newly created post-eruption sites are both still active.
A new technique for measuring conductive heat flux in a lake was adapted from the marine environment to allow for multiple measurements to be made in areas where bottom sediment cover is sparse, or even absent. This thermal blanket technique, pioneered in the deep ocean for use in volcanic mid-ocean rift environments, was recently used in the geothermally active Lake Rotomahana, New Zealand. Heat flow from the lake floor propagates into the 0.5 m diameter blanket and establishes a thermal gradient across the known blanket thickness and thereby provides an estimate of the conductive heat flux of the underlying terrain. This approach allows conductive heat flux to be measured over a spatially dense set of stations in a relatively short period of time. We used 10 blankets and deployed them for 1 day each to complete 110 stations over an 11-day program in the 6 x 3 km lake. Results show that Lake Rotomahana has a total conductive heat flux of about 47 MW averaging 6 W/m2 over the geothermally active lake. The western half of the lake has two main areas of high heat flux; 1) a high heat flux area averaging 21.3 W/m2 along the western shoreline, which is likely the location of the pre-existing geothermal system that fed the famous Pink Terraces, mostly destroyed during the 1886 eruption 2) a region southwest of Patiti Island with a heat flux averaging 13.1 W/m2 that appears to be related to the explosive rift that formed the lake in the 1886 Tarawera eruption. A small rise in bottom water temperature over the survey period of 0.01 °C/day suggests the total thermal output of the lake is ~ 112-132 MW and when compared to the conductive heat output suggests that 18-42% of the total thermal energy is by conductive heat transfer.
From April 2010 through February 2011, CO2 flux surveys were performed on Lake Rotomahana, New Zealand. The area has been hydrothermally active with fumaroles and sublacustrine hydrothermal activity before and since the eruption of Mt Tarawera in 1886. The total CO2 emission from the lake calculated by sequential Gaussian simulation is 549 ± 72 t day-1. Two different mechanisms of degassing, diffusion through the water-air interface and bubbling, are distinguished using a graphical statistical approach. The carbon dioxide budget calculated for the lake confirms that the main source of CO2 to the atmosphere is by diffusion covering 94.5 % of the lake area (mean CO2 flux 25 g m-2 day-1) and to a lesser extent, bubbling (mean CO2 flux 1297 g m-2 day-1). Mapping of the CO2 flux over the entire lake, including over lakefloor vents detected during the survey, correlates with eruption craters formed during the 1886 eruption. These surveys also follow regional tectonic patterns present in the southeastern sector of Lake Rotomahana suggesting a deep magmatic source (~ 10 km) for CO2 and different pathways for the gas to escape to the surface. The values of δ13CCO2 (-2.88 and -2.39 ‰) confirm the magmatic origin of CO2.
Gold and silver from a selection of springs at Waiotapu, New Zealand, was preconcentrated onto activated charcoal and analyzed by ICP-MS. The measured gold concentrations were combined with field and laboratory analyses of other components, thermodynamic data and geochemical modeling software to calculate the gold saturation index in each spring, assuming that reduced sulfur ligands largely control gold solubility. The springs that were selected for analysis have elevated concentrations of components that are residually enriched by boiling, so their composition is strongly related to that of the geothermal reservoir. Therefore, these analyses provide information about geochemical processes that operate beneath the springs as well as those at work within the springs. Previous geochemical investigations at Waiotapu indicated that dissolved gold concentrations are elevated within Champagne Pool and in precipitates surrounding this spring. Therefore, it is likely that the reservoir fluid that feeds springs at Waiotapu also contains dissolved gold. Champagne Pool has the highest gold concentration measured in this study, 109 ngL(-1) dissolved and 362 ngL(-1) total. This spring is slightly undersaturated with gold in solution, but the total concentration is higher than the solubility of Au(s). Undersaturation with respect to Au(s) is consistent with deposition of gold by adsorption and concentration within an As- and Sb-sulfide precipitate that forms around Champagne Pool and is similar in magnitude to that expected from modeling of gold adsorption onto As- and Sb-sulfide precipitates. Elevated An concentrations of gold (40-90 ngL(-1)) at two sites downstream from Champagne Pool indicate that deposition of gold within Champagne Pool is inefficient. The two downstream sites are substantially oversaturated with respect to reduced S-Au species; however, assumptions used in solubility calculations re unlikely to be valid at these sites because the oxidation state of the fluids after discharge was not determined. Despite uncertainty in the saturation index calculated at these sites, the elevated concentrations of gold and apparent oversaturation indicate that gold is transported by other ligands, such as polysulfides and thiosulfates or as colloidal particles downstream from Champagne Pool. Several springs at Waiotapu with moderate concentrations of dissolved reduced sulfur (1-6 mgL(-1)) have yen, low dissolved concentrations of gold and are substantially undersaturated with respect to Au(s). Deposition 4 gold by precipitation requires loss of reduced sulfur ligands through processes such as boiling, oxidation, acidification or sulfide precipitation. Therefore, the low concentrations of gold in springs that contain substantial reduced sulfur indicates that gold is deposited by processes that can cause substantial undersaturation of Au(s), such as adsorption, coprecipitation, or both. Deposition of gold by adsorption or coprecipitation is consistent with the occurrence of gold as impurities in epithermal sulfide minerals, These results do not rule Out direct precipitation of Au(s) at Waiotapu but indicate that other depositional mechanisms could also be important in the geothermal system beneath the springs.
The hydrology of the long-lived Rotomahana-Waimangu hydrothermal system of New Zealand was changed irreversibly by the brief 1886 Tarawera Rift basalt eruption. The nature of the pre-1886 surface thermal activity indicates that boiling conditions prevailed in the upflow zone beneath the vicinity of the then-existing shallow Lake Rotomahana. On June 10, 1886, magma erupted through this part of the system, triggering violent volcanic and hydrothermal explosions that led to the formation of new fluid conduits and a large crater that filled to form the present Lake Rotomahana. Several years after the eruption, hot springs broke out along the line of 1886 craters southwest of Lake Rotomahana. The evolution of these features has been punctuated by spectacular geysers from 1900 to 1904 and a substantial hydrothermal eruption in 1917. The main effect of the 1886 volcanic eruption on the hydrothermal system was the perturbation of pressure gradients, causing abrupt near-surface cooling followed by gradual reheating.
Gold-silver ore grade precipitates are actively forming from hot springs and drillhole discharges in three thermal areas along the eastern margin of the Taupo Volcanic Zone, New Zealand. They occur as red-orange amorphous sulfides with opaline silica and contain up to 2% As, 10% Sb, 85 ppm Au, 500 ppm Ag, 2,000 ppm Hg, and 1,000 ppm T1, although the transporting waters carry at the most only 8 ppm As, 0.3 ppm Sb, 4 × 10 -5 ppm Au, 6 × 10 -4 ppm Ag, 7 × 10 -3 ppm T1 and 120 ppm total sulfide sulfur. At depths near 1 km, the hydrothermal solutions are slightly alkaline (pH 6 to 7) sodium-potassium-chloride-bicarbonate waters at 200 to 290° C (near the boiling point versus depth curve). They ascend via fissure zones and permeable strata through a sequence of near horizontal stratified silicic Quaternary volcanic rocks, 1.5 to 3.5 km thick, overlying probable Mesozoic graywacke basement. A zoned alteration pattern is developed in the country rocks with adularia, sericite, and quartz in fissure zones; albite, wairakite, sericite, and quartz outward from these fissure zones; and shallow, lower temperature argillic alteration to montmorillonite and illite mineral assemblages. Pyrite, calcite, and chlorite are common accessory minerals. High natural discharge rates (e.g., 1.6 × 10 6 kg/hr, Wairakei system, 1951) combined with long lifetimes (e.g., 5 × 10 5 yr, Wairakei) are adequate to form, from these dilute solutions, economic gold deposits similar to the epithermal type "invisible" gold ores that occur in the western U.S. A. at the Getcheil, White Caps, Carlin, Cortez, and Mircur deposit
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