排序方式： 共有21条查询结果，搜索用时 15 毫秒
1.
2.
Mapping block-and-ash flow hazards based on Titan 2D simulations: a case study from Mt. Taranaki,NZ 总被引：1，自引：0，他引：1
Jonathan N. Procter Shane J. Cronin Thomas Platz Abani Patra Keith Dalbey Michael Sheridan Vince Neall 《Natural Hazards》2010,53(3):483-501
Numerical models for simulation of mass flows are typically focussed upon accurately predicting the paths, travel times and
inundation from a single flow or collapse event. When considering catchment-based hazards from a volcano, this is complicated
by often being faced with several possible scenarios. Over the last 800 years at Mt. Taranaki/Egmont, a number of dome growth
and collapse events have resulted in the genesis and emplacement of block-and-ash flows (BAFs). Each BAF was directed northwestward
by a breach in the crater rim. The latest dome collapse events in the AD 1880s and AD 1755 inundated the northwestern flank
and had run-out lengths 10 km from source. Future activity of this type could have a devastating effect on the Taranaki region’s
communities, infrastructure and economy. Hazard planning has involved constructing volcanic hazard maps based upon the areas
inundated by past volcanic flows, with little consideration of present-day topography. Here, a numerical geophysical mass
flow modelling approach is used to forecast the hazards of future comparable BAF events on NW Mt. Taranaki. The Titan2D programme
encompasses a “shallow water”, continuum solution-based, granular flow model. Flow mechanical properties needed for this approach
include estimates of internal and basal friction as well as the physical dimensions of the initial collapse. Before this model
can be applied to Taranaki BAFs, the input parameters must be calibrated by simulating a range of past collapse events. By
using AD 1860 and AD 1755 scenarios, initial collapse volumes can be well constrained and internal and basal friction angles
can be evaluated through an iterative approach from previous run-out lengths. A range of possible input parameters was, therefore,
determined to produce a suite of potentially inundated areas under present-day terrain. A suite of 10 forecasts from a uniformly
distributed range were combined to create a map of relative probabilities of inundation by future BAF events. These results
were combined in a GIS package to produce hazard zones related to user-specified hazard thresholds. Using these input parameter
constraints, future hazard forecasts for this scale and type of event can also take into account changing summit and topographic
configurations following future eruptive or collapse events. 相似文献
3.
V. E. Neall 《新西兰海洋与淡水研究杂志》2013,47(2):117-125
Neothyris lecticularis (Deshayes, 1839) live mainly south o'f 44°S in waters 90–180 m (extremes 18–384 m) deep where bottom temperatures are always >7°c. Fossil N. “avails” (Hutton, 1886) in the early Pleistocene limestone at Castlepoint (41 °S) are associated with an assemblage of animals generioally the same as the living N. lenticularis assemblage of Foveaux Strait. The granular substrate occupied by the living animals is similar to the matrix of the Castlepoint limestone. Thus the early Pleistocene marine climate in 90–180 m at 43°S may have been about 5°c cooler than it is today; the possible use is mentioned of the presence of the fossil assemblage in studies of palaeoelimates. Population analysis of living and fossil stocks show a constant bias toward the older age‐groups; this finding is discussed. Various ecological observations are recorded. 相似文献
4.
Michael B. Turner Shane J. Cronin Ian E. Smith Robert B. Stewart Vince E. Neall 《Journal of Volcanology and Geothermal Research》2008
Eruption episodes, where a series of eruption events are generically related, can include the eruption of a wide spectrum of volcanic activity over decadal periods. This paper concentrates on the opening phases of an eruption episode which occurred approximately 1800 yrs BP from Mt Taranaki, New Zealand. These events spanned the eruption of differing bulk compositions and styles from two distinct vent locations; an andesitic sub-plinian eruption from the summit vent and a scoria cone-building eruption of basaltic magma from a satellite vent. Compositional profiles and zoning textures of plagioclase, amphibole and clinopyroxene phenocrysts from the opening andesitic event show evidence of magma mixing and subsequent crystallisation just prior to the initiation of the eruption episode. Titanomagnetite grain morphology and Ti variation suggest that the magma mixing event occurred within a few days to weeks before the eruption acting as a trigger for it. We present a magmatic model which is constrained by the petrological observations and eruptions of the episode. In this model magma differentiation at depth causes its rise and recharging of a mid-crustal magma storage area at 5–7 km. Although the recharging magma differed slightly in oxygen fugacity and temperature, it was compositionally and physically similar enough to the residing andesitic magma to allow efficient mixing. The petrological characteristics described here can be readily observed and enable identification of mixing events in other recent eruption episodes. 相似文献
5.
Katherine A. Holt R. Clel Wallace Vincent E. Neall Barry P. Kohn David J. Lowe 《第四纪科学杂志》2010,25(7):1169-1178
Tephras provide one of the most reliable methods of time control and synchronisation within Quaternary sequences. We report on the identification of two widespread rhyolitic tephras – the Kawakawa and Rangitawa tephras – preserved in extensive peat deposits on Chatham Island ～900 km east of New Zealand. The tephras, both products of supereruptions from the Taupo Volcanic Zone, occur as pale, fine‐ash dominated layers typically 10–150 mm thick. Mineralogically they are dominated by rhyolitic glass, together with subordinate amounts of quartz, feldspar, hypersthene, hornblende, Fe–Ti oxides and zircon. Phlogopite/biotite was identified additionally in Rangitawa Tephra. Ages for each tephra were obtained via mineralogical and major element glass composition‐based correlation with well‐dated equivalent deposits on mainland New Zealand, and we also obtained a new zircon fission‐track age for Rangitawa Tephra (350 ± 50 ka) on Chatham Island. Both tephras were erupted at critical times for palaeoenvironmental reconstructions in the New Zealand region: the Kawakawa at ca. 27 cal. ka, near the beginning of the ‘extended’ LGM early in marine isotope stage (MIS) 2; and the Rangitawa at ca. 350 ka near the end of MIS 10. The time constraints provided by the tephras demonstrate that Chatham Island peats contain long‐distance pollen derived from mainland New Zealand, which provides a reliable proxy for identifying glacial–interglacial climate conditions, in this case during the MIS 11–10 and MIS 2–1 cycles. The two tephras thus provide important chronostratigraphic tie‐points that facilitate correlation and synchronisation not only across the Quaternary deposits of the Chatham Islands group but also with climatically significant terrestrial and marine records in the wider New Zealand region. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
6.
Late Holocene volcanic activity at Ruapehu has been characterizedby the generation of small (<105 m3) to very large (>107 m3) lahars and repeated,small to medium (VEI 1-3) tephra-producing eruptions. The Onetapu Formation groupsall lahar deposits that accumulated during the last 2,000 years on the southeastern Ruapehu ring plain. The andesitic tephras are grouped within the Tufa Trig Formation and are intercalated within the laharic sequence. By correlating these two formations with new radiocarbon ages obtained on interbedded paleosols, we reconstruct a detailed volcanic history of Ruapehu for this period.Clast assemblages identified in the laharic sequences record thelithologies of synchronous tephras and rocks within the source region. These assemblages suggest a strong genetic link between the development of Crater Lake, the variation in eruptivestyles, and the production of lahars.Lahar-triggering mechanisms include: (1) flank collapse ofhydrothermally altered and unstable portions of the cone; (2) phreatic and phreatomagmatic eruptions favoring the generation of snow-rich slurries and hyperconcentrated stream flows; (3) suddenCrater Lake rim collapse, releasing large amounts of water inducing debris flows; and (4) eruptions that generate large volumes of tephra on snow-covered slopes, later remobilized by heavy rain.Two major lahars in the Onetapu sequence had a volume 4 × 107 m3, roughly 1 to 2 orders of magnitude larger than the 1953event leading to the Tangiwai disaster (151 casualties). One of these lahars crossed over a lowinterfluve currently separating the Whangaehu River from a stream feeding the Tongariro River,sometime since peat accumulated between AD 1400 and AD 1660. A repetition of such a large-scaleevent would have devastating consequences on the infrastructure, economy and environment withinthe distal areas of the two catchments. The 1995–1996 eruptions were a timely reminder ofthe hazards posed by the volcano. 相似文献
7.
Agronomic impact of tephra fallout from the 1995 and 1996 Ruapehu Volcano eruptions, New Zealand 总被引：2，自引：0，他引：2
Eruptions from Ruapehu Volcano on 11 and 14 October 1995 and 17 June 1996 distributed at least 36×106 m3 of sulphur(S)-rich tephra over the central and eastern North Island of New Zealand. The tephras added between 30–1500 kg
ha–1 S to at least 25 000 km2 of land in primary production. Smaller but beneficial amounts of selenium (Se) and in some areas potassium and magnesium
were also supplied. Addition of S to the soils in the form of sulphate and elemental S resulted in a drop in soil pH and an
increase in pasture S contents within seven weeks of the eruptions. The soils affected by the tephra are naturally low in
S and Se, but following the eruptions S was not required in fertilizer applications in many areas. The strongest and longest
lasting effects of S and Se deposition were in high anion-retention soils particularly Hapludands (moist, moderately weathered
soils, derived from volcanic ash). Soluble fluorine concentrations within the tephras were low compared to historic Icelandic
and Chilean examples. However, pastoral livestock deaths were apparently caused by fluorosis in addition to starvation when
tephra covered feed. The Ruapehu tephra contained very low concentrations of other soluble toxic elements.
Received: 17 January 1997 · Accepted: 31 March 1997 相似文献
8.
Environmental hazards of fluoride in volcanic ash: a case study from Ruapehu volcano, New Zealand 总被引：1，自引：0，他引：1
Shane J. Cronin V. E. Neall J. A. Lecointre M. J. Hedley P. Loganathan 《Journal of Volcanology and Geothermal Research》2003,121(3-4):271-291
The vent-hosted hydrothermal system of Ruapehu volcano is normally covered by a c. 10 million m3 acidic crater lake where volcanic gases accumulate. Through analysis of eruption observations, granulometry, mineralogy and chemistry of volcanic ash from the 1995–1996 Ruapehu eruptions we report on the varying influences on environmental hazards associated with the deposits. All measured parameters are more dependent on the eruptive style than on distance from the vent. Early phreatic and phreatomagmatic eruption phases from crater lakes similar to that on Ruapehu are likely to contain the greatest concentrations of environmentally significant elements, especially sulphur and fluoride. These elements are contained within altered xenolithic material extracted from the hydrothermal system by steam explosions, as well as in residue hydrothermal fluids adsorbed on to particle surfaces. In particular, total F in the ash may be enriched by a factor of 6 relative to original magmatic contents, although immediately soluble F does not show such dramatic increases. Highly soluble NaF and CaSiF6 phases, demonstrated to be the carriers of ‘available’ F in purely magmatic eruptive systems, are probably not dominant in the products of phreatomagmatic eruptions through hydrothermal systems. Instead, slowly soluble compounds such as CaF2, AlF3 and Ca5(PO4)3F dominate. Fluoride in these phases is released over longer periods, where only one third is leached in a single 24-h water extraction. This implies that estimation of soluble F in such ashes based on a single leach leads to underestimation of the F impact, especially of a potential longer-term environmental hazard. In addition, a large proportion of the total F in the ash is apparently soluble in the digestive system of grazing animals. In the Ruapehu case this led to several thousand sheep deaths from fluorosis. 相似文献
9.
Sally H. Potter Bradley J Scott Gill E Jolly Vince E Neall David M Johnston 《Bulletin of Volcanology》2015,77(9):77
Accurately observing and interpreting volcanic unrest phenomena contributes towards better forecasting of volcanic eruptions, thus potentially saving lives. Volcanic unrest is recorded by volcano observatories and may include seismic, geodetic, degassing and/or geothermal phenomena. The multivariate datasets are often complex and can contain a large amount of data in a variety of formats. Low levels of unrest are frequently recorded, causing the distinction between background activity and unrest to be blurred, despite the widespread usage of these terms in unrest literature (including probabilistic eruption-forecasting models) and in Volcanic Alert Level (VAL) systems. Frequencies and intensities of unrest episodes are not easily comparable over time or between volcanoes. Complex unrest information is difficult to communicate simply to civil defence personnel and other non-scientists. The Volcanic Unrest Index (VUI) is presented here to address these issues. The purpose of the VUI is to provide a semi-quantitative rating of unrest intensity relative to each volcano’s past level of unrest and to that of analogous volcanoes. The VUI is calculated using a worksheet of observed phenomena. Ranges for each phenomenon within the worksheet can be customised for individual volcanoes, as demonstrated in the companion paper for Taupo Volcanic Centre, New Zealand (Potter et al. 2015). The VUI can be determined retrospectively for historical episodes of unrest based on qualitative observations, as well as for recent episodes with state-of-the-art monitoring. This enables a long time series of unrest occurrence and intensity to be constructed and easily communicated to end users. The VUI can also assist with VAL decision-making. We present and discuss two approaches to the concept of unrest. 相似文献
10.
A. V. Zernack S. J. Cronin V. E. Neall J. N. Procter 《International Journal of Earth Sciences》2011,100(8):1937-1966
The >25 ka volcaniclastic ring-plain succession in south-west Taranaki has been remapped to establish a much more detailed
understanding of the older stratigraphic record of Mt. Taranaki. Coastal cliff exposures show a range of volcaniclastic lithofacies,
including debris-avalanche and lahar deposits, and allow a detailed chronological reconstruction of past volcanic and sedimentary
events. Five new debris-avalanche deposits were identified, and their distribution in coastal cross-sections mapped. In addition,
four previously described units were renamed and their stratigraphic position and lateral extent redefined. Chronostratigraphic
control of the younger (<50 ka) sequence was obtained by radiocarbon dating of wood found within, or peat interbedded with,
the deposits. Emplacement ages of the older units were estimated from their stratigraphic position and underlying marine wave-cut
surfaces. Overall, at least 14 widespread debris-avalanche deposits occur within the <200 ka ring-plain record of Mt. Taranaki,
suggesting one major edifice failure on average every 14,000 years, with an increase in frequency since 40 ka. The stratigraphic
reconstruction of the ring-plain succession showed that the same pattern of deposition was repeatedly produced throughout
the existence of Mt. Taranaki. Depending on their sedimentological characteristics, the different volcanic and sedimentary
lithofacies can be related to phases of edifice-construction or collapse events. Based on the identified cyclic sedimentation
pattern, we present a new episodic stratigraphy that integrates existing and new lithostratigraphic units into a coherent
chronostratigraphic framework that can be applied to the entire volcanic and volcaniclastic succession at Mt. Taranaki. This
model takes into account the complex geological processes that have taken place on the volcano and provides a more uniform
stratigraphic terminology that could be applied to repeatedly collapsing stratovolcanoes elsewhere. 相似文献