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The Middle Jurassic Kirkpatrick flood basalts and comagmatic Ferrar intrusions in the Transantarctic Mountains represent
a major pulse of tholeiitic magmatism related to early stages in the breakup of Gondwana. A record of the volcano-tectonic
events leading to formation of this continental flood-basalt province is provided by strata underlying and only slightly predating
the Kirkpatrick lavas. In the central Transantarctic Mountains, the lavas rest on widespread (≥7500 km2) tholeiitic pyroclastic deposits of the Prebble Formation. The Prebble Formation is dominated by lahar deposits and is an
unusual example of a regionally developed basaltic lahar field. Related, partly fault-controlled pyroclastic intrusions cut
underlying strata, and vents are represented by the preserved flanks of two small tephra cones associated with a volcanic
neck. Lahar and air-fall deposits typically contain 50–60% accidental lithic fragments and sand grains derived from underlying
Triassic – Lower Jurassic strata in the upper part of the Beacon Supergroup. Juvenile basaltic ash and fine lapilli consist
of nonvesicular to scoriaceous tachylite, sideromelane, and palagonite, and have characteristics indicating derivation from
hydrovolcanic eruptions. The abundance of accidental debris from underlying Beacon strata points to explosive phreatomagmatic
interaction of basaltic magma with wet sediment and groundwater, which appears to have occurred in particular where rising
magma intersected upper Beacon sand aquifers. Composite clasts in the lahar deposits exhibit complex peperitic textures formed
during fine-scale intermixing of basaltic magma with wet sand and record steps in subsurface fuel-coolant interactions leading
to explosive eruption.
The widespread, sustained phreatomagmatic activity is inferred to have occurred in a groundwater-rich topographic basin linked
to an evolving Jurassic rift zone in the Transantarctic Mountains. Coeval basaltic phreatomagmatic deposits of the Mawson
and Exposure Hill Formations, which underlie exposures of the Kirkpatrick Basalt up to 1500 km to the north along strike in
Victoria Land, appear to represent other parts of a regional, extension-related Middle Jurassic phreatomagmatic province which
developed immediately prior to rapid outpouring of the flood basalts. This is consistent with models which assign an important
role to lithospheric stretching in the generation of flood-basalt provinces.
Received: 28 August 1995 / Accepted: 18 April 1996 相似文献
2.
A. M. F. Lagmay K. S. Rodolfo F. P. Siringan H. Uy C. Remotigue P. Zamora M. Lapus R. Rodolfo J. Ong 《Bulletin of Volcanology》2007,69(7):797-809
The 1991 Pinatubo eruption left 5–6 km3 of debris on the volcano slopes, much of which has been mobilized into large lahars in the following rainy seasons. Also
during the eruption, collapse, localized in part along preexisting faults, left a caldera 2.5 km in diameter that almost immediately
began to accumulate a 1.6 × 108 m3 lake. By 2001, the water had risen to the fault-controlled Maraunot Notch, the lowest, northwestern portion of the caldera
rim comprising the physiographic sill of the Caldera Lake. That year, a narrow artificial canal dug into an old volcanic breccia
underlying the outlet channel failed to induce a deliberate lake breakout, but discharge from heavy rains in July 2002 rapidly
deepened the notch by 23 m, releasing an estimated 6.5 × 107 m3 of lake water that bulked up into lahars with a volume well in excess of 1.6 × 108 m3. Lakes in other volcanoes have experienced multiple breakouts, providing practical motivation for this study. Fieldwork and
high-resolution digital elevation models reveal andesites and ancient lacustrine deposits, strongly fractured and deformed
along a segment of the Maraunot Fault, a prominent, steeply dipping, left-lateral fault zone that trends N35°–40°W within
and parallel to the notch. Seismicity in 1991 demonstrated that the Maraunot Fault is still active. The fault zone appears
to have previously been the erosional locus for a large channel, filled with avalanche or landslide deposits of an earlier
eruption that were exhumed by the 2002 breakout floods. The deformed lacustrine sediments, with an uncalibrated 14C age of 14,760 ± 40 year BP from a single charcoal sample, attest to the existence of an earlier lake, possibly within the
Tayawan Caldera, rim remnants of which survive as arcuate escarpments. That lake may well have experienced one or more ancient
breakouts as well. The 2002 event greatly reduced the possibility of another such event by scouring away the erodible breccia,
leaving less erodible fractured andesites and lacustrine rocks, and by enlarging the outlet channel and its discharge capacity.
Several lines of evidence indicate, however, that future lahar-generating lake breakouts at the notch may keep populations
of Botolan municipality downstream at risk: (1) a volume of 9.5 × 107 m3 of lake water remains perched 0.8 km above sea level; (2) seismicity in 1991 demonstrated that the Maraunot Fault is still
active and movements of sufficient magnitude could enlarge the outlet and the discharge through it; (3) more likely, however,
with or without earthquake activity, landslides from the steep to overhanging channel walls could block the channel again,
and a major rainstorm could then cause a rise in lake level and sudden breakouts; (4) intrusion of a new dome into the bottom
of the lake, possibly accompanied by phreatic explosions, could expel large volumes of lahar-generating water. 相似文献
3.
Joseph S. Walder 《Bulletin of Volcanology》2000,62(2):105-118
Received: 15 March 1999 / Accepted: 9 December 1999 相似文献
4.
Paolo Canuti Nicola Casagli Filippo Catani Giacomo Falorni 《Physics and Chemistry of the Earth》2002,27(36):1587-1599
Lahars, here defined as debris flows of volcanic origin, are rapid mass movements that pose a serious threat to cities located in the vicinity of many volcanoes. Quito, capital city of Ecuador and placed at the foot of the Pichincha volcano complex, is exposed to serious inundation hazard as part of the city is built on numerous deposits of large lahars that have occurred in the last 10,000 years.The objective of this paper is to model the potential lahars of the Pichincha volcano to predict inundation areas within the city of Quito. For this purpose two models that apply different approaches were utilized and their results were compared.The programs used were LAHARZ, a semi-empirical model conceived by the United States Geological Survey (USGS), and FLO-2D, a hydraulic model distributed by FLO Software Inc. LAHARZ is designed as a rapid, objective and reproducible automated method for mapping areas of potential lahar inundation (Proc. First Int. Conf. on Debris Flow Hazards Mitigation, San Francisco, USA, ASCE, 1998, p. 176). FLO-2D is a two-dimensional flood routing model for simulating overland flow on complex surfaces such as floodplains, alluvial fans or urbanized areas (FLO-2D Users manual, version 99.2). Both models run within geographical information systems (GIS).Fieldwork was focused on collecting all available information involved in lahar modeling. A total of 49 channel cross-sections were measured along the two main streams and stratigraphic investigations were carried out on the fans to estimate the volume of previous events. A global positioning system was utilized to determine the coordinates of each cross-section. Further data collection concerned topography, rainfall characteristics and ashfall thicknesses. All fieldwork was carried out in cooperation with the Instituto Geofisico of the Escuela Politecnica Nacional.Modeling in a GIS environment greatly aided the exportation of results for the creation of thematic maps and facilitated model comparison. Evaluation of the models was performed by comparing simulation results against each other and against the geometry of existing lahar deposits. 相似文献
5.
Empirical modelling of the May 1998 small debris flows in Sarno (Italy) using LAHARZ 总被引:1,自引:0,他引:1
D. Oramas Dorta G. Toyos C. Oppenheimer M. T. Pareschi R. Sulpizio G. Zanchetta 《Natural Hazards》2007,40(2):381-396
The catastrophic events that occurred in May 1998 in the area of Sarno (Southern Italy) highlight the destructive potential
of debris flows, even when they are of relatively low magnitude. More than 130 people were killed and severe property damage
took place when volcaniclastic debris flows triggered by heavy rainfall inundated various towns located in piedmont areas.
This work investigates the suitability of LAHARZ, a GIS-assisted method for the automatic delineation of lahar inundation
areas, for reproducing the May 1998 flows at Sarno. It was found that recalibration of the empirical relationship employed
by LAHARZ is required in order to realistically hind-cast the inundation areas of considered events. The potential for further
improvements in prediction outputs for this type of geomorphic setting is discussed, taking into account the observed lower
mobility of these small volcaniclastic debris flows as compared to lahars of similar size. 相似文献
6.
Statistical Analysis of Landslide Events in Central America and their Run-out Distance 总被引:3,自引:0,他引:3
Graziella Devoli Fabio V. De Blasio Anders Elverhøi Kaare Høeg 《Geotechnical and Geological Engineering》2009,27(1):23-42
Statistical analyses of landslide deposits from similar areas provide information on dynamics and rheology, and are the basis
for empirical relationships for the prediction of future events. In Central America landslides represent an important threat
in both volcanic and non-volcanic areas. Data, mainly from 348 landslides in Nicaragua, and 19 in other Central American countries
have been analyzed to describe landslide characteristics and to search for possible correlations and empirical relationships.
The mobility of a landslide, expressed as the ratio between height of fall (H) and run-out distance (L) as a function of the
volume and height of fall; and the relationship between the height of fall and run-out distance were studied for rock falls,
slides, debris flows and debris avalanches. The data show differences in run-out distance and landslide mobility among different
types of landslides and between debris flows in volcanic and non-volcanic areas. The new Central American data add to and
seem consistent with data published from other regions. Studies combining field observations and empirical relationships with
laboratory studies and numerical simulations will help in the development of more reliable empirical equations for the prediction
of landslide run-out, with applications to hazard zonation and design of optimal risk mitigation measures. 相似文献
7.
Christopher F. Waythomas 《Bulletin of Volcanology》1999,61(3):141-161
Akutan Volcano is one of the most active volcanoes in the Aleutian arc, but until recently little was known about its history
and eruptive character. Following a brief but sustained period of intense seismic activity in March 1996, the Alaska Volcano
Observatory began investigating the geology of the volcano and evaluating potential volcanic hazards that could affect residents
of Akutan Island. During these studies new information was obtained about the Holocene eruptive history of the volcano on
the basis of stratigraphic studies of volcaniclastic deposits and radiocarbon dating of associated buried soils and peat.
A black, scoria-bearing, lapilli tephra, informally named the "Akutan tephra," is up to 2 m thick and is found over most of
the island, primarily east of the volcano summit. Six radiocarbon ages on the humic fraction of soil A-horizons beneath the
tephra indicate that the Akutan tephra was erupted approximately 1611 years B.P. At several locations the Akutan tephra is
within a conformable stratigraphic sequence of pyroclastic-flow and lahar deposits that are all part of the same eruptive
sequence. The thickness, widespread distribution, and conformable stratigraphic association with overlying pyroclastic-flow
and lahar deposits indicate that the Akutan tephra likely records a major eruption of Akutan Volcano that may have formed
the present summit caldera. Noncohesive lahar and pyroclastic-flow deposits that predate the Akutan tephra occur in the major
valleys that head on the volcano and are evidence for six to eight earlier Holocene eruptions. These eruptions were strombolian
to subplinian events that generated limited amounts of tephra and small pyroclastic flows that extended only a few kilometers
from the vent. The pyroclastic flows melted snow and ice on the volcano flanks and formed lahars that traveled several kilometers
down broad, formerly glaciated valleys, reaching the coast as thin, watery, hyperconcentrated flows or water floods. Slightly
cohesive lahars in Hot Springs valley and Long valley could have formed from minor flank collapses of hydrothermally altered
volcanic bedrock. These lahars may be unrelated to eruptive activity.
Received: 31 August 1998 / Accepted: 30 January 1999 相似文献
8.
In subaerial volcaniclastic sequences structures formed by ice blocks can provide information about a volcano's history of lahar generation by glacier melt. At Volcán Hudson in Chile, catastrophic lahars were initiated by eruption-induced melting of glacier ice in August and October 1991. They transported large ice blocks 50 km down the Rio de los Huemules valley to the sea. Large current crescents with lee-side lenses were formed where ice blocks were deposited during waning stages of the flood. When stranded blocks of ice melted, they left cone-shaped and ring-shaped heaps of ice-rafted debris on the sediment surface. Several hundred ice blocks were completely buried within the aggrading lahar sediment, and when these melted circular collapse pits formed in the sediment. Collapse types included subsided coherent blocks of sediment bounded by an outward-dipping ring-fracture, trapdoor structures with horseshoe-shaped fractures, downsag pits with centroclinal dips locally up to 60°, pits with peripheral graben and crevasses, piecemeal (highly fragmented) collapse structures and funnel-shaped pits containing disaggregated sediment. A sequence of progressive collapse is inferred in which initial downsag and subsidence on an outward-dipping ring fracture produces a small diameter pit. This is followed by widening of the pit by progressive development of concentric ring fractures and downsag outside the early formed pit, and by collapse of overhanging pit walls to produce vertical to inward-dipping walls and aprons of collapse debris on the pit floor. The various structures have potential for preservation even in regions prone to high rainfall and flooding, and they can be used to indicate that former lahars contained abundant blocks of ice. 相似文献
9.
Esperanza Muñoz-Salinas C. S. Renschler D. Palacios L. M. Namikawa 《Natural Hazards》2008,45(2):309-320
In contrast to dramatic flow regime changes by less frequent large-scale volcanic eruptions, those caused by more frequent
small-scale processes in volcanic landscapes may also drastically change the direction and dynamics of flow in a drainage
system formed solely by fluvial processes. During such periods of channel morphology change, it is necessary to frequently
update channel flow parameters to assess preventive measures for civil protection purposes. Often aerial photography is impracticable,
since parts of the channels are covered by dense vegetation, while total station and laser topographic surveys are often too
slow and costly, particularly during a high frequency of events. This article introduces and validates a new methodology for
updating the representation of channel morphology in Digital Elevation Models (DEM) used specifically for assessing the dangers
of frequently occurring lahars along gorges in volcanic landscapes during eruptive and non-eruptive periods. The updating
of channel cross-sections was achieved by inserting more detailed representative profiles of homogeneous channel sectors in
DEMs derived from existing less detailed topographic maps. The channel profiles were surveyed along the thalweg in equidistant
points according to Universal Transverse Mercator (UTM) (x,y) coordinates and elevation derived from the existing DEM. The
proposed technique was applied at Tenenepanco-Huiloac Gorge on Popocatépetl volcano, Mexico, in an area affected by major
lahars during the volcano’s most recent eruptive period from 1994 to 2005. The proposed method can reduce the cost and person-hours
of a regular channel topographic survey dramatically and the enhanced DEM can determine volume parameters and flood zones
associated with the 1 July 1997 and 21 January 2001 lahars, respectively. In addition, the updated DEM with better channel
representation allowed a more realistic fluid flow and lahar simulation with the process-based TITAN2D model. 相似文献
10.
Joseph S. Walder 《Bulletin of Volcanology》2000,62(2):119-129
Received: 15 March 1999 / Accepted: 9 December 1999 相似文献
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