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Avalanche Deposits (avalanche + deposit)

Distribution by Scientific Domains
Earth and Environmental Science40%

Selected Abstracts

Wet Snow Avalanche Deposits in the French Alps: Structure and Sedimentology

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1-2 2001
Vincent Jomelli
We analyse the morphology and sedimentology of 25 dirty snow avalanche deposits in the French Alps. The deposits typically have either a snow-ball structure or a massive structure with sliding planes. The snow balls show a longitudinal and a vertical sorting that reflects a sieve effect, similar to that observed in other rapid inertial granular flows. The massive type results from snow compaction when the avalanche is channelled by a gully or when it reaches the distal part of the scree. Velocity decrease and compaction limit the deformation to a zone at the base of the snow mass and cause the formation of distinctive sliding planes. These appear as smooth recrystallised surfaces due to local melt from frictional heating. The flow can be assimilated to a frictional granular flow. No systematic variation of size and shape of the rock debris has been observed along the profiles in both types of deposit. The distribution of rock debris and its fabric suggest that the clasts are transported passively and do not undergo any sorting during displacement. Snow melt after avalanching causes a redistribution of rock debris particularly when the snow thickness is important. This redistribution does not generate new sedimentological characteristics such as enhanced sorting or fabric. [source]

Stratigraphy and volcanology of the Türkbükü volcanics: products of a stratovolcano in the Bodrum Peninsula, SW Anatolia

GEOLOGICAL JOURNAL, Issue 2 2006
Zekiye Karacik
Abstract The Middle-Upper Miocene Bodrum magmatic complex of the Aegean region, southwestern Turkey, is mainly represented by intermediate stocks, lavas, pyroclastic and volcaniclastic deposits. Monzonitic stocks and connected porphyry intrusions and extrusions are the first products of the magmatism. These are followed by a volcanic succession consisting of andesitic-latitic lavas, autobrecciated lavas, pyroclastic and volcaniclastic deposits. The final stage is represented by basaltic and basaltic andesitic flows and dykes intruded into previous units. The volcanic succession crops out in the northern part of the Bodrum peninsula. In the lower part of this succession are widespread pyroclastic deposits, composed of pyroclastic fall and flow units, alternating with epiclastic deposits. Grain size, volume and thickness of the pyroclastic deposits were mainly controlled by the type, magnitude and intensity of the eruption. Further up the section, there are two horizons of debris avalanche deposits forming the coarsest and thickest deposits of the volcaniclastic succession. The debris avalanche deposits indicate at least two different flank collapses coeval with the volcanism. The stratigraphy and map pattern of these volcanic units imply that the northern part of the Bodrum peninsula was the north-facing flank of a stratovolcano during the mid-Late Miocene. Copyright © 2006 John Wiley & Sons, Ltd. [source]

The clay mineralogy of sediments related to the marine Mjølnir impact crater

METEORITICS & PLANETARY SCIENCE, Issue 10 2003
Henning DYPVIK
It was formed about 142 ± 2.6 Myr ago by the impact of a 1,2 km asteroid into the shallow shelf clays of the Hekkingen Formation and the underlying Triassic to Jurassic sedimentary strata. A core recovered from the central high within the crater contains slump and avalanche deposits from the collapse of the transient crater and central high. These beds are overlain by gravity flow conglomerates, with laminated shales and marls on top. Here, impact and post-impact deposits in this core are studied with focus on clay mineralogy obtained from XRD decomposition and simulation analysis methods. The clay-sized fractions are dominated by kaolinite, illite, mixed-layered clay minerals and quartz. Detailed analyses showed rather similar composition throughout the core, but some noticeable differences were detected, including varying crystal size of kaolinite and different types of illites and illite/smectite. These minerals may have been formed by diagenetic changes in the more porous/fractured beds in the crater compared to time-equivalent beds outside the crater rim. Long-term post-impact changes in clay mineralogy are assumed to have been minor, due to the shallow burial depth and minor thermal influence from impact-heated target rocks. Instead, the clay mineral assemblages, especially the abundance of chlorite, reflect the impact and post-impact reworking of older material. Previously, an ejecta layer (the Sindre Bed) was recognized in a nearby well outside the crater, represented by an increase in smectite-rich clay minerals, genetically equivalent to the smectite occurring in proximal ejecta deposits of the Chicxulub crater. Such alteration products from impact glasses were not detected in this study, indicating that little, if any, impact glass was deposited within the upper part of the crater fill. Crater-fill deposits inherited their mineral composition from Triassic and Jurassic sediments underlying the impact site. [source]

Edge-roundness of boulders of Torridonian Sandstone (northwest Scotland): applications for relative dating and implications for warm and cold climate weathering rates

BOREAS, Issue 2 2010
MARTIN P. KIRKBRIDE
Kirkbride, M.P. & Bell, C.M. 2009: Edge-roundness of boulders of Torridonian Sandstone (northwest Scotland): applications for relative dating and implications for warm and cold climate weathering rates. Boreas, 10.1111/j. 1502-3885.2009.00131.x. ISSN 0300-9483. The relative ages of late Quaternary morainic and rock avalanche deposits on Late Precambrian Torridonian Sandstone are determined from the characteristic edge-roundness of constituent boulders. Because weathering of sandstone is manifest as edge-rounding by granular disintegration, a relative chronology can be derived by measuring the effective radii of curvature of a sample of boulder edges. Thirteen samples totalling 597 individual boulder edges fall into two statistically distinct groups. Moraines of inferred Younger Dryas age (12.9,11.5 kyr BP) are distinguished from moraines of the Wester Ross Re-advance (,14.0 kyr BP). One moraine previously assumed to be of Younger Dryas age is reassigned to the older group. The method allows spatial extrapolation of deposit ages from dated sites where lithological and sampling criteria are met. Calculated rates of edge-rounding imply that granular disintegration was several times more rapid during cold stadial climates than during the Holocene. Used as a proxy for boulder ,erosion rate', this indicates that surface loss of grains in glacial climates exceeds that during interglacials by a factor of 2,5, with implications for the calculation of exposure ages from cosmogenic nuclides. [source]