Tephra layers : a controlling factor on submarine translational sliding?.

Harders, Rieka, Kutterolf, Steffen, Hensen, Christian, Moerz, Tobias and Brückmann, Warner (2010) Tephra layers : a controlling factor on submarine translational sliding?. Geochemistry Geophysics Geosystems, 11 (5). DOI 10.1029/2009GC002844.

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Abstract

Submarine slope failures occur at all continental margins, but the processes generating different mass wasting phenomena remain poorly understood. Multibeam bathymetry mapping of the Middle America Trench reveals numerous continental slope failures of different dimensions and origin. For example, large rotational slumps have been interpreted to be caused by slope collapse in the wake of subducting seamounts. In contrast, the mechanisms generating translational slides have not yet been described. Lithology, shear strength measurements, density, and pore water alkalinity from a sediment core across a slide plane indicate that a few centimeters thick intercalated volcanic tephra layer marks the detachment surface. The ash layer can be correlated to the San Antonio tephra, emplaced by the 6000 year old caldera-forming eruption from Masaya-Caldera, Nicaragua. The distal deposits of this eruption are widespread along the continental slope and ocean plate offshore Nicaragua. Grain size measurements permit us to estimate the reconstruction of the original ash layer thickness at the investigated slide. Direct shear test experiments on Middle American ashes show a high volume reduction during shearing. This indicates that marine tephra layers have the highest hydraulic conductivity of the different types of slope sediment, enabling significant volume reduction to take place under undrained conditions. This makes ash layers mechanically distinct within slope sediment sequences. Here we propose a mechanism by which ash layers may become weak planes that promote translational sliding. The mechanism implies that ground shaking by large earthquakes induces rearrangement of ash shards causing their compaction (volume reduction) and produces a rapid accumulation of water in the upper part of the layer that is capped by impermeable clay. The water-rich veneer abruptly reduces shear strength, creating a detachment plane for translational sliding. Tephra layers might act as slide detachment planes at convergent margins of subducting zones, at submarine slopes of volcanic islands, and at submerged volcano slopes in lakes.

Document Type: Article
Keywords: Sedimentology; Geophysics; Submarine landslides, mass wasting, ash layers, liquefaction, translational sliding, permeability, SFB574
Research affiliation: OceanRep > SFB 574 > C4
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > SFB 574 > B2
OceanRep > SFB 574
OceanRep > SFB 574 > B5
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1029/2009GC002844
ISSN: 1525-2027
Projects: Future Ocean, SFB574
Contribution Number:
ProjectNumber
SFB 574136
Expeditions/Models/Experiments:
Date Deposited: 18 May 2010 11:01
Last Modified: 14 Mar 2018 10:44
URI: http://oceanrep.geomar.de/id/eprint/3534

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