Éditeur(s) : HAL CCSD Wiley
Résumé : SUBSURF
International audience
Similarity of form between subaerial and submarine landscapes affected by erosion could suggest similarities in the process of erosion, such as by runoff and sedimentary flows, respectively. On the other hand, if aspects of form vary, its characteristics may be used to identify the environmental origin of erosion. Towards these goals, this contribution addresses the morphology of submarine volcanoes (seamounts) with widely differing histories of erosion. One set from the Pacific Ocean never exposed above sea level includes Cretaceous-age seamounts near Hawai'i (including Apu'upu'u Seamount), two seamounts of < 3 Ma in age near a mid-ocean ridge and the 11-4 Ma Jasper Seamount. These seamounts are all isolated from continents and hence from any erosion associated with mass wasting of unstable terrigenous deposits. In such isolated submarine environments, surfaces erode slowly from in situ weathering, mass wasting and scouring by sedimentary flows initiated by slope failure in pelagic or bedrock materials. The Pacific seamounts are compared with Valencia Seamount in the western Mediterranean, exposed subaerially for 100-400 k.y. during the Messinian Salinity Crisis before 5 Ma. Multibeam and deeply towed sidescan sonar data of Valencia Seamount reveal features typical of subaerial erosion of volcanic islands, such as canyons and relatively uneroded sectors (planezes) between them. Using a simple topographical reconstruction, the apparent erosion depth typically reaches 100 m within canyons and up to 180 m in places. Whereas the younger Pacific seamounts do not show these erosional features, the much older Cretaceous seamounts do have channels, which in one example suggests up to 200 m of incision. Both Valencia and Apu'upu'u seamounts have channel longitudinal profiles that are steep and typically linear to concave upwards. The erosion depth of Apu'upu'u Seamount is significant, despite the seamount's persistent submarine environment, because of its greater age, steeper flanks and greater contributing areas to channels compared with Valencia Seamount. These results illustrate that the channel morphology resulting from submarine erosion can become similar to that produced by subaerial erosion given sufficient time.
ISSN: 0950-091X

hal-00411425
https://hal.archives-ouvertes.fr/hal-00411425
DOI : 10.1111/j.1365-2117.2008.00355.x

Éditeur(s) : Amer Geophysical Union
Résumé : New high-resolution multichannel seismic data (GWADASEIS-2009 and JC45/46-2010 cruises; 72 and 60 channels, respectively) combined with previous data (AGUADOMAR-1999 and CARAVAL-2002; 6 and 24 channels, respectively) allow a detailed investigation of mass-wasting processes around the volcanic island of Montserrat in the Lesser Antilles. Seven submarine deposits have sources on the flanks of Montserrat, while three are related to the nearby Kahouanne submarine volcanoes. The most voluminous deposit (similar to 20 km(3)) within the Bouillante-Montserrat half-graben has not been described previously and is probably related to a flank instability of the Centre Hills Volcano on Montserrat, while other events are related to the younger South Soufriere Hills-Soufriere Hills volcanic complex. All deposits are located to the south or southeast of the island in an area delimited by faults of the Bouillante-Montserrat half-graben. They cover a large part of the southeast quarter of the surrounding seafloor (similar to 520 km(2)), with a total volume of similar to 40 km(3). Our observations suggest that the Bouillante-Montserrat half-graben exerts a control on the extent and propagation of the most voluminous deposits. We propose an interpretation for mass-wasting processes around Montserrat similar to what has happened for the southern islands of the Lesser Antilles.
Geochemistry Geophysics Geosystems (1525-2027) (Amer Geophysical Union), 2011-05 , Vol. 12 , N. 5 , P. Q05006

Droits : Copyright 2011 by the American Geophysical Union
http://archimer.ifremer.fr/doc/00200/31100/29510.pdf
DOI:10.1029/2010GC003451
http://archimer.ifremer.fr/doc/00200/31100/

Éditeur(s) : Springer
Résumé : Based on new multibeam bathymetric data, seismic-reflection profiles and side-scan sonar images, a great number of submarine failures of various types and sizes was identified along the northern margin of the Ligurian Basin and characterized with 3 distinct end-members concerning their location on the margin, sedimentary processes and possible triggering mechanisms. They include superficial landslides mainly located in the vicinity of the main mountain-supplied rivers and on the inner walls of canyons (typically smaller that 10(8) m(3) in volume: Type 1), deep scars 100-500 m high along the base of the continental slope (Type 2), and large-scale scars and Mass Transport Deposits (MTDs) affecting the upper part of the slope (Type 3 failures). The MTDs are located in different environmental contexts of the margin, including the deep Var Sedimentary Ridge (VSR) and the upper part of the continental slope in the Gulf of Genova (Finale Slide and Portofino Slide), with volumes of missing sediment reaching up to 1.5 x 10(9) m(3). High sedimentation rates related to hyperpycnal flows, faults and earthquake activity, together with sea-level fluctuations are the main factors invoked to explain the distribution and sizes of these different failure types.
Marine Geophysical Research (0025-3235) (Springer), 2011-03 , Vol. 32 , N. 1-2 , P. 225-243

Droits : Springer Science+Business Media B.V. 2011
http://archimer.ifremer.fr/doc/00043/15387/14028.pdf
DOI:10.1007/s11001-011-9123-3
http://archimer.ifremer.fr/doc/00043/15387/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : We present a preliminary probabilistic tsunami hazard assessment of Canadian coastlines from local and far-field, earthquake, and large submarine landslide sources. Analyses involve published historical, palaeotsunami and palaeoseismic data, modelling, and empirical relations between fault area, earthquake magnitude, and tsunami run-up. The cumulative estimated tsunami hazard for potentially damaging run-up (≥1.5 m) of the outer Pacific coastline is ~40-80 % in 50 years, respectively one and two orders of magnitude greater than the outer Atlantic (~1-15 %) and the Arctic (<1 %). For larger run-up with significant damage potential (≥3 m), Pacific hazard is ~10-30 % in 50 years, again much larger than both the Atlantic (~1-5 %) and Arctic (<1 %). For outer Pacific coastlines, the ≥1.5 m run-up hazard is dominated by far-field subduction zones, but the probability of run-up ≥3 m is highest for local megathrust sources, particularly the Cascadia subduction zone; thrust sources further north are also significant, as illustrated by the 2012 Haida Gwaii event. For Juan de Fuca and Georgia Straits, the Cascadia megathrust dominates the hazard at both levels. Tsunami hazard on the Atlantic coastline is dominated by poorly constrained far-field subduction sources; a lesser hazard is posed by near-field continental slope failures similar to the 1929 Grand Banks event. Tsunami hazard on the Arctic coastline is poorly constrained, but is likely dominated by continental slope failures; a hypothetical earthquake source beneath the Mackenzie delta requires further study. We highlight areas susceptible to locally damaging landslide-generated tsunamis, but do not quantify the hazard.
ISSN: 0921-030X

hal-00963614
https://hal.archives-ouvertes.fr/hal-00963614
DOI : 10.1007/s11069-013-0809-5

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Despite convergent margins being unstable systems, most reports of huge submarine slope failure have come from oceanic volcanoes and passive margins. Swath bathymetry and seismic profiles of the northern Hikurangi subduction system, New Zealand, show a tapering 65-30 km wide by 65 km deep margin indentation, with a giant, 3150+_630 km 3, blocky, debris avalanche deposit projecting 40 km out across horizontal trench fill, and a debris flow deposit projecting over 100 km. Slide blocks are well-bedded, up to 18 km across and 1.2 km high, the largest being at the avalanche deposit's leading edge. Samples dredged from them are mainly Miocene shelf calc-mudstones similar to those outcropping around the indentation. Cores from cover beds suggest that failure occurred-170 +_40 ka, possibly synchronously with a major extension collapse in the upper indentation. However, the northern part of the indentation is much older. The steep, straight northern wall is close to the direction of plate convergence and probably formed around 2.0-0.16 Ma as a large seamount subducted, leaving in its wake a deep groove obliquely across the margin and an unstable triangle of fractured rock in the 60 ø angle between groove and oversteepened margin front. The triangle collapsed as a blocky avalanche, leaving a scalloped southern wall and probably causing a large tsunami. Tentative calculations of compacted volumes suggest that the indentation is over 600 km 3 larger than the avalanche, supporting a two-stage origin that includes subduction erosion. Since failure, convergence has carried the deposits-9 km back toward the margin, causing internal compression. The eventual subduction/accretion of the Ruatoria avalanche explains the scarcity of such features on active margins and perhaps the nature of olistostromes in fold belts.
ISSN: 2169-9275

hal-01261406
https://hal.archives-ouvertes.fr/hal-01261406
https://hal.archives-ouvertes.fr/hal-01261406/document
https://hal.archives-ouvertes.fr/hal-01261406/file/CollotJGR2001.pdf
DOI : 10.1029/2001JB900004