Late Quaternary sediment, sediment mass flow processes and slope stability on the Scotian Slope, Canada

Abstract

The study area, just to the west of the Verrill Canyon on the Scotian Slope, eastern Canada, exhibits both large and small scale sediment mass movement features. Study of high resolution seismic reflection and sidescan sonar data shows that a large portion (approximately 70%) of the near surface sediment (<20 m) in the area has undergone erosion, rotational slumping and internal deformation. Remoulded sediment observed in physical properties profiles of piston cores and sediment deformation structures are further evidence of slumping. Small scale mass flow events are recorded by abundant turbidites and debris flow deposits noted in piston cores. Sediment physical properties are highly dependent on sediment type (lithofacies). Frequent facies changes, both temporally and spatially, make correlation between cores difficult. Although the small scale mass movement events correlate with glacial recession on the continental shelf and lower relative sea levels, the triggering mechanisms for the large scale events are less obvious. Slope stability analyses indicate that, at present, the seabed is stable. The most plausible explanation for large scale slope failures in this region are ground accelerations related to earthquake shock. Our analyses demonstrate that it is unlikely that large magnitude, distant earthquakes, such as those previously proposed in the Laurentian Slope Seismic Zone (LSP) model, could initiate failure of sediment in the study region. Our data support the interpretation that more frequent, lower magnitude earthquakes, closer to the study region, as previously proposed in the Eastern Slope Experimental Source Zone (ESX) model, are the likely causes of large scale slope failures. Furthermore, excess pore pressures resulting from shallow gas and/or high sedimentation rates during deglaciation contribute to slope failure.

The Gebra Slide: a submarine slide on the Trinity Peninsula Margin, Antarctica

“…The Verrill Canyon area on the Scotian Slope and successive landslides in the Canary Islands illustrate such multi-phase mass-wasting processes (Mosher et al, 1994;Masson et al, 1998;Gee et al, 2001). The Humboldt Slide, on the northern California continental margin, is interpreted as a large shear-dominated retrogressive slope failure (Gardner et al, 1999).…”

“…the loading of a grounded ice sheet); (3) seepage of shallow methane gases or destabilization of gas hydrates; (4) oversteepening of the margin ; (5) erosion at the toe of the slope ; (6) tectonic setting; and (7) earthquakes (Bugge et al, 1987;Mosher et al, 1994;Mulder and Moran, 1995;Dimakis et al, 2000;Laberg and Vorren, 2000a). Below, we will tentatively evaluate the potential of each of these controlling factors for having triggered the Gebra Slide.…”

“…The reasons for glacial margins to be highly unstable are numerous, but all are directly or indirectly related to the dynamics of the ice sheet: oversteepening of the margin by glacial-marine sedimentation processes, loading/unloading by a grounded ice sheet, glacio-eustatic sea-level variations, glacio-isostatic e¡ects, seismicity, etc. (Bugge et al, 1987;Mosher et al, 1994;Mulder and Moran, 1995).…”

“…Large-scale submarine slides are particularly well documented along the glacial continental margins of the North Atlantic : the Norwegian Sea (the Storegga Slide, the Tr×nadjupet Slide and the AndÖya Slide), the Svalbard^Barents Sea (BjÖrnÖyrenna Slide and the Isfjorden Slide) 0025-3227 / 02 / $^see front matter ß 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0025-3227(02) and eastern Canada (the Verrill Canyon area and the northeast Newfoundland slope) (Bugge et al, 1987;Aksu and Hiscott, 1992;Piper et al, 1999;Laberg and Vorren, 2000a;Mosher et al, 1994;Mulder and Moran, 1995). The reasons for glacial margins to be highly unstable are numerous, but all are directly or indirectly related to the dynamics of the ice sheet: oversteepening of the margin by glacial-marine sedimentation processes, loading/unloading by a grounded ice sheet, glacio-eustatic sea-level variations, glacio-isostatic e¡ects, seismicity, etc.…”

El problema genético de los fondos de fiordo Norpatagónicos

“…La frecuencia con que aparecen deslizamientos compactos es congruente con la suavidad de las pendientes. Las formas de compresión vertiente abajo (sedimentos remoldeados y punta de compresión) deben haberse producido también lentamente, sin perjuicio de incidencias cataclismáticas sísmicas, como puede deducirse de otros casos (Mosher et al, 1994;Anastasakis y Piper, 1991) y de rugosidades aisladas en estructuras laminadas de estos ejemplos. Por otra parte, si las capas de la explanada tienen detalles de estratificación cambiante y sólo algunas coinciden con la posición de la punta de compresión de deslizamiento, lo más probable es que ellas se relacionen con procesos diferentes en las vertientes, desde licuefacciones hasta deslizamientos, activando el flujo licuefacto, la corriente de turbidez y el flujo de deslizamiento, como deducen Myrow y Hiscott (1991) a partir de observaciones subaéreas.…”