9. Glaciers, humans, and enduring ice

A knowledge of glaciation is important because it provides us with an understanding of glaciers as Earth surface systems face climate change and of the glacial materials beneath the surface. Crucial are glacier-related hazards impacting directly on human society and glacial landforms and sediments lying at the surface of some of the most densely populated parts of our planet. ‘Glaciers, humans, and enduring ice’ considers glacial hazards, such as glacial lake outburst floods, and important engineering considerations, including sediment failure and seepage. It discusses the valuable legacy of past glaciations and asks if Earth is entering a new phase of ice-free conditions, the like of which it has not endured for more than 35 million years.

Surficial sediment failures due to the 1929 Grand Banks Earthquake, St Pierre Slope

A Mw 7.2 earthquake centred beneath the upper Laurentian Fan of the SW Newfoundland continental slope triggered a damaging turbidity current and tsunami on 18 November 1929. The turbidity current broke telecommunication cables, and the tsunami killed 28 people and caused major infrastructure damage along the south coast of Newfoundland. Both events are believed to have been derived from sediment mass failure as a result of the earthquake. This study aims to identify the volume and kinematics of the 1929 slope failure in order to understand the geohazard potential of this style of sediment failure. Ultra-high-resolution seismic reflection and multibeam swath bathymetry data are used to determine: (1) the dimension of the failure area; (2) the thickness and volume of failed sediment; (3) fault patterns and displacements; and (4) styles of sediment failure. The total failure area at St Pierre Slope is estimated to be 5200 km2, recognized by escarpments, debris fields and eroded zones on the seafloor. Escarpments are typically 20–100 m high, suggesting failed sediment consisted of this uppermost portion of the sediment column. Landslide deposits consist mostly of debris flows with evidence of translational, retrogressive sliding in deeper water (>1700 m) and evidence of instantaneous sediment failure along fault scarps in shallower water (730–1300 m). Two failure mechanisms therefore seem to be involved in the 1929 submarine landslide: faulting and translation. The main surficial sediment failure concentrated along the deep-water escarpments consisted of widely distributed, translational, retrogressive failure that liquefied to become a debris flow and rapidly evolved into a massive channelized turbidity current. Although most of the surficial failures occurred at these deeper head scarps, their deep-water location and retrogressive nature make them an unlikely main contributor to the tsunami generation. The localized fault scarps in shallower water are a more likely candidate for the generation of the tsunami, but further research is needed in order to address the characteristics of these fault scarps.

Owen Ridge deep-water submarine landslides: implications for tsunami hazard along the Oman coast

The recent discovery of voluminous submarine landslides along the Owen Ridge may represent a source of tsunami hazard for the nearby Oman coast. We assess the severity of this potential hazard by performing numerical simulations of tsunami generation and propagation from the biggest landslide (40 km3 in volume) observed along the Owen Ridge. A finite-difference model, assimilating the landslide to a visco-plastic flow, simulates tsunami generation. Computation results show that Salalah city (190 000 inhabitants) is impacted by 2.5 m-high tsunami waves one hour after sediment failure. Higher wave elevation values (4 m) are reached in the low populated Sawqara Bay over 80 min after slide initiation. Although large submarine failures along remote oceanic ridges are infrequent, this study reveals an underestimated source of tsunami hazard in the Arabian Sea.