INVESTIGATION OF SUBMARINE LANDSLIDES AND ASSOCIATED HAZARDS OF PANGNIRTUNG FJORD, EASTERN BAFFIN ISLAND, NUNAVUT

Fiords are susceptible to both subaerial and submarine slope failures. Recent investigations have shown that past landslides in fiords of Greenland and Alaska have generated devastating tsunamis. Since coastal communities inhabit these high-latitude fiords, it is critical to understand the slope failure recurrence time, their potential triggers, and their ability to generate tsunamis. In this study we identified submarine landslides in Pangnirtung Fiord, eastern Baffin Island, Nunavut using multibeam bathymetric data, sub-bottom profiler data, and sediment gravity-cores collected in 2019. Morphometric and morphological analyses were carried out on > 50 submarine landslide deposits to quantify their spatial and temporal distribution throughout the fiord and to evaluate the factors that may have triggered the slope failures.

Combining bathymetric with topographic data from unmanned aerial vehicle imagery, we found that most slope failures are associated with river runoff, outwash fans, or steep fiord sidewalls. The largest landslide deposit (~ 2 km²) is located directly downslope from the Kulik River, located in front of the Hamlet of Pangnirtung, indicating that it is likely related to high rates of sediment supply and flooding events. Smaller landslide deposits (~ 150 m²) are associated with outwash fans and steep fiord sidewalls. Slope failure initiation depths vary spatially, although the majority lie between the intertidal zone and ~20 m water depth, an area shallower than what can be examined on the bathymetric data. The apparent relationship between subaerial features and submarine landslide distribution suggests a subaerial influence on the triggering of most submarine slope failures in Pangnirtung Fiord. However, because of the location of the head scarps in the unmapped shallow-water zone, determining the trigger of the submarine slope failure is challenging. Potential triggers include rapid floodwater input, subaerial debris flows, and sea-ice loading during low tide. This research shows that slope failures in an Arctic fiord are affected by the interaction of numerous subaerial and submarine processes, leading us to speculate that a potential increase in the frequency of subaerial debris flows and river floods due to climate change may increase the recurrence of submarine landslides.