The timely topic of tsunami geology was addressed during a recent international workshop sponsored by the U.S. National Science Foundation (NSF). Participants from 15 nations compared criteria for identifying tsunamis by their geologic signatures; explored applications to plate tectonics, hazard assessment, and public education; and discussed recommendations for research priorities. A post‐workshop trip occasioned heartfelt exchanges with Washington state coastal residents two days after a local tsunami scare.
Glacier mass loss due to anthropogenic climate change has far-reaching implications, one of which is the destabilization of paraglacial slopes. The buttressing force, or the support provided by the glacier to adjacent valley walls, changes and eventually decreases to zero as glaciers dwindle. However, the processes governing this (de-)buttressing, the amount of support glaciers can provide, and to what extent glacier retreat is responsible for landslide (re-)mobilization are still poorly understood. Paraglacial landslides can be hazardous, especially in the proximity of deep water, where a catastrophic failure has the potential to produce a tsunami. We investigated eight large (roughly 20 to 500 million m3) paraglacial landslides in southern Alaska, a region which is experiencing some of the fastest glacier retreat worldwide. The selected landslides have varying degrees of ice contact: some are still experiencing active glacier retreat and thinning, others have already lost contact with the glacier. One of the selected landslides has undergone catastrophic failure, the others have not. We reconstructed the deformation history of the eight sites using Landsat images from the 1980s to present and automated and manual feature tracking. The slope evolution was then compared to ice thinning rates, ice velocity changes, the proximity of the landslide to the glacier terminus, environmental conditions, and seismic energy.  We found that both thinning and retreat are sufficient conditions for landslide (re-)activation. In two cases we documented periods of acceleration for slopes where ice is still present at the landslide toe but thinning rapidly. In two further cases, substantial thinning did not correspond to any detectable motion. In four cases we observed a rapid retreat of the glacier terminus as the glacier retreated progressively up-fjord which led to the sudden onset of slope motion. This acceleration suggests decreased stability, which may be important in close proximity to water-filled basins, where rapid retreat due to calving is common and catastrophic landslides can cause tsunamis if they impact the water. The association of reduced glacier-slope contact, especially at rapidly retreating termini, with accelerated slope deformation suggests that buttressing is indeed an important stabilizer for paraglacial slopes. Furthermore, the off-and-on nature of deformation suggests there are critical thresholds for buttressing that, when crossed, leave slopes prone to rapid change.
There is widespread recognition that Arctic conditions can challenge marine oil spill response by limiting countermeasure effectiveness and, in extreme cases, even preventing their use. The Arctic Council's Emergency Prevention, Preparedness, and Response (EPPR) Workgroup implemented a response viability analysis to estimate how often different types of response systems could be deployed in different areas of the Arctic based on historical met ocean conditions. This approach, implemented previously in several circumpolar sub-regions, quantifies the effects of met ocean conditions on response techniques by comparing the operating limits for different response systems to a hind cast of met ocean data. Response systems include options for mechanical recovery, chemical dispersants, and in-situ burning. Met ocean conditions in the dataset used include wind, sea state, temperature, sea ice coverage, horizontal visibility, and daylight/darkness. Additional conditions are discussed qualitatively. For each response system studied, the results indicate how often use of that system may be favorable, marginal, or not recommended. Seasonal and geographic variations in the results can inform response contingency planning. Examining the met ocean condition that most frequently impacts a system can also inform needed technological improvements or modifications. EPPR convened experts to provide input to the analysis, including the initial project scoping and development of baseline systems and limits. This paper discusses the project process as well as the analytical methodology, key inputs, assumptions, and results.
Abstract We describe and model the evolution of a recent landslide, tsunami, outburst flood, and sediment plume in the southern Coast Mountains, British Columbia, Canada. On November 28, 2020, about 18 million m 3 of rock descended 1,000 m from a steep valley wall and traveled across the toe of a glacier before entering a 0.6 km 2 glacier lake and producing >100‐m high run‐up. Water overtopped the lake outlet and scoured a 10‐km long channel before depositing debris on a 2‐km 2 fan below the lake outlet. Floodwater, organic debris, and fine sediment entered a fjord where it produced a 60+km long sediment plume and altered turbidity, water temperature, and water chemistry for weeks. The outburst flood destroyed forest and salmon spawning habitat. Physically based models of the landslide, tsunami, and flood provide real‐time simulations of the event and can improve understanding of similar hazard cascades and the risk they pose.
