Landslides in Alaska are a significant emerging hazard, for which we have neither significant monitoring capacity nor a useful model for forecasting frictional behavior, and therefore potential for catastrophic failure. Since 2012 there have been 120 documented catastrophic bedrock landslides in Alaska greater than 10⁶ m³ in volume (Figure 1; Higman et al., in prep). Of these landslides, 6 produced tsunamis, including Taan Fiord in 2015 (193 m runup) and Tracy Arm in 2025 (> 400 m runup). To underscore our lack of a clear mechanistic understanding of these landslides, Taan exhibited creep for years prior to its failure (Higman et al., 2018), whereas Tracy Arm accelerated over a much shorter period before failing (Alaska Earthquake Center, 2025) and the topography showed no signs of an imminent failure.  Indeed, of the 120 documented catastrophic landslides in Alaska since 2012, only 27% were associated with active precursory slow landslide deformation that was visually evident in remote sensing data (Higman et al., in prep).  This implies that while many landslides exist in a state of stable creep for years there is also a process or set of processes through which creep can evolve to catastrophic failure (Lacroix et al., 2020).  

One clue that might aid in better forecasting where and when catastrophic landslides will actually occur, given that creep in landslides may not be a strong predictor of catastrophic failure potential, comes from considering the history of recent glacial retreat.  The coincidence between glacial retreat and landslide acceleration is strong (e.g., Kos et al. 2016; Fey et al. 2017; Cody et al. 2020; Lacroix et al. 2022; Dai et al. 2020; Walden et al. 2025), providing empirical evidence for the intuitive idea that at some level glacier debuttressing is a factor in loss of slope stability.  

That said, rapid glacier retreat, alone, is unlikely to be an important trigger of landslide failure unless the glaciated valley has been significantly eroded since the last time it was ice free.  Thus, it’s likely that slope failure related to debuttressing should concentrate in areas where buttressing has persisted long enough for erosion to progress more. Hence, glacial retreat that proceeds beyond recent ice-minima (e.g., Holocene minimum) will expose slopes that are more likely to have experienced erosion, pushing them into a slope geometry window that is unstable without ice being present. This could create hidden thresholds in retreat that correspond to dramatic increases in failure probability that aren’t well-correlated with changes in retreat rate.

As a preliminary test of this idea, we compiled a small subset of landslide-generated tsunamis since 1825 occurring within Alaska, USA, and British Columbia, Canada, where we have relatively more events and focused scientific attention to document them. Tsunamis that denude forested slopes leave evidence that can persist for many decades, and thus are more likely to be documented even if they were initially missed. For example, a tsunami trim line in Lituya Bay from a mid-1800s tsunami was documented by geologists about a century later.

This exercise identified 14 events, most of which occurred on slopes in contact with retreating glaciers (Fig. 2). Through most of the period we examined, these events occurred once every couple of decades, however during the final decade since 2015 there were 6 events. 

Taken at face-value, this increase in the incidence of these events is far more rapid than the change in temperature, the increase in water exposed to landslides, or the rate of glacial thinning - consistent with threshold increases in landslide probability as glaciers retreat. For example, rates of ice retreat and thinning for tidewater glaciers have been relatively steady since the 1950’s in at least one of the major regions we study here, Prince William Sound (Maraldo 2020). This increase suggests greatly elevated risk of these events in coming decades, particularly on slopes that are newly exposed by glacial retreat.  

Together these results suggest that targeted research in a few areas could aid Alaskan landslide hazard mitigation. Specifically, detailed observations of landslide deformation and hydrology are needed to inform frictional rheology and hence elucidate fundamental controls on landslide failure style. At the same time, a clearer understanding of the pre-LIA history of glaciation in coastal Alaska, while not trivial to determine, would greatly aid in understanding where ice is currently retreating into steep landslides that may not have been ice free for millenia and where landslide probabilities are thus much higher.

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References

Alaska Earthquake Center, 2025, Major landslide in Southeast Alaska fjord: Alaska Earthquake Center, posted August 12, 2025, accessed March 9, 2025, at  https://earthquake.alaska.edu/major-landslide-southeast-alaska-fjord  

Dai, C., Higman, B., Lynett, P. J., Jacquemart, M., Howat, I. M., Liljedahl, A. K., ... & Haeussler, P. J. (2020). Detection and assessment of a large and potentially tsunamigenic periglacial landslide in Barry Arm, Alaska. Geophysical Research Letters, 47(22), e2020GL089800.

Cody, E., Anderson, B. M., McColl, S. T., Fuller, I. C., & Purdie, H. L. (2020). Paraglacial adjustment  of sediment slopes during and immediately after glacial debuttressing. Geomorphology, 371, 107411.

Fey, C., Wichmann, V., & Zangerl, C. (2017). Reconstructing the evolution of a deep seated rockslide (Marzell) and its response to glacial retreat based on historic and remote sensing data. Geomorphology, 298, 72-85.

Higman, B., Shugar, D. H., Stark, C. P., Ekström, G., Koppes, M. N., Lynett, P., ... & Loso, M. (2018). The 2015 landslide and tsunami in Taan Fiord, Alaska. Scientific reports, 8(1), 12993.

Higman et al., in preparation, What is the Landslide Life Cycle?

Kos, A., Amann, F., Strozzi, T., Delaloye, R., von Ruette, J., & Springman, S. (2016). Contemporary glacier retreat triggers a rapid landslide response, Great Aletsch Glacier, Switzerland. Geophysical Research Letters, 43(24), 12-466.

Lacroix, P., Handwerger, A. L., & Bièvre, G. (2020). Life and death of slow-moving landslides. Nature Reviews Earth & Environment, 1(8), 404-419.

Lacroix, P., Belart, J. M., Berthier, E., Sæmundsson, Þ., & Jónsdóttir, K. (2022). Mechanisms of landslide destabilization induced by glacier‐retreat on Tungnakvíslarjökull area, Iceland. Geophysical Research Letters, 49(14), e2022GL098302.

Maraldo, D. R. (2020). Accelerated retreat of coastal glaciers in the Western Prince William Sound, Alaska. Arctic, Antarctic, and Alpine Research, 52(1), 617-634.

Walden, J., Jacquemart, M., Higman, B., Hugonnet, R., Manconi, A., & Farinotti, D. (2025). Landslide activation during deglaciation in a fjord-dominated landscape: observations from southern Alaska (1984–2022). Natural Hazards and Earth System Sciences, 25(6), 2045-2073.

Ballantyne, C. K., Sandeman, G. F., Stone, J. O., & Wilson, P. (2014). Rock-slope failure following Late Pleistocene deglaciation on tectonically stable mountainous terrain. Quaternary Science Reviews, 86, 144-157.

Barclay, D. J., Barclay, J. L., Calkin, P. E., & Wiles, G. C. (2006). A revised and extended Holocene glacial history of Icy Bay, southern Alaska, USA. Arctic, Antarctic, and Alpine Research, 38(2), 153-162.

Brinkerhoff, D., Truffer, M., & Aschwanden, A. (2017). Sediment transport drives tidewater glacier periodicity. Nature communications, 8(1), 90.

Carlson, A. E., Kilmer, Z., Ziegler, L. B., Stoner, J. S., Wiles, G. C., Starr, K., ... & Hatfield, R. G. (2017). Recent retreat of Columbia Glacier, Alaska: millennial context. Geology, 45(6), 547-550.

Geertsema, M., Menounos, B., Bullard, G., Carrivick, J. L., Clague, J. J., Dai, C., ... & Sharp, M. A. (2022). The 28 November 2020 landslide, tsunami, and outburst flood–A hazard cascade associated with rapid deglaciation at Elliot Creek, British Columbia, Canada. Geophysical research letters, 49(6), e2021GL096716.

Lemaire, E., Dufresne, A., Hamdi, P., Higman, B., Wolken, G. J., & Amann, F. (2024). Back-analysis of the paraglacial slope failure at Grewingk Glacier and Lake, Alaska. Landslides, 21(4), 775-789.

McColl, S. T., Davies, T. R. H., & McSaveney, M. J. (2010, September). Glacier retreat and rock-slope stability: debunking debuttressing. In 11th Congress of the International Association for Engineering Geology and the Environment (pp. 467-474). Auckland, New Zealand: CRC Press.

McColl, S. T., & Davies, T. R. (2013). Large ice‐contact slope movements: Glacial buttressing, deformation and erosion. Earth Surface Processes and Landforms, 38(10), 1102-1115.

Miller, D. J. (1960). The Alaska earthquake of July 10, 1958: giant wave in Lituya Bay. Bulletin of the Seismological Society of America, 50(2), 253-266.

Pánek, T., Břežný, M., Smedley, R., Winocur, D., Schoenfeldt, E., Agliardi, F., & Fenn, K. (2023). The largest rock avalanches in Patagonia: timing and relation to Patagonian Ice Sheet retreat. Quaternary Science Reviews, 302, 107962.

Roberts, N. J., McKillop, R. J., Lawrence, M. S., Psutka, J. F., Clague, J. J., Brideau, M. A., & Ward, B. C. (2013). Impacts of the 2007 landslide-generated tsunami in Chehalis Lake, Canada. In Landslide Science and Practice: Volume 6: Risk Assessment, Management and Mitigation (pp. 133-140). Berlin, Heidelberg: Springer Berlin Heidelberg.

Schaefer, L. N., Kim, J., Staley, D. M., Lu, Z., & Barnhart, K. R. (2024). Satellite interferometry landslide detection and preliminary tsunamigenic plausibility assessment in Prince William Sound, Southcentral Alaska (No. 2023-1099). US Geological Survey.

Tarr, R. S., & Martin, L. (1914). Alaskan Glacier Studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and Lower Copper River Regions. National geographic society.

Wikstrom Jones, K.M., and Larsen, M.C. (2025). Susceptibility to deep-seated landslides in Alaska: Alaska Division of Geological & Geophysical Surveys Preliminary Interpretive Report 2025-3, 5 p., 1 sheet. https://doi.org/10.14509/31691

Wiles, G. C., & Calkin, P. E. (1992). Reconstruction of a debris-slide-initiated flood in the southern Kenai Mountains, Alaska. Geomorphology, 5(6), 535-546.