When permafrost thaw reaches concentrations of ice underneath the surface, it may trigger local soil instability.
Climate change is driving periods of unusually high temperature across large swaths of the planet. These heat waves are especially detrimental in the Arctic, where they can push surface temperatures in regions of significant permafrost past the melting point of ice lenses. Melting ice injects liquid water into the soil, reducing its strength and increasing the likelihood of landslides. In populated areas, these events can cause economic damage and loss of life.
Mithan et al. investigate a shallow-landslide formation mechanism called active layer detachment (ALD), in which the upper, unfrozen—or active—layer of soil separates from the underlying solid permafrost base. They analyze the topography in the vicinity of ALD landslides spread over a 100-square-kilometer region of Alaska to characterize the factors that govern such events. This region experienced many ALD landsides after a period of unusually high temperature in 2004.
The authors identified 188 events in the study area using satellite imagery and established the local topography using a U.S. Geological Survey digital elevation model. To analyze the relationship between ALD landslides and topography, they simulated such events using a set of common software tools.
Because many Arctic regions have relatively shallow slopes, their modeling finds that the simple flow of water is generally unable to generate sufficient water pressure between soil grains to kick-start a landslide. Rather, a major factor in ALD events appears to be the presence of ice lenses, concentrated bodies of ice that grow underground. When a heat wave pushes the thawing point of the permafrost to the depth of these ice accumulations, their melting strongly raises the local water pressure, creating the conditions for a landslide.
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