Permafrost—ground that remains frozen for at least two years—allows soil substrate to act like bedrock. So when permafrost thaws there can be major problems for structures built atop of it. Imagine if the granite of Mount Rushmore turned to sand… goodbye George, Tom, Teddy, and Abe. Thawing permafrost can pose a severe threat to roads, bridges, and pipelines that unite people and resources and such infrastructure destruction can cause both safety and environmental hazards. So, it is important to have the ability to pinpoint where permafrost is likely to thaw.
Today, during this year’s AGU meeting in San Francisco, Dr. Stuart Stothoff and colleagues share their approach for assessing at-risk infrastructure in regions that have seasonally frozen soils atop permafrost. Their risk assessment gauges the potential risk of landslides, land subsidence, slumps, and erosion—all of which can damage infrastructure.
Permafrost is controlled largely by the average annual air temperature, but microclimatic influences of hillside sun exposure, snow cover, vegetation cover, soil texture and content all influence the amount of energy transferred between atmosphere and ground. This makes risk calculation an interplay of vegetation parameters (such as root cohesion and vegetation weight), soil parameters (cohesion, thickness, weight, moisture), and slope (sun exposure, friction angle). The authors used Digital Elevation Models to derive slope, while vegetation and soil parameters came from a Landsat-derived classification map originally produced for the National Park Service by Torre Jorgenson et al.
Given present-day climatic conditions, upland areas—which typically have steeper slopes and shallow soil—are at greatest risk for slope failures (and therefore potential infrastructure collapse). In the study area, this is especially so for the south-facing slopes that get more direct sun exposure. Other at-risk locations include steep riverbanks and lowlands that have low-cohesion soils (cohesion refers to how soils particles hold together; sand has a low-cohesion and clay has high-cohesion). In all areas, as the moisture in the soil increases so do the chances for slope failure.
Stothoff and his team have produced slope failure risk maps based on their findings. They have also modeled risk scenarios for a warming climate predicting where permafrost is likely to thaw under future climate scenarios. The authors used the Alaskan Kobuk Valley National Park as their study area for this research; their methods can be extended to other regions where permafrost thawing could have negative repercussions for infrastructure.
References:
Stothoff, S., C.L. Dinwiddie, G.R. Walter, M. Necsoiu 2011. Ranking Slope Stability.AGU Fall Meeting 5–9 December 2011, C51B-07.