Graphs

The change in the elevation of the land over time for the control and the experimentally warmed plots.

Summary Points

What is it: When ice in soil melts, the ground above it is unsupported and collapses in a process known as subsidence.
Non-Scientific name: Ground collapse from soil ice melt
Why do we measure it: When the ground collapses or sinks, many ecosystem changes can occur. First, the surface of the ground moves closer to the water table (the part of the soil that is fully saturated with water). This causes upper soil layers to become saturated and even swampy or marshy, which can water-log plants and microbes living in the soil and alter their ability to uptake or release carbon.Monitoring ground collapse over time reveals the degree of permafrost thaw - either from experimental or regional warming.
How was it measured: We use a high-accuracy GPS instrument to measure the elevation of the ground throughout the duration of the warming experiment. The instrument we use has an accuracy of 1cm (for reference, most cell phones have an accuracy of 3m!). The high accuracy of this instrument allows us to capture small changes in the ground elevation.
Long term trends:

High and low trends: Ground subsidence has increased every year since 2009 when the Warming experiment was established. Subsidence was nearly 2 times greater in plots where soil was warmed with snow fences (red and dark red lines in the figure), compared to control plots. Where snow fences were used, the ground collapsed as much as 5 ft since 2009. In some parts of the Warming experiment site, subsidence has caused ponding of water in depressions on the landscape (see photo), fully saturating these plots and causing plants to die off.
What happened in 2025: [UPDATES NEEDED] Subsidence continued in 2024, but more slowly. This leveling-off could be because there is little soil ice left to melt, or because the snow fence treatment was not applied.

Where is this science going?: These results show that permafrost thaw has already caused ground to collapse in current conditions from warmer temperatures (as shown by ~0.5 ft of subsidence in control plots). Additional warming will increase the severity of ground collapse, which may affect human infrastructure like housing, roads and pipelines, and alter ecosystem functioning.

The same plots in 2009 before the warming experiment began and in 2021, after 11 years of subsidence caused by soil ice melt.