From documentation to prediction: raising the bar for thermokarst research

Excerpt

Rapid warming in the Arctic and the resulting loss of permafrost have caused dramatic changes in Arctic landscapes through thermokarst activity. Thermokarst refers to subsidence of the land surface driven not by chemical dissolution of material but instead by the phase change of ice to water in the subsurface (French 2007). Subsidence arising from this phase change may result from several related processes: (1) the loss of volume due to the phase change of ice to water; (2) the compaction and settling of soil grains no longer supported by ice; (3) compaction of soil matrix due to the loss of pore pressures and water volume resulting from drainage of fluid from the unfrozen soil matrix; and (4) to a much smaller and slower extent, the loss of organic material due to increased microbial degradation under unfrozen conditions. Understanding of the first three of these processes requires quantification of coupled thermal, hydrological, and mechanical processes in the thawing soils and bulk ice. Freeze-thaw processes during annual cycles in the active layer may result in recoverable subsidence as pore water refreezes, resulting in cryosuction and frost heave. Non-recoverable subsidence is typically of greater interest and importance to infrastructure, local hydrology, and biogeochemical feedbacks (Kokelj and Jorgenson 2013). This land surface deformation occurs due to melting of bulk ice, either in ice wedges (large vertically oriented ice inclusions) or ice lenses (thin, horizontally oriented ice layers), or as previously unfrozen ice-rich soil loses the structural support of ice. …