Why can roads and airfields sink when the permafrost beneath them thaws?

Roads and airfields sink when the permafrost beneath them thaws primarily due to the melting of ground ice, which leads to the subsidence of the surface.12

When permafrost contains significant amounts of ice, the structural integrity of the ground relies on that ice remaining frozen. As the permafrost thaws—often triggered by the disturbance of vegetation or the construction of engineering works—the ice melts and the ground settles unevenly. This process creates thermokarst topography, characterized by features such as pits, sinkholes, and hummocks.324

Furthermore, the thawing process increases the thickness of the active layer, which becomes water-saturated and loses its bearing strength during the summer. Because permafrost is impermeable to water, this excess moisture cannot drain effectively, further destabilizing the foundation for structures like roads and airfields. Consequently, constant maintenance and resurfacing are often required to level tracks and roadways that have been displaced by these shifts.356