Why can relict patterned ground remain after permafrost has thawed?

Relict patterned ground can persist after permafrost has thawed primarily due to the physical deformation and soil disturbance caused by the original formation process.

When ice wedges form in permafrost, they create vertical or subvertical cracks in the soil that are filled with ice. As these wedges grow, they compress and deform the surrounding sediment. Even after the ice within these wedges melts during a period of warmer climate, the structural disturbance to the soil remains. Furthermore, as the ice melts, sediment may be washed into the resulting voids, helping to preserve the original geometric patterns in the landscape long after the permafrost itself has disappeared.1

These features, often referred to as ice-wedge casts, serve as important geological evidence of the former extent of permafrost and colder conditions during past glacial periods.2