dead ice

The advance of even a continent-sized ice sheet eventually grinds to a stop. This stalled, slowly melting ice (think of a landlocked iceberg) is said to be dead. Dead ice has a potent afterlife, however, despite its name. Large tracts of remnant blocks of ice created the wet, jumbled, pothole-and-hummock landscape of the coteau uplands of North and South Dakota. Debris in the ice and soil deposited on its surface was shed from the melting ice as a semifrozen gumbo of gravel and earth to form dead-ice moraines. Where the surface of the dead ice was insulated by a thicker crust of sediment, variations in the melt of the underlying ice allowed the soil to collapse into landscape features as round as a doughnut (a ring of glacial debris) and boggy as a kettle (a sink formed when a core of dead ice surrounded by earth eventually melts). These features collect rain and snowmelt and are favored by migrating waterfowl.

D. J. Waldie