NORTH DAKOTA STATE UNIVERSITY - FARGO, N D
In regions where there were thick masses of stagnating continental ice, steep-sided holes through the dead ice occasionally held lakes. Water was retained in these lakes by the ice walls. Fine-grained sediments (muds) accumulated on the lake bottoms. Once the ice walls melted away, however, the lakes drained, leaving the lake bottoms as plateau-like features underlain by fine-grained sediments.
Ice-walled lake plains, such as this one south of Medina, N.D., are common but anomalous features on the otherwise-hummocky landscape of the Missouri Coteau of central North Dakota. Unlike those of the surrounding landscape, the soils of these plateaus are particularly suitable for cultivation. Thus, these lake plains are often best viewed from the air as patches of intensive cultivation within hummocky grasslands.
In this photograph, the students are standing on the flanks of an ice-walled lake plain (flat surface, right foreground). The valley beyond represents a meltwater channel, and the hummocky topography of the Missouri Coteau forms the horizon.