What have those geologists been drinking? First of all, the word "moraine" is an 18th century French word that simply means a heap of earth or stony debris. I don't know when the term was first used to refer
to glacial deposits. I'll explain the "dead" part later.
Fig. 1. Areas where dead-ice moraine is found in North Dakota. The brown areas area the Missouri Coteau, the Turtle Mountains, and the Prairie Coteau.
North Dakota's vast tracts of dead-ice moraine generally make for poor farmland as they are rough, bouldery, and undrained. They do, however, include a lot of excellent rangeland and thousands of undrained depressions - lakes, ponds, and sloughs known collectively as prairie potholes - that serve as important nesting and feeding areas for waterfowl (the so-called North Dakota "duck factory"). The dead-ice moraine of the Missouri Coteau is essentially undrained, except very locally. No rivers run through it. No streams flow all the way through the Turtle Mountains or for any distance through or across the Missouri or Prairie Coteau either.
Dead-ice moraine formed when the glaciers advanced against and over steep escarpments as they flowed onto the uplands. The land rises as much as 650 feet in little more than a mile along parts of the Missouri Escarpment, which marks the eastern and northeastern edge of the Missouri Coteau. Similar prominent escarpments border the Prairie Coteau and the Turtle Mountains, especially the west side of the Turtle Mountains near Carbury. When the glaciers advanced over these escarpments, the internal stress that resulted in the ice caused shearing. The shearing brought large amounts of rock and sediment from beneath the glacier into the ice and to its surface.
Eventually, as the Ice Age climate moderated, the glaciers stopped advancing and stagnated over the uplands (they "died"). As the stagnant glaciers melted, large amounts of sediment that had been dispersed through the glacier tended to accumulate on top of the ice, which was several hundred feet thick. This thick cover of sediment helped to insulate the underlying ice so that it took several thousand years for it to melt. Our geologists have determined that stagnant glacial ice continued to exist in the Turtle Mountains and on the Missouri Coteau until about 9,000 years ago, nearly 3,000 years after the actively moving glaciers had disappeared from North Dakota.
In places where the debris on top of the ice was thickest, the glacier melted most slowly. Over nearby areas, where little or no insulating debris covered on the glaciers, melting was rapid and the land was entirely free of ice 12,000 years ago. As the stagnant ice on the uplands slowly melted, and the glacier surface became more and more irregular, the soupy debris on top of the ice continually slumped and slid, flowing into lower areas, forming the hummocky, collapsed glacial topography - dead-ice moraine - found today over the Turtle Mountains, Missouri Coteau, and Prairie Coteau.
As the stagnant glacial ice melted, and debris slid from high areas to lower ones, a variety of unusual features resulted. Long ridges formed when sediment slid into cracks in the ice. Such ridges may be straight or irregular, depending on the shape of the cracks. In some places, streams followed the cracks, resulting in eskers. In other places, mounds of material collected in holes and depressions in the ice and ring-shaped hummocks ("doughnuts") formed if the mounds were cored by ice. When the ice cores melted, the centers of the mounds collapsed, forming circular doughnut-shaped ridges.
Fig. 2. Diagram showing how a "doughnut" forms.
Fig. 3 Diagram showing how various kinds of disintegration trenches form.
In places, the insulating blanket of debris on top of the stagnant glacial ice was so thick that the cold temperatures of the ice had little or no effect on the surface of the ground. Trees, grasses, and animals established themselves on the debris on top of the stagnant ice.
Fig. 4. Diagram showing how other kinds of disintegration trenches form.
Fig. 5. Diagram showing how a ringed lake forms in dead-ice moraine.
Fig. 6. Photo of debris-covered and forested glacier. The Martin River glacier in Alaska.
Fig. 7. Dead-ice moraine in Stutsman County.
Fig. 8. Air view of the Turtle Mountains.
Fig. 9. Air view of dead-ice moraine in Stutsman County.
Fig. 10. Typical dead-ice moraine in Ward County.
Fig. 11. Perched lake plain near McClusky, in Sheridan County.
Fig. 12. Diagram showing how an elevated (perched) lake plain forms.