| Summary: | about 16,000 years ago, it was nearly 4,000 years before the ice melted from most of eastern North Dakota; the ice on the Missouri Coteau and Turtle Mountains took another 3,000 years to melt away completely. The weight of the glacier ice caused the earth's crust to sag. Slow rebound of the crust followed the retreat of the glaciers; since the ice was thicker and heavier in the north than in the south, the amount of crustal depression (and subsequent rebound) was more in the north. It is theorized that the earth's crust was depressed about one foot for every three feet of ice and the ice was several thousand feet thick in northeastern North Dakota. Crustal rebound is still taking place to the north of North Dakota; in the Hudson Bay area, near Churchill, where the ice was much thicker and melted more recently, the land is still rising at the rate of 4 feet per century. North Dakota's modern landscape bears the legacy of the late Pleistocene glaciations, which eroded and reshaped the land surface. Broad areas of hummocky moraine formed when thick layers of stagnant glacial ice melted over the Turtle Mountains and the Missouri Coteau. Hilly areas of intensely thrust topography such as Sully's Hill are found in parts of eastern North Dakota along with ranges of rugged hills ("end moraines"). Eskers like those at Dahlen and Benedict occur where rivers once flowed in tunnels and cracks in the glacier. The Missouri and Sheyenne valleys are just a few of the routes used by water flowing from the melting water from the melting ice. Meltwater lakes like Lake Souris and Lake Agassiz were also the result of glaciation. Broad areas of sand dunes found on old river deltas in the lake plains were shaped by the wind in the time since the end of the glacial epoch. Even in southwestern North Dakota, which was never reached by the glaciers, a tundra climate during the Pleistocene resulted in frost polygons and other frozen-ground features, many of which persist today. Climate [Most of the information in this section on climate has been taken from a book by Ray E. Jensen, climatologist for the North Dakota National Weather Service. The 48-page book, titled Climate of North Dakota was published in by the North Dakota Agricultural Experiment Station in Fargo]. North Dakota's location at the center of North America results in a typical sub- humid, continental climate. The climate of the state is characterized by large annual, and day-to-day temperature changes, light to moderate precipitation which tends to be irregular in time and coverage, low relative humidity, plentiful sunshine, and nearly continuous air movement. Annual mean precipitation in the state ranges from 13 inches in the northwest to more than 20 inches in the extreme east and southeast. 516 Chapter 12 Physical Characteristics and Resources of North Dakota
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