Geology of the Devils Lake Basin

Geologic Features

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Geologic features of the Devils Lake Basin primarily are a result of the depositional and erosional effects of continental glaciation, which ended about 10,000 years ago (Aronow, 1957; Bluemle, 1981). Glacial deposits include outwash deposits, lake deposits, and glacial till; glacial landforms include ground and end moraines, eskers, and kames. Glacial sediments range in size from microscopic clay particles to large cobbles and boulders. These sediments were deposited either as stratified layers of clay, silt, sand, and gravel (outwash and lake deposits) or as poorly sorted mixtures of variously sized material (glacial till). Lake deposits and glacial till mantle the land surface over much of the area around Devils Lake as well as most of the the Devils Lake Basin. Pierre Shale underlies the glacial sediments in most of the Devils Lake area.

Glaciation and the Landscape

The landscape of the Devils Lake Basin was much different before glaciation than it is today. Black shale of the Pierre Shale constituted the land surface. Preglacial rivers, such as the ancient Cannonball River, carved deep valleys into the shale. As glaciation occurred, preglacial rivers were dammed at ice fronts to form lakes. Overflow from these lakes carved diversion channels that subsequently were filled with outwash material (typically sand and gravel). Preglacial valleys and diversion channels were formed at different times and cross one another in a complicated manner that makes the subsurface geology complex (Hobbs and Bluemle, 1987). Subsequent glacial advance and retreats across the Devils Lake Basin deposited several layers of glacial sediments that buried the preglacial valleys and diversion channels. Hobbs and Bluemle (1987) stated that "in North Dakota, more than four major glacial events occurred."

Scouring and thrusting as the glaciers advanced and retreated also helps shape the surface of the Pierre Shale. In some areas of the Devils Lake Basin, the glaciers gouged out large depression in the shale. In other areas, such as at Devils Lake, large blocks of shale were detached from their original site of deposition and redeposited in the glacial drift. As the glaciers advanced, they overrode the saturated sediments that had filled the Cannonball River Valley. The weight of the advancing glaciers increased ground-water pressure in the Cannonball River Valley sediments, the overlying material was lifted up into the advancing glacier, and an excavated depression was created. The glaciers then pushed or thrust the material a few miles to the south-southwest. The excavated depression now is occupied by Devils Lake, and the material thrust to the south-southwest is known as Sully's Hill (Bluemle, 1981; J.P. Bluemle, written commun., 1991).

Formation of Devils Lake

Steps of the Formation:

(a) and (b) As the glaciers advanced, they overrode the saturated sediments that had filled the Cannonball River Valley.

(c) The weight of the advancing glaciers increased ground-water pressure in the Cannonball River Valley sediments, and the overlying material was lifted up into the advancing glacier.

(d) An excavated depression was created. The glaciers then pushed or thrust the material a few miles to the south-southwest. The excavated depression now is occupied by Devils Lake, and the material thrust to the south-southwest is known as Sully's Hill.

Aquifers

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Although the earth beneath the Devils Lake area is saturated with water below certain depths, some sediments, such as sand and gravel deposited in the preglacial valleys and diversion channels, yield larger quantities of water than other sediments, such as clay or silt. The sediments that yield sufficient quantities of water to wells or springs to be useful are termed aquifers (Paulson, 1983). Sand and gravel deposits in preglacial valleys and diversion channels constituted the major buried-valley aquifers in the area. Outwash materials deposited during the last glacial advance and retreat comprise the major near-surface aquifers in the area.

Aquifers generally are described as confined or unconfined. A confined aquifer is overlain and underlain by beds of less permeable material. The water within a confined aquifer is under pressure. If a well is drilled into the aquifer, water will rise in the well to some level higher than the top of the aquifer. The water levels in a number of such wells define an imaginary surface known as the potentiometric surface. An unconfined aquifer is not overlain by beds of less permeable material. The water surface in an unconfined aquifer is referred to as the water table. In wells completed in unconfined aquifers, the water will rise only to the level of the water table.

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Sand and gravel deposited in the valley of the ancient Cannonball River is termed the Spiritwood aquifer system. The Spiritwood aquifer system in North Dakota is an extensive buried-valley aquifer that trends in a southeasterly direction from the Canadian border in Towner County to the South Dakota border (North Dakota State Water Commission, 1986). In the Devils Lake area, the Spiritwood aquifer system as outlined by Hobbs and Bluemle (1987) is about 1 to 10 miles wide and 30 to 300 feet thick. About 100 to 200 feet of lake deposits and glacial till overlies and confines the Spiritwood aquifer system. The lake deposits and till have minimal permeability and, thus, do not yield water to wells rapidly enough to be of practical use for water supplies. Test drilling indicates that the Spiritwood aquifer system underlies Devils Lake and East Devils Lake. Southeast of Devils Lake, the Spiritwood aquifer system underlies the Sheyenne River Valley. Water levels in wells completed in the Spiritwood aquifer system vary from 150 feet below land surface on top of Devils Lake Mountain to several feet above land surface near Devils Lake. About 1 million acre-feet of ground water is stored in the Spiritwood aquifer system in the Devils Lake area (Trapp, 1968; Downey, 1973; Randich, 1977; Hutchinson and Klausing, 1980). By comparison, Devils Lake contains about 675,000 acre-feet of water when the lake is at an elevation of 1,425 feet above sea level.

Other aquifers in the Devils Lake area include the Starkweather aquifer, the McVille aquifer, the Warwick aquifer, the Tokio aquifer, and the Sheyenne River aquifer. A total of more than 1 million acre-feet of ground water is stored in all of these aquifers (Trapp, 1968; Downey, 1973; Randich, 1977; Hutchinson and Klausing, 1980).

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Surface Drainage

The eastern, western, and northern boundaries of the Devils Lake Basin are poorly defined low divides. The southern boundary is made up of a series of recessional moraines that lie between Devils Lake and the Sheyenne River. Edmore, Starkweather, and Calio Coulees originate in southern Cavalier County and flow in a south-southwesterly direction. Mauvais Coulee originates along the southern flanks of the Turtle Mountains 300 to 400 feet above the elevation of Devils Lake and generally flows in a southerly direction. Little Coulee originates in southern Rolette County and flows in a south-southeasterly direction.

Before 1979, streamflow from the principal streams flowed into the interconnected chain of lakes (Sweetwater Lake, Morrison Lake, Dry Lake, Mikes Lake, Chain Lake, Lake Alice, and Lake Irvine), and all streamflow from the chain of lakes flowed downstream through Big Coulee into Devils Lake. In 1979, the Ramsey County and Cavalier County Water Management Boards constructed Channel A, which connects Dry Lake to Sixmile Bay on Devils Lake. A levee also was constructed across the natural outlet of Dry Lake in 1979. The construction of Channel A and the levee on Dry Lake modified the drainage pattern in the basin. Discharge from Dry Lake to Sixmile Bay via Channel A is regulated by an adjustable head gate control at the south shore of the lake. Runoff into Sweetwater, Morrison, and Dry Lakes discharges through Channel A into Devils Lake; the remaining runoff discharges along the natural watercourse through Big Coulee into Devils Lake. A small quantity of runoff also enters Devils Lake by overland flow from drainage areas adjacent to the lake.

Edmore Coulee is the principal tributary to Sweetwater and Morrison Lakes. After Sweetwater and Morrison Lakes fill to the outlet elevation of about 1,458.5 feet above sea level, water flows into Dry Lake via Webster Coulee. Webster Coulee and Starkweather Coulee are the principal tributaries to Dry Lake.

Chain Lake receives inflow from Mikes Lake and Calio Coulee. When Chain Lake reaches an elevation of 1,440.8 feet above sea level, it spills into Lake Alice. Lake Alice also receives inflow from Mauvais Coulee. A channel connects Lake Alice to Lake Irvine, which has an outlet to Big Coulee at an elevation of about 1,436.6 feet above sea level.