Sunday, February 04, 2007

North Dakota Geology

Since I have been spending quite a bit of time in North Dakota, I figured it was about time I wrote something about North Dakota's Geology. Most people would consider the North Dakota Landscape to be pretty boring. Certainly, they do have the most boring Continental Divide I have ever seen. However, the terrain in North Dakota is some what varied. The Missouri River winds through there and cuts a very impressive swath, especially where the Garrison Dam was built that created Lake Sakakawea, which is the third largest man-made lake in the United States. North Dakota also boasts the Natural Devil's Lake or Spirit Lake as it is called by the Native Sioux. Devil's Lake has no outlet and the water level has fallen and risen drastically in recorded history, After dropping to Historic lows in 1941 the lake has gradually risen to where it reached it's maximum height after a wet cycle that began in 1993, when it rose 26.5 ft and flooded 140 square miles of primarily Agricultural land. In April of 2000, the surface elevation of Devil's Lake was 1446.3 feet. If the elevation had raised to 1447 feet it would have begun to overflow into the Stump Lakes, which empty into the Sheyenne River. Another 12 feet, and it would have overflowed directly into Sheyenne. It has already reached this point at least twice in 4000 years.

North Dakota's landscape North and East of the Missouri River is heavily marked by glaciation. It is my opinion that the latest Wisconsin Glacier got hung up on the Turtle Mountain area which straddles the border of Canada and North Central North Dakota. This LandSat Image shows the Turtle Mountain area in the upper right. The International Boundary is visible in the slight coloration difference across the center on the Reddish Oval Mass that is the Turtle Mountains. The faint straight line further South is a glitch of a dropped Scan Line in the Photo.

The result of this Stagnation of the Glacier caused the Central Plains of North Dakota to be Primarily of Till: (Compact glacial sediments that are non-layered.) This also results in the creation of many Pothole Lakes and Ponds. As the ice melts, it leaves large chunks sitting all over the place, gradually melting, as the weather goes through warming and cooling cycles. The weight of the ice depresses the land, so they end up dead lakes with no actual outlets. Nearer the edges of the glaciation, the deposits are of the OutWash Variety. This picture was taken near Valley City.

Another Geological Feature that you see in North Dakota is when the Glacier is still moving and had pushed up huge piles of the local terrain and gouging out valleys behind these piles. These are called Ice Thrust Masses and can be quite spectacular. There is a substantial Ice Thrust Mass to the South West of Devil's Lake, as well.

To the South and West of the Missouri River, the Terrain in North Dakota is considerably different, not being scoured by the glaciers, which seemed to stall at that point. Much of the Badlands area demonstrate's the Geological feature known as the Slump. A Slump is a sort of landslide where the mass slides down the slope, doing a sort of slow tumble, so you can see the same features down slope and slightly tilted from what is at the top still sitting level. These canyons were carved by the huge amounts of water running off the glaciers, especially during the time that the North Flowing Red River was blocked by the ice mass. The Little Missouri also flowed Northward into Canada, and the combined water that collected probably cut the channel in a very short period of time, eventually carving the two channels, the present day Missouri, flowing South and East into the Mississippi and the Little Missouri from Wyoming into the Missouri at Afore-mentioned Lake Sakakawea. Even the Yellowstone flowed into Canada before the Glaciers blocked the Northern flow. The Red, in the meantime, reverted to flowing Northerly after the glaciers, but it has flooded practically every spring since. The characteristic of this majr river to flow North has the natural consequence of blocking itself every Spring with melt ice. As the warmer temperatures in the South hits earlier, this ice break-up moves Northerly Down River and can form considerable blockage in that area still not open. It can only be imagined what would have happened in years that the Hudson's Bay end never completely thawed at the tail end of the glaciation period. The result was a huge Inland Sea, known as Lake Agassiz that stretched from the Southern border of North Dakota to beyond Lake Winnepeg in Canada and from Red Lake in Minnesota, to the East and to the West to Larimore in North Dakota, which is nearly to the Devil's Lake Basin. The difference in elevation from Larimore to Devil's Lake never gets higher than 1535 feet and nowhere falling below 1425, so it nearly included that huge basin as well. This huge lake brewed incredible storms that churned the Glacial Till on that landscape to a nearly level condition and later, as the Lake opened and closed each year, the ice break-up pushed up huge piles of Sand and Gravel around the Lake's perimeter in ever decreasing concentric rings, as the water level went down, especially on the South and East Sides. This is clearly evident in the area around Trail, Minnesota in the area known as the Sand Hills. The various "Beaches" surrounding the Ancient Lake Agassiz have been clearly defined and named. The listed number is fourteen.

There is a natural tendency of Flood Rivers to dike themselves. As the water overflows the normal banks, the sediment it carries, deposits most heavily close to the river, and as a result, all major flooding rivers have high banks as you approach the river. You might climb several hundred feet before going over the top and plunging down into the valley on either side of the river. This River Characteristic is especiaaly noticeable along the Missouri in Western and Southern North Dakota. The Red River Valley also has these characteristic shoreline natural dikes, but they are far from the present water level.