Traces Remain Of Glacial Lake Agassiz

by

Marlyce Cleem

In dealing with a history of a region the common practiceis to begin as far back in the dim ages of time as possible. In drawingthe background of the history of the northwestern Minnesota and KittsonCounty we start with the early geologic areas of Archean and Paleozoic time,millions of years ago. In these two eras this area seemed to have been landarea without rock formations. Some scientists believe that it was then theinside of a large continent as now and with many changes that continentbecame North America. Through most of the Mesozoic era Minnesota was a landarea. The vegetable and animal life of the period was slowly changing fromPaleozoic, or primitive form, but had not yet changed completely to themodern form which characterizes the Cenozoic Age.

But near the end of the Cretaceus period in the late Mesozoictime western Minnesota was beneath the sea. Cretaceus shales and sandstoneswere found in the central and southern parts of the state, and at differentpoints deep wells sticking out of the thick layers of glacial drift contactCretaceus strata, sometimes being as thick as several hundred feet. Eversince the Red River basin has risen, from the Cretaceus sea, it has remainedabove sea level as the absence of marine sediments in that period. The greatglacial drifts from the north in prehistoric time affected the soil.

The Red River basin was slowly being shaped by rains andstreams through the Tertiary Era, and during part of the short Quarternaryera it was covered by snow and ice somewhat like the ice sheets that surroundthe interior of Greenland and the Antarctic Continent.

The last completed period of Geology was the Ice Age. Thenorthern half of North America and northern Europe then became surroundedwith thick sheets of snow and ice, probably caused by lifting of the landas high plateaus, getting snowfall throughout the year. Atlantic and Pacificcoasts of the north part of North America show the land to have been elevated2,000 to 3,000 feet higher than now.

Under the weight of the ice sheets, the lands sank to theirpresent level, or lower, when the temperate climates in Southern portionswas restored. The ice sheets then melted away. In certain places the driftwas left in hills and ridges during the closing stage of the Glacial period.On the greater part of Minnesota and North Dakota the only hills are formedof this morainic drift, usually 25 to 75 or 100 feet, but much higher, asin the Leaf hills of Otter Tail County, Minnesota, which are 100 to 350feet above the country on each side.

When the ice sheets, melting, returned northward dividingthe basin of the Minnesota River from the Red River, a lake, remained atthe feet of the ice along the valley of the Red River to Lake Winnipeg.The lake is called Lake Agassiz for Louis Agassiz, the Swiss scientist.It is believed that the lake formed just after the glacial period in a depressedarea now included within the Red River Valley. The lake is supposed to havebeen larger than the Laurentian (Great) Lakes or more than 110,000 squaremiles in width.

At the time of its largest length it stretched from thesouthern shore of what now is Lake Traverse on the Minnesota - Dakota boundarynorth to the 55th parallel. At its southern end it was narrow, at firstmeasuring from one to three miles in width with a length of 30 miles. Withthe retreat of the ice sheet, the lake increased in size, becoming muchwider at the north where it included all the land between the Pembina mountainsin North Dakota and the eastern end of Rainy Lake in Minnesota. The areaof the lake was always changing, but it was highest at 700 miles long and250 miles (at the international boundary) and it had a depth in Manitobaof six or seven hundred feet above the present level of Lake Winnipeg.

Agassiz was in what now is the United States. Governmentgeologists have explored its area in the United States, particularly onthe prairies. They have found existence of this old lake in certain thingswhich prove that at one time streams flowed over water sheds. In other placescliffs have been found which show erosion by water as on a shore, whilein the area of the valley are found delta deposits, beaches and sedimentswhich record the history of this vast body of water.

The level of the water in Lake Agassiz stayed the sameduring the period of its expansion, but the depth changed due to the gradualslope of the lake bottom, the greatest depth being at the north end of thelake.

Leveling along the upper beaches shows that Lake Agassizin its earliest and highest stage was nearly 200 feet deep above Moorheadand Fargo, a little more than 300 feet deep above Grand Forks and Crookston,about 450 feet above Pembina, St.Vincent and Emerson, and about 500 and600 feet above Lakes Manitoba and Winnipeg.

Some interesting geological findings due to the glacierand lake are found in Kittson County and neighboring places. Farm boys findsea shells and pebbles which were carried from different parts of the country.

Deltas were formed by the Sand Hill and Buffalo Riversin Minnesota and by the Shayenne, Pembina and Elk Rivers in North Dakota.

Another interesting feature of the lake is Beltrami Islandin Minnesota. This is an island north of Red Lake. The land has been surveyedand found to be at the highest point about 100 feet above the highest levelof Lake Agassiz. It is estimated as about 40 miles in diameter and has beennamed in honor of the man who in 1823 explored the northern source of theMississippi, Count Beltrami. Some authorities believe the lake existed between6,000 and 10,000 years ago. Many only think that the lake existed only about1,000 years.

There are many mysteries and unknowns about Lake Agassiz,but I hope that what I have shared with you can help you understand thebackground and history of our Minnesota.

 

B I B L I O G R A P H Y

Extension Division of the University of North Dakota. LakeAgassiz. Brochure information.

Kittson County Enterprise. Northwestern Minnesota Oncean Inland Sea 50th Anniversary Edition P. 2

World Book Encyclopedia. Facets of Lake Agassiz. Volume12 P. 37ition P. 2

World Book Encyclopedia. Facets of Lake Agassiz. Volume12 P. 37