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August 2007

This article was contained in the museum’s archive. It was glued onto a page on which the museum founder, Axel Niemi, wrote that it was written in 1957 by Dr. George M Schwartz from the University of Minnesota. The source of publishing was not noted.

Origin of Lake Superior

Lake Superior

Lake Superior, is the largest body of fresh water in the world and also one of the deepest. The term, superior, referring to its position as the upper lake of the five Great Lakes of North America was first used according to Grace Lee Nute in the Jesuit Relation of 1647-1648. The lake is 300 miles long and has a maximum width of 160 miles with an area of about 32,000 square miles. Its normal surface level is 602 feet above sea level and the greatest depth 1,290 feet.

In view of its great size and depth, it is natural that there should be much interest in the origin of the lake. In addition to its size, another fact of importance in considering the origin is occurrence of the lake in the trough of a great syncline or down fold in the rocks. That this structure of rocks has had an important effect on the origin of the lake is certain, but that the down folding of the rocks is the primary cause of the present lake is doubted inn view of the great length of time since the folding. The folding can be fairly closely dated as late Keweenawan or some 600,000 years ago. This would seem to allow plenty of time for any depression formed by the folding to have been filled with sediments.

Another fundamental fact to be considered in the origin of the present lake is the great depth of the bottom of the lake below sea level. The depression could therefore not have formed by stream erosion unless this whole portion of the continent once was much higher with respect to sea level than it is at present. While there have been changes in both continental and sea levels, there is no good evidence that these were on a scale to account for the Superior depression.

There are two main possible explanations: (1) The lake was scoured out by successive ice lobes which probably occupied the rock basin culminating in the Superior lobe of Late Wisconsin time. The glacial erosion was probably guided by a deep river valley in the structural basin. (2) Depression of the basin by faulting at a sufficiently late date for it to have escaped filling with sediment.

Difficulties with the fault hypothesis are the lack of evidence of late faulting anywhere at this portion of the North American continent and the lack of good evidence of faults in the proper positions to account for the depression. Certain great faults are known to exist in the Superior region and it is reasonable to assume that erosion was modified by their existence.

The hypothesis of glacial erosion has more obvious support. The movement of the Superior ice lobe down the axis of the lobe was one of the last great geologic events in the region. The timing to account for the present depression is excellent. Furthermore it is evident form the moraines of the Superior lobe as shown by Leverett’s maps that a great deal of rock debris was picked up by the ice lobe and deposited to the southwest of the present lake. It is also shown by glacial drift to the southwest in Minnesota that earlier ice sheets passed over the superior region and gathered up enormous amounts of rock debris and carried it on to the south. It is reasonable to suppose therefore that the Superior syncline was occupied by previous lobes that moved along the length of the basin gouging it out to a greater extent each time it was occupied by a lobe of ice.

In summary it may be said that Lake Superior probably owes its origin to a combination of conditions. The first important event was the formation of the great syncline following the extensive igneous extrusions and intrusions of the Keweenawan. This syncline no doubt was expressed at a surface by a basin that was filled by later and softer rocks than the older rocks round the edges. Faulting at a still later time modified the structure of portions of the syncline. Some of the faulting has been considered of late Keweenawan age, part of the movement is Paleozoic or later. The immediate cause of the present topographic basin was erosion by successive lobes of glacial ice that occupied the bottom of the syncline and eroded out the soft sediments but modified only in a moderate degree the resistant pre-Cambrian rocks on the sides. It is generally assumed that a large river valley occupied the present site of the lake and guided the early glacial erosion.



History's Gems Archives

May 2007
(The Telescope Story)

June 2007
(The Story of the Grand Marais "Meteor")

July 2007
(Hints on Hunting Glacial Agate Article)

August 2007
(Lake Superior Origin from 1957)

Fall 2007
(Tourist Information from the 1920s)

December 2007
(Lake Superior Editorial)

January 2008
(Grand Marais Tourist Signpost)

February 2008
(Unusual Wedding Invitation)

March 2008
(1915 Rules for Teachers)

April 2008
(Cedar Stump article from 1962)

May 2008
(Old Postcards)

June 2008
(Pictured Rocks National Lakeshore Proposal Proposal Proposal-Part 1)

Summer 2008
(Pictured Rocks National Lakeshore Proposal Proposal-Part 2)

Summer 2008
(Pictured Rocks National Lakeshore Proposal Proposal-Part 3)

October 2008
(Pictured Rocks National Lakeshore Proposal Proposal-Part 4)

November 2008
(Pictured Rocks National Lakeshore Proposal-Part 5)

December 2008
(Agate Leaflet from 1927)

January 2009
(Old Postcards)

February 2009
(Snowstorm Article from 1988)

March 2009
(Lake Superior Agate Poem)

Spring 2009
(History of M77)

July 2009
(Axel Niemi Photo)

August 2009
(Ship Travel on Lake Superior)

September 2009
(Hints on Hunting and Finding Agates)

Fall 2009
(Hints on Hunting and Finding Agates Part 2)

February 2010
(The Story of Grand Marais Part 1)

February 2010
(The Story of Grand Marais Part 2)

April/May 2010
(The Story of Grand Marais Part 3)

June 2010
(Box of Rocks Gets Diploma)

July 2010
(Shipwrecks at Agate Beach)

August/September 2010
(1958 Detroit News Article about Axel Niemi)

Fall 2010
(Reprint from the Douglas Houghton Expedition)

Winter 2011
(Old Postcards and Pictures)

Spring 2011
(1905 Grand Marais Article)

September 2011
(Michigan Log Marks)

March 2012
(John Keating)

January 2012
(Axel Remembered)

March 2012
(John Keating)

June 2012
(The Shark: Post 1)

September 2012
(The Shark: Post 2)

March 2013
(The Shark: Post 3)

August 2013
(All That Glitters. . .)

November 2013
(Excerpts from The Grand Marais Herald)

April 2014
(Souvenir View Book of Sault Ste. Marie)

September 2014
(Michigan Beach Stones)

February 2015
(Michiganís Mystic Dunes)

June 2015
(Vintage Grand Marais Photos)

November 2015
(Gitchee Agomowin)

June 2016
(Grand Marais Poems)

August 2016
(1981 Article about Grand Marais)

March 2017
(Logging Era Photos)

 

 


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