Geology of Lake Minnetonka

Geology of Lake Minnetonka (HM14PG)

Location: Excelsior, MN 55331 Hennepin County
Country: United States of America

N 44° 54.271', W 93° 33.916'

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Inscription
Like most lakes in Minnesota, Lake Minnetonka was formed during the Ice Age of the last two million years. During several separate glacial periods, ice advanced along different routes across the state. The glaciers, along with large volumes of sediment (clay, silt, sand, gravel, and boulders) trapped in the ice, altered the pre-existing terrain and created the landscape we see today.

Before glacial action, the surface of this region consisted of sandstones and limestones, which formed from sediments deposited in seas that covered the area 300 to 500 million years ago. After the seas retreated, rivers carved a valley system into the sedimentary bedrock. This ancient valley system had provided southward drainage through the region. The bedrock floor of a principal valley of that ancient system now lies as much as 122 meters below the surface of Lake Minnetonka.

About 25,000 years ago, at the peak of the last glacial period, or Wisconsin glaciation, an advancing glacier, which was passing over the ancient river valley that now lies beneath Lake Minnetonka, filled the valley with ice. Sediment that melted out of the overriding glacier then buried the ice trapped in the valley. The glacial ice and sediment were later covered by additional sediment from more recent glacial advances. As a result, when glaciers last receded from Minnesota 10,000 years ago, large blocks of ice were buried deep in the ancient valley under thick piles of sediment. When the ice blocks melted, the overlying sediment collapsed and created numerous depressions that filled with water, which are called kettle lakes. At Lake Minnetonka, the ice blocks were so big and close together that the depressions coalesced to form the large, composite kettle lake that we see today.

Erected by the Geological Society of Minnesota in partnership with the
Minnesota Department of Transportation and the Minnesota Geological Survey 1998
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Details
HM NumberHM14PG
Tags
Year Placed1998
Placed ByThe Geological Society of Minnesota in partnership with the Minnesota Department of Transportation and the Minnesota Geological Survey
Marker ConditionNo reports yet
Date Added Tuesday, September 2nd, 2014 at 2:31pm PDT -07:00
Locationbig map
UTM (WGS84 Datum)15T E 455374 N 4972498
Decimal Degrees44.90451667, -93.56526667
Degrees and Decimal MinutesN 44° 54.271', W 93° 33.916'
Degrees, Minutes and Seconds44° 54' 16.26" N, 93° 33' 54.96" W
Driving DirectionsGoogle Maps
Area Code(s)952, 612
Closest Postal AddressAt or near 399 Lake St, Excelsior MN 55331, US
Alternative Maps Google Maps, MapQuest, Bing Maps, Yahoo Maps, MSR Maps, OpenCycleMap, MyTopo Maps, OpenStreetMap

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