Created by FIRE & ICE – The World’s Largest
Freshwater Lake
Standing before you is the confluence of
the Gooseberry River with the Great Lake Superior. A small
informative sign nearby outlines some figures that describes the
enormous size of the lake. Geologically, Lake Superior and the
North Shore were formed by the fire of volcanism and the ice of
glaciation.
The North Shore of Lake Superior in
Minnesota lies on the north side of the Midcontinent Rift System
which ran 1,300 miles northwest; through what is now Lake Superior,
and southwest. About one billion years ago the granitic crust was
torn apart by continental drift; lava flowed out from 30 to 60
miles under the crust and formed a basalt crust (birthplace of Lake
Superior agates) some 20,000 feet thick. When the rifting stopped,
the lava cooled and the heavy crust sank and was filled with
sediment.
About two million years ago, glaciers
advanced into the region. During the Wisconsin glaciation
10,000 years ago the
ice began to recede, ice covered the region at a thickness of
1.25 miles. During this period, a large amount of the basalt
and sandstone, which erode much more easily than granite does,
was removed by the glaciers. This formed the rough, rugged
shoreline on the North Shore today. As the glaciers retreated,
they took with them eroded igneous material, much of which
covers the rocky beaches on the North Shore. The Wisconsin
side of the basin and the bottom of the basin itself, however,
filled with the residue from the eroded sandstone and thus are
sandy beaches today. Without the immense weight of the ice,
the land rebounded, and a drainage outlet formed at Sault Ste.
Marie.
Lake Superior is the world’s largest
freshwater lake by surface area… 3 quadrillion gallons of water!
The lake is so large that is significantly modifies the local
climate. On average the surrounding air is 5 to 20 degrees F warmer
in winter and 5 to 20 degrees F cooler in summer. The surface
water temperature of the lake averages about 40 degrees F.
TO LOG THIS CACHE:
1) What are the words in RED on the sign in front of
you?
2) What’s the surface water and the air temperature the day of your
visit? (Include the difference in temperature in your
log)
E-mail me the
answers
HERE.
Links:
Sources:
- Wikipedia
- MN DNR – State Park Literature
- MN Geological Society