Monday, May 6, 2013

Notes on Being Driftless

Sinsinawa Mound viewed from the east

I visited the Driftless Area a few of weeks ago. The Driftless Area is so named due to the lack of glacial drift in an area of the upper Midwest otherwise dominated by glaciated landscapes. Most of the Driftless Area is in southwest Wisconsin with a bit of an overlay into southeastern Minnesota, northeastern Iowa and extreme northwest Illinois. For some reason during the last glacial period the continental ice went around this area and for a period of time it was a large island of ice free land surrounded by glacial ice.
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Driftless Area is the area circled by the blue hatched line
Blue hatched line is early Wisconsin ice extent
Green hatched line is late Wisconsin ice extent
(National Map)

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Southwest Wisconsin shaded relief (National Map)
The lack of glaciation means the soils here are different and the stream systems are much more fully incised into the landscape. The Mississippi River flows through the area giving the area some topographic relief such that there are many deep narrow canyons and high steep bluffs along this section of the river.

The hill in picture is not much to look at by Washington State standards, but it is the highest summit for many miles. And it has some history - an Indian/pioneer battle, a very old convent, lead mining. And the term mound is interesting. In this case the mound is natural, but there are a number of man made mounds in the area that were built in the shape of animals and Mima-like mounds that are man made.

No island-like Driftless Areas are present in Washington State. At the beginning of my trip I had views of mountain ranges with clear evidence of past glaciations: tracks-of-bull-lake-and-pinedale-glaciations and alluvial-fans-and-glacial-moraines. But another range, the Blue Mountains in southeast Washington was not glaciated.

View of the northern Blue Mountains, Washington State

The Blue Mountains in Washington State are over 6,000 feet, but no glacial cirques or glacial deposits have been mapped in the range. Somewhat higher portions of the range to the south in Oregon were glaciated. The topography of the range is consistent with the range not being glaciated. If glaciers did exist, they did not leave any of the classic U-shaped valleys or any readily identified moraines or cirques. That said, I once was doing some geology work in a lower range in Montana and came across a previously unidentified glacial moraine. But regardless, the lack of glaciation in the Blue Mountains of Washington is a bit of a curiosity.

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Shaded relief map of Blue Mountains

1 comment:

Geoffrey Middaugh said...

In my younger days, we visited caves of Wisconsin in the SW. This area was known to have the only caves in WI because it was driftless. They were terrible, because we were spoiled by MO and AR caves. The caves were very small, wet, and as Bretz would say: the mud and clay were unctuous. The Blues of WA I think are driftless, but the Elkhorns and Eagle caps sure aren't.