To claim this as a find you will need to complete the three
tasks outlined below. Failure to complete the tasks may result in
the deletion of your log without notice. Be sure to Bring Your
Camera – you may want to keep it out and visible while at the
park*.
You are on top of a hill overlooking Lake Monona, with the
Yahara River running through the lake. 50,000 years ago, if you
were here overlooking the Yahara River, the view would have been
much different.
You would have been standing at the top of a deep, narrow, river
valley, with the Yahara River flowing far below you. Before the
last glacier the Yahara River flowed at the bottom of a steep
valley, with the valley walls soaring as much as 600 feet above the
river. After cutting through resistant Black River limestone, the
weak St Peter sandstone beneath would create short, steep slopes on
the valley wall. Next was a resistant layer of Lower Magnesian
limestone followed at the bottom of the river valley by weak
Cambrian sandstone. The surrounding area was also characterized by
tall, steep hillsides running down to streams and rivers.
The last advancement of Pleistocene glaciation, the
“Wisconsin Stage” generated a massive tongue of ice
known as the Green Bay Lobe which flowed from the northeast to the
southwest. The Green Bay Lobe flowed over the Madison area,
grinding down hilltops and filling up valleys with glacial
deposits. As the Late Pleistocene global climate began to moderate,
the ice edge fluctuated back and forth across the area for several
thousand years, dumping and reworking quantities of glacial debris
sufficient to nearly fill the ancient river valley. Because the
Yahara River was in the weak Cambrian sandstone, the glacier was
able to scoop out the sandstone and greatly deepen and broaden the
river valley, creating the lake basin.
When the glacier finally retreated from the area, between 10,000
and 12,000 years ago, it left behind a chain of lakes - Mendota,
Monona, Waubesa, and Kegonsa where the steep, deep, Yahara River
valley used to be.
To claim this find you must complete the three tasks
below:
1. Estimate the change in the visible relief due to the
glacier using the following steps and email your estimates to me
when posting your "found it" log
Across the lake to your left is the Monona Terrace, a rounded
building with large windows right on the lakefront:
a) Estimate the height of the Monona Terrace
b) Imagine how the area looked before the glacier arrived. How many
Monona Terraces would you have to stack one on top of the other to
reach from the bottom of the river valley to the top of the valley
walls?
c) How many Monona Terraces would you have to stack one on top of
the other to reach from the lake surface to the top of the hill
you’re standing on now?
d) What’s the difference in the number of Monona
Terraces?
2. Do you think the glacier had a major impact in the
topology of the area? Why or why not?
3. BRING YOUR CAMERA. Although no longer required, we
would appreciate a photo of you/your team with your GPSr at Olin
Park, with the lake and Monona Terrace in the background. If you
are solo caching, a photo of your GPSr with the lake and Monona
Terrace in the background will also be appreciated. Please upload
your photo(s) with your "found it" log.
Resources:
1. The Physical Geography of Wisconsin by Lawrence
Martin
2. Lakeshore Nature Preserve - www.lakeshorepreserve.wisc.edu