Festge Park: Where the Glacier Stopped EarthCache

This is an Earthcache originally created by Odysseus2000. It was transferred to CommanderUSN in March 2021, and then to MTCLMBR in November 2023. It has no physical container or log to sign.  It is a geology lesson that requires you to answer a few questions to prove you were here.

The overlook at Festge Park gives you a great view of Black Earth Creek and the valley it runs through. From here you can see the effects of the glacier, which stopped about a mile east of here, and what its meltwater, loess deposits and erosion did to the land.

View of Black Earth Creek Valley from Overlook at Festge Park

One of the most dramatic aspects of Dane County Geology is that the edge of the most recent glaciation ice sheet ran diagonally through Dane County. This makes it an excellent area to view the effects of that ice on the landforms. The far southwest corner was untouched by the ice sheet itself, and referred to as the Driftless Area, while the north and east parts were under approximately 800 feet thick sheet of ice and the land was greatly re-formed by the glacier. But even the areas not covered by the ice were greatly changed by it.

THE GLACIERS:

The map above shows the lobes approximately 20,000 years ago, during their maximum reach into Wisconsin

Approximately from 60 to 2.4 million years ago, the cooling Earth created huge continental ice sheets in the northern hemisphere which surged and ebbed. Only the most recent glaciation, the Wisconsin Glaciation, left a visible and major imprint on our landscape. The glacier smoothed the land, scraped off hilltops and filled in valleys. An enormous glacier, called the Laurentide Ice Sheet, moved into our area about 25,000 years ago. The Green Bay Lobe of that sheet covered the eastern two-thirds of Dane County under 800 feet of ice. Here at Festge Park Overlook you are standing just west of the furthest reach of the glacier and looking down into the valley formed by the meltwaters of its retreat.

The Driftless Area of western Dane County escaped glaciation; its landscape evolved from millions of years of erosion

Approximately 20,000 years ago, when the melting of the ice near the glacier edge equaled the amount of ice being carried to the margin, a balance was reached and the margin stabilized. But the stable glacier continued to modify the landscape by eroding rock and soil and transporting the resulting rock, sand, silt, and clay southwestward toward the glacier edge. When the climate began to warm approximately 15,000 years ago, and melting finally exceeded ice flow toward the margin, the glacier shrank back toward the northeast, leaving behind distinctive landforms in parts of Dane County.

Even though glaciers never covered the Driftless Area, they did alter the landforms. Black Earth Creek and the Wisconsin and Sugar Rivers carried vast amounts of glacial meltwater, and their valleys now contain thick outwash, sand and gravel that was deposited by wide, braided streams.

Braided stream image courtesy of www.geologyclass.org

At the time of the glacial maximum, the climate was cold, and tundra plants dominated the ridgetops and slopes. Spruce, protected from the bitter winds blowing off the ice sheet, probably survived in valley bottoms. Clouds of silt-sized dust, called loess, windswept from the floodplains of meltwater rivers, particularly the Mississippi, settled on the land surface of southern Wisconsin.

Summer thawing of frozen ground produced severe erosion on slopes—much more than takes place today. Some rocks, such as solid, unweathered dolomite and well cemented sandstone, resisted the forces of erosion and now form steep cliffs. Softer sandstone and weathered dolomite slope gently. Outcrops (exposures) of both rock types can be seen along river valleys and in roadcuts.

Much of the time the glacier was at or near its maximum position, the bed was frozen in a zone that was 5 to 10 miles wide near the ice margin, damming the drainage of meltwater from under the glacier. When water did escape from under the ice, it cut tunnel channels—large caverns that were gouged partly into the ice and partly into the glacier’s bed —through which water flowed, sometimes with great force, breaking the ice dam. These channels carried huge volumes of water for short periods of time, perhaps only days, before water pressure was reduced and the tunnel closed. The meltwater floods were likely short-lived, but they had a great impact on our landscape. The tunnel channels are now valleys, like Black Earth Creek Valley, that are partly filled with sand and gravel.

Smaller channels formed as water produced by surface melting flowed along, away from, and sometimes under the thin ice near the glacier margin. Broad streams having channels with a braided pattern flowed away from the glacier in pre-existing valleys toward the Wisconsin and Rock Rivers. These rivers carried large amounts of sand and gravel outwash derived from debris-rich ice and till at the ice margin. This material accumulated to thicknesses of more than 200 feet in major valleys such as Black Earth Creek, the Sugar River, and the Yahara River.

BLACK EARTH CREEK

When the glacier was building the Johnstown moraine, broad outwash streams choked with gravel and sand flowed to the west and south.

Stand at the overlook at Festge County Park and picture a sunny summer day 15,000 years ago, when the whole foreground would have been covered with fast-flowing, crisscrossing river channels too deep to wade.

By Bo Mertz (CC-BY-SA-2.0) via Wikimedia Commons

The glacier was a mountain of ice extending about 1 mile beyond the quarry to the east. The hills on which you are standing, and those across the valley, were not covered by ice, but by tundra grasses, sedges, and low shrubs, with only scattered patches of spruce, birch, and willow. Mammoths and musk ox grazed this nearly barren landscape.

Mammoths foraged for food in the relatively barren tundra

Millions of years of stream erosion, not glaciation, formed the hills and valleys here. Glacial ice filled much of the lowland directly to the north and east of the point where you are standing. The edge of the glacier crossed the Wisconsin River at the Lake Wisconsin dam. The ice front in this part of the county did not carry enough debris to build a moraine. Instead, only a scattering of erratics, large boulders that the glacier carried hundreds of miles from north and east of Lake Superior, and their absence farther west, indicate that the ice stopped on this hill.

REQUIRED - QUESTIONS;

To log this Earthcache as a find, please send your answers to the following questions by clicking send message to the cache owner listed on the webpage:
All answers can be found at the Earthcache location.

Q1: From the overlook, can you see Black Earth and/or Cross Plains?

Q2: a.) What type of rock forms these cliffs and b.) what tree grows on them when it is too dry for oaks?

Q3: The glacier’s deposited gravel and meltwater outwash makes Black Earth Creek ideal for what current use?

Reference Section:

• Landscapes of Dane County, Wisconsin by David M. Mickelson, Susan L. Hunt, illustrator, Wisconsin Geological and Natural History Survey Educational Series 43 | 2007
• Glaciation of Wisconsin, Educational Series 36 | 2011, Fourth edition by Wisconsin Geological and Natural History Survey
• Geology of Ice Age National Scientific Reserve of Wisconsin, NPS Scientific Monograph No. 2, CHAPTER 6: Cross Plains Terminal Moraine
• Generalized glacial geological map of Dane County, Wisconsin; Wisconsin Geological and Natural History Survey; UW Extension 2007