The Eureka Moraine
In Wisconsin, United States
Size:  (not chosen)
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This is an EarthCache, and thus no container to find.
To log this as a find, you will need to do some research and answer a few questions.
When it comes to glacial formations, Winnebago County and the Fox River lowland is not a well-known region for discovery of evidence left behind. However, the effects of a glacier, known as the Green Bay Lobe, that covered east-central Wisconsin approximately 21,000 years ago can be found all across Winnebago County. During that time period the glacier moved it’s way southwest along the state completely covering the county.
Throughout the lifespan of the glacier, the Green Bay Lobe readvanced back into Winnebago County and the Fox River lowland twice, including around 15,200 years ago. As the glacier receded, the melting back of the Lobe to the north resulted in the formation of numerous small lakes including Cottonwood, Island, Gleason, and Bradley Lakes. Eventually, these small lakes drained into the larger glacial Lake Oshkosh, which was the predecessor to Lake Winnebago and much of the lower Fox River system.
The glacial readvance also resulted in the formation of a fairly prominent moraine in front of the ice margin, known as the Eureka Moraine - a prominent ridge that cuts across southern Winnebago County and extends around the perimeter of Lake Winnebago. This terminal moraine formed at the margin of the Green Bay Lobe when it stabilized at its maximum extent during the lobe’s first readvance into Wisconsin around 15,000 years ago.
A terminal moraine is an accumulation of separated glacial debris, such as soil and rock, that forms at the extent of a glacial advance where the glacier has melted. The moraine size and shape is determined by whether the glacier is advancing, receding or at equilibrium. Moraines are fed by sediments melting out of stagnate ice at the toe of ice. Usually they lack stratification but can be bedded with coarse-grained soil deposits. To form large scale dump moraines the glacier must be at or near an equilibrium mass balance for extended amounts of time to ensure a steady amount of sediment supply. The longer the end of the glacier stays in one place, the more debris will accumulate in the moraine.
Under the glacier behind the moraine, it is common to find other formations such as eskers - the built up bed of an under glacier stream, and drumlins – elongated hills smoothed by glacial abrasion. Many of the drumlins and eskers that formed behind this moraine have since been buried beneath lake sediment left behind by glacial Lake Oshkosh, but the ridge of the moraine is still prominently evident in many places.
The posted coordinates for this EarthCache will take you to a point located on top of the Eureka moraine that provides an excellent location to view the surrounding landscape. As you look to the north of the Eureka moraine, the landscape is relatively flat and is dominated by red till and lake sediment deposited in glacial Lake Oshkosh as mentioned previously. However, an examination to the south will reveal a landscape is dominated by a rolling topography consisting mainly of drumlins that were formed when the Green Bay Lobe was receding from its maximum extent, around 17,000 years ago.
The Eureka moraine is not only important because it marks the limit of the readvancing Green Bay Lobe and represents a potential resource of sand and gravel, but because it divides the region into two areas where the surface materials consist predominantly of sand to the south and fine-grained lake sediment consisting of silt and clay to the north. Representative grain-size analysis of these sediments show a dramatic increase in sand in the surface materials, from about 20 percent to 65 percent as the moraine is crossed. Such a dramatic difference in sand content of surface materials plays a major role in storm-water infiltration and runoff. The surface sediment south of the moraine is more permeable and likely to adsorb surface-water runoff. To the north of the moraine, however, the land surface is less permeable and runoff is more likely to occur.
To log this find, send me the answers to the following:
1. FILL IN THE BLANKS: The moraine was formed during one of the readvances of the Green Bay Lobe which was a part of the __________ Ice Sheet that covered a large part of North America during the last ice age. During the formation of the moraine at this particular location, the melting of the Lobe resulted in the formation of the small glacial Lake ___________ at this spot which eventually drained into Glacial Lake Oshkosh.
2. The results of the moraine have provided ideal conditions for a business to have something at Site #1. QUESTION: What is it, what is the site number (not the street address) and why is this a good spot for it?
3. Examine the soil in the ditch near Site #2. QUESTION: The soil could be described as – (a.) red-brown and clay-like; (b.) light brown and sandy; -or- (c.) gray-brown and crumbly?
4. Take elevation readings both waypoints, then subtract the two to determine the estimated height of the formation.
NOTE: Do NOT post your answers in your log. Any of these inclusions may result in your log being deleted.
General Geology and Natural Resources of Winnebago County, WI Field Trip Guide Book. University of Wisconsin–Extension © 2004
Quartinary Geology of Winnebago County, Wisconsin. Wisconsin Geological and Natural History Survey ©2008
(No hints available.)
Last Updated: on 1/31/2017 10:16:30 PM (UTC-08:00) Pacific Time (US & Canada) (6:16 AM GMT)
Coordinates are in the WGS84 datum