What is an Esker?
An esker is a long winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions of Europe and North America. Eskers are frequently several miles long and, because of their peculiar uniform shape, are somewhat like railroad embankments.
Eskers were deposited by streams and rivers that flowed on top of the glacier, in cracks in the glacier or, in some cases, in tunnels beneath the ice. Imagine a river flowing in a valley or crack in the glacier. The banks of the river were ice and, in some places, the floor was also ice. These ice age rivers and streams deposited gravel and sand in their ice valleys, just as a modern stream deposits sediment in its valley. The very important difference is that the banks of the esker rivers eventually melted away, leaving the gravel deposits standing as ridges, a complete reversal of topography. What had been a valley became a ridge. The landscape has become inverted; it is "upside down" from what it was when it was forming.
Eskers are the ridges of gravel and sand that mark the routes of streams and rivers that flowed on, in, and beneath the glaciers. Eskers are, in effect, inverted river channels that snake their way across the countryside. They may be more than 100 feet high, a few hundred feet wide, and several miles long. Some esker ridges have nearly level crests. Typically, eskers are winding features, seldom straight for very far. The streams that formed these ridges flowed entirely on solid ground (but with ice walls). Other eskers are uneven on top, suggesting that the streams flowed over glacial ice in places. When the ice beneath the stream beds melted, the overlying gravel slumped, resulting in irregular, sometimes discontinuous features, a string of small hills.
Typically, the gravel found in eskers is coarse and contains layers and lenses of silt and clay. The gravel typically contains fine and coarse materials mixed together so that the quality of the gravel is usually not suitable for construction purposes. One of the reasons for this is that, while the glacier was melting, debris contained in the ice melted out and slid, in the form of mud flows, into the streams, becoming mixed with the stream sediment. Cobbles and boulders also slid off the ice into the streams. These can be seen today, mixed in with the stream sediment and littering the surfaces of the eskers.
Local Information
The posted coordinates will take you near the northernmost end of an esker located within Sleepy Hollow State Park. Park hours are from 8:00 AM until 10:00 PM. A Michigan State Park Pass is required for entry into the park. Be advised that hunting is allowed in the park from September 15th through March 31st. Please wear orange during this period for obvious safety reasons. Parking is available at: N 42° 55.215 W 084° 25.448. The walk from the parking area to the posted coordinates is about 0.6 miles. The final waypoint is 0.2 miles farther along the trail. At this final waypoint you will see a small gorge that has been cut through the esker. The total length of this esker is about 1/2 mile long.
Logging Requirements
- Go to N 42° 55.212 W 084° 24.941. At this point you must do three things:
A) Take a picture of you or your entire team on top of the esker with the lake in the background. If you do not wish to post your picture, you may take a picture of your GPS on top of the esker with the lake in the background. *Photographs are optional per Earthcaching guidelines.*
B) Estimate the width of the top of the esker at this location.
C) Take an elevation reading at this location.
- Go to N 42° 55.205 W 084° 24.909. Take an elevation reading at this location. Based on the difference in elevation at the two points, what is the height of the esker?
To gain credit for this earthcache, post the picture from #1A with your online log. Also, send an email to me via my profile with the answers for the questions regarding the width and height of the esker. Both the picture and the email must be done within 48 hours of logging the cache as a find. Any logs not meeting the above criteria will be deleted.
This earthcache was developed with permission from Sleepy Hollow State Park.
