Shoepac Sinkhole Splender EarthCache
Shoepac Sinkhole Splender
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Thanks to the Department of Natural Resources for permission to experience this earth feature. Take only memories, leave only footprints.
CONGRATULATIONS TO beenhere ON THIS EARTHCACHE FTF
A sinkhole is a naturally or unnaturally occurring depression or hole in the surface topography caused by the removal of bedrock and/or soil by water. Sinkholes can vary in size from less than 5 feet to hundreds of feet both in diameter and depth. Sinkholes vary in form from soil and tree-lined bowls, to bedrock-edged chasms. Also, the sinkhole may be able to hold water allowing it to form a pond or lake. They may be formed gradually or suddenly, and are found around the world.
Many mechanisms can form sinkholes including the slow removal of slightly soluble bedrock (such as limestone) by underground water, the collapse of a cave roof, or when there is a natural (or unnatural) lowering of the water table. Occasionally a sinkhole may form in urban areas from human activity when a sewer line collapses or from a water main break.
Sinkholes are usually but not always linked with karst landscapes. This area of Presque Isle County, and NE Lower Michigan, is made up of limestone and shale which was laid down between 345 and 395 million years ago (in the Devonian Period). The upper most layer of bedrock consists of limestone of the Traverse Group. Shoepac Lake and the Shoepac Sinkholes are only a small part of a large karst system that runs eastward to Lake Huron. Karst refers to a topography shaped by soluble layers of bedrock like limestone and shale. This limestone is readily dissolved by slightly acidic water, probably by an underground river aided by rainfall. This underground river carves out large caves and caverns in the limestone. Some of these caves collapse in on themselves creating the sinkholes that are located here.
One interesting aspect of this area is Shoepac Lake is a water-filled series of sinkholes that form the lake and the Shoepac sinkholes are a series of dry sinkholes. Silt and clay brought in by small streams have thoroughly sealed the bottoms of the sinkholes that make up Shoepac Lake This sediment is responsible for the formation of Shoepac Lake. The sinkholes to the east do not contain this sediment and therefore water can seep through the ground and the sinkholes remain dry.
Some sinkhole lakes can experience significant fluctuations in their water levels. Nearby Rainy Lake, about four miles east of Shoepac Lake, has seen four such water level drops between 1890 and 1985. The temporary loss of the silt and clay “drain plugs” and/or the continuing collapse of the sinkholes beneath the lake are the cause of these water fluctuations.
There have been two recent active karst collapse occurrences - one in 1976 and one 1994. Evidence of these collapses can be seen at the eastern edge of Shoepac Lake, providing evidence of the ongoing collapse of the sinkholes beneath the lake.
EXERCISE CAUTION AT ALL TIMES WHEN NEAR THE SINKHOLES
PLEASE KEEP ALL VEHICLES ON THE ESTABLISHED ROADS
The above coordinates will take you to a parking area for the Shoepac Sinkhole Pathway. The parking area is located off Shoepac Lake Road. Here you have an opportunity to experience a sinkhole at the top and bottom of the sink. Take the foot path the short distance to the steps leading to the bottom of the sinkhole. REMEMBER: If you take the steps (over 235 steps) down you have to take them back up – be sure you are prepared for trip up. You can complete the earthcache without leaving the trail or infrastructure which is in place. In order to log this earthcache you must perform the following tasks:
1. Utilizing your gps unit, take an elevation reading at the top and at the bottom of the sinkhole. Email me the two readings and the elevation difference in feet.
2. Estimate the diameter, in feet, of the sinkhole at the top and at the bottom of the sinkhole. Please do not do any bushwhacking to determine the diameters.
Email me your answers to parts 1 and 2. Do not post them in your log.
3. Post a picture of yourself, with your gps unit, on the top viewing platform with the sinkhole in the background.
The United State Geological Survey: (visit link)
Wikipedia: (visit link)
Michigan Department of Natural Resources: www.mi.gov/dnr
Additional Hints
(Decrypt)
VG VF 237 FGRCF QBJA NAQ 237 FGRCF HC.
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