In geology, a glacial erratic is a boulder carried by glacial ice and deposited some distance from its place of origin. In some cases they have traveled hundreds of miles. Geologists have suggested that landslides or rock falls initially dropped the rocks on top of glacial ice. The glaciers continued to move, carrying the rocks with them. When the ice melted, the erratics were left in their present locations. Glacial erratics range from a few millimeters to several yards in diameter.
Located at the coordinates posted for this Earth Cache is a glacial erratic that dropped not far from its present location during the last glacial advance sometime before 14,000 years ago. It was moved out of the way of infrastructure being developed during the park construction. It is an igneous rock consisting two types of granite; primarily Granodiorite with inclusions of Feldspar. Igneous rocks begin as hot, fluid material, and the word "igneous" comes from the Latin for fire. They are crystalline solids which formed directly from the cooling of the molten rock. It is very likely that this erratic came from the Canadian Shield, an area of bedrock close to the surface stretching in a “U” shape from northern mid-western Canada south east to northern Michigan and north east to north-eastern Canada. It represents some of the oldest basement rock on earth.
How do we know that this rock did not just come from a quarry located near here?
The bed rock found beneath the soil in this area is sedimentary rock not igneous rock. The sedimentary bedrock here is Dundee Limestone and Dolomite, formed in the Devonian period about 400 million years ago. Sedimentary rocks are made from sediments, usually in water. As they settle, they pile up and form layers. Eventually the continuous pressure force them to bind together forming rock.
All large rocks setting around are not necessarily erratics. There is a large rock in Oakwoods Metropark near the bike trail. (N 42 06.109 W 083 20.287) It turns out to be limestone which came from a quarry and was left over from a construction project.
Equipment required: Camera, tape measure, and calculator.
To complete this Earth Cache please do the following:
1.(Optional) Post a photograph of the glacial erratic including something to make the picture unique such as a member of your team, your GPS, backpack, Dog, etc on this Web page.
2. Answer the following questions on an answer retrieval form by clicking HERE.
- Describe the two types of rock observed in this erratic.
All rocks are subject to weathering; the breaking down of rock to form sediments.
- From your observations of this erratic which of the two types of rock seem to be more resistant to weathering?
- Measure the maximum length, width and height of the rock in feet.
- Since the rock is not a perfect cube, estimate the average length, width and height.
- Calculate the approximate volume of the rock. Volume = Length x Width x height.
The density of rock is about 180 pounds per cubic foot.
Weight = Volume x Density
- Calculate the approximate weight of the rock.
After visiting the erratic stop in at nature center. Mention to them at the desk that you were visiting the glacial erratic. Nature Center Hours: 10 a.m. to 5 p.m. weekends only. Closed week days.
Luc, the live eagle may be seen in his new home at the coordinates in the Waypoint Table. Stop by and learn his story.
Extra Credit: On your Geocaching travels keep your eyes open for other erratics. If you find one that is larger than this one please E-mail us with a description and coordinates. We will include them in a table on our special Erie Erratic web page.
This cache is located within Lake Erie Metropark, a part of the Huron-Clinton Metropolitan Authority park system. A Metropark Vehicle Entry Permit is required: Annual Permit $35. Senior (62+) Permit $21. Daily Permit $10.
For General information please call 810-227-2752 or
800-47-PARKS. Or visit our website at: WWW.metroparks.com.
All park rules and regulations apply. Park in parking lots only.
The Hours for Lake Erie Metropark are from 7:00 AM to 8:00 PM.
Dogs are allowed in this section of the park.
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Have fun!
The permit for this cache was renewed prior to the 4/15/2021 deadline and again was approved by Kevin Arnold | Southern District Interpretive Services Supervisor Huron-Clinton Metroparks on 04/13/21