Alpena Glacial Striations EarthCache

There are different ways to tell that a glacier has moved across exposed bedrock. One way is by glacial striations, or grooves made in the bedrock as a glacier moved over it.

Things you will need to log this Earthcache:

1. Camera
2. GPS or compass
3. Tape measure or ruler

The logging requirements for this Earthcache are:

1. Post to your online log a photo of your GPS with the breakwater in the background. Your face can be included if you so wish.
   E-mail me, via my profile, the answers to the following questions:
   
   1. Use a compass or your GPS to tell me the two headings that the grooves follow. Such as 45 degrees and 225 degrees. Although not the natural position I would like the striation's current heading.
   2. What is the average depth of the striations.
   3. What is the average width of the striations.

A glacier is a mass of compacted snow which deforms and flows due to gravity. Glaciers contain ice and sediments that becomes part of the glaciers load. Once sediment becomes part of the glacier, it moves with it. This sediment is then able to act as an abrasive force on the bedrock.

Glacial striations are grooves or scratches in bedrock that were made by glaciers as they moved across the bedrock. The glaciers would pick pieces of hard rock and grind them into the softer bedrock, causing the striations. Striations will be parallel to each other. Most striations are rather shallow but can be deeper. Below is a photo of the glacial striations on Kellys Island in Lake Erie north of Sandusky, Ohio which are some of the best in the world.

The glacier that caused these striations covered this area over 10,000 to 12,000 years ago which is when the ice sheet started to retreat. The ice sheet was over a mile high and was present for thousands of years.

At this site the glacial striations are not anywhere as pronounced as those on Kellys Island. Nor is this example in it's natural position. The rock you are looking for came from a nearby quarry. The mine safety rules restrict the access to mines and quarries unless you have proper safety training. It is about 3' x 3' square and can be easily spotted from the paved sidewalk.

The striations that cover the surface of this rock are shallow. This tells us that the rocks that scratched the bedrock were also small in size. The direction of movement can be determined by looking for the overall pattern of the striations. All the scratches will be aligned in the direction that the glacier was moving. The problem with this rock is since it was moved here we don't know the exact heading of the striations.