This earthcache is located in the Bob Hunter Memorial Park, which is part of the Rouge National Urban Park. Enjoy the trails within this park! The Park is under the jurisdiction of the Toronto and Region Conservation Authority (TRCA) and permission has been obtained for publication of this cache.
At the posted coordinates you will find two plaques. One titled "Looking at the landscape - Change is natural" and the other "Meet nature's bulldozer - the glacier". These informative plaques describe some of the changes that have occured in the area over the last 10,000 years and how glaciers impacted the region. Information about some of the various types of glacial erratics commonly found in this area and where they generally originate from can also be found on the plaques.
The Markham area, as with many regions in Ontario, has a lot of boulders. Numerous boulders of varying size are still dug up during construction-related excavations, and local farmers and homeowners continue to remove stones and boulders from their fields or gardens. All of these stones and boulders had to originate from somewhere.
Over 13,000 years ago, this area of Ontario was covered in glacial ice around a kilometer thick.
The glaciers flowed to this area from what is now central Quebec and northern Ontario, gathering blocks of bedrock along the way. As the glaciers retreated, they left an assortment of rocks in their paths. Some of these rocks have distinctive characteristics that indicate where the glaciers picked them up. Rocks carried here from areas outside of the Markham area are called Glacial Erratics. You can see some erratics near the posted coordinates and along the trail you hiked to the posted coordinates.
Glacial erratics get picked up in two main ways:
- Glaciers scrape over top of surface rock, smoothing it out and accumulating debris ranging from sand and small pebbles to large boulders near the bottom of the glacier. As the glacier moves, this abrasion tends to wear down rocks and smooth them out or break them into smaller pieces.
- A glacier could undercut a rock face and cause rocks to avalanche down on top of the glacier. The fallen rocks then travel on the glacier until ultimately being dropped off when the glacier melts. Such glacial erratics tend not to see much abrasion and often keep their jagged edges and rough textures.
If you go to your local library, or use your favourite internet web browser, you can search for "Glacial Erratics" and you can find many more sources of information. Many very large erratics are popular attractions such as the "Big Rock" (or Okotoks) in Alberta, and the "Madison Boulder" in New Hampshire.
To Log this Earth Cache:
Send me a message through the Geocaching.com Message Centre with your answers to the following questions:
1) Describe the rock in the middle of the small clearing at the posted coordinates. What type of rock is it, is it smooth or rough, the approximate size, and do you believe it is an erratic?
Using the information plaques:
2) Where do you think the erratics in the area originated?
3) What sizes of erratics can be found in Bob Hunter Park?
4) How can geologists track the paths of glaciers?
OPTIONAL: Post with your log a photo of you and/or your GPS in front of an erratic that you think is interesting that you encountered either on your hike or at the posted coordinates .