Pothole Location
Rockwood is filled with potholes...about 300 of them. Many of the potholes in Rockwood are just partial ones. It is rare to find one that has it's full shape and still completely in tact. Here you will find one such an example. This pothole is located along a trail that runs through the Carolinian forest of the north west side of Rockwood Conservation Area.
Pothole Formation
At least four ice advances, often called ice ages, have moved south into the region and beyond. They are the Nebraskan, Kansan, Illinoian and the Wisconsin. Most of the evidence of glaciers in the area is from the most recent advance, the Wisconsin Glacial Period. About 30,000 years ago, North America had a similar climate to modern time. Familiar animals lived here, but so did unique animals like saber-toothed tigers, giant ground sloths, beavers the size of wolves, deer the size of horses and other prehistoric animals. For unknown reasons, the climate of the earth began to cool. Ice sheets in the arctic regions began slowly spreading in all directions. In the Northern Hemisphere, this glacier was called the Laurentide Continental Glacier and was several kms thick in the center while the edges were around 200 meters thick. The glacier moved very slowly, sometimes only a meter or two a year. The edge of the glacier often advanced in the winter, only to partially melt back in the summer. Like a giant bulldozer, the glacier scraped the land, removing vegetation and soil, and flattening hills and ridges. On the top, edges and underneath the glacier, ice melted and flowed in rivers carrying sand, pebbles and boulders. Near the glacier, the climate was very cold. Winter lasted for six months and the annual temperature was 8° to 10° C cooler than the current climate. About 13,000 years ago, the Laurentide Continental Glacier was at its greatest size, and covered two-thirds of North America, including the the entire part of southern Ontario. Again the climate changed, becoming warmer, and the giant blanket of ice quickly melted and retreated. Animals and plants slowly repopulated the warming lands, but many of the prehistoric animals became extinct.
A pothole usually is a hole that is worn into the bedrock of a stream at the base of waterfalls or in strong rapids. The moving water spins sand, gravel and rock fragments in any small indentation in the bedrock. After enough time, the sand and stones carve out an elliptical hole. Potholes may also form under or near the edge of glaciers by the action of glacial meltwater. This Pothole was formed during the Wisconsin Glacial Period between 30,000 and 11,000 years ago. A meltwater stream flowing on top of the glacier probably broke through a crevasse (a crack in the glacier) and fell to the bedrock hundreds of feet below.
There was enough force generated by the falling water to begin a whirling motion of rock fragments in a small depression. As the rock fragments swirled and bumped each other, they carved the bedrock, making the depression deeper and larger. The rock fragments eventually were reduced to tiny particles, but new rock fragments continually tumbled into the hole, enabling the grinding process to continue. As the glacier moved, so did the crevasse. Sand, gravel and rounded stones often filled in the potholes as the glacier moved and the moving ice sheets through the same process caused more potholes to form.
Rockwood Pothole
The pothole that this earthcache brings you too is a well preserved and in tact example and sits alone in it's environment here, unlike many clusters of other potholes in other areas of the park. It is about 3 feet wide and has 6 feet deep vertical walls. The opening of the pothole is at ground level which is most likely the reason that the pothole has remained in such great shape. It is protected by the nearby cliffs and sediment that has been deposited around it. Close examination will reveal the various layers within the pothole.
Tasks and Logging Requirements
1) How many distinct layers are visible in wall of the pothole and how wide is each of the layers?
2) Is there any formation or evidence above ground level that would indicate that the pothole may have been taller at some point?
3) What is at the bottom of the pothole? You can examine this by poking it with a hiking or other long stick. How much sediment has gathered within it?
4) Put your hand on the inside wall of the pothole. What do you feel and observe?
5) Based on the area and what you have learned, do you think the pothole will get bigger or smaller or maybe even disappear completely.
6) As you walked along this section of trail, did you find any other potholes that were in tact too. If yes, were they bigger or small than this pothole?
Email me the answers to the above questions and then go ahead and log this earthcache. Feel free to post pictures too.
** Please note that there is a fee to enter Rockwood Conservation Area. See additional waypoints for entrance location.