Fish River Glacial Pots EarthCache
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This earthcache bring you to an area having a high concentration of glacial potholes that are evidence of the powerful erosion forces caused by torrents of glacial melt water.
The early settlers were aware of the potholes often referring to them as well holes, cooking kettles, Indian mortars, and Indian ovens, while some even thought that the Indians made them and used as cooking utensils. Originally it was believed that these holes were formed through the rotation of a giant boulder or “millstone”, which ground a hole into the rock. The flowing water, mechanically eroding the solid rock and rounding and smoothing the cavity, swirled around the large stones accumulating in the pothole. It is now believed that as melt-water plunges through crevasses in the glacier’s surface the water flowed down in torrents. Whirlpools form in some places. This water, which is under very high pressure and traveling at up to 200 km/h, erodes the rocks. Erosion was caused not by a large erratic boulder but mainly by the sand and gravel contained in the turbid melt-water.
As the last glacial episode in this area came to an end when climatic warming forced the Laurentide ice sheet to stop and begin to recede as early as 21,000 years ago. The ice sheet moved back and forth it deposited a large amount of material called glacial till forming a moraine just up stream. This material built up finally blocking what was the Fish River just up stream of this location. The melting of the ice sheet released more water then is possible to imagine and as it filled the valley behind the moraine it formed what was called Lake Madawaska. As the rapid melting of the glacier continued to released great quantities of water it finally found its way over the top of the moraine where it took the path of least resistance, quickly eroded the moraine. The water became heavily laden with sand and gravels moving down stream quickly carving a path as it went toward the ocean. In other words glacial streams filled with sand and gravel physically drilled these potholes as the melt water swirled in circular basins. The sand and gravel carried by the stream served as an abrasive and cut into the soft limestone bedrock thus forming the round, smooth-sided potholes.
How important are these pothole to geologist? In 1879 a man named George Stone examined and measured a number of pothole on the coast of Maine near Bath. He realized these were different then the general pothole found along river and were carved in the bedrock by melt water streams beneath the glacier, using highly charged with coarse sediment. In 1892 Dr. O. C. Farrington cut one of the pothole from the bed rock and hipped it to Washington DC. The specimen is now still on display in the Smithsonian Institution National Museum of Natural History listed as specimen #27079 catalog #60880 which was accessioned on June 19, 1893 as a "glacial pothole," collected by O. C. Farrington.
To log this Earthcache: You must visit the area and answer an earth science question. There is no container or logbook for you to sign just a beautiful natural feature to observe. You must post a photo of yourself and your GPS with one of the pothole in the background and then send an email with an estimate of the pothole’s depth. As you look at the potholes think about the force that it must have taken to form these glacial features. The photo will give others something to look forward to when they visit. Make sure to include the name of the earthcache in your email.
If you enjoy this earthcache you may want to check the Maine Geological Survey located at (visit link)
They have developed a number of information sheets or field localities giving a great deal of information about geologic features. They also have a number of books and maps about Maine’s natural history/ geology that you might find interesting.
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