Gibraltar Rock: A Glacial Erratic EarthCache
Gibraltar Rock: A Glacial Erratic
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This cache was originally placed by Northwoods Explorer.
This is a short hike on the Gibralter Rock Trail will take you to a very large erratic. This earthcache is along a coastal woodland trail in Herring Cove Provincial Park.
Welcome to Herring Cove Provincial Park, a 1,049 acres Provincial Park located on Campobello Island, New Brunswick near the Maine border that is best known for its trails, golf course and beautiful sand beach. Along one of the trails in a very gently rolling woodland section you will find a very large erratic.
An erratic is a piece of rock that has been eroded and transported by a glacier to a different area; it is left behind when the ice melts, simply dropped in place. Boulders that differ from the bedrock beneath or sitting on top are call erratics. The word erratic comes from the old French “erratique” which is derived from the Latin “errare” meaning "to wander." Glacial erratics are important to scientists because they give information about the direction of ice movement and distances of transport. Glacial erratics can be any size from small pebbles to large boulders the size of a house, like this one. This area is a classical example of the type of boulders that were carried here by the glacier and dropped when glacier melted. The ridge behind these erratic is covers but many smaller boulders. Their placement tells an interesting story not only due to their size but how they were piled as the glacier melted and the power it must have taken to move them. The most recent glacial episode in New Brunswick began about 25,000 years ago, when the Laurentide ice sheet overspread New England and Eastern Canada. During its peak development, this ice sheet was centered over eastern Canada and flowed east to southeast across Maine and the Maritimes. It became several thousand feet thick and shaped the land as we see it today. Climatic warming forced the Laurentide ice sheet to start receding as early as 21,000 years ago.
Most glacial erratics appear worn and rounded, and sometimes include beveled or faceted surfaces. During the course of their journey, the rocks were jostled against other erratics or scraped against the underlying bedrock, rounding off corners and smoothing surfaces, eventually producing their characteristic appearance. Glacial transport also caused some boulders to fracture, producing fresh angular edges. As you look at these erratic imagine the forces necessary to break something of that size or the size of the ice sheet that must have moved them to this area.
The composition of glacial erratics can often lead to identification of their point of origin and thereby provide some specific information about the direction of ice movement. In this case if you look carefully at the sides and edges of the erratic you will notice very little wear from movement which generally indicates that the rock has not traveled a great distance. Geologists identify erratics by studying the rocks surrounding the position of the erratic and the rock of the erratic itself. It is easy to see why erratics were once considered evidence of a biblical flood, but in the 19th Century scientists gradually came to accept that erratics pointed to an ice age in Earth's past. Geologists have also suggested that perhaps landslides or rockfalls initially dropped the rocks on top of glacial ice. The glaciers continued to move, carrying the rocks with it. When the glacier slowed and finally stop it began to melt. This melting slowly and gently dropped the boulders that it was carrying. Occasionally these boulders came to rest precariously perched on other erratics.
To log this Earthcache: You must send an email to me through my profile with the following information: At the posted coordinates describe size of the larger erratic and how it might have come to rest in that position. When you post your log please include a photo you or your hand, your GPS and with the erratic in background. Please begin your email with the name of the earthcache and make sure your log includes the number of people in your group. You must answer the question and post a photo or your log will be deleted. In your log please take the time to describe what you find interesting about this location.
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