What does erratic boulder mean?
Glacial erratics, often simply called erratics, or erratic boulders, are rocks that have been transported by ice and deposited elsewhere. For example, an erratic could be a boulder of sandstone is picked up by a glacier, transported, and deposited on top of a limestone bedrock.
What are erratic rocks?
Glacial erratics are stones and rocks that were transported by a glacier, and then left behind after the glacier melted. Erratics can be carried for hundreds of kilometers, and can range in size from pebbles to large boulders. Scientists sometimes use erratics to help determine ancient glacier movement.
What is a glacial erratic and how do we know a rock could be a glacial erratic?
Glaciers can pick up chunks of rocks and transport them over long distances. When they drop these rocks, they are often far from their origin—the outcrop or bedrock from which they were plucked. These rocks are known as glacial erratics. Erratics record the story of a glacier’s travels.
Where can you find erratic rocks?
Athabasca River Valley
The boulders and smaller gravel, which comprises the Foothills Erratics Train, consist of Lower Cambrian shallow marine quartzite and conglomeratic quartzite, which occurs only within the Gog Group and is found in the Athabasca River Valley of central western Alberta.
What is an erratic and how do they form?
In geology, an erratic is material moved by geologic forces from one location to another, usually by a glacier. Erratics are formed by glacial ice erosion resulting from the movement of ice. Glaciers crack pieces of bedrock off in the process of plucking, producing the larger erratics.
What does an erratic look like?
Erratics may be embedded in till or occur on the ground surface and may range in size from pebbles to huge boulders weighing thousands of tons. Erratics composed of unusual and distinctive rock types can be traced to their source of origin and serve as indicators of the direction of glacial movement.
How does a erratic form?
How do you identify a glacial erratic?
Geologists identify erratics by studying the rocks surrounding the position of the erratic and the composition of the erratic itself. Erratics are significant because: They can be transported by glaciers, and they are thereby one of a series of indicators which mark the path of prehistoric glacier movement.
How did glaciers move boulders?
Glacier Bed: Glaciers move by sliding over bedrock or underlying gravel and rock debris. With the increased pressure in the glacier because of the weight, the individual ice grains slide past one another and the ice moves slowly downhill.
What is an erratic and how is it formed?
In geology, an erratic is material moved by geologic forces from one location to another, usually by a glacier. Erratics are formed by glacial ice erosion resulting from the movement of ice. Glaciers erode by multiple processes: abrasion/scouring, plucking, ice thrusting and glacially-induced spalling.
Why is Okotoks Erratic important?
The Okotoks Erratic is an important location for many of the First Nation groups in the area, but is often associated with the Blackfoot First Nations and a story of Napi, the supernatural trickster, explaining how the rock got to its current resting place and why the rock is split down the middle.
How is boulder clay formed?
Boulder clay is a geological deposit of clay, often full of boulders, which is formed out of the ground moraine material of glaciers and ice-sheets. An ice sheet pushes rocks, boulders and everything else in its path, which in turn wears the rock into silt-like grain, which makes up the clay.
What makes Ingleborough’s erratic boulders so special?
The striking erratic boulders resting on the pavements around Ingleborough are some of the most endearing features of the Dales landscape. So ‘out of place’ do these geological oddities appear that they draw the camera of even the most casual visitor.
What are erratics?
In simple terms, erratics are boulders scraped from the valley sides by moving ice and dumped at a new location – most notably on limestone pavements and benches. When the deposited rock is not limestone, the contrast is particularly stark and the contrasting hues in the opposing rocks make a superb subject for the photographer.
Why are there so many boulders on the Dale?
The source of the boulders is clear on the north-west flank of the dale, and the ice has transported these only hundreds of metres, rather than a great distance. Nevertheless, these boulders remain a source of great debate to geologists for a number of reasons. Erratic deposition. Image by Elizabeth Pickett
What are the Norber erratics?
The most famous of the Norber Erratics, where a block of greywacke rests on a precarious pedestal of limestone, protected from erosion by the umbrella effect of the boulder itself. Stephen Oldfield