Erratic
by Jon Burch Photography
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Price
$750
Dimensions
24.000 x 16.000 inches
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Title
Erratic
Artist
Jon Burch Photography
Medium
Photograph - Digital Capture/vintage Film
Description
Pardon me, but you dropped your rock... Then, Paul Bunyan split it with his ax - or, maybe not. Don't worry, it's just an "erratic"...
A glacial erratic is a piece of rock that differs from the size and type of rock native to the area in which it rests. "Erratics" take their name from the Latin word errare, and are carried by glacial ice, often over distances of hundreds of miles. Erratics can range in size from pebbles to large boulders such as the 'Big Rock' weighing about 15,000 tons in Alberta, Canada.
Geologists identify erratics by studying the rocks surrounding the position of the erratic and the composition of the rock itself.
Since they are transported by glaciers, they are one of a series of indicators which mark the path of prehistoric glacier movement. Their lithographic origin can be traced to the parent bedrock, allowing for confirmation of the ice flow route. As an example, they can be transported by ice-rafting. This allows quantification of the extent of glacial flooding resulting from ice dam failure which release the waters stored in proglacial lakes such as Lake Missoula. Erratics released by ice-rafts that were stranded and subsequently melt, dropping their load, allow characterization of the high-water marks for transient floods in areas like temporary Lake Lewis.
Erratics dropped by icebergs melting in the ocean can be used to track Antarctic and Arctic-region glacial movements for periods prior to record retention. Also known as dropstones, these can be correlated with ocean temperatures and levels to better understand and calibrate models of the global climate.
The term "erratic" also is commonly used to refer to erratic blocks described as large masses of rock, often as big as a house, that have been transported by glacier-ice, and have been lodged in a prominent position in the glacier valleys or have been scattered over hills and plains. And examination of their mineralogical character leads the identification of their sources. In geology, an erratic is material moved by geologic forces from one location to another, usually by a glacier.
Glaciers erode by multiple processes: abrasion/scouring, plucking, ice thrusting and glacially-induced spalling. They crack pieces of bedrock off in the process of plucking, producing larger examples like you see here. In an abrasion process, debris in the basal ice scrapes along the bed, polishing and gouging the underlying rocks, similar to sandpaper on wood, producing smaller glacial till. In ice thrusting, the glacier freezes to its bed, then as it surges (meaning only one or two centimeters each year - if you want to call that 'surging'...) forward, it moves large sheets of frozen sediment at the base along with the glacier.
This glacial erratic was found along the trail to Cub Lake in Rocky Mountain National Park in northern Colorado. The glacier that dropped it was of course, long gone - but if you drive to the top of Trail Ridge Road in the park, you can see its remnants.
Image copyright 2013 Jon Burch Photography
Uploaded
October 7th, 2013
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