Respuesta :
Answer;
C. the direction of glacial movement
Explanation;
-Striations are scratches formed on a rock surface by rock fragments frozen into the bottom of a moving glacier.Rocks embedded in the bottom of the glacier scrape along the newly exposed bedrock and leave behind line-shaped scratch marks called glacial striations. The direction of the scratch marks tells us the direction that the glacier flowed
-Glacial grooves and striations are gouged or scratched into bedrock as the glacier moves downstream. Boulders and coarse gravel get trapped under the glacial ice, and abrade the land as the glacier pushes and pulls them along.
The direction of the glacial movement is determined by the geologists through the scratches as a result of the glacial striations on the bedrock.
Further Explanation:
The glacial striations are formed due to the passage of heavyweight ice over the rocks which causes scratches on the underlying bedrock. The rocks, boulders, and pebbles are trapped under the glacier as it moves down the bedrock. With the movement of the glacier the pressure and mass increase further pushing the glacier. This results in the gouging out of the rocks from the rockbed as the lower surface of the glacier contains sediments acting as a cutting tool. The ice in itself cannot change the shape of the bedrock, but the rock particles embedded into it are hard enough to cause abrasions.
The rate of abrasion can be affected by the following:
- The hardness of the sediments embedded in the glacial ice must be higher than the bedrock.
- The basal surface must contain a large amount of rock debris, large enough to cause abrasions.
- The thicker the ice more is the force and pressure applied on the bedrock by abrading fragments.
- The bedrock is disrupted faster if the speed of the glacier is faster.
- The fragments which are smaller in size are less effective in producing scratches on the bedrock as compared to the large fragments.
The glacial striations help geologists ascertain and understand the direction of the glacier. This is because as the glacier moves it creates scratches on its way due to the presence of rock fragments. These gouged rocks help explain whether the glacier moved upwards or downwards.These striations also help in determining the speed of the glacier because of the glacier carried too much of rock debris within it, its speed must be slow. The striations also reveal the type of debris that was moved along with the glacier. For example, if the scratches on the bedrock are deep, it implied that the glacier must have carried large boulders with it.
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Answer Details:
Grade: High School
Subject: Biology
Chapter: Geology-Glacial Striations
Keywords:
Glacial striations, scratches, gouges, bedrock, glacier, rocks, pebbles, boulders, abrasions, glacial movement, glacial speed.
