Photo A . At the base of glaciers a fine powder composed of ground up rock mater
ID: 298119 • Letter: P
Question
Photo A. At the base of glaciers a fine powder composed of ground up rock material acts
as a polishing agent. As the overlying ice moves slowly up or down a valley the fine powder under the pressure exerted by the overlying ice polishes the rock beneath the ice. When this polished surface is later exposed after the glacier has melted it is slowly worn away via abrasion and weathering. Can you pick out the polished versus the weathered
surface? The bedrock in the photo is granite.
Photo B. The ridge above Olmsted Point is in places highly polished and sitting above
this surface are large boulders of rock that appear to be completely out of place. These are believed to be boulders that were carried in the glacial ice, and then when it melted
the boulders came to rest on the polished surface.
Question # 11: In Photo A what part of the photograph is glacial polish and what part is exposed granite? Briefly explain your answer.
Question # 12: In Photo B how do we know that the boulders were deposited after the glacier melted and before the modern day topography was developed?
TOPO! map printed on 04/17/05 from Untitled,tpo 119 30'00" W WGS84 119 29 00 W Photos A and 119 30'00" W WGS84 119 2900 W METERSExplanation / Answer
answer- In the photograph of A , the granite rock is exposed, In this photograph centre region of the granite is represents the polished area it is formed when the glacier consists of gravel and sand grains. when glacier move above this region it pilished the bed rock surface. this polished region represents the direction of the glacial movement. it periphery region or outer region of granite is exposed to weathering when the coarse grain particle like gravel and cobble collide the bedrock surface. by the attrition process this region is exposed to mechanical weathering. there is presence of roughed surface that is formed by the weathering.
answer- In the photograph B, Boulder are showing at the bottom of valley. and the question is how these boulder were deposited. and these boulder were deposited when glacier melt it contain boulder and coarse grain particle like cobble , pebble and coarse grain sand. boulder lies at the bottom of the glacier. when the glacier move downslope and found the flat terrain it deposit its boulder due to its heavy weigth depsit first and rest water and other fine grain particle like sand and clay silt move ahead from the region. those boulder which deposited in flat terrain are showing the photograph B.