Q.10 7. After observing a glacier for several years, you conclude (1) that the g

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Q.10

7. After observing a glacier for several years, you conclude (1) that the glacier's terminus has retreated 2 km, and yet (2) debris on the glacier's surface has moved 1 km toward the terminus. How can you explain these observations? 8. How does the Milankovitch theory account for the onset 9. What kinds of evidence do geologists rely on to deter- 10. The image below shows the terminus of the Lowell Gla of glacial ages? mine the climates of the Pleistocene? cier in Canada. Identify and explain the origin of the de- posits of se Lowell glacier Deposits of sand and gravel

Explanation / Answer

The sediment taken by a glacier can be of two types, first is the material that is fallling from the down side of the valley that is deposits of sand & gravel shown in picture, from which the glacier is originated and this material (debris) is known as supraglacial debris the other type of sediments are those which are picked up by the bottom of the glacier that is from the Lowell glacier and this material is known as basal debris cumulatively these sediments are known as glacial till when the sediments are not lithified and is known as tillite if the sediments are lithified. If we see the texture of this glacial till then we'll find out that they are coarsed size mostly of the size range of gravel and some sand in it, they are poorly sorted, angular in nature. These characteristics of till is very similar to the alluvial fans deposits which are formed by Fluvial process. The thing which is different in both the sediments is the size range as in the case of alluvial fans the size varies from clay, silt and sand. And hence if we see particle size in the range of gravel then we can call it as glacial till.

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