While taking a break from a hike in the Northern Rockies with a fellow geology e

Question

While taking a break from a hike in the Northern Rockies with a fellow geology enthusiast, you notice that the boulder you are sitting on is part of a deposit that consists of a jumbled mixture of many different sediment sizes. Since you are in an area tha once had extensive vally glaciers, your colleague suggests that the deposit must be glacial till. Although you know this is a certainly a good possibility, you remind your companion that other processes in mountain areas also produce unsorted deposits What might such a process be? How might you and your friend determine wether this deposit is actually glacial till?

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 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 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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