Assignment 14: Glacial Processes and Landforms

Introduction

Glaciers have played an important role in the shaping of landscapes in the middle and high latitudes and in alpine environments. Their ability to erode soil and rock, transport sediment, and deposit sediment is extraordinary. During the last glacial period, more than 50 million square kilometers of the land surface were geomorphically influenced by the presence of glaciers.

Two major erosional processes occur at the base of a glacier. First, at the base of a glacier, large amounts of loose rock and sediment are incorporated into the moving glacial ice by partial melting and refreezing. The second process of erosion involves the abrasive action of the held rock and sediment held by the ice on the surface underneath the glacier. This abrasive process is known as scouring. Scouring creates a variety of features. The most conspicuous feature of scouring is striations. Striations appear as scratches of various size on rock surfaces. In some cases, abrasion can polish the surface of some rock types smooth. This geomorphic feature is known as glacial polish. The abrasive action of scouring also produces a fine clay-sized sediment that is often transported away from the glacier by meltwater. As a result of this process, glacial meltwater can have a light, cloudy appearance, and is called glacial milk.

The second major erosional process that occurs at the base of a glacier is plucking. Plucking is the process of particle detachment by moving glacial ice. In this process, basal ice freezes in rock surface cracks. As the main body of the glacial ice moves material around the ice in the cracks is pulled and plucked out. The intensity of the plucking process is greatest on the lee-side of rock mounds. When combined with glacial abrasion, the action of plucking on rock mounds produces a unique asymmetrical feature known as roche moutonnee. Roche moutonnee is smooth on the side of ice advancement and steep and jagged on the opposite side.

Directions: 

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