Vocabularies

First of all, study vocabularies. You can find them in your study materials (Studijní materiály - Ice), or you can use the following link.   

GLACIER

Glaciers are a hot topic these days and are a frequent subject of debate when discussing global climate change or the fate of polar bears. Do you ever find yourself asking what glaciers have to do with global warming? Have you ever wondered what exactly your friend meant when she told you that you moved at a glacial pace?

What a glacier is?

A glacier is essentially a huge mass of ice resting on land or floating in the sea next to land. Moving extremely slowly, a glacier acts similarly to an immense river of ice, often merging with other glaciers in a stream-like manner. Regions with continuous snowfall and constant freezing temperatures foster the development of these frozen rivers. It is so cold in these regions that when a snowflake hits the ground it does not melt, but instead combines with other snowflakes to form larger grains of ice. As more and more snow accumulates, mounting weight and pressure squeeze these grains of ice together to form a glacier.

GLACIAL EROSION

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 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 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 are smooth on the side of ice advancement and steep and jagged on the opposite side.

Some of the other features associated with glacier erosion in alpine regions are cirques, horns, and arêtes. Cirques are the bowl shaped depressions found at the head of glacial valleys. For most alpine glaciers, cirques are the areas in the alpine valleys where snow first accumulated and was modified into glacial ice. The glaciers that occupy cirques are called cirque glaciers. Horns are pyramidal peaks that form when several cirques chisel a mountain from three or more sides. The most famous horn is the Matterhorn found in the Swiss Alps. Arêtes are the narrow serrated ridges found in glaciated alpine areas. Arêtes form when two opposing cirques back erode a mountain ridge.

GLACIAL DEPOSITION

A large part of the surface of a glacier is covered with a coating of sediment and rock debris. This is especially prevalent near the snout of the glacier, where most of the ice has been lost to ablation and sediment is left behind. Sediment is added to glacial ice in two ways. Large quantities of sediment are picked up by abrasion and plucking at the base of the ice.

Geomorphologists call the later deposits glaciofluvial deposits. The technical term used to describe material deposited by the ice is called till or moraine. All glacial deposits are by and large known as glacial drift. Till is a heterogeneous combination of unstratified sediments ranging in size from large boulders to minute particles of clay. When till is deposited along the edge of a glacier it tends to form irregular hills and mounds known as moraines. A terminal moraine is a deposit that mark, the farthest advance of a glacier. Moraine deposits created during halts in the retreat of the glacier are called recessional moraines. The debris that falls from valley side slopes can be concentrated in a narrow belt and cause a deposit known as a lateral moraine. When two glaciers flow together, two lateral moraines can merge to form an interior belt of debris, called a medial moraine (see picture).

 

Exercises

There are some exercises for you. Go through them! You can find them in Study Materials (Studijní materiály -> Odpovědníky) or you can use the following link.