8 Surface processes THE ACTION OF GLACIERS UNIT 8 Surface processes THE ACTION OF GLACIERS Biology and Geology 3. Secondary Education 1

UNIT 8 The action of glaciers Glaciers are enormous masses of ice which are formed due to accumulation, compaction and re-crystallisation of the snow deposited in very cold regions (the majority of them remote) of the earth’s surface. The ice in the glaciers can flow and, like all moving objects, it has energy which enables it to cause erosion, transportation and sedimentation on the materials that make up the terrain. This enables glaciers to modify the land relief. As it slides along, the ice rips off fragments of rock (erosion). The fragments of rock are carried to lower areas (transportation). At the end of its course, the glacier deposits the transported fragments (sedimentation). Biology and Geology 3. Secondary Education 2

8 The action of glaciers Glaciers erode the terrain in two ways: UNIT 8 The action of glaciers EROSION Glaciers erode the terrain in two ways: By entrainment: as the ice moves down-slope across a surface with fractures, due to frost weathering, it lifts up blocks of rock of all sizes, which are incorporated into the mass of ice. By abrasion: the fragments of rock carried by the glacier rub against the surface, smoothing it and polishing it (like sandpaper) or creating grooves called glacial striations, which make it possible to know the direction of movement of the ice after it has receded. The speed of erosion by the glacier depends on how fast the ice moves, the size of the fragments it carries and the type of soil the glacier moves across. Biology and Geology 3. Secondary Education 3

U-shaped glacier valley UNIT 8 The action of glaciers FORMS CREATED BY EROSION Once the glaciers have receded, we can identify the following forms of erosion: • Glacial valleys. They are wide and U-shaped. They transform into V-shaped river valleys as watercourses flow down them. U-shaped glacier valley V-shaped river valley Biology and Geology 3. Secondary Education 4

8 The action of glaciers FORMS CREATED BY EROSION UNIT 8 The action of glaciers FORMS CREATED BY EROSION Once the glaciers have receded, we can identify the following forms of erosion: • Glacial valleys. They are wide and U-shaped. They transform into V-shaped river valleys as watercourses flow down them. Terrain after the glaciers have receded Valley glaciers during glaciation (30,000 years ago) Biology and Geology 3. Secondary Education 5

8 The action of glaciers FORMS CREATED BY EROSION UNIT 8 The action of glaciers FORMS CREATED BY EROSION Once the glaciers have receded, we can identify the following forms of erosion: • Glacier valleys. They are wide and U-shaped. They transform into V-shaped river valleys as watercourses flow down them. • Glacier cirques. They are large depressions which remain in the former area of accumulation of the glacier. They often have lakes. • Horn and arêtes. These are the sharp peaks and crests of the mountains around the cirque, formed by erosion. • Roche moutonée. These are the rocks on the valley bottom, polished by the glacier. • Fjords. They are former glacial valleys whose final section is flooded by the sea. Glacial cirques Horn Arête U-shaped valleys Biology and Geology 3. Secondary Education 6

8 The action of glaciers TRANSPORTATION AND SEDIMENTATION UNIT 8 The action of glaciers TRANSPORTATION AND SEDIMENTATION As the glaciers move slowly, eroding the valleys, they incorporate and transport a large quantity of rock fragments. When the ice of the glaciers recedes, all those materials are deposited, creating different forms of glacial sedimentation, general known as tills o tillites. Biology and Geology 3. Secondary Education 7

8 The action of glaciers TRANSPORTATION AND SEDIMENTATION UNIT 8 TRANSPORTATION AND SEDIMENTATION As the glaciers move slowly, eroding the valleys, they incorporate and transport a large quantity of rock fragments. . The action of glaciers When the ice of the glaciers recedes, all those materials are deposited, creating different forms of glacial sedimentation, generally known as tills or tillites. Tills are an unsorted mixture of angular fragments of different sizes, from sands or gravels to large blocks. Biology and Geology 3. Secondary Education 8

8 The action of glaciers TRANSPORTATION AND SEDIMENTATION UNIT 8 TRANSPORTATION AND SEDIMENTATION As the glaciers move slowly, eroding the valleys, they incorporate and transport a large quantity of rock fragments. The action of glaciers When the ice of the glaciers recedes, all those materials are deposited, creating different forms of glacial sedimentation, general known as tills o tillites. Tills are an unsorted mixture of angular fragments of different sizes, from sands or gravels to large blocks. The most common forms of transportation and deposition are the moraines, which may be lateral, central, terminal or ground. Lateral moraines Central moraine Ground moraine Terminal moraines Biology and Geology 3. Secondary Education 9