HOW GLACIERS MODEL THE LAND UNIT 11 The evolution of landforms HOW GLACIERS MODEL THE LAND Biology and Geology 4. Secondary Education

11 How glaciers model the land UNIT 11 How glaciers model the land Glaciers are enormous masses of ice which are formed by accumulation, compaction and re-crystallisation of the snow deposited in very cold (and mostly remote) regions on 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 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 4. Secondary Education

11 How glaciers model the land Glaciers erode the terrain in two ways: UNIT 11 How glaciers model the land EROSION Glaciers erode the terrain in two ways: By entrainment: as the ice moves down the slope of 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 of the glacier depends on how fast the ice moves, its thickness, the size of the fragments it carries and the type of soil the glacier moves across. Biology and Geology 4. Secondary Education

11 How glaciers model the land LANDFORMS CREATED BY EROSION UNIT 11 How glaciers model the land LANDFORMS 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 fluvial valleys as watercourses flow down them. U-shaped glacial valley V-shaped fluvial valley Biology and Geology 4. Secondary Education

11 How glaciers model the land LANDFORMS CREATED BY EROSION UNIT 11 How glaciers model the land LANDFORMS 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 fluvial valleys as watercourses flow down them. Terrain after the glaciers have receded Valley glaciers during glaciation (30,000 years ago) Biology and Geology 4. Secondary Education

11 How glaciers model the land LANDFORMS CREATED BY EROSION UNIT 11 How glaciers model the land LANDFORMS 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 fluvial valleys as watercourses flow down them. • Glacial cirques. They are large depressions which remain in the former area of accumulation of the glacier. They often have lakes. • Horns and arêtes (or ridges) They are the sharp peaks and crests on the mountains around the cirque, which have been formed by erosion. • Roches moutonnées They are the rocks on the valley bottom, which have been 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 4. Secondary Education

Transportation of matter by the ice flow UNIT 11 How glaciers model the land TRANSPORTATION AND SEDIMENTATION As the glaciers move slowly, eroding the valleys, they incorporate and transport a large quantity of rock fragments. When the ice from the glaciers recedes, all those materials are deposited, creating different forms of glacial sedimentation, generally known as tills or tillites. Entry into the system Exit from the system Snow Evaporation Transportation of matter by the ice flow Fusion and drainage Biology and Geology 4. Secondary Education

11 How glaciers model the land TRANSPORTATION AND SEDIMENTATION UNIT TRANSPORTATION AND SEDIMENTATION As the glaciers move slowly, eroding the valleys, they incorporate and transport a large quantity of rock fragments. 11 How glaciers model the land When the ice from 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 4. Secondary Education

11 How glaciers model the land TRANSPORTATION AND SEDIMENTATION UNIT TRANSPORTATION AND SEDIMENTATION As the glaciers move slowly, eroding the valleys, they incorporate and transport a large quantity of rock fragments. 11 How glaciers model the land When the ice from 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. The most common forms of transportation and deposition are moraines, which may be lateral, medial, ground or terminal. Lateral moraines Medial moraine Ground moraine Terminal moraines Biology and Geology 4. Secondary Education