Notes: Glaciers: Chapter 15 Part A Vocabulary you should know has been highlighted in green. Don’t forget to check the included illustrations and pictures. GLACIERS cover about 10% of the land surface. They are also found in high mountains. During the last ice age, they covered 30% of the land surface. There are even some glaciers that are on the equator (at very high elevations). EROSION and DEPOSITION left by glaciers give clues about the past. GLACIERS: “rivers of ice,” solid ice that move extremely slowly along the land surface. More snow falls than melts each year. High latitudes can have glaciers at sea level. Low latitudes will have glaciers at high altitudes. (high in the mountains) SNOW LINE: the lowest elevation at which the layer of permanent snow occurs in summer. EX: If a mountain is completely covered with snow in the winter but without snow in the summer, it has no snow line. Ultimately it would not have a glacier either. Snow line fluctuates according to total yearly snowfall and amount of sun exposure. HOW GLACIERS FORM FIRN (aka névé): compressed snow that recrystallizes into rough, granular ice material. - Firn is important to understand because it helps explain how glaciers flow downward and outward. - The weight of the material at the top of the ice compresses the ice below turning the firn into solid ice. The weight of the overlying snow and firn, coupled with gravity allows for the glacier to advance. - TYPES OF GLACIERS: CONTINENTAL GLACIER: large ice sheets that cover relatively flat ground. They flow OUTWARD from where the greatest amount of snow and ice accumulate. Circular in shape - form in areas where all precipitation falls as snow (polar regions) - thousands of meters thick and have been forming for thousands of years. - Smaller continental glaciers are called ICE CAPS. - ICEBERG: forms when the glacier reaches the sea and a big chunk breaks off. The chunk is called the iceberg. The process of breakage is called CALVING. VALLEY GLACIER (aka ALPINE GLACIER): flow DOWNHILL through mountains along existing valleys, often river valleys. They move WITHIN valley walls. - large river of ice and snow. - Alps in south-central Europe is where the name APINE glacier came from. - Form in regions high enough to be in the colder part of the Earth’s atmosphere.(High elevations) - At the equator: high elevations - Exist on every continent EXCEPT for AUSTRALIA. These are the ONLY two continental glaciers currently on Earth. - Cirque Valley Glacier with medial moraines GLACIAL MOVEMENT The weight of the snow and ice, along with gravity, allow for such a massive thing to move. As it moves, it weathers, erodes and deposits sediments. Move more rapidly after winters of heavy snowfall, on steep slopes, and in summer. Friction between the ice and the valley floor/walls slows movement. A typical glacier moves most rapidly at its center and surface. BASAL SLIP: movement at the base of a glacier due to the partial melting and freezing of the ice at the base. Reduces friction and allows for the glacier to slip at a faster rate. Responsible for movement at the base ONLY. In extremely cold areas, basal slip will not occur because it is too cold for the ice to melt. PLASTIC FLOW: occurs in the interior of the glacier. The grains of ice deform, change shape, and allow for the grains of ice to slip past each other to create forward movement. CREVASSES form across the width of the glacier when the glacier comes to a steep downward slope. The cracks form because the ice near the surface of a glacier is rigid. The ice breaks. The crevasses rarely go deeper than 50 meters, since below that depth, plastic flow is occurring. Scientists know that glaciers move and therefore study the rates of movement by stakes and satellites. GLACIAL WEATHERING AND EROSION Glaciers pick up and transport sediment in various ways. Glaciers have the ability to pick up tiny pieces of sediment to large boulders as big as a house. PLUCKING: occurs when a glacier picks up/plucks a rock from the land and embeds the rock in the ice and transports it to another location. Glacial STRIATIONS: are grooves in rock that help determine the glaciers direction of movement. They form when the rocks frozen to the bottom of a glacier scratch the underlying land and rock. The scratches are caused by the massive ice above as well as the embedded sediment within the ice. Glaciers carve a “U” shaped valley due to its massive side. The glacier cuts through a valley and widens the valleys and steepens the walls. HANGING VALLEY: forms where the main glacier cuts off a tributary glacier and creates a cliff. HANGING VALLEY WATERFALLS can be created.