chapter topics review.docx

5 Pages
Unlock Document

Earth Sciences
Maureen Padden

Chapter 16-Glaciers A glacier is a large, perennial mass of ice that forms on land and moves under the influence of gravity. A glacier can form wherever more snow accumulates than is lost. Ice sheets and valley glaciers are the two most important types of glaciers. Glaciers move downward from where the most snow accumulates toward where the most ice is wasted. A glacier moves both by basal sliding and by internal flow. The upper portion of a glacier tends to remain rigid and is carried along by the ice moving beneath it. Glaciers advance and recede in response to changes in climate. A receding glacier has a negative budget and an advancing one has a positive budget. A glacier's budget for the year can be determined by noting the relative position of the equilibrium line. Snow recrystallizes into firn, which eventually becomes converted to glacier ice. Glacier ice is lost (or ablated) by melting, by breaking off as icebergs, and by direct evaporation of the ice into the air. A glacier erodes by plucking and the grinding action of the rock it carries. The grinding produces rock flour and faceted and polished rock fragments. Bedrock over which a glacier moves is generally polished, striated, and grooved. A mountain area showing the erosional effects of alpine glaciation possesses relatively straight valleys with U-shaped cross-profiles. A glacial valley often has a cirque at its head and descends as a series of rock steps. Small tarn lakes are commonly found along the steps and in cirques. A hanging valley indicates that a smaller tributary joined the main glacier. A horn is a peak between several cirques. Arêtes usually separate adjacent glacial valleys. A glacier deposits unsorted rock debris or till, which contrasts sharply with the sorted and layered deposits of glacial outwash. Till forms till plains, drumlins, and various types of moraines. Fine silt and clay may settle as varves in a lake in front of a glacier, each pair of layers representing a year's accumulation. Multiple till deposits and other glacial features indicate several major episodes of glaciation during the late Cenozoic Era. During each of these episodes, large ice sheets covered most of northern Europe and northern North America , and glaciation in mountain areas of the world was much more extensive than at present. At the peak of glaciation about a third of the Earth's land surface was glaciated (in contrast to the 10 percent of the land surface currently under glaciers). Warmer climates prevailed during interglacial episodes. The glacial ages also affected regions never covered by ice. Because of wetter climate in the past, large lakes formed in now-arid regions of the United States. Sea level was considerably lower. Glacial ages also occurred in the more distant geologic past, as indicated by late Paleozoic and Precambrian tillites. Permafrost is ground that has remained frozen for two or more years and can reach thicknesses of up to several hundred metres in high-latitude regions. Ground ice, ice wedges, pingos, and patterned ground are found in areas underlain by permafrost. Thermokarst is the subsidence and collapse of the ground surface caused by thawing of permafrost. Dealing with permafrost is a major issue for urban development in Canada's north. Chapter 13-Waste Mass wasting is the movement of a mass of debris (soil and loose rock fragments) or bedrock toward the base of a slope. Movement can take place as a flow, slide, or fall. Gravity is the driving force. The component of gravitational force that propels mass wasting is the shear force, which occurs parallel to the slopes. The resistance to that force is the shear strength of rock or debris. If shear force exceeds shear strength, mass wasting takes place. Water is an important factor in mass wasting. A number of other factors determine whether movement will occur and, if it does, the rate of movement. The slowest type of movement, creep, occurs mostly on relatively gentle slopes, usually aided by water in the soil. In colder climates, repeated freezing and thawing of water within the soil contributes to creep. Landsliding is a general term for more rapid mass wasting of rock, debris, or both. Flows include creep, earthflows, mudflows, and debris avalanches. Earthflows vary greatly in velocity although they are not as rapid as debris avalanches, which are turbulent masses of debris, water, and air. Gelifluction, a special variety of earthflow, usually takes place in arctic or subarctic climates where ground is permanently frozen (permafrost). A mudflow is a slurry of debris and water. Most mudflows flow in channels much as streams do. Rockfall is the fall of broken rock down a vertical or near-vertical slope. A rockslide is a slab of rock sliding down a less-than-vertical surface. Debris falls and debris slides involve unconsolidated material rather than bedrock. Landslides also take place underwater. The larger ones of these are vastly bigger than any that have occurred on land. Chapter 18-Beaches Wind blowing over the sea surface forms waves, which transfer some of the wind's energy to shorelines. Orbital water motion extends to a depth equal to half the wavelength. As a wave moves into shallow water, the ocean bottom flattens the orbital motion and causes the wave to slow and peak up, eventually forming a breaker whose crest topples forward. The turbulence of surf is an important agent of sediment erosion and transportation. Wave refraction bends wave crests and makes them more parallel to shore. Few waves actually become parallel to the shore, and so longshore currents develop in the surf zone. Rip currents carry water seaward from the surf zone. A beach consists of a berm, beach face, and marine terrace. Summer beaches have a wide berm and a smooth offshore profile. Winter beaches are narrow, with offshore bars. Longshore drift of sand is caused by the waves hitting the beach face at an angle and also by longshore currents. Deposition of sand that is drifting along the shore can form spits and baymouth bars. Drifting sand may also be deposited against jetties or groins or inside breakwaters. Rivers supply most sand to beaches, although local erosion may also contribute sediment. If the river supply of sand is cut off by dams, the beaches gradually disappear. Coasts may be erosional or depositional, drowned or uplifted, or shaped by organisms such as corals and mangroves. Coastal strai
More Less

Related notes for EARTHSC 1G03

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.