Chapter 18: Amazing Ice: Glaciers and Ice Age Glaciers are moving bodies of ice.o Form from the accumulation and compaction of snow.o Form under low temperatures (high latitudes – closer to the poles, high altitudes) in wet regions.o Move under the influence of gravity.  Ice Ages : periods during which the earth’s climate is significantly cooler than usual. Ice Ages are composed of:o Glacial periods – cool, accumulate o Interglacial periods – warm, retreat Types of Glaciers :o Alpine Glaciers : Confined to mountain valleys; tend to be erosionalo Continental Ice Sheets : Unconfined, blankets topography, large. (Modern Ex.: Antarctica, Greenland); depositional Requisites for a glacier :o Coldo Snow – more snow than melts The glacier is always in motion, even if it is not physically getting larger. Accumulation zone : where snowfall builds up Ablation zone/zone of wasting : where glaciers lose materialo If accumulation > ablation = glacier front advanceso If accumulation = ablation = glacier front remains the sameo If accumulation < ablation = glacier front retreatso Ablation can be: Melting Calving : ice breaks off (e.g. icebergs in the ocean) Sublimation : ice evaporates (solid to a gas) Wind Erosion As glaciers move over the land surfaces, they act as a transport agent, moving (eroding) material from one location to another (deposition). Rivers form “V-shaped” valleys. [meandering streams with floodplains might not] How do glaciers erode and shape the landscape?o Glacial ice is not clean; it contains rock fragments. Flowing ice pulls up rocks and the grinding action abrades a path as it moves.o Wet glaciers move by basal slipo Cold, dry glaciers: grains shear and pull themselves; move by plastic flowo Fastest movement in center of the surfaceo Slowest movement on the sides Erosional features of Alpine Glaciers (you will need to be able to identify erosional and depositional features for the exam)o Glacial striations : parallel scratches show the direction of movemento Glaciers carve out steep sided, “U-shaped” valleys, steep-walled, bowl-shaped.o Hanging valley : tributary valley that has been isolated by down-cutting of the glacier in the main valleyo Arête : jagged ridges along the divide produced by erosion of cirque or tributary glacierso Horn : pyramidal peak surrounded by three or more cirques (e.g. The Matterhorn in Switzerland)o Fjord : a glacial valley flooded by seawatero Cirque : steep-walled, bowl-shaped feature at the end of ‘glacier’ at edge of hanging valley Tarn : lake in the cirque Surface features of glacierso Crevasse : deep fissure or crack in a glacier; caused by brittle behavior of ice at the surface as the deeper ice moves plastically over an uneven surface. Depositional features of glacierso When ice melts, unsorted sediment called till is deposited: a random mixture of rock debris in a fine-grained matrix. The different moraines are just an accumulation of till found at different parts of the glacier.o Depositional Alpine Features: Moraine : collection of till Lateral Moraine : rock debris (till) which collects between the glacier and mountain Medial Moraine : rock debris (till) which is trapped where two glaciers join End Moraine : till deposited at the end of a glacier (e.g. conveyor belt)- Terminal Moraine : end moraine that marks the furthest advance of a glacier- Recessional Moraine : end moraine caused as glacier retreats Ground Moraine : till underneath the glacier itselfo Outwash plain : sediment being transported by a braided stream Continental Ice Sheet Featureso Typically, topography resulting from continental ice sheet glaciation is mostly deposition. o Surface features often affect the glacial features. Holes in glaciers that water flows through connect surface streams to subsurface streams. Sediment deposition forms: Kames : caused by sediment deposition from water flowing through a circular opening on the glacier; cone-shaped hill of sand and gravel.o Sub-glacial streams drain from the surface of the glacier and flow along its base. Streams can be 10-km in length or more and sediments are deposited in an ice cave beneath the glacier and can form: (& the water can also cause glacial surges) Esker : Long-sinuous ridge formed by sediment deposition in sub-glacial streams Drumlin : an asymmetric elongate hill (steep side – glacier is coming; shallow side – glacier is dragging it away with it), parallel to the ice flow direction, made of glacially deposited sediments Kettles : lake formed from buried ice block in outwash Erratic : a glacially deposited rock different from the bedrock on which it rests. Large boulders left by glaciers in areas where they obviously don’t belong. Moraines : ground, end, recessional, and terminal – same as those found in Alpine Glaciation; each is composed of poorly sorted glacial sediments called till Till : poorly sorted glacial sediments Outwash plain : stream deposited sediments at the front of the glacier. Characterized by braided streams Loess : Wind blown