Glaciers and the Hydrologic Cycle: glaciers are masses of ice that move over land by plastic flow and basal slip. They presently contain 2.15% of all the water on Earth, 75% of the fresh water and cover about 10% of the land surface.
Origin of Glacial Ice: metamorphic rock that develops from a sediment (snow) through the intermediate step of firn - analogous to sand -> sandstone -> quartzite
Types of Glaciers: valley glaciers flow from higher to lower elevations while confined within mountain valleys. Continental glaciers or ice sheets flow outward in all directions from a zone of accumulation and cover large areas.
The Glacial Budget: glaciers form when winter snowfall exceeds summer melt and some of the snow accumulates from one year to the next. After compaction and becoming transformed to ice, the glacier will begin to flow under its' own weight once its' thickness exceeds 40 meters. The behavior of a glacier depends on its budget - the balance between accumulation and melting (wastage). A balanced budget means a stationary terminus (and the formation of a terminal moraine). Positive and negative budgets result in advance and retreat of the terminus respectively. At no time does any individual volume of ice actually move backwards.
Rates of Glacial Movement: rate of movement depends on slope, discharge and season. Valley glaciers tend to move more rapidly than do continental glaciers.
Glacial Erosion and Transport: glaciers erode and move significant amounts of sediment because they are moving solids. They have both a large competence and capacity. Glaciers are potent erosive forces, especially of unconsolidated sediment and soils. Most of the sediment carried by continental glaciers is carried in the lower levels (where it is picked up) while valley glaciers carry significant sediment on their surfaces and throughout the ice column.
Erosional Landforms of Valley Glaciers: typically form sharp angular landforms such as cirques, aretes, horns, U-shaped valleys, hanging valleys and fjords.
Erosional Landforms of Continental Glaciers: typically erode high areas producing smooth, rounded landscapes with poor drainage.
Glacial Deposits: both kinds of glaciers can produce largely the same kinds of depositional landforms which include:
Pleistocene Glaciation: glaciers covered about 30% of the land surface, especially in the Northern Hemisphere and Antarctica. There were multiple episodes of advance and retreat during the Pleistocene. Glacial maximum occurred about 18,000 years ago.
Pleistocene Climates: affected climates globally, compressing climatic belts towards the equator. Effects include:
Glaciers and Isostacy: loading of the crust caused isostatic subsidence - rebound began when the glaciers started to retreat and continues today. Has significant archeological affect especially in northern Europe.
Causes of Glaciation: first order effect must be the shifting of the Earth's plates which cause changes in oceanic and atmospheric circulation patterns. In addition, roles are played by: