GLACIATION: the term applied to periods of time when glaciers advanced and retreated on different portions of the Earth's surface.
PLEISTOCENE EPOCH - "ICE AGES" or a period of several glaciation episodes in Earth's "recent" geologic past that began roughly 2 million and "ended" roughly 10,000 years ago. "Ice Age"-style glaciation is still in progress in Antarctica, Greenland, and in many other arctic and mountainous regions of the globe.
Causes of Ice Ages remains in debate. Many complex Earth "systems" are involved in the advance and retreat of glaciers including global temperatures, atmospheric patterns, marine circulation patterns, and more. Extraterrestrial factors may also important. Factors relating to the amount of INSOLATION (INcoming SOLar radiATION) are predicted by the "Milankovitch Theory" a theory involving the study of "solar cycles." Factors that influence the amount of "insolation" in polar regions include:
Other possible "trigger" for glaciation may massive volcanism episodes or asteroid collisions?
A "typical" solar cycle results in an Ice Age that lasts approximately 200,000 years (+/- 150,000 years); This is followed by a roughly 20,000 year "warm period." (The last "ice age" ended about 18,000 years ago.)
There have been at least 4 "major" glaciation cycles in the last 1-2 million years, with as many as 16 or more lesser cycles.
The impact of human activity (including the "Greenhouse Effect") on climatic cycles is unknown.
When glaciers "form" sea level goes down. When glaciers "melt" sea level rises. Estimates vary, but the maximum fall of sea level may have been as much as 450 feet (150 meters). When the earth was much warmer before the "ice ages" sea level was anywhere between 50 to 300 feet HIGHER that today.
CREVASSES form on the surface of glaciers where the flow of ice is hindered by rough terrane on the bedrock. Crevasses can open up suddenly (which sometimes results in the accumulation of DEAD mountain climbers and/or GEOLOGY PROFESSORS!)
RATE OF FLOW measured in feet per year; fast 10-100s feet/day.
SURGE - rapid sudden movement from major snow falls.
DRIFT - glacial deposits (TWO KINDS)
MORAINES - hills of rock debris left by a glacier.
LOESS - wind blown silt from an outwash plain (forms dunes); example, upper Missouri River Valley (IOWA) is covered with loess; it weathers into rich soil good for agriculture.
KETTLES - large blocks ice buried by till melt and form ponds.
KAMES - stratified drift deposited by a glacial stream in the form of a small hill (where a creek drains of the end of a glacier).
ESKERS - streams under ice deposit snake-like gravel ridges.
DRUMLINS - gravel piles smoothed over by moving glaciers.
GLACIAL FEATURES IN MOUNTAIN REGIONS
GREAT LAKES - These North American lakes were carved by advancing continental glaciers; many ancient larger lakes drained when ice age glaciers melted causing incredible floods - and may have caused sea level to rise almost over night!
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