{"id":3640,"date":"2020-01-01T19:02:01","date_gmt":"2020-01-01T19:02:01","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/colorado-wmopen-geology\/?post_type=chapter&p=3640"},"modified":"2025-01-18T01:28:40","modified_gmt":"2025-01-18T01:28:40","slug":"glacier-basics-distribution-and-types","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/colorado-wmopen-geology\/chapter\/glacier-basics-distribution-and-types\/","title":{"raw":"Glacier Basics-- Distribution and Types","rendered":"Glacier Basics– Distribution and Types"},"content":{"raw":"

What is a Glacier?<\/h2>\r\nA glacier is a large mass of snow and ice<\/em>, <\/span>\r\nwith ice at the base<\/em>, <\/span>\r\nresting on land<\/em>, <\/span>\r\nlong-lived and capable of movement.<\/em><\/span>\r\n\r\nBelow is an air-photo that shows some glaciers in Greenland coalescing into a larger glacier mass.\r\nThe tributary glaciers are of a type called alpine glaciers<\/span>; meaning that they flow out of mountain valleys.\r\nSo, Greenland has mountains that contain alpine (valley) glaciers.\r\n\r\nBut,\r\nGreenland also happens to be one of two places where massive continental glaciers<\/span> are present today (the other is Antarctica).\r\nContinental glaciers (as the name implies) are huge features that cover thousands of square miles and are exceptionally thick, upwards of 10-15 thousand feet in some cases!\u00a0 In contrast, alpine glaciers are constrained to valleys, and rarely more than a couple kilometers in width (although can be quite long), and are at most a few thousand feet thick.\r\n\r\n[caption id=\"attachment_3655\" align=\"alignleft\" width=\"300\"]\"\"<\/a> Aerial Photo Glaciers in Greenland[\/caption]\r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n\"\"<\/a>\r\n\r\n\"\"<\/a>\r\n\r\nHere is glaciated terrain in the Indian Peaks Wilderness, about 50 miles northeast of Denver, Colorado.\u00a0 In this case, \"glaciated\" means that there were once major Pleistocene glaciers here (appr. 20ky ago) but the snow in these photographs are not glaciers!\r\nOn the flanks of Mt Toll here, we see what are best called \"snowfields.\"\r\nA snowfield may persist, even through the summer months, but they don't show movement and the classic features of glaciers.\r\nWe'll see more of the features of Glacial Erosion (mountains and valleys and ridges) in a later section.\r\n

Glacial Ice<\/h2>\r\nReally, a lot like a metamorphic rock!\r\nBelow, a piece of glacial ice that has \"calved\" off of a coastal glacier (ice breaking off and floating into the water).\r\n\r\n[caption id=\"attachment_3689\" align=\"alignnone\" width=\"300\"]\"\"<\/a> From-- https:\/\/en.wikipedia.org\/wiki\/Blue_iceberg[\/caption]\r\n\r\nGlacial ice starts out as snow.\r\nCompaction leads to recrystallization as ice crystals, and over time these flow and even\r\ngrow into each other.\r\nJust like a metamorphic rock-- recrystallization and re-growth of mineral grains.\r\n(Solid H2O, if natural, meets the definition of mineral.)\r\n<\/span>\r\n\r\n[caption id=\"attachment_3690\" align=\"alignright\" width=\"300\"]\"\"<\/a> USGS photomicrograph of glacial ice.\u00a0 Each grain is a little under a millimeter in diameter.[\/caption]\r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n

Glacial Movement<\/h2>\r\n\"\"<\/a>\"\"<\/a>\r\n\r\nA feature of real glaciers, like this Argentinian one on the left, are the fractures into the ice called crevasses.\u00a0 A typical crevasse can be relatively shallow, or hundreds of feet deep.\r\nCrevasses form because the upper part of glaciers are \"brittle.\"\r\n\r\nDeep in the glacier, the ice moves in a plastic kind of manner.\r\nIt deforms more like silly-putty or toothpaste!\u00a0 This is much like the region of the mantle called the asthenosphere, which you may recall is a plastic zone, atop which the more brittle lithosphere moves (hence, plate tectonics!).\r\n\r\nCheck out the cross sectional look into a glacier, below.\r\nThe differential speed of movement with depth is what causes the brittle deformation into\r\n\r\n\"\"<\/a>\r\n\r\nAbove image from S. Earle, Physical Geology, OER text\r\n\r\nBelow is an interesting animation of glacial movement and crevasse formation.\r\nNote that crevasse formation is enhanced by a glacial flexure, a bend as it goes from shallow to steeper gradient-- as would be expected with a brittle material.\r\n\r\nhttp:\/\/highered.mheducation.com\/olcweb\/cgi\/pluginpop.cgi?it=swf::640::480::\/sites\/dl\/free\/0072402466\/30425\/12_09.swf::Fig.%2012.9%20-%20Crevasses%20on%20a%20Glacier<\/a>\r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n ","rendered":"

What is a Glacier?<\/h2>\n

A glacier is a large mass of snow and ice<\/em>, <\/span>
\nwith ice at the base<\/em>, <\/span>
\nresting on land<\/em>, <\/span>
\nlong-lived and capable of movement.<\/em><\/span><\/p>\n

Below is an air-photo that shows some glaciers in Greenland coalescing into a larger glacier mass.
\nThe tributary glaciers are of a type called alpine glaciers<\/span>; meaning that they flow out of mountain valleys.
\nSo, Greenland has mountains that contain alpine (valley) glaciers.<\/p>\n

But,
\nGreenland also happens to be one of two places where massive continental glaciers<\/span> are present today (the other is Antarctica).
\nContinental glaciers (as the name implies) are huge features that cover thousands of square miles and are exceptionally thick, upwards of 10-15 thousand feet in some cases!\u00a0 In contrast, alpine glaciers are constrained to valleys, and rarely more than a couple kilometers in width (although can be quite long), and are at most a few thousand feet thick.<\/p>\n

\"\"<\/a><\/p>\n

Aerial Photo Glaciers in Greenland<\/p>\n<\/div>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

\"\"<\/a><\/p>\n

\"\"<\/a><\/p>\n

Here is glaciated terrain in the Indian Peaks Wilderness, about 50 miles northeast of Denver, Colorado.\u00a0 In this case, “glaciated” means that there were once major Pleistocene glaciers here (appr. 20ky ago) but the snow in these photographs are not glaciers!
\nOn the flanks of Mt Toll here, we see what are best called “snowfields.”
\nA snowfield may persist, even through the summer months, but they don’t show movement and the classic features of glaciers.
\nWe’ll see more of the features of Glacial Erosion (mountains and valleys and ridges) in a later section.<\/p>\n

Glacial Ice<\/h2>\n

Really, a lot like a metamorphic rock!
\nBelow, a piece of glacial ice that has “calved” off of a coastal glacier (ice breaking off and floating into the water).<\/p>\n

\"\"<\/a><\/p>\n

From– https:\/\/en.wikipedia.org\/wiki\/Blue_iceberg<\/p>\n<\/div>\n

Glacial ice starts out as snow.
\nCompaction leads to recrystallization as ice crystals, and over time these flow and even
\ngrow into each other.
\nJust like a metamorphic rock– recrystallization and re-growth of mineral grains.
\n(Solid H2O, if natural, meets the definition of mineral.)
\n<\/span><\/p>\n

\"\"<\/a><\/p>\n

USGS photomicrograph of glacial ice.\u00a0 Each grain is a little under a millimeter in diameter.<\/p>\n<\/div>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

Glacial Movement<\/h2>\n

\"\"<\/a>\"\"<\/a><\/p>\n

A feature of real glaciers, like this Argentinian one on the left, are the fractures into the ice called crevasses.\u00a0 A typical crevasse can be relatively shallow, or hundreds of feet deep.
\nCrevasses form because the upper part of glaciers are “brittle.”<\/p>\n

Deep in the glacier, the ice moves in a plastic kind of manner.
\nIt deforms more like silly-putty or toothpaste!\u00a0 This is much like the region of the mantle called the asthenosphere, which you may recall is a plastic zone, atop which the more brittle lithosphere moves (hence, plate tectonics!).<\/p>\n

Check out the cross sectional look into a glacier, below.
\nThe differential speed of movement with depth is what causes the brittle deformation into<\/p>\n

\"\"<\/a><\/p>\n

Above image from S. Earle, Physical Geology, OER text<\/p>\n

Below is an interesting animation of glacial movement and crevasse formation.
\nNote that crevasse formation is enhanced by a glacial flexure, a bend as it goes from shallow to steeper gradient– as would be expected with a brittle material.<\/p>\n

http:\/\/highered.mheducation.com\/olcweb\/cgi\/pluginpop.cgi?it=swf::640::480::\/sites\/dl\/free\/0072402466\/30425\/12_09.swf::Fig.%2012.9%20-%20Crevasses%20on%20a%20Glacier<\/a><\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

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