{"id":3642,"date":"2020-01-01T19:02:27","date_gmt":"2020-01-01T19:02:27","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/colorado-wmopen-geology\/?post_type=chapter&p=3642"},"modified":"2023-06-28T23:04:01","modified_gmt":"2023-06-28T23:04:01","slug":"glacial-erosion","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/colorado-wmopen-geology\/chapter\/glacial-erosion\/","title":{"raw":"Glacial Erosion and Deposition","rendered":"Glacial Erosion and Deposition"},"content":{"raw":"

What Happens to Landscapes That Were Glaciated?<\/h2>\r\nGlaciers erode landscapes AND they deposit material.\r\nGlacial landscapes have both erosional and depositional features.\"\"<\/a>\r\n\r\n\"\"<\/a>\r\n\r\nOn the right is Yosemite Valley National Park.\u00a0 Spectacular granite walls.\u00a0 In the vicinity of 20ky (20 thousand years) ago, Yosemite probably looked like this place in Alaska, on the right, the Ruth Gorge.\u00a0 Indeed the highest portions of big cliffs (like El Capitan on the right) were not glaciated, just like the scene in the Ruth Gorge.\r\n\r\n \r\n\r\n\"\"<\/a>\r\n\r\nThe cartoon image at right shows some key features of glaciated mountainous terrain.\r\nGlaciers effectively slice into mountain sides forming steep ridges (aretes<\/strong>) and pointy summits (horns<\/strong>).\r\nCirques<\/strong> are bowl shaped regions at the head (or source region) of a glacier.\r\nIn the image, we see a trunk glacier<\/strong> (called \"Valley Glacier\") fed by tributary glaciers<\/strong>.\u00a0 Each glacier has a pile of debris on its sides, called lateral moraines<\/strong>, which consist of loose unconsolidated and poorly sorted and stratified glacial sediment (called till).\u00a0 Where the tributary glaciers entre the trunk glacier, their lateral moraines become sediment piles within the trunk glacier and are then called medial moraines<\/strong>.\r\n\r\n\"\"<\/a>\r\n\r\nHere is a glacial valley-- characterized by a U-shape, such that the floor of the valley is typically relatively flat, and the stream or river seems a bit small to have generated such a major feature.\u00a0 Note the earlier picture of Yosemite Valley and its \"flat floor.\"\"\"<\/a>\r\n\r\nIf glacial valleys contained exposed bedrock, the rock will often show glacial striae<\/strong>, like those on the right (formed by the glacier sliding over the rock).\r\n\r\n \r\n\r\n \r\n\r\n\"\"<\/a>\r\n\r\n\"\"<\/a><\/span>\r\n\r\nOn the left, loose unconsolidated and poorly sorted rock left behind by glacial activity-- till, in a moraine.\u00a0 And, on the right, an air-photo of recessional moraines cutting across a lake, representing various stages of terminal moraines during glacial retreat-- Lake Granby, Colorado.\r\n\r\nIn summary,\r\nmoraines (a geomorphic feature), which consist of till (a kind of sediment) are <\/span>depositional features<\/em><\/strong>;\r\nwhereas, cirques, aretes, horns, and U-shaped valleys are all <\/span>erosional features<\/em>.<\/span><\/strong>\r\n

<\/h2>\r\n

Evolution of Glacial Landscapes<\/h2>\r\nGlaciers create rather tell-tale landscape features.\r\nThe mountain peaks that have, or have had, glaciation tend to be pointy and rugged (horns and aretes!).\r\nEven if a cirque glacier is largely gone and melted away, that eroded region will typically contain a glacier lake called a tarn.\r\nDownstream from the tarn, one sometimes finds a string of lakes called paternoster lakes, which formed in small scoops downstream from the glacial cirque.\u00a0 A trunk glacier will leave behind a U-shaped valley.\r\nThe following is an interesting animation, created by ....\u00a0 which shows how a hypothetical landscape might change after a couple phases of glacial formation, advance, and retreat.\r\n\r\nhttp:\/\/www.youtube.com\/watch?v=D5uDaEpJHjE&feature=related","rendered":"

What Happens to Landscapes That Were Glaciated?<\/h2>\n

Glaciers erode landscapes AND they deposit material.
\nGlacial landscapes have both erosional and depositional features.\"\"<\/a><\/p>\n

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

On the right is Yosemite Valley National Park.\u00a0 Spectacular granite walls.\u00a0 In the vicinity of 20ky (20 thousand years) ago, Yosemite probably looked like this place in Alaska, on the right, the Ruth Gorge.\u00a0 Indeed the highest portions of big cliffs (like El Capitan on the right) were not glaciated, just like the scene in the Ruth Gorge.<\/p>\n

 <\/p>\n

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

The cartoon image at right shows some key features of glaciated mountainous terrain.
\nGlaciers effectively slice into mountain sides forming steep ridges (aretes<\/strong>) and pointy summits (horns<\/strong>).
\nCirques<\/strong> are bowl shaped regions at the head (or source region) of a glacier.
\nIn the image, we see a trunk glacier<\/strong> (called “Valley Glacier”) fed by tributary glaciers<\/strong>.\u00a0 Each glacier has a pile of debris on its sides, called lateral moraines<\/strong>, which consist of loose unconsolidated and poorly sorted and stratified glacial sediment (called till).\u00a0 Where the tributary glaciers entre the trunk glacier, their lateral moraines become sediment piles within the trunk glacier and are then called medial moraines<\/strong>.<\/p>\n

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

Here is a glacial valley– characterized by a U-shape, such that the floor of the valley is typically relatively flat, and the stream or river seems a bit small to have generated such a major feature.\u00a0 Note the earlier picture of Yosemite Valley and its “flat floor.”\"\"<\/a><\/p>\n

If glacial valleys contained exposed bedrock, the rock will often show glacial striae<\/strong>, like those on the right (formed by the glacier sliding over the rock).<\/p>\n

 <\/p>\n

 <\/p>\n

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

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

On the left, loose unconsolidated and poorly sorted rock left behind by glacial activity– till, in a moraine.\u00a0 And, on the right, an air-photo of recessional moraines cutting across a lake, representing various stages of terminal moraines during glacial retreat– Lake Granby, Colorado.<\/p>\n

In summary,
\nmoraines (a geomorphic feature), which consist of till (a kind of sediment) are <\/span>depositional features<\/em><\/strong>;
\nwhereas, cirques, aretes, horns, and U-shaped valleys are all <\/span>erosional features<\/em>.<\/span><\/strong><\/p>\n

<\/h2>\n

Evolution of Glacial Landscapes<\/h2>\n

Glaciers create rather tell-tale landscape features.
\nThe mountain peaks that have, or have had, glaciation tend to be pointy and rugged (horns and aretes!).
\nEven if a cirque glacier is largely gone and melted away, that eroded region will typically contain a glacier lake called a tarn.
\nDownstream from the tarn, one sometimes finds a string of lakes called paternoster lakes, which formed in small scoops downstream from the glacial cirque.\u00a0 A trunk glacier will leave behind a U-shaped valley.
\nThe following is an interesting animation, created by ….\u00a0 which shows how a hypothetical landscape might change after a couple phases of glacial formation, advance, and retreat.<\/p>\n