{"id":718,"date":"2018-03-05T21:01:06","date_gmt":"2018-03-06T02:01:06","guid":{"rendered":"https:\/\/opentextbc.ca\/physicalgeologyh5p\/chapter\/17-1-types-of-glaciers\/"},"modified":"2023-07-04T13:14:18","modified_gmt":"2023-07-04T17:14:18","slug":"types-of-glaciers","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/physicalgeologyh5p\/chapter\/types-of-glaciers\/","title":{"raw":"17.1 Types of Glaciers","rendered":"17.1 Types of Glaciers"},"content":{"raw":"There are two main types of glaciers: continental glaciers and alpine glaciers. Latitude, topography, and global and regional climate patterns are important controls on the distribution and size of these glaciers.\r\n

Continental Glaciers<\/h1>\r\nContinental glaciers<\/strong> cover vast areas of land. Today, continental glaciers are only present in extreme polar regions: Antarctica and Greenland (Figure 17.3). Historically, continental glaciers also covered large regions of Canada Europe, and Asia, and they are responsible for many distinctive topographic features in these regions (Section 17.2 and 17.3).\r\n\r\nContinent glaciers can form and grow when climate conditions in a region cool over extended periods of time. Snow can build up over time in regions that do not warm up seasonally, and if the snow accumulates in vast amounts, it can compact under its own weight and form ice.\r\n\r\nEarth\u2019s two current continental glaciers, the Antarctic and Greenland Ice Sheets, comprise about 99% of Earth\u2019s glacial ice, and approximately 68% of Earth\u2019s fresh water. The Antarctic Ice Sheet is vastly larger than the Greenland Ice Sheet (Figure 17.4) and contains about 17 times as much ice. If the entire Antarctic Ice Sheet melted, sea level would rise by about 80 m and most of Earth\u2019s major coastal cities would be submerged.\r\n\r\n[caption id=\"attachment_707\" align=\"aligncenter\" width=\"669\"]\"\" Figure 17.4<\/strong> Simplified cross-section profiles of the Antarctic and Greenland continental ice sheets. Both ice sheets are drawn to the same scale (exaggerated in the vertical direction). Source: Steven Earle (2015), CC BY 4.0. Image source.<\/a>[\/caption]\r\n

Continental glaciers generally cover areas that are flat, but the force of gravity still acts on them and causes them to flow. Continental glacier ice flows from the region where it is thickest toward the edges where it is thinner (Figure 17.5). In the central thickest parts, the ice flows almost vertically down toward the base, while at the edges of the glacier, it flows horizontally out toward the margins. In continental glaciers like the Antarctic and Greenland Ice Sheets, the thickest parts (4,000 m and 3,000 m thick, respectively) are the areas where the rate of snowfall, and therefore of ice accumulation, are greatest. In Antarctica, the ice sheet flows out over the ocean, forming ice shelves. Ice shelves can slow the flow of continental glaciers outward. Conversely, if ice shelves break down continental glacier flow can speed up.<\/span><\/p>\r\n\r\n\r\n[caption id=\"attachment_708\" align=\"aligncenter\" width=\"624\"]\"\" Figure 17.5<\/strong> Cross-section showing ice-flow in the Antarctic Ice Sheet. Source: <\/em>Steven Earle (2015), CC BY 4.0. Image source.<\/a>[\/caption]\r\n

Alpine Glaciers<\/h1>\r\nAlpine glaciers<\/strong> (also called valley glaciers<\/strong>) originate high up in the mountains, mostly in temperate and polar regions (Figure 17.1), but also in tropical regions in high mountains (e.g. in the Andes Mountains of South America).\r\n\r\nThe flow of alpine glaciers is driven by gravity, and primarily controlled by the slope of the ice surface (Figure 17.6). Alpine glaciers grow due to accumulation of snow over time. In the zone of accumulation<\/strong>, the rate of snowfall is greater than the rate of melting. In other words, not all of the snow that falls each winter melts during the following summer, and the ice surface in the zone of accumulation does not lose its annual accumulation of snow cover over the course of the year. In the zone of ablation<\/strong>, the rate of melting exceeds accumulation. The equilibrium line<\/strong> marks the boundary between the zones of accumulation (above) and ablation (below) (Figure 17.6).\r\n\r\n[caption id=\"attachment_709\" align=\"aligncenter\" width=\"439\"]\"\" Figure 17.6<\/strong> Schematic diagram illustrating alpine glacier ice-flow. Source: Steven Earle (2015) CC BY 4.0 Image source.<\/a>[\/caption]\r\n\r\nAbove the equilibrium line of a glacier, winter snow will remain even after summer melting, so snow gradually accumulates on the glacier over time. The snow layer from each year is covered and compacted by subsequent snow, and it is gradually compressed and converted to firn <\/strong>(Figure 17.7).\r\n\r\n[caption id=\"attachment_710\" align=\"aligncenter\" width=\"510\"]\"\" Figure 17.7<\/strong> Steps in the process of formation of glacial ice from snow, granules, and firn. Source: Steven Earle (2015), CC BY 4.0. Image source.<\/a>[\/caption]\r\n\r\nFirn<\/strong> is a form of ice that forms when snowflakes lose their delicate shapes and become granules due to compression. With more compression, the granules are squeezed together, and air is forced out. Eventually the granules are \u201cwelded\u201d together to create glacial ice (Figure 17.7). Downward percolation and freezing of water from melting contributes to the process of ice formation.<\/span>\r\n

The equilibrium line of a glacier near Whistler, BC, is shown in Figure 17.8. Below this line is the zone of ablation. In the zone of ablation, bare ice is exposed because the previous winter\u2019s snow has all melted. Above this line the ice is still mostly covered with snow from the previous winter.<\/span><\/p>\r\n\r\n\r\n[caption id=\"attachment_711\" align=\"aligncenter\" width=\"623\"]\"\" Figure 17.8<\/strong> The approximate location of the equilibrium line (red) in September 2013 on the Overlord Glacier, near Whistler, B.C. Source: Steven Earle (2015), CC BY 4.0, after Isaac Earle (n.d.), CC BY 4.0. Image source.<\/a>[\/caption]\r\n

The position of the equilibrium line changes from year to year as a function of the balance between snow accumulation in the winter, and snow and ice melt during the summer. If there is more winter snow and less summer melting, this favours the advance of the equilibrium line down the glacier (and ultimately increases the size of the glacier). Between accumulation and melting, the summer melt matters most to a glacier\u2019s ice budget. Cool summers promote an increase in glacier size, and thus lead to advance of the equilibrium line. Warm summers promote melting, and retreat of the equilibrium line. <\/span><\/p>\r\n\r\n

\r\n\r\n<\/a>Do You Know Your Glacier Types?<\/strong>\r\n\r\n
Fill in the missing words.<\/strong>\r\n\r\nThe Antarctic Ice Sheet is an example of a \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span>. These cover vast areas of land. These glaciers are \"self-flattening\" in the sense that gravity causes ice to flow horizontally away from thickened \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span> toward the thinner \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span> even though the glacier is on flat terrain.\r\n\r\nYou can find \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span> high in the mountains. Flow in these glaciers is controlled by the \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span> of the ice surface.\r\n\r\nIn the zone of \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span>, more snow falls each year than melts. With added pressure, snow transforms to \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span>, then \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span>, then ice. In the zone of \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span>, there's more melting than accumulation. The \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span> marks the boundary between these zones.\r\n\r\nFill-in-the-blank options:\r\n