glaciers - Physical Geology 101 30. Ice and Glaciers (p....

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Unformatted text preview: Physical Geology 101 30. Ice and Glaciers (p. 484-502) Glaciers What is the definition of a glacier? ___________________________________________________ ________ ______ ______ ______ ______ ______ ______ ________ ______ ______ ______ ______ ___ Types of Glaciers The ice in glac iers can be variable in temper ature. At low and middle latitudes, the ice temperature may be close to melting point. What do we call these types of glaciers? _________________________ The high ice temperature results in an excess of ____________________ In the polar regions and at high altitudes , where mean annual temperatures are below freezing, the ice temperature is always low , with very little melting. What do we call these types of glaciers? _________________________ Both categories of glac ier can vary in shape and s ize, s o we classify glac iers into two main varieties based on their visible character istics . These are: 1. _ _____ ______ ______ _____ an d 2 . _ ______ _ ________ ______ __ Valley (or Alpine) glaciers resembles r ivers in that larger glaciers may have smaller glaciers flowing into them called _______________________________. How big can valley glaciers get? Length: ____________ Width: ____________ Thickness: ____________ What type of glacier is produced when a valley glacier exits a valley and spreads out over a w ide plain? ________ ______ ______ ______ __ What is another name for continental glaciers ? ________________ ( must be at least 50,000 km2 in size). If they are smaller than this , we call them _________________. Where are ice caps ty pically found? ___________________________________ How thick can ice sheets get? __________________ Where are the only two places on Earth where we see ice sheets today? ________ ______ ______ ___ and ________ ______ ______ ___ In w hat direc tion do ice sheets flow ? _____________________________________ 1 Physical Geology 101 What is the main control on the motion of ice sheets ? __________________________ Evolut ion of Glaciers Glacier size changes in response to changes in temper ature and precipitation. The amount of snow that gets added to a glacier is called ____________________. Most of this snow falls at the ____________ of the glac ier (the highest par t), which is also therefore referred to as the _____________________________. Any loss in ice and snow is an overall process called ___________________. This may occur by melting in the summer or when ice turns into vapor by ___________________. Most ablation occurs at the downward end of the glacier, or the ______________________. This part of the glacier is referred to as the _____________________________. If the glacier flows over water, blocks of ice may fall off to form _________________. The difference between accumulation and ablation determines whether the glacier has enough ice to advance or if it must recede. The difference between the two is called the ________________________. If the two are equal, the glac ier is stagnant (does n’t adv ance or recede) . How fas t do glaciers move under the influence of gravity? _______________________ Ice at the ter minus of a glacier probably took hundreds of years to reach that point s ince falling as s now at the head of the glacier. If a glacier suddenly jumps forward at rates of up to 10s of meters per day, the event is called a ________ ______ ____ . The movement of a glacier is measured by plac ing a line of markers across the surface of the glacial ice. As time passes , the markers start to move as the ice moves. Where is the motion of the glacier the fas test? ____________________________________________ What are the two types of motion of the ice within a glacier? ________ ______ ______ ___ a nd ___ ______ _____ ________ __. Int ernal flow occurs because the weight of overlying ic e causes ice crystals deep in the glacier to slide over each other along crystal planes oriented parallel to the motion direction. This process is called ______________ (a type of plastic flow motion) . At the sur face of the glacier , ice behaves in a very brittle manner, and breaks easily . So if the glac ier bends to move down a s teeper slope, the ice fractures at the surface to for m deep fissures called ________ ______ ____ . 2 Physical Geology 101 Basal sliding occurs when the ice moves by sliding along its base. This occurs when meltwater lubricates the bottom of the glacier, and may account for _____% of the overall movement of temperate glaciers. Polar glaciers only move by internal flow . Erosion by Glaciers Glaciers are capable of carrying huge amounts of sediment and may result in highly eroded landscapes. The three principal erosional processes are: • __________________ – where a glacier pushes unconsolidated sediments ahead of it like a giant snow plow. • __________________– this is where ice gets into crac ks in rock below the glacier, causing chunks of rock to be ripped off as the glacier moves forward. Feature that is produced: _______________________. Make a sketch: *(indicate which way the steep side faces relative to the ice flow direction) • __________________– this is the erosion caused by the fric tional force of the ice moving over bedrock, like sandpaper . The rock surface gets s moothed, producing a highly polished sur face called a _______________________. Grooves scratched into this sur face by rock fragments at the base of the glacier are called _____________________. Abrasion can also pulverize rock into a fine dust called ________________. Glaciers may pick up sediment through these erosional processes, or material may be blown onto the glaciers, or may fall on top through mass wasting processes along the glacial valley walls. What is the shape of a valley before it gets eroded by glaciers? _________________ What types of valleys are produced by glacier eros ion? _____________________ These valleys usually have s teep eroded w alls and flat bottoms . If it gets filled with s ea w ater after sea level rises , it is called a _____________, and can be over 1 k m deep. There are many types of erosional f eatures produced by valley glaciers : • _____________________– where a glacier sliced off the end of a ridge along the sides of a Ushaped valley. • ______________ – a bowl-shaped depression eroded into the side of a mountain at the head of a glacier. After the ice melts, the cirque may contain a small lake called a ___________. Small lakes further down the valley from the cirque are called ______________________________. • ______________– narrow ridge of rock that separates two cirques or valleys. 3 Physical Geology 101 • ______________– s teep-walled, pyramid-like mountain peak that may be surrounded by cirques eroding back into it. Example: __________________________ • ____________________ – these form along a U-shaped valley where a tributary glacier joined the more deeply eroded main valley . When the ice melts , the tributary valley is left hanging high above the floor of the main valley. Deposition by Glaciers Any material depos ited direc tly by glac iers can be refer red to as _______________ (also called ___________). It has no internal layering- everything just gets dumped in a big heap of poorly sor ted sediment. Sometimes, glaciers carry huge boulders of rock to locations far away from their origin. The boulder is different to all the surrounding rocks , and is called an ______________. The sediment that is trans ported on top of a glacier is c alled ________________. The five types are: 1) ________________________ - moraine along the edges of the glacier 2) ________________________- moraine in the middle of the glacier How can you tell from look ing at a glacier how many tr ibutary glaciers joined together to for m it? __________________________________________ 3) ___________________ or ___________- moraine at the end of the glacier 4) ____________________- moraine along the base of the glacier 5) ____________________- many end moraines left behind as a glacier retreats Ice sheets may for m a type of till deposit along their bases consis ting of rounded hills like inverted teaspoons , and are called ________________. They c an be up to 50m high and 1 k m long. One s ide is steep, and faces towards the direc tion the ice came ____________. This is opposite to the steep side of a roche moutonnée (which is erosional, not depos itional). Make a sketch: Some glacial drift deposits are stratified, and usually for m in the flat-lying region in front of the glacier called an _______________________where meltw ater flows aw ay from the glacier in the for m of braided streams . Blocks of ice that fall off the front of the glacier leave depressions in the outwas h plain after the ice melts or retreats. If filled with water, they form __________________. 4 Physical Geology 101 Outwash plains may also contain long, sinuous r idges of till called ______________. Thes e are stream deposits that for med underneath an ice sheet by meltw ater flowing through ice tunnels up to 500 k m long. Finally, depressions on a glacier surface sometimes get filled w ith sediment. When the ice melts, the sediment is left behind in the form of rounded hills on the outwas h plain called _____________. 5 ...
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This note was uploaded on 01/13/2012 for the course GEOL 101 taught by Professor Williams,t during the Fall '08 term at Idaho.

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