30. Ice and Glaciers (p )

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1 30. Ice and Glaciers (p ) Glaciers What is the definition of a glacier? Types of Glaciers The ice in glaciers can be variable in temperature. 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 glacier can vary in shape and size, so we classify glaciers into two main varieties based on their visible characteristics. These are: 1. and 2. Valley (or Alpine) glaciers resembles rivers 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 wide plain? What is another name for continental glaciers? (must be at least 50,000 km 2 in size). If they are smaller than this, we call them. Where are ice caps typically found? How thick can ice sheets get? Where are the only two places on Earth where we see ice sheets today? and In what direction do ice sheets flow? 1

2 What is the main control on the motion of ice sheets? Evolution of Glaciers Glacier size changes in response to changes in temperature and precipitation. The amount of snow that gets added to a glacier is called. Most of this snow falls at the of the glacier (the highest part), 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 glacier is stagnant (doesn t advance or recede). How fast do glaciers move under the influence of gravity? Ice at the terminus of a glacier probably took hundreds of years to reach that point since falling as snow 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 placing 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 fastest? What are the two types of motion of the ice within a glacier? and. Internal flow occurs because the weight of overlying ice 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 surface of the glacier, ice behaves in a very brittle manner, and breaks easily. So if the glacier bends to move down a steeper slope, the ice fractures at the surface to form deep fissures called. 2

3 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 cracks 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 frictional force of the ice moving over bedrock, like sandpaper. The rock surface gets smoothed, producing a highly polished surface called a. Grooves scratched into this surface 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 erosion? These valleys usually have steep eroded walls and flat bottoms. If it gets filled with sea water after sea level rises, it is called a, and can be over 1 km deep. There are many types of erosional features produced by valley glaciers: where a glacier sliced off the end of a ridge along the sides of a U- shaped 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

4 steep-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 deposited directly by glaciers can be referred to as (also called ). It has no internal layering- everything just gets dumped in a big heap of poorly sorted 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 transported on top of a glacier is called. 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 looking at a glacier how many tributary glaciers joined together to form 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 form a type of till deposit along their bases consisting of rounded hills like inverted teaspoons, and are called. They can be up to 50m high and 1 km long. One side is steep, and faces towards the direction the ice came. This is opposite to the steep side of a roche moutonnée (which is erosional, not depositional). Make a sketch: Some glacial drift deposits are stratified, and usually form in the flat-lying region in front of the glacier called an where meltwater flows away from the glacier in the form of braided streams. Blocks of ice that fall off the front of the glacier leave depressions in the outwash plain after the ice melts or retreats. If filled with water, they form. 4

5 Outwash plains may also contain long, sinuous ridges of till called. These are stream deposits that formed underneath an ice sheet by meltwater flowing through ice tunnels up to 500 km long. Finally, depressions on a glacier surface sometimes get filled with sediment. When the ice melts, the sediment is left behind in the form of rounded hills on the outwash plain called. 5