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Glaciers We wouldn’t be here without them. What are glaciers? A Glacier is an accumulation of snow that is large enough to survive the summer melt. How do these large masses of ice move? These large ice masses begin to move down hill by gravity. It can move several centimeters to several meters a year depending on its size. The steeper the slope or the warmer the temperatures the faster the rate. These glaciers will settle into lower lying areas as they move. The two types of glaciers we will talk about are alpine glaciers and continental glaciers. Alpine glaciers : • Are found at high elevations • Are found at high latitudes. (North or South Pole) • Move downhill into valleys • Carve out U-shaped valleys Why would high mountain tops be a good place to find a glacier? What side of a mountain in the northern hemisphere is more likely to have the glacier? • It is colder at the top of a mountain. • The north side is in the shade all day. Why is this glacier dirty? It picks up the dark sediment as it moves over the landscape. What will happen when a glacier rubs against the side of the valley? Material will be removed from the side causing a lateral moraine. Because there is friction on the sides of the glacier, the middle is the fastest, just like a river. What happens when two alpine glaciers meet into one valley? • One large glacier will form • A section of unsorted material will form in the middle called a medial moraine. Medial moraines What type of valley is formed from an alpine glacier? The U-shaped valley starts as a Vshaped river valley. The glacier moves in. When the ice melts, a U-shaped valley is left behind. U-Shaped Valley What happens when glaciers meet water? Icebergs are large pieces of glacier that break off into the water. Continental Glaciers are also known as ice sheets. These large sheets can cover thousands of square miles and are responsible for most of the features we see in New York State and Long Island. They are different than alpine glaciers because they do not need to be at high altitudes or on the north side of a mountain When continental glaciers move across the landscape they pick up a lot of material and move forward. This is called advancing. When the glacier stops moving forward, they will melt, this is called retreating. The material left behind will be left in unsorted piles called terminal moraines Long Island was formed in this manner Most continental glaciers have advanced and retreated many times. How was Long Island formed? Unsorted piles of sediment called moraines were deposited when the glaciers started to melt or retreat. When a glacier moves it carries the material from one place to another. • This is called transported soil Once any type of glacier moves over the landscape, it leaves behind a path of deeply scratches rocks. These scratches called striations are caused by rocks already suspended in the glacier scratching the ground rock by abrasion. Striations What causes these scratches or straitions in the rock? Material trapped in the glacier is dragged over the surface and scratches it. Glaciers also drop unsorted material called till into piles. Then the glacier advances over them. These piles are called drumlins. Drumlins These piles are unsorted and unlayered Deeper and steeper on the side the glacier came from, usually they come from the north and move south. As the ice passes it rips out large portions of the ground. When the ice melts, these holes fill with water. This other glacial feature is called a Kettle Lake. Lake Ronkonkoma is a kettle lake. The ice sheet advanced to the where the middle of Long Island is today. The middle of Long Island is where you will find the moraines. All areas south are called outwash plains (flood plains), where the meltwater flowed. These are areas where the landscape is flat and the area is fine sediment. There are very few natural, large boulders. This sandy, silty, milky looking water is called outwash. This material formed the land we live on today. Outwash Plain Remember we said the glaciers deposit material in unsorted piles. This is because all different size particles can be carried by a glacier. Every once in a while we find large boulders that don’t fit in with the surrounding material. These are called Erratics. Glacial erratics do not match the surrounding bedrock. Here is the whole picture all together. Why can’t you find any glaciers in New York State today? The ice and snow all melts during the summer. What is the difference between transported soil and residual soil? Transported soil was deposited by an agent of erosion. What is a glacial erratic and why are they not found around here? A glacial erratic is a larger boulder left behind by a glacier that does not match the surrounding bedrock. You don’t find them around here because we are located on an outwash plain and the meltwater was not strong enough the carry the large rocks.