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 © ALPINE GLACIERS

  Many times in the earths history glaciers have expanded and retreated do to climate change and small changes in the earths orbit of the sun. Some scientists think the suns out put of energy was lower at times. Today we are living in an interglacial period of warmer conditions but 25,000 to 13, 000 years ago during the Pleistocene time the climate was colder than today. Lake Bonneville filled most of the valleys in west central Utah. One of the lake filled valleys now called Salt lake valley butts up against the Wasatch Mountains along the Wasatch fault system. A canyon called little cottonwood canyon at the south east extremity of Salt lake valley was filled by an Alpine glacier during the time of lake Bonneville. This canyon shows many signs of containing a glacier. The first thing you notice as you drive up or down the canyon is how straight the canyon is compared to other mountain canyons with winding curves. The next thing you notice is how broad the canyon is and how much the canyon profile resembles a U rather than the normal V shaped river cut canyon, this is some times referred to as a glacial trough.

Many boulders are found through out the canyon and have been removed to a different location by glacial quarrying. Alpine glaciers are formed from the yearly build up of snow high in the mountains at a hollow in the mountain side called a cirque. shown below


As the snow becomes deeper and deeper the lower part of the snow becomes ice the ice starts to flow because of the weight on top of it and because gravity starts to pull down on the glacier as well. Another factor is the steep slopes the glaciers forms on which accelerates the flow of the glacier. As the glacier moves down the canyon it picks up abrasive debris such as medium to large rocks and smaller sediment such as clay and sand and small pebbles. With the movement of the glacier this sediment scourers the rock at the sides and bottom of the glacier till the load becomes too great. Deposition occurs along the path of the glacier forming long narrow mounds called moraines. A terminal moraine forms at the foot of the glacier. A lateral moraine forms at the side or sides of a glacier. Shown below  the letters a,b,c are earthquake fracture zones called faults cutting across a lateral moraine that formed at the mouth of the canyon were the glacier would have entered Lake Bonneville
 


When this glacier met the waters of Lake Bonneville at the mouth of the canyon large chunks of the glacier fell or broke off in to Lake Bonneville forming small icebergs that floated in the icy cold waters of the lake. Some times large rocks were caught up in the small icebergs and when the iceberg melted it dropped its load of rock far out into the valley. notice the large rock field at the left of the picture

 

These large chunks of rock are called erratics. When the glacier began to melt  at the foot of the glacier large amounts of water was discharged from the glacier some times the water was milky white in color and is sometimes known as glacial milk.
 



The great volume of water discharge from this canyon and other drainage systems around Lake Bonneville filled it to over flowing. Many wild Pleistocene animals live near and around the lake like the wooly mammoth, early camels, musk ox and huge bison as well as saber-toothed cats.