Initial Publication Date: August 18, 2014

Mountains of Ice

Part A: Glaciers and Ice Sheets

Our warming atmosphere and changing weather patterns are causing ice all over our planet to melt at an alarming rate. The Arctic sea ice is melting at twice the rate of any region on Earth. It is dwindling at a rate of more than 10% per decade. If that rate continues, the Arctic will be ice-free by 2030. The impacts of dwindling ice cover in the Arctic are far reaching, from the extinction of many animal species, to enhanced global warming, and to the weakening or shutdown of global ocean circulation.

Mountain glaciers, a significant depository of our fresh water supply, are melting at an unprecedented rate. Recently, scientists have estimated that the large glaciers in Glacier National Park will disappear entirely by 2020 if melting rates continue at the present rate.

First, watch the video of a Retreating Glacier and answer the following questions.

Stop and Think

1. What do you think happens to all the sediment being carried by the glacier?

2. What happens to the edge of the glacier as it advances and reaches the ocean?

During the Pleistocene, the Cordilleran ice sheet covered much of the northwestern part of the Northern Hemisphere, including most of Southern Alaska and extending into the Gulf of Alaska. At the same point in geologic time the Laurentide ice sheet blanketed the eastern part of the Northern Hemisphere, covering Michigan, Chicago, and New York. Expedition 341 scientists will analyze sediment cores from Alaska to gain a better understanding of the maximum extent of the northwestern Cordilleran ice sheet. In addition, scientists will analyze the glacial/interglacial depositional sequences to better understand the timing of the advance and retreat of this massive ice sheet.

As an ice sheet travels over continental areas, it erodes the underlying rock by two processes: abrasion the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion. and plucking a glacial phenomenon that is responsible for the erosion and transportation of large blocks of bedrock. As a glacier moves down a valley, friction causes the ice at the bottom of the glacier to melt and infiltrate joints in the bedrock.. As the thick layer of ice pushes against the underlying rock, it scrapes and polishes the rock surface below. As glaciers flow, they scratch and erode the landscape below with the sediment and rocky material they are carrying. Also as the ice sheet slowly moves over the rock, glacial melt water seeps into cracks and fractures of the underlying rock. As the water freezes, it pushes pieces of rock out of the underlying rock surface. These pieces of rock get plucked out and carried away by the flowing ice of the moving glacier. The ice sheet essentially acts like a giant bulldozer pushing up and carrying enormous amounts of sand, dirt, and rocks.

Now that you know a little more about glacial activity, watch the following Ice Sheet Animation video that shows how the ice sheets covering North America have receded over the past 11,000 years. Pause the video as needed to note the date and status of the ice sheet.

Laurentide Ice Sheet from CSDMS

Finally, run the video again and pause it at 32 seconds, and then answer the question below.

Stop and Think

3. What is the location of the last remnant of the Cordilleran ice sheet?