Transcript Glaciers
Glacial Processes and Landforms What is a glacier? How do glaciers form? What is a glacier? • A glacier is year-round ice on the landscape. •two types: continental ice sheets and valley glaciers How do glaciers form? • Glaciers form whenever snowfall exceeds snowmelt year after year. •The snow accumulates, gravity squishes it, and it is changed into ice Current Extent of Glaciation about 10% of land surface Maximum Extent of Pleistocene Glaciation 1/3 of land surface Most recent glacial maximum peaked 18,000 years ago and is considered to have ended 10,000 B.P. Valley Glaciers Why is a glacier the only thing that is ever coming and going at the same time? Erosion by Glaciers •striations • rocks of all sizes moved. • valley glaciers change V-shaped valleys to U-shaped. Valleys created by glaciers Fjords Deposition by Glaciers • drift is any material deposited by glaciers or their meltwater. •Till is that unsorted material that is deposited directly by ice. • Moraines are linear features deposited at bottom or along sides of glaciers. • Glacial erratics are enormous boulders transported and deposited by glaciers, often far from their source region. Moraines drumlin • Long, low, tear-shaped mounds of till formed by a glacier • Usually found in groups, clusters • Route 1 is on a drumlin; they are common in this area Transportation by Glaciers •Water in, on, and under glaciers (pluvial processes) moves much sediment as well. Franz Joseph Glacier and Outwash Plain, New Zealand Continental Glaciers or Ice Sheets • only two true ice sheets exist today: Greenland and Antarctica • where they meet the sea they can form ice sheets. • vary in thickness from hundreds of feet to two miles deep • scour away all soil and vegetation and dramatically reshape the landscape and ecology of large regions. Ellesmere Island, Canada Continental Glaciers or Ice Sheets Continental Glaciers or Ice Sheets Finger Lakes Region, New York • In its retreat, the Wisconsin glaciation left terminal moraines that form Long Island, Nantucket and Cape Cod Glacial Geology of RI • The last glacier to pass through Rhode Island approximately 10,000 years ago abruptly ended in South Kingstown. The gravel and boulders that were caught in the glacier were left in place as the ice mass retreated north. Mixed with the stone and gravel debris were massive blocks of ice that melted to form kettle ponds. The Matunuck Hills region is an excellent example of a kettle pond landscape. Most Likely Cause of Ice Ages Most Likely Cause of Ice Ages • Milankovitch cycles: 1. Shape of Earth’s orbit varies every 100,000 years from circular to elongated 2. Tilt of Earth’s axis varies every 41,000 years 3. Precession of Earth’s axis changes every 26,000 years • These cycles cause a change in amount of sun that hits the Earth History of ice ages Calving • Largest calving ever recorded MODELING GLACIERS • First go to the following website: http://phet.colorado.edu/en/simulation/glaciers • Select “Run Now.” Play around for a bit, then address the following learning prompts: 1. Explain how ice moves within a glacier; describe and illustrate flow within a glacier. 2. Explain/illustrate how glaciers (a) stay at equilibrium, (b) grow/advance, and (c) shrink/retreat; compare climatic conditions leading to each. 3. Determine and illustrate how multiple advance-retreat cycles affect the record of terminal moraines. Other glacier interactives • Learn about glaciers • Glaciers of the Himalayas: before and after • Olympic National Park glacier interactive map • Glacier feature ID quiz