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Dynamics of Earth Surface and Shallow Subsurface Process

Dynamics of Earth Surface and Shallow Subsurface Process

An erratic boulder North of Ilullisat in West Greenland, about 500 meters from the Greenland Ice Sheet margin. Ages of boulders here constrain the history of retreat of the Greenland Ice Sheet in the Holocene.

A number of noble gas isotopes are produced in geological materials exposed at the Earth's surface by interaction with cosmic rays. This provides a "label" of those materials and can be used both to date surface exposure time and to determine erosion rates. Using noble gases for surface exposure studies has two distinct advantages. First, sample size requirements (particularly for 3He) and chemical processing are substantially easier than for AMS (Accelerator Mass Spectrometry) measurements of nuclides such as 10Be, 26Al, or 36Cl. Second, because the cosmogenic noble gases are stable (21Ne and 3He are the main isotopes measured) they integrate exposure over long time periods, and this can be useful when studying old deposits or material subjected to repeated cycles of burial, exposure, and erosion, particularly in conjunction with radioactive cosmogenic nuclides. Exposure dating studies allow investigation of the rates of tectonic events in the Pacific Northwest and around the world, the dynamics of glaciers and ice caps during the last ice age and Holocene, evolution of landscapes like the Coast Range, Cascades, and Himalaya, and the development and application of new measurement techniques.