Experimental Recreation of the Sub-Glacial System, an Analysis of Hold Time versus Strengthening to Shed Light on the Mechanics of Stick-Slip Ice Streams

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2015-04-14
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McBrearty, Ian
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Geological and Atmospheric Sciences

The Department of Geological and Atmospheric Sciences offers majors in three areas: Geology (traditional, environmental, or hydrogeology, for work as a surveyor or in mineral exploration), Meteorology (studies in global atmosphere, weather technology, and modeling for work as a meteorologist), and Earth Sciences (interdisciplinary mixture of geology, meteorology, and other natural sciences, with option of teacher-licensure).

History
The Department of Geology and Mining was founded in 1898. In 1902 its name changed to the Department of Geology. In 1965 its name changed to the Department of Earth Science. In 1977 its name changed to the Department of Earth Sciences. In 1989 its name changed to the Department of Geological and Atmospheric Sciences.

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1898-present

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  • Department of Geology and Mining (1898-1902)
  • Department of Geology (1902-1965)
  • Department of Earth Science (1965-1977)
  • Department of Earth Sciences (1977-1989)

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Symposium on Undergraduate Research and Creative Expression
Iowa State University Conferences and Symposia

The Symposium provides undergraduates from all academic disciplines with an opportunity to share their research with the university community and other guests through conference-style oral presentations. The Symposium represents part of a larger effort of Iowa State University to enhance, support, and celebrate undergraduate research activity.

Though coordinated by the University Honors Program, all undergraduate students are eligible and encouraged to participate in the Symposium. Undergraduates conducting research but not yet ready to present their work are encouraged to attend the Symposium to learn about the presentation process and students not currently involved in research are encouraged to attend the Symposium to learn about the broad range of undergraduate research activities that are taking place at ISU.

The first Symposium was held in April 2007. The 39 students who presented research and their mentors collectively represented all of ISU's Colleges: Agriculture and Life Sciences, Business, Design, Engineering, Human Sciences, Liberal Arts and Sciences, Veterinary Medicine, and the Graduate College. The event has grown to regularly include more than 100 students presenting on topics that span the broad range of disciplines studied at ISU.

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Geological and Atmospheric Sciences
Abstract

Ice streams in Antarctica are known to move ice rapidly, in a narrow band, over a loose permeable substrate to the sea- contributing to sea-level rise and the decay of the Antarctic Ice Sheet. It has been observed that some of these ice streams move in a “stick-slip” fashion, lurching ahead small steps at a time. Past workers have proposed this observation is indicative of temporal strengthening in the ice stream when it’s sitting at rest, but have not satisfactorily concluded which components of the glacial system are directly causing the strengthening. To understand the mechanics dictating ice stream motion, and in turn put better constraints on predictions regarding the continued decay of the Antarctic Ice Sheet, we have resorted to experimentally recreating the sub-glacial system in the lab, in two “ringshear” devices designed by Dr. Iverson at Iowa State University. Two main questions we wanted answered were: (A) “Do we observe a significant relationship between hold time and strengthening?” and (B) “Which component(s) (ice, water, and sediment) contribute to the strengthening, and by how much does each contribute?” To do this we ran a suite of “slide-hold-slide” experiments, in each case adding one more component of the glacial system, where time held still (corresponding to the “stick” phase of motion), was measured against the maximum strength the material achieved upon forcing it to undergo further shear (corresponding to the “slip” phase of motion). Our results indicate that there is indeed a significant relationship between hold times and strengthening, and that all three components (ice, water, sediment) contribute to strengthening- however, with each component contributing differently depending on how long of a hold time they have undergone. These results are in agreement with first order physical principles, but further work is required to develop the mathematical relationships relating strengthening to hold time for each component of the system.

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