HR: 1340h
AN: C43C-0241    [Abstracts]
TI: Video Observations of Anchor Ice/Sediment Interactions in Two Rocky Mountain Streams
AU: * Kempema, E W
EM: kempema@uwyo.edu
AF: University of Wyoming, Geology and Geophysics , Laramie, WY 82071 United States
AU: McGee, B W
EM: cyvira@uwyo.edu
AF: University of Wyoming, Geology and Geophysics , Laramie, WY 82071 United States
AU: Pueblitz, L
EM: teleskier65@msn.com
AF: University of Wyoming, Geology and Geophysics , Laramie, WY 82071 United States
AB: Anchor ice is submerged ice that is attached or anchored to the bottom of rivers, lakes, and shallow seas. It forms in turbulent, supercooled water. In rivers, anchor ice usually forms at night and is released from the riverbed in the morning as the sun warms the water column. Released anchor ice often contains significant amounts of coarse-grained sediment. This entrained sediment can be transported (ice rafted) long distances downstream before it is released from the buoyant, floating ice back to the riverbed. Understanding sediment entrainment into anchor ice requires knowledge of the processes occurring at the sediment/ice interface. Viewing this interface through a freezing water column is a difficult task. Removing anchor ice from the water usually destroys the fragile contact between the ice and entrained sediment. In this study, we used an underwater video system to document anchor ice/sediment interactions in two small Rocky Mountain rivers. The video system allowed us to view: (1) the contact between attached anchor ice and the streambed; (2) the distribution of sediment in attached and released anchor ice masses; (3) the release of anchor ice from the bed; and (4) ice rafting of sediment in released anchor ice masses. One of the greatest benefits of the video system is the ability to see the in situ sediment distribution in attached and recently released anchor ice. Analysis of the video reveals that gravel concentrations are high on the top and bottom surfaces of anchor ice masses with relatively little gravel in the interior. The video system is not perfect for viewing ice underwater, however. The small difference between the refractive indices of ice and water makes it very difficult to discern ice crystal shapes and the exact nature of ice/sediment contacts. We are continuing to develop ways to enhance the image quality of ice crystals in water. Even with this shortcoming, the underwater video system is a very useful tool for observing in situ anchor ice/sediment relationships with minimal disturbance.
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting