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Disenchantment Bay

Two people in a boat at a glacier
Lieutenant JG Laurel Jennings and Survey Tech Matt Boles of the Rainier conduct a CTD cast near the face of Hubbard Glacier. CTD casts measure temperature, salinity and pressure in the water column and are used to estimate sound speed through water. The change in sound speed through water is one of the correctors applied to multi-beam echo sounder data to improve depth accuracy.

In September of 2006, the NOAA Ship Rainier conducted a special hydrographic survey of Disenchantment Bay located just north of the town of Yakutat, AK per request of scientists from the University of Alaska and the USGS. Disenchantment Bay is home to Hubbard Glacier, the largest tidewater glacier on the North American Continent. Multibeam sonar systems mounted on the Rainier and her launches were used to collect bathymetry data near the face of the glacier.The survey was conducted to assess any changes in seafloor topography following the substantial advancement of Hubbard Glacier in recent years. Disenchantment Bay was last surveyed by the Rainier in 1999, and since that time, the glacier face has advanced significantly beyond the charted terminus, up to 600 meters at some locations.Hubbard Glacier is a popular tourism destination, and is visited frequently by large cruise ships in the summer season.

Hubbard Glacier has been advancing seaward for about a century. In July of 2002, the glacier’s terminal moraine pushed forward far enough to dam the entrance to Russell Fjord.The dam was breached that August following a period of heavy rains.

When the dam between Russell Fjord and Disenchantment Bay burst, the powerful flood of water washed out the sediment from the terminal moraine blocking the fjord. The Rainier was tasked specifically to map the bottom near Gilbert Point to determine how significantly the redistribution of sediment had changed the topography of the sea floor following this major geologic event.

Dr. Roman Motyka, a Research Professor at the University of Alaska Fairbanks was on board the Rainier during survey acquisition. He hopes to use the collected bathymetry data to improve the accuracy of computer models developed to predict the advancement and recession of the Hubbard Glacier. Using the model it may be possible to predict if and when the glacier will next close Russell Fjord. If Russell Fjord were to become dammed permanently by the glacier, the resulting brackish lake could overflow it’s southern bank and drain into the Situk River. The people of Yakutat depend on the Situk River and its world class trout fishery to sustain tourism and the local population.

 A Digital Terrain Model (DTM) of the ocean floor colored by depth generated from RAINIER bathymetric data overlaid on chart 16761 and satellite-acquired Synthetic Aperture Radar (SAR) imagery.
A Digital Terrain Model (DTM) of the ocean floor colored by depth generated from Rainier bathymetric data. The DTM is overlaid on chart 16761 and satellite-acquired Synthetic Aperture Radar (SAR) imagery supplied to the ship by Bill Pichel from NESDIS. If you look closely at the bottom right hand corner of the DTM graphic you will see a white spot on the SAR image, the Rainier as seen from outer space.

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