Spring Multibeam Cruise in Glacier Bay Provides Spectacular Images
Paul Carlson and Andy Stevenson of CMG Menlo Park joined Philip Hooge and four other biologists
from the BRD Glacier Bay Field Station on a 9-day cruise (May 28th-June 5th) that acquired superb
multibeam imagery from Glacier Bay, Alaska. The scientists collected data at resolutions of 5 m
per pixel and better using a RESON SeaBat 8111 system on the M/V Davidson, a former NOAA vessel.
The cruise was funded by a joint GD-BRD grant (to Hooge and Carlson) plus an equal share of the
cost provided by Glacier Bay National Park. The GD-BRD cruise was linked to a preceding cruise
off Southeast Alaska financed by the Alaska Department of Fish and Game, and a subsequent cruise
off the Semidi Islands financed by NOAA. These cooperative ventures were mutually productive
because of the high mobilization costs for work in Alaskan waters. Contractor Thales GeoSolutions
(Pacific), Inc., of Anchorage collected the data on all three cruises. Bathymetric data are already
under study, and co-located backscatter data are being edited and prepared by the contractor.
Map of Alaska and Glacier Bay. Red lines show glacial terminus positions and dates during retreat of the
Little Ice Age glacier. Green polygon outlines approximate area mapped by multibeam system in
Previous sidescan-sonar data had given some indication of the geomorphic complexity of the floor
of Glacier Bay, but none of the project members had any idea of the widespread nature of Little Ice
Age gouges in the lower bay. The gouges in the lowermost portions of Glacier Bay are shown in the
multibeam image of Sitakaday Narrows (see image below). Sidescan-sonar imagery from Whidbey Passage,
collected in 1998 as part of a study of benthic habitats, first revealed the presence of complex
iceberg-gouge patterns in gravelly mud in more than 100 m of water. Some gouges are >10 m wide,
>800 m long, and 1 to 2 m deep. The glacier that filled Glacier Bay during the Little Ice Age began
its retreat from the mouth of the bay more than 200 years ago and has exposed a magnificent fjord
system about 100 km long. The massive glacier retreated past Sitakaday Narrows ~190 years ago,
retreated past Whidbey Passage ~160 years ago, and reached the upper end of the main bay by 1860
(~140 years ago). There the glacier bifurcated and the multibeam data set terminates. The amount
of fine sediment reaching the lower bay is largely restricted to local runoff and plankton debris.
In addition, the currents through Sitakaday Narrows can be as fast as 7 kt, scouring the bottom of
fine sediment. So a long history of morphologies is clearly visible on the bottom.
Numerous iceberg gouges are visible in this multibeam image of the bathymetry of the moraine and
adjacent fjord floor in Sitakaday.
The multibeam data collected in the recent cruise will be used in a joint study of the biological
and physical characteristics of bay-floor habitats, especially as related to Dungeness crab and halibut.
Results of the study will provide guidance to the National Park Service in its management of recreational
and commercial fishing in the Bay.
in this issue:
Mapping Puget Sound
Biscayne Nat'l Park
Glacier Bay Cruise
GIS Group Teaches Science
Geologic Discipline EMAC
Closing the Circle
NAGT Summer Interns
Woods Hole Interns
Jerry Parker Memorial
Gaye Farris Re-Elected to STC Exec Board
"Natural Gas Hydrates" Book
July Publications List