2000 MULTIBEAM SONAR SURVEY OF CRATER LAKE, OREGON

Crater Lake, the deepest lake in the United States, occupies a caldera in Mount Mazama, a Cascade Range volcano that once stood about 3,700 meters (12,000 feet) above sea level (Figure 1). About 7,700 years ago in a catastrophic eruption that lasted only a few days, Mount Mazama ejected about 50 cubic kilometers (12 cubic miles) of magma in the form of pumice and ash. Near the end of the eruption, the mountain collapsed upon itself to form a large caldera. After this climactic event, volcanic activity resumed within the caldera, creating Wizard Island and other new landforms. All but the uppermost portion of the Wizard Island volcano is hidden from view below the surface of Crater Lake.

Figure 1. Location of Crater Lake in the Cascade Mountain Range, Oregon, USA

Until recently, nobody knew what the bottom of Crater Lake looked like in detail. The first indications of the lake depths came from an 1886 survey by a joint USGS/U.S. Army expedition led by William G. Steel and under the direction Maj. Clarence E. Dutton (Dutton, 1889). This mapping survey collected 186 soundings using a Millers lead-line sounding machine. A better indication of the lake depths came from a 1959 survey by the U.S. Coast and Geodetic Survey. This survey used an acoustic echo sounder and radar navigation to collect 4000 soundings. The data were contoured by Williams (1961) and Byrne (1962) and resulted in a fairly detailed map of the large-scale features within Crater Lake. By the late 1990`s however, maps generated from this survey were proving inadequate for the scientific research being conducted in and around the lake.

In the summer of 2000, the U.S. Geological Survey, Pacific Seafloor Mapping Project in cooperation with the National Park Service and the Center for Coastal and Ocean Mapping, University of New Hampshire used a state-of-the-art multibeam sonar system to collect high-resolution bathymetry and calibrated, co-registered acoustic backscatter to support both biological and geological research in the area (aquatic biology, geochemistry, volcanic processes, etc). This survey collected over 16 million soundings and the resulting data portrays the bottom of Crater Lake at a spatial resolution of 2 meters. For more information about the multibeam sonar system and the survey please see USGS Open-File Report 00-405.

For more information about Crater Lake including spatial data downloads, visit the Crater Lake Data Clearinghouse.

Also, two large-format, color maps of Crater Lake can be purchaced from the USGS. The map series is entitled "Bathymetry and Selected Perspective Views of Crater Lake Oregon, USGS Water Resources Investigations Report 01-4046". The maps show the same perspective views seen in the Perspective Views section of this CD-ROM. To purchase the maps contact;

USGS
Information Services
Box 25286
Denver, CO 80225
Telephone (888) ASK-USGS

This CD-ROM is published for the scientific community, the general public, and as a teaching tool. This CD-ROM contains the raw multibeam bathymetry and backscatter data as well as a GIS ArcExplorer 2.0 project for the scientific community to use in research. Computer-generated images and a fly-by movie allow any user to visualize the lake floor. A QuickTime movie and photographs of the helicopter operations shows how the multibeam survey took place and a list ofCrater Lake publications and related websites can be used for further Crater Lake research and general interest.

CONTENTS

To the left side of all the browser pages on this CD-ROM is a table of contents. The contents include,

INTRODUCTION - Brief history of Crater Lake and Mount Mazama, shows a location map, and briefly explains why and how the Crater Lake mapping survey took place.

ARCEXPLORER - ArcExplorer 2.0 project showing both the multibeam bathymetry and backscatter data from Crater Lake. ArcExplorer is a freeware, lightweight GIS software package published by ESRI.

PERSPECTIVE VIEWS - Selected perspective views of the bottom of Crater Lake and surrounding caldera walls generated from the multibeam survey data. Each view is accompanied by a geologic interpretation and a 300dpi TIFF image that can be downloaded by the user.

FLY-BY MOVIE - A QuickTime movie that simulates a flight around the bottom of Crater Lake to view the deepest parts of the lake, Wizard Island, Merriam Cone, and underwater landslides.

HELICOPTER MOVIE - A QuickTime movie of the helicopter transporting the RV Surf Surveyor into Crater Lake. At the time of the survey there was no boat on the lake capable of conducting the multibeam survey. The survey vessel, RV Surf Surveyor, could not be towed down the Cleetwood Cove trail, the only trail down to the lake surface and a 200-m (650-ft) elevation change. The RV Surf Surveyor had to be transported to and from the lake surface by a Chinook helicopter operated by the U.S. Army Reserve.

DATA - Multibeam bathymetry and backscatter data in XYZ format and ArcInfo GRID format with accompanying metadata.

PHOTOGRAPHS - A selection of photographs taken by the survey crew during the helicopter transport of the survey vessel into and out of Crater Lake.

PUBLICATIONS - A reference list of selected Crater Lake publications.

LINKS - Selected links to other websites about Crater Lake.

References

Byrne, J.V., 1962. Bathymetry of Crater Lake, Pregon. The Ore Bin. Vol. 24, p. 161-164

Dutton, C.E., 1889. USGS 8th Annual Report for 1886-87, Part 1: p. 156-159 (report dated Jily 1, 1887).

Williams, H. 1961. The floor of Crater Lake, Oregon. Amer. Jour. Sci. Vol 259, p. 81-83.