The dipping reflections are truncated by a sharp unconformity at approximately 200 to 250 nanoseconds and are buried by younger material, most of which was probably deposited by a large flood in 1983. Prior to the work in Medicine Lake, it was outfitted with a new system for collecting high-resolution profile data and a canvas covering to protect instruments and operators from the hot sun. Medicine Lake, located in Siskiyou County in northern California, sits at an elevation of about 7,000 ft, within the ancient caldera of the Medicine Lake volcano complex. The most recent Medicine Lake volcano eruption occurred about 0.9 ka. At least 17 eruptions have occurred since 12 ka, or between one and two eruptions per century on average.
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The reflection data were particularly interesting, revealing structure to 40 m and more beneath the lake bottom. The lake sediments proved, unfortunately, relatively impenetrable to the small hand-coring instruments available, and further investigation will have to await a vibracoring effort planned for next year. Once the lake sediments are sampled, USGS researchers hope to use them to unravel the volcanic and climate history of the region and the geochemical behavior of mercury in volcanic terrains. Medicine Lake is a popular camping and fishing spot, and considerable public interest has been expressed in a new bathymetric map to replace the old one that dates back to 1955. Using the bathymetric data collected last September, we have just completed such a map, soon to be published.