Probing – 18 Radioisotopes and Nuclear Weapons

Probing the Depths of Crater Lake: A Century of Scientific Research by Douglas Larson


Deep-sea Nansen-type water bottle. Photo courtesy of the National Park Service

Their purpose was to determine whether the fallout of tritium, strontium-90, and other radioisotopes associated with nuclear weapons testing was greater over oceans than over land. Volchok and other investigators considered Crater Lake an ideal study site. The lake’s surface area comprises nearly 80 percent of the entire drainage basin, and only about 0.5 percent of the lake’s total volume is lost to seepage each year. They also believed that the lake mixed entirely each year, which meant that the tritium content could be estimated during any season. The total strontium-90 in lake water and sediments was estimated at 4.2 curies, roughly equivalent to the amount of strontium-90 reported for land areas around the lake and elsewhere in Oregon. (33)  In August 1966 and again in July 1969, Raymond Smith and John Tyler of Scripps measured the distribution of natural light to a depth of 330 feet using an instrument called the Scripps spectroradiometer, which Tyler had originally tested at Crater Lake in 1965. Their optical measurements confirmed earlier reports about the lake’s exceptional water clarity and provided precise baseline data, which gave future scientists information so they could determine how and to what extent the lake’s optical properties might have changed.

In February 1971, Victor Neal, Stephen Neshyba, and Warren Denner-oceanographers from OSU-became the first scientists to conduct research on the lake during winter. Theirs was a difficult and hazardous task. They had to negotiate a single, precipitous trail that switchbacked for over a mile down the steep caldera wall while facing storms with high winds and poor visibility The snow was as much as fifty feet deep, and there was a constant threat of avalanches. The team had visited the lake over the previous two years to make precise measurements of the lake’s seasonal temperature gradients.(35)  This initial winter data provided a better understanding of the lake’s yearly temperature characteristics and effects, particularly about why the lake rarely froze over and whether lake temperatures were uniformly low at all depths throughout the winter. By June 1971, however, this work and Donaldson’s limnological program came to an end, apparently due to a lack of adequate funding.

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