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Kadko, David C.

Dr. David C. Kadko

University of Miami
Miami, FL

My research interests lie in utilizing naturally occurring radioactivity for the purpose of tracing the pathways and discovering the rates of various earth processes. Because naturally occurring radioisotopes have half-lives ranging from seconds to many years, it is possible to study processes that encompass a great variety of temporal and spatial scales. This has also given me the opportunity to be involved in studies crossing over different disciplines of earth science.

One area of interest has been the study of geochemical processes associated with the mid-ocean ridge spreading systems. I have used radioisotopes to constrain the residence time of the hydrothermal fluid within the ocean crust, to evaluate the chemical changes within the spreading hydrothermal effluent plume, and to examine the growth rate of associated sulfide deposits. A complementary project involves study of the crustal residence time of fluids circulating through hydrothermal systems of Iceland. Significantly, the ready availability of subsurface rock samples from drill holes throughout Iceland offers a striking advantage over similar studies in submarine areas where inability to access subsurface rock samples necessitate assumptions regarding initial isotopic ratios used in residence time calculations. Such a problem is obviated in Iceland where there are extensive collections of samples from the surface to hundreds of meters depth. In addition, I have utilized an in-situ gamma detector within well waters of Iceland to perform remote, detailed, time-series measurements of radon gas. Previous work has shown that radon measurements have great potential as an earthquake prediction tool. A gamma detection system (measuring radon by proxy) allows measurements to be made without the need for on-site sampling. Figure 1 shows how air pressure affects crustal strain, which in turn alters the radon activity of the borehole fluids from the Selfoss geothermal site in 2003. Figure 2 shows similar, but expanded results from Selfoss in July 2004. The effect of earthtides on crustal strain and radon is noted. It is anticipated that these techniques can be readily transferred to other geothermal locations.