In parallel, field studies are being conducted on the Ito pyroclastic flow deposit in Japan, which was deposited over a vast area of extremely rugged landscape, and at two volcanoes in Italy. Figure 1 shows one of the fossil hydrothermal systems that we are using as an analog for hydrothermal processes at Yucca Mountain. The original depth of the dike was about 300m. The dike was injected into silicic tuffs, mainly ash fall and flow beds, which make up the white exposures in the foreground. Heat and volatiles from the cooling dike drove hydrothermal circulation of groundwater, which in turn altered the mineralogy and chemistry of the tuffs.
Altered tuffs form the orange-colored patches on either side of the dike.
The background ridge is an uplifted block of tuff, much like Yucca Mountain itself, into which the dike extends. Field, analytical, and numerical modeling approaches are being combined to understand the extent and nature of this hydrothermal system and other similar analogs, in order to improve our predictions of hazards to the potential Yucca Mountain repository. Colors represent magma temperature. The initial Rayleigh number is approximately 5 x 107. The bottom half of the chamber is thermally stable.