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. The upper half is unstable, so that plumes of cool fluid sink from the roof toward the floor, where they stagnate. Upwelling is very weak. As the magma cools the dominant plumes are frozen in place, producing lateral temperature variations that may be preserved as crystal size variations in the geologic record.