A combination of field experiments and numerical modeling will be used to study three specific aspects of the freezing of basalts: (1) the cooling effect of wind, (2) the hardening of the crust on a flow, and (3) dynamic crystallization within the flow. The ongoing eruption of Kilauea volcano is expected to continue to provide an excellent natural laboratory for the field experiments. The numerical modeling is necessary to translate the findings in Hawai'i to basaltic liquids in general. Cooling by the wind is the dominant heat loss mechanism for pahoehoe lava flows, but the actual heat fluxes are only very poorly constrained - to no better than a factor of two. A new set of instrumentation, based on hot-wire anemometers, will allow heat flux estimates to be improved by about an order of magnitude. The rheology of the crust on a lava flow is more important in controlling its motion than the theology of the pure liquid. An improved penetrometer will be used to obtain field measurements of the hardening of the crust on pahoehoe lobes. While work on the cooling and crystallization of lava lakes has provided vital new information to link laboratory studies to ancient rocks, relatively little has been done with the more rapidly cooling lava flows. In these flows the effects of dynamic crystallization are readily observed. These observations will be quantified by a combination of in situ measurements and detailed petrographic studies of samples from active flows to place "real-world" constraints on thermodynamic variables measured in the laboratory. Overall, the field experiments will be used to constrain a numerical model for pahoehoe lobes that includes cooling, crystallization, and motion. The individual components of this model will be constructed to be transportable to models for the freezing of basaltic liquids in other situations.
