Kilauea 1991-2002: Insights into the Cooling, Crystallization, and Hardening of Pahoehoe Lava Flows

The since 1986 (with the beginning of episode 48) activity at Kilauea has been dominated by pahoehoe lavas. The nearly continuous presence of active pahoehoe lava flows in the past decade has allowed for repeated field experiments to refine models for different aspects of the emplacement of pahoehoe lava flows. For example, in 1995 a simple field experiment was conducted to verify theoretical predictions for the cooling at the base of pahoehoe lava flows. The thermocouple temperatures from the base of pahoehoe lobes showed an unexpected increase in temperature a few minutes after the lobe was extruded. The proposed explanation was that the dynamics of crystallization led to a rapid release of latent after a few tens of degrees of super-cooling had developed. Field experiments in 1999 were conducted in which pahoehoe lobes were quenched at various points in their early cooling history, allowing the temporal progression of crystallization to be directly observed. The conclusions of this experiment will be presented. Another example is the comparison of different heat loss mechanisms determined by tuning a numerical model to match 1991-1995 radiometer and thermocouple data for the cooling of the top of pahoehoe lava flows. The results indicated that cooling by the wind was the dominant heat loss term, over the life of a pahoehoe lava flow. However, this term was extremely poorly constrained, requiring a new set of field measurements. While attempts to collect these field data started in 1995, the complexity of quantifying the turbulent airflow over active lava defeated us until 2002. The results from this series of field experiments will be presented. Theoretical and field studies of the rheology of pahoehoe flows have also been conducted. It had been suggested that a visco-elastic layer, close to the solidus temperature, controlled much of the behavior of pahoehoe lava flows. Field measurements from 1991 and 2002 on the rheological properties of the initial skin to form on pahoehoe lava will be reported on.