MEASUREMENTS OF THE COOLING AT THE BASE OF PAHOEHOE FLOWS

Temperature measurements were made in August and October of 1994 at th e base of small active pahoehoe flow lobes on Kilauea Volcano, Hawai'i . Surprisingly, after about 2 minutes of initial rapid cooling, the ba sal temperatures increased significantly before resuming a slower cool ing trend The recorded temperatures are also warmer than those predict ed by simple conductive cooling models. Preliminary calculations sugge st that these observations can be explained by the insulating effect o f microfractures in the underlying flow and the kinetics of crystalliz ation. The initial cooling may be rapid enough to supercool the lava s uch that the onset of crystallization is delayed. When crystallization does begin, it is initially rapid, releasing sufficient latent heat t o re-heat the lava. As the system equilibrates, the now resumes a slow cooling.