Numerical modeling of lava flow cooling applied to the 1997 Okmok eruption: Comparison with advanced very high resolution radiometer thermal imagery

Abstract

Throughout February and March 1997, Okmok Volcano, in the eastern Aleutian Islands of Alaska, erupted a 6‐km‐long lava flow of basaltic ′a′a within its caldera. In the first part of the study a numerical model for lava flow cooling was developed by Patrick et al. and applied to the flow to better understand the nature of its cooling. In this second part of the study, the model predictions for lava surface temperature over a 200‐day cooling period were compared to advanced very high resolution radiometer (AVHRR) thermal imagery. Various methods were used to extract the subpixel lava temperature from the AVHRR pixel‐integrated values, including the dual‐band method and pixel merging. Inherent to these approaches is the multicomponent modeling of the lava surface temperature. Whereas active flows have been shown to have several thermal components, so, too, do flows undergoing extended cooling. Because of the dependence of the methods on the AVHRR instantaneous field of view (IFOV), the scan‐dependent IFOV dimensions and overlap values were considered. Results from Patrick et al. indicate that convective heat loss from the surface largely controls surface temperature during extended cooling, but the functions governing this heat loss mechanism are poorly understood. AVHRR‐derived temperatures from this part of the study suggest that values for the convective heat transfer coefficient for this flow were most commonly between 50 and 100 W m−2 K−1 and generally above 25 W m−2 K−1. These results are in agreement with previously measured values from the field but are significantly higher than those assumed in other remote sensing studies of cooling lava. Also, the AVHRR data corroborate the modeled prediction of seasonal warming of the lava surface.