Lava volume from the 1997 Eruption of Okmok volcano, Alaska, estimated using spaceborne and airborne interferometric synthetic aperture radar

Interferometric synthetic aperture radar (InSAR) techniques are used to calculate the volume of eruption at Okmok volcano, Alaska by constructing precise digital elevation models (DEMs) that represent volcano topography before and after the eruption. The pre-eruption DEM is generated using TOPSAR data where a three-dimensional multiaffined transformation is used to account for the misalignments between different DEM patches. The post-eruption DEM is produced using repeat-pass ERS data; multiple interferograms are required to reduce errors due to atmospheric contribution. The eruption volume associated with the 1997 eruption of Okmok volcano is 0.165±0.028 km. The thickest portion is ~50 m, although field measurements of the flow margin's height don’t exceed 20 m. Therefore, the in-situ measurements at lava edges are not representative of total thickness and precise DEM data are absolutely essential to calculate eruption volume based on lava thickness estimations. This is an example that demonstrates how InSAR will play a significant role on studying arctic volcanoes. INTRODUCTION Estimating eruption volume is a critical component of volcanology. Accurate mapping of the erupted material is valuable for constraining magma supply and understanding magma plumbing system [e.g., Wadge 1977; Crisp 1984; Dvorak and Dzurisin, 1993; Rowland et al., 1999]. Calculating eruption volume requires accurate mapping of the preand post-eruption digital elevation models (DEMs). In the absence of high-precision DEMs, the eruptive volume is often calculated by multiplying the extent of new lava and the average thickness of the eruptive material, estimated at several points along the lava edges. Therefore accurate calculation of the eruptive volume has been generally not feasible. For Alaska volcanoes, the remote locations, difficult logistics, and persistent