Analysis of surface processes using SAR data: Westdahl Volcano, Alaska

Abstract

Seasat, Earth Resource Satellite (ERS-1) and Japan Earth Resource Satellite (JERS-1) Synthetic Aperture Radar (SAR) data were used to investigate surface geomorphic and topographic changes caused by volcanic eruptions of Westdahl Volcano, Alaska. This volcano is located at the west end of Unimak Island, Alaska, approximately 1200 km southwest of Anchorage. This remote, ice-capped volcano has erupted three times in the last 34 years. The eruptions have melted portions of the ice-cap which have been replenished by winter snow. Changes in terrain were studied by comparing seasonal and inter-annual SAR data acquired over a 17 year period prior to, during and after two eruptions. The SAR data provided a record of geological and environmental processes between 1978 and 1995. Time sequential data recorded the formation of landforms and subsequent burial by snow. A series of winter images showed that changing environmental conditions, thought to be predominantly snow moisture, influence the detection and ability to analyse landforms, such as lava flows, by affecting the contrast between features and surrounding ground. Backscatter values of lava flows indicate that it would be difficult to distinguish them solely by radiometric response due to seasonal and annual fluctuations. A colour composite, formed using multi-temporal data, improved the detection of landforms and surface changes related to the eruption as well as environmental changes during the winter.