This project is an oblique photogrammetric survey of the 2004-2007 dome-building eruption of Mount St. Helens volcano with two primary objectives: (1) to evaluate the potential of a new rapid and low-cost technique to create digital elevation models (DEMs) and subsequently calculate dome volumes and extrusion rates at Mount St. Helens; and (2) to attempt to understand mechanics associated with lava dome extrusion and collapse by analyzing volumetric and extrusion rate measurements in the context of dome height measurements, seismicity data, and migration of the locus of dome growth.
The new method uses sets of oblique aerial photographs, acquired from a helicopter with a standard digital camera, and commercially available photogrammetry software to create DEMs. Twelve sets of overlapping digital images from November 2004 to April 2007 of the growing dome inside the crater of Mount St. Helens were used to produce DEMs. Analyses of the digital images were carried out using PhotoModeler software, which produces three dimensional coordinates of points identified in multiple photos.
The DEMs were used for qualitative and quantitative descriptions of the 2004-2007 eruption. The DEMs were used to calculate height, volume, and extrusion rate, and to track changes in these quantities through time. These quantities show a decreasing extrusion rate through time that has remained lower than 1 m3/s since October 2005. Total dome volume had reached 94x106 m3 as of April 2007, a larger volume than that of the 1980-1986 Dome. Quantitative evaluation of the DEMs also shows a relationship between dome height and extrusion rate, which varies with the character of eruptive activity.
Results were validated by comparing volume measurements derived from traditional aerophotogrammetric surveys run by the USGS Cascades Volcano Observatory. The new oblique photogrammetric technique yields estimates of eruptive volume consistently within 5% of the volumes estimated with traditional surveys. The end result of this project is a new technique that provides inexpensive, rapid assessment of volcanic activity that can be an important supplement to volcano monitoring worldwide
