The Base Contour
Crandell has suggested the 1220 meter contour as the base. However, this contour cannot be used directly because it encloses a substantial area that is not part of the volcano. The 1845 meter contour does separate the volcano from the adjacent high ground to the northeast and this contour was used to make a mask to isolate the base of the cone.
Defining the Base
IDRISI was used to define the base of the cone. First RECLASS was used to make a mask with all elevations above 1845 meters equal to one and all elevations below 1845 meters equal to zero. GROUP was used to assign mumbers to all patches of the image with value equal to one. One large patch was found to correspond to the volcano at 1845 meters. RECLASS was used to set this area equal to one and all others equal to zero. The process was repeated to eliminate small islands within the 1845 meter patch. BUFFER was applied to the resulting image to expand the patch outwards by 5200 meters to enclose the 1220 meter contour. The result of this image was multiplied by the SRTM DEM supplied by NASA-USGS to obtain the image shown below, which follow approximately the 1220 meter contour on the northwest side of the volcano.
