SLOPES OF WESTERN GALAPAGOS VOLCANOS FROM AIRBORNE INTERFEROMETRIC RADAR

The distribution of slopes on the six basaltic shield volcanoes in the Western Galapagos Islands is investigated using a digital elevation m odel derived from airborne interferometric radar (TOPSAR) data. These measurements have a spatial sampling of 10 m/pixel, a vertical accurac y of 3 to 5 m, and constitute the highest resolution, most complete, t opographic data set available for the islands. Volcano heights are det ermined to range from 1,124 m (Sierra Negra) to 1,710 m (Wolf). Over e xtensive areas of each volcano, slopes exceed 25 degrees, with the hig hest slopes being similar to 37 degrees on Wolf and similar to 36 degr ees on Fernandina. We confirm that two morphologic subgroups exist: Ce rro Azul, Fernandina, and Wolf, with deep calderas (depth between 40-6 0% of the subaerial height of the volcano) and steep (>20 degrees) max imum slopes at elevations between similar to 60 and 80% of the volcano height; and Alcedo, Darwin, and Sierra Negra, with shallow calderas ( depth <25% of subaerial height) and slopes that remain <15 degrees unt il similar to 90% of the total height is reached. Our data show that s teep slopes are not uniquely correlated with the occurrence of arcuate fissures at the summit, leaving the origin of the steep slopes unreso lved.