Slopes, lava flow volumes, and vent distributions on Volcan Fernandina, Galapagos Islands

S.K. Rowland
Hawaii Institute of Geophysics and Planetology University of Hawaii at Manoa 2525 Correa Rd. Honolulu, Hawaii 96822

Abstract:

Digital elevation data from TOPSAR, an airborne synthetic aperture radar system that uses interferometry to derive topography, are used to determine slope distributions and lava flow thicknesses on Fernandina Volcano, Galapagos Islands. Four extra-caldera slope regions are defined (from the coast inland): A coastal plain (average slope ), an apron (6-), steep slopes 250-600 m high (20-), and a 0.5 to 1 km-wide summit platform (). Lava flows and vents are mapped using SIR-C radar, SPOT, Landsat TM, and air photos. Over 500 flows are identified and categorized as young, intermediate, or old based on albedo, vegetation cover, and margin preservation. By area, young flows comprise 55% of the island, 34% is intermediate, and 7% is old. The aa:pahoehoe ratio of the young flows is 85:15 whereas for the intermediate flows it is 58:42. Of the 423 vents that were classified, 236 are radial and 80% of these are in the apron, 143 are arcuate and 94% of these are in the summit platform, and 46 have transitional orientations and are about equally divided between the steep slopes and summit platform; 95% of all vents are within 13 km of the caldera center. TOPSAR data allow flow volumes to be estimated, and young flows range from <0.01 to 0.12 km, with a total volume of 2.3 km. By volume, 91% of the young lava erupted from radial vents below the steep slopes, many of which are concentrated within the SE apron about 5-6 km from the caldera. Similar concentrations to the NE, NW, and SW consist of young and intermediate flows. Different proportions of lava flows and vents form the different slope regions; the coastal plain averages 0.1 vents/km and the slightly steeper apron averages 0.6 to 0.9 vents/km, increasing inland. The summit platform averages 4.7 vent/km, and this concentration supports previously-proposed mechanisms for producing higher elevations and steeper slopes in the central part of the volcano. Temporal changes in the plumbing system and/or magma supply rate are suggested by the change in aa-to-pahoehoe ratio; it appears that in the past, low effusion-rate eruptions were more common (perhaps from a filled caldera) whereas more recently, high effusion-rate eruptions have dominated.

AGU Index Terms: 8400 Volcanology; 8429 Lava rheology and morphology; 5464 Remote sensing; 8499 General or miscellaneous
Keywords/Free Terms: Volcano morphology, radar interferometry, eruptive history

JGR-Solid Earth 96JB02649
Vol. 101 , No. B12 , p. 27,657