HR: 0800h
AN: T51C-1353    [Abstracts]
TI: Geophysical expression of the Gadamota caldera within the central Ethiopian Rift
AU: * TADESSE, K
EM: ktadesse@utep.edu
AF: Department of Geological Sciences, University of Texas at El Paso, 500 West University Ave, El Paso, TX 79968 8900 United States
AU: MICKUS, K
EM: klm983f@smsu.edu
AF: Department of Geography, Geology, and Planning, Southwest Missouri State University , 901 S. National Ave, Springfield, MO 65804 United States
AU: KELLER, G R
EM: keller@geo.utep.edu
AF: Department of Geological Sciences, University of Texas at El Paso, 500 West University Ave, El Paso, TX 79968 8900 United States
AB: One of the main characteristics of the Ethiopian rift is the distribution of several quaternary calderas on the rift floor. The majority of these calderas have been analyzed geologically in some detail. However, the Gadamota caldera has not been studied in detail. In this study, we present the results of a gravity investigation of the Gadamota caldera, which lies within the central section of the main Ethiopian Rift. This caldera has a physiographic expression on its western side; however its eastern side is not clearly visible. In order to define the lateral extent and the structural setting of this caldera, a gravity survey was conducted in the summer of 2005. The data were acquired using a Lacoste and Romberg Model G-780 gravity meter and Trimble 4000 SSE GPS instruments for high precision measurements. From our preliminary analyzes, we are able to delineate the extent of the caldera to be about 18 km wide. DEM data together with ETM Landsat data also assisted in the control of surface features such as the extent of the caldera rim and the shape of the caldera. The western and northwestern caldera rim can be seen clearly in the field and on SRTM 90-meter DEM data. In addition, numerous northeast-trending faults are depicted outside the caldera on the Landsat image, which can be associated with the Wonji Fault Belt system but do not cut the caldera. The caldera is evidenced by a gravity maximum whose apex occupies the southeastern portion of the caldera. This anomaly has been previously detected in part both on the gravity and refraction seismic profiles that were part of the first phase of the EAGLE project. The gravity survey has proved that a high density causative body is situated in the southeastern portion of the caldera and that the volcanic fill is shallow. The distinct gravity anomaly we detected shows that the Gadamota caldera is a separate feature from the Aluto volcano.
DE: 1200 GEODESY AND GRAVITY
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 7205 Continental crust (1219)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Tectonophysics [T]
MN: Fall Meeting 2005