University of Twente Student Theses


Insight in to the surface and subsurface expressions of Buranga geothermal field, Uganda

Fernando, Chandima (2012) Insight in to the surface and subsurface expressions of Buranga geothermal field, Uganda.

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Abstract:Previous seismic studies over the Buranga area, Uganda have identified an evidence for the existence of a hot degassing magma body in the subsurface which is considered as the heat source for the Buranga hot springs. Surface geothermal expressions identification over the Buranga geothermal field in Uganda and its link to the subsurface geothermal source are the main objective of this study. Various types of remotely sensed data were used to pinpoint the surface geothermal expressions. To indicate hot spring alteration minerals, band ratio of SWIR ASTER bands, after masking vegetation, (B5+B7)/B6, (B6+B9)/(B7+B8) and B5/B4 respectively was used to indicate the occurrence of Al-OH containing minerals, Mg-OH containing minerals and gypsum. The sub pixel size hot spot identification method was applied to the MODIS aqua night thermal Infrared images to identify the surface temperature anomalies associated with geothermal activities. The resulted ratio images of the radiant temperature images were threshold using hotspot identification algorithm. The 3 directional hill shaded ASTER Global DEM version 2 and the directionally filtered multispectral ASTER band 2 were used to identify the surface geological structures. The distribution of the minerals containing Al-OH as a main absorption feature was found mainly related to clay minerals in flood plains (also within rivers) and less around hot springs due to alteration. The band ratio that was used for Mg-OH containing minerals didn’t enhance the hot springs area and only identified the areas where carbonate is dominant as calcareous sandstone due to CO3 2- bond which overlaps the Mg-OH absorption feature. The areas outlined after applying the band ratio for gypsum were found mainly in recent sediments, lakes and close to oil seepages.The temperature variation of the area is mostly governed by the vegetation and moisture contents. The resulted pixels with hotspot from thresholding values of the ratio images of radiant temperature don’t show any relation to the geothermal hot springs. Hotspot pixels, after applying hotspot detection algorithms, were found related to places rich in water content such as flood plains along rivers and crater lakes. The surface structural interpretation indicated three prominent lineament patterns, NNE normal faults demarcating the rift valley and Ruwenzori mountain block; and two linear features trending NW and NE to ENE. The Buranga hot spring is located on one of the NE trending lineament on the rift valley. Integration of the seismic P wave velocity anomalies with the interpreted structural map showed a relationship between the surface structural faults and the subsurface intrusion body which is thought to be the feeder of the hot springs throughout the upwelling hot fluids along these faults.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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