Contrasting Geothermal Fields Along the Magmatic Banda Arc, Nusa Tenggara, Indonesia

Fourteen geothermal fields have been identified along the Banda Arc from Bali in the West to Alor in the East. Only three of these fields have been drilled to confirm reservoir conditions, with all three encountering high temperatures and having discharging wells. The remaining fields have been investigated to various levels commensurate with the development prospectivity of each field. Previously unpublished surface spring chemical analyses are presented for several fields on Sumbawa and Flores Islands and these are compared with the surface and subsurface characteristics of the thermal fluids, and the geological setting of the other geothermal fields along the arc. This has highlighted some contrasting features of the geothermal activity from individual islands. This contrast is highlighted by the geothermal fields in the neighbouring islands of Sumbawa, where thermal features consisting of hot springs are located at low elevations close to the coast, and Flores, where boiling springs and fumaroles are found inland at high elevations. In general there is a close association of geothermal activity with active volcanic centres on Flores while on Sumbawa the thermal activity lies south of the active magmatic arc within younger Tertiary volcanic rocks. Thus the differing styles of geothermal activity can be related to the location of the active magmatic front along the Banda Arc.