revised operational-proposal: ICDP-06/07 (accepted: 15.01.2007)

ICDP Proposal for the Scientific Exploitation of Deep Geothermal Drillings on Piton de la Fournaise Volcano (La Reunion, Indian Ocean)

by Jean Lénat

Abstract

Reunion Island is a large oceanic shield volcanic system, located in the south-eastern Indian Ocean, 750 km east of Madagascar. It is a 7 to 8 km high, elliptical flattened volcanic cone, 220 to 240 km in diameter at the level of the surrounding sea floor. Its growth is attributed to the activity of a mantle hot spot. The active volcano of the island, Piton de la Fournaise is among Earth's most active volcanoes. In 2000, the Regional Council of La Reunion started a project for the evaluation of the geothermal resource on the island. New geological, geophysical and geochemical surveys have been carried out between 2001 and 2004. In 2005, a decision to drill 2 or 3 reconnaissance, 1-1.5 km deep, wells on Piton de la Fournaise volcano have been taken. The Regional Council has expressed a strong willingness to open the drillings (with some restrictions) to the scientific community. Such drillings are expected to provide different types of scientific results and at different scales, from that of the hot spot system to that of the detailed volcanic and geothermal processes in the vicinity of the wells. Although this project is not exactly similar to the recent Hilo drilling in Hawaii (or the older NSF drilling at Kilauea), its bears some similarities with them in the global and local geological issues. Drilling operations are now planned to start in September 2007. Because the presence of a geothermal resource in the selected area remains speculative, the slim hole technique has been preferred in order to reduce the costs. However, in order to strengthen the scientific valorisation, a large portion of at least the first well will be cored and the samples will be given to the scientific community. The French CNRS (National Council for Scientific Research) is organising and funding the response of the scientific community though the INSU (National Institute for Universe Sciences). Preliminary scientific projects have been submitted to the INSU by different groups but the project remains open to contributions from other groups in the national and international community. ICDP is expected to be a major partner of the project through the use of DIS, its assistance in borehole logging and in the organization of an international workshop. An international workshop will be organized in La Réunion in 2009, after the end of the drilling operations, when preliminary results will be available.

Scientific Objectives

Deep drill holes on active volcanoes are exceptionally carried out (e.g. Kilauea, Unzen, Iceland). Although the planned dill-holes on Piton de la Fournaise are not intended for scientific purpose, they offer an extraordinary opportunity to acquire highly valuable information on La Réunion volcanism. We expect to learn much about : • The structure and evolution of the volcano • The nature and the evolution of the magmas of the hot spot • The volcano-tectonic processes • The hydrothermal activity • The alteration of the edifice • The microbiological population at depth and its interactions with the fluids and the rocks • The hydrogeological system • The physical properties of the terrains • The calibration of the geophysical methods

Keywords

drilling scientific valorisation ,  hot spot volcanism ,  ICDP-06/07 ,  la reunion ,  piton de la fournaise ,  thermal regimes ,  volcanic systems

Location

Indian Ocean, La Réunion, Piton de la Fournaise Volcano: 21° 14' 13.38'' S, 55° 40' 29.07'' E

open