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Subsurface combustion in Mali: Refutation of the active volcanism hypothesis in West Africa

¹ Physics of Geological Processes, University of Oslo, P.O. Box 1048 Blindern, 0316 Oslo, Norway
² The Bridge Group, Billingstadsletta 46, P.O. Box 229, 1377 Billingstad, Norway
³ Direction Nationale de la Geologie et des Mines (DNGM), Bamako, BP 223, Mali
⁴ Volcanic Basin Petroleum Research (VBPR), Gaustadalléen 21, 0349 Oslo, Norway, and Physics of Geological Processes, University of Oslo, P.O. Box 1048 Blindern, 0316 Oslo, Norway

Surface heat anomalies have been known in the Timbuktu region in northern Mali for more than a century. Since about 1960, several authors have argued that these heat anomalies are caused by incipient volcanic and hydrothermal activity. Surface temperatures as high as 765 °C were measured locally in January 2002, and smoke emanated from holes and fractures in the ground. We demonstrate that subsurface combustion of organic material is the source of the heat and the gases. Several square kilometers are currently active or have been affected by subsurface fires since 2001. Self-ignition during biological degradation of organic-rich layers in the lacustrine deposits is the most likely mechanism that started the subsurface combustion that caused the heat anomalies in the area. An important consequence of this conclusion is that West Africa should still be regarded as volcanologically inactive, and that possible reactivations of the major EW-trending Guinean-Nubian lineament are not associated with volcanism. We suggest that the subsurface combustion in the Timbuktu region today represents a phenomenon with a very long record in the Trans-Saharan region.

Key Words: subsurface fires • self-ignition • incipient volcanism • Mali • West Africa

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