Geology

Rock Barbeque

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Science  04 Jul 2003:
Vol. 301, Issue 5629, pp. 19
DOI: 10.1126/science.301.5629.19c

High surface heat flux, smoke and hot gases emanating from holes, and fractures in the Timbuktu region of northern Mali have been recorded since the late 1800s. Studies in the second half of the 1900s interpreted these features as a hydrothermal system developing from a growing magma body produced by tectonic processes. On the other hand, West Africa is part of a stable craton, and there is not much evidence for volcanism.

Thermal activity increased near Lac Faguibine in April 2001. Svensen et al. conducted a field study and found that the volcanism is actually subsurface combustion. Buried beneath diatomaceous clay, an organic-rich peat layer dries, heats up via exothermal microbial decomposition, self-ignites, and propagates radially or along a fracture at a rate of 3 cm per hour. The overlying diatomite warms and the iron oxidizes, turning the clay layer from gray to red. Red diatomite is common in the trans-Saharan region, where many lakes dried up during a Holocene climate change, and therefore may provide a marker to estimate the extent and effect of subsurface combustion on the environment. — LR

Geology 31, 581 (2003).

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