The orogenesis of Spa-Francorchamps

One of the more surprising conclusions to be drawn from modern geology, is that the greatest motor racing circuit on the current Formula 1 calendar, is the combined result of orogenesis, localised plastic strain, and periglacial erosion.

Spa-Francorchamps is a rich seam of asphalt found within the Ardennes Massif, a region created by tectonic uplift between 345 and 225 million years ago. Counter-intuitively, perhaps, the Ardennes was not covered by ice during the last ice age (a reassuringly decimal multiple of 10,000 years ago). It was, however, on the border of the glaciated region, and by definition was therefore affected by the less dramatic contribution of periglacial processes, which seem largely to involve permafrost and the creation of scree.

Thus, the Ardennes is characterised by deep-sided valleys, not because of glacial erosion, but because the tectonic uplift raised all the rivers high above their base level, and under such conditions downcutting will take place faster than lateral erosion, creating steep, V-shaped valleys.

During orogeny (mountain-building), the sedimentary rocks in the Ardennes underwent substantial compressive loads. Now, under protracted load, rock tends to suffer irreversible 'plastic' deformation. Jean-Pierre Burg emphasises the role of plastic strain instability within the Ardennes, arguing in Tectonophysics 309 that shear instabilities "appear necessary to explain complex, even contradictory relationships between cleavage, folds, thrusts, coeval normal faults and a downward decreasing strain and displacement."

One might, in fact, represent the stresses and strains of the Ardennes Massif with exactly the same type of Finite Element Analysis software, also used to design the conveniently deformable Formula 1 cars which will caress its skin this very weekend.