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Saturday Volcano Art: Poulett Scrope and Jaujac 25 April 2009

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George Poulett Scrope, view of Jaujac (1827)

This view of the town of Jaujac and its setting, in the Ardèche region of south-eastern France, was drawn by the British geologist and economist George Poulett Scrope (1797-1876) and published in the first edition of his Memoir on the Geology of Central France in 1827.

The viewpoint of the picture is towards the south. The river Lignon is in the foreground in its steep-sided gorge, with Jaujac and its bridge above it. Beyond the town the land rises, and directly ahead of us is a clearly volcanic landscape feature: a low hill with a crater, open towards the north. This is an extinct volcanic cone known as la coupe de Jaujac. The vent is thought to have been active around 16000 years ago. It produced a thick lava flow, on part of which the town now stands.

Poulett Scrope’s picture does not merely depict the physical arrangement of the town, the river and the volcano. It is also concerned with temporal relationships. Since the middle of the eighteenth century, when Jean-Étienne Guettard (1715-86) first identified lava flows and volcanic features in Massif Central (the Chaîne des Puys of Auvergne, and the volcanoes of Ardèche) and Nicolas Desmarest (1725-1815) used evidence from the same region to argue that basalt was a volcanic and not a sedimentary rock, the relationship between the volcanoes and their lava flows and the deep-cut river valleys had been a topic of great interest to geologists. The rivers had cut through some lava flows, yet in other cases lava had flowed into existing river valleys. When the English geologist Charles Daubeny (1795-1867) visited the region in 1819 he called these ‘ancient’ and ‘modern’ flows respectively, reflecting his belief that they had been erupted before and after the creation of the valleys. He also used the terms ‘ante-diluvial’ and ‘post-diluvial’, suggesting that some great inundation had occurred between the two, reshaping the landscape which was then newly eroded by river valleys.

When George Poulett Scrope visited the same landscapes shortly after Daubeney he interpreted what he saw rather differently. He explicitly rejected the distinction between ‘ancient’ and ‘modern’ volcanic eruptions. Rather than seeing distinct epochs of volcanic activity, he saw a continual process of eruptions and erosion. His illustration shows the lava flow cut through by the deep gorge of the Lignon river, and the volcanic cone which had erupted the lava still extant and well-preserved. If a flood had reshaped the landscape between the lava being erupted and the river eroding its gorge, the cone would surely have been erased as well, yet it remains. Poulett Scrope’s explanation was that eruptions were continually happening, and erosion was continually occurring, across the vast range of geological time.

The full image from Poulett Scrope’s Memoir on the Geology of Central France (1827), from which the detail reproduced above is taken, can be found at the Linda Hall Library of Science, Engineering & Technology.

For all ‘Saturday volcano art’ articles: Saturday volcano art « The Volcanism Blog.

References

Coupe de Jaujac et ruisseau des Salindres (Inventaire des Zones Naturelles d’interet Ecologique, Faunistique et Floristique, 2nd edition, 2007) [PDF].

Martin J. S. Rudwick, ‘Poulett Scrope on the volcanoes of the Auvergne: Lyellian time and political economy’, British Journal for the History of Science, vol. 7, no. 3 (November 1974), pp. 205-242.

Martin J. S. Rudwick, Worlds Before Adam: The Reconstruction of Geohistory in the Age of Reform (Chicago, IL: University of Chicago Press, 2007).

Alwyn Scarth & Jean-Claude Tanguy, Volcanoes of Europe (Oxford: Oxford University Press, 2001).

Jeunes volcans d’Ardèche – information about Jaujac from Le volcanisme d’Ardèche.

Volcanism at Jaujac – field-trip photographs and commentary from 2006.

Volcanisme de Jaujac – field-trip notes and photographs (Académie de Grenoble)

The Volcanism Blog