Inverted volcanic relief: Its importance in illustrating geological change and its geoheritage potential

Abstract

We describe volcanic inverted relief sites around the world, making a comparative analysis of those most significant sites found from literature and our own search on imagery and global topographic maps. Over fifty significant areas of volcanic inverted relief were found. The comparative analysis is based on geoscience values defined by the main geological and landscape elements that define inverted relief. This subjective analysis is open and can be verified and extended if other significant sites emerge, thus forming the basis of a future, exhaustive global comparison of this important geomorphological feature. Inverted relief occurs when valleys transform to ridges due to differential erosion of relatively resistant valley-fill, and weaker slope lithologies. It is found in various geological settings, and it is very common in volcanic terrains, especially monogenetic volcanic fields, where most examples are inverted lava flows. Relief inversion provides a clear indication of slow geological changes and landscape evolution through erosion and can be thought of in popular terms as a geological clock. Volcanic inverted relief was recognised in the 18th - 19th centuries in the Chaîne des Puys (Auvergne, France), and used as evidence to first support plutonism by Nicolas Desmarest and then support uniformitarianism by George Poulett Scrope. We review the geological and geomorphological features of volcanic inverted relief world-wide, with an emphasis on the classical Auvergne. We explore how volcanic relief inversion chart geological changes, and their value for studying geological systems and landscape evolution. With our comparative analysis we can propose sites with the greatest geoheritage potential for representing inverted relief globally and suggest how this can be valued as geoheritage. As volcanic inverted relief is an important sub-set of all inverted relief, and is generally associated with important surface, volcanic and tectonic processes, and is often ongoing, it can be an important geoheritage component in natural sites. We suggest that it should should be present in the International Union of Geological Sciences (IUGS) Global Geosite list, can be a component of geosites in UNESCO Global Geoparks. It is also a feature for geological criteria (viii) in UNESCO World Heritage sites, where it fulfils all the requirements being both a major geomorphological feature and a fingerprint of significant geological processes in Earth evolution.