The magnitude rule in geoheritage site inventories

Since the 1990s, an international consensus has been emerging with respect to the methods used to identify and assess geosites. These conventional methodologies generally differentiate between the intrinsic or scientific-natural dimension and the social dimension in the potential value of the geological elements. The aim of this article is to analyse the possible existence of other concepts that may underlie these criteria and that could be operating as evaluation parameters even though they are not explicitly and formally described as such in the published studies. An exhaustive analysis of articles on geosite inventories published in Science Citation Index journals in the last 15 years revealed a systematic reference to conceptions of magnitude (in the sense of degree of development and physical prominence) in geosite descriptions around the world, and in particular with respect to sites of geomorphological interest. To contrast this indication, we subjected the geosites inventory of Lanzarote (Canary Islands, Spain) to a Magnitude Rule hypothesis. This inventory is part of the Spanish Geosites Inventory (IELIG, for its initials in Spanish), which was carried out using conventional assessment procedures. Applying this rule, according to which each geosite is the most prominent example of its typology within the reference geological domain, we obtained an almost complete match. That is, geomorphological sites that were selected, a priori, according to intrinsic and social dimension were also (or one could even say ‘actually’) selected, implicitly, on the predominant basis of magnitude. This paper discusses why and how the magnitude parameter may be playing a key role as a subliminal non-explicit driver in the evaluation of geosite relevance, and how this finding may open new perspectives and bring methodological advantages in the inventory of geological heritage.