Gypsum tumuli

Gypsum tumuli are morphological forms known from many places on earth, formed in the weathering zone of the gypsum rock. Gypsum tumuli are small domed forms of relief, with a diameter of several decimeters to several meters and a height exceeding 1 m, formed by detachment of the surface layer of weathering gypsum rocks under semi-arid climate or microclimate conditions. Most likely, they are formed as a result of cyclic soaking and drying of the rock, within which, in pore spaces, gypsum dissolves and crystallizes, exerting pressure on the pore walls (due to the crystallization pressure) – as a result, causing an increase in volume and detachment of the surface layer of the rock (Jarzyna et al. 2020).

Fig 1. An example of a gypsum tumulus with a characteristic dome shape in cross-section in Spain. In the photo during documentation in April 2023 Msc Monika Czajkowska.

The most characteristic place on Earth and the first where these forms were recognized is south-eastern Spain – the vicinity of the city of Sorbas. They occur in the area of a vast plateau, complementing the rich relief of this area.