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Hydration of anhydrite to gypsum (gypsification of anhydrite) in the weathering zone sometimes causes a volume increase. This can lead to local detachments of the surface layer of the weathering anhydrite rocks and creation of the hydration cavities and rare hydration caves (or swelling caves; German: Quellungshöhlen) inside domes formed by the uplifted layer. Currently growing hydration cavities at the anhydrite bottom of the abandoned quarry at Dingwall, Canada, were studied with the use of photogrammetric, statistic, and petrographic methods. Seventy seven cavities were documented including 48 caves (cavities with the height ≥0.30 m large enough to accommodate an adult man). Forty three caves had proper entrances (inlets large enough for an adult to get inside). The cavities contain one flat domed or, less often, tepee-like chamber generally similar in shape to the host hydration landform. The majority of cavities showed the length <4.6 m, the width <3.0 m, and the height <0.85 m. Only 3 caves had the length >8.00 m and the height ≥0.80 m. The largest and the highest cave showed the sizes 10.7 × 6.6 × 1.1 m measured in 2008 which changed into 8.87 × 2.97 × 1.35 m in 2019. The other caves and cavities exhibit also morphological changes with time due to vertical and horizontal movements of rocks slabs and collapse of the roofs depending mainly on the location of expansive gypsification and its intensity. Precipitation (rain- and meltwater) accumulating at the foot of the initial uplift intensifies the hydration in this zone causing a centripetal pressure towards the landform and contributing to its further rising and enlargement of the cavity height. The basic condition required for hydration cave formation is temperature between 0 and 30 °C in which the solubility of gypsum is much lower than that of anhydrite. The meteoric water solution infiltrating in the vadose zone is dissolving the anhydrite and gradually reaches Ca sulphate concentration higher than the level of gypsum and lower than the level of anhydrite solubility. Then, the dissolving anhydrite yields a solution supersaturated with gypsum, capable of its precipitation, and the dissolution of anhydrite is simultaneous with in situ replacive/displacive gypsum crystallization. The crystallization pressure of gypsum is a direct cause of the rock deformations and creation of hydration caves. [Display omitted] • Morphology and origin of anhydrite hydration caves and cavities are presented. • The caves develop due to expansive gypsification of anhydrite in the weathering zone. • Caves form within domed and tepee-like landforms growing at the quarry bottom. • Hydration caves reach length up to 8.87 m and height up to 1.35 m. • Anhydrite gypsification requires a precipitation and temperature range of 0 °C to 30 °C. [ABSTRACT FROM AUTHOR]

The knowledge of the soil variability is essential for its hydrologic characterization, for irrigation management and planning and especially for water movement modeling. Nevertheless, the scarcity of soil information in Spain precludes its use in irrigation management and, particularly, in the on-going irrigation modernization process. The Violada Irrigation District (VID) comprises 5234 ha and is located in a semi-arid gypsum-rich region in northeast Spain. VID has been under flood irrigation since the mid-20th Century and has been modernized recently to sprinkler irrigation. Since the early 1980s water balances in VID have been based on average soil properties and bulk irrigation data. The current irrigation system provides detailed irrigation data at plot level, thus allowing for performing distributed balances (in hydrologic homogenous zones) that require detailed or semi-detailed soil information in the form of a soil map. The objective of this two-part study is to define homogeneous zones in relation to hydrological properties relevant for irrigation management, first defining the soil variability within the VID and then analyzing the soils hydrologic and salinity features (in a companion paper). The specific objectives of this paper were (i) to draw the VID semi-detailed soil map; (ii) to explain the variability of soil properties; and (iii) to map the main soil characteristics related to irrigation management. Thirty four soil pits, located on all the different geomorphological areas, were opened and described. Samples were taken from all the horizons and analyzed for chemical and physical properties. The limits of soil units were drawn with the aid of 32 additional auger holes, the data from 72 pits opened during the irrigation transformation works, and all the previous soil information available. Finally the soils were classified down to family level. The main soil formation processes in VID were carbonation and gypsification. Thirteen soil units were defined, included in five soil subgroups and six particle size families. “Fine” particle sizes were dominant along the gypsum-rich valley bottoms. Coarser textures were found on the heights and showed higher CaCO 3 equivalent content and no presence of gypsum accumulations. A priori, the main limitation for irrigation in the valley soils was the limited drainage (due to fine textures and reduced slope) while in the highland soils it might be constrained by their low retention capacity. The high gypsum and carbonate content of the VID soils may prevent the development of infiltration problems. The soil properties map in this work will be the basis for a companion paper delineating the hydrologic properties of the soils, the basis for improved soil water balances. [ABSTRACT FROM AUTHOR]