gypsum cave

   Both vadose and phreatic caves can form in gypsum, which is very soluble in water, but they are uncommon because gypsum rock rarely survives total dissolution in the near-surface environments associated with explorable caves. Gypsum caves certainly exist at depth within buried evaporate sequences. In areas of wet climate gypsum caves are generally seen only if encountered by man-made excavations. In contrast, gypsum caves are more common and more extensive in areas that have experienced a long period of dominantly arid climate. The most spectacular gypsum caves are in the Podolie region of the Ukraine, where joint guided mazecave systems are very extensive — Optimisticeskaja has around 180km of passsage [9].