Hidden Earth 2024

Sulphate caves and karst in the South Harz Mountains, Central Germany

45 minute Lecture|John Gunn

Abstract

Globally the majority of caves are epigenic (formed by water descending from the surface) and have formed in carbonate rocks but there are also fascinating and extensive caves in sulphate rocks (gypsum and anhydrite) many of which were formed by hypogenic processes (fluids rising from depth). In the South Harz area of Central Germany there is a 100 km long continuous belt of evaporitic rock of Upper Permian (Zechstein) age within which there are large areas of outcropping gypsum rocks with anhydrite at depth underlain by carbonate rocks. Surface karst landforms include over 20,000 dolines, and there are 170 caves most of which are hypogenic and developed in shallow or deep phreatic settings. The latter, which are commonly referred to as “Schlotten” were discovered by mining for a metalliferous Copper Shale that underlies the anhydrite and carbonate. There are no speleothems in the sulphate caves but they display varied and beautiful passage morphologies, extensive breakdown and exfoliation, and rock features that include spectacular alabaster balls, large cupolas, small-scale solution cusps and facetted walls. This talk will provide a brief introduction to the surface landforms, a discussion of how the caves were formed followed by a tour through the deep phreatic Elisabethschacht Schlotte and five shallow phreatic caves: Barbarossahöhle (670 m long), Jettenhöhle (750 m), Marthahöhle (450 m), Questenhöhle and Heimkehle (1780m). During WW2 the German army turned the latter cave into a bombproof production site for aircraft parts and, reputedly, for V-weapons. Prisoners from a concentration camp provided forced labour and in one of the chambers there is a memorial to the many who died.