The role of tectonic structures and density-driven groundwater flow for salt karst formation

Groundwater circulation in evaporite bearing horizons and the resulting evolution of karst frequently causes geotechnical problems such as land subsidence or collapses. Even comparably small subsidence rates can significantly affect sensitive urban infrastructure. Dissolution of deep-seated evaporites occurs when groundwater, undersaturated with respect to highly soluble minerals, enters into contact with an evaporite body. Groundwater can interact from all directions in space. Laboratory dissolution experiments were carried out to study the effect of freshwater in contact with rock salt, accounting for the effect of dipping interfaces as an abstraction of inclined geological formations. The dissolution experiments were carried out both in 2D and 3D. The approach allows studying dissolution in a normal fault juxtaposing a developing intrastratal salt karst against a salt layer or against a poorly soluble layer. Modeling experiments were conducted to study the effect of variable density flow in inclined aquifers bordering halite formations and the effect of different fault geometries. The numerical simulations of density driven flow were evaluated along 1,000 m long and 150 m deep 2D cross sections to study the effect of tectonic horst and graben structures. Results show that a large fault zone consisting of a set of smaller hydraulically higher conductive faults is a major factor for dissolution.