The area exhibits karst morphology, with bedrock largely consisting of limestones and comparatively small areas of dolomites and Quaternary sediments. Eocene flysch forms the southwest boundary of the catchment area, towards which the catchment basin drains and where the Ombla rises. The rocks were formed as a thick series of carbonate sediments were deposited between the Norian and Late Cretaceous as the Adriatic Carbonate Platform, up to deep. In the Eocene and early Oligocene, the Adriatic Plate moved north and north-east, contributing to the Alpine orogeny via the tectonic uplift of the Dinarides. The basin's karst topography developed from the carbonate platform's exposure to weathering. Karstification largely began after the Dinarides' final uplift in the Oligocene and the Miocene, when the carbonates were exposed to atmospheric effects; this extended to the level of below the present sea level, exposed during the Last Glacial Maximum. Some karst formations were created during earlier sea level drops, most notably the Messinian salinity crisis. The geological structure of the area indicates recent tectonic activity in the catchment, with a fault running between Hum and the Ombla. A recent strong earthquake in the wider region was the 1979 Montenegro earthquake, measuring 7.0 on the Richter scale. The only strong historical earthquake in the immediate area was the 1667 Dubrovnik earthquake, which was followed by a tsunami.