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  18.12.2020, 07:02h

The underground world of karst: the cave Miljacka III


The cave stands out due to its length of 113 metres, which is highly unusual for a travertine cave

The Miljacka III cave (also called the Cave under the waterfall) was accidentally discovered in 1988 when examining the banks of the Krka River under the travertine barrier at the Miljacka waterfall. It is positioned within the course of the Krka River. The cave stands out due to its length of 113 metres, which is highly unusual for a travertine cave. It is 6.6 metres deep. It can only be accessed by diving. During periods of high water, entrance is not possible. The hydrological conditions are also interesting in the cave, for in this section, the water flows both through the cave and along the surface in the Krka River, so it flows at two different levels.

In terms of its morphology, the Miljacka III cave is a simple cave with only one main channel and no branches. The cave is a constant source, with water appearing in it both as percolating water and as dripping water. In the channel expansions, there are abundant depositions of speleothems in the form of stalactites, flowstone and speleothem crusts on the channel walls.

The cave was formed in travertine deposits (an elongated travertine body), and is likely of Holocene age, and more precisely lies in the zone of contact between the travertine and base rock upon which the travertine was deposited. In the rock, micro-relief forms are visible, such as troughs and eddy pots, created by erosion. The main part of the cave is formed in travertine, as it is softer than the base rock and therefore more strongly affected by erosion. In addition to erosion, the channel has also been shaped by cave-ins, with karst rock and large blocks of travertine also found in the sediments on the floor.

In the Miljacka III cave, erosional remnants of sediments are found along the entire profile of the channel (on the floor, walls and ceiling). These sediments were likely deposited during phreatic (submerged) conditions in the geological past of the cave.  The phreatic sediments of the Miljacka III cave were also deposited onto the stalactites that formed under dry air conditions, so it can be concluded that this cave has undergone numerous stages of alternating dry air and submerged conditions.

Research of the laminate cave sediments and stalactites in the submerged part of the cave channel in Miljacka III indicated the recrystallisation of speleothems following the circulation of pore water, presenting a problem in dating these samples.

Unusual organic, white to yellowish formations have been discovered in the Miljacka III cave, attached to the submerged cave walls. Analysis of these formations indicated that these are anthozoan type of colonies likely containing more than 30 bacterial species. Read more about Miljacka III cave here.

Photograph: Nenad Buzjak