Walking in the landscape above the caves you will see some characteristic depressions of the surface of the area, for instance in the area above the cave entrance. At some places the sink holes have developed as the result of soil breaking through tunnel holes, or higher situated tunnels having collapsed causing material to fall down.In fact there have been recent examples of collapses. A couple of years ago the ground collapsed at Mønsted School, this indicating the existence of mine tunnels in this area too. The sink holes can also form through collapsing caverns which have formed in a natural way in the limestone as a result of water dissolving the limestone.
In the illuminated tunnels you can see heaps of earth and sand that have fallen through holes in the ceiling of the tunnel.The materials come from mining tunnels above as mentioned before. Quantities of the sand and earth will gradually find their way to the deeper tunnels..