Vatnshellir_9315
In Snæfellsnes. 8000 year old lava tube created by volcanic eruption from a nearby crater. When the lava river dryed from underneath the crust surface it left behind empty tube with roof on top that gradually cooled down.
The roof may not look trustworthy, but the experience tells that stones falling from the roof happen mainly while the tube is relatively new. In Reykjanes with all its seizmic activity there is very very seldom that stones fall from the roof of the many lavatubes in similar caves.
Vatnshellir_9315
In Snæfellsnes. 8000 year old lava tube created by volcanic eruption from a nearby crater. When the lava river dryed from underneath the crust surface it left behind empty tube with roof on top that gradually cooled down.
The roof may not look trustworthy, but the experience tells that stones falling from the roof happen mainly while the tube is relatively new. In Reykjanes with all its seizmic activity there is very very seldom that stones fall from the roof of the many lavatubes in similar caves.