DE
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FRHow the cave formed
A reef from the Devonian sea, water that dissolves limestone, and dripstones that take their time.
The way down
390 million years in one cross-section.
The limestone you walk through is an ancient reef. The cave inside it formed much later – and the dripstones are still growing.
8 °C
Cool all year round
All year round it is around 8 °C in the cave, with high humidity. A jacket and sturdy shoes are part of the visit.
1 cm
In 100 years
Since the discovery in 1927 a dripstone has grown about one centimetre. So please do not touch: the natural oils of the skin can stop growth at the spot that was touched.
30 m
The deepest point
At the deepest point of the tour you stand 30 metres underground, right in the Devonian limestone.
Diagram: the depths 0, 7 and 30 m come from the tour; layer thicknesses and the course of the passages are simplified. Geology after the Geological Survey of NRW (geotope GK-5011-002).
Timeline
390 million years, four moments
- 390 million years
A reef in the Devonian sea
In the Middle Devonian, today’s Bergisches Land lies under a warm sea. Corals and other lime-forming organisms build a reef. It becomes limestone – an isolated “limestone nest” between sandstone and clay slate. (time not dated)
Later: water dissolves the rock
On its way through soil and rock, rainwater absorbs carbon dioxide and dissolves the limestone in fine cracks. Over a very long time they become passages and chambers. The Geologischer Dienst NRW describes the cave as formed “by dissolution of Devonian limestones”; when this happened in Wiehl has not been dated.- around 1860
A chance find in the quarry
Blasting in the limestone quarry at Pfaffenberg opens up cavities. The find attracts hardly any attention at first. - 1927
The show cave opens
On 4 August 1927 the first public tour begins. Since then, the drips have gone on – quite calmly.
Sources: Geologischer Dienst NRW (Geological Survey of North Rhine-Westphalia, geosite GK-5011-002) on rock and cave formation; chemie.de encyclopaedia entry “Tropfstein” on growth (roughly 8 to 15 mm per 100 years, varying widely).
Earth science in 45 minutes
Water dissolves, water builds.
Later, lime-rich water drips from the ceiling. In the air it releases part of its carbon dioxide, and a tiny remnant of lime is left behind. Drop by drop, the dripstones form.
CaCO₃ + H₂O + CO₂ ⇌ Ca(HCO₃)₂Limestone + water + carbon dioxide ⇌ dissolved lime. To the right the water dissolves the rock, to the left it deposits it again as dripstone.
1 cm ≈ 100 years
Stalactite
Hangs down from the ceiling like an icicle. It grows where water drips off.
Stalagmite
Grows up from the floor, where the drops land. It is usually thicker and sturdier than its counterpart.
Column
When a stalactite and a stalagmite meet, they grow together into a column.
When water does not drip but runs as a thin film over wall and floor, flowstone sheets, curtains and stepped cascades form. The lime is deposited here in thin layers – the white and reddish tones of the walls come from this.
