The longest cave on earth

You’d better not get lost in its dark corridors: the labyrinth of the Mammoth Cave in the US state of Kentucky stretches a full 591 kilometres. That is about as far as from Karlsruhe to Kiel. This makes Mammoth Cave the longest known cave on earth.

Its widely ramified network of passages and chambers runs through a soft layer of limestone. This is about 400 metres thick and was deposited in a shallow sea a good 300 million years ago. Later, the limestone layer protruded from the sea and was leached out by acid rainwater: a hilly karst landscape full of fantastic caves emerged, whose passages are even spread over several storeys.

The caves have been known to man for thousands of years. This is proven by finds of sandals, torches and even mummified human bodies. The mummies come from people who lived more than 2000 years ago and probably sought plaster in the cave. They certainly did not live here in the dark. Because only extremely adapted creatures like the cave blind fish, eyeless crayfish, beetles or crickets can do that.

Today, the Mammoth Cave attracts tourists in particular. It is one of the oldest tourist attractions in North America; tours into the belly of the earth have been offered here since 1816.

Lost John” – the mummy in the mammoth cave

Seven mummies have been found in the Mammoth Cave to date. All of them are over 2000 years old and have been preserved by the special cave climate. The last mummy to date was discovered in 1935 and named “Lost John” because of its history: It comes from a man about 1.60 metres tall and about 45 years old, who died when the cave ceiling collapsed on him. “Lost John” lived about 2300 years ago and is the only one of the seven mummies that has survived. All the others were destroyed after being removed from the cave’s preservative atmosphere.

How are caves formed?

Caves have always had something mysterious for people: fairy tales and legends tell of devils, dragons, dwarfs and other creatures who live in dark cavities deep inside the earth. But caves exist not only in fantasy, but also in reality.

What they all have in common is that hardly any sunlight penetrates from outside. That is why it is cool and dark here inside the earth. To be considered caves, they must be at least large enough for people to enter and must also have formed naturally. How this happens, however, varies.

Many caves form where water washes out soluble rock. Rock salt and gypsum are among the rocks that are already dissolved in pure water. Limestone, on the other hand, is only soluble in acidic water. The solution is washed away; sometimes entire streams or even rivers flow through the earth’s interior. What remains are underground cavities that grow larger and larger over time. A whole labyrinth of passages can form here. These processes are also referred to as karst.

Some caves are formed not after, but at the same time as the rock. After a volcanic eruption, something like this is possible. When thin lava cools and solidifies on the surface, hot lava can still flow beneath this layer. When this lava flow has finally drained away, tunnels remain in the solidified rock that can be hundreds of metres long. Such lava caves can be found in Hawaii, for example.

Because little light penetrates into the natural cavities, only a few creatures are at home here. Well adapted to the rather hostile conditions are tiny animals such as the cave olm or the cave flea crab. Humans, on the other hand, only visit caves occasionally – as a shelter to protect themselves from wind and weather.

From rock to grain of sand – weathering

Today, northern Canada is a gently undulating landscape. Many millions of years ago, however, a mountain range stood here. In fact, over a very long time, even high mountains can turn into small hills.

The reason for this transformation: the rock on the earth’s surface is constantly exposed to wind and weather. If, for example, water penetrates into cracks in the rock and freezes, it blasts the stone apart. This process is called frost blasting. Changes in temperature between day and night and the force of water and wind also cause the rock to become friable. In other words, it weathers. This process can also be observed on buildings or stone figures. During weathering, the rock breaks down into smaller and smaller components down to fine grains of sand and dust. Different rocks weather at different rates: granite, for example, is much more resistant than the comparatively loose sandstone.

Some types of rock even dissolve completely when they come into contact with water, for example rock salt and lime. Rock salt is chemically the same as table salt – and that already dissolves in ordinary water. Lime is somewhat more resistant, but limestone also dissolves in acidic water. Acid is formed, for example, when rainwater in the air reacts with the gas carbon dioxide. This “acid rain” attacks the limestone and dissolves it over time. On the earth’s surface, weathering leaves behind fissured limestone landscapes, while caves form underground.

But it is not only solution weathering, but also heat and pressure that wear down and crumble rock beneath the earth’s surface. Where plants grow, roots dig in, blast the rock apart piece by piece and also ensure that it is eroded millimetre by millimetre.

In this way, weathering not only works on individual rocks, it gnaws away at entire mountain ranges. But it will take a few million years before the Black Forest is as flat as northern Canada.

Karst – Landscape with holes

The landscape of the Swabian Alb is almost as perforated as an Emmental cheese. There are around 2,500 caves here. Some of them can be visited, including the Falkenhöhle in the north or the Bärenhöhle in Wolfstal. But why are there so many large holes in the ground in this area of Germany in particular?

The reason for this is that the rock of the Swabian Alb consists of lime. This limestone is soluble in acidic water. Rainwater has the necessary acidity in the form of carbonic acid: it is formed from the reaction of the water with the gas carbon dioxide from the air. The limestone of the Swabian Alb thus gradually dissolves in the seeping acid rainwater, similar to effervescent powder in a glass of water.

The weathering of the limestone already begins at the earth’s surface. The acid rain digs gullies and fissures into the rock and forms jagged humps that become steeper and steeper. The water penetrates the earth’s interior through cracks and joints until it encounters a water-impermeable layer like clay. By then it dissolves the calcareous rock: small holes become large cavities, fine gullies become wide ditches. A widely ramified network of underground rivers, valleys and caves develops.

There is a lot of lime in the water that runs off. When this calcareous water evaporates, the dissolved lime remains and is deposited again. Dripstones grow in such places. Sometimes the cavities also sink or collapse under the weight of the rock cover. In these places, hollows called sinkholes can be seen on the earth’s surface.

Such cave landscapes of weathered limestone are not only to be found in the Swabian Alb. They also exist in many other places on earth, for example in Slovenia. This is also where the name for this type of landscape, which we call karst, comes from. The Slovenian expression for it is similar, namely Kras.

Sedimentary rocks

Some rocks look as if they are striped. In the Dolomites, for example, such transverse bands are often clearly visible. Sandstone or limestone quarries also sometimes have similarly pretty patterns.

The “stripe design” is already created during the formation of the rock. The starting material is weathering debris that is carried away by water or wind. Rivers, glaciers and dust storms lose their power at some point: river courses slow down towards their mouths and eventually flow into the sea or a lake. Glaciers advance into warmer regions and melt. Dust storms also weaken at some point. Then they can no longer carry dust, sand and debris. The crushed rock that is dragged along settles. Over time, the deposited material forms an ever higher layer – the sediment. Especially on the seabed and on the bottom of lakes, where rivers wash up a lot of material, such sediments accumulate, including remains of dead animals or calcareous shells.

Gradually, different sediments are layered on top of each other. One layer may consist of sandstone, for example: In dry times, the wind has blown desert sand onto it. When the sea level rises again, this layer is covered by water: calcareous shells of marine animals sink to the seabed and deposit another layer on top of the sand. Over millions of years, the climate changed again and again, causing the sea level to fluctuate. This allowed different layers to be deposited.

Over time, the sediment cover becomes thicker and thicker. Under the weight of their own weight, the initially loose sediments are compressed more and more, small cavities disappear, the mass thickens. Further layers are deposited on top, the sediment becomes increasingly solid and finally, under pressure, sedimentary rock. In geology, this process is also called diagenesis. If, for example, the shells of tiny marine animals are pressed into stone, limestone is formed. Fine grains of quartz sand cement together under high pressure to form sandstone.

In addition to debris, dead animals, for example fish, also settle on the seabed. Sealed airtight, their bones and scales were preserved and fossilised. Such fossils have immortalised themselves in the stone. Even after millions of years, they reveal a lot about the time when the sediment was formed. This is why geologists can read the rock layers like a history book.

Normally, only the top layer is visible to us. However, when a river digs through the sedimentary rock, it is uplifted during mountain building or blasted free in a quarry, we get a view of the cross-section. The individual sediment layers are then clearly visible as “stripes” or bands in the rock.

How do dripstones get into a cave?

It is dark, cool and often damp inside a stalactite cave. It is not particularly cosy here, but with a little lighting you can see fantastic formations on the ceiling and floor: the stalactites. But how do they get into the cave?

The answer to this is already revealed by their name: stalactites are created by the dripping of water. The decisive factor here is that it is not pure water. The water droplets contain lime that has dissolved from the surrounding limestone. When the water saturated with lime evaporates, lime residues remain. We know similar lime traces from areas where “hard water”, i.e. water with a high lime content, flows from the tap. There, limescale residues settle on the sink or on the bottom of a kettle. But what causes ugly stains there creates fantastic shapes in the caves: Very slowly and gradually, the lime deposits grow down from the ceiling as moist, shiny cones: the stalactites.

When calcareous water drips down from the stalactites, stalagmites also form directly below them as if in a mirror image: the stalagmites. If stalactites and stalagmites are large enough, they grow together and form a column. Besides the stalactites, there are other interesting formations in such a cave. Where water runs along the ceiling, lime traces are left behind that look something like curtains. They are therefore also called “stone curtains”.

On average, dripstones grow about one millimetre in ten years. How fast it actually goes depends on the amount of water dripping down and how much lime is dissolved in it. The temperature in the cave also plays a role: the warmer it is, the more water evaporates. This leaves more lime behind and the dripstones grow faster.

If you want to visit a stalactite cave, you can go to the Swabian Alb: There are a lot of them in this karst region. But dripstone caves can also be found in other parts of Germany, for example the Atta Cave in the Sauerland or the Iberg Dripstone Cave in the Harz Mountains.

Missing person rescued from Falkenstein cave

The four students who were reported missing on Sunday morning have been rescued. They had entered the Falkenstein cave near Bad Urach on Saturday. After a thunderstorm, the water level in the cave had suddenly risen so much that their way back was blocked. Divers from the cave rescue service were able to free the four trapped people on Sunday.

The students were sufficiently equipped for a normal ascent of the cave: When they set off on Saturday morning at around 9 a.m., they wore helmets, suitable caving clothing, had light and provisions with them and reached their destination without any problems, the Eisele burst just 3 kilometres from the cave entrance. Here the passage ends due to a collapse of the cave ceiling.

What the four cave visitors had not expected, however, was that at around 5 p.m. a heavy thunderstorm broke out near Bad Urach. Immediately after the heavy rain, the run-off water in the cave rose so much that the students could not make their way back without a diving suit. Their disappearance was noticed because they were expected at a party in the evening. When they did not appear there, their acquaintances alerted the police on Sunday morning. At around 10.20 a.m., four divers from the cave rescue service entered the cave and found the missing men in the “Reutlinger Halle”, an elevation inside the cave. With the help of the divers, they saw daylight again at 12.45 p.m. unharmed.

The great danger of the Falkenstein Cave

Throughout the year, the Elsach River flows through the Falkenstein Cave. This watercourse is the great danger when entering the cave. After rainfall or when the snow melts, the water level can rise so much that large parts of the cave are completely submerged. Such floods have already led to people being trapped inside on several occasions. In 1964, too, four people were trapped until they were finally rescued from the bowels of the earth by experienced cave divers after two and a half days. If the weather is dry, on the other hand, visitors can safely walk through the front part of the Falkenstein Cave, up to about 150 metres into its interior. However, rubber boots are recommended to keep feet dry.

Magical dripstone cave discovered

Workers at the Biggethal lime works in the Sauerland region were astonished when they suddenly looked directly into the belly of the earth on 19 July. A blast in the limestone had exposed a crevice in the rock. Driven by curiosity, they crawled inside. What they saw inside left them speechless: a fabulous landscape of stalactites and other limestone figures adorned the ceilings, floor and walls. The quarrymen had opened the entrance to an underground magic world.

However, the discovery of the cave was not completely unexpected. The search for a dripstone cave around the Hanseatic town of Attendorn had been going on for several years. The intention was to market it profitably as a tourist attraction. It was not without reason that people hoped and suspected that there might be such a cave worth seeing: During work in the limestone, rock holes with stalactites had already been found several times, but not in the necessary size.

So it is all the nicer for the people of Attendorn that their wishes have now come true. A name has also been found for the subterranean wonder of nature: It is to be called Atta Cave, after Princess Atta, who gave her name to the town of Attendorn.

No access to the Atta Cave for the time being

Mayor Heim wrote to the District Administrator on 24 July 1907 to inform him of the discovery of the dripstone cave and its provisional securing:

“In the limestone quarry of the Biggethal lime works a cave has been uncovered which, according to the information of several gentlemen who have inspected the cave, is characterised by exceptionally interesting dripstone formations. Precautions have been taken to prevent unauthorised persons from entering the cave in order to avoid damage to the formations.”