ENVIRONMENT
“Further erosion and collapse transforms these cracks into networks of tunnels and caves”
Cave creation How do huge parts of the Earth get hollowed out? Caves can form anywhere whether it’s in the surface of the Earth, underwater or even inside mountains. In fact, any lump of rock has the potential to turn into a cave because they’re created by erosion, which can happen by a number of means. The most common kind of cave is called a solution cave. These tend to be made of rocks such as limestone or gypsum, as they dissolve faster in water than other kinds of rock. Water falling as rain collects carbon dioxide from the atmosphere before descending through the ground. The carbon dioxide mixed with rainwater can form carbonic acid, which is a key ingredient in dissolving the rock, especially in places where there is an existing fissure. Further erosion and collapse transforms these cracks into networks of tunnels and caves. The water will either stay in the base of the cave once it reaches rock that it can’t dissolve, or flows out through a hole to begin the whole process again. Some of the most incredible formations in cave structures are stalactites and stalagmites. Stalactites are the pointy shards that descend from the roof of a cave. These are created when the dripping rainwater collects calcium carbonate on its way through the rock. Once it reaches the open space the calcium carbonate solidifies. This builds up as water drips along the stalactite before hardening. Stalagmites are made of calcium carbonate too, but build from the base of the cave upward if the water has dripped down before becoming solid. Underwater and overground caves are formed in similar ways. Rock is repeatedly attacked by a force of nature, such as ocean tides, winds or sand. This bombardment wears away at the rock, creating a dent that gets steadily bigger until a cave is formed.
Inside a cave
How the Earth goes from whole to hollow
Stalactites The permeating water collects calcium carbonate, which hardens when it reaches the air, creating a stalactite.
Underground waterfalls Over time, so much of the rock can be eroded that waterfalls descend into the cave.
Cave revelations As well as being natural marvels, caves can tell us a whole host of things about life in the past. Archaeologists in China have unearthed evidence of humans making fire in caves as far back as 400,000 years ago. Meanwhile, the Cowboy Caves of Utah revealed
032 | How It Works
Rainfall As rain falls it collects carbon dioxide and forms carbonic acid, which dissolves the rock, especially in places with existing cracks.
6,300-year-old milling stones that were used to grind wheat into flour, showing that our ancestors were getting creative with their food from before 4000 BCE. Another notable discovery occurred in 1924 in Lovelock Cave, Nevada. Among the 10,000 items found were ‘duck decoys’ – devices used to lure ducks toward hunters who would catch them for food!
Erosion
Further erosion
The dissolved rock is washed away through underground streams, leaving larger and larger spaces.
Over a period of thousands of years the continued erosion creates enormous underground caves.
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