2.7 Caves

Where would you look for a spectacular cave like this one?

Groundwater dissolves minerals and rocks into ions. Groundwater deposits those ions into different types of structures. Limestone caves are the best place to see these structures. Water erodes the cave and it has deposits structures like stalactites and stalagmites. The cave pictured here is Carlsbad Caverns in New Mexico.

Caves are natural openings within the earth that usually extend deep beyond the reach of light. They are found in many types of rock, but are most common in limestone and gypsum. These caves were formed by water under the surface of the earth. A second type of cave is the lava cave, formed as liquid lava flows. A third type of cave is the sea cave. Sea caves were formed along cliffs and rocky seashores.

The study of caves is known as speleology, and those who explore caves are called speleologists.

Visit the Paleolithic Cave at Lascaux

The Lascaux cave was discovered in 1940 by four teenagers. The cave is located in the Bordeaux region of France on the river Vézère. There are more than 100 Paleolithic caves in the region.

The Lescaux cave is rich with things to discover. Each section of the cave has unique and fascinating depictions.

The sections of the Lascaux cave:

•The Painted Gallery
•The Great Hall of the Bulls
•The Chamber of Felines
•The Chamber of Engravings
•The Main Gallery
•The Shaft of the Dead Man

The cave drawings in the Lascaux cave originate from the prehistoric era — 15,000 to 13,000 BCE. The many paintings, drawings, and engravings give us insight into the world of these early people. Many of the cave images are of animals such as bulls, bison, and horses. This is very significant, as these early people were hunters. They relied on animals for food, for life itself. These drawings tell us about the lives of the people who made them.Make your classroom into a “Talking Wall.” After your explorer teams learn about Lascaux, give them a chance to record images from their own culture. Visit the Talking Wall site below and learn about the ways historical detectives learn about cultures by analyzing the images that those cultures leave behind.

The Lascaux cave was open to the public until 1963. After World War II, the entrance to the cave was widened for visitors and over a thousand people came to see it every day. By 1955 it was clear that the drawings were starting to become damaged. The carbon dioxide that the visitors breathed out was leading to the corrosion of the walls of the cave.

Caves in the United States

There are thousands of caves in the United States, including a number of spectacular proportions. Mammoth Cave, in Kentucky, has over 300 miles of passageways. Carlsbad Caverns, in New Mexico, has a cavern that is the size of eight football fields.

Most American caves are found in limestone rock. The caves began as water made cracks in the limestone and the cracks got bigger and bigger. The opening grew into underwater streams and rivers. When the water was gone, these underground waterways became cave tunnels and caverns. It can take from 10,000 to 100,000 years to make a cave that is large enough for humans to explore.

Water drips constantly in caves. The water carries minerals that accumulate into formations, as the water dries out. Cave formations grow over thousands of years.

Sea caves were formed by waves crashing against rocky coastline or coral reefs. Waves can hit sea cliffs with blows averaging several hundred pounds per square inch, which erode the soil and rock, and after many years create sea caves.

CAVE ANIMALS:

Animals use caves in different ways. Some animals, including humans, use caves only for temporary shelter. Other creatures are dependent on the cave environment for their survival. Trogloxenes (literally “cave guests”), such as raccoons or bats, live near the cave entrance, and venture into the cave to find food or shelter from the elements. Troglophiles(literally “cave lovers”) are animals such as daddy longlegs and cave salamanders that sometimes live in caves but can also be found elsewhere. Finally,troglobytes, such as the blind Texas salamander and the blind flatworm, are animals that live in caves and depend on the cave for survival.

Cave Deposits

Caves are known for their spectacular mineral structures. Caves are likely to be found in limestone where the groundwater level has gone down. This exposes the cave and its features. Stalactites are beautiful icicle-like formations. They form as water containing calcium carbonate drips from the ceiling of a cave. The word stalactite has a c, and it forms from the ceiling. Stalagmites form as calcium carbonate drips from the ceiling to the floor of a cave. The stalagmite grow upward. The “g” in stalagmite means it forms on the ground. You can see examples of both stalactites and stalagmites below (Figurebelow).

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Stalactites hang from the ceiling and stalagmites rise from the floor of a cave. The two together form a column.

If a stalactite and stalagmite join together, they form a column. One of the wonders of visiting a cave is to witness the beauty of these amazing and strangely captivating structures.

Giant Crystals

Some of the largest, and most beautiful, natural crystals can be found in the Naica mine, in Mexico. These gypsum crystals were formed over thousands of years. Groundwater that is rich in calcium and sulfur flowed through an underground cave. Check it out:

Naica Mine-Gypsum-Selenite at http://www.youtube.com/watch?v=6drrYFj91Ko(2:40)

Vocabulary

column: Solid cave feature formed when a stalactite and a stalagmite grow together.
stalactite: Icicle-like formation of calcium carbonate; forms from water dripping from the ceiling of a cave.
stalagmite: Deposit of calcium carbonate that grows upward in caves as water drips onto the floor.

Summary

Groundwater dissolves minerals and carries the ions in solution.
Groundwater deposits the material in caves as stalactites, stalagmites, and columns.
Giant crystals may be found in caves.