Along a cliff, weathering and erosion can form caves, arches, stacks, and stumps. Caves form as waves smash through fissures in the cliff face. The water carries sand and other things that grind away at the rock, eventually forming a cave from the fissures. Arches are areas where the roof has collapsed, leaving an open space under some trees or beside a road. Stacks are groups of more than one cave with connections between them. In stacks, the wind usually gets into the gaps between the rocks and moves from cave to cave until it reaches another opening. Finally, stumps are old trees that remain after a forest fire or when the trunk breaks off below the ground.
Caves can be used for shelter, but they also pose many dangers for humans. If you go inside a cave expecting to find dry air and clear passages, you might not come out for days. Cave-dwelling creatures have no choice but to adapt to this kind of environment. Some use their sense of smell to find food and water, while others make do with vision. Some species can even detect vibrations in the ground from large animals such as elephants that might be approaching.
People have used caves for shelter since ancient times. Early humans probably used caves for protection from danger and to find food and water. They may also have used caves to pray or give thanks.
When the arch falls, the headland on one side and a stack (a towering column of rock) on the other are left. The stack will be assaulted from the bottom, similar to how a wave-cut notch is generated. Rock that was once part of the cliff has been scoured away to leave a vertical wall with a shallow cave at the top. This is called a shingle bank because the notched rock resembles the scales on a fish.
Stacks can also form where two cliffs meet. Here the energy of the falling rocks is dissipated as heat rather than sound. Sticks and leaves find their way into the cracks and holes created by the falling rocks. In time, wood decays and drops out again, leaving only the stone remains which can still be seen today.
Stacks can be large or small. Some are merely boulders that have fallen off a cliff edge but others such as Cheshire's Stack Bridge are made up of several smaller stones set in concrete which cross a road near Chester.
The Isle of Man looks like a giant rock from space! It is an island located between Ireland and England, about 16 miles from the coast of Northern Ireland. The Isle of Man is mostly made of gneiss which is a hard greenish rock that forms when molten magma rises quickly through the Earth's crust, causing crystals to grow along its path.
Depending on the type of cave, it might have developed as a result of water erosion, chemical processes, or even molten rock from a volcano. There are sea caves and other caves hollowed out by water pressure erosion, as well as volcanic caves produced by empty lava tubes.
Caves can also be used as shelters from nature's disasters such as floods, tornadoes, and hurricanes. Human-made structures such as mines and tunnels with no natural exit could lead to death from asphyxiation if not found otherwise.
Finally, some caves may be the result of natural processes after an eruption or landslide. These are called "geological caves" and often contain beautiful formations such as arches, windows, and draperies.
The meaning of life is difficult to define. Some scientists say that life exists because it can survive. Other scientists say that life is a phenomenon that occurs when atoms combine together. Still others say that life is nothing but a series of electrical signals traveling through molecules. Defining life itself is impossible because it depends on what you want to call living.
Human beings are responsible for many changes to Earth's environment. They cut trees down for timber and soil protection, pollute our air and water, and leave debris behind when they move away from their campsites.
Ground water moves slowly via minor fissures over many years. The water dissolves and transports the solid rock, gradually expanding the fractures and building a cave. Caves can also be formed by violent processes that destroy part of the roof of the cave cavity (avalanche, flood). This causes the remaining rock to collapse into itself.
The direction of groundwater flow is usually indicated by the orientation of cave walls. If water flows toward the center of the cave, then the wall material should be sandstone or siltstone; if it flows away from the center, then the material should be limestone or dolomite.
Cave formation is a major concern for those who live in cave areas because water can quickly erode away any exposed soil or rock. The only way to prevent this erosion is by covering the surface with vegetation. The cave community helps protect humans by providing shelter from rain and snow, food for animals, and places to hide from predators.
Caves have been used for various purposes throughout history. Some people take advantage of the cool temperatures and low levels of humidity found inside caves as shelters from heat, cold, and wind. Others use their caves for hiding from police, criminals, or enemies.
Caves have been important factors in the evolution of life on Earth.
Erosional caves are ones produced by water or wind transporting abrasive particles capable of cutting rock. Erosion creates lofty, canyon-like channels. Running water on glaciers can sink into crevasses and melt a route through the glacier, resulting in the formation of glacier caves. In deserts, wind can wear away sand grains until only quartz is left, which cannot be eroded any further. This produces fine silica dust that can be carried by winds for great distances. When this dust settles, it forms shallow depressions in the ground called cairns.
Caves formed by erosional processes can contain anything from dry bones to beautiful stalactites and stalagmites. Because they are made of solid material, bones do not decay in caves as they do outside the cave walls. They become fossilized.
Cave formations are changed by light levels inside the cave. Where there is more light, such as near the surface, plants grow which use the carbon dioxide we exhale and add oxygen to their tissues. These plants produce organic matter such as leaves and sticks that can be blown into the cave. Without sunlight to break them down, these materials would accumulate in the cave and block out some of the light. Over time, this could cause the formation of shadows under which organisms may live. However, deep within the cave, far from any source of light, life must make its own electricity using chemicals derived from the food we eat.