Imagine walking along the sidewalk and suddenly the ground drops away! Where the road or sidewalk used to be, there is a hole instead. This
sudden disappearance of land is called a cover-collapse sinkhole. The other type of sinkhole is a cover-subsidence sinkhole. The second type is less drastic
and less dangerous. The ground slowly disappears or sinks over a long period of time. Depending on the situation, sinkholes can be very different. They
can be just a few feet deep and wide to hundreds of feet deep and wide. In cities, these big sinkholes can make entire cars or buildings disappear. In 2010, a
sinkhole in Guatemala was so big (65 feet across by 100 feet deep) it swallowed a 30-story building!

• Sinkholes can be caused by humans and by nature.
• They are most common in “Karst Terrain.”
• Karst Terrain happens when groundwater naturally dissolves rock underneath the surface of the land. Large caverns sometimes form underneath the land, and when they can no longer support the surface, it collapses.
• The bigger the cavern, the more dangerous the sinkhole.
• It can take a long time for these sinkholes to appear.
• The process for creating sinkholes is called erosion.
• Erosion happens when the earth gradually moves or is destroyed by wind or water.
• Usually, people think of erosion as something that happens on the earth’s surface along beaches or mountains.
• Erosion can also happen underground. It can happen anywhere there is water or wind.
• If water is acidic, it can dissolve rock quickly.
• The more acidic the water, the faster the rock will dissolve.
• Carbonate rocks like limestone are chalk-like and commonly dissolve to form sinkholes.

Humans can also contribute to erosion and to creating sinkholes. Common causes are mining, old sewers collapsing and pumping ground water. When
humans change how the water moves under the ground, it can change the ground as well. Also, heavy buildings may make a sinkhole appear because the
buildings are too heavy for the surface soil to support. Sometimes in urban areas, people can predict sinkholes, but usually, they are a surprise. This makes
them very dangerous in crowded cities. They can also have long-term effects when they destroy parts of cities. These collapses can release toxic chemicals
into the groundwater that people use for drinking water.

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