How did the hell hole form?

When the land above the caves collapses, "hell hole" will appear and can swallow cars and houses.

The large pit appeared in Guatemala's capital after the tropical storm Agatha.Photo: National Geographic.

After the tropical storm Agatha killed 123 people and 59 people were missing last week, a hole with a depth of about 100 m (equivalent to a 30-storey building) and a diameter of 18 m appeared between Guatemala City - the capital of Guatemala republic. National Geographic reported that a three-story building had fallen into the pit.

According to Livescience, like all other "hell holes" in the world, the hole in Guatemala formed when a piece of land collapsed, leaving a land subsidence.

The phenomenon occurs most commonly in the states of Florida, Texas, Alabama, Missouri, Kentucky, Tennessee and Pennsylvania, according to the US Geological Survey. The soil in these states contains many easily soluble or soluble solids such as limestone, carbonate and salt. When groundwater flows through those hard substances, they will decompose or dissolve, leaving underground holes and caves. When the caves of the underground caves collapsed, it followed the land above that made the cave appear.

Some "hell holes" gradually disappear due to sand and soil falling and covering. Many other holes subsided when decaying rocks were exposed to rain and wind.

The "hell holes" collapse unexpectedly can be dangerous. In some cases, underground water disappears due to droughts or changes in human groundwater flow (mining, irrigation or pumping water to the ground). When there is no water to support the cave, the land above collapses. In the case of water still in the underground cave, their arches become weakened due to the mass of the upper layer of soil should collapse.

When the land above the cave collapsed unexpectedly, it could swallow cars, houses and empty ponds. In September 1999, Lake Jackson near the city of Tallahassee, Florida, in an area of ​​more than 16 km ² - abruptly drained by a pit 15 meters deep. Florida Geological Survey said Lake Jackson was continuously depleted and filled with a 25-year cycle. Thus, people near the lake will see water there after 14 years.