, Sept. 30 -- Sinkholes are sudden holes that open up in the ground when the surface layer drops into empty spaces below. They can be as small as a dip in a garden or so big that they swallow houses, cars, and even whole streets. To understand why some sinkholes are more dangerous than others, it helps to know how and why they form. Let's find out the most deadliest sinkholes around the world .

How Sinkholes Form in a Natural Way

Most sinkholes form in places where the rock under the ground can slowly dissolve in water, such as limestone, dolomite, or gypsum. Rainwater becomes slightly acidic after mixing with gases in the air and soil, and over many years it eats away at these rocks, creating gaps and hidden caves underground. As time ...