These are nothing but Sinkholes, it is one of the world's scariest natural phenomena. Over time, water erodes the soil under the planet's surface until in some cases, quite suddenly, the land above gives way and collapses into the earth. Many sinkholes occur naturally while others are the result of human intervention. Displacing groundwater can open cavities while broken pipes can erode otherwise stable subterranean sediments. Urban sinkholes, up to hundreds of feet deep have formed and consumed parts of city blocks, sidewalks and even entire buildings.