Onlookers in China watched in shock as a massive sinkhole swallowed up a building complex this week.
The group of buildings was part of a complex built near the construction site of a new underground train station in Guangzhou, the Telegraph reports. A total of four buildings fell into a hole that measured about 30 feet across, Discovery News notes.
About 300 nearby residents were evacuated, and streets in the area were also closed. Fortunately, no one was hurt.
In 2010, a similar sinkhole swallowed up a three-story building in Guatemala City, killing one man, Vanity Fair reports.
The magazine noted that these occurrences are generally caused when circulating ground water dissolves rock below the ground:
As the sediment dissolves, caves and air pockets develop underneath the land surface. If there is not enough support for the land above the spaces, then the ground collapses and results in a sinkhole.
Heavy rainfall, or poor drainage in urban areas can exacerbate the problem.
Last year, David Weary, a research geologist with the U.S. Geological Survey, told ABC News that sinkholes can be triggered by natural and man-made causes.
"Usually you get a collapse because something occurred that transported the material, creating the void that the sinkhole falls into,” Weary said. “If there’s a cave underground filled with soil and sediment and you get an episode of high rainfall or a change in groundwater flow, the dirt that filled the void will be hollowed. Once it hollows out close to the ground surface, it becomes thin enough that it can’t support what is on top of it and it falls in.”
Weary added that while still relatively rare, sinkholes seemed to be occurring with more and more frequency in urban areas due to drainage issues.