We think of the ground under our feet as the most solid thing there is. Buildings rest on it, roads run across it, and we rarely give it a second thought. But in some places, the earth can open up without much warning and take whatever sits on top of it.
The most famous example happened on May 30, 2010, in Guatemala City. A nearly round hole about 65 feet wide suddenly opened in the city's Zona 2 neighborhood and swallowed a three-story building and a house. Heavy rain from Tropical Storm Agatha, combined with leaking sewer pipes and soft ground, was blamed for the collapse.
A Hole That Looked Unreal
Photos of the Guatemala City hole spread around the world because it looked almost fake. The walls dropped straight down, and the opening was close to a perfect circle. Reports of its depth vary, from about 100 feet to around 300 feet.
The city is built on deposits of volcanic pumice, a light, loose material that erodes easily when water flows through it. Leaking pipes went unfixed long enough to wash out a hidden cavity underground. Then torrential rain from Agatha widened it until the surface finally gave way. A similar hole had opened nearby in 2007, which may also have been caused by broken sewer pipes.
Was It Really a Sinkhole?
Here's a twist. Some geologists say it wasn't a true sinkhole at all. Natural sinkholes usually form in limestone, and there's no limestone for hundreds of meters beneath Guatemala City. One geologist called the name a misnomer, since this hole was mainly caused by people rather than nature. Some experts call it a "piping feature" instead.
Real sinkholes form when water slowly dissolves soluble rock like limestone, gypsum, or salt underground. That creates hidden voids. Soil may gently settle into them, forming a shallow dip. But when too much soil drains into the voids, the surface can collapse suddenly, sometimes with catastrophic results.
Florida's Famous Sinkhole
Americans have their own legendary example. On the evening of May 8, 1981, a sinkhole opened in Winter Park, Florida, during a period of record-low water levels in the state's limestone aquifer. Within hours, a 40-year-old sycamore tree had disappeared into it.
By the next day, the hole was swallowing homeowner Mae Rose Williams's property. She described hearing a sound "like giant beavers chewing." Her family got out with their belongings, and that afternoon her house slid into the pit.
The hole eventually grew to 320 feet wide and 90 feet deep. It also swallowed five Porsches from a repair shop, a pickup truck with a camper top, part of the city's municipal pool, and chunks of two streets. Damage was estimated at $2 million to $4 million. Engineers called it the largest sinkhole event ever witnessed that resulted from natural causes.
Where Sinkholes Strike
The most likely places for a sinkhole collapse are areas that already have lots of sinkholes, because their presence shows unstable voids underground. Human activity can raise the risk, too, by changing how water drains through the ground.
Winter Park's hole was eventually stabilized and became a lake. Two of those Porsches are still believed to be down there, along with the house. It's a strange monument, and a reminder that the solid ground under our feet isn't always as solid as it seems.
