This week, reporters strolling by the White House lawn noticed a growing depression in the well-manicured grass. The White House called it a sinkhole and after surrounding it with caution tape and cones, covered the small pit with a slab of green plywood.
But while sinkholes — depressions in the ground caused by a collapse or sinking of land — can grow into rather unsettling, gaping holes capable of swallowing houses in some parts of the U.S., it’s extremely unlikely that anything of this sort will happen near the White House.
“The geology just isn’t right,” Dave Weary, a U.S. Geological Survey research scientist, said in an interview. “It’s doubtful this one will get really big — it won’t get 100-feet wide.”
Washington D.C. doesn’t have a vast system of caves and voids beneath the ground in the same way that places in Florida, Texas, and New Mexico do. Called Karst systems, these parts of the country are made up of massive deposits of limestone and other dissolvable rocks, which naturally gets eaten away by slightly acidic groundwater over millennia.
These limestone worlds are home to massive subterranean spaces, such as the cathedral-like Carlsbad Caverns in southeastern New Mexico.
“But there’s no limestone, at least in the near surface, in the D.C. area,” Ming Ye, an expert on groundwater hydrology and sinkhole formation at Florida State University, said in an interview.
The White House sinkhole “will not be big, and it probably won’t grow large in scale,” Ye added.
So what is happening beneath the White House lawn?
“It’s suspicious that this occurred right after this raining event,” said Weary, referencing the deluges that hit the area in the past few days, flooding roads and pouring into train stations. “That implies wet weather triggered it [the sinkhole].”
While there likely aren’t any caverns under the White House lawn, Weary noted that the capital area is home to a lot of “unnatural terrain,” filled with ancient building debris and wood. And when this stuff rots away, it can open up smaller voids, which are susceptible to collapse when water starts moving dirt around during heavy rainfall events.
The colored areas on this USGS map show areas with soluable subterranean rocks with potential for cave or sinkhole formation.
The White House, in particular, had a lot of underground infrastructure put in during the Roosevelt and Truman administrations, noted Weary. So, associated construction or landfill might have also resulted in the formation of a small void.
It might even be something pretty mundane.
“It could just be a leaky pipe,” said Weary.
The White House doesn’t appear to be too concerned — publicly, at least. The National Park Service, which is monitoring the sinkhole, issued a statement Tuesday saying that they “do not believe it poses any risk to the White House or is representative of a larger problem.”
If the White House sinkhole were going to grow in size, however, geologists would have some obvious hints. Circular cracks or ruptures in the ground called “ring fractures” would form around the sinkhole — which doesn’t appear to have happened.
“As you’re approaching the hole you don’t want to walk across these things,” said Weary.
If there was some concern about the sinkhole’s potential for growth, geologists could conduct geophysical surveys by sending signals into the ground that bounce back, giving scientists a map of whatever is going on underground.
“It’s like a CT scan or X-ray for geologists,” said Ye.
A thousand miles south, in Florida — where sinkholes have eaten cars and homes — such a small sinkhole probably wouldn’t be too alarming.
“Something even worse is happening in Florida today,” said Ye.