They’re called sinkholes, and you see them on the news all the time threatening some of the more beleaguered parts of the developing world—Florida, for example. Acidic rainwater drains into the soil and eats away at limestone, eventually creating underground caverns. When these caverns collapse without warning, the results can be terrifying in a biblical sort of way. A factory in Guatemala or a Chevy dealership in Tampa can just disappear from the face of the earth in seconds. But what would a sinkhole the size of a small country look like? For that we have to go to the Qattara Depression of northern Egypt.
The Qattara Depression is a treacherous lowland covering 7,500 square miles in area near the Egyptian-Libyan border. It’s shaped roughly like a huge footprint, as if a giant had stepped from the Mediterranean into the Sahara, and left a big squishy mess. (“Qattara,” appropriately, is Arabic for “dripping.”)
The world’s biggest sinkhole formed over millennia, as salts in the soil eroded the rock into sand, which was then blown away by the fierce Saharan winds. Eventually hundreds of feet of bedrock were eaten away, exposing the water table beneath. The area is now a sludgy, salty, quicksand-like pit about the size of Lake Ontario.
Bedouins in the vast Sahara have known about—and mostly avoided—the Qattara Depression for centuries, but scientists first discovered it less than a hundred years ago. At 436 feet below sea level, it’s the second lowest point in Africa, a result so surprising that the British Army didn’t believe it and had to recheck their barometers. During World War II, the sinkhole proved crucial in the Allied victories at El Alamein. Its shifting sands are impassable to vehicles, which prevented the Germans from outflanking the British general Montgomery.
The Qattara Depression is so low that it could someday be used to power much of Egypt. Theoretically, a 50-mile tunnel could be dug downhill from the Mediterranean, filling the sinkhole with seawater. New water would continue to flood into this new Dead Sea-type lake as it evaporated, providing vast amounts of hydroelectric power along the way. In fact, Jules Verne proposed a similar project in the Sahara in his last novel, Invasion of the Sea, way back in 1905.
More From Condé Nast Traveler: