After learning that Yellowstone was a supervolcano (one capable of essentially exploding into an eruption thousands of times larger than that of a mild-mannered, glasses-wearing volcano), geologists were rightly curious about how many other apocalyptic magma cannons had been built over by oblivious engineers, resort planners and goat-footed Hollywood directors. The answer is at least six.
6A Secret Weapons Lab
The Los Alamos National Laboratory, which housed the development of the Manhattan Project, was built almost directly above a supervolcano dubbed Valles Caldera (presumably so if the atomic bomb turned out to be a failure, we would still get to see something explode). Despite its age (1 to 2 million years), the volcano is still showing subterranean activity, which, despite sounding like a compliment you would pay a septuagenarian who can get an erection without having to take beta blockers and change his underpants, means that the thing could technically erupt at any given time.
Witold Skrypczak / Getty
Silent but world-breaking.