It was a rainy December morning in San Francisco when the Earth opened up. The ground suddenly fell away into a 12-meter-deep sinkhole that engulfed a garage, part of a street, and a multi-million-dollar mansion. Sinkholes can seem to strike out of nowhere, but they’re more common than people often think. So, how do they form? Elise Cutts details what’s happening just below your feet. Lesson by Elise Cutts, directed by Evandro D'Hipolito.