A geyser in Yellowstone’s Biscuit Basin suddenly and violently exploded at about 10 a.m. local time on Tuesday because of a hydrothermal explosion underground, sending debris and boiling water and steam showering down on the area.

Some of these pieces of rock were up to 3 feet in diameter and weighed more than a person, according to an update from Yellowstone National Park and the United States Geological Survey.