Steamboat Geyser

Steamboat Geyser is the world’s largest active geyser, and Yellowstone National Park officials said it erupted last Thursday for the first time since September 2014. This photo shows a steam plume from the 2014 eruption.

The world’s largest active geyser roared back life in Yellowstone National Park last week.

Based on temperature and seismic data from the Norris Geyser Basin, Yellowstone officials confirmed that Steamboat Geyser erupted at 5:30 a.m. Thursday.

But because most of the park’s roads are closed because of spring plowing, park officials said nobody witnessed Steamboat going off.

Later on Thursday, park employees saw a steam plume billowing from the geyser, and on Friday geologists caught the steam on video. As of Monday at 3 p.m., the steam plume was still visible.

Steamboat Geyser is the world’s largest active geyser, but it only erupts sporadically and it is impossible for geologists to pinpoint when it will go off. Since May 2000, there have only been 10 eruptions. Before Thursday, the last eruption was on Sept. 3, 2014.

Geysers are constricted hot springs that erupt as the water heats up. Steamboat’s major eruptions can shoot steam to heights of 300 to 400 feet.

By comparison, steam from Yellowstone’s world-renowned Old Faithful Geyser, which erupts like clockwork more than a dozen times daily, averages 130 feet in height.