Watch a geyser throw boiling water fifteen meters into the air

Strokkur is a pool of clear water in a steaming field at Geysir, and every few minutes it empties itself upwards. Nothing else in the field does much. The other vents sit and steam, which is most of what makes the one that performs worth standing in front of.

There is no schedule and no announcement. A crowd gathers at the rope, phones already up, and waits on a pool that is doing nothing at all. The wait is the whole ritual, and it is never quite long enough to get bored and never quite short enough to relax.

The warning is about a second long. The surface swells into a dome of pale blue, holds, and then breaks. Everyone gasps anyway, as though it had not done exactly this a few minutes earlier, and everyone who pressed the shutter a moment late settles in for the next one.

That dome has been measured. It lasts around seven tenths of a second and rises up to half a meter before it ruptures, and how high it gets is a rough predictor of how high the column goes. The column is usually fifteen to twenty meters, and it has been known to reach forty. Which is to say the eruption announces itself in advance, to anybody who knows to watch the water instead of the sky.