Ask An Expert: How Do Geysers Erupt?

Geysers are some of the most popular natural phenomena to be observed and studied — there’s just something fun about seeing the Earth let out a great big belch every once in a while. But how and why do geysers erupt? We went to Ríkey Júlíusdóttir, a geologist at the Icelandic Met Office, for an explanation.

“I would be oversimplifying things if I would say that they’re all the same. Geysers are each their own characters, much like volcanoes. They have their own cycles, their own frequency of eruption, their own chemical composition and their own eruption style,” Ríkey explains.

Geysir is probably the most popular — hey, the name “Geysir” being the base of all other geysers in the world is nothing to sneeze at. However, Geysir’s easy accessibility definitely plays a big part in its status. That accessibility allowed German chemist Robert Bunsen to study Geysir back in the middle of the 19th century and most of his theories and explanations hold up to this day. The geysers in the Russian Kamchatka area or even Yellowstone Park in the U.S., meanwhile, are at higher altitudes and quite a bit harder to reach, observe and study.

“What they all have in common, though, is that they are related to geothermal areas. Here in Iceland, they are all located around the volcanic belt,” Ríkey says. That belt of geothermal activity stretches all the way from the Reykjanes peninsula in the southwest, cutting diagonally across the island to the northeast.

But how a geyser actually blows, Ríkey explains, comes down to their shape and physical properties.

“Geysir has a so-called silica bowl of around 15 metres in diameter and around two metres in depth. At the centre of the bowl you have a long conduit going deeper into the Earth. At 23 metres down, (the conduit itself gets too narrow to measure deeper than that), the water temperature is around 120°C, but it can’t reach a boiling point because of the pressure of the water column above. Further up in the conduit, at a depth of about 15 metres, the water gets very close to a boiling point, but still not quite. However, if there’s any kind of disturbance in the water column — an earthquake or anything else to jostle that downward pressure — the water mixes around, finally comes to a boil and expands, heading in the only direction it can go: up.”

The OG Geysir has been mostly dormant for years, probably because of silica clogging up its conduit, so unless it gets seriously disturbed by seismic activity, as last happened in 2016, it’ll likely remain quiet. In the meantime, neighbouring Strokkur, while not as big, does a valiant job of keeping hot-water-watchers entertained, shooting boiling H2O into the air every couple of minutes to rounds of applause.