Looped plumbing causes geysers to erupt

Why does a geyser erupt, but a hot spring only bubbles? The difference is in the shape of the pipes that lie beneath the ground, pumping the hot water to the surface.
According to a new study, the plumping that supply geysers with heated water and steam is characterized by twists, turns and loop-the-loops -- small intricacies where steam can gather.
As researchers at the University of California, Berkeley recently confirmed, water in geysers actually boils downward -- and rapidly.
The process begins when magma below the Earth heats deep-dwelling water, pushing it back through small tunnels in the porous rock that form the geyser's chamber. Steam rises and collects in loops, side champers and other unique twists and turns in the geyser's plumbing. Some of that collecting steam escapes to slowly heat the top of the water.
Eventually enough of the water reaches boiling point at the top and begins to bubble. The boil decreases pressure in the lower water columns, triggering a rapid boil downward and releasing the trapped steam and superheated water. This series of events creates an eruption of steam and water up through the chamber and outward.
"Most geysers appear to have a bubble trap accumulating the steam injected from below, and the release of the steam from the trap gets the geyser ready to erupt," Michael Manga, a UC Berkeley professor of earth and planetary science, explained in a press release. "You can see the water column warming up and warming up until enough water reaches the boiling point that, once the top layer begins to boil, the boiling becomes self-perpetuating."
Manga and his colleagues aren't the first to formulate such an explanation. German chemist Robert Bunsen first proffered the basic theory of the downward boil in 1846.
But Manga and his fellow researchers were able to prove Bunsen to be correct by sticking temperature and pressure gauges down a geyser in Chile called El Jefe -- confirming that a geyser's rapid boil begins at the top. Researchers have previously stuck cameras down geysers, proving the geothermal phenomena regularly features oddly routed pipes. Bunsen didn't know about that part.
The study was published this week in the Journal of Volcanology and Geothermal Research.