Yellowstone National Park's Old Faithful mystifies and delights tourists with its recurrent eruptions. But because of its popularity, it is heavily protected: the government limits access to curious scientists and restricts experiments on its plumbing. At least 80 smaller but equally percussive geysers also burst forth in Chile's Atacama Desert, offering an analogous opportunity to probe the earth's inner workings. Geologists laden with temperature and pressure sensors, GoPro cameras and a host of other gadgets recently observed one such geyser, nicknamed El Jefe, over the course of five days and more than 3,500 eruptions—one every 132 seconds. The result? The most detailed data set yet on the explosive choreography between water and steam.

El Jefe's flare-ups occur more regularly than those at many other geysers, but the plumbing is largely the same: a deep underground reservoir of water feeding a narrow channel that leads to the surface. As heat from the earth's core transfers to the reservoir, bubbles of steam rise through the water and up through the channel until they are caught in a small side chamber, a “bubble trap.” When enough steam collects there, it escapes and, with water, overflows the geyser's top. Eventually these escaping bubbles make the water in the channel so hot that it boils and triggers a full eruption; the low pressure from the boiling water at the top of the column starts a downward-propagating reaction that lowers the boiling point of the water underneath so that steam and hot water from the whole column shoot up all at once. (These stages, followed by a recharge stage when the water filters back down into the reservoir to resume cycling, are shown in the group's laboratory model above.) The observations were published in February in the Journal of Volcanology and Geothermal Research.

The measurements, taken at a range of depths, will yield a better understanding of the geyser's cycle and boiling patterns, says Michael Manga, a geologist on the El Jefe project at the University of California, Berkeley. Previous studies had captured either pressure or temperature, but both are necessary to gain insights into how heat travels through water below the earth's surface. Steven Ingebritsen, a researcher at the U.S. Geological Survey, is intrigued by what this more complete picture of geysers can tell geologists about other geothermal phenomena, such as volcanoes, which operate primarily underground and are incredibly challenging to probe—instruments would melt, for starters. The same flow of magma below the surface powers both types of eruptions. “They got their probes as deep as was feasible,” Ingebritsen says. “But you wonder what's going on down deeper.”