Geysers need loops and bumps

Only geological bubble traps ensure regular outbreaks

Outbreak of the geyser "Old Faithful" in Yellowstone National Park. © UC Berkeley
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Outbreak to the minute: Only "bubble traps" in the vent of a geyser allow the well-known regular outbreaks of geysers like the "Old Faithful" in Yellowstone Park, as geologists have now found out. These special conditions explain why these fascinating volcanic springs are so rare, the researchers write in the "Journal of Volcanology and Geothermal Research"

Geysers are a fascinating form of volcanism: instead of merely boiling as a hot spring, they can shoot a fountain of steam and boiling water up to 60 meters high into the sky. On some geysers, these eruptions happen so regularly that you could put them almost one o'clock after that: "Old Faithful" in Yellowstone National Park is particularly reliable and spits its fountain almost every 91 minutes.

Special geological conditions

In a geyser, deep magma heats the water column of a spring. However, this water must not be present in a shallow pond, but must be in a narrow but deep vent. The pressure makes the water in the depth cook only at much higher temperatures. This slowly heats up the entire water column. Only when it begins to boil on the surface, the pressure falls in the underlying layers of water, so that they can evaporate. The entire water in the vent evaporates almost suddenly: The geyser breaks out.

Temperature measurements on a geyser vent in the Chilean "El Tatio" geyser field. © Michael Manga, UC Berkeley

This basic principle has been known for over 150 years, but it is too simple: geysers are rare, there are fewer than a thousand worldwide. Moreover, they are very different in their behavior. So there have to be special conditions to turn a volcanic source into a geyser.

Curves and bumps as a bubble trap

Geologists in the Yellowstone Park and El Tatio geyser field in Chile have been studying geysers using pressure sensors, temperature measurements and seismic gauges. Michael Manga from the University of California, Berkeley, Canada, is investigating these conditions. In Chile, they were even allowed to sink video cameras inside the geysers. display

They found out that loops, bumps and small caves in the vent are apparently responsible for the behavior of a geyser. They act as "bubble traps": "Most geysers seem to have a bubble trap that collects steam from below, " explains Manga. The heat stored in the steam heats the water column more and more until it breaks out. Occasionally escaping vapor bubbles cause minor eruptions of the geyser, often initiating a larger fountain.

Why are geysers breaking out? UC Berkeley

From laboratory geyser to the volcano

Based on their findings, the researchers also built a mini glass geyser in the lab. On this model, they can better understand characteristics such as the temperature profile at different depths and also make longer-term video recordings. However, the laboratory geyser only reliably produced regular eruptions after a few loops in its glass vent formed the necessary bubble trap.

These new findings are not only important for geysers: Manga sees many similarities to volcanic eruptions. However, volcanoes are even more complicated to study than geysers: no sensors and cameras can be dipped into their vents. However, geologists believe that the principle of geysers could also serve as a model for many volcanoes. (Journal of Volcanology and Geothermal Research, 2015; doi: 10.1016 / j.jvolgeores.2015.01.002)

(University of California Berkeley, 25.02.2015 - AKR)