What’s the Difference Between a Volcano and a Geyser?

The other day, an old memory of the world’s only “captive geyser” in the town where I grew up—Soda Springs, Idaho—rose to the surface of my mind. As I pondered the fact that the captive Soda Springs geyser goes off very regularly—at the top of every hour, due to the manmade timer it is set to—I began to wonder just what makes a geyser a geyser. Why aren’t geysers considered volcanoes? Both volcanoes and geysers are known to erupt, so what makes one eruption a volcano and the other a geyser?

Photo of the Soda Springs Geyser erupting from kasabubu at https://pixabay.com/en/soda-springs-geyser-idaho-usa-1768623/
Soda Springs Geyser from kasabubu at https://pixabay.com/en/soda-springs-geyser-idaho-usa-1768623/

Curiosity got the better of me and I had to look it up. According to Geology.com, a “geyser is a vent in [the] Earth’s surface that periodically ejects a column of hot water and steam.” A volcano, on the other hand, is not just a vent, but a crack in the crust of a planet which allows material from down deeper under the surface to escape.

Notice how the definition of a geyser mentions water and steam? Where did that water and steam that is ejected during a geyser’s eruption come from in the first place? It turns out that it originates from the surface, working its way down through cracks, getting deeper and deeper, moving toward the planet’s core. As the water gets deeper, the temperature rises, causing some of it to become steam. When enough water reaches the right amount of pressure and temperature, it gets forced up through a (vent) geyser all at once—in what we see on the surface as the geyser erupting.

Volcano erupting at night with lava flowing down mountainside from Skeeze at https://pixabay.com/en/volcano-erupting-mountain-krakatoa-609104/
Volcano erupting from Skeeze at https://pixabay.com/en/volcano-erupting-mountain-krakatoa-609104/

Volcanoes erupt stuff to the surface, too, but what they erupt is magma (the liquid rock down deep in the Earth’s crust) which is called lava once it reaches the Earth’s surface. Gases and ash material from deep under the Earth’s surface can be spewed up along with the lava, as well.

Eruptions have also been seen on other planets and moons in our solar system. Most of these are known as cryogeysers or cryovolcanoes, which are geysers or volcanoes which spew frozen material instead of hot water and magma. The following NASA web short video by NASA Goddard/Katrina Jackson, Producer/Dawn mission from https://svs.gsfc.nasa.gov/12346 explains ice volcanoes very well.

The way I explain it to myself is like this: With a geyser, what goes down comes back up (If you wanted to be really gross, you could think of it like throwing up) and with a volcano, whatever’s down there in the first place explodes to the surface out of nowhere (Again, if you want to be gross, it would be like breaking a bone so bad it would poke up through your skin from out of your insides). And even though both geysers and volcanoes can be kinda gross with their belching everything up, geysers are a little bit more predictable than volcanoes, which often erupt without warning.

… And I just can’t end the post without telling you about some of the cool volcanoes and geysers I found out about.

  • Mount Stromboli—a volcano in the Tyrrhenian Sea—forms part of the Aeoli Islands of Italy and has been almost continuously erupting since 1932.
  • Strokkur geyser near Reykjavík, Iceland erupts once every 4 to 8 minutes, sometimes going as high as 40 meters (but usually only reaching 15 to 20 meters).
  • Kilauea—one of the most active volcanoes in the world—has currently been erupting since 1983. The U.S. Geological Survey maintains live webcam feeds of Kilauea and Mauna Loa that can be seen here (https://hvo.wr.usgs.gov/cams/) plus they’ve made available the following video of Kilauea erupting.
  • If you live in the United States, you’ve probably heard of Old Faithful in Yellowstone National Park. Old Faithful is not very good at staying on a set schedule, though—its’ eruptions range from every 35 minutes to 2 hours. It is tall, though—reaching 27 to 55 meters high. The National Park Service maintains a live webcam of Old Faithful that can be seen here. (https://www.nps.gov/yell/learn/photosmultimedia/webcams.htm) Below is a video of Old Faithful erupting from Geology.com.


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