What Is a Volcano?

From Chile to Hawai‛i to Yellowstone to Oregon, volcanoes have been "erupting" in the headlines over the past week. Each one of these powerful eruptions has its own unique story. How do volcanoes form? Are eruptions always dangerous?

Sabrina Stierwalt, PhD
5-minute read
Episode #145

Oregon’s Axial Mount

About 250 miles off the coast of Oregon and Washington, at the site of 2 diverging tectonic plates, the active, underwater Axial Volcano is believed to have also erupted this week. Thousands of small earthquakes have been detected, and the sea floor surrounding the volcano has dropped by eight feet, suggesting magma is shifting and even escaping. Luckily for residents of the northwestern US, the seismic activity is not expected to reach land or be intense enough to cause any tsunamis.

The activity is well documented, as the Axial Volcano is home to NeMO—the first underwater volcano observatory that studies the biology, chemistry, and geology of such eruptions on the sea floor.

Underwater volcanic eruptions bring heat to the surface that then creates hot springs called hydrothermal vents. These vents provide a unique environment for life not found elsewhere on Earth, and may actually be close analogs to where life on our planet originally began.

Kilauea, the Most Active Volcano

The Hawai‛ian Islands, which were formed by volcanic activity, are not near converging or diverging tectonic plates, but instead lie in the middle of the Pacific Plate. They were formed over a “hot spot,” or location where a relative increase in temperature causes magma to erupt from the surface. This hot spot is fixed, but the tectonic plate moves, so geologists believe the island chain formed as the plate moved over the hot spot.

Kilauea, on the island of Hawai‛i, may be the most active volcano in the world. Fortunately for residents of the Big Island, Kilauea is a shield volcano, or one that is built up from fluid magma flows. Shield volcanoes are large in size, but tend to send erupted material in all directions, and that lava can travel much farther before solidifying. These events end up being calmer than more directed, high-speed eruptions.

Kilauea has been known for constant eruptions for over 30 years, and during that time its activity level has varied. Two of its craters, Halema‛uma‛u and Pu‛u O‛o, are filled with lakes of lava, the heights of which are observed to rise and fall. The volcano has made news recently because the lava lake at Halema‛uma‛u has overflowed, taking part of the crater’s edge with it. This crater is well within the confines of the edges of the very large volcano, however, and thus is not cause for concern.

Yellowstone Supervolcano

Another hot spot like the one that created the Hawai‛ian Islands lies beneath the surface of Yellowstone National Park. The pressure and magma build up caused by some hot spots is not always able to break through, causing an ever-increasing pool of magma to accumulate below the surface. This build up can create supervolcanoes, or volcanoes capable of spewing more than a volume of 1,000 cubic kilometers (240 cubic miles) of molten rock and gas in an eruption.

The Yellowstone supervolcano was known to be large, but a recent study found it to extend far beyond what was originally thought. The size of the magma reservoir was traced by seismic waves, which travel slower through hot, molten rock than they do through cold, solid rock. The seismologists found two reservoirs that supply Yellowstone: one as deep as 50 kilometers, and a shallower one that reaches only 17 kilometers in depth but extends about 90 kilometers long (2.5 times the size estimated by a previous study).

However, the overall volume of the magma we know to sit below the surface at Yellowstone has not changed, and so these findings don’t affect the hazard rank for the volcano. Instead, geologists have a better understanding of how far the volcano’s influence extends and what powers such a supervolcano.

You can check the status of Yellowstone, Kilauea, and other U.S. volcanoes on the United States Geological Survey website.

Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.

Tungurahua Volcano eruptionErupting volcano near water, and Volcanic terrain landscape illustration images from Shutterstock.



About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.