students in Hawaii
Bruce Nelson
Earth and Space Sciences’ GeoClub students in Hawaii.

When thinking of the “biggest” mountains on Earth, many people immediately think of Mount Everest or Denali, but some of the biggest mountains actually start below sea level and grow into islands. At over 33,000 feet, Mauna Kea in Hawaii reigns supreme as the biggest mountain on Earth as measured from base to top. Let’s explore the ways in which these mountains are different, both in how they are made and their geologic setting.

Mountains like Mount Everest or the Rockies are made by tectonic forces that crumple the crust and cause an enormous uplift. By contrast, Hawaiian volcanoes are formed by magma with origins from very deep in the earth when a plume forms from near the Earth’s core and rises up to form the volcano. The plume from the core-mantle boundary is solid – it is essentially hot rock at this point, so it flows very slowly and starts melting into material that turns into lava from 120-200 km below the surface of the Earth. We sat down with Earth and Space Sciences professor Bruce Nelson to talk about 10 facts people may not know about the Hawaiian volcanoes.

  1. The magma that rose up to form all of the Hawaiian volcanoes including Mauna Kea came from near the Earth’s core. This material is the closest we can get to getting indirect samples from the bottom of the Earth’s mantle (2,900 km deep).
  2. Mauna Kea and Mauna Loa formed very quickly, geologically speaking. They formed in a few hundred thousand years, as opposed to other non-volcanic mountains around the world which typically require tens of millions of years.
  3. Part of the life history of very large mountains is that they become gravitationally unstable. Most Hawaiian volcanoes have grown too big to support themselves and have collapsed under their own weight, possibly generating giant tsunamis. This hasn’t happened anytime in human history, but studies have shown that collapse events are frequent over geological time scales. When looking at outlines of the Hawaiian Islands, you may notice that some volcanoes look like they have been cut in half, or had large “bites” taken out of them, instead of appearing to be a perfect circle. This is because a large part of the volcano has slid into the sea. It’s rare to see a perfectly circular ocean volcano.
  4. Dormant volcanoes aren’t growing at all and can only decrease in size.
  5. Islands slowly sink under the surface of the sea over time. The tectonic plate they’re on moves them away from the hot plume so the volcanoes and underlying crust are cooling off and starting to sink. The tectonic plate is constantly moving to the northwest. So, new Hawaiian Islands are constantly being formed under the sea.
  6. The Hawaiian mountains that we see are just one end of a long chain of mountains that reach all the way to Japan, and all the way to the ocean floor. Right now, Kīlauea and Mauna Loa are over the plume and are considered “under construction.” Every other mountain to the north is under destruction.
  7. The newest Hawaiian volcano, Lo’ihi, is 980 m under the surface of the ocean and still growing. In two to three hundred thousand years, it will emerge as a new Hawaiian island.
  8. There are three ways in which Hawaiian volcanoes can disappear: landslides, erosion and sinking. Once a volcano sinks just below the ocean surface, and if they are within about 30 degrees of the equator, they are crowned with a coral reef. Eventually that also sinks below the depth of sunlight penetration and dies.
  9. Mauna Kea forms and sustains five different ecosystems as you go from top of the mountain to ground level, and three to four ecosystems from water level to the base of the mountain. Mountains provide water, influence climate and preserve ecosystems. Part of the importance of mountains is their biology.
  10. Around the world, mountains have significance to local cultures. Mauna Kea has special religious, spiritual and cultural significance to the indigenous Hawaiian people. Dozens of archeological sites at high elevations attest to its cultural importance over thousands of years.

We hope you learned something new about the Hawaiian volcanoes from this article! Next time you’re planning a tropical vacation to ocean volcanoes, be sure to impress those around you with these fun facts. Happy International Mountain Day!