29 January 2011

Kaboom! An undersea volcano blows its top…

This spectacular video of an erupting undersea volcano recently came through the geoscience grapevine, and thought I would share it here.  Enjoy!

According to the anonymous voice accompanying the video, the volcano is Kavachi (9.02° S 157.95° E), near the Solomon Islands.  The eruptive history of Kavachi has been recorded since 1939 and numerous periods of volcanism have been documented in that time.  Although the date of this video is uncertain, the most recent known eruption occurred in early April 2007 following a magnitude 8.1 earthquake.  Kavachi has emerged above the ocean surface to form an island on nine occasions, only to subside again due to erosion.

Kavachi is a forearc volcano located about 30 km northeast of the convergent boundary between two oceanic plates--the Pacific plate (on which Kavachi sits) and the Indo-Australian (IA) plate.  The IA plate is being subducted (i.e., recycled into the mantle) to the northeast below the Pacific plate at a rate of about five centimeters per year.

In the map below (courtesy of Google), Kavachi is indicated by the green marker.  Just southwest of Kavachi, the San Cristobal trench, which marks the plate boundary, can be seen running northwest/southeast.
The Solomon Islands form an island arc, a characteristic feature of ocean-ocean subduction zones.  Other examples of island arcs include the Aleutians extending west from Alaska, the Mariana Islands in the western pacific, and the Antilles in the Caribbean.

On the worthy-of-patent-status-but-not-actually-patented +/- Science Awesomeness Meter, I rate this video as…

References and more information:

Baker, E.T. et al. (2002) Observations and sampling of an ongoing subsurface eruption of Kavachi volcano, Solomon Islands, May 2000, Geology, 30, 975-978.

Tregoning, P. et al. (1998) Present-day crustal motion in the Solomon Islands from GPS observations, Geophys. Res. Letters, 25, 3627-3630.

Update (added 1 February 2011, 11:30 am)

A nice graphic from the National Science Foundation showing the basic process of island-building by a submarine volcano:

(image by Zina Deretsky, National Science Foundation)
It illustrates pretty well how an island formed in this way is typically just the top-most portion of the volcano.  A prominent example is Mauna Kea, on the big island of Hawaii, which peaks at almost 14,000 feet above sea level.  This represents only about 40 percent of the total height of the volcano, though, with the rest rising from the sea floor to the surface.


  1. I'm totally digging your awesomeness meter -- what a great idea!

    Excuse my unfamiliarity with this topic, but how many islands are created this way?

  2. I agree on the awesomeness meter, its a great visual. I love the video, technology has really done amazing things for showcasing how cool science can be.

  3. Really cool. I wonder how much sediment an eruption like that spits out? What does it take to get a Hawaii?

  4. I saw that on HuffPo! Really cool stuff, I wonder when I can buy real estate. Well I would at least have to wait for primary succession to kick in. How long might that take?

    Joe D.

  5. Thanks for the comments guys! I saw an estimate that there are (thought to be) around 5000 active undersea volcanoes. Most of these are no where near reaching the ocean surface, so they're not about to form islands in the near future.

    As far as islands formed this way in the past...there are lots! Almost all island arc islands were/are formed through subduction zone volcanism. Japan is an exception in that it is a continental fragment that was torn from Asia.

    It takes a quite a lot of erupted material to form an island (although it depends largely on the sea floor depth where it is located), not to mention a lot of time. Hawaii is similar but different from Kavachi and island arc islands. Mauna Kea and the other Hawaiian islands also formed through volcanism (there are, of course, still active volcanoes going in Hawaii), but they're hot spot volcanoes, rather than subduction-zone related.

    Joe, I wouldn't buy real estate on Kavachi just yet...it's apparently formed an island many times in the (recorded) past. It doesn't have a consistent enough eruptive flow of magma etc., though, so it always loses out to pesky erosion by the sea surface.


  6. Great video, Tim! It's interesting to have it be so active and yet not create an island. If you compared it to the creation of the Hawaiian islands, where the volcanoes tend to ooze more than blow, is that a more effective way of making a land mass?

  7. Tim,
    Very nice graphics, both the video and the graphics. I'm waiting for St. Helen's to start acting up again so I can see what you have on it.

  8. Does it depend on how close to the surface (of the water) a volcano becomes for it to have a chance to become an island? Or is it more a matter of volume of activity?

  9. I'm not sure that there is necessarily one formula for volcanic island formation, but in general it depends on a number of aspects including proximity to the surface (which is affected by the sea floor depth where it is located and how much the volcano has already grown below the sea surface), the volume of material erupted, as well as the rate/consistency at which the material is erupted.

    Touching on Deb's point, there is greater flow of magma to the surface in the Hawaiian volcanoes. Additionally, the Hawaiian magma is basaltic, which means among other things it is more prone to ooze slowly and pile up on itself. Both of these factors contribute(d) to Hawaiian island formation. From what I've read about Kavachi, the magma is thought be a bit more andesitic, which is more viscous and tends to be more explosive when erupted.

    Tom M.: I might actually be stopping out at Mt. St. Helens pretty soon. Should be pretty cool...hopefully I'll be able to put up a post about it.