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Earth Science

Hawaii's Oahu Used To Be a Bigger Island 44

Posted by timothy
from the back-in-my-day-we-called-it-Oooooaaahhhuuu dept.
sciencehabit (1205606) writes "The two volcanoes long thought to have formed the Hawaiian island of Oahu had a head start: They grew on top of an older volcano that's now submerged northwest of the island and partially covered by it, new research suggests. Tests indicate that the long-lost peak—now dubbed Kaena volcano—grew from the sea floor and broke through the ocean's surface about 3.5 million years ago, eventually reaching a height of about 1000 meters above sea level before it began sinking back into the sea. At its largest, ancient Oahu would have measured about 1900 square kilometers (about 20% larger than modern-day Oahu) or larger. Over the course of its lifetime, Kaena volcano spilled between 20,000 and 27,000 cubic kilometers of molten rock, the researchers estimate. When Kaena volcano became largely extinct isn't clear."
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Hawaii's Oahu Used To Be a Bigger Island

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  • by Anonymous Coward on Saturday May 24, 2014 @02:27PM (#47083747)

    27,000 cubic kilometers is 56608 gigabuttloads.

  • by Anonymous Coward

    The same thing happens to me every time I eat Chipotle.

  • "New" volcanos? (Score:5, Interesting)

    by Immerman (2627577) on Saturday May 24, 2014 @02:35PM (#47083799)

    So in exactly what sense are these "new" volcanoes not just new vents in the old volcano? Seems to me if they weren't using the old magma channels they wouldn't have opened near the top of an existing volcano - instead they would have opened someplace around the base (underwater) instead. Perhaps more to the point - in exactly what sense is an old volcano which is still spewing lava from it's slopes extinct?

    As I understand it it's not exactly uncommon for a volcano to go dormant for a while and then sprout new calderas on it's slopes when it gets active again, particularly if a magma "cork" formed in the old caldera, or the old magma channels collapsed while it was dormant. Seems to me the actual summary should be something along the lines of "what was long thought to be two volcanoes forming Oahu has been discovered to actually be a pair of relatively recent new calderas on a single older, larger volcano."

    • Re:"New" volcanos? (Score:5, Informative)

      by riverat1 (1048260) on Saturday May 24, 2014 @03:51PM (#47084133)

      In the case of the Hawaiian Islands they form a chain of islands over a hot spot in the Earth's mantle. You can trace the path of the sea floor over the hot spot by following it island arc. So the original volcano formed and as the position of the hot spot moved southeast the volcanoes that comprise the present day Oahu formed on its flanks. The same thing is presently happening on the Big Island, Hawaii where the current volcanic activity is mostly on the southeast at Kilauea and 22 miles out to sea at Loihi Seamount [wikipedia.org] while the northwest part of the island is eroding away.

      So obviously the hot spot is forming new magma channels as the sea floor moves over it and whether any particular vent on the flanks of a volcano is a breakout from old channels or a new one is a moot point. Any specific channel won't last for long (in geological time) as the hot spot moves on.

      • by Anonymous Coward

        I believe the hotspot is stationary. The sea floor, the Pacific Plate, is moving in a north westerly direction over the Asthenosphere, which is why you have 5 volcanoes on the Big Island with it's most active, Kilauea, at it's Southern end. BTW, Mauna Loa is still an active volcano, and the very active Loihi seamount is around 3000 feet below the surface of the ocean, as the Big Island creeps Northwest. The area around the oldest volcano in the North of the Big Island, Kohala, is shearing off and slowly sin

  • by Anonymous Coward on Saturday May 24, 2014 @02:43PM (#47083847)

    Of course it used to be larger. Hawaii is growing, all the rest of the islands are shrinking (because they are no longer growing).

    I knew a marine geologist in Honolulu when I lived out there who was trying to predict the size of the tsunami that would result the next time a huge chunk of Oahu breaks off and falls into the sea. Apparently some pretty large chunks have fallen off in the past.

    • by HiThere (15173) <charleshixsn@ e a r t h l i nk.net> on Saturday May 24, 2014 @02:53PM (#47083909)

      Bingo!

      This is the correct answer. The Hawaian islands form over a "hot spot" under the sea floor that doesn't move with the plate. When the plate moves enough, a new volcanic vent appears. The entire chain of islands is the result of this process. Note that Hawaii, "The big island" is currently over the hot spot, and all the other islands are no longer active. The further away (in a line!) from the hot spot they are, they more they've eroded, so the smaller they are.

    • by ShanghaiBill (739463) on Saturday May 24, 2014 @02:59PM (#47083947)

      Hawaii is growing, all the rest of the islands are shrinking.

      Lo'ihi [wikipedia.org] is also growing. Although, technically, it isn't an island (yet).

    • by RockDoctor (15477)
      I don't know the count around the Hawaiian islands, but when I was on a volcanology holiday on Tenerife, Islas Canarias, a couple of years ago the count of "sector collapse" scars identified on the seabed around the islands was in the mid-20, and only likely to go up. That points to around one collapse every couple of hundred thousand years.

      If I lived on a coastline exposed to that threat, I'd have included it in my considerations over where to move. As it was I just counted storms, global warming and the

  • I'll probably sound crazy for asking this, or get modded off-topic, but... My understanding is that the scenario in the movie Waterworld can't happen by melting the polar ice caps because there isn't enough water frozen in them to rise enough enough to cover the continents. Goodbye to Florida and similar areas, but most of the continents would remain. (And thanks to global warming, we'll likely see that scenario... >.<)

    But it seems to me as though one way in which it could happen is if we greatly e

    • We don't currently possess the technology to extract that much energy from tectonics. By the time we do have the ability, if we live that long, we should have easier ways to make energy.

      So we should be OK. Well, not US. But 20 or 30 generations from now.

      Nice handle btw.

    • by dbIII (701233)
      It's very shallow two dimensional fiction at the level of which most childrens cartoons can't get away with without criticism. It only resonates with us because it we've got a "the flood was thiiis big (arms spread wide)" story from Sumeria in our culture because it was adopted to make a few points in the Bible. Think about it - does the Bible really suggest everyone is descended from Noah or just everyone considered important to the intended readers?
  • This is news? (Score:4, Insightful)

    by Drathos (1092) on Saturday May 24, 2014 @04:46PM (#47084303)

    My first reaction was "Um.. Duh?"

    I learned this in middle school, I believe. The Hawaiian Islands are a chain that's formed by the movement of the Pacific Plate across a hot spot. As it passes over, a volcano builds up and builds up, eventually forming an island that keeps growing as long as the vent stays over the hot spot. Eventually, it will move on and start eroding, while another volcano starts up at the ocean floor. All of the Hawaiian Islands except for Hawai'i (The Big Island) are currently shrinking, while Hawai'i is still growing. If you look at charts of the Pacific Ocean's floor, you can see a long chain going all the way to the subduction zone at the Aleutian Trench.

    • The headline is not news. Everyone knows that the islands are all eroding away, except where new material is being added through volcanic action. But the story is about the ancient volcano that predated the volcano that we knew built the island. That's news, just poorly presented, in slashdot editorial tradition.

  • by gkndivebum (664421) on Saturday May 24, 2014 @05:23PM (#47084443) Homepage

    http://maps.ngdc.noaa.gov/view... [noaa.gov]

    Zoom in on the Hawaiian archipelago; de-selecting multibeam bathymetry surveys and switching the base map to "Shaded Relief (GEBCO_08) will give
    you a nice image of what the chain looks like under water. Kaena Pt is the westermost tip of the island of Oahu. Also note that Maui Nui was once a much
    larger island, encompassing Maui, Molokai, Lanai and Kahoolawe. Loihi is visible to the the southeast of the island of Hawaii.

  • Glad someone finally figured that out, I was getting worried.
  • ...that one of the islands will tip over [snopes.com].
  • For years and years the bathametry off the islands was classified. The reason was that our submarines would hide in the oddly rugged land forms of the subsurface. The lay of the sea floor was declassified when it was felt that our enemies had already mapped it. When the data were made available they unleashed a bonanza of geologic investigation for it became clear that there was a very active process taking place. Much of the strange forms around the islands, all of them, are due to very large slumps, wher

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