On May 2nd, scientists at the University of Hawaii, Monterey Bay Aquarium and the French National Center for Scientific Research announced the discovery of a previously unrecognized volcano on the seafloor between the islands of Oahu and Kauai.
Together with the two known volcanoes of Wai‘anae and Ko‘olau, they said, it formed the island of Oahu.
They found it in the submarine area, extending west-southwest some 62 miles (100 km) from Oahu’s western tip, that used to be called Ka’ena Ridge. High-quality mapping recently showed it had some unusual features. Researchers then collected samples and geophysical data and confirmed it’s not part of Wai‘anae or Ko‘olau.
In fact, they say, Ka’ena Volcano came first, and Wai‘anae and Ko‘olau formed on its flanks.
The Hawaiian Volcano Observatory monitors the state’s volcanoes for the United States Geological Service. They say the mostly submarine mountain chain that today’s Hawaiian Islands belong to began to form more than 70 million years ago above a hot spot in the Earth’s mantle.
This plume of rising magma has remained relatively stationary compared to the restless movement of tectonic plates that form Earth’s crust. Today a line of mountains on the sea floor shows where the Pacific plate has rolled more or less north and then northwestward over the Hawaiian hot spot.
Right now the hot spot is underneath the southeastern part of the Big Island, where Kilauea currently is erupting. Here’s a September 2011 news video about a fissure eruption at Kilauea earlier in the year:
Several other volcanoes also have formed over the hot spot, including Mauna Loa (active), Hualalai (active), Lo’hi (active, underwater, frequently erupting), Mauna Kea (dormant) and Kohala (extinct). Together with Kilauea, they form the big island of Hawai’i.
Indeed, each Hawaiian island is made of one or more shield volcanoes whose tops have only reached the ocean surface after many eruptions.
What happens when the Pacific plate carries these volcanoes away from the hot spot? They eventually stop erupting, and since such massive things tend to erode and sink when not erupting, they will disappear underneath the waves – it’s the fate of all the Hawaiian Islands that we know. Don’t worry. In millions of years, by the time the Big Island is gone, a whole new set of islands will exist.
Over time, this process has left a vast track across the bottom of the Pacific Ocean.
What we think of today as Hawaii is actually a tiny part of a very long chain of islands and underwater mountains (called seamounts) that stretches all the way to the Aleutian Islands. This Hawaiian Ridge-Emperor Seamount chain even shows evidence that the Pacific plate direction of movement changed once in the distant past.
“We thought we knew where all the Hawaiian volcanoes were, and here’s one we didn’t really know about,” John Sinton, University of Hawaii geologist and lead author of the study, is quoted by Reuters as saying on the 19th.
Sinton and his fellow researchers believe that Ka’ena started erupting about 5 million years ago, when it was closer to the hot spot. The continents we know existed back then but were as much as 150 miles (250 km) away from their present positions.
They think that Ka’ena’s summit got up to around 3,300 feet (1 km) above sea level, a little higher than Ko‘olau is today, before the volcano quieted down and submerged again. Oahu’s present-day volcanoes were late bloomers, with Wai‘anae arising from Ka’ena’s flank about 4 million years ago and Ko‘olau (PDF) doing the same thing some 3 million years ago. At one point, all three volcanoes were above the water.
Will Ka’ena erupt again? I have read that it’s dormant, just like most of the Cascade volcanoes back on the mainland. Wai‘anae is said to be extinct, but if you read the link in the previous paragraph for Ko‘olau, they’re not ruling out a future eruption there.
We once thought we knew all about Hawaiian volcanoes, and here scientists have just found a new one. It’s probably best not to rule out anything on Planet Earth. You never know what you’ll come across next.
Categories: Sunday morning volcano