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February 12, 1998

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

From Big Island to Japan only 63 million years

Japan--only 63 million years away! Advertising like that would put a shipping company out of business, but the Plate Tectonic Express has no competitors when it comes to moving continents and oceanic plates around the globe.

Many readers are familiar with the theory of plate tectonics, which describes the Earth's crust as a series of plates moving from zones of upwelling (oceanic ridges) toward subduction zones (oceanic trenches). Also familiar is the idea that the Hawaiian Island chain has formed because the Pacific plate is moving slowly across a hot spot. The hot spot, rooted deep in the Earth's mantle, drives the melting that ultimately leads to volcanism and island building. Old islands drift beyond the hot spot and new islands form. Where will the Big Island go as it moves from the focus of heat and volcanism?

Presently the Hawaiian Islands and our part of the Pacific plate are moving northwest at about 100 mm (4 in.) per year, relative to the island-producing hot spot. The trajectory of motion points toward Hokkaido on the northern part of the Japanese Island chain, 6,300 km (3,900 mi) away. A subduction zone offshore of Japan consumes the Pacific plate, which is partly melted to create the volcanoes of Japan. If the Plate Tectonic Express operates without change for 63 million years, the Big Island will be headed down the Japanese trench, within hailing distance of Sapporo. At the same time, new Hawaiian islands will be forming, each at roughly the same distance from Japan as we are today.

The geographic feature actually subducted will be a seamount or submarine peak, not an island. As the Big Island moves away from the hot spot it will slowly subside. Our Big Island will become a not-so-big coral atoll and finally a so-so seamount long before it gets halfway to the subduction zone.

Will the Big Island-turned-seamount really reach Japan? Probably not. The Earth's plates move with apparent uniformity for a few million years but then abruptly change direction. It's unlikely that the Pacific plate will continue its northwestward motion uninterrupted for the tens of millions of years needed to subduct the Big Island beneath Japan. The final result is still the same. Regardless of which circum-Pacific trench finally gets the prize, the site we know as the Big Island will be consumed someday by subduction and recycled into the mantle. Auwe! [Too bad!]

Eruption and Earthquake Update, 12 February

The east rift zone eruption of Kilauea Volcano shows few apparent changes in the past week. Lava had been visible only rarely at the Pu`u `O`o until Wednesday, February 11. Since then, lava has been visible in the crater vent. The lava enters tubes near the vent and flows continuously to the coast. Lava escapes sporadically from the tube system along the coastal plain, but the flows have been of limited extent. The tube system discharges lava into the ocean at two locations - Waha`ula and Kamokuna. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying the frequent collapses of the lava delta. The steam clouds are highly acidic and laced with glass particles.

Two earthquakes were reported felt during the past week, both in the Puna district. On February 10 at 9:45 p.m., an earthquake located 4 km (1.2 mi) west of `Opihikao was felt by residents of Leilani Estates. The earthquake had a magnitude of 2.2 and originated from a depth of 1.3 km (0.8 mi). A second earthquake at 9:19 a.m. on Thursday, February 12, was felt in the same area. The magnitude 1.9 earthquake was located near shore in the Cape Kumukahi area at a depth of 2 km (1.2 mi).

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