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September 28, 2000

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

Hawaiian lava flows help in the study of 3-billion-year-old lava flows

Lava flows and volcanic eruptions played a major role in the Earth's history since it was formed some four billion years ago. We can look at rocks that are almost that age and see structures and crystals similar to those that form today.

But a particular type of lava was much more common in the early days of the Earth. Named komatiite (koh-mat-tee-ite) after the Komati River in South Africa where first described, these lava flows have never been observed erupting, and their volcanic nature has been deduced from the properties and textures of the rocks. Except for one occurrence about 80 million years in age, all komatiites are about three billion years old or older. Komatiites are unique for three reasons. First, tabular crystals as large as one meter (three feet) formed just beneath their surface. Anyone can pick up a piece of lava on the Big Island and sometimes see either green crystals of olivine, white crystals of plagioclase, or black crystals of pyroxene. Except in rare instances, these crystals are less than 1 cm (one-half inch) wide. Second, komatiite lavas erupted much hotter, at a temperature around 1,600 degrees C (2,900 degrees F) rather than at 1,150 degrees C (2,100 degrees F), the temperature typical for Hawaiian eruptions. Third, komatiites contain commercially economic amounts of nickel.

Being so old, komatiites have had a lot of time to be buried by younger lava and sediment. They are found today only in areas where the Earth's crust has been squeezed and folded or sheared, then eroded to expose the extent of the folding. Most of the komatiites that one can visit are now vertical rather than horizontal in the way they were originally formed. The billions of years between their formation and exposure have changed more than their orientation. Exposure to the heat and water beneath the pile of overlying rocks has changed the minerals within.

After correcting for the heat, the addition of water, the squeezing and folding, and the cracking along faults, we can get a picture of what these lavas looked like when they were active. Like Hawaiian lava flows, komatiite flows formed tubes and channels; however, their dimensions were extraordinary. Some of the channels appear to be nearly 1 km (3000 feet) wide. Many komatiite flows have glassy tops like Hawaiian flows. Many komatiite flows are about 1 meter (3 feet) thick, but a few are very thick - about 100 m (300 feet). Komatiite flows seem to be extensive, but because of their limited exposure (remember the squeezing, folding, and cracking), none have ever been completely traced from one edge to the other or from the vent to the flow's toe.

What really drives research into the nature of komatiite lavas is the fact that they contain large amounts of nickel. The nickel is found preferentially at the base of komatiite channels as if it were deposited there while the channel was full of flowing lava. Some researchers think that the nickel was extracted from sulfur-rich sediments by the komatiite liquid flowing over and melting the sediments. The nickel would then be carried in the komatiite lava as immiscible blobs (like the blobs in a lava lamp).

The nickel is not found in every channel, nor is it found at every place along a channel. Although difficult to reconstruct, the nickel seemed to be found in bends in the channel or plunge pools beneath komatiite falls. In modern lava channels, these would be the places where the liquid lava would slow down. The nickel seems to be deposited by the komatiite liquid just as a river deposits its bedload sediment.

Much of the komatiite story has been deciphered by comparing modern lavas and komatiites. Hawaiian lavas seem to be the closest modern analogue. The connection is so strong that several "nickel geologists" from countries as far away as Australia, Canada, and Finland have been coming to Hawai`i Volcanoes National Park nearly every year for a workshop to see modern analogues to the structures they find only partially preserved in their respective countries.

Eruption Update

At 9:00 p.m. on the night of September 24, an accelerated uplift of the Kilauea summit region commenced. The rapid inflation of the volcano lasted 50 minutes and more than seven microradians of tilt was recorded before deflation began. A brief surge in eruptive activity at the Pu`u `O`o vent ensued. The increased volume of lava caused breakouts from the old tube system near the 2,300-ft elevation and fed three flows that advanced down Pulama pali. Activity returned to normal by Monday afternoon, and the three new flows stagnated. The old flow reported last week in the coastal flats slowly wended its way toward the coast near Kamokuna and entered the sea on Saturday, September 23. The public is reminded that the ocean-entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The active lava flows are hot and have places with very thin crust. The steam clouds are highly acidic and laced with glass particles.

A resident of Waimea reported feeling an earthquake at 13 minutes after midnight on September 26. The magnitude-2.8 earthquake was located 3 km (1.8 mi) south of Kawaihae at a depth of 26.6 km (16 miles).

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Updated: October 3, 2000