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September 3, 1998

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


The Chain of Craters at Kilauea

The Chain of Craters marks the location of Kilauea's upper east rift zone. The chain reaches southeastward from the summit caldera and then gradually bends into the overall east-northeast trend of the rift zone. It is a distinct segment of the rift zone, but one that many visitors to Hawaii Volcanoes National Park pay scant attention to in their hurry to reach the coastline and hopefully catch a glimpse of flowing lava.

The Chain of Craters starts at tiny Lua Manu, just inside the boundary of the summit caldera but about 1 km (0.6 miles) outside the obvious modern caldera. Keanakako`i Crater, along Crater Rim Drive at the edge of the modern caldera, may be part of the chain, but it lies off the trend of the rest of the chain.

Puhimau, Ko`oko`olau, Devil's Throat, the double craters at Hi`iaka, and the triple craters at Pauahi are the next links down the chain. To casual visitors, they are also the last links, because from Pauahi the modern Chain of Craters Road swings southward away from the rift zone. The largest craters, however, are still to come.

`Alo`i and the double `Alae pit craters, once popular stops along the old highway, were completely filled by lava flows in 1969 and 1970 during the Mauna Ulu eruption. `Alo`i was small, but `Alae was the third largest of all the craters, about 440 m (1450 ft) wide by 165 m (540 ft) deep.

Makaopuhi is the next crater, actually a composite of two intersecting craters. It is 1.6 km by 1.0 km (1 mi by 0.6 mi) wide and, before partial filling during the Mauna Ulu eruption, was more than 210 m (700 ft) deep. The former highway turned southward from the overlook at Makaopuhi and joined the present highway just above the big hairpin bend.

Most people, even those visiting before the Mauna Ulu eruption, have never seen the three remaining craters along the chain. They are broad, shallow Napau, small but precipitous Pua`i`alua, and an unnamed pit just east of Napau.

The craters are all young, since they developed in lava flows no older than about 750 years; most, in fact, are probably less than 400 years old. They apparently formed by collapse. Had they formed by explosion, debris from the explosion would litter the landscape. Such debris was found around only one of the craters, `Alae, before it was buried by pahoehoe from Mauna Ulu. Dense rocks 6 cm (2.5 inches) across, the products of a powerful explosion, have been found as far as 7 km (4 miles) southwest of `Alae.

Collapse must occur into a void, but the nature of that void is a mystery. Abundant geophysical and geologic evidence indicates that pockets of magma reside at shallow depth within the east rift zone. Emptying of those pockets by down-rift eruption or transfer of magma could remove support for the overlying material, which then might collapse into the void. Intersecting faults and cracks might help provide space for magma intrusion.

Hot or once-hot ground occurs just north of Puhimau and near Hi`iaka, Devil's Throat, `Alo`i, and Napau. Such steaming areas imply the underground presence of hot rock or magma to supply the heat. Some hot water is acidic and can weaken rocks by changing them partly to clay. Possibly this helps facilitate collapse. Perhaps hot ground and weakened rocks once occupied the site of each crater but were engulfed when the crater formed. The youngest steaming area, 400 m (a quarter of a mile) south of Puhimau, began to form in 1936-37. Will it eventually collapse to form a pit crater?

Nature hates holes and tries to fill them quickly. `Alo`i and `Alae are examples. Enjoy the Chain of Craters while you can. The next eruption after Pu`u `O`o stops could fill one or more of the remaining pits.

Eruption and Earthquake Update

Eruptive activity from the Pu`u `O`o vent on the east rift zone of Kilauea Volcano continued unabated during the past week. About 50 percent of the lava output is flowing through the old tube system and entering the ocean at Kamokuna. The other half is feeding a flow that is entering the ocean about 400 m (1/4 mi) west of Kamokuna. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying frequent collapses of the lava delta. The steam clouds are highly acidic and laced with glass particles.

There were no earthquakes reported felt since August 24.

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Updated: 10 Sep 1998