HAWAII VOLCANO OBSERVATORY PHOTO
This shatter ring is only about 100 yards across but dwarfed
people nearby. It stands apart from the pahoehoe around it,
so is used as a landmark for hikers across the flow field.
It formed in the summer of 1999 on the flat below Pulama pali.

Kilauea scientist
solves mystery of
huge rings of
shattered lava

Similar features flank Italy's
Mount Etna and volcanoes in Australia

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By Rod Thompson
Star-Bulletin

HILO >> Hikers on Kilauea volcano's coastal lava fields see flat, barren views except for an odd mound of broken rocks that come into view as hikers walk nearly three miles past the end of Chain of Craters Road.

Closer inspection reveals jagged rocks in a ring the size of a football field surrounded by a sea of smooth, hardened pahoehoe lava.

The hikers have discovered a little-known feature that scientists are calling a "shatter ring."

As recently as 1998, Hawaiian Volcano Observatory scientist Jim Kauahikaua was describing the features for the first time to other scientists during a conference in Australia, he said.

The features and the name describing them remain obscure. Just this week, a national park ranger said he and some of his colleagues had not heard of them.

Volcano Observatory head scientist Don Swanson recently posted a description of shatter rings and pictures of them on the observatory Web site, hvo.wr.usgs.gov/kilauea/ update/main.html.

Kauahikaua said a colleague in Italy told him such features had been seen on Mount Etna lava flows, but how they formed was unknown.

Other such features, 120,000 years old, have been identified on lava flows in Queensland, Australia.

"A lot of these things from the air look like doughnuts," Kauahikaua said.

The mystery of their formation has now been solved, since Kauahikaua has watched the rings being created in Kilauea lava.

The process starts with a river of lava developing a rock crust on its top, thereby creating a lava tube.

At times the tube gets partially blocked, and pressure in the tube creates a mound upstream. Kauahikaua has seen such a mound, 300 feet across, swell 6 feet high in a day.

The center of the mound remains smooth, but along its edge the rocks are broken and broken again.

"You just constantly hear the rock grinding," Kauahikaua said.

Eventually, pressure in the tube is released and the mount subsides, but since a weak spot in the tube has been created, the next blockage brings a new bulge and more breaking of rock.

Kauahikaua said he has seen circles of broken rock 12 feet high.