Pahala meeting will prepare for various volcano scenarios

While chances of the seismic activity at Kilauea reaching catastrophic levels are very slim, a community meeting in Pahala seeks to keep everyone informed and prepared.

Hawaii County Civil Defense is holding the meeting at 6 p.m. Thursday at Pahala Community Center to address the various scenarios stemming from a possible explosive event at Halemaumau Crater. The state Highways Division will be on hand to discuss possible evacuation routes, and the U.S. Geological Survey will present information on the latest occurrences at Kilauea.

“We did one for Volcano, and the Pahala community asked for the same kind of briefing,” said Hawaii County spokeswoman Janet Snyder. “It’s always good to keep people informed.”

The meeting is scheduled just days after a lava bomb went through the roof of a tour boat, injuring 23, near the lava’s ocean entry point off of Ahalanui. At least 706 homes and structures have been destroyed by the eruption, so far, and 12.5 square miles covered with lava.

For Pahala residents, evacuation routes, adequate supplies and air quality are the top concerns, according to Jessie Marques, executive director of the Ka‘u Rural Health Community Association.

“Many of the people in our community are concerned about resources in the anticipation of having a big collapse at the summit,” said Marques, “about evacuation, and the roads in particular.”

Meanwhile, USGS reported Tuesday that fissure 8 continued to erupt lava into the perched channel leading northeast from the event, with no end in sight going into the 11th week.

To date there have been 52 “collapse explosions,” which are events in which the floor of Halemaumau Crater collapses after magma beneath it empties into the lower East Rift Zone, resulting in energy that goes into the ground, according to USGS geologist Janet Babb.

The latest collapse explosion occurred at 11:43 a.m. Monday at Halemaumau Crater, with energy equal to a 5.4-magnitude earthquake.

USGS said it expects a high rate of low-magnitude earthquakes — 25 to 35 per hour — to continue until the next collapse explosion event, which occurs about every 30 hours.

Since early May the floor of Halemaumau Crater has dropped about 1,480 feet, according to USGS, and the rim’s diameter is double its original size.

“Right now the collapse events involve just a small part of the caldera floor,” said Babb. “The public is asking if it could involve more of the floor and become a catastrophic event. While the probability is low, the possibility is not zero.”

The meeting will offer the public information on all the possibilities.

In mid-June USGS began referring to the events as “collapse explosions” to more accurately describe the occurrences. Instead of the ash plumes of 9,500 feet and upward in early May, Babb said these collapse events are more like a “pressure pulse” into the ground with the energy of 5.0-magnitude earthquakes.

The collapse comes with small bursts of ash and gas, and plumes of only about 1,000 feet above the caldera floor, she said.

At the lava flow’s ocean entry, on the other hand, conditions are ripe for explosions, said Babb, due to the large volume combined with more shallow topography at Ahalanui.

Whenever molten, 2,000-degree lava meets cool seawater, a steam explosion results, blasting fragments of solidified or semisolidified lava fragments — some of which are larger than a breadbox — up into the air.

Babb said the current volume of lava flowing out of fissure 8 is much higher, at about 50 to 100 cubic meters per second, compared with the “61g flow” of 2016, where lava from Puu Oo pumped out about three to four cubic meters per second.

In addition, the Kamukona lava ocean entry’s offshore topography was very steep. The lava entering the ocean at Kamukona hit a steep slope and was quickly carried down to deeper parts of the ocean, said Babb.

As of Tuesday evening the southern margin of the flow was just under a half-mile from the boat ramp at Isaac Hale Park. The lava continues to ooze out at several points along the 3.7-mile-wide flow front into the ocean.