Eruption from summit crater could trigger huge ash cloud, hurl boulders

(Image: USGS)
(Image: USGS)
(Image: USGS)
(Image: USGS)

KILAUEA VOLCANO, BIG ISLAND (HawaiiNewsNow) - Eruptions at Kilauea's summit crater could trigger explosions so violent they fling 10-ton boulders as far as a half mile away and send ash columns miles into the sky, scientists are warning.

Fears of an eruption prompted the Hawaii Volcanoes National Park to shut down indefinitely Friday.

On Saturday morning, a steady, vigorous plume of steam and varying amounts of ash rose from the Overlook vent at the summit, according to officials. ash could spread near Kilauea's summit and downwind, depending on wind conditions.

Officials are warning that massive boulders could come raining down from the sky near the crater, and they're asking people to be prepared.

"It could be large rocks, it could be boulders the size of cows," said Jessica Ferracane, of the Hawaii Volcanoes National Park. "But the larger rocks are going to fall closer to the vent. So if you are, I believe, a half-mile radius of the eruption site — that's where it could be deadly."

Since the park is closed, though, the biggest effect on residents near the summit would likely be an ashfall.

Authorities say ash plumes could affect areas as many as 12 miles away.

Civil Defense authorities said:

  • The danger from this eruption is ash fallout. The major response is to protect yourself from fallout.
  • If this event occurs while you are at home, stay indoors with the windows closed.
  • If you are in your car, keep the windows closed. Drive with extreme caution, or pull over and park.

The last time such eruptions happened was nearly a century ago, when shooting debris killed one and left a layer of ash over homes and cars.

Researchers don't know when the explosive activity will occur, how large the explosions could be or how long they'd last.

But they warn that as fissures continue to open in Puna and lava travels downslope toward the sea, the chance for "explosive eruptions" at Halemaumau Crater on the summit of the volcano will continue to rise.

That's because a lava lake at the summit is dropping. When it hits the level of the water table beneath the Kilauea caldera, likely sometime mid-month, the influx of water into the conduit could trigger steam-driven eruptions, geologists said.

"If an explosion happens, there's a risk at all scales. If you're near the crater within a half a mile or so, then you would be subject to a bombardment by ballistic blocks weighing as much as 10 or 12 tons," said Don Swanson, of the Hawaiian Volcano Observatory.

"If you're within several miles of the summit of the volcano, of the lava lake, then you would be subject to falls of marble sized rocks, ash, finer grain material. and if you're beyond that say you're 10 miles, 15, 20 downwind, you could experience fine ash floating from the sky like snow."

  • Here's a look at what to prepare for and what a series of explosions in 1924 can tell us:

What to be prepared for 

The biggest potential hazards of an explosion are ballistic projectiles and ashfall.

Officials are urging residents who live around the Kilauea summit to learn about the hazards of ashfall, stay informed about the status of the volcano and area closures, and review family and business emergency plans.

During steam-driven explosions, ballistic boulders up to two yards across could be thrown in all directions to a distance of about a half mile. These boulders could weigh a few pounds to several tons.

Smaller (pebble-size) rocks could be sent several miles from Halemaumau, mostly downwind.

Presently, during the drawdown of the lava column, rockfalls from the steep enclosing walls of the crater are hitting the lava lake and producing ash clouds that dissipate quickly. These clouds can result in dustings of ash downwind.

Should steam-driven explosions begin, ash clouds will rise to greater elevations, meaning that minor ashfall could happen over much wider areas.

In 1924, explosive events at the summit lasted for two and a half weeks and ash may have reached as high as 20,000 feet above sea level. Small amounts of fine ash fell as far as lower Puna and Waiohinu.

Gas emitted during steam-drive explosions will be mainly steam, but will include some sulfur dioxide as well. Currently, emissions remain elevated.

USGS geologists say that they expect the water table to be infiltrated by lava by the middle of the month.

Steam-driven explosions at volcanoes typically happen with very little warning and the first sign of a problem might be continuous ashy plumes.

What happened at the crater in 1924

The first explosion at the summit in 1924 was neither seen nor heard.

It took place during the night of May 9, and small rocks were thrown out of the crater. Larger explosions followed, starting on May 13 and spaced a few hours apart. At the same time, Halemaumau continued to collapse, its failing walls contributing to the debris thrown from the crater.

Clouds of rock particles ejected into the air often obscured the crater from view. Toward the end, it became difficult to distinguish the cloud pouring from the crater from the dust cloud generated by a rock avalanche.

Consequently, the end date of the eruption is somewhat uncertain — but is taken to be May 27, when the last observed object was ejected from the crater.

During the event, explosion clouds reached as high as 5.5 miles.

Trade winds were blowing from the northeast during the eruption, yet wet ash fell at least once on railroad tracks in lower Puna, Gutters on the roof of a store in Glenwood, 10 miles northeast of Halemaumau, collapsed from the weight of muddy ash.

The largest explosion may have taken place on May 18, 1924; a number of people were near Halemaumau when it happened, and one was killed by debris.

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