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'Ballistic blocks' shot from Hawaii volcano could mark onset of explosive eruptions

Eruptions of large rocks, last seen nearly a century ago, have been a looming threat since Kilauea, one of the world's most active volcanoes, erupted nearly two weeks ago.

Eruptions of boulders have been a looming threat since Kilauea began exploding 2 weeks ago

People play golf as an ash plume rises in the distance from the Kilauea volcano on Hawaii's Big Island on Tuesday in Hawaii Volcanoes National Park, Hawaii. (Mario Tama/Getty Images)

"Ballistic blocks" the size of microwave ovens shot from Hawaii's Kilauea volcano on Wednesday in what may be the start of explosive eruptions that could spew huge ash plumes and hurl smaller rocks for several kilometres, the U.S. Geological Survey said.

Such eruptions, last seen nearly a century ago, have been a looming threat since Kilauea, one of the world's most active volcanoes, erupted nearly two weeks ago.

Jolon Clinton, 15, left, and her sister, Halcy, 17, take photos of a fissure near their home on the outskirts of Pahoa on Monday. (Terray Sylvester/Reuters)

The explosive, steam-driven eruptions could drive a 6,100-metre ash plume out of the crater, hurl boulders the size of small cars up to 800 metres and scatter smaller rocks over 19 kilometres, the USGS has warned.

This type of eruption has the potential to carpet the Big Island in much thicker ash falls than those up to now and possibly spread ash and volcanic smog across the Hawaiian islands and farther afield if it enters the stratosphere.

This morning, dense ballistic blocks up to 60 centimetres across were found in a parking lot a few hundred metres from Kilauea's crater, the USGS said in a statement. "These reflect the most energetic explosions yet observed and could reflect the onset of steam-driven explosive activity."

'More powerful' blasts expected

The USGS cautioned that "additional such explosions are expected and could be more powerful."

A 4.2 magnitude earthquake at the volcano at 8.36 a.m. local time prompted authorities to issue an alert reassuring rattled Big Island residents that there was no risk of a tsunami from the volcanic activity.

Smog from Hawaii's Kilauea volcano drifted north up the island chain after communities south of its summit were warned of up to six millimetres of ashfall as the nearly two-week eruption intensified.

Linda Dee Souza, 72, of Kalapana-Seaview, kisses one of her parrots at a Red Cross evacuation centre in Pahoa on Tuesday. (Terray Sylvester/Reuters)

Explosions in Kilauea's crater sparked an aviation red alert due to risks ash could blow into aircraft routes and damage jet engines. There was no effect on air carrier operations to Hawaii on Wednesday, Federal Aviation Administration spokesperson Ian Gregor said in an email.

"The Big Island is going to have a lot of vog [volcanic smog] today and maybe Maui," National Weather Service meteorologist Matt Foster said.

Ash is a new hazard for Hawaii's Big Island, already grappling with volcanic gas and lava that has destroyed 37 homes and other structures and forced the evacuation of about 2,000 residents from communities in the southeast Puna district.

Lava has burst from 21 giant ground cracks or fissures and torn through housing developments and farmland, threatening two highways that are exit routes for coastal areas.

Several fissures shot lava into the air on Wednesday, but one flow had not advanced any farther toward coastal Highway 137, which remains around 1.6 kilometres distant, County of Hawaii Civil Defense said in a statement.

No serious injuries or deaths have been reported from the eruption.

Massive plume of toxic ash spews more than 3,600 metres into the air 0:56