First serious injury as lava severs highway escape route after weeks of intensified volcanic eruptions on Kilauea.

A man was hit with lava spatter while he sat on his balcony in Hawaii, the first serious injury sustained after weeks of heightened volcanic activity on the Big Island.

The homeowner on Noni Farms Road on a third-floor balcony had his leg shattered from his shin to his foot when hit by lava spatter, said Janet Snyder, a spokesperson for the Office of the Mayor, County of Hawaii, on Sunday.

Lava spatters “can weigh as much as a refrigerator and even small pieces of spatter can kill”, Snyder said. No other information was immediately available.

A stream of lava blocked a Hawaii highway that serves as an escape route for coastal residents fleeing the Kilauea volcano.

The erupting lava, which can reach a blistering 1,093 degrees Celsius, crossed Highway 137 shortly before midnight local time (10:00 GMT), Hawaii’s Civil Defense Agency said, and sent lava flowing into the ocean.

That prompted warnings of laze – clouds of hydrochloric acid and steam embedded with fine glass particles formed when hot lava hits ocean water.

‘World of uncertainty’

As magma destroyed four more homes, molten rock from two huge cracks merged into a single stream, threatening to block other escape routes and touching off brush fires.

Scientists can’t say whether lava flows from nearly two dozen fissures will continue to advance or stop.

“We have no way of knowing whether this is really the beginning or toward the end of this eruption,” said Tom Shea, a volcanologist at the University of Hawaii. “We’re kind of all right now in this world of uncertainty.”

Authorities were trying on Sunday to open up a road that was blocked by lava in 2014 to serve as an alternative escape route, Jessica Ferracane of the National Park Service, told reporters.

The park service is working to bulldoze almost half a kilometre of hardened lava out of the way on nearby Highway 11, which has been impassable, she added.

The Hawaii National Guard has warned of mandatory evacuations if more roads become blocked.

Officials went house-to-house in the area to urge more residents to flee, Snyder said, though no head count of the new evacuation was available early Sunday.

Hotter lava

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For weeks, geologists have warned that hotter, fresher magma from Kilauea’s summit would run underground and emerge some 50km east in the lower Puna district, where older, cooler lava has already destroyed 44 homes and other structures.

Carolyn Pearcheta, operational geologist at the Hawaii Volcano Authority, told reporters hotter and more viscous lava could be on the way with fountains spurting as high as 183 metres, as seen in a 1955 eruption.

“We’ve seen the clearing out of the system,” she said. “We call that the ‘throat clearing’ phase.”

Scientists expect a series of eruptions from Kilauea, one of the world’s most active volcanoes, that could spread ash and volcanic smog across the Big Island, the southernmost of the Hawaiian archipelago.

That could pose a hazard to aircraft if it blows into their routes at about 9,144 metres.

Thousands of residents have voluntarily left their homes because of life-threatening levels of toxic sulfur dioxide gas spewing from vents in the volcanic fissures.