White plumes of acid and extremely fine shards of glass billowed into the sky over Hawaii as molten rock from the Kilauea volcano poured into the ocean, creating yet another hazard from an eruption that began more than two weeks ago.

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Authorities warned the public to stay away from the toxic steam cloud, which is formed by a chemical reaction when lava touches seawater.

Further upslope, lava continued to gush out of large cracks in the ground that formed in residential neighborhoods in a rural part of the Big Island. The molten rock formed rivers that bisected forests and farms as it meandered toward the coast.

The rate of sulfur dioxide gas shooting from the ground fissures tripled, leading Hawaii county to repeat warnings about air quality. At the volcano’s summit, two explosive eruptions unleashed clouds of ash. Winds carried much of the ash towards Wood Valley, Pahala, Naalehu and Waiohinu in the south-west of the island.

Officials said one small eruption produced an ash plume that reached about 7,000ft. The county of Hawaii issued a civil defense message early on Monday, warning those in affected areas to stay indoors with windows closed and to drive with caution.

Joseph Kekedi, an orchid grower who lives and works about three miles from where lava dropped into the sea, said at one point the lava was about a mile upslope from his property in the coastal community of Kapoho. He said residents could not do much but stay informed and be ready to get out of the way.

Facebook Twitter Pinterest Lava pours from Kilauea volcano’s lower East Rift zone. Photograph: USGS/Zuma Wire/Rex/Shutterstock

“Here’s nature reminding us again who’s boss,” Kekedi said.

Scientists said the steam clouds at the spots where lava entered the ocean were laced with hydrochloric acid and fine glass particles that can irritate the skin and eyes and cause breathing problems.

The lava haze, or “laze”, spread as far as 15 miles west of where the lava met the ocean on the Big Island’s southern coast. It was just offshore and running parallel to the coast, said US Geological Survey scientist Wendy Stovall.

Scientists said the acid in the plume was about as corrosive as diluted battery acid. The glass was in the form of fine glass shards. Getting hit by it might feel like being sprinkled with glitter. “If you’re feeling stinging on your skin, go inside,” Stovall said. Authorities warned that the plume could shift direction if the winds changed.

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The coast guard said it was enforcing a safety zone extending 984ft around the ocean entry point. Lt Cmdr John Bannon said in a statement that “getting too close to the lava can result in serious injury or death”.

Governor David Ige told reporters in Hilo that the state was monitoring the volcano and keeping people safe.

“Like typical eruptions and lava flows, it’s really allowing Madam Pele to run its course,” he said, referring to the Hawaiian goddess of volcanoes and fire. Ige said he was thankful that the current flows were not risking homes and hoped it would stay that way.

Play Video 0:24 Plumes of ash billow from Hawaii's Kilauea volcano – video

On Saturday, the eruption caused its first major injury. David Mace, a spokesman for the Federal Emergency Management Agency (Fema) who was helping Hawaii county respond to the disaster, said a man was struck in the leg by a flying piece of lava. He did not have further details, including what condition the man was in.

Kilauea has burned 40 structures, including two dozen homes, since it began erupting in the Leilani Estates neighborhood on 3 May. About 2,000 people have evacuated their homes, including 300 who were staying in shelters.

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In recent days, the lava began to move more quickly and emerge from the ground in greater volume. Scientists said that was because the lava that first erupted was magma left over from a 1955 eruption that had been stored in the ground for six decades. The molten rock that began emerging over the past few days was from magma that has recently moved down the volcano’s eastern flank from one or two craters that sit further upslope – the Pu’u ‘O’o crater and the summit crater.

The new lava is hotter, moves faster and has spread over a wider area. Scientists say they do not know how long the eruption will last. The volcano has opened more than 20 vents, including four that have merged into one large crack. This vent has been gushing lava high into the sky and sending a river of molten rock toward the ocean at about 300 yards per hour.

Hawaii tourism officials have stressed that most of the Big Island remains unaffected by the eruption and is open for business.