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There is an increased chance of explosive eruptions from the Kilauea volcano in Hawaii that could shoot rocks for miles and bring ashfall covering potentially dozens of miles, the U.S. Geological Survey said Wednesday.

The steady lowering of a lava lake at the summit of the volcano has increased the potential for explosive eruptions in the coming weeks, the USGS said in a statement. If the lava column dropped to the level of groundwater beneath Kilauea's caldera, a massive volcanic crater, an influx of water could cause "steam-driven explosions," the statement said.

Those explosions could shoot pebble-size rocks over several miles and larger ones for up to half a mile, the USGS said. The larger rocks could weigh a few pounds to several tons.

Minor ashfall could also occur up to several dozen miles from the area.

"At this time, we cannot say with certainty that explosive activity will occur, how large the explosions could be, or how long such explosive activity could continue," the statement said.

Police went door-to-door in Hawaii late Tuesday to roust residents near two new vents emitting dangerous gases in areas where lava has been pouring into streets and backyards for the past week.

Authorities ordered nearly 2,000 residents to leave two communities in the mostly rural district of Puna on Hawaii's Big Island last Thursday. Some ignored the order and stayed to watch over their property.

But on Tuesday, the emergence of the two new vents prompted Hawaii County to issue a cellphone alert ordering stragglers in Lanipuna Gardens to get out immediately. Police followed up with personal visits.

"There were a number of people at their residences," Talmadge Magno, the administrator for Hawaii County Civil Defense, said at a news briefing. There was no sign of holdouts in Lanipuna afterward, he said.

Edwin Montoya, 76, had planned to stay to care for animals and keep looters away from his family's property in neighboring Leilani Estates. But he was forced to evacuate after the new fissures emerged, including one just a mile away.

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"I'm in my truck right now on my way up the road," he said. "The police came down here and made me."