Hawaii’s famed Kilauea volcano, which has been erupting continuously since 1983 and has long been a destination for tourists, underwent a new eruption Thursday that threatened neighborhoods with red-hot lava on the eastern edge of Hawaii Island, prompting evacuations.

A giant crack about 500 feet long formed directly in the lower-elevation neighborhood of Leilani Estates, which has a population of about 1,500. From the crack, lava was shooting to heights of up to 100 feet, as if a garden hose filled with running water had been sliced along its length, said U.S. Geological Survey volcanologist Wendy Stovall, an expert on Kilauea.

Residents of Leilani Estates -- about 25 miles east of the volcano’s highest point -- on Wednesday reported cracks in the ground..

Late Thursday, Stovall said the lava flows erupted for about two hours, and the USGS said the flows had paused by about 6:30 p.m. local time (9:30 p.m. PDT). During that time, lava traveled less than about 33 feet from the crack.

The USGS said sulfur gas is noticeable around the fissure. The agency said new cracks could appear in the ground, gushing lava, but experts can’t say when or where. Areas downhill remain at risk of being inundated by lava.

More than 300 earthquakes have been reported in recent days on the volcano’s eastern flank, with a magnitude 5 temblor felt about six hours before the eruption began.

A lava eruption from Kilauea out of a fissure in the ground has not occurred in a residential area since 1960. An eruption and subsequent lava flow that year destroyed the town of Kapoho after weeks of efforts to divert lava away from neighborhoods failed.

Kilauea is the island of Hawaii’s youngest volcano, and is located on the southeastern flank of the iconic Mauna Loa.

“USGS volcanologists are on the ground and we are monitoring the situation 24/7,” Stovall said. “How the eruption proceeds from this point is yet to be seen. ... It just depends upon whether there is enough magma in the system to keep on supplying what’s been coming out of the surface.”

In 2014, a flow of lava spilled out of the volcano and at one point threatened the town of Pahoa for five months, but the flows shut off before the town could be inundated with lava. Only a few homes and a waste treatment facility were destroyed.

Hawaii officials have ordered evacuations for the communities of Leilani Estates and Lanipuna Gardens. The National Park Service on Wednesday closed off nearly 16,000 acres near the volcano, citing recent instability.

The instability began Monday. Since 1983, lava has been flowing out of Kilauea from a site on the volcano’s eastern shoulder from the bottom of a crater called Puu Oo. The crater acted as a reservoir, holding lava as it came up to the surface before it flowed back underground and eventually out to sea.

But Monday, that reservoir for lava suddenly collapsed. “The bottom kind of fell out,” Stovall said.

Magma then went into a fissure system underground to the east, along the volcano’s eastern section known as the East Rift Zone, downhill. USGS scientists were able to track the new underground path of the magma by tracking hundreds of earthquakes. Eventually, cracks started to appear Leilani Estates, in the area of Mohala Street.

Drone images broadcast by Hawaii News Now showed a long line of hot lava gushing up into the air out of a long crack in the ground. After the lava shot up, Stovall said, it fell to the ground and created flows from there.

Kilauea volcano has a very wide region of volcanic activity. The eruption in 1983 began in what is the middle elevations of the volcano’s east side, known as the Middle East Rift Zone. Separately, the summit of the volcano began erupting in 2008, and continues to emit lava to this day. Thursday’s eruption occurred in the lower elevations of the volcano’s east side, known as the Lower East Rift Zone.

“It’s unusual to have an eruption at the summit simultaneous to an eruption in the Lower East Rift Zone. This is new territory,” Stovall said.

The eruption that began in 1983 has been destructive at times, and began in a similar way to Thursday’s eruption -- cracks in the ground that unleashed lava spurting into the air like a fountain, followed by the fissure zipping up until there was just a single point sending a geyser of lava up as high as 835 feet, Stovall said. Lava flows from Puu Oo reached the sparsely populated Royal Gardens subdivision just outside Kalapana later that year, destroying some homes.

In 1986, the lava fountains stopped, and the flow of lava shifted a bit further down the volcano, and began flowing from a new location at a much faster pace. That eruption entered what was its most destructive moment by March 1990, according to the USGS. Lava flows of up to 80 feet high buried the town of Kalapana, known for its historical sites and black sand beaches, destroying 100 homes, a church and a store.

By 1992, the center of activity returned higher in elevation back to Puu Oo, where lava quietly flowed into the ocean without dramatic erupting lava fountains, Stovall said. Lava flows flowed through a natural underground tube system that pushed lava downhill.

Occasionally, lava would spill out from the Puu Oo crater, such as the time in 2014 when lava threatened Pahoa, but flows dried up before the town could be inundated, Stovall said.

The eruption in 1960 that eventually wiped out the town of Kapoho started differently than Thursday’s eruption -- the ground cracks in Kapoho were much larger than has been seen in Leilani Estates this week, Stovall said. In the 1960 event, lava fountains as high as 330 feet spewed out of a crack 3,000 feet long, and the crack zipped up to just a point where lava erupted into an even higher geyser.

Multiple efforts to build barriers to block lava flows from homes failed. Kapoho managed to survive for two weeks after the first eruption, but its fortunes changed when a more fluid lava poured out and overwhelmed the town.

“They tried to do things to stop the lava -- they built dams, they built barriers,” Stovall said. “That didn’t do anything to stop the lava. ... You can’t really stop a volcano from erupting. If there’s magma coming into the system continually, it’s just going to push everything out of its way. The eruption will stop when the eruption stops.”

In contrast to volcanoes in California and the Pacific Northwest, Kilauea volcano has a gentle slope, and only reaches a height of 4,091 feet. Mount St. Helens in Washington state rises 8,330 feet, while California’s Mt. Shasta has an elevation of 14,163 feet.

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