By Aya Elamroussi and Holly Yan, CNN
First, the good news: The lava spilling out of Hawaii’s Mauna Loa volcano is slowing down, spreading out and not an immediate threat to people on the ground.
Now the bad news: Possible health hazards remain as two volcanoes keep erupting on Hawaii’s Big Island, sending acidic gases into the air.
The world’s largest active volcano, Mauna Loa, shot fountains of lava up to 148 feet tall on Tuesday, but has since spewed shorter spurts, the US Geological Survey said.
Mauna Loa’s eruption this week — the first since 1984 — has led to concerns that lava could threaten Big Island’s main highway.
Saddle Road, also known as Daniel K. Inouye Highway, is the fastest route linking the east and west sides of the island. Lava from Mauna Loa has been creeping toward the highway, coming within 3.6 miles on Wednesday.
But it could be a week before lava reaches Saddle Road, the US Geological Survey said Thursday.
“Note, we just got a revised estimate based upon the flow-front location measured by our team on the ground,” the USGS tweeted. “Because of the spreading flow front and flat topography, it could be a week before it intersects the road.”
What could happen
Local officials and the state’s transportation department have been working on a plan to shut down the highway if the lava gets close enough to become dangerous, said Adam Weintraub, communication director for the Hawaii Emergency Management Agency.
Fortunately, the lava was moving into a relatively flat area — “so it is slowing down and spreading out,” Weintraub said.
But If the highway is closed, commuters won’t have any pleasant options.
Emmanuel Carrasco Escalante, a landscape worker, said he would then have to decide between the northside or southside coastal roadways to get from Hilo to Kona.
“It’s a hassle to drive all the way around the island,” he told CNN. “If the road closes, that would add almost two hours, more gas, and more miles so hopefully it (lava) doesn’t cross that road.”
Hawaii’s transportation department shared a preliminary plan for the possibility of closure.
The transportation department can provide a six-hour notice of the road’s closure, Weintraub said.
“And the staff at the Hawaiian Volcano Observatory say that they can provide at least 24-48 hours advance warning if the lava appears to be threatening the roadway,” he said.
And if emergencies arise during a possible highway closure, there are hospitals and first responders on each side of the island, Weintraub said.
2 volcanoes and lots of gases
Just 21 miles away from Mauna Loa, another volcano is also erupting in Hawai’i Volcanoes National Park.
Kilauea has been erupting since last year. But this is the first time in decades that both volcanoes have erupted simultaneously.
State health officials have warned of potential air quality issues, including vog — or volcanic smog.
Residents and visitors can expect “vog conditions, ash in the air, and levels of sulfur dioxide to increase and fluctuate in various areas of the state,” the Hawaii health department said.
And plumes of dark clouds billowing out of the volcanoes aren’t smoke — they’re “volcanic gases, which are acid gases. You don’t want to breathe them in,” volcanologist Jess Phoenix said.
“You’re talking hydrogen fluoride, hydrogen sulfide, carbon dioxide. These are all gases that are really not fun for average folks to breathe in, let alone if you have any sort of respiratory issue,” Phoenix said.
“So the Hawaiian Civil Defense Authority and the US Geological Survey will closely monitor the volcanic smog … and they will let any communities affected know well in advance if people with respiratory issues should stay inside.”
Volcanic gas, fine ash and Pele’s Hair (strands of volcanic glass) could be carried downwind, the US Geological Survey said.
Children, the elderly and those with respiratory conditions should reduce outdoor activities that cause heavy breathing and reduce exposure by staying indoors and closing windows and doors if vog conditions develop, the health department said.
While evacuation orders have not been issued, Hawaii Gov. David Ige said he signed an emergency proclamation as a “proactive” measure.
The governor acknowledged Wednesday the potential for air hazards and said officials are tracking air quality monitors across the island.
“The concern is about dangerous gases from the fissures. And the most dangerous is sulfur dioxide,” Ige said. “Observing the volcano should occur at a distance. It’s not safe to get up close.”
Volcanoes are also erupting in Alaska
More than 3,000 miles to the north, officials in Alaska are also monitoring two erupting volcanoes in their state.
Both the Pavlof Volcano and Great Sitkin Volcano are experiencing low-level eruptions in the remote Aleutian Islands chain, said Cheryl Searcy, duty scientist at the Alaska Volcano Observatory.
“Pavlof has been erupting for over a year,” Searcy told CNN in a phone interview from Anchorage. “Roughly 15 months of activity, longer than any of the previous eruptions.”
During that time, Pavlof — which stands at 8,261 feet– has not produced a high ash cloud, posing no threat to aviation, Searcy said.
As for the Great Sitkin Volcano, lava is still erupting in its summit crater, according to a report from the state’s volcano observatory. Searcy noted the 5,709-foot Great Sitkin has also been active for quite a while.
Researchers are also keeping an eye on three other volcanoes that have shown signs of unrest, including the Semisopochnoi, Takawangha and Cleveland volcanoes.
Overall, Alaska has more than 40 active volcanoes stretching across the Aleutian Islands chain.
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CNN’s Hannah Sarisohn, Sara Smart, Paradise Afshar and Dave Alsup contributed to this report.