The lava flowing from Hawaii’s Mauna Loa, which is the world’s largest active volcano and erupted this week, is edging closer to the Big Island’s main highway.

The U.S. Geological Survey’s Hawaiian Volcano Observatory reported Friday that the main front of the lava flow was 5.2 kilometers away from the Daniel K. Inouye Highway, also known as Saddle Road, and could possibly reach it in a week.

But the USGS also said that because of the unpredictable nature of lava flows, it’s “difficult to estimate when or if the flow will impact” the highway, which is the island’s main east-west road.

If the main highway is cut off, Hawaii county officials say, traffic will be forced onto coastal roads, crowding them and adding hours onto a trip from Hilo, the largest city on the Big Island, to Kona, a tourist magnet, which takes just 90 minutes on the Daniel K. Inouye Highway.

Talmadge Magno, administrator of Hawaii County’s Civil Defense Agency, told reporters this week that if lava flows onto the highway it would likely take the federal government a few months to get it passable again once the flows halt.

After the eruption on Sunday, the lava initially moved quickly down steep slopes. Over the past day, it reached a flatter area and slowed significantly, moving at just 40 meters per hour. The sight has attracted visitors to the “once in a lifetime” spectacle.

The USGS says many variables influence exactly where the lava will move and at what speed. On flatter ground, lava flows spread out and “inflate” — creating individual lobes that can advance quickly and then stall.

Mauna Loa rises 4,169 meters above the Pacific Ocean, part of a chain of volcanoes that formed the islands of Hawaii. It last erupted in 1984.
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