Watch: Mauna Loa volcano's eruption in 38 years threatens populated areas

Waves of orange, glowing lava and smoky ash erupted Monday from the world's largest active volcano with people living on Hawaii's Big Island asked to be ready in the event of a worst-case scenario.

The eruption of Mauna Loa wasn't immediately endangering towns, but officials told residents to be ready to evacuate if lava flows started heading toward populated areas.

Many now living in the area weren't around when Mauna Loa last erupted 38 years ago.

The U.S. Geological Survey warned the roughly 200,000 people on the Big Island that an eruption "can be very dynamic, and the location and advance of lava flows can change rapidly."

There's been a surge of development on the Big Island in recent decades - its population has more than doubled, from 92,000 in 1980.

More than a third of the island's residents live either in the city of Kailua-Kona to the west of the volcano, which has about 23,000 people, and Hilo to the east, with about 45,000.

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