The U.S. Geological Survey (USGS) Thursday issued red alerts regarding the ongoing eruption of Hawaii’s Mauna Loa Volcano — the world’s largest active volcano — as lava flows from the eruption are posing a threat to a major highway.

The agency’s red alert warning means a volcanic eruption is underway that poses limited hazards to ground-based communities. The alert includes an aviation warning, as significant emission of ash into the atmosphere could affect air traffic.

The USGS says lava from Mauna Loa is flowing from two active fissures, and the most active flow is moving toward the Daniel K. Inouye Highway, also known as Saddle Road. The highway is considered the major highway on Hawaii’s Big Island where Mauna Loa is located.

In its report, the USGS said the largest lava flow was about 5.8 kilometers from the highway, and as of Thursday had slowed to about 24 meters per hour. The report said the flows are reaching a relatively flat area and are beginning to slow down.

The USGS explained that as this happens, the lava flow will spread out and inflate. Forecasts indicate it may take two days for the lava flows to reach the highway.

The U.S. National Oceanic and Atmospheric Administration (NOAA) reported Wednesday that lava from the eruption crossed the access road to NOAA’s Mauna Loa Observatory — which measures carbon dioxide in the atmosphere — and had taken out power lines to the site.

The Associated Press reported that the federal government is looking for a temporary alternate site on the Hawaiian island, as well as considering flying a generator to the observatory to get its power back up.

Mauna Loa began erupting Sunday for the first time since 1984, ending its longest quiet period in recorded history. It last erupted in March and April 1984, sending a flow of lava within 8.05 kilometers of Hilo, the Big Island’s largest city.

Mauna Loa is 4,169 meters high and part of the chain of volcanoes that formed the Hawaiian Islands in the Pacific Ocean more than 5,800 kilometers from the U.S. mainland.

Some information for this report came from The Associated Press and Reuters.