Volcano Watch: Remembering Mauna Loa’s eruption from July 5-6, 1975

USGS photo by D.W. Peterson A July 6, 1975, aerial view of a portion of the north flank of Mauna Loa, looking north. In red is the ʻaʻa lava flow that nearly made it to the Mauna Loa NOAA Weather Observatory road. After this photo was taken, the flow advanced to the four-wheel drive summit access road before stopping.

Mauna Loa erupted 46 years ago this week, from July 5-6, 1975, in a 20-hour event with vents confined to the summit region (the area above 3,660 m/12,000 ft) and lava flows descending to just below 3,170 m (10,400 ft). This was the first eruption in 25 years. At the time, it was the longest quiet stretch since 1843 (we are currently in the longest stretch at 37 years and counting).