1942 – A Secret Eruption

By Mauna Loa

Scientists looking into the bright glow of Mauna Loa's 1942 eruptiv... — Scientists looking into the bright glow of Mauna Loa's 1942 eruptive vent. Eruption occurred during WWII and was not publicized to prevent Japanese war planes from navigating to the island at night. (Public domain.)

Mauna Loa's "secret" eruption began on April 26, 1942. With World War II underway, nighttime blackouts were imposed on Hawai‘i. American officials feared that if the eruption were publicized, the Japanese military could use the bright glow of lava at night to guide warplanes to Hawai‘i. The eruption began on the western rim of Mauna Loa's summit caldera but then migrated down the volcano's Northeast Rift Zone. By the time the eruption ended on May 9, lava had reached to within 7 miles of the upper Waiākea Uka area of Hilo.

See the table summarizing Mauna Loa activity over the past ~200 years here.

Aerial photograph of the 1942 Mauna Loa lava flow spreading downslo... — Aerial photograph of the 1942 Mauna Loa lava flow spreading downslope toward Hilo; smoke from burning trees in center of flow. Scattered cinder cones at the summit of Mauna Kea, top of photograph. (Public domain.)