Images

As magma rises toward Earth's surface, gases dissolved in the molten rock bubble out and escape through surface vents called fumaroles. HVO established sensors atop Mauna Loa in late 2005 to continuously monitor the concentration of carbon dioxide and sulfur dioxide gases and fumarole temperature within Moku‘āweoweo, the summit caldera.

USGS Hawaiian Volcano Observatory geophysicist Ingrid Johanson measures gravity with a gravimeter on the slope of Mauna Loa with Mauna Kea visible in the background. USGS photo.

Earthquakes beneath Mauna Loa's summit prior to 1975 and 1984 eruptions. Green circles 0-5 km (0-3 mi) deep, red circles 5-10 km (3-10 mi) deep.

Earthquakes at Mauna Loa from June 2013 to June 2015. Green circles are 0-5 km (0-3 mi) deep and similar to ones prior to 1975 and 1984 eruptions, but cluster of 5-10 km (3-6 mi) deep quakes missing.

‘A‘ā lava flows erupt from the Northeast Rift Zone of Mauna Loa on March 25, 1984—the first day of the volcano's most recent eruption. USGS photo.

Map showing the lava flows that have erupted on Mauna Loa Volcano from 1843-1984.

A wide view of Kīlauea and Mauna Loa volcanoes, looking northwest. Pu‘u ‘Ō‘ō Crater, on Kīlauea's East Rift Zone, is the large fuming crater just to the left of the image center.

A sketch by Joseph Nāwahī showing the 1881 lava flow approaching Hilo. (Courtesy of National Park Service, Hawai‘i Volcanoes National Park, HAVO 394, Volcano House Guest Register 1873 to 1885, illustration by Joseph Nāwahī, February 21, 1881.)

Preview image for video: This Quicktime video shows a time-lapse sequence spanning from dawn to dusk on Tuesday, January 28, using images collected by our webcam near the summit of Mauna Loa Volcano (13,680 ft above sea level).

Preview image for video: This Quicktime video shows a time-lapse sequence spanning from dawn to dusk on Tuesday, January 28, using images collected by our webcam near the summit of Mauna Loa Volcano (13,680 ft above sea level).

Erupting vents on Mauna Loa's Northeast Rift Zone near Pu‘u‘Ula‘ula (Red Hill) on Mar. 25, 1984—just hours after the eruption began—sent massive ‘A‘ā lava flows moving toward Hilo at 4 miles per hour. By the time the eruption ended on April 15, lava flows had reached to within four miles of Hilo city limits. USGS photo.

Island of Hawai‘i map, showing Mauna Loa and the other four volcanoes that make up the island. Mauna Loa structural features include summit caldera, rift zones, radial vents, and historical lava flows.

Thomas Jaggar and his wife, Isabel, hiking on Mauna Loa during the September 1919 Southwest Rift Zone eruption.

The summit of Mauna Loa (left) rises above the vog layer on the leeward side of the Island of Hawai‘i in November 2012. The flank of Hualālai is visible at right.

The Hawaiian Volcano Observatory and Jaggar Museum, shown in this photo, sit atop the summit of Kīlauea Volcano. The snow-capped summit of Mauna Loa, nearly 10,000 feet higher than Kīlauea, looms in the background.

The Hawaiian Volcano Observatory and Jaggar Museum, shown in this photo, sit atop the summit of Kīlauea Volcano. The snow-capped summit of Mauna Loa, nearly 10,000 feet higher than Kīlauea, looms in the background.

Erupting vents on Mauna Loa's northeast rift zone near Pu‘u ‘Ula‘ula (Red Hill) on March 25, 1984, sent massive ‘A‘ā lava flows down the rift toward Kulani.

View looking downslope at the various cones that dot Mauna Loa's Northeast Rift Zone. The edge of North Pit, on the north side of Moku‘āweoweo, is in the foreground.

Aerial view of Mauna Loa's upper northeast rift zone near the area where it intersects Moku‘āweoweo, the summit caldera. Pāhoehoe flows visible in the foreground were erupted in 1942. Distant steep cliffs (right background) are the west wall of the summit caldera.

This view of Mauna Loa's summit is looking toward the northeast. The east flank of Mauna Kea is to the left, and North Pit, on the northeast end of Moku‘āweoweo, is straight ahead.

A view of Moku‘āweoweo, the summit caldera of Mauna Loa, as seen from South Pit (looking to the north-northwest). An eruption in 1940 created the cinder-and-spatter cone visible on the caldera floor (right center). This cone, which is about 114 m (373 feet) high, is the largest cone at Mauna Loa's summit.