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Mauna Loa in Hawaii erupts for the first time in over 40 years

Long Mountain began erupting at its summit caldera Moku’āweoweo in the early morning hours today. Located on the Big Island of Hawai’i, the enormous shield volcano has not been active for 38 years. The eruption follows the profile of most Hawaiian-style eruptions, with a fissure opening at the top with lava fountains and lava flows exiting the new vent (see above).

The USGS Hawaiian Volcano Observatory moved the alert status for Mauna Loa to Red/Warning with this new activity. At the moment there is no threat to the people living around the volcano because this eruption is likely to remain confined to the summit. However, views from the summit show lava flows rapidly covering the ground (see above).

UPDATE 11:30 a.m. ET: The USGS reports that lava flows poured from the summit caldera to the southwest, but the eruption is still coming from the summit.

Animated GIF of activity at Mauna Loa from Nov. 27 to early Nov. 28, showing the start of the new eruption. Credit: USGS/HVO.

However, it is not excluded that new vents may open outside the summit caldera. Historic Mauna Loa lava flows have occurred on all sides of the giant volcano, including some in the 1880s that reached what is now Hilo. It also has the potential to produce flows that could reach south Kona on the other side of the island. Thus, the threat is there for potential lava flows that could reach the southwest, northeast, and northwest of Mauna Loa. Depending on the vigor of the eruption, volcanic fog (or vog) could also be a respiratory hazard.

UPDATE 2:30 PM ET: This makes look like cracks have opened on the northeast rift of Mauna Loa outside the caldera (see below), but the threat to communities is still low according to the USGS. Summit activity also appears to have decreased. Also, flights to/from Hilo were also impacted by the activity.

Lava has been flowing on Mauna Loa’s NE Rift since the November 28, 2022 eruption. Credit: USGS/HVO.

As the lava flow map of the past 200 years suggests, Mauna Loa is a very active volcano. This gap of nearly 40 years in eruptions is relatively rare in its modern history. There have been signs over the past few months that an eruption was underway, with increased seismic activity within the volcano. Looks like there was little deformation at the top until just before the start of the new eruption.

Lava has been flowing from Mauna Loa for the past ~200 years. Credit: USGS/HVO.

The new eruption means Mauna Loa and Kilauea break out on the Big Island. Dual eruptions are not uncommon in Hawai’i, although there have been suggestions over the past 1,000 years that the two volcanoes may alternate in activity. Both volcanoes erupted in 1975 and 1984, but since the mid-1980s there are only summer Kilauea erupting.

Both volcanoes are ultimately fed by the hotspot under Hawaii – a hot mantle plume that rises from deep within the planet and melts when it reaches the base of the oceanic crust miles below the island. Although both volcanoes are caused by this mantle plume, the trace element and isotopic composition of the lava that erupted from Mauna Loa and Kīlauea are quite distinct that geologists who study Hawaiian volcanoes believe they may be fed by separate parts of the plume.

The glow of the new eruption seen atop Mauna Loa from the middle portion of Mauna Loa’s Southwest Rift Zone. Credit: USGS/HVO.

The HVO has a number of webcams pointed to the summit of Mauna Loa that show current activity, including a Thermal camera which can break through some of the fog that collects at the 12,000+ foot summit of the volcano. Right now, this eruption is the best of all worlds: lava flows confined to the caldera of a closely watched volcano. It means that it is a great chance to watch a rash and know that people must be out of danger.

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