Decade Volcano: Mauna Loa

Hawaii’s Mauna Loa is world famous, but do you know what it looks like? (Hint: That’s it up above, looming over Kilauea’s new summit crater.)

Videos of Kilauea’s 2018 eruption sometimes refer to a low hill in the distance as Mauna Loa. And perhaps you’ve seen pictures of lava flowing downslope towards city lights (the city is Hilo and that eruption was in 1984).

Here’s the thing: Kilauea is on the south shore; Hilo, built on lava that flowed down Mauna Loa’s flank in the early 1880s, is on the northeast coast.

Everything in between Kilauea and Hilo is Mauna Loa.

So is the southwestern part of the island, where the largest development in the US — Hawaiian Ocean View Estates — sits on fissures that erupted last in 1887.

About half of the Big Island, in fact, is Mauna Loa (Hawaiian for “Long Mountain”). The other volcanoes here don’t even come close to matching its size!

That distant hill may appear low, but its summit turns white with snow in cold weather and was glaciated during the last ice age because it sits more than 13,000 feet above sea level.

Images just don’t do this “long mountain” justice. But there is even more than this to Mauna Loa.

Its flanks extend down under the waves another 16,000 feet or so. Then the weight of some 18,000 cubic miles of Mauna Loa’s igneous rock depresses the sea floor a further 26,200 feet, making this volcano almost 56,000 feet tall from base to summit! (Hawaiian Volcano Observatory)

Mauna Loa is the planet’s largest active volcano and second largest known volcanic structure (after Tamu Massif, off Japan’s eastern coast).

Yet one hardly notices Mauna Loa — unless it is erupting, as it has done over 30 times since 1843.

Once again, we laypeople learn that volcanoes don’t always come in that familiar pointy shape. Sometimes they look like the hills, gullies, canyons, and flow fields of central Hawaii County (another name for the Big Island).

Certainly, human lives and property are at risk here. Mauna Loa became a Decade Volcano in part because it erupts frequently, and not just from the summit pouring out huge volumes of very fluid lava almost every time.

Hilo lucked out in 1984 when the approaching lava stopped a few miles short of the city line. But to the southwest, where terrain is steeper, residents of Ocean View and other places may only have a few hours to get out of the way.

Mauna Loa also offered the Decade Volcano Project the world’s best documented prehistoric record of eruptive activity, in an easily accessible location. Earth scientists and hazard management specialists can now compare their computer models of volcanic processes and risks throughout the world with real-life data archived in Mauna Loa’s rocky records. (Lockwood and Rhodes)

As well, a variety of crisis planning and hazard mapping tools developed through this program. (Newhall)


19.475° N, 155.608° W, Hawaii, United States. The GVP Volcano Number is 332028.

Nearby Population:

Per the Global Volcanism Program website:

  • Within 5 km (3 miles): 45
  • Within 10 km (6 miles): 45
  • Within 30 km (19 miles): 1,906
  • Within 100 km (62 miles): 175,315

Current Status:

Aviation Code Yellow, per the Hawaiian Volcano Observatory. Close monitoring has not yet shown signs of an imminent eruption. Mauna Loa appears to be slowly filling with magma for its next round of activity some time in the future.


  • Eruption styles: Mauna Loa has had at least three explosive eruptions in the distant past that only seem to have affected the summit area; volcanologists are still trying to understand what caused these. Most often, eruptions here, while larger in volume, look much like Kilauea’s 2018 Lower Puna eruption, with fissuring, fountains, and swift-moving lava flows.
  • Biggest recorded event: The one that volcanologists refer to with much respect happened in 1950, when a fissure high on the volcano erupted a lava flow that traveled 15 miles to the sea in under three hours. Another flow during this 23-day eruption was clocked at speeds of 10 to 30 mph! The rate of lava discharge in 1950 was Mauna Loa’s personal best in recorded history. An 1859 eruption produced the same volume (enough, per Hirji, to fill the Empire State Building more than 358 times), but took 10 times as long to do this. Twice as much lava was erupted from the summit in 1872 during an eruption lasting about 1,200 days. The Hawaiian Volcano Observatory notes on its website that these are the three largest eruptions at Mauna Loa in the last two centuries.
  • Most recent eruption: 1984.
  • Past history: According to the Hawaiian Volcano Observatory, Mauna Loa — the second youngest volcano on the Big Island — first appeared on the sea floor some 600,000 to 1,000,000 years ago.It probably broke through the ocean’s surface, about 300,000 years ago.

    See the GVP for details. Most Eruptions listed here are mostly VEI 0, with a few 1’s and rare 2’s.

    Edited April 4, 2020. Please see separate post for sources.

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