Mauna Loa

Update, May 8, 2021: The HVO’s Volcano Watch this week focuses on small but important changes st the volcano’s summit. Key take-away point:

Because this is the first time we’ve observed this level of detail, it is difficult to know what the data might indicate about the volcano’s future. Mauna Loa may become quiet again and return to background, like it did in 2005, or it may not.

Mauna Loa is currently at “advisory”, only the second out of four levels in the USGS Volcano Alert-Level System. We expect that there will be additional indicators, such as increased gas emissions and a sustained increase in seismicity, before any future eruption. These recent observations remind us that Mauna Loa is a restless volcano and they are part of why HVO encourages everyone to think about how a Mauna Loa eruption might affect them and plan accordingly.

Update, April 3, 2021, 5:02 p.m., Pacific: There was an M4.3 quake on Mauna Loa’s south flank today. Per the HVO information statement:

According to HVO Scientist-in-Charge Ken Hon, the earthquake had no apparent effect on Mauna Loa or Kīlauea volcanoes. “At this time, we have not observed any changes in activity at Mauna Loa or Kīlauea as a result of this earthquake. Please be aware that aftershocks are possible and may be felt. HVO continues to monitor Kīlauea and other Hawaiian volcanoes for any changes.”

Both the magnitude-4.3 and magnitude-3.9 earthquakes appear to be slip along vertical faults caused by southeast motion of Mauna Loa’s south flank. Today’s earthquakes are significantly shallower and west of the location of the ongoing seismic swarm under the Pāhala area that began in August 2019.

This does not represent a significant departure from the seismic activity observed over the past year and the Volcano Alert Level for Mauna Loa remains at ADVISORY. Other Mauna Loa monitoring data streams show no significant change in deformation rates or patterns that would indicate increased volcanic hazard at this time.

I had just scheduled this for Sunday, the 4th, when I saw news about the earthquake swarm and decided to post this now, just in case Mauna Loa does let loose soon (will do a new post about that). There are links in the text below to current USGS articles about the volcano’s hazards and possible eruption in the near future. It’s not erupting yet, though. Per the new HVO statement:

These earthquakes may result from changes in the magma storage system and/or may be part of normal re-adjustments of the volcano due to changing stresses within it. Other monitoring data streams for Mauna Loa and Kīlauea, including ground deformation, gas, and imagery, show no significant changes in activity.

Let’s simply start with the Sunday Morning Volcano intro, look at the background on Mauna Loa, and wait and see how things go over coming days, weeks, and perhaps even months.

All Decade Volcanoes are cool, but this last excerpt, slightly edited, from my eBook about them (which is on sale through April 5th) is the Mauna Loa chapter because the volcano is keeping experts busy these days, although it isn’t erupting yet.

Hawaii’s Mauna Loa is world famous, but just off the top of your head, do you know what it looks like?

At best, those of us who haven’t visited the islands only catch a few glimpses of it in the media.

For instance, in the image above, Mauna Loa looms in the distance beyond Kilauea’s 2018 summit crater.

And perhaps you’ve seen pictures of lava flooding downslope at night towards city lights (the city is Hilo and that eruption was Mauna Loa’s last to date, in 1984).

But no single ground-based image can convey the true shape of this Decade Volcano.

It’s simply too big.

Kilauea Volcano is on the Big Island’s south shore.

The city of Hilo, built on lava that flowed down Mauna Loa’s flank in the early 1880s, is on Hawaii’s northeast coast.

Get this: Everything in between Kilauea and Hilo is Mauna Loa!

So is the southwestern part of the island, where the largest development in the United States — Hawaiian Ocean View Estates (HOVE) — sits on fissures that drained lava in 1887.

Here is a drone view of just one HOVE neighborhood.

About half of the island of Hawaii, in fact, is Mauna Loa (Hawaiian for “Long Mountain”): from that whaleback of a summit to the island’s central hills, gullies, canyons, vents, and flow fields.

The other volcanoes here don’t even come close to matching it in size!

Besides bulk, Mauna Loa also has height.

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

Underwater, the gigantic volcano’s flanks extend down another 16,000 feet or so.

Then the weight of some 18,000 cubic miles of Mauna Loa rock depresses the Pacific seafloor a further 26,200 feet.

That makes this volcano almost 56,000 feet tall from base to summit, per the Hawaiian Volcano Observatory, dwarfing Mount Everest’s “puny” 29,000-foot elevation.

Even people who live there or visit Hawaii can’t see Mauna Loa as it really is.

Human lives and property are at risk here, too.

Mauna Loa became a Decade Volcano in part because it erupts frequently — and not just from the summit — pouring out huge volumes of very runny lava each time.

Hilo actually 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, the peril is even worse.

If lava erupts from the west flank, residents of Ocean View and other populated areas may only have a few hours to get out of the way.

Another reason experts selected Mauna Loa as a Decade Volcano is because it has the world’s best documented prehistoric record of eruptive activity.

And to check it out, volcanologists can simply catch the next flight to Hawaii. Mauna Loa is very accessible.

Thanks to those studies, earth scientists and risk managers now make better computer models of processes and hazards at any volcano by using some of the real-life eruption data retrieved from Mauna Loa’s rocky archives. (Lockwood and Rhodes; Newhall)

Vacation Videos:

Mauna Loa is so large, it’s hard to find a travel video that captures everything.

Here is a local news story from 2015 with lots of information and spectacular views of the 1984 eruption:

And here is someone driving up the world’s largest active volcano as far as possible and then walking the rest of the way — and making it!

If that’s too much lava for you, Mauna Loa’s magnificent summit caldera (formed long ago when lava below it drained away) comes into view at around the 13-minute mark. They reach the summit shortly after 16 minutes.


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. There aren’t any signs of an imminent eruption. Mauna Loa just appears to be slowly filling up again for another round of activity in the future.


  • Eruption styles: Mauna Loa has had at least three explosive eruptions in the distant past. Since Hawaiian volcanoes usually have red “runny” lava, not the gray “explosive” type, volcanologists are still trying to understand what caused those.

    Most often, Mauna Loa’s eruptions, while larger in volume and more intense, look 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 let loose a lava flow that traveled 15 miles to the sea in under three hours.

    Other flows were clocked at even higher speeds. Overall, the rate of lava discharge in 1950 was Mauna Loa’s personal best, at least during recorded history.

    An 1859 eruption produced the same volume of lava as in 1950 (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 as either of these events was erupted from the summit in 1872 during an eruption that lasted about 1,200 days.

    The Hawaiian Volcano Observatory notes on its website that these are the three largest eruptions at Mauna Loa — 1859, 1872, and 1950 — in the last two centuries.

  • Most recent eruption: 1984.
  • Past history: According to the Hawaiian Volcano Observatory, Mauna Loa — the second youngest Hawaiian volcano above the waves — 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 this volcano’s eruption history.


    The Hawaiian Volcano Observatory.

    They also have online webcams. Yes, at this time of year there is some snow up there!

    The Washington Volcanic Ash Advisory Center (VAAC) monitors Hawaiian volcanoes and issues aviation advisories as needed.

    Featured image: National Park Service/J.Wei, public domain.


    European Volcanology Society. n. d. Decade volcano program 1990/2000.

    Hawaiian Volcano Observatory (multiple web pages). 2020. Last accessed October 20, 2020.

    Hirji, Z. n.d. Living in the shadow of Mauna Loa.

    Lockwood, J. P., and Rhodes, J. M. 1995. Mauna Loa revealed: Structure, composition, history, and hazards. Washington, DC. American Geophysical Union Monograph Series, 92.

    Newhall, C. 1996. IAVCEI/International Council of Scientific Union’s Decade Volcano projects: Reducing volcanic disaster. status report. US Geological Survey, Washington, DC. Retrieved from

    Oregon State University: Volcano World. 2020. Mauna Loa. Last accessed March 28, 2020.

    Varsino, M. 2013. Taming the ‘West’.

    Wikipedia. 2020. Mauna Loa. Last accessed March 19, 2020.

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