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Mauna Loa is still the largest ACTIVE volcano on Earth

September 13, 2013

Mauna Loa, the Earth’s largest active volcano, towers 3,000 m (9,800 ft) above Kīlauea caldera (left center). Hualālai Volcano is in upper right. Photo by Jim Griggs, USGS

The following is this week’s edition of “Volcano Watch” from the USGS Hawaiian Volcano Observatory:

Despite reports to the contrary, Mauna Loa is still the largest ACTIVE volcano on Earth. The volcano off the east coast of Japan, which made the news last week—touted as the largest volcano in the solar system—last erupted 146 million years ago, possibly around the time the Pacific Ocean Basin was first formed.

Mauna Loa, on the other hand, has erupted 33 times in the past 170 years—most recently in 1984—and future eruptions are a certainty. The USGS Hawaiian Volcano Observatory, with recently upgraded monitoring networks, keeps a close watch on any changes beneath the volcano that might signal its next eruption.

The Mauna Loa 1984 summit eruption. (USGS)

Speaking of which, on September 5-7, 2013—seemingly timed almost perfectly to respond to the news stories that challenged Mauna Loa’s stature as Earth’s largest volcano—HVO seismic networks recorded a small, 3-day-long earthquake swarm just west of its summit. The swarm consisted of more than 350 detected and tightly clustered earthquakes at a depth of about 7 km (4 mi), but only about 25 were strong enough to be located. The strongest was a magnitude-2.4 earthquake, and none were reported as felt.

The swarm was in the same region where earthquakes began to occur a year or more before Mauna Loa’s 1975 and 1984 eruptions. It’s an area to which HVO pays especially close attention because of this connection.

While last week’s swarm was small in historical terms, it was the first cluster of earthquakes in this region of Mauna Loa since its 1984 eruption. Therefore, it caught HVO’s attention as a possible, but not definite, precursor to the next eruption of Mauna Loa. Only through continued monitoring over the coming weeks-to-months will the true meaning of the recent small earthquake swarm be known.

But this swarm is not the only Mauna Loa activity to have occurred recently. After the eruption in 1984, Mauna Loa immediately began re-inflating as magma once again filled and pressurized storage reservoirs beneath the summit caldera. Inflation waned in 1993, then resumed in May 2002.

(USGS Image)

In the second half of 2004, there was an intense swarm of about 2,000 long-period earthquakes more than 30 km (19 mi) below the summit of the volcano. This swarm was possibly part of the deep magma system that fed the ongoing inflation.

The rate of inflation increased in 2004, but started to slow in 2006. These data fit the pattern produced by magma intruding 4–8 km (2.5–5 mi) beneath the summit area. After 2009, Mauna Loa inflation continued, but very slowly and sporadically, so the volcano is poised for its next eruption.

This is indeed an interesting time for Mauna Loa, and HVO is well-prepared to characterize any future changes on the volcano. Until the 1990s, our deformation measurements were made by timing a laser pulse across Mauna Loa’s summit caldera and by standard surveying techniques. It was hard work, and it couldn’t be done as often as we wished, due to limited personnel and severe weather during the winters.

By the turn of the century, we were able to make many more deformation measurements automatically, continuously, and in near real-time, using GPS technology. The upgrade of our seismic monitoring network, funded by the American Recovery and Reinvestment Act of 2009, provided a robust and more sensitive monitoring tool. This enhanced seismic network, along with the GPS network, is ideal for tracking the activity of Hawaiian volcanoes.

HVO also offers increased availability of real-time earthquake data to the public—locations and the actual seismometer traces (webicorders) can be viewed at http://hvo.wr.usgs.gov/seismic/volcweb/earthquakes/. To view webicorder sites closest to the area in which the recent swarm occurred, click on Webicorders and choose ALEP or TOUO.

HVO has good geophysical data prior to and during Mauna Loa’s previous two eruptions, and we are comparing those data with the recently observed events on the volcano. For now, there’s no need to worry—but we should never lose sight of the fact that Mauna Loa is an active volcano, the largest on Earth, and it will erupt again.

8 Comments leave one →
  1. Hawaii Big Island Travel Guru permalink
    September 13, 2013 4:02 pm

    Wonderful rebuttal to the underwater Tamu Massif Volcano news last week ~ and a great reminder that our backyard contains a sleeping giant. Mahalo USGS Scientists for yet another interesting “Volcano Watch!”

  2. Dennis Joseph Quinn permalink
    September 14, 2013 8:34 pm

    I REMEMBER THE 1984 ERUPTION VERY WELL. FROM MY HOUSE IN ORCHIDLAND, I COULD SEE THE LAVA FLOWING DOWN MAUNA LOA’S SLOPE, CREEPING,EVER CLOSER AND CLOSER TOWARD HILO. IT WAS A BEAUTIFUL AND AWE INSPIRING SIGHT. WHEN PU’U’OO VENT FIRST OPENED UP, IT WAS FOUNTAINING OVER 1900′ IN THE AIR, AND FROM MT.VIEW, IT SOUNDED LIKE A 747 OUT IN THE DISTANCE. PELE HAS BEEN BUSY FOR ALMOST 30 YEARS NOW.
    IN DECEMBER I’M RETURNING TO THE BIG ISLAND, TO SPEND THE REMAINING YEARS OF MY LIFE,IN HAWAII’S BEAUTIFUL & AWSOME EMBRACE.ALOHA. D.Q.

    • Pacific Island Ranger permalink*
      September 15, 2013 6:13 pm

      Thank you so much for sharing your personal accounts of the eruptions of Mauna Loa and Kilauea! All the best on your return to Hawaii. Aloha!

    • Cheryl permalink
      July 14, 2014 9:23 am

      Hui! I remember driving to Hilo from direction of Hamakua Coast and seeing the awesome fountain of Pu’u Oo! I remember watching the eruption while standing in Waiakea Uka and it looked like it was on it’s way pronto to Hilo! I too look forward to returning to the Big Island, my home, to spend the remaining years of my life there!

  3. Ethan Tweedie permalink
    September 17, 2013 12:50 pm

    This is a great article. Who knew there was a swarm!

    I will never forget the 1984 eruption of Mauna Loa, I was a junior in HS at Parker School. Early that morning around 4 am my Dad came knocking on my door…or more like a thud thud thud….”Ethan wake up! Mauna Loa is erupting!” My initial reaction was, “do we need to run?” but he said we are loading up the car to go watch it from Hale Pohaku! It was a sight I wont forget for as long as I live! We got up there before sun up and you could see the curtain of fire or fountaining along the rift zone probably at around 12,500 feet, the whole sky was aglow. Later in the eruption it became more difficult to see from the west side of the island as the eruption created it’s own weather and the mountain was obscured quite a bit. I do remember seeing the glow each night and just staring at it.

    When she goes again it will be quite a site, hopefully not too much disruption.

    Aloha,

    Ethan

    • Pacific Island Ranger permalink*
      September 17, 2013 3:20 pm

      Thanks so much Ethan for sharing about your personal experience of Mauna Loa’s eruption! It must have been amazing to witness. Aloha! GC

      • Ethan Tweedie permalink
        September 17, 2013 3:29 pm

        Thanks for posting the article!!!!

  4. Andrew permalink
    September 22, 2013 8:16 pm

    Sorry guys.. the world’s largest active volcano is NOT in Hawai’i. Tallest sure but that’s becuse the really big ones do not form peaks but blow massive holes in the landscape. Biggest volcano in the United States is in the northwest corner of my home state. Aloha from Wyoming.

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