Scientists “Discover” Largest Shield Volcano on Earth

Guest “How about that geology fans?” by David Middleton

And it’s not Mauna Loa…

UH researchers reveal largest and hottest shield volcano on Earth
Posted on May 13, 2020 by Marcie Grabowski

In a recently published study, researchers from the University of Hawai‘i at Mānoa School of Ocean and Earth Science and Technology revealed the largest and hottest shield volcano on Earth. A team of volcanologists and ocean explorers used several lines of evidence to determine Pūhāhonu, a volcano within the Papahānaumokuākea Marine National Monument, now holds this distinction.

Geoscientists and the public have long thought Mauna Loa, a culturally-significant and active shield volcano on the Big Island of Hawai‘i, was the largest volcano in the world. However, after surveying the ocean floor along the mostly submarine Hawaiian leeward volcano chain, chemically analyzing rocks in the UH Mānoa rock collection, and modeling the results of these studies, the research team came to a new conclusion. Pūhāhonu, meaning ‘turtle rising for breath’ in Hawaiian, is nearly twice as big as Mauna Loa.

“It has been proposed that hotspots that produce volcano chains like Hawai‘i undergo progressive cooling over 1-2 million years and then die,” said Michael Garcia, lead author of the study and retired professor of Earth Sciences at SOEST. “However, we have learned from this study that hotspots can undergo pulses of melt production. A small pulse created the Midway cluster of now extinct volcanoes and another, much bigger one created Pūhāhonu. This will rewrite the textbooks on how mantle plumes work.”


University of Hawai‘i at Mānoa School of Ocean and Earth Science and Technology
World’s biggest volcano is barely visible.” Photo: NOAA

Despite being barely visible above water, Pūhāhonunis huge, larger than the Big Island.

Pūhāhonu (AKA Gardner Pinnacles) is part of the Northwestern Hawaiian (AKA Leeward) Islands.

Pūhāhonu is estimated to be 14 million years old (Middle Miocene). Interestingly (to me, anyway), this coincides with what may have been the coldest part of the Miocene Epoch, when atmospheric carbon dioxide was at a multi-million year low.

“Late Oligocene–Miocene stomatal index records, inferred atmospheric CO2 fluctuations, and effects on global temperature compared with major events in terrestrial ecosystems.” Kürschner et al., 2008.

The phrase “largest and hottest shield volcano on Earth” seemed odd, because Pūhāhonu is very extinct. The “hottest” bit is the explanation as to why it is so large.

We considered four testable mechanisms to increase magma production, including 1) thinner lithosphere, 2) slower propagation rate, 3) more fertile source, and 4) hotter mantle. The first three of these have been ruled out. The lithosphere was old (∼88 Myrs) when Pūhāhonu was formed, and thus, too thick and cold to allow for greater extents of partial melting. The propagation rate was relatively fast when it erupted (87 km/Myr), so this is another unlikely reason. Source fertility was Kea-like and no more fertile than for other much smaller NWHR volcanoes. A hotter mantle remains the best mechanism to produce the large magma volumes and is consistent with the high forsteritic olivine phenocryst compositions (up to 91.8%) and the calculated high percent of melting (24%). Thus, the gargantuan size of Pūhāhonu reflects its high melting temperature, the highest reported for any Cenozoic basalt. A solitary wave within the Hawaiian plume is the probable cause of Pūhāhonu’s higher melting temperature and the resulting increased volume flux given the absence of a more fertile source for Pūhāhonu basalts, as found for many basalts from the Hawaiian Islands.

Garcia et al., 2020


Garcia, Michael O., Jonathan P. Tree, Paul Wessel, John R. Smith,
Pūhāhonu: Earth’s biggest and hottest shield volcano,
Earth and Planetary Science Letters, Volume 542, 2020, 116296,
ISSN 0012-821X,

Kürschner, Wolfram M., Zlatko Kvaček, David L. Dilcher. “The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of terrestrial ecosystems”. Proceedings of the National Academy of Sciences. Jan 2008, 105 (2) 449-453; DOI: 10.1073/pnas.0708588105

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May 15, 2020 2:14 pm

Somebody has to say it, David, so I will. You rock.

Reply to  F4F111Col
May 15, 2020 11:10 pm


Reply to  F4F111Col
May 21, 2020 7:29 am

Read entire article.

Still no clue what a “shield” volcano is.

May 15, 2020 2:17 pm


High Treason
May 15, 2020 2:30 pm

How much CO2 is released when one of these babies lows its top? Looking at Google earth, there are a number of such large subterranean volcanoes in this chain. If the ocean floor were not so deep here, it would have been one spectacular and beautiful chain of tropical islands.
It is only a matter of time before a new volcano emerges from the depths of the ocean along the plate line. When it does, there will be a huge release of CO2 and perhaps a tsunami or two. The SJWs and fearmongerers will once again be shouting out that it is the fault of human CO2. They will once again demand power, control and taxes-a pattern that pervades history-a decent in to paganism.

Jeff Alberts
Reply to  High Treason
May 15, 2020 3:08 pm

It’s my understanding that these types of volcanoes tend to NOT blow their tops, but rather boil and simmer slowly over very long periods of time.

Here’s a recent “new” volcanic island:

Reply to  Jeff Alberts
May 15, 2020 9:51 pm

Exactly, shield volcanoes are a totally different beast from the explosive stratospheric eruptions which are usually associated with climatic effects.

A team of volcanologists and ocean explorers used several lines of evidence to determine…

It seems that “lines of evidence” thinking is becoming popular as an alternative to actually proving a scientific result these days.

Several inconclusive results supporting a leaky hypothesis is now considered proof.

James F. Evans
Reply to  David Middleton
May 16, 2020 9:18 am

“‘Lines of evidence’ is how science has almost always worked.”

Field sciences, yes (such as geology & astrophysics), but “controlled laboratory experiment” where variables can be controlled & adjusted resulting in observation & measurement in fine detail has resulted in the greatest advances in human understanding.

The study of physics in the laboratory has led to humanity’s advanced technological world of today.

Lines of evidence or “lines of reasoning” without an ability to test a hypothesis (an ability to falsify the hypothesis being proposed) has led to erroneous conclusions.

With one experiment that can be replicated with the same result and demonstrates a physical relationship, one person can disprove every other scientist and overturn so-called “scientific consensus.”

Scientific experiments are the antidote to erroneous “group-think.”

The fact that climate science can not be reduced to laboratory experiments is why climate alarmists have gotten away with so much B. S. and led many people to believe CO2 rise will cause catastrophe.

Without experiments science is ripe for political and economic manipulation and agendas.

Never undersell the value of scientific experiments in a laboratory or even in the field, so to speak… how man learned to fly… the Wright brothers at Kitty Hawk.

How man learned to fly wasn’t through “lines of evidence.”

Reply to  Greg
May 16, 2020 10:53 am

Did you meamn Strato volcanoes? They have complex 9 internal structures well described in the literature, so can explode from various point on the cone, and, as said elsewhere, simple shield volcanoes with steady erupotions from the same cone are much less “randomly” explosive. It seems some here are typing what they think rather than what they know – making it up – the basics are well described in High school texts – if you want to know them.

Curious George
May 15, 2020 2:30 pm

What makes them sure that it is one volcano and not five?

Tom Abbott
May 15, 2020 2:56 pm

From the article: ” Hawai‘i ”

What is the source of the spelling of Hawaii the way it is done above?

Jeff Alberts
Reply to  David Middleton
May 15, 2020 3:09 pm


Ron Long
May 15, 2020 2:58 pm

Interesting report, David. I’m not sure what UH Researchers mean by the “hotspot” or “mantle plume” lasts 1 or 2 million years and then dies, but the volcanic chain, leeward and windward, that ends at the Big Island of Hawaii is 14 million years in total age, including the proposed Puhahono. This is the same minimum age as the Yellowstone mantle plume, and it is still going strong (watch out!). The Yellowstone mantle plume rises through continental crust, whereas the Hawaii mantle plume rises through oceanic crust. Why do we care? Because the Yellowstone mantle plume magma produces gold deposits! Stay sane and safe (day 53, held prisoner today, but tomorrow the dogs and I bust out).

Jeff Alberts
Reply to  Ron Long
May 15, 2020 3:10 pm

You sure the dogs haven’t eaten you already, and are now posting under your name?

Don K
Reply to  Ron Long
May 15, 2020 4:42 pm

The Hawaiian chain and its continuation — the Emperor Seamounts — are older than mid-Miocene. They extend to Kure atoll NW of Midway beyond which the water gets too cold to support the tropical reef corals that keep the islands above water. But the seamounts extend nearly to Kamchatka. IIRC “they” have dredged Cretaceous lavas from the (presumably) oldest seamounts at the Northwest end of the chain.

Robert W. Turner
Reply to  Ron Long
May 15, 2020 4:49 pm

Didn’t the Yellowstone hotspot only deposit gold during its first few eruptions?

Ron Long
Reply to  Robert W. Turner
May 15, 2020 5:57 pm

Robert and David, the continental crust riding over the Yellowstone mantle plume produced both the Columbia River Basalt and the Miocene Rifts in northern Nevada. There are felsic/rhyolitic segregates in both igneous provinces and the gold deposits are associated with these (like Grassy Mountain in Oregon and Sleeper in Nevada). At Yellowstone proper the trail down to the lower Falls observation platform has chalcedony-adularia veinlets with oxidized pyrite and very small pieces of free gold (that’s not free gold like you can take some, the Park Rangers frown on that). Several times “fishermen” along the river below the falls were caught with gold pans in their backpacks and vials of placer gold (not golden trout!). The gold at Yellowstone is therefore not associated with the youngest eruption (Yellowstone Lake), but that may be a matter of depth of exposure.

Clyde Spencer
Reply to  Ron Long
May 15, 2020 9:58 pm

Now we wouldn’t want to deplete Yellowstone of the gold that is there, which tourists can’t see unless they pan for it, would we?

Reply to  Clyde Spencer
May 16, 2020 10:29 am

Too many people panning at the same time can increase silt levels in the water, which is bad for fish.
Not saying the rangers aren’t over doing it, but they do have their reasons.

Clyde Spencer
Reply to  Clyde Spencer
May 18, 2020 12:18 pm

Silt can be bad for the eggs of spawning fish. However, fish do just fine living and eating in muddy water such as during Spring floods.

The proper thing to do is monitor the situation and issue permits (if actually necessary) and or have seasonal restrictions. There is little justification for a blanket prohibition. Taking gold is little different from taking fish. It is a natural resource that is replenished as erosion takes place.

Jack Roth
Reply to  Clyde Spencer
May 18, 2020 4:40 pm

Clyde, your comment is well stated. Blanket prohibitions are applied across the board at National Parks, except of course if one is a major company or friend of the Superintendent.

For example: use of drones, which is blanket banned in all Parks. Yet Yellowstone National Park itself uses drones, or allows their use, for their marketing media. Perfect example is Grand Prysmatic Pool, which looks amazing in any picture, as long as it’s taken from at least 100 ft above it. At eye level, it doesn’t look like anything. The drone pictures of it however are splashed along every single page of Yellowstone National Park promotional media and books.

Drones flown above a certain altitude are silent and practically invisible. The FAA is currently requiring registration and sanctioned training for the use of most serious drones. It would have been easy for the Park Service to require both FAA registration and perhaps other restrictions in order for drone operators to fly their drones in parks, in order not to bother visitors and wildlife. The Park Service could have partnered with Drone Clubs and associations to help police their use, as the FCC has done for decades with Ham Radio operators.

But instead there’s a blanket ban for drones across all parks period.
Result: a lot of people, most of whom are untrained, are flying their drones into Parks illegally, likely bothering animals and visitors.
Yet another example of the government seeing its role as keeping as many people as possible from enjoying their resources, instead of assisting them.

Moderately Cross of East Anglia
May 15, 2020 3:02 pm

Fascinating post. Is this “new ” volcano created by the same hotspot which created Hawaii’s islands or a previous hotspot now extinct or dormant?

Rud Istvan
May 15, 2020 3:07 pm

Many thanks for spotting this. I did some quickie research. If this deep mantle plume volcano is 14 mya, then the plume must have started several my before to create the whole Hawaiian leewards. And the deep mantle plume under what is now Yellowstone can be traced back To eastern Oregon western Idaho flood basalts dating about 17mya.

But, two basic questions unanswered, although there are competing theories.
1. What is the cause/source of deep mantle plumes? One theory is core/mantle interactions at the boundary (so called D” (D prime) layer. A form of viscous convection. Only place there is a large steep temperature gradient. But then, why Very few concentrated heat plumes?
2. Why so stable for so long in one small spot? Normal convection is fairly unstable if there is a uniform base (pot of boiling water unless the bottom is scratched so bubbles form there repeatedly). Mantle Chemical inhomogeneities equivalent to pot scratches should smooth out over time thanks to diffusion. And 17my is a Fairly long time even in geology.

More Dunnos.

Jeff Alberts
Reply to  Rud Istvan
May 15, 2020 3:12 pm

Zoe will be along shortly to inform us that the entire field of vulcanology is wrong.

Rud Istvan
Reply to  David Middleton
May 15, 2020 4:24 pm

Dave, I spent my late afternoon looking also after triggered by your post. Concluded there is much we now know (plate tectonics in geology) and much more we don’t—and that is just in geology. To think that epigenics now ‘explains’ Lamarckian —not Darwinian— evolution is an insight debunking the ‘junk DNA‘ hypothesis that was prominent when I was running the MOT gene chip effort…a guest post over at Judiths, using Mesoamerican dried beans as the Penultimate illustration. One genome, essentially now still the same as the original wild type Vulgaris domesticated maybe 8000 years ago ; yet many obviously different phenotypes—navy beans, black beans, pinto beans, white beans, red beans….

Jack Black
Reply to  Rud Istvan
May 15, 2020 11:35 pm

What about Human Beans?

Reply to  Jack Black
May 16, 2020 1:36 pm

They make good coffee

Robert W. Turner
Reply to  Rud Istvan
May 15, 2020 4:57 pm

As far as stability in one spot and then jumping to the next, that’s due to the neck of the mantle source feeding the crustal magma chamber being stretched as the plate moves over it. Once the neck is stretched enough it breaks off from feeding that chamber and a new chamber is formed directly over the plume.

That’s at least how it is thought to work for Yellowstone.

Reply to  Rud Istvan
May 15, 2020 6:46 pm

Most “conventional wisdom” about mantle plumes is idle-minded speculation based on one-dimensional modeling (there you go again) of poorly constrained eruption ages from volcanic vents that remain active for several million years. If the Hawaiian chain represents the linear trace of a “mantle hot spot” that has been chugging out magma for 70 million years, where are the other traces of other active vents elsewhere in the Pacific basin? It’s a damned big chunk of real estate to only have one singular vent-trace over that length of time. And remember, the sea floor itself is constantly in motion from spreading ridges to trenches where old sea floor is consumed and recycled. The vectors of those motions change over time too.

Read research papers by Warren Hamilton (USGS; CO School of Mines; Nat Acad Sciences) about the irrational concept of “deep mantle plumes” – Plumes cannot exist because they would have to cross well known physical/thermal/mechanical boundary layers in the mantle that can be imaged by seismic waves. And you’re right, Rud, on the grounds that turbulence in a narrow conduit would destroy a “plume” in short order anyway, just as in the well-known mushroom cloud.

The Yellowstone caldera is most certainly NOT located at the eastern (“leading”) front of a mythical mantle plume. The Great Basin has been spreading by extension for at least the last 25 million years while Montana, northern Idaho, and western Oregon have not. The boundary between extending area to the south (Nevada and Utah mostly) and the more rigid areas to the north is marked by volcanic activity starting near the common boundary of Nevada, Idaho, and Oregon about 25 my ago. As the extension continued, the volcanism progressed northeastward through southern Idaho AND northwestward through southern Oregon throughout Miocene and Pliocene time to the present. The youngest volcanic centers in the northern Great Basin are at Newberry in central Oregon AND at Yellowstone in northwestern Wyoming. Both of these trends are marked by spatially sequential eruptions of rhyolitic and basaltic volcanic rocks

It’s rather hard to explain two “mantle-plume hot-spot tracks” simultaneously trending about 140 degrees divergent from each other, especially when they both started in the same spot at the same time.

But it’s rather easy to understand both as the result of concurrent extension, thinning the lithosphere, and creation of numerous fault-facilitated pathways for magma to leak to the surface

Len Werner
Reply to  David Middleton
May 15, 2020 8:03 pm

” If the Hawaiian chain represents the linear trace of a “mantle hot spot” that has been chugging out magma for 70 million years, where are the other traces of other active vents elsewhere in the Pacific basin?”

Tuamoto-Line Islands?

Jack Black
Reply to  Len Werner
May 15, 2020 11:40 pm

Italy? 🌋
Vesuvius to Etna ?
What do you think, Dave?

Joel Heinrich
Reply to  Len Werner
May 16, 2020 2:17 am

there are quite a lot of them. Easter, Galapagos, Canary, Helena, Reunion islands…

comment image

Adam Gallon
Reply to  Len Werner
May 16, 2020 2:25 am

Vesuvius & Etna, aren’t shield volcanoes, with mantle plumes beneath them. They’re on the boundaries of the European & African plates, so are classic Subduction Zone volcanoes.

Don K
Reply to  David Middleton
May 16, 2020 1:58 am


“In its most simplistic form, the mantle plumes don’t move. The crust moves over them.”

Sure seems to be the case. Not only is the Hawaii-Emperor volcanic chain pretty impressive, consider the Great Meteor hotspot which appears to track from the Canadian Arctic thru Ontario, Quebec(Montreal), New England, the Western Atlantic (the New England seamounts), across the mid-Atlantic Ridge, to its current position off the coast of Africa. That’s persistence.

I wouldn’t be terribly surprised if someone eventually manages to associate the Hawaiian hotspot with a string of ancient volcanoes somewhere in Eastern Asia although I couldn’t begin to guess where the track of the hotspot might be after (if) it crosses off the Pacific Plate.

Reply to  Don K
May 16, 2020 11:08 am

If you check out the Louisville Ridge East of New Zealand there is another submarine chain very similar to the Emperor ridge being subducted into the Tonga trench at 24cm pa. But no hotspot smoking gun around…. Wavis ridge is not the same beast.

The American plate will eventually slide over the Yellowstone hotspot so will melt a gap through the great basin from the Pacific to reach the great plains – making a hole in the Rockies you can drive an SUV through, if vehicles and humans still exist. At least the Bison can still use it. The politicians will have evolved into snakes by then. IMO

Ron Long
Reply to  GeologyJim
May 16, 2020 6:30 am

GeologyJIm, you have mixed together several geology ideas and come up with some right and some wrong comments. Not only do mantle plumes remain stationary and the crust moves over them, but the mantle plume manifests itself as heat only in the crust. This is clearly shown by the lithology of the produced volcanism reflecting the composition of the underlying crust, oceanic crust in the case of Hawaii and continental crust in the case of Yellowstone. Newberry Crater is the product of Cascade subduction volcanism, whereas Yellowstone is produced by mantle plume melting, very different. The geologists working in gold exploration in Nevada follow these ideas very carefully (used to follow it in Oregon also until anti-mining laws associated with a lurch toward socialism). The geologists following these ideas in Nevada would include myself, and I have discoveries to show for it. Warren Hamilton? I used his ideas about greenschist grade metamorphism related to large pluton margins in my thesis area in western Idaho. So he got some things right and some things wrong, which is true of every geologist that stands up and says something. Geology is complex, but not totally unknown, and the commercial practioners have to be able to function at a reasonable level, or no more drill money for you.

May 15, 2020 3:44 pm

“Scientists “Discover” Largest Shield Volcano on Earth”, so far. The 70 % of the planet that is ocean might have more surprises, yet.

Curious George
May 15, 2020 4:31 pm

Just thinking aloud.. This convection is unlike atmospheric convection. Speeds of motion are probably in meters per century. The density of the rock is somewhere around 3000 kg/m3. The motion will be dominated by inertia. Friction is probably very uneven, highly dependent on temperature – this might be a stabilizing factor. Once you have a hot vertical plume, it can’t move horizontally.

Allen Heinrich
May 15, 2020 4:39 pm

Here is a more definitive discussion of the Hawaii -Emperor Seamount Chain.
It runs from essentially the Aleutians to the Hawaiian Islands, and continues to grow via the
seamount Lo’ihi to the SE of the Big Island ( Isl of Hawaii) which is still under a couple thousand feet of water.
Oldest section is about 70my old. There is a kink in the middle where the plates sliding over the hot spot
changed direction.

May 15, 2020 7:31 pm

I think there is a new hotspot forming right now 60 km west of Tonapah, NV. Either that or somebody is filming the latest “Tremors” sequel. Over 140 earthquakes in the last 12 hours! See USGS earthquake website.
It is most likely the Basin and Range doing some extension work. What I find interesting is that this is the third major earthquake swarm I’ve seen over the last four months. The first was just west of Salt Lake City, the second up in Idaho.

May 16, 2020 12:37 am

Interesting work. By coincidence, I saw the article at Science mag, and updated the Wikipedia article on Pūhāhonu/ Gardner Pinnacles an hour or so ago:
Keep up the good work

May 16, 2020 1:34 am

Lots of Garderning. A pinnacle, even.

Moderately Cross of East Anglia
May 16, 2020 1:49 am

Still, an interesting question posed above is why are there not more of these large active hotspot plumes?

Presumably it would be reasonable to suggest that in much earlier Earth history there were many of them, which leads to the thought that we might have a relatively rare relic hotspot which is a sort of living fossil from a more violent past.

Isn’t geology refreshing after the mind-numbing vacuum that is climate science.

Joel Heinrich
Reply to  Moderately Cross of East Anglia
May 16, 2020 2:24 am

but there are more. see my post above. or just search for hotspot volcanism.

Moderately Cross of East Anglia
Reply to  Joel Heinrich
May 16, 2020 8:45 am

Thanks Joel. I was aware that there are more, the Galapagos for one example. The point I was raising was whether such hotspots have been declining in number and are now diminished in comparison to earlier Earth history.

John Tillman
Reply to  Moderately Cross of East Anglia
May 16, 2020 7:38 pm

There are many. Please check out the Reunion Island hotspot in the Indian Ocean. India’s Deccan Traps flood basalt flows occurred as the Indian Plate was passing over that hotspot, at the Cretaceous-Paleogene boundary.

Joel O'Bryan
May 16, 2020 10:58 am

I think that’s where the SS Minnow is beached.

comment image

Richard of NZ
May 16, 2020 1:02 pm

I always have doubts about the discovery of “the largest ever” type stories. How does this volcano compare, for example, with the Reunion Hotspot which is considered to have formed the Deccan Traps, several thousand miles away, along with many island chains?

John Tillman
Reply to  Richard of NZ
May 16, 2020 7:41 pm

As above, the Traps are now far from the Reunion hotspot because the Indian Plate has moved northward in the past 66 million years. Same as the Pacific Plate has moved westward and changed direction since first passing over the Hawai(‘)ian hotspot.

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