Hawaii’s Mauna Loa Volcano Just Had Its Alert Level Raised. Here’s Why

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A brief sunrise seen through the clouds of Mauna Loa volcano is viewed on December 17, 2016, along the Kona Kailua Coast, Hawaii (George Rose/Getty Images)

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Unless you live on its slopes or even in the same state, the prolific, game-changing eruption of Hawaii’s Kīlauea back in 2018 might already seem an age away. That paroxysm officially gave up the ghost in December after dumping a total of 320,000 Olympic-sized swimming pools’ worth of lava onto the surface and into the Pacific Ocean. America’s most hazardous volcano might be having a nap three-and-a-half decades in the making for the time being, but that hardly means the United States Geological Survey is taking its eye off the ball: after all, it’s not the only volcano in the region that’s known to get a little excited.

Case in point: Mauna Loa, an impressively gigantic shield volcano just up the road from Kīlauea, is stirring in its sleep a fair bit right now. In fact, the surface deformation and seismic activity has led the USGS’s Hawaiian Volcano Observatory (HVO) to raise the volcano’s alert level to YELLOW/ADVISORY as a result. This, along with the customary all caps font style, can look a little daunting.

Aside from already fielding questions from somewhat concerned people, I’ve also noticed that well-meaning outlets have also led with this fact without explaining right away what it actually means. Predictably, the shit-stirring tabloids have also unceremoniously claimed that doom is upon us all.

The TL;dr version of this is that there’s nothing to worry about right now when it comes to Mauna Loa. This is the USGS being cautious and conservative, as ever. Let’s dive into the details to find out why.

What exactly does the alert level mean?

The USGS has a two-part alert level system: one part that advises people on the ground as to what a volcano is doing, and one that advises those flying near the volcano.

The former has four stages: NORMAL, ADVISORY, WATCH and WARNING. NORMAL is where plenty of volcanoes spend their time: this just means that, based on the historic data scientists have, the volcano is not erupting and is behaving – shaking, inflating/deflating, belching gases and so forth – in a manner that is considered to be normal. The activity is said to be at ‘background levels’.

ADVISORY means that the volcano is showing signs of elevated unrest in some way that’s not qualifiable as background levels; WATCH is a stage higher, with the potential for an eruption likely higher (albeit with an uncertain timeframe), and WARNING means that an eruption is about to happen, is happening, or is otherwise very likely to occur. As you can tell, it’s not an exact science deciding when to change the alert level for the most part.

The aviation segment of the alert code – also in all caps for some reason – includes GREEN, YELLOW, ORANGE AND RED. Although a little similar to the ground-based component, it also attempts to suggest the presence of an ashy plume, the sort that can stall airplane engines. ORANGE, for example, implies the existence of at most a minor ash plume, whereas RED indicates plenty of ash is getting up into the atmosphere. YELLOW means there isn’t an ash column present.

Right now, Mauna Loa is at YELLOW/ADVISORY, up from NORMAL. Per the HVO report, this is because seismic stations have recorded roughly 50 shallow, small-magnitude quakes under the volcano’s summit, beneath one of its rift zones (where the ground is gradually being torn apart) and on its upper west flank ever since a sustained quake swarm took place back in October 2018. These are taking place in locations similar to those that took place before two of Mauna Loa’s recent eruptions.

At the same time, GPS instruments and satellite-based radar has shown that the ground here is deforming. Volcanic regions do this pretty frequently without incident; in this case, the deformation is a sign that magma is entering Mauna Loa’s shallow reservoirs.

Crucially, Mauna Loa has been at an ADVISORY state before, as recently as the first half of 2018. No eruption occurred, and that’s what you need to remember: an increase in the alert level doesn’t mean an eruption is ultimately guaranteed. It just means that there’s some magmatic shenanigans going on down there that’s a little more hyper than it tends to be.

The data simply suggests that “magma is accumulating within the storage complex, straining the overlying rocks, causing earthquakes and inflating enough to push benchmarks on the top of the volcano up and out,” Christina Neal, the scientist-in-charge at the HVO, told me. She added that the HVO cannot yet say how much magma is getting into the shallow cache, but “our geodesists will be working on that.”

A HVO scientist walks along the Mauna Loa summit path, with Mauna Kea visible in the background.

USGS

Sure, the quakes are comparable to those that preceded a couple of recent eruptions. But the ground deformation is a little like what took place in 2005 and from 2014 to 2018, and no eruption took place after that. Remember, when it comes to volcanoes, rule number one (arguably) is that each volcano is idiosyncratic. They tend to play a little by their own rules, so without being entirely sure what’s to come next, the USGS are doing the safest thing by letting everyone know magma is on the move and they are observing the shield volcano closely.

“As has happened before, it is possible that current low-level unrest will continue and vary in intensity for many months, or even years without an eruption,” the advisory notice reads. “It is also possible that the current unrest is an early precursor to an eventual eruption. At this time, we cannot determine which of these possibilities is more likely.”

In any case: no, an eruption is not *ahem* ‘imminent’. If Mauna Loa is going to erupt, the USGS will get clear warning signs anywhere from several weeks out to, in a worst-case scenario, a few hours – but it won’t suddenly erupt with zero warning, because that’s not how volcanoes work.

What’s the deal with Mauna Loa?

This volcano is a beast, reaching a height of 4,170 metres (13,681 feet) above sea level, which is higher than Mount Fuji. That’s nothing compared to its ‘true’ elevation: Mauna Loa, per the Smithsonian’s Global Volcanism Program (GVP), rises 9,000 metres (29,600 feet) or so from the sea floor. That’s the same height as more than 16 One World Observatory’s stacked on top of one another.

It’s the world’s largest (in terms of volume) active volcano, which means (per the USGS’s definition) that it has erupted at least once in the last 12,000 years or so. It’s actually erupted plenty in historical times, with the most recent being in the spring of 1984.

Between late-March and mid-April of that year, fissures opened up, lava burst forth, and at one point it looked like the lava would inundate the town of Hilo. Fortunately, due to a variety of factors – extra-gloopy lava, dense vegetation blocked its path, gentle slopes and the decline of the eruption itself – it never quite reached it. It definitely could have, and eruptions in the past have smothered villages and towns. Future eruptions could go either way.

With no eruption since 1984, Mauna Loa is currently in its longest quiet period in recorded history. That doesn’t mean it’s going to erupt in the near future, although there is a chance that it could, hence the change in alert level.

Are Kīlauea and Mauna Loa connected?

There is some evidence that the deep-seated magma supply tapped by these two neighbouring volcanoes – separated by only 35 kilometres (22 miles) or so at the surface – may be the same. A 2012 Nature Geoscience paper suggested that the two volcanoes essentially compete for the supply of magma brewing down there, which may explain why one tends to be more active while the other enters a period of quiescence.

The evidence is still somewhat limited in this respect, though – it’s an ongoing scientific debate with not a great deal of solid evidence to go on, excellent though that study was. No-one at present can say with any certainty that because one volcano is behaving in one way, the other must be about to erupt/fall silent.

A double rainbow at Mauna Loa’s summit caldera, a cauldron-shaped depression named Moku‘āweoweo.

USGS

The notion that an eruption at one volcano can trigger an eruption at another is also highly speculative, far more so than the idea that tectonic earthquakes can sometimes trigger volcanic eruptions. It’s been noted that, in some parts of the world, one volcano erupted shortly after one very close by also spewed the melty goods, but it’s incredibly difficult to say whether or not this was a coincidence or not. Sure, like Kīlauea and Mauna Loa, they may share part of the same underlying magmatic plumbing system, but we don’t know enough about them to say whether one eruption can trigger another.

Their deep and potentially shared source of magma aside, per the USGS, Mauna Loa and Kīlauea “have separate shallow magma reservoirs that don’t seem to affect each other.” They add that “the timing of historic eruptions at Mauna Loa and Kilauea strongly suggests that an eruption at one volcano does not cause or trigger an eruption at the other volcano.”

In other words, don’t look to 2018’s eruption at Kīlauea to give you any idea of what Mauna Loa is about to, or not about to, do.

Who should I look to for updates?

Stay away from the tabloids, avoid anything that instinctively feels like clickbait, and (if I may be so bold) follow along here (or on my byline elsewhere, who knows where this may lead) for updates. Otherwise, and really first and foremost, listen to the USGS’s updates to find out what’s going on at Mauna Loa.

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