The headlines on Kilauea this week have often been — well, explosive.

“With the Kilauea volcano expected to explode, here’s what you need to know about visiting Hawaii” (Market Watch); “Kilauea Eruption: Five Other Volcanoes That Could Explode Next” (Newsweek); “Hawaii Kilauea volcano could soon explode in once-in-a-century eruption” (CBS Evening News).

Such headlines may have some Big Islanders laughing in derision — and mainland relatives phoning in a panic.

Those headlines may be driven by a combination of misunderstood terminology. Nor is the problem limited to the media. Terms such as “explosive eruption” or “fallout” — more familiarly associated with atom bombs than volcanoes and specialized warning codes — may mean one thing to scientists and another to the public, and can lead to alarm and confusion.

Anthony Quintano/Civil Beat

Explosive Eruptions

In fact, Kilauea is experiencing explosive eruptions; the first one happened on Thursday, and more are expected to follow. In fact, at a press conference Saturday, volcanologist Don Swanson referred to Kilauea as an “explosive volcano,” based on the fact that over the past 2,500 years, Kilauea has had more periods of explosive activity than of quieter lava eruptions. In fact, some past episodes of explosive activity lasted for centuries.

But Kilauea isn’t exploding. There’s an important difference between the two.

Kilauea is a different type of volcano from St. Helen, Krakatoa and Mt. Vesuvius, which literally have blown their tops. The latter three are what’s called “composite volcanoes” or “stratovolcanoes.”

According to the U.S. Geological Survey and other sources, composite volcanoes are steep cones built up by alternate layers of tephra (loose rock thrown out by previous explosions), pyroclastic flows (superheated avalanches of mixed rock dust and fine ash) and relatively cool, viscous lava. That thick lava doesn’t flow far, creating a tall, steep mountain that’s prone to have flank collapses, exposing their hot innards.

The USGS Volcano Hazards site for Mount St. Helens, for instance, explains that “During the 1980 eruption the upper 400 m (1,300 ft) of the summit was removed by a huge debris avalanche.” A Science News article notes that the lava in Krakatoa also contains a lot of silica, which makes it even more viscous, trapping gas that can expand explosively when it finally hits the surface.

Kilauea, by contrast, is a shield volcano. It’s located over a “hot spot:” a place of super-hot, very liquid, low-silica magma that comes straight from the earth’s mantle blowtorches its way through the crust and then can flow a long way, either on the surface or in underground rifts, creating a broad, low, shield-shaped base. They’re bigger, bulkier, more stable, and very hard to blow apart. But they still can host smaller explosions, in exactly the way that’s happening now.

To make matters even more confusing, the Environmental Protection Agency and the Hawaii Department of Health use a different color code for sulfur dioxide hazards, with six colors.

Hawaiian Volcano Observatory scientists, including Swanson, frequently compare the current event at the summit to the last “explosive eruption,” which occurred in 1924. The USGS website on explosive eruptions explains that, in 1924, lava sank so far down Halemaumau’s throat that it fell below the water table.

Water flowed in, hit the hot rock and changed to steam — which didn’t matter until rocks falling from the walls created a plug. Then steam built up until it blew the rocks out. These shotgun-blast-like explosions happened over and over until the lava rose again.

When Hawaiian Volcano Observatory or Hawaii County Civil Defense issues a bulletin about an “explosive eruption” or “explosive event” it’s that sort of event that they’re referring to: Kilauea is literally clearing its throat, not blowing its top.

Such events are still nothing to underestimate. At press briefings, HVO and county spokespersons have sometimes mentioned “refrigerator-sized” boulders that blew out of Halemaumau crater’s throat during the 1924 revent. Those boulders landed a maximum of only about a half-mile away, within Kilauea Caldera. (Halemaumau the site of Kilauea’s lava lake until a few days ago, lies within the much larger caldera, or depression at the mountain’s summit).

But during the 1924 explosive eruption smaller rocks did fall beyond the caldera rim, killing one man. One explosion on Thursday reportedly did fling a 2-foot rock out of the crater — maybe dormitory-fridge-sized. Park officials have cited the hazard of those smaller rocks as reason to close the summit area of the park.

The real problem with these summit explosive events, though, is volcanic ash, which is not a combustion product, but finely pulverized rock. The Thursday explosions threw ash more than 20,000 feet into the air, causing a hazard for aircraft. The event deposited a layer of ash on cars and homes in the Volcano Golf Course area of Volcano Village, and a reported 4 inches of ash at Volcano Observatory on the caldera rim.

A Mixed-Palette Of Warnings

Which brings up another source of confusion: color-coded warnings.

On Wednesday, Civil Defense crews were out canvassing door-to-door in Volcano, locating homes with elderly or disabled occupants, whom they said they’d check on first if an evacuation was ordered. They also passed out emergency preparedness literature, including a sheet titled, “Toxic Gas Exposure Policy,” which described three color-coded levels of preparedness (blue, orange and red), and summarized what to do at each level. When asked if this visit meant people with impaired lungs should evacuate, one canvasser replied, “No, it’s code blue.”

But the Kilauea page of the USGS Volcano Hazards Program website, that evening, held an orangish-red banner with the words: “Alert level: WARNING: Color code: RED.”

The Civil Defense literature had included a hand-written phone number to call with questions. When called about the “red alert” on the website, the worker on that line confirmed “Yes, it’s Red,” but said that was “because of the ash,” not gas.

That’s an important distinction. There are different responses to ash and sulfur dioxide. Ash is not good to breathe, and it can create hazardous driving conditions. The Civil Defense worker recommended closing all the doors and windows and sheltering in place.

USGS

But if a Red Alert is for sulfur dioxide, persons with breathing problems, especially, should “prepare for possible evacuation,” according to the Civil Defense handout.

In fact, the color code on the USGS website probably referred to a hazard code for aviation. Another USGS page explains:

“Alert Levels are intended to inform people on the ground about a volcano’s status and are issued in conjunction with the Aviation Color Code.”

The USGS code tiers start with “Normal,” (non-eruptive state) then progress through “Advisory” (the volcano shows “signs of elevated unrest”), “Watch” (the volcano shows evidence of “increased potential of eruption, time frame uncertain” or an eruption is “underway but poses limited hazards”) and finally “Warning” (Eruption is “imminent, underway, or suspected”). The Aviation Hazard color equivalents for Normal, Advisory, Warning and Watch are Green, Yellow, Orange and Red.

To make matters even more confusing, the Environmental Protection Agency and the Hawaii Department of Health use a different color code for sulfur dioxide hazards, with six colors: Green (“good”), Yellow (“moderate”) Orange (“unhealthy for sensitive subjects”), Red (“unhealthy”), Purple (“very unhealthy”) Purple (“hazardous”).

Residents who know this system, used on sites such as the EPA’s AirNow site (which, by the way, does not have monitoring stations in Volcano or Lower Puna; if you put in Volcano’s zip code, you get the air quality in Mountain View), could mistake Civil Defenses’ Code Red for the Health Department’s Code Red, and make the wrong life-or-death decision.

All of this can be a source of major confusion, especially for mainlanders and malihini (newcomers to Hawaii), including mainland reporters. A Business Insider article, for instance, originally conflated the summit explosive eruption with the lava eruption in lower Puna, apparently confused the aviation alert with red alert for gas in the Lanipuna subdivision, and described thousands of people fleeing the upcoming potential explosion, rather than the gas and lava in Lower Puna. That article has since been corrected — but others haven’t.

Residents may well be advised to contact their mainland relatives and loved ones and send them links to more reliable first-hand news sources such as the Hawaii Civil Defense site — and information sources such as the numerous USGS Volcano Hazard Program pages and then be ready to explain some things.

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