Hazards in Hawaii: Most of the State Is Just Fine, Thanks

I wasn’t going to do this, because hazard information is best left to emergency officials and experts.

But I don’t want the videos and images I’m sharing to mislead people into thinking this event is larger-scale than it is. It’s overwhelming to those who have lost homes or had to evacuate. I don’t want to downplay what they’re going through. At the same time, major hazards are confined to a very limited area, yet news media are whipping this up to apocalyptic proportions and tossing out headlines with “fears” and “anxieties” and “major” to scare people. I don’t want to add to their hype. A volcanic eruption one can watch from a few miles away without dying is moderate, not major.

So let me try to give a rundown of Kilauea hazards, and why I think it’s not greedy nor crazy for officials to be urging tourists not to cancel their visits.

Hazards from the Current Kilauea Eruption

Despite the drama at Kilauea’s summit and the East Rift Zone, the affected area is a small part of the 4000+ mi2 Big Island of Hawai’i, Other islands like Oahu are hundreds of miles away.

To give you a sense of scale, here’s a 2004 USGS Map showing most of the Big Island:

Caption from USGS: “Lava flows erupted from Kilauea since A.D. 1790 (shown in red) have originated from the summit caldera or the rift zones. Flows from the present eruption (shown in yellow) span more than 9 miles (15 km) along the coast and straddle the national park boundary (green line). The Island of Hawai‘i consists of five volcanoes:  vis, Mauna Kea, Hualalai, Mauna Loa, and Kilauea.”

We’re seeing ash and steam explosions within Kilauea Caldera, which is closed to the public, and lava flows in the lower Puna District from the word “zone” on that map eastward.

Here’s yesterday’s map showing new fissures in red. Red flows on the map above are purple on this one:

USGS East Rift Zone Map, May 18, 1PM, showing extent of lava and fissures (red) Old flows are marked in purple.
More detailed info on eruption’s HAZARDs so far:
Ash Plume, Steam Plume,  and Steam Explosions

These hazards are occurring within Kilauea Caldera, on the summit of the volcano, currently closed to visitors:

USGS – “Map of the summit area of Kilauea showing the location of the Halema’uma’u Overlook vent. Kilauea’s caldera is located within Hawai’i Volcanoes National Park.”

Halema’uma’u Crater (1km across) within the larger caldera has been steaming heavily (white plume visible in webcam)  since about May 11. The steam plume itself is harmless, although it’s a sign that groundwater is seeping into the chimney and turning to steam.

Explainer time: USGS primer, “What is volcanic ash?” TL;DR: Powdered lava dust.

When rocks from the sides of the vent fall into the lava lake below, they often send up a burst of ash. A lot of people are mistaking those for steam explosions. Here’s a 2011 video showing this process quite clearly, when the lava lake was high above the water table:

On May 9, HVO scientists started warning about the possibility of steam explosions (“phreatic eruption”)  if the lava lake dropped below the level of groundwater. Here’s why, according to a fact sheet posted by USGS several years ago:

From USGS Factsheet“: “Explosive eruptions at Kilauea are thought to be caused when water comes into contact with hot or molten rock (magma) and flashes into steam. In 1924, this happened after the level of the lava lake in Halema’uma’u Crater dropped below the water table. The walls of the crater then collapsed and blocked the opening down which the lava had drained, allowing steam pressure to build up and cause violent explosions.”

Here’s a helpful and comprehensible article in Popular Science explaining why even Kilauea’s rare, larger steam explosions are so much smaller than big blasts from stratovolcanoes like Krakatoa and Mount St. Helens.

During Kilauea’s 1924 steam explosions, boulders “as large as cows” were tossed out less than a mile. the crater. Rocks larger than 4 inches traveled no farther than 1km (0.6 miles) from Halema’uma’u Crater. Ash fell up to 20 miles away. (Hilo is 32 miles away.)

Regarding the current summit eruption, reportedly, “[USGS] Officials say that if explosions become more energetic, there could be boulders that fall up to a mile away or pea-sized fragments up to 4 miles away.

As of May 19, there has not been a steam explosion as large as the 1924 eruptions. Instead:

  1. May 9, 8:27 AM, a rockfall into the lava lake, triggered by a local 3.1 earthqauke, sent up a brief plume of ash 6000 feet.
  2. May 15, 11:05 AM: A rockfall-triggered ash cloud rose 12,000 feet, provided an interesting backdrop for golfers, and prompted the USGS to issue a red alert aviation advisory. warning pilots to steer clear of the summit. News media went into meltdown, trumpeting dire proclamations of a MAJOR ERUPTION IN PROGRESS!!! Um, no.
  3. May 16, 8:36 AM A 4.2 earthquake triggered another rockfall-and-ash-explosion, including a few  “dense ballistic blocks up to 60 cm (2 feet) across were found in the parking lot a few hundred yards from Halemaumau.”

News media began screaming about boulders “as large as refrigerators” being thrown out of the crater, omitting that whole “[flying] a few hundred yards” bit. Here they be, with photographer shadow for scale:

USGS photo of “ballistic rocks” found in parking lot next to Halema’uma’u Crater, INSIDE Kilauea Caldera, morning of May 16

Okay, yes, I wouldn’t want that to fall on me, but that’s why they closed Hawai’i Volcanoes National Park.

4. On Thursday May 17, 4:17 AM HST, an honest-to-gosh steam explosion from Halema’uma’u Crater sent a cloud of ash 30,000 feet straight up— it still has a long way to go to reach  a Mount St. Helens 12-mile-high ash column—  which carried fine ash downwind to the northeast. The golfers 2.5 miles away got dusted, but I think they’ll survive:

Ashfall, morning of May 17, Volcano Golf and Country Club Subdivision [Source]
5. Just before midnight last night (Friday May 18), another explosion sent a plume of ash up 10,000 feet, with some ashfall to the southwest [USGS].

The HVO’s “Resources for 2018 Kilauea Lower East Rift Zone and Summit Activity” has a map near the bottom of the page showing likely extent of ashfall if a steam explosion the same size as the May 17 event were to happen with current weather conditions.

Tthe Inter Volcanic Healh Hazard Network has a good page the USGS and Civil Defense have been recommending on how to cope with volcanic ash. Note that 3M Particulate Matter N95 masks are available on Amazon.

VOG — Volcanic Smog

Volcanic gasses have been a problem for Big Island residents for 35 years, ever since Pu’u O’o started spewing lava. Is it going to be any worse now the main lava eruption site is shifting downrift? Here’s a good HVO explainer on vog.

See the Hawaii Interagency Vog Information Dashboard on both ash and vog hazards. Also, here’s the University of Hawai’i current vog maps monitoring the most common volcanic gasses that cause problems (including SO2).

I have seen multiple experts remind us that Particulate Matter masks like those I mentioned above don’t help with volcanic gasses like SO2; those masks filter out dust (“particulate matter”), not air.


Honestly, out of all of the dangers, this is the one I’d have to think about. I’ve experienced a strong 5 and 7s farther away, and the worst that happened was a din of car alarms. But it’s hard to relax when the ground’s jittering.

The 6.9 earthquake on May 4 was no joke, the largest earthquake in Hawaii since 1975. Here’s the USGS “Did you feel it?” shakemap where people reported their experiences. Here’s the Honolulu Standard-Advertiser rundown of the damage caused by this earthquake: 14,000 people lost power, and a few buildings reported minor damage. Also, there were some rockslides/landslides in Hawaii Volcanoes Park and the “coastal backcountry” (Photo, article: Big Island Video News). I haven’t found any reports of injuries.

So here’s the question. Apart from that 6.9— which hasn’t happened in 40 years, so what’re the chances?— how much are people feeling this week’s earthquakes? Would we feel them, if we visited?

As a Californian, I know just the tool to find out. Go to the USGS seismicity (earthquake) map of Hawai’i for recent earthquakes, click on the 4s and 5s in the list, and check out their “Did You Feel It?” shakemaps. The light blue “Hey, was that an earthquake, or did the cat just hop on the table?” reports at any distance from Puna are reassuring.


Tsunamis need two things: movement of the sea floor (normally from a fault that’s in the water, which Kilauea isn’t), and a massive quake, like the 8s and 9s that have battered Japan, Indonesia, and Chile. They usually happen along long subduction zones at the edge of plates, not from a mid-ocean hotspot. Source? Dr. Lucy Jones, California’s premier earthquake expert, among others.

But what about undersea landslides?

A lot of people are asking about the Hilina Slump: the flank of Kilauea is settling, like incredibly slow fallen arches, towards the sea. The USGS has addressed this question here. Short answer: no. Longer answer from old USGS 2001 paper that may have been superseded: in 1975, the slump moved during the last big earthquake, causing a local tsunami and damage in parts of Hawaii, and very minor damage in California. Not good if you’re snorkling in Hilo, but that’s no megatsunami.


Yep, they’re dramatic, and they’re highly dangerous if you get close to them.

Here’s the thing. Leilani subdivision and the Lower Puna District— even the East Rift Zone— are a tiny portion of the state. And that rift zone is a narrow line. Lava will flow from there downhill. So…

(Oops. The islands are all made of lava, and I’m too lazy to correct it. Pretend it says “hot lava.”)

These eruptions are a severe hardship for people living in that small area.

The only major disaster for the rest of the Big Island is massive layoffs and a serious shortfall for businesses that depend on tourism. Sadly, some of those affected are evacuees who have lost the homes they bought in a cheap area because they couldn’t afford to live in Hilo or the expensive resort areas where they work.

If you’re feeling like a Hawai’i vacation, this might be a good time to bargain hunt on one of the other islands, or on the north side of the Big Island. It might be a way to take a vacation and help some businesses being impacted indirectly by all this.