Geotripper on How to Plan a Perfect Volcanic Eruption, Hawai'i Style!

So you want to demonstrate a volcanic eruption for your field geology course, and are unsure how to proceed? Let the crew (of one) here at Geotripper help you to plan out the very best eruption experience for your students! There are several important steps and considerations:

1) Pick a volcano

This is a pretty important first step. Some volcanoes can be very dangerous, and we at Geotripper feel that safety is a hugely important consideration. We have chosen the Big Island of Hawai'i for our demonstration, as eruptions there TEND to be on the quiet side, although there are important exceptions.

Kilauea Caldera and Kilauea Iki in the distance

2) Do a site evaluation

Take a hike out to the potential eruption site. This is kind of critical, because we want to choose a site that is isolated and away from buildings and populated areas. Yet we also want the site to be visible once the eruption begins, since this is the whole point of planning such things.

Hiking out to the Ka'u Desert ("Footprints Trail") on May 29, 2024

3) Consult with the local volcanic deities:

Painting of the Hawaiian goddess Pele at the Kilauea Visitor Center with the artist, Arthur Johnson (Source: NPS).

Once again a critical factor. One doesn't conduct eruptions without the permission and cooperation of the deities that inhabit the place. In our current example we are dealing with Pele, also known as Pele-honua-mea ("Pele of the sacred land") and Ka wahine ʻai honua ("The earth-eating woman"). 

A side note: the gist of this post is tongue-in-cheek, but I take Pele pretty seriously. Check out my interaction with a mysterious woman on the flanks of Kilauea a few years ago. Who was she??

4) Start the Field Trip

Taking twenty students to the Hawaiian Islands for two weeks is no small task, and we here at Geotripper strongly suggest planning the trip many months in advance of the eruption. Remember to consider such logistics as hotels, transportation, airline flights, food, and group interpersonal interactions.

5) Educate your students on the basics of volcanoes and vulcanism

There are many ways to do this. One of my favorites is to pay a visit to the 
Hawaiian Volcano Observatory (currently based in Hilo, Hawai'i after their original home on the brink of the Kilauea caldera was damaged by an eruption in 2018). Our expert host provided an excellent introduction to the methods and technology of volcano monitoring.

6) Subtly prepare the group for the experience of the eruption

This step requires some public relation skills. We don't want to have the experience spoiled by high expectations and the like. We want our group to be both surprised and prepared when the eruption happens. There are a number of ways to do do this. For instance, have them look at seismic records and see if they notice the uptick in earthquakes in recent days. Ask a Hawaii Volcanoes National Park ranger leading questions like "why did you close the Devastated Area Trail yesterday?" You can make jokes, like "Wouldn't it be interesting if an eruption were to happen while we are on the trip?". Don't overdo it, though.

7. Conduct the Eruption

In many ways this is the easiest step, since the Earth does all the work. If you arrange for the eruption overnight, you can plan on an early departure from the hotel to beat the tourists to all the best overlooks. If you have prepared in the way that we have put forth here, your students will be duly impressed even if they can't stick things into the lava flow or even see spewing lava. Seeing the ash and steam rising from the distant rift zone will be more than enough!

Oh, I see a hand in the back...what was your question? How do we actually cause the eruption to happen at the perfect time? Oh, it's kind of complicated. We don't really have time enough to explain...

8. Provide a cooling down period

Go to the national park visitor center and hang around for awhile. Get interviewed by the local news media. Use the restrooms. Then continue on the rest of your trip, wondering how you'll ever top this experience!

So yeah, it pretty much happened this way while we were in Hawai'i recently (except for the actual organizing of any eruption). Our students and my co-leader were in fact interviewed on local Hawaiian news (see the story here: HVO: Eruption at Kilauea’s summit has paused, but activity in region remains dynamic (hawaiinewsnow.com)).

The eruption itself was somewhat of a surprise. There had been upticks in the seismicity and uplift in some nearby areas, but the precise spot where the rift opened up was unexpected. It was a very short-lived eruption, lasting only about 12 hours, and the volume of lava was limited. You can see the USGS review of the eruption here: https://www.usgs.gov/observatories/hvo/science/recent-eruption.

Source: USGS Hawaii Volcanoes Observatory

All things considered, it was one of the most satisfying moments of my teaching career... 

Here's my video of the eruption from the site of the old Jagger Museum and Hawaiian Volcano Observatory: https://vimeo.com/959288135?share=copy

Here's the direct access: 

Walking on Broken Glass, Literally: And what is slabby pahoehoe?

Some places on our planet are just not like anywhere else.

Kilauea, on the Big Island of Hawai'i is one of the most volcanically active places on Earth, and very few parts of its surface are older than a thousand years, and most are much younger. It's a place where erosion is essentially a non-existent process. There is only the addition of rock during eruptions, or the collapse of rock (into caldera or pit craters).

Walking on a landscape that has existed for only a few years is truly an otherworldly experience. A raw surface, unsoftened by soil formation or plant cover, is not a normal experience for most human beings. I was at Kilauea in May for a conference and field trip, and we had a chance to walk across one of Kilauea's more recent extrusions, a lava flow near Halemaumau Crater in the caldera that erupted in 1982. The eruption destroyed several hundred feet of the highway that travels around the caldera. It was quickly repaired, but has been closed more recently because of the ongoing (since 2009) eruption in the depths of Halemaumau that is putting out deadly fumes and gases, and the occasional explosion of debris. We were allowed to enter the area on this particular day.

Even if you have walked on basalt flows on the U.S. mainland, the experience is not like this one was. I've always thought of lava flows as being firm and solid, but when they are new, that is not always the case. The entire flow seemed to be covered by loose flakes about the size of potato chips.

One could never sneak up on an adversary on a surface like this. Every step produced loud crunching sounds. A close inspection of the loose chips showed why. The chips were composed not of basalt, but of glassy obsidian!

The more familiar kinds of obsidian most often seen around volcanoes is richer in silica, and is usually associated with lava domes or plug domes, a type of volcano not found in Hawai'i. But all lavas can form glass when they cool rapidly, and that is what happened at the surface of this flow. As the lava was exposed to the cooler air, it quickly solidified, forming a glassy crust. One would think that would be the end of it, and that the whole flow would solidify almost as quickly. But it doesn't. Six weeks after the eruption ended, bulldozers were realigning the highway, and overturned slabs still glowed red.

Such flows continue to be mobile after the crust forms, and lava beneath the crust is still quite molten (it is insulated by the crust). The flow can actually inflate with molten lava, becoming a great deal thicker before a breakout occurs, and the lava drains away. The surface can rise and fall, breaking here and there into large slabs. At the same time, the cooling rock at the surface contracts, and the surface breaks up into the chips we were walking on. In videos of such flows, one can often make out the tinkling sound of the rocks snapping off.

The amount of deflation in this particular flow was considerable, as can be seen in the photograph above, exceeding seven meters or so (about 20 feet). The lava reminded me of a sheet on an unmade bed, partly pulled up over a pillow.

The cliffs were unusual for a Hawaiian-type volcano. They were made up of distinct layers that looked almost sedimentary. They didn't result from any sedimentary process, however. They record a series of violent ash eruptions that culminated in a very explosive event in 1790 that killed dozens, maybe hundreds of Hawaiian warriors, and changed the course of history on the island (the army was facing off against King Kamehameha, and the tragedy was seen as a sign from the gods). Kamehameha soon thereafter united all the islands under his rule.

We climbed the cliff for a perspective of the main part of the flow and steaming cauldron of Halemaumau in the near distance. Halemaumau is the abode of the volcano goddess Pele, and many people take her existence seriously, providing offerings and prayers.

I was fascinated by the swirls that became visible from our vantage point a hundred feet or so above the lava flow. It is much smoother than the lavas I experienced on previous trips along the southeast rift zone of Kilauea. Compare it, for instance, with the pahoehoe flows near the former village of Kalapana that I visited in 2004, only days after they were extruded. They have a more "ropy" lobe-like shape, but note the silvery color. That silver color is also a thin layer of glass. After a few decades or centuries, that silvery luster will weather away, and the flow will have the forbidding black color that most people associate with basalt lava.

What the Heck is a Superelevated Lava Flow Anyway? 1974 Basalt Flow near Keanakāko‘i Crater

Talk about catnip for a geologist... "Do Not Enter", "Stop Here", "Go no closer to the eruption", and "Roads and Trails Closed Beyond This Point". How could any self-respecting geologist ignore such signage? And yes, that is a volcanic plume emanating from a crater on the far right side of the picture. We headed right on by the signs and headed down the road...

I suppose I should mention that we were there legally as guests of the park service, on an officially sanctioned field trip. I know that takes a bit of fun out of the story, but I suppose it's better than documenting an adventure in trespassing. We were exploring the evidence for explosive eruptive activity at the Kilauea caldera in Hawai'i Volcanoes National Park, and were walking along the edge of Keanakāko‘i Crater.

Keanakāko‘i Crater ("cave of the adzes"), probably formed in the 1400s and for centuries it was an important source of a particularly hard form of basalt that could be used to make adzes, the tools used to carve canoes and logs for walls. The adze quarry was covered by a lava flow in 1877, and a later flow in 1974 buried the quarry even deeper. It was the 1974 lava flow that we were having a look at.

The flow emanated from a rift opening just up the slope and traveled down a gully towards the main part of the Kilauea caldera. It coated the gully walls with a thin layer of pahoehoe (smooth-surfaced) basalt as it drained into the deeper crater. In other words, it was less of a lava flow than a covering layer on the gully walls. This odd occurrence revealed something interesting.

Downflow, the lava appeared to be thicker, but as we walked lower, it was apparent that it was only thick on one side. What did that mean? It meant that we were looking at a superelevated flow. And no, I'd never heard of the term either.

This was a fast-moving flow, and as it moved down the gully it made a tight turn. With an estimated velocity of 30 kilometers per hour (19 mph), the flow climbed high up the slope as it banked to the right. That's how one bank ended up around 10 meters higher than the other. It was superelevated...

The flow must have been quite a sight as it careened down the canyon but I strongly doubt there were any witnesses, as it would have been incredibly dangerous and the radiant heat would have been deadly. Then again, someone would have put up warning signs, and any geologists would have found the signs irresistible. Maybe someone saw it after all!

Would You Go? The Pit Craters of Kilauea Volcano

Eddie Aikau is a Hawai'i legend. Born in 1946, he was an ancestor of Hawaiian kings, who in antiquity were the only ones allowed to surf. Eddie trained himself to become one of the great surfers of his day, but more importantly he was the first state paid lifeguard on the North Shore of Oahu. He ultimately saved 500 people, often under terrifying conditions. He lost is life in 1978 trying to rescue a crew of a Polynesian-style voyaging canoe. They were trying to travel 2,500 miles to Tahiti, but only made it 12 miles offshore of Molokai before floundering. Eddy, who had volunteered as a crew member, offered to swim for help. The crew was later rescued, but Eddy was never found. Not long afterward, the phrase "Eddie would go" was heard throughout the islands.

I thought of Eddie when I encountered Devils Throat on Chain of Craters Road in Hawai'i Volcanoes National Park. Devils Throat is a stark example of a pit crater. There are a number of them along Chain of Craters Road (you didn't guess that one, did you?), Some of them are hundreds of feet deep. They are odd because there are no lava flows associated with their origin. They form when underground magma chambers on the rift zone of Kilauea drain, causing the land above to suddenly collapse inwards.

Devils Throat is unique in that it formed in historical time, in 1912. When discovered, the opening was only 20 feet across, but it was found to be more than 250 deep. The Eddie connection? When it was discovered, a man was lowered by rope into the dark pit. What do you think? Would you have gone?

What he found inside was an immense inverted cone more than 200 feet across at the bottom. All the walls of the pit were overhanging. Given the fragmented nature of basaltic lava flows, such overhangs are extremely unstable. Boulders started falling essentially from the moment the pit formed. Over time, debris filled the bottom of the pit so that today it is 161 feet deep, and the opening has expanded to 164 feet. The National Park Service has never really publicized the existence of the pit over fears that people would get too close to the edge and have the rock collapse beneath them.

Today, the vertical walls of the pit may be a bit more stable, but who can really say? It's a fascinating place to visit if you can find it (a bit of map work is all it takes; it's just a few hundred feet from Chain of Craters Road).

Volcanoes in Hawai'i: Rock Finds a Way (to destroy life)

The summit of Mauna Kea in the distance, and the forested lower slopes of Mauna Loa in the foreground

My last entry on the geological drama of Hawai'i concerned the stubbornness of life in a harsh volcanic environment, such as that which is found on the highest slopes of Mauna Loa and Mauna Kea on the Big Island of Hawai'i. I was echoing of course one of the memorable lines from the movie "Jurassic Park". As I started to review my next set of pictures from my recent trip, I realized the opposite supposition also holds true: rock finds a way (to kill life).

Lua Manu Crater on Chain of Craters Road. It formed by collapsing several hundred years ago, and was later filled with lava flows in 1974. 

Now obviously, it couldn't be clearer that lava destroys life as it flows through and burns forests. The aftermath of many a flow is a barren plain with no sign of life of any kind. In the tropical climate of Hawai'i, life returns quickly as wind and water aid in the propagation of seeds from the nearby forest. Sometimes it is bird droppings that scatter the seed and provide the first nutrients that lead to a rebirth of life. The surface of the Big Island gets made over repeatedly over the millennia.

The battle between rock and life does take unusual forms sometimes, which is what I wanted to illustrate in today's post. Basaltic lava is not always the all-consuming fiery hell we often take it to be. It may be in excess of 2,000 degrees Fahrenheit (1,100 degrees Celsius) as it flows from the vent, but when the lava encounters cold objects, the surface of the lava can freeze quickly. When the object is a tree, strange things can happen.

On the slopes of Kilauea or Mauna Loa, the most common tree is the Ohi'a, which I wrote of in the previous post. In 1974, the Keanakāko‘i flow overwhelmed an Ohi'a forest near Chain of Craters Road in Hawai'i Volcanoes National Park. The lava froze around the trunks as the trees themselves caught fire and burned away.

The resulting cavities are called tree molds, and they were spread widely in the Keanakāko‘i flow. The charcoal from the former tree can still be seen in some of the molds after forty years (below).

At times, the molds perfectly preserve the pattern of the bark, as can be seen below.

There is another odd phenomena that occurs in these events. The lava flows past the trees, solidifying around the trunk, and continuing on. It's not always obvious, but as lava flows by, the thickness can change, and the level of the flow can drop around the trees. The tree molds are left behind as towers of basalt with hollow centers (lava trees). It's actually kind of eerie to encounter such ghosts in the midst of a living forest (below), and easy to understand how ancient people considered these to be people turned to stone by the gods.

The 1974 has hundreds of these lava trees, and some take bizarre shapes, as in the case below, where a multiple-trunked tree (or a clump of several) was preserved.

It's obvious that life is slowly being reestablished on the flow, as we were surrounded by Ohi'a trees and other species at various stages of growth.

It turns out that the tree molds themselves offer a hospitable environment for life, with nutrients provided by the charcoal, and cooler wetter conditions below the surface.

The lava forests can be seen in several places. By far the easiest is at Lava Tree State Monument in the Pahoa area. It resulted from a flow in 1790, and the park offers paved accessible trails and interpretive signs. If you want to see the Keanakāko‘i ghost forest, you'll find it in the vicinity of Lua Manu Crater on Chain of Craters Road in Hawai'i Volcanoes National Park. There are no signs and no trails, so you are in for a bit more of a rugged adventure. Be prepared with water, sturdy shoes, and the other usual things you need for a wilderness outing. And...be careful while studying the ghost trees. Many are unstable and fragile and could be destroyed by a thoughtless climb or push. And having one fall on you can't possibly end well.

Answer to a Hawaiian Mystery, and a Cautionary Tale

If you've had a geology or earth science course, do you remember what you learned about basalt? Basalt, the low-silica volcanic rock, the one that flows instead of exploding. The one that isn't all that dangerous. Even if you haven't had such a class, you've heard that visiting volcanoes on the Hawaiian Islands is one of the things tourists can do. Helicopters fly over the lava flows, and people watch lava pouring into the sea from a few hundred yards (or feet) away. Basalt is the black volcanic rock with holes in it.

Pele's Hair collected near the edge of Kilauea Caldera

In my last post, I provided a bit of a mystery, a series of circles found in the barren plains near the summit of the Kilauea caldera on the Big Island. I'm going to provide the answer (and yes, someone accurately solved it), but first I'd like to show you some unusual things you'll see if you get access to some parts of the Kilauea volcano complex.

First off, the stuff in the first two pictures. These fibers are found around the summit area of Kilauea, and in protected hollows they can accumulate in large masses. It's called Pele's Hair, and it's made of natural volcanic glass, otherwise known as obsidian. Glass is not usually associated with basalt in the minds of most people, but glass can form around any lava that cools so quickly that crystals can't readily form. This odd feature develops around spattering edges of lava lakes like that which currently resides in the crater of Halemaumau. As globs of liquid are thrown into the air, some of the liquid trails behind as a thin fiber, which then breaks off and floats away in the turbulent hot air currents. If you visit the Big Island, you can usually find some near the Jagger Museum on the crater rim.

Reticulite from Kilauea Caldera

Then there is this weird material that can also be found around the summit region of Kilauea. It made me think of old weathered sponge rubber, but it is no such thing. It is a rock. It's composed of volcanic glass, and could be described as a sort of golden pumice, but it is distinctly different from any pumice I've ever seen. It's lighter, for one thing, and that is hard to believe, even while holding it in your hand. Most pumice is between 64-94% air bubbles, but this material exceeds 95% air. The walls of the bubbles are so thin that many are open, and this rock will not float the way that pumice can because it fills with water too quickly. It is called reticulite. It's so light that it can be blown a long ways from a crater by high winds. It is so delicate it can be crushed between one's fingers, and it can't be expected to last long in most geological environments.

Close up of reticulite from Kilauea

And finally there is this rock outcrop on the rim of Kilauea Caldera. It looks, well, almost like sedimentary layers! That is most decidedly not the kind of thing one expects to find on the edge of a basaltic shield volcano, the edifice that is supposedly constructed by multitudes of basaltic lava flows. What the heck is going on here, and what does it have to do with the strange circles of our little mystery?

A closer look reveals that these are layers of volcanic ash and scoria, the smaller particles that are associated with explosive eruptions, the kind we expect to find on the slopes of a Mt. St. Helens or a Mt. Shasta, the stratovolcanoes found on continental landmasses near subduction zones. What was going on here? The layers are more than 30 feet thick, and have been named the Keanakāko‘i Tephra.

Keanakāko‘i Tephra partially covered by a 1983 basalt flow.

It's clear that what we get taught about basaltic lava is not the entire story. Sometimes basalt erupts violently, and as such it can be exceedingly dangerous. An eruption in 1790 killed several hundred Hawaiian warriors on the eve of a major battle, and the event changed Hawaiian history, as the tragedy was seen as the judgment of the gods. These deposits were once thought to be the results of the 1790 eruption, but it turns out that they include dozens of explosive eruptions that took place between about 1500 and the early 1800s.

Exposures of the Keanakāko‘i Tephra on the margin of the Kilauea Caldera. A 1983 basalt flow can be seen below on the right.

What caused this explosive activity? In a word: water. When rising magma encounters groundwater, the water can flash to steam, causing intense explosions. Apparently the caldera collapsed to a depth great enough to reach the regional water table, and huge explosions ensued. Something like this happened at Kilauea in 1924 (see the picture below), but the massive explosions totaled only about 1% the volume of the 1790 and earlier eruptions. There have been some seriously dangerous eruptions throughout time on this volcano.

1924 eruption of Kilauea Caldera, courtesy of the USGS and Bishop Museum

And that brings us to the strange circles of the mystery. In 1924 some huge blocks were thrown out of Halemaumau crater and were thrown a thousand or more meters. When they landed, they produced bowl-shaped craters. One of the biggest from 1924 weighed 8 tons, and can be seen in the picture below.

Subsequent eruptions produced Pele's Hair, reticulite, and small cinders or coarse ash. All of these particles blew across the landscape, and accumulated in the shallow craters. The blocks remain visible in the centers of some of the craters, while others are buried. The filled craters in some cases trap water more efficiently than other surfaces, so plants are able to gain a foothold (roothold?) in the craters.

The evidence of 300+ years of explosive eruptive activity around Kilauea is sobering. Such eruptions have the potential to do serious damage to surrounding communities around the caldera and in the Puna District to the east. Current research is seeking to better understand the cycle of activity surrounding these periods of violence.

It was a real privilege to explore the flanks of Kilauea Caldera with Don Swanson, Tina Neal, and Frank Trusdell of the Hawai'i Volcano Observatory during my visit to the islands last week. It was a fascinating learning adventure. More stories to come!