Kīlauea’s Eruption Explained

Forecasting Fire: Ken Hon on Living with Hawaiʻi’s Restless Earth

By Kolby Akamu Moser

Hawaiʻi Island does not pretend to be permanent.

“We live on a very dynamic island,” said volcanologist Ken Hon. “And that’s something that is not news to Native Hawaiians. Their culture wrapped around how dynamic these islands are.”

For those new to the ʻāina, though, that dynamism can be jarring.

“It’s not like Ohio,” Hon said. “Where your land is your land is your land. Maybe you have a tornado — but the land itself doesn’t change.”

Here, it does.

In recent months, communities from Volcano to Pāhala have watched fountains of lava rise thousands of feet into the sky. Roads have disappeared under ash. Windshields have been scratched by falling rock. Fine, glittering dust — tiny shards of volcanic glass — has drifted miles from the summit.

For many residents, it feels unprecedented. For geologists, it is part of a much longer story.

When Rock Takes Flight

Much of Kīlauea’s lava simply pours from the vent and feeds lava flows within Halemaʻumaʻu crater. But during high fountain events, something different happens.

The molten rock fragments.

“We call it tephra,” Hon explained. “That’s just a fancy word for any rock that gets carried by the air.”

As magma rises, dissolved water inside it behaves like carbon dioxide in a shaken soda bottle. The pressure drops. Gas bubbles form. The magma froths.

“You can think of it like foam,” Hon said. “Like soap bubbles in your sink. They’re light. They float.”

Some of that foam hardens midair. Some falls back into the crater. But a fraction — even a small fraction — is enough to blanket entire communities.

During one recent eruption, the plume reached nearly 38,000 feet.

“That’s a lot of stuff,” Hon said.

Near the summit, larger fragments — some the size of grapefruits — rained down. Farther away, the material became finer: delicate strands of Pele’s hair and dust-like particles that shimmer in sunlight but slice skin if rubbed between fingers.

“It looks like dust,” he said. “But it’s tiny glass fragments. Sharp edges. Spiky. They’re nasty little things.”

For those downwind, especially in Pāhala, the impact has been relentless.

“I feel for the people there,” Hon said. “They’ve taken the brunt of this.”

A Historic Moment

The accumulation near the vents is staggering — tens of feet thick in places, piling up into what will become part of the geologic record.

But not all eruptions are alike.

Many have drawn comparisons to the deadly 1790 eruption, memorialized in oral histories and etched into the landscape at Kaʻū Desert.

“This is very different,” Hon said.

Today’s fountains are driven by water dissolved inside the magma itself — like bubbles in soda. The 1790 explosions, by contrast, were triggered when magma interacted violently with groundwater.

“That’s more like dropping water into hot oil,” he explained. “It explodes outward.”

The difference matters. It determines how fine the ash becomes, how far it travels, and how dangerous it is.

In other words: not all fire behaves the same.

Predicting the Unpredictable

Perhaps most striking is not the spectacle — but the science behind anticipating it.

Hon is careful with language. He prefers “forecast” to “prediction.”

“To be a true forecast,” he said, “you have to know where it’s going to happen, what’s going to happen, and when.”

The first two are relatively certain. The vents are fixed. The activity — high fountains — is consistent.

The challenge is timing.

Deep beneath the summit lies a shallow magma reservoir. After each eruptive episode, the chamber deflates. The summit physically sinks — sometimes by mere micro radians, a measurement so small Hon compares it to placing a dime under one end of a 3,000-foot-long board.

Sensitive instruments detect those shifts.

“The volcano tilts up when it’s full,” Hon said. “It tilts down when it empties.”

By measuring how much it tilts — and how quickly it refills — scientists model the likely window for the next event. They use regression lines, power-law curves, Monte Carlo simulations, physics-based models.

“We’re not just guessing,” Hon said.

Still, there is humility in the process.

“Sometimes stuff happens,” he said, recalling a recent seismic swarm that temporarily disrupted magma recharge. “The volcano is not that consistent.”

Or, as interviewer Naka Nathaniel put it: “Tūtū Pele will decide.”

Hon smiled at that.

The models provide guidance. The earth retains final say.

Living With Change

For longtime residents, especially Kānaka ʻŌiwi, volcanic dynamism is not disruption — it is identity.

For others, it can feel destabilizing.

Hon acknowledges that every person carries their own story of interaction with the land.

“What we try to provide is factual information,” he said. “But how it impacts their lives — that’s personal. That’s unique.”

On one recent Saturday, even Hon found himself unexpectedly in the path of falling rock while driving with his wife — also a volcanologist.

Softball-sized fragments struck their new car. Windows scratched. Paint chipped.

“She was not pleased,” he admitted.

A career hazard, perhaps. A reminder, certainly.

The island is alive.

And while ash settles, roads are cleared, and the next forecast window approaches, the larger lesson remains.

Hawaiʻi does not promise stillness.

It offers something else: transformation — measured in micro radians, in inches of ash, in centuries of layered glass and stone — and in the enduring relationship between people and a land that continues to create itself.

Listen to the full episode with Ken Hon on the Hawai’i Radio Hour’s YouTube channel