An explosion as lava meets the sea sends rocks flying into the air off Kapoho

Underwater explosion captured from above near lava ocean entry
Published: Jul. 11, 2018 at 2:50 PM HST|Updated: Jul. 12, 2018 at 5:10 PM HST
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KAPOHO, BIG ISLAND (HawaiiNewsNow) - Volcano eruptions can be explosive. And apparently, so can lava flows.

On Thursday, Mick Kalber of Tropical Visions Video captured aerial footage of an explosion off Kapoho, where lava is flowing into the sea.

The explosion just offshore of a lava delta threw plumes of smoke and rock high into the air.

So what's behind the explosion?

It's all a part of the process that has already created about 655 of acres of new land on The Big Island as ongoing eruptions continue.

Janet Babb, a geologist with the U.S Geological Survey, said the interaction of molten lava with cool seawater can cause pulsating "littoral explosions," which can throw fragments of molten lava and pieces of solidified glass lava "high into the air."

"At the current ocean entry, these dark-colored lava particles have been blasted skyward through billowing white clouds of seawater steam (laze)," Babb told Hawaii News Now. "Ocean entry littoral explosions can create hazardous conditions both on land and at sea because the lava fragments can be thrown far inland, as well as seaward."

But the largest and most dangerous types of explosions are triggered when newly-formed land collapses.

And truly understanding how the new "lava delta" in Kapoho might collapse — along with the dangers it may present — takes a little more explanation.

Kenneth Rubin, chair of the University of Hawaii's Department of Geology and Geophysics, said the current lava flow is entering the ocean in many small streams. When this happens, the lava often cools into fragments.

"Most of this fragmentation makes sand-sized to pebble-size particles," he said.

The accumulation of these particles creates the base of a lava delta.

And as lava continues to flow over the top of this base and create new land, it tends to lock up the particles below.

"But the bottom of the new land can be fairly unstable because it contains this broken up material," Rubin said.

USGS geologists have warned that lava deltas typically collapse without warning.

But at this point, it's hard to say if a delta collapse may occur in Kapoho.

"How stable that new land is really depends on pre-existing offshore topography," Babb said.

"If (the delta) continues to grow and push farther out into the ocean where ... we do get a steeper drop off to the ocean floor, that's when things would become more unstable and more likely to fail and cause delta collapses."

In warning about ocean entry hazards, the USGS has said that explosions from a delta collapse in previous volcanic episodes have hurled hot rocks about a yard in size as far as about 273 yards inland.

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