No, Kilauea won’t cause mass destruction

Kilauea isn’t about to become another Krakatoa. So let’s just stop that rumor right there.

Twitter was awash last weekend in indignant volcanologists responding to a now-corrected Associated Press story that appeared to link the Hawaii volcano to the so-called Ring of Fire, and suggest its eruption could spark others in the ring. That’s just wrong, for a number of reasons.

The Ring of Fire is a picturesque description of the hundreds of volcanoes that surround the Pacific Ocean. Tectonic plates converge along all sides of the Pacific, and where you have converging tectonic plates, you have volcanoes. But an eruption at Mount St. Helens in the Cascades mountain range in the United States, for example, cannot trigger an eruption at Indonesia’s Krakatoa.

Furthermore, Kilauea isn’t at the edge of a tectonic plate. The volcano, along with the other volcanoes that formed the Hawaiian Islands, sits in the center of the Pacific plate. Those volcanoes, some extinct and some still active, have all been fed by a hot spot, a plume of magma rising from deep within Earth’s mantle.

Another Twitter post — also now deleted, thanks to many angry volcanologists — suggested that Kilauea was about to blow, and that it could be as devastating as the planet-scale eruption of Krakatoa in 1883 that killed tens of thousands of people. Also wrong. Yes, the U.S. Geological Survey, or USGS, has said that there is an increasing chance that a steam explosion will happen at Kilauea. And in fact, Kilauea has had such steam explosions before, most recently in 1924.

But the danger to communities from a steam explosion at Kilauea is pretty limited. One reason that Kilauea and Krakatoa are so different in their explosiveness is silica. Krakatoa, which last erupted in 2017, is a stratovolcano, with tall, steep sides made of ash and lava. Its magma is relatively high in silica, which is also what makes it so explosive. The high silica concentration means the magma is more viscous, or resistant to flow — so any gases it contains struggle to expand. But the change in pressure when the magma reaches Earth’s surface means the gases can suddenly expand — and they do, explosively. 

Kilauea, by contrast, is a shield volcano: Its magma is relatively low in silica and flows easily, oozing out in characteristic ropy flows called pahoehoe and thick, blocky flows called aa. Kilauea’s magma tends to be lower in gas concentrations, as well, and what gas there is finds it easier to escape, so that less pressure builds up within the magma. As a result, the volcano is far less explosive.

The Hawaiian volcano has been erupting more or less continuously since 1983. Its most recent phase, which began in April, has garnered persistent media attention in part because of the location of the newest fissures: along the east flank of the volcano in the middle of a populated subdivision. More than 1,700 residents have been forced to evacuate and watch as slowly encroaching lava swallows houses, roads and cars. Thanks to the ongoing eruption, it’s not clear when they will be able to return home.

USGS’ volcano observatory on Hawaii’s Big Island has been closely monitoring the eruption. Twenty fissures along Kilauea’s east rift zone now are oozing lava. Some small earthquakes continue to shake that area, indicating the ongoing movement of magma through the rift area. A lava lake once visible within the volcano’s summit has completely sunk out of sight, USGS scientists said in a daily news briefing May 15.

That’s a cause for some concern, because it’s where the threat of a steam explosion comes in. As the magma drops further within the central column of the volcano, rocks forming the column may become unstable and topple into the magma. Meanwhile, groundwater in the rocks around the column may also seep in. That potent mix of water and hot rocks could produce steam explosions that could send bits of that rockfall shooting back out of the crater.

The good news is that these volcanic bombs, as those rocks shooting out of a crater are called, have a limited range and won’t travel past the bounds of the national park surrounding the summit, USGS said. As a safety precaution, the National Park Service closed much of the park on May 11, and it remains closed for now while the threat still looms.

But that’s about as explosive as Kilauea is likely to get, and it isn’t likely to have much effect on most people living on the Big Island, let alone the rest of the Hawaiian chain. For now, the main danger to people on the Big Island is ash shooting out the summit crater. As of May 15, USGS noted that the crater is nearly continuously emitting ash that can rise in plumes as much as one to two kilometers above the ground. That ash can make roadways slick, contaminate open water reservoirs and cause some respiratory problems to people living in areas downwind.

Meanwhile, volcanologists continue to keep close watch on the volcano and the oozing lava on its lower east rift zone. Scientists are currently analyzing ash samples to determine their water content, to better understand how large a role water is currently playing in the ash plumes. But so far, according to USGS Hawaii Volcano Observatory deputy scientist in charge Steve Brantley, there’s no evidence of the kind of vigorous explosive activity at the summit that led to its last steam explosions. So not only is Kilauea no Krakatoa, it’s not yet clear whether it’ll be as explosive as it was nearly a century ago.