Hawaii Volcano Eruption: Small Explosion at Kilauea May Be First of Many—Here's Why

The Kilauea volcano produced a plume of ash and steam on Wednesday at about 8:30 a.m. local time. The explosion came shortly after the U.S. Geological Survey issued a warning of potential such events.

So far, the volcano's most dramatic activity has been slow-moving lava leaks. However, scientists monitoring the volcano have been concerned about the possibility it could switch to a more explosive stage since May 2. That's when the lava lake at the crater of Kilauea, called Halea'uma'u, began retreating. A similar phenomenon preceded the volcano's last explosive period in 1924 as well.

According to a USGS statement released almost two hours after, the explosion was caused by a rock falling into the lava lake. The agency added that the surface of the lake hasn't retreated far enough to signal a switch to a more explosive state.

Read more: Decades-long Kilauea Eruption May Solve Volcanic Lava Mystery

If the surface of the lava lake begins to drop below the water table, the volcano would reach a crucial point. That lets water sneak into hot rock—and if enough water becomes hot enough, it can power an explosion.

Even just a few months ago, when the volcano was still quietly oozing lava without causing much concern, scientists were keeping their eyes peeled for a sudden drop in lava levels. "That would be a pretty big red flag that we might be moving into some sort of explosive behavior," Tina Neal, the scientist in charge of the U.S. Geological Survey's Hawaiian Volcano Observatory, told Newsweek in December.

Switching to an explosive phase would affect the dangers associated with the eruption as well. Right now, the main concerns have been slow but steady lava flows, earthquakes caused by magma moving around underground, and sulfur dioxide gas released through fissures in the ground.

The receding lava lake of Kilauea, as seen on May 6. U.S. Geological Survey via Getty Images

If Kilauea becomes explosive, ash and what scientists call ballistics would become much more concerning than they have been so far. Ballistics are large chunks of rocks flung out of the volcano, sometimes more than half a mile away. Volcanic ash, despite the name, is actually tiny pieces of rock and volcanic glass.

Another explosive phase could completely change the dynamics of the volcano. After the 1924 eruption, the lava lake disappeared for 85 years, only becoming visible again in 2009. But volcanoes are notoriously unpredictable, as the U.S. Geological Survey emphasizes in its statement, "At this time, we cannot say with certainty that explosive activity will occur, how large the explosions could be, or how long such explosive activity could continue."

Even if Kilauea does transition fully to an explosive phase, there will be one key difference from the 1924 eruption. No one saw or heard the first explosion of that event, they just noticed rocks flung out of the crater overnight. That would never happen today; scientists are armed with a host of technology that can help them watch for changes at the site.