The steady lowering of the lava lake within Halemaumau at the summit of Kilauea Volcano has increased the potential for explosive eruptions in the coming weeks.
According to the U.S. Geological Survey, if the lava level drops to the level of groundwater beneath Kilauea Caldera, the influx of water could mix with the magma and cause steam-driven explosions.
Debris expelled during such explosions could impact the area surrounding Halemaumau and the Kilauea summit.
“Similar to what happened in 1924, when there were these large explosions, and those are more vigorous and there was more energy involved, so larger fragments can be blown out in greater distances,” said U.S. Geological Survey Hawaiian Volcano Observatory geologist Janet Babb.
The threat of potential explosions prompted park officials to announced the indefinite closure of most of Hawaii Volcanoes National Park starting Friday, May 11. Only the Kahuku Unit will be open during its normal hours, Friday through Sunday, 9 a.m. to 3 p.m.
Steam-driven explosions at volcanoes typically provide very little warning. Once the lava level reaches the groundwater elevation, onset of continuous ashy plumes or a sequence of violent steam-driven explosions may be the first sign that activity of concern has commenced.
Scientists say there’s no telling how large the explosions could be, or how long such explosive activity could continue, or even if explosive activity will occur.
Residents who live around the Kilauea summit should beware of the risk of ashfall, stay informed of the status of the volcano and area closures and review family and business emergency plans.
The primary hazards of concern should this activity occur are ballistic projectiles and ashfall.
Ballistic projectiles: During steam-driven explosions, ballistic blocks up to 2 meters across could be thrown in all directions to a distance of 1 kilometer (0.6 miles) or more. These blocks could weigh a few pounds to several tons. Smaller, pebble-sized rocks could be sent several kilometers or miles from Halemaumau, mostly in a downwind direction.
Ashfall: Presently, rockfalls impact the lake and produce small ash clouds. These clouds are very dilute and result in dustings of ash, particles smaller than 2 millimeters, downwind. Should steam-driven explosions begin, ash clouds will rise to greater elevations above ground. Minor ashfall could occur over much wider areas, even up to several tens of miles from Halemaumau.
In 1924, ash may have reached as high as 20,000 feet above sea level. Small amounts of fine ash from these explosions fell over a wide area as far north as North Hilo (Hakalau), in lower Puna, and as far south as Waiohinu.
“(Ashfall) is not in itself a life-threatening phenomenon. It’s an irritant, a nuisance, especially if it goes on for many weeks,” said Tina Neal, HVO scientist-in-charge. “I’ve been in many of them in Alaska and what I recall being the most difficult part is keeping it out of your eyes, so wearing goggles if you have to go out, and be particularly careful if you wear contacts, because if ash gets behind the contacts, it can actually scratch your eye.”
Gas: Gas emitted during steam-drive explosions will be mainly steam, but will include some sulfur dioxide (SO2) as well. Currently, SO2 emissions remain elevated.
Kilauea’s lava lake began to drop on May 2. From its peak on May 2 to the most recent measurement at 9 p.m. on May 6, the lava lake surface dropped a total of more than 200 meters (656 feet).
Subsequent measurements have not been possible due to thick fumes and the increasing depth to the lava surface. However, thermal images indicate continued lowering of the lake surface since that time, consistent with deflationary tilt recorded at Kilauea’s summit.
A 3-D model of Overlook crater was created from thermal images collected during an early afternoon helicopter overflight on May 8. Based on the 3-D model, the lake level was about 295 meters (970 feet) below the floor of Halemaumau Crater.
Earthquake activity in the summit remains elevated. Many of these earthquakes are related to the ongoing shift of the summit area and earthquakes beneath the south flank of the volcano.
According to experts, because the summit is so far inland, any explosive activity is unlikely to trigger a tsunami.
“With that said, we are still in a period of significant potential aftershocks, so there is the possibility of certainly a large felt earthquake,” Neal noted.
The explosion at around 8:30 a.m. on May 9, 2018 was triggered by a rockfall from the steep walls of Overlook crater, and not caused by the interaction of the lava lake with the water table. The lava lake surface is still above the water table.