This short-lived explosion occurred at Halema‘uma‘u crater in Hawai'i Volcanoes National Park on Wednesday morning/U.S. Geological Survey

After cracking open the earth and spewing lava fountains more than 200 feet high at times, Kīlauea Volcano at Hawai'i Volcanoes National Park next could produce explosive eruptions that eject ballistic blocks 6 feet wide and weighing a ton or more, according to the Hawaii Volcano Observatory.

Volcanic and seismic activity from Kīlauea have increased in recent weeks, becoming much more dangerous last Thursday with fissures opening along the East Rift Zone down below the volcano's main crater. While those fissures spewed lava, at times ejecting towering fountains of molten rock and starting fires that destroyed vehicles and homes, in the weeks to come the activity could become more violent, the observatory staff predicted Wednesday. 

"The steady lowering of the lava lake in 'Overlook crater' within Halemaʻumaʻu at the summit of Kīlauea Volcano has raised the potential for explosive eruptions in the coming weeks. If the lava column drops to the level of groundwater beneath Kīlauea Caldera, influx of water into the conduit could cause steam-driven explosions," the observatory said in an alert. "Debris expelled during such explosions could impact the area surrounding Halemaʻumaʻu and the Kīlauea summit. 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."

The staff also said there could be ashfalls that create problems for area residents, who were urged to read about the hazards of volcanic ash.

"During steam-driven explosions," the observatory staff said, "ballistic blocks up to 2 m (yards) across could be thrown in all directions to a distance of 1 km (0.6 miles) or more. These blocks could weigh a few kilograms (pounds) to several tons. Smaller (pebble-size) rocks could be sent several kilometers (miles) from Halemaʻumaʻu, mostly in a downwind direction."

While ash generation so far has been light, the staff said ash clouds would "rise to greater elevations" with steam-driven explosions from the volcano.

"Minor ashfall could occur over much wider areas, even up to several tens of miles from Halemaʻumaʻu," it added. "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."

Due to the unpredictable nature of steam-driven explosions, the observatory staff said there likely would be "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," it said.

Visitors at Jaggar Museum overlook on Sunday evening, May 6, 2018, enjoy the glow emanating from the lava lake deep within Halema‘uma‘u Crater. Temporary new operating hours for the park are 7 a.m. to 10 p.m. daily/NPS volunteer Janice Wei

Hawaii Volcano Observatory Background On Kīlauea’s Recent Activity

Kīlauea’s lava lake began to drop on May 2, 2018. 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 m (656 ft). The subsidence was at a relatively constant rate of about 2 meters (yards) per hour.

Measurements of subsidence have not been possible since May 6 because of thick fume 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 Kīlauea’s summit. Therefore, we infer that the lake surface continues to drop at roughly the same rate. So, while HVO cannot report exact depths of the receding lava lake, we can monitor the overall trend.

USGS and HVO scientists are monitoring changes at the summit 24/7 and watching for signs that hazardous conditions have increased, or may increase. HVO is working closely with Hawai‘i Volcanoes National Park and Hawai‘i County Civil Defense to respond to this situation.

At Hawai'i Volcanoes National Park, staff have reduced vistation hours to 7 a.m. to 10 p.m. daily. Kīlauea Visitor Center has resumed normal operating hours, 9 a.m. to 5 p.m., and Jaggar Museum has resumed normal operating hours from 10 a.m. to 8 p.m. Much of the park remains closed.

In addition to KVC and Jaggar Museum, the following areas are also open:

* The outdoor overlook at Jaggar Museum

* Sulphur Banks Trail

* Steam Vents parking lot

* Crater Rim Trail from Kīlauea Overlook to Jaggar Museum only

* The Entrance Station to Mauna Ulu parking lot

* Mauna Ulu to Pu‘uhuluhulu (Nāpau Trail is closed past Pu‘uhuluhulu)

* Kīpukapuaulu and trail

* Kahuku will resume its regular Friday through Sunday schedule, 9 a.m. to 3 p.m.

“It’s a dynamic and fluid situation in the park that can change at any minute,” said park Superintendent Cindy Orlando. “Visitors should continue to expect changing conditions and unannounced closures, as safety remains our top priority.”