USGS Hawai‘i Volcanoes Observatory scientists address Volcano Village area residents’ concerns at an informational meeting Wednesday evening, May 9. The meeting was held before a standing-room-only crowd at Hawai‘i Volcanoes National Park Visitor Center Auditorium. (L–R) Geophysicist Kyle Anderson, Research Geologist Don Swanson and HVO Scientist-in-Charge Tina Neal. PC: J.M. Buck
A community informational meeting was held at the Volcano Community Center on the evening of May 9.
Hawaiian Volcano Observatory experts presented scientific background regarding the current eruption.
Geophysicist Kyle Anderson, Research Geologist Don Swanson and HVO Scientist-in-Charge Tina Neal shared information and answered questions from a standing-room-only group of concerned Volcano Village area residents.
The meeting was held to further explain the reason an HVO/USGS Volcanic Activity Notice was sent out on Wednesday, May 9, 8:02 a.m.
The notice said that 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.
New 3D model of the summit lava lake: The summit lava lake in Halema‘uma‘u crater has dropped substantially over the past week due to intrusive and eruptive activity on the lower East Rift zone. This 3D model of the crater was created from thermal images collected during a helicopter overflight on May 8. The lake at this time was roughly 970 feet below the floor of Halema‘uma‘u Crater.
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If the lava column drops to the level of groundwater beneath Kīlauea Caldera, influx of water into the conduit could cause steam-driven explosions.
Debris expelled during such explosions could impact the area surrounding Halemaʻumaʻu and the Kīlauea Summit.
USGS geologists cannot say with certainty that explosive activity will occur, how large the explosions could be, or how long such explosive activity could continue.
The notice recommended that residents of the Kīlauea summit area should learn about the hazards of ashfall, stay informed of the status of the volcano and area closures, and review family and business emergency plans.
Then, within an hour of the notice’s distribution, area residents experienced an explosive event at Kīlauea Volcano summit lava lake—Halema‘uma‘u crater, the largest crater in Kīlauea Caldera.
Ash column rises from the Overlook Crater at the summit of Kīlauea Volcano, 8:29 a.m. on May 9. The photograph above was taken from the Jaggar Museum overlook. PC: USGS
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At about 8:32 a.m. a large rockfall from the steep crater walls into the retreating lake triggered an explosion that generated an ash column above the crater; the ash was blown toward the south-southwest.
A huge ash column was observed rising from Halema‘uma‘u, also called “Overlook Crater.”
The explosion was short-lived. Geologists examining the ash deposits on the rim of Halema‘uma‘u crater found fresh lava fragments hurled from the lava lake.
This explosion was not caused by the interaction of the lava lake with the water table. When the ash cleared from the crater about an hour after the explosion, geologists were able to observe the lava lake surface, which is still above the water table.
Ash was reported as far south as Na‘alehu. Residents reported a slight but very noticeable accumulation of fine ash particles on outside surfaces. The ash was described as a “very, very fine cindery ash dusting that is not visible but definitely palpable and very inhalable.”
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The experts told residents that they will continue to experience ashfall after these rockfall events, but it is likely there will be no need for an evacuation.
They said that this event “is unprecedented since 1924.”
Halema‘uma‘u was the site of over 50 explosive events during a 2.5-week period in May 1924.
The explosions were the most powerful at Kīlauea since the early 19th century, throwing blocks weighing as much as 14 tons from the crater.
Halema‘uma‘u doubled in diameter, deepened to about 1,300 feet, and drastically changed in behavior—for the next 85 years it no longer hosted a long-lived lava lake, until one returned in 2009.
As of a May 9 HVO report, earthquake activity in the summit remains elevated. Many of these earthquakes are related to the ongoing subsidence of the summit area and earthquakes beneath the south flank of the volcano.
Nā Leo TV will replay the meeting on Emergency Broadcast Channel 55 at 9 p.m. on Thursday, May 10.
HAZARDS Primary hazards of concern should this activity occur are ballistic projectiles and ashfall.
BALLISTIC PROJECTILES
During steam-driven explosions, 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.
ASHFALL
Presently, during the drawdown of the lava column, rockfalls from the steep enclosing walls of the Overlook crater vent impact the lake and produce small ash clouds. These clouds are very dilute and result in dustings of ash (particles smaller than 2 mm) 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 Halemaʻumaʻu. 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.
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.
WARNING TIME
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.
BACKGROUND
Kīlauea’s lava lake began to drop on May 2, 2018. From its peak on May 2 to the most recent measurement at 9 pm 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.
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