Attention shifted back to the summit on May 9, when a 3.1 earthquake set off a rockfall that agitated the lava lake and sent up a 6000-foot poof of ash (video clip National Parks site):
Rockfalls caused poofs of ash like this even back when the lava lake was full, but that was more than usual. (See also USGS video from May 7, when lava lake was still visible, showing how falling rocks agitate it).
However, that was just a teaser. The big news was the dropping lava lake…
Doooowwwwnnn she goes!
Watch this thermal webcam video showing how the summit lava lake at #Kilauea #volcano dropped way down during the eruption over the past few days. From @USGSVolcanoes webcams via @volcanodiscover pic.twitter.com/zbh4eMwxZk
— Oliver Lamb (@olamb245) May 8, 2018
…prompted HVO to issue its first warning about steam explosions if the lava dropped below the water table.
Hawaii Volcanoes National Park closed Friday May 11 as a precaution, since the lava lake was projected to reach the water table sometime that day. For the next few days it continued to send up a white plume of steam and/or ash clouds when rocks from the sides of the chimney fell in:
On steam (phreatic) explosions:
Kilauea last had a steam eruption in 1924, when boulders and rocks flew over half a mile from Halema’uma’u crater (this is what’s meant by “ballistic rocks”), and ash went much farther.
See USGS May 8 report explaining the hazards, or read geologist Erik Klemetti’s excellent “Kilauea Might Have a Change of Personality” column in Discover magazine explaining different kinds of steam explosions and Kilauea’s past history with them (good photos). Eos also has an excellent article on Kilauea steam explosions.
And see ScienceNews “No, Kilauea Won’t Cause Mass Destruction”
May 10 morning USGS video update with Tina Neal