"Ballistic blocks" shot from Kilauea's Halemaumau crater Wednesday, according to the U.S. Geological Survey, which says it is the first time such an event has been seen at the Hawaiian volcano in nearly a century.
"This morning dense ballistic blocks up to 60 cm (2 feet) across were found in the parking lot a few hundred yards from Halemaumau," USGS wrote in an advisory on Wednesday. "These reflect the most energetic explosions yet observed and could reflect the onset of steam-driven explosive activity."
"Further observations are necessary to asses this interpretation. Additional such explosions are expected and could be more powerful," it cautioned.
A 4.2-magnitude earthquake struck the region early Wednesday and another 3.5-magnitude temblor was felt around noon. The quakes "caused noticeable structural damage" in buildings at the state's Hawaii Volcanoes National Park, according to Hawaii Public Radio.
As Hawaii News Now reports:
"Geologists say the quakes are being caused by the ongoing deflation at the summit and as lava levels continue to decline. As of Wednesday afternoon, the floor of the Kilauea caldera has dropped about 3 feet.
"Because the tremors are shallow, they cause greater shaking — and increase the potential for damage."
Plumes of sulfur dioxide gas at Kilauea have caused "vog" and volcanic ash – which can be destructive to aircraft engines — and what prompted USGS on Tuesday to raise its aviation alert level to "red." However, the ash did not affect regular commercial air service in Hawaii, Federal Aviation Administration spokesman Ian Gregor said in an email to Reuters.
"Smog from Kilauea drifted north up the island chain as the districts of Kau, Puna, and North and South Hilo were told by the National Weather Service to expect ashfall. Hawaii County Civil Defense said a dusting of ash was visible on property and advised residents to avoid exposure to the powdered rock, which can cause irritation to eyes and airways," according to the news agency.
USGS has warned that steam-driven eruptions could send ash as high as 20,000-foot and hurl boulders weighing as much as 12 tons up to a half mile from the crater.