Halemaumau Crater summit collapse occurs after longer interval

The U.S. Geological Survey Hawaiian Volcano Observatory reported a collapse event at 12:09 p.m. Thursday at Halemaumau Crater, with energy equal to a 5.4-magnitude earthquake.

There was no tsunami threat to the island of Hawaii, according to the Pacific Tsunami Warning Center.

However, there was a longer than usual gap between Thursday’s collapse event and the last one, which occurred at 6:41 a.m. Tuesday with energy equal to a 5.5-magnitude earthquake.

Nearly 60 of the collapse events at the summit have been recorded since eruptions began May 3; they are typically spaced about 30 to 35 hours apart and are similar in magnitude.

The collapse events occur when magma withdraws from beneath the crater floor, heading down the lower East Rift Zone, resulting in instability and rocks falling.

USGS scientists said that while the longer-than-usual interval between events was unusual, it is too soon to draw any conclusions, including whether it signals a decrease in these collapse events.

“This is unprecedented territory,” said USGS geophysicist Ingrid Johanson. “It’s much too soon to tell. For now there is some variability in how frequently these events occur. This was outside the typical range. I think we really have to look for a couple more to see if this timing continues to lengthen and activity decreases.”

Usually there are a series of smaller earthquakes, up to 25 to 30 per hour at the summit, with magnitudes of 3.0 or lower, leading up to the collapse. But these collapse events are more like a “pressure wave,” according to USGS geologist Janet Babb, with energy released into the ground rather than exploding upward and outward.

Babb said while there have been some variations in the pattern of the collapse events, scientists will be waiting and watching what happens in coming weeks. As long as the Kilauea eruption continues, these summit collapse events are likely to occur.