The Nāhuku lava tube in Hawaiʻi Volcanoes National Park is closed until further notice.  The closure, which took place on Sunday, comes after data from a crackmeter revealed that a fracture near a large overhanging rock slab at the apex of the lava tube has narrowed by 2.47 mm since Saturday, July 30.

The narrowing movement could indicate the crack is adjusting in response to other fractures widening in the lava tube, making the large overhead chunk of rock unstable and potentially dangerous. The slab measures about 7.1 x 10.5 feet and 8 inches thick.

On Sunday, July 31, National Park Service geomorphologist Dr. Eric Bilderback alerted park management that the crackmeter in the middle of Nāhuku had moved 1.96 mm over the course of several hours on Saturday night and then moved another 0.51 mm by Monday morning.

Bilderback said while the movement is slow and not accelerating, these movements of a large rock slab are unusual in the monitoring record. A return of movement similar to the previous record would need to occur before the lava tube would be considered safe to reopen. It is not clear how long that will take as further monitoring is required to determine if the tube can safely reopen.

Prior to this weekend’s fractural changes, data from the monitors revealed little change to the cave’s structural integrity showing less than 1 mm of movement since November 2019.

Large rocks in Nāhuku were dislodged during the 2018 eruption and summit collapse of Kīlauea volcano. Two crackmeters were installed in the lava tube’s ceiling to monitor their movement.

Restrooms and the parking area near Nāhuku continue to remain open.

 

Photo credit: National Park Service