Thurston Lava Tube closed indefinitely after cracks shift in ceiling

The Thurston Lava Tube in Hawaii Volcanoes National Park is closed until further notice after instruments detected slight movement in a crack in the tube’s ceiling.

According to an HVNP news release, National Park Service geomorphologist Eric Bilderback noted that a crackmeter installed in the tube had shifted by 1.96 mm over several hours Saturday night, and had moved another half a millimeter by Monday morning.

The crackmeter was installed in 2019 to monitor a crack in a rock slab about 7 feet wide, 10 feet long and 8 inches thick. The movement of the crackmeter indicates that the crack has narrowed since Saturday, which could indicate that other fractures are widening elsewhere in the tube.

Bilderback said that the movements of the slab are unusual in the monitoring record — before last weekend, the instrument has moved less than one millimeter since November 2019. In order for the tube to be considered safe again, Bilderback said, the instrument would have to return to similar movement patterns from before last weekend. It is not clear how long that would take.

The lava tube — also known as Nahuku — was closed following the 2018 Kilauea eruption, which dislodged some rocks in the tube and led to the installation of the crackmeters to monitor its structural integrity.

The restrooms and parking area near the tube remain open.