Volcano Watch — Surface flows erupting; lava bench movement measured

Several large surface lava flows from the eruption along Kīlauea's east rift zone occurred this past week. The largest of these flowed down the east side of the flow field between the Kamoamoa flows and those that surrounded Waha'ula several years ago. However, most of the lava continues to enter the ocean near Lae'apuki at the end of Chain of Craters Road. When lava enters the ocean, it heats the water to boiling, thus producing an enormous acidic steam plume. The water that reaches the boiling point mixes with adjacent unheated water in complex patterns, but, depending on the currents and waves, scalding water can occur hundreds of feet away from the lava entry point.

On Tuesday evening, two visitors to Hawaii Volcanoes National Park were scalded adjacent to the lava entry point when a rogue wave broke over the lava bench. One of the men suffered second-degree burns on his legs, arms and chest. The second suffered second-degree burns on his lower legs. These visitors had entered areas that the rangers had closed precisely because they were dangerous to the public. The large wave was generated by hurricane John as it passed far to the south of the islands. Other waves, small local tsunami, can be generated by the collapse of the lava bench. This type of wave washes onto the bench where it can scald unwary visitors who have ventured too close. It is possible to get washed out to sea by these waves.

The lava benches grow seaward over loose black sand and collapse into the sea as small landslides. Most of the landslide occurs underwater as, first, the deepest part slides away from beneath the lava bench. The upper and shoreward parts of the landslide then follow and slide into the sea. We commonly record these small landslides on a nearby seismometer which detects a continuous shaking before, and as, the bench slides into the sea. This shaking is apparently caused by movement of the deeper offshore parts of the landslide and is the ultimate warning that the bench is about to collapse.

As the submarine part of the landslide moves downslope, it pulls the overlying water down with it. Adjacent water quickly fills the low area and produces the tsunami. We have mapped large boulders carried onto the lava bench by such tsunami.

The landslide is bounded on the landward side by cracks which widen as the slide creeps seaward. Needless to say, any area that is seaward of cracks that parallel the coastline is actually part of the creeping landslide and can fail catastrophically at any time. If you are on the part that fails, you will be carried into the ocean. It is a toss-up whether you will drown or be scalded to death. This past week, a bench collapse occurred immediately after rangers removed 20 people from the exact area that collapsed.

We have begun to measure the rates of creep of the lava bench in an effort to predict the catastrophic failures and better understand the landslide process. At times we have measured seaward motion of the bench as great as 3.5 inches per day. These are extremely rapid movement rates. In general, the rate of movement of the lava bench accelerates until the bench fails, then starts over with slow creep, which again accelerates before the subsequent failure. However, we have not yet been able to predict the bench collapses accurately.

The National Park Service has closed areas that we advise them are unstable or unsafe for visitors. There are many hazards in the area. Just because it looks safe to go beyond these area closure signs, does not mean that it is. Obey all the posted signs; to do otherwise is to gamble with your life.