Volcano Watch — Missing visitor a tragic reminder of Kīlauea's danger

he missing visitor to Hawai`i Volcanoes National Park serves as a tragic reminder that active volcanoes can be unpredictable and dangerous, however passive and approachable their eruptions. Kīlauea is no exception. 

Previous columns have emphasized the numerous hazards that visitors to the lava flows or eruptive vents need to acknowledge. These hazards are very real and, as we were reminded this past week, they can be lethal. 

When our trained and experienced field geologists and technicians work around the flows, they are always cautious and alert. They have great respect for the hazards they face on a regular basis and are aware that a single error in judgment can be their last. 

The National Park Service posts clear warning signs to prevent the less experienced visitors from wandering into those areas where the hazards are more extreme. At Lae`apuki, where the flows have been entering the sea for the past several weeks, such signs are posted and orange cones mark an area where the flows can be viewed in relative safety. 

The lava deltas or benches that form where the lava enters the sea are highly unstable and prone to collapse into the sea with little or no warning. Last Tuesday evening at 9:43 p.m., such a collapse occurred at Lae`apuki, when a section of the lava bench 690-feet long, 45-feet wide, and 25-feet thick slid into the ocean. Prem Nagar of Kealakakua was on this bench with several other people when they felt several small earthquakes and the flow into the ocean became more active, probably as a smaller outer slice of the lava bench slid away. The others moved away from the ocean, but Mr. Nagar returned to the edge just as the larger bench, where he now stood alone, slid into the ocean. 

As the bench slid away, hot, solidified lava in the bench came in contact with sea water, and a steam explosion hurled incandescent blocks of lava as large as 2.5 feet in diameter up to 550 feet inland. The blocks fell on the viewing area within the cones and up the trail towards the highway. Approximately 25 other visitors in and near the viewing area were pelted by the blocks, but amazingly, no one was seriously hurt. Many suffered lacerations as they fled the area in the dark and tripped and fell on the fresh, glassy lava. 

The visitors who had been out on the lava bench, but who had retreated when they felt the earthquakes, were scalded by seawater heated by lava. The heated seawater washed over the 25-foot-tall sea cliff in a surge. In total, about 20 visitors suffered minor injuries.

The lava deltas or benches are unstable because the lava extends into the ocean on top of a layer of black sand. It is akin to building a house on an unstable foundation. The flows also tend to spread out along the coast in a narrow strip that is poorly attached to the sea cliff behind it. As the flows extend into the sea, the loose sand fails in a small landslide; the overlying lava delta fractures (hence the small earthquakes), and then slides down the steep slope offshore. Such collapses appear to occur where the lava bench has already been fractured, so the warning signs are placed landward of any large cracks we have observed during our surveys.

During the nearly eight years of this eruption, when lava flowed into the sea (starting in late 1986), there have been numerous such collapses along the coast. Certain points of entry appear to be particularly susceptible to such collapses. The Kapa`ahu tube that delivered lava from the Kupaianaha vent to the ocean from May 1988 until June 1989 suffered at least 30 separate bench collapses. Many of these collapses were accompanied by steam explosions that ejected lava blocks ballistically up onto the shore. Other lava entries during the period from 1986 to 1991 were more stable and suffered only rare or small collapse events.

The Kamoamoa flows that entered the sea from last November until late January were also relatively stable; the few collapses that occurred were small. One small collapse resulted in secondary lava fountains as sea water and lava mixed inside the lava tube. This mixing was less violent than the steam explosion that occurred Tuesday evening, although it produced lava fountains nearly 300 feet high. 

The Lae`apuki flows have had several earlier bench collapses, including one that occurred last Saturday morning (we "saw" it only as a trace on our seismic records). That the Lae`apuki lava bench has already collapsed three times in the few weeks that these flows have been entering the sea suggests that this site may be particularly unstable, perhaps because the slope offshore is steeper than it is elsewhere along the coast. In any case, we anticipate future collapses occurring here as the lava builds new benches on the steep, sand-covered slope offshore. Some of these collapses could be large enough to again initiate steam explosions capable of throwing large lava blocks through the air. In addition, the western end of the lava bench of the Kamoamoa flows exhibited several large cracks parallel to the coast this week; this could also be the site of a a future bench collapse.

Remember, the National Park is not Disneyland. Unexpected and sometimes dangerous events occur. Be careful out there.