Volcano Watch — When lava tubes go incontinent

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A few days before the long Labor Day weekend, Hawai'i County officials closed the newly opened Lava Viewing road because a surface lava flow was threatening to cross it. Fortunately, the lava flow stopped just after it crossed the road, and the road was reopened a few days later. For some, it was a revelation that this could happen so soon. Others realized it was business as usual.

Highway 130 and later roads laid along its course have been covered many times in the last 15 years. The previous version of the road was originally carved out of 1986-1991 vintage lavas to allow residents of Royal Gardens access to their properties. Over the last several years, more and more of that road has been covered by progressive eastward expansion of the episode 55 flow field. The most recent surge of activity ended in May 2001, with the establishment of an ocean entry and the lava tube that feeds it.

Of course, viewing the spectacle of lava entering the ocean is the whole reason that the road was improved and reopened. That entry is made possible by an established lava tube bringing a relatively constant supply of lava from Pu'u 'O'o to the ocean.

Surface lava flows almost always originate from a rupture or blockage of a lava tube. With the ocean-entry tube (what else would we call it?), located only 700 m (2300 feet) from the end of the access road and the start of the trail to the viewing area, some might expect frequent surface flows to threaten the road and trail.

The Labor Day surface flow was not the first to break out so close to the road in the last few months, but it was easily the biggest. For a few days prior to closure of the viewing area, the flow had been advancing more than 250 m (820 feet) per day. The area was closed by Hawai'i County Civil Defense when the flow was less than 250 m (820 feet) from the road.

The Labor Day flow started in a portion of the lava tube, almost 2 km (1.2 miles) uptube of the ocean entry, from where several small flows have started in the last four months. Most of them last for a few days before they stagnate. The Labor Day flow was active for about 2 weeks. Since Labor Day, there have been other small surface flows and another large one that flowed west and away from the lava-viewing road.

What makes some sections of a lava tube more prone to ruptures that produce surface flows? In some tube systems, the answer would be that the tube is weakest at sharp bends or abrupt changes in width. In the case of the ocean-entry tube, we believe that the tube roof is very thin in the areas of persistent ruptures. We know that because that same portion of the tube was unusually visible in our aerial infrared scans conducted in May right after the tube formed. Infrared scanning is a method of visualizing heat; if the tube roof were thin, it would allow lava heat to be conducted more easily to the surface than in an area where the tube roof is thicker.

How much lava pressure would need to be exerted in order to break through the tube roof? The answer to that is unknown. However, students of the local construction industry know that some ancient tube roofs have buckled when a 54-ton D-9 bulldozer rolls over them. Yet many of these tubes survive.

We will not be surprised if surface flows threaten the viewing area a few times a year. In fact, such occurrences should be viewed as another kind of lava-viewing opportunity rather than a threat, especially in light of the real threats we were all recently forced to acknowledge.

Volcano Activity Update

Eruptive activity of Kīlauea Volcano continued unabated at the Pu`u `O`o vent during the past week. Lavamoves away from the vent toward the ocean in a network of tubes and descends Pulama pali in several separate tubes. The two surface flows reported on the pali last week are now crusted over. Many surface flow are active on the coastal flats, and one is within 0.5 km (0.3 mi) of the ocean in the area west of Kamokuna. Lava also continues to enter the ocean in the area east of Kupapa`u and provides visitors to the viewing area a great show.

The public is reminded that the bench of the ocean entry is very hazardous, with possible collapses of the new land. The steam cloud is extremely hot, highly acidic, and laced with glass particles. Swimming at the black sand beach of the bench can be a blistering or even deadly venture.

There were no earthquakes reported felt during the week ending on September 27.