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Volcanowatch

September 14, 2000

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Lava Viewing 101

Those of you who pay attention to the goings-on of the volcano are well aware that the quality of lava viewing is highly uneven. Some days you can hike for sweltering hours over recently active flows without seeing any red lava. But when conditions are at their best, as they were last Friday and Saturday, all you have to do is drive to the end of Chain of Craters Road to see rivers of lava coursing down the steep slopes of Pulama pali.

The show on the pali usually folds after a few days, sometimes after only a few hours. Then there's likely to be a period when hikers can find oozing pahoehoe flows on the coastal flats between the base of the pali and the shoreline as the lava wends its way toward the sea. Eventually the surface flows stagnate, and from the end of the road, all you'll see is the distant glow from the ocean entry after dark.

Just when you've about given up on the volcano as a spectator sport, you'll hear us announcing that the eruption has "paused." Should you lose all hope of having anything to show your auntie from Kaua'i? Absolutely not! Pauses are usually brief, and the best lava-viewing is almost always right after they end.

Why's that? Because during the pause, the lava tubes leading from the vent to the ocean can be plugged by rocks that fall from the unsupported walls and roof of the drained tubes. When lava reoccupies the tube, it encounters an obstacle course of debris. Sometimes the lava stream can sweep this rubble aside, but other times the dams hold, and the lava is forced out onto the surface. Lava may take advantage of an existing skylight, or it may literally "break out," lifting and shattering slabs of rock that form the roof of the tube.

If the tube stays blocked, the surface flows will persist until new tubes form within the new flows. Breakouts on the pali are especially frequent after a pause, because the tubes are more unstable on the steep slope, and blockages develop easily.

What happened in the last few weeks was a bit more complicated, because the tube developed a blockage high above the pali, and surface flows broke out at the 2,300- and 2,175-foot elevations before the pause began.

When the four-day-long pause ended, lava reoccupied the tube to the 2,300-foot elevation and broke out again. The flows puttered around above the pali for 11 days, then got serious and roared down the pali on Friday and Saturday.

Those of you who happened to be at the end of the road on either day had a great view of rivers of 'a'a and slabby pahoehoe pouring down the back of a thick 'a'a flow of 1985 vintage. The new flow reached the coastal plain on Saturday and fanned out on the flow field that was active through the summer.

By Sunday, the beautiful channeled flows on the pali had mostly roofed over, forming the beginnings of a tube. New flows cascaded over the pali intermittently through mid-week, and sporadic breakouts will continue on the pali until a stable tube forms.

As of Wednesday, the flows were 1.8 km from the coast. Now the big game is guessing when and where lava will enter the ocean. The "where" isn't hard?if nothing changes upslope, the coastal flows will enter the ocean near the eastern boundary of Hawai`i Volcanoes National Park, close to where the ocean entries were all summer.

The "when" is problematic. Flows can dally on the coastal plain for weeks, spreading this way and that, in no hurry to hit the surf. The process can go faster if the flows follow a straight line to the shore. In either case, it's still going to be a long hike to see the lava. If you're determined to try, be sure to check with the National Park and find out the latest lava conditions and hazards.

Next time you hear there's a pause, check the park's eruption update line (985-6000) or the HVO website (http://hvo.wr.usgs.gov) frequently, and be ready spend an evening at the end of Chain of Craters Road when flows start coming down the pali.

There were no felt earthquakes on the island in the last week.


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Updated: October 3, 2000