Volcano Watch — 11th anniversary of Kīlauea eruption nears

The eruption on Kīlauea's East Rift Zone is rapidly approaching another milestone as its 11th anniversary takes place on January 3. This column will feature an extended summary of the eruption, which is by far the most long-lived during historic time.

At this time last year, we were anticipating that the eruption might be winding down because activity had been episodic for most of 1992, and the volume of lava erupted each day had declined sharply from the previous several years. However, starting in mid-February, the eruption returned to higher volume and nearly constant eruption. The steadiness of eruptive activity since February is reminiscent of the roughly five years of steady eruption from the Kupaianaha vent from July 1986 until mid-1991.

During the past several weeks, lava has continued to pour into the ocean at the west edge of the Kamoamoa lava delta. This lava is transported to the coast inside underground tubes from two vent areas adjacent to the Pu`u `O`o cinder and spatter cone. These vent areas have been crusted over for several months so that no lava can be seen. The tube system has several places where the top of the tube has collapsed, forming openings where one can see the lava flowing through the tube. These openings, or skylights, are important observation and sampling locations, and we generally collect a lava sample from the flowing lava river and measure the rate of flow inside the tube each week.

The tubes change shape and size as lava flows through them, and the skylights can seal up as lava solidifies across the opening. The presently active tube system contains fewer open skylights than it did a few months ago, making it more difficult to monitor the flow of lava. We have also used an infrared video camera, flown at dawn, to see the heat emitted through the top of the tube system and thereby map the parts of the system that are still active.

Where the lava flows into the ocean, it spreads out laterally along the coast, forming elongate, narrow lava benches. These benches grow on top of black sand beach deposits that form from explosive interaction of the lava and seawater. These lava benches are unstable and, occasionally, slide into the sea. A large collapse took place at 9:28 p.m. on November 26, when a bench roughly 1,150 feet long and up to 200 feet wide slid into the sea at the west end of the Kamoamoa lava delta. Last April, when a similar collapse occurred at Lae`apuki, a visitor to the National Park was killed. This time, however, no one was killed or injured, as visitors were located behind the area-closure signs posted by the National Park Service. As the bench slid into the sea, a large wave washed up onto the shore. This wave was a small tsunami resulting from the displacement of seawater by the lava bench as it entered the water. Fortunately, no one was close enough to be caught by the wave, since the seawater adjacent to the lava entries is heated to near boiling. This collapse removed not only the youngest lava bench, but also some of the lava delta just inland from the bench. It is the first time we have observed a collapse that removed more than the most recently formed bench.

Most of the time, the entry of lava into the sea is quite passive, but, occasionally, spatter is thrown high in the air as water and lava mix and produce steam. These events are particularly common immediately following disruption and collapse of the lava benches.

On December 1, a new surface flow began above the pali. This flow began at a skylight at 2,100 feet elevation and advanced over the pali on the east side of the flow field. This small flow was no longer active the following day and, since then, no additional surface flows have occurred farther inland than the active bench.

There is still an active lava pond inside the Pu`u `O`o cone. The pond has remained at a nearly constant depth below the rim of the cone for many months. During the period of episodic activity in 1992, the level of the pond rose and fell by many tens of feet. Future changes in activity at the vents may be preceded by changes in the level of the pond.

Volcano Activity Update

There have been three earthquakes with magnitudes greater than 3.0 this past week. The first was a deep earthquake beneath the north flank of Mauna Kea Volcano. The second was beneath the south flank of Kīlauea Volcano and the last was beneath the Namakani Paio campground near the summit of Kīlauea Volcano. All three earthquakes were felt, although none were strong.