Volcano Watch — Kīlauea's East Rift Zone rests for a month

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The ongoing eruption on Kīlauea's East Rift Zone has continued with little change for the last month. Lava is erupting from both the episode 51 and 53 vents, both located on the southwest flank of the Puu Oo cone.

Kīlauea's East Rift Zone rests for a month

(Public domain.)

The ongoing eruption on Kīlauea's East Rift Zone has continued with little change for the last month. Lava is erupting from both the episode 51 and 53 vents, both located on the southwest flank of the Puu Oo cone.

At both vents, the lava no longer reaches the surface, but instead, goes directly into lava tubes that lie several tens of feet below the inactive spatter cones which mark the vents. As a result, the only signs of an active eruption near these vents are gas plumes and intense heat. The lava pond at the bottom of the Puu Oo Crater is still active at a depth of 280 feet below the crater rim. Below the ground surface, the Puu Oo ventis connected to the 51 and 53 vents. For this reason, large changes in the level of the Puu Oo pond presage changes in the output of the 51 and 53 vents.

The lava tube system leading from the vents extends all the way to the coast, where lava enters the ocean near the former site of Kamoamoa. Periodically, collapses in the lava tubes or surges in the lava supply cause lava to break out of the tube and form surface flows. In the last month, however, the lava has been confined to the tube system, and we have seen only a few, very small, surface flows.

A lava bench is continuously forming where the lava enters the sea. The bench is downstepped 2-6 feet below the level of the former sea cliff, and it grows as lava spreads laterally (parallel to the sea cliff) as well as seaward. Currently, the bench is about 900 feet long and extends about 100 feet seaward. The main tube breaks up into several shallow tubes on the bench, and lava enters the ocean at several points, which can change location from day-to-day. Surface flows occur frequently on the bench as the roofs of the shallow tubes collapse. The bench extends out over a steep, unstable slope of lava flows, loose blocks of lava, and black sand. Frequent landslides and slumps on this submarine slope can cause all or part of the bench to collapse without warning. For this reason, the wise visitor heeds the National Park's warning signs and stays well away from the bench.

Seismically speaking, it's been a quiet month, with only three earthquakes of magnitude 3 or greater. The first was on Kīlauea's upper East Rift Zone, on September 2, at 0450 hrs, at a depth of 3.4 miles; the second was offshore of South Point, on September 16, at 0440 hrs; and the last was offshore of North Kona, on September 18, at 0703 hrs. All three had magnitudes of 3.0; the depths of the offshore earthquakes cannot be determined accurately because there are no offshore stations.
We've said goodbye to the last of our student helpers as another summer comes to an end. The Hawaiian Volcano Observatory is filled to overflowing during the summer, when students from universities in Hawaii, Europe, and on the mainland flock to Kīlauea. Some of these students volunteer at the Observatory in return for a chance to experience the volcano first-hand; others come to work on their own research projects. Many from this island are hired under programs such as Alu Like and Minority Participation in Earth Sciences to assist the staff in all phases of volcano-monitoring.

Although the summer is our busiest time, the Observatory plays host to a steady stream of visiting scientists throughout the year. In the last few weeks, we've seen many new faces as scientists on their way to an international meeting of volcanologists in Canberra, Australia dropped by to visit the volcano and share ideas.