# Volcano Watch — A small eruption leads to world-class research

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Great oaks from little acorns grow. Who would have thought that a little eruption in a small pit crater would be the seed from which a great oak of research grew at Kīlauea? Such is the legacy of the Christmas Eve and Day eruption in 1965.

Waiting for St. Nicholas in their house in Hawai‘i Volcanoes National Park, Dick and Pat Fiske heard the rattling of windows at about 7:30 p.m. as Pele arrived instead, shaking the ground with volcanic tremor. Dick, a recent arrival on the scientific staff of the Hawaiian Volcano Observatory, rushed to his office with others close behind. They waited until a brilliant orange glow rose above the upper east rift zone at about 9:30 p.m., marking the start of the eruption in ‘Ālo‘i Crater, one of the smallest in the Chain of Craters.

The group sped toward the crater, but dense fume kept them from seeing the eruption for 2 hours. Eventually Dick got his first view of lava as the eruption began to wane. At midnight, the observers reached the overlook at ‘Ālo‘i, only to see that the eruption there was nearly over, leaving a lava pond 14 m deep. Glow showed continued activity at several sites as far away as Kāne Nui o Hamo, 3 km east of ‘Ālo‘i. It, too, tapered away, and the eruption was finished before sunrise on Christmas Day.

Dick and seismologist Bob Koyanagi described many intriguing features of the small, 6-hour eruption in their published research paper. The one that was least expected and most important was the severe ground movement and accompanying earthquake swarm. Hundreds, probably thousands, of ground cracks crossed the Chain of Craters and Hilina Pali roads, splitting open the Koa‘e fault system connecting the upper east rift and the southwest rift zones. At the time, the Koa‘e was little known and less appreciated as a geologic structure. Better known now, it is still off the beaten track of most researchers.

The Hilina Pali Road was broken by faulting along Kulanaokuaiki Pali, near the campground of the same name. Surveying a leveling line along the road—fortuitously measured before the eruption—showed that the pavement across the pali was offset vertically almost 2.6 m (8.5 ft). The north side of the pali, which forms the southern boundary of the Koa‘e fault system, dropped 1.8 m (6 ft), and much of the road on the northeast side also subsided. The south side of the pali, however, moved up 73 cm (2.4 ft). This information, combined with tilts measured at several stations in and adjacent to the Koa‘e, led Dick to suggest that the south flank of Kīlauea moved seaward during the eruption and faulting event.

A year before the eruption, HVO scientists Jim Moore and Harold Krivoy interpreted the south flank as a huge slide. While acknowledging that as an option, Dick put forth the notion that the south flank was moving because of "lateral wedging due to forceful intrusion of magma in the upper east rift zone." The two competing ideas for what drives south flank movement were thereby spelled out, and they remain controversial issues today.

Over the next 2 years, Dick made the Koa‘e his scientific focus. In 1966, he briefly travelled to Japan, where he had earlier spent a few years, and saw how the large Matsushiro landslide was being monitored; he returned with ideas and techniques in mind. Aided by Jeffrey Judd, he quickly established three leveling lines across the Koa‘e and several crack measuring stations. Two of the leveling lines are still occupied today (one yearly, the other less frequently), and two of the crack stations at the intersection of the Hilina Pali and Chain of Craters roads are often remeasured, showing accumulated widening of 66 cm (26 inches) and 34 cm (13.4 inches), respectively, between 1966 and now.

The research started by Dick as a result of the Christmas Eve eruption led to expanded studies of the entire south flank soon thereafter. Over the years, new instrumentation has provided ever more detailed data for south-flank motions, and scientists around the world attempt to model the dynamic process. Understanding Kīlauea's south flank is important to local residents, because its movement leads to large earthquakes and tsunami, such as those of November 1975. No one on Christmas Eve 1965 could have guessed the lasting importance of that eruption.

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### Volcano Activity Update

A lava lake present within the Halema‘uma‘u Overlook vent over the past week resulted in night-time glow that was visible from the Jaggar Museum overlook. The lake, which is about 75–100 m (245-330 ft) below the floor of Halema‘uma‘u Crater and visible by HVO's Webcam, rose and fell slightly during the week in response to deflation-inflation cycles.

On Kīlauea's east rift zone, surface lava flows advanced across the coastal plain and reached the ocean at West Kailiili, within the National Park, on December 9. Flows continued to be active in the abandoned Royal Gardens subdivision over the past week, as well. The flows traveled through a lava tube fed by the September 21 fissure on the upper east flank of the Pu‘u ‘Ō‘ō cone. Within Pu‘u ‘Ō‘ō crater, small flows were erupted sporadically on the eastern crater floor.

Three earthquakes beneath Hawai‘i Island were reported felt this past week. A magnitude-2.0 earthquake occurred at 11:01 p.m., HST, on Thursday, December 8, 2011, and was located 4 km (3 mi) north of Kawaihae at a depth of 26 km (16 mi). A magnitude-2.1 earthquake occurred at 9:39 p.m. on Friday, December 9, and was located 5 km (3 mi) southeast of Captain Cook at a depth of 11 km (7 mi). A magnitude-3.5 earthquake occurred at 1:03 p.m. on Saturday, December 10, and was located 6 km (4 mi) southeast of Kīlauea summit at a depth of 26 km (16 mi).