This week, the Hawaiian Volcano Observatory is saying goodbye to two good friends: Jessica Johnson and Ben McLeod. They arrived in Hawaii in October 2011, when Johnson accepted an offer to be a post-doctoral research fellow at HVO through the University of Hawaii at Hilo.
Before coming to Hawaii, Johnson and McLeod lived in Wellington, New Zealand — McLeod’s home, and where Johnson (originally from England) completed a doctoral degree in geophysics, at Victoria University of Wellington. Johnson specialized in seismic anisotropy — a way of detecting whether seismic waves travel through the Earth faster in one direction than another. A change in this directionality can signal an important change in volcanic activity. She quickly became one of the world’s experts in the field.
Upon arriving in Hawaii, Johnson analyzed more than 2,000 earthquakes that occurred between 2007 and 2011. She found the orientation of “fast” seismic waves changed at about the start of Kilauea’s summit eruption in 2008. Such “fast directions” are usually interpreted to be a sign of a structural grain in the Earth — caused by aligned cracks, for instance — or of stress imposed by an inflating magma chamber.
Neither of these hypotheses fits the changes that Johnson measured at Kilauea. The fast directions she detected in 2008 were perpendicular to the structural grain of Kilauea Caldera and occurred at the time the magma chamber beneath the caldera was deflating. So what caused the changes?
Johnson hypothesized that increased gas emissions during the start of the summit eruption — a time of the highest gas emission levels ever recorded at Kilauea — might be the culprit. In early 2008, volcanic gas probably filled much of the pore space in the lava flows that make up the caldera floor. As gas pressure increased, the pore space expanded, causing cracks aligned with the magma chamber to open and change the orientation of the fast seismic waves. Over time, this gas pressure gradually dissipated, causing the seismic signature to return to normal by 2009. This unique conclusion can be applied to volcanoes elsewhere around the world — especially in remote locations that might have seismic, but not gas, monitoring. Johnson’s results were published this year in the journal Nature Communications.
While Johnson studied seismic waves, McLeod assisted the seismic monitoring group at the observatory. HVO depends on accurate locations for earthquakes to interpret whether or not changes in seismic activity indicate an impending change in eruptive activity. This requires that most earthquakes be located by hand — a time-consuming process that requires careful analysis of seismic waves recorded by stations across Hawaii Island. McLeod’s work focused mostly on precisely locating earthquakes that accompanied Kilauea lava outbreaks in 2011, and the catalog he helped form will be invaluable to better understanding those eruptions.
McLeod and Johnson also contributed to aspects of HVO’s and UH-Hilo’s missions beyond their scientific work. They frequently helped with field operations, provided tours of HVO facilities to visitors, gave talks at community events, and even taught classes, both to UH-Hilo students and as part of international volcanology courses. They truly became part of the HVO family during their two years on the island.
Johnson and McLeod also took advantage of their tropical surroundings. Accomplished scuba divers, they explored the underwater environment around the state. They spent weekends hiking and camping and even found time to get engaged. Now they are on their way to England, where Johnson will begin a position at the University of Bristol, while McLeod completes a degree in geography.
Aloha, Johnson and McLeod. Thank you for being such wonderful colleagues and friends. We hope to see you again.
Other news: Two HVO talks about Hawaii’s destructive earthquakes will be presented Tuesday at the Kilauea Visitor Center in Hawaii Volcanoes National Park and in UCB 100 at UH-Hilo. Details are posted at hvo.wr.usgs.gov.
Kilauea activity update
A lava lake within the Halemaumau Overlook vent produced nighttime glow visible from the Jaggar Museum overlook and via HVO’s webcam during the past week. No deflation-inflation cycles occurred this week as of Thursday, and the lava lake level was correspondingly steady. DI events, however, have been occurring at the rate of about one per week, and the present pattern has them happening at the end of the week.
On Kilauea’s East Rift Zone, two small breakouts from the Peace Day tube are active above the pali. The lower breakout is barely visible from the visitor area in Kalapana. The Kahaualea 2 flow, fed from a spatter cone on the northeast edge of the Puu Oo crater, continues to burn forest north of Puu Oo. There are no active flows on the coastal plain, and there is no ocean entry.
Two earthquakes were reported felt in the past week on Hawaii Island. At 7:10 p.m. Sept. 19, a magnitude 2.5 earthquake occurred 4 miles southeast of Pahoa at a depth of 2 miles. At 8:36 a.m. Thursday, a magnitude 3.6 earthquake occurred 7 miles west of Kalapana at a depth of 6 miles.
Visit hvo.wr.usgs.gov for Kilauea, Mauna Loa and Hualalai activity updates, recent volcano photos, recent earthquakes and more; call 967-8862 for a Kilauea summary; email questions to askHVO@usgs.gov.
Volcano Watch is a weekly article and activity update written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.
