Recent contributions of our Hawaiian Volcano Observatory (HVO) Volcano Watch column have presented very interesting observations from Kilauea. These include mention of the numerous deflation-inflation (DI) cycles seen at both Kilauea’s summit caldera and at Pu‘uO‘o on the east rift zone, an unusual earthquake swarm just west of the summit caldera in February, and detailed studies of the chemistry of fresh lava samples that point to how magma is stored and transported beneath the surface.
Later this spring, we expect to record another of Kilauea’s tantalizing behaviors — a slow slip event (SSE). SSEs are episodes of fault slip occurring over the course of 1-2 days beneath Kilauea’s south flank. If all that slip took place abruptly, it would generate the equivalent of an M6 earthquake. Because the slip occurs over days, however, the SSE motion is detectable only with sensitive geodetic or deformation monitoring instruments.
Over the past decade, SSEs have been observed here and in a number of other places around the world, including Japan, Mexico and the United States Pacific Northwest. They occur on the same faults that produce large and occasionally destructive earthquakes. In Washington state and Oregon, SSEs occur so regularly that they can be predicted. It is also thought that SSEs can possibly trigger large, destructive earthquakes; thus, they are well worth studying.
Since they were initially recognized at Kilauea in November 2000, we have identified 10 SSEs occurring beneath the volcano’s south flank. While the Kilauea SSEs are not strictly periodic, our observations over the past decade suggest that an 11th SSE in the sequence might occur by mid-June of this year. Kilauea’s south flank has experienced damaging earthquakes in 1989 (M6.2) and 1975 (M7.2). The flank lies adjacent to Kilauea’s rift zones, and it is understood that magma in the rift zones can, at times, produce stresses that lead to flank movement.
On Father’s Day, June 17, 2007, magma intruded along the most active segment of Kilauea’s east rift zone, specifically, near Kane Nui o Hamo, just to the east of Mauna Ulu. The intruding dike opened the rift zone there and, on June 19, a small eruption followed. Thanks to a number of Global Positioning System (GPS) instruments and tiltmeters monitoring the rift zone and south flank, this activity was very well-recorded. The data, however, were not fully accounted for simply by the dike intrusion and eruption. In addition, the dike intrusion had triggered an SSE beneath the south flank.
The 2007 SSE is the only one in Hawaii that has been associated with a specific external driving force — the intruded dike. Studying additional events of similar origin will help to extend the overall understanding of SSE and fault behaviors in general, and HVO’s seismic, GPS, and tilt monitoring networks are well-situated to provide key data.
Despite recent advances, there remains much to understand about how and why SSEs occur. For example, a characteristic of SSEs observed elsewhere is that they are accompanied by seismic tremor, as though the fault is chattering during the SSE. Thus far, we have not been able to clearly detect and identify tremor with any of the Kilauea SSEs. Of course, at an erupting volcano like Kilauea, there is a considerable amount of volcanic tremor that makes such observations challenging.
Almost literally putting our ears to the ground, we have deployed a number of temporary seismometers to listen for non-volcanic tremor that might occur during the next Kilauea SSE. We eagerly await the event as it offers an opportunity to learn something more. If there is tremor, where is it coming from, and how does it relate to the SSE fault slip? If we conclude that there is no tremor, why not?
While we await the next SSE, we continue to monitor and study Kilauea’s other complex behaviors, and, like the 2007 Fathers’ Day intrusion, eruption and SSE, look to see how these might be connected. For example, was the February 2012 earthquake swarm related to a magma surge through Kilauea? What does the increased frequency of DI occurrence in 2012 reflect? Wait with us and follow this column for more of Kilauea’s fascinating — and puzzling — behaviors.
Kilauea activity
update
A lava lake present within the Halema‘uma‘u Overlook vent during the past week resulted in night-time glow that was visible from the Jaggar Museum overlook. The lake, which is normally about 295 to 377 feet below the floor of Halema‘uma‘u Crater and visible by HVO’s webcam, rose and fell slightly during the week in response to a series of deflation-inflation cycles.
On Kilauea’s east rift zone, surface lava flows were active on the pali and coastal plain in Royal Gardens subdivision over the past week. As of Wednesday, April 11, the flows on the coastal plain were advancing towards the ocean but were still almost a mile from the water. One earthquake beneath Hawaii Island was reported felt this past week. A magnitude-3.4 earthquake occurred at 12:24 p.m. on Monday, April 9, 3 miles northeast of Waikoloa at a depth of 17 miles.
Visit the HVO website (http://hvo.wr.usgs.gov) for detailed Kilauea and Mauna Loa 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.
