Report on South Sarigan Seamount (United States) — September 2014
Bulletin of the Global Volcanism Network, vol. 39, no. 9 (September 2014)
Managing Editor: Richard Wunderman.
South Sarigan Seamount (United States) Studies reveal former summit removed and replaced by large crater due to the enigmatic May 2010 eruption
Please cite this report as:
Global Volcanism Program, 2014. Report on South Sarigan Seamount (United States) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 39:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN201409-284193
South Sarigan Seamount
16.58°N, 145.78°E; summit elev. -184 m
All times are local (unless otherwise noted)
The last Bulletin report (BGVN 35:05) on South Sarigan Seamount was mistakenly catalogued under reports for Sarigan Island. In that report, a description of the 28-29 May 2010 eruption was discussed. Recently, Bulletin editors discovered that significant research has been completed concerning the South Sarigan Seamount's 2010 eruption. In this Bulletin report, we will discuss some of that research.
This new research concluded that the South Sarigan Seamount is "part of a volcanic centre comprised of multiple cone edifices…" (Green and others, 2013). The northerly cone of this volcanic center is believed to be the source of the 2010 eruption, which was observed visually when an eruption plume, was seen rising from the ocean (Embley and others, 2013). The plume rose ~12 km through the atmosphere and was tracked by satellite. The Washington Volcanic Ash Advisory Center (VAAC) put out a report to inform the aviation community of the plume (Embley and others, 2013).
The 2010 eruption has been defined seismo-acoustically, and studied with multibeam and in situ sampling. It lasted ~3 days beginning on 27 May 2010. This eruption dramatically altered the northerly cone's morphology, whose summit depth was initially ~184 m below sea level (Embley and others, 2013; Searcy, 2013). According to Embley and others (2013) the eruption led the formation of a breached crater, 350 m in diameter, and a substantial deposit on the W flank (figure 2). After the eruption, the crater floor dropped ~200 m beneath the pre-eruption summit (Embley and others, 2013).
Much of the research on the South Sarigan Seamount was completed as the result of research vessels (RVs) cruises, and submarine remotely operated vehicles (ROVs) observing and documenting the eruptive deposits and morphologic changes at the vent. Multibeam data was also collected. The findings have been chronicled in several papers, some of which are discussed here (Tamura and others, 2013; Embley and others, 2013; and Green and others, 2013).
Green and others (2013), Searcy (2013) and Snellen and others (2011) used various combinations of hydroacoustic, infrasound, and seismic signals to study the pace and phases of the eruption from a geophysical perspective. Green and others (2013) found that the eruption occurred in three stages, separated by three-hour periods of quiescence. In brief, these stages included "(1) A 46 h period during which broadband impulsive hydroacoustic signals were generated . . . [a total of] 7602 identified events . . .(2) a 5-hour period of 10 Hz hydroacoustic tremor, interspersed with large-amplitude, broadband signals…(3) An hour-long period of transient broadband events [that] culminated in two large-amplitude hydroacoustic events and one broadband infrasound signal."
According to Green and others (2013), the first phase began at ~0241 UTC on 27 May 2010 when clustered hydroacoustic signals were detected by two hydroacoustic stations located on Wake Island and Queen Charlotte Islands. During this time, discolored water was also observed 8-11 km S of Sarigan Island. The second phase was detected at ~0330 UTC on 29 May with a near continuous tremor that lasted ~5 hours. The third phase, according to Green and others (2013) began at ~1137 UTC and at ~1209 UTC a distinctive tremor signal was detected. In addition to the seismic activity that occurred during the third phase, the ~12 km eruption plume was also generated.
Tamura and others (2013) noted a multibeam survey by R/V Melville conducted in early February 2013 over the unsurveyed main peak of South Sarigan Seamount volcanic center and over some of the previously surveyed peaks, enabling a comparison with the available older surveys. The older surveys consist of a 2002 survey by RV Ewing [EW0202] and a 2003 survey by RV Thompson [TN153] of the north peak where the 2010 eruption was believed to have taken place. Their comparisons show that downslope and W of the breach in the crater, a zone of positive depth changes of over 50 m occurs to ~2000 m depth on the volcano's flank. This is interpreted to be the deposit of material from the 2010 eruption together with part of the western flank that failed during the eruption. The volume of the downslope deposit is approximately twice as large as the amount of material lost from the summit. ROV dives on the volcano during 14-22 June 2013 showed that the northern wall of the crater appears to be "dominantly well-jointed andesite, with some interlayered basalt. No hydrothermal venting was observed in the crater, except weak shimmering water at the top of the crater wall."
Embley and others (2013) employed an ROV to retrieve downslope samples, including pumice believed to have been associated with the 2010 eruption. The pumice collected was found to be andesitic in composition. Lava blocks, believed to be from older lava flows, were also sampled. Both the andesitic pumice and lava blocks contained similar weight percentages of SiO2 and MgO, while the pumice had a slightly higher weight percentage of K2O. Embley and others (2013) concluded that due to the abundance of andesite found in samples from the crater and the W flank deposit, both the older and the 2010 eruption of the South Sarigan Seamount were dominantly andesite in composition.
According to Embley and others (2013): "The South Sarigan event is one of the first instances of an explosive, relatively deep, submarine eruption that breached the surface ocean and for which we have quantitative data for the size and extent of the cratering event and deposits to match with seismic and hydroacoustic monitoring information. Submarine craters the size of the one formed during the eruption of South Sarigan are relatively common on seamounts along intra-oceanic arcs... This event, and a deeper and much larger event at Havre Seamount in the Kermadec arc in 2012... underscores how little is known of the eruption history of most submarine arc volcanoes."
References: Embley, R.W., Y. Tamura, S.G. Merle, T. Sato, O. Ishizuka, W.W. Chadwick Jr., D.A. Wiens, P. Shore, and R.J. Stern. 2014. Eruption of South Sarigan Seamount, Northern Mariana Islands: Insights into hazards from submarine volcanic eruptions. Oceanography 27(2):24–31, http://dx.doi.org/10.5670/oceanog.2014.37.
Green, D. N., Evers, L. G., Fee, D., Matoza, R. S., Snellen, M., Smets, P., & Simons, D., 2013, Hydroacoustic, infrasonic and seismic monitoring of the submarine eruptive activity and sub-aerial plume generation at South Sarigan, May 2010. Journal of Volcanology and Geothermal Research, 257, 31-43.
Searcy, C. 2013. Seismicity associated with the May 2010 eruption of South Sarigan Seamount, northern Mariana Islands. Seismological Research Letters 84(6):1,055–1,061, http://dx.doi.org/10.1785/0220120168
Snellen, M., Evers, L., and Simons, D. G. (2011). "Modeling the long-range acoustic propagation for the May 2010 Sarigan volcano eruption," in Underwater Acoustics Measurements, edited by J. S. Papadakis (Kluwer, Kos, Greece), pp. 1361–1368
Tamura, Y.; Embley, R. W.; Nichols, A. R.; Ishizuka, O.; Merle, S. G.; Chadwick, B.; Stern, R. J.; Sato, T.; Wiens, D. A.; Shore, P., 2013, ROV Hyper-Dolphin Survey at the May 2010 Eruption Site on South Sarigan Seamount, Mariana Arc, Eos, Transactions of the American Geophysical Union [Paper presented at the 2013 Fall AGU Meeting], San Francisco, California, Abstract V31G-02
Geological Summary. South Sarigan seamount, rising to within about 184 meters of the sea surface 12 km south of Sarigan Island, was the site of a short-term explosive submarine eruption in May 2010 that produced a plume of ash and steam to 12 km altitude. Sidescan Sonar imagery taken in 2003 shows an irregular summit with multiple peaks, including a possibly young cone at about 350 m depth, and flank morphology suggests it is a frequently active volcano.
Information Contacts: Pacific Marine Environmental Laboratory, Ocean Environment Research Division, EOI Program, Hatfield Marine Science Center, 2115 S.E. OSU Dr., Newport, OR 97365.