Hydroacoustic, Seismic, and Bathymetric Observations of the 2014 Submarine Eruption at Ahyi Seamount, Mariana Arc

Abstract

Ahyi seamount, a shallow submarine volcano in the Northern Mariana Islands, began erupting on 23 April 2014. Hydroacoustic eruption signals were observed on the regional Mariana seismic network and on distant hydrophones, and National Oceanic and Atmospheric Administration (NOAA) scuba divers working in the area soon after the eruption began heard and felt underwater explosion sounds. The NOAA crew observed yellow‐orange bubble mats along the shore of neighboring Farallon de Pájaros Island, but no other surface manifestations of the eruption were reported by the crew or observed in satellite data. Here, we detail the eruption chronology and its morphologic impacts through analysis of seismic and hydroacoustic recordings and repeat bathymetric mapping. Throughout the 2‐week‐long eruption, Ahyi produced several thousand short, impulsive hydroacoustic signals that we interpret as underwater explosions as well as tremor near the beginning and end of the sequence. The initial tremor, which occurred for 2 hr, is interpreted as small phreatomagmatic explosions. This tremor was followed by a 90‐min pause before the characteristic impulsive signals began. Occasional tremor (lasting up to a few minutes) during the last 1.5 days of the eruption is interpreted as more sustained eruptive activity. Bathymetric changes show that a new crater, about 150 m deep, formed near the former summit and a large landslide chute formed on the southeastern flank. Comparing to other geophysically detected submarine eruptions, we find that the signals from the 2014 Ahyi eruption were more similar to those from other shallow or at‐surface submarine eruptions than those at deep (>500 m) eruptions.

Chemical Fluxes From a Recently Erupted Shallow Submarine Volcano on the Mariana Arc

“…In February 2003, a mapping and hydrological survey of Ahyi detected a low level of hydrothermal activity evident only as a weak 3 He plume (Resing et al, ). On 23 April 2014, USGS seismometers on Saipan, Pagan, Sarigan, and Anatahan islands recorded T‐wave signals indicating the beginning of a 17 day period of explosive eruptive activity (Global Volcanism Program, ; Haney et al, ; Tepp et al, ). The period of intense seismic activity ended on 8 May, with a few sporadic events continuing until 17 May.…”

“…On 14 May 2014, a reconnaissance expedition aboard the NOAA ship Hi'ialakai verified Ahyi as the eruption site. Bathymetric data collected posteruption found the summit had deepened by 25 m and a crater with a floor depth of 195 m had formed since the 2003 survey (Haney et al, ; Tepp et al, ). Additionally, three CTD casts were conducted, which also produced evidence of posteruptive hydrothermal plumes.…”

Interpretation of detections of volcanic activity at Ioto Island obtained from in situ seismometers and remote hydrophones of the International Monitoring System

“…The SOFAR channel acts as a natural acoustic waveguide for hydroacoustic waves and minimizes energy loss from interaction with boundaries, thus enabling the detection of events over long ranges 5–7 . Hydroacoustic signals from high intensity acoustic events can be detected at even greater ranges, for example hydroacoustic signals associated with the Monowai undersea eruptions in 2011 and the Ahyi undersea eruptions in 2014 were detected by hydrophones at a distance in excess of 15,000 km 8,9 .…”

“…Additionally, ocean bottom seismometers were used to record seismo-acoustic arrivals from undersea volcanoes in the northwestern Pacific Ocean 30,31 ; and a combination of a seismic network on a volcanic island and water-column hydrophones were used to identify seismic events originating from the vicinity of the Cape Verde Island in the Atlantic Ocean 32 . A combination of a regional seismic network and distant water-column hydrophones was also used to study the 2014 undersea eruption of Ahyi seamount in the northwestern Pacific Ocean 9 .…”

WORKSHOP REPORT: Securing Legacy Seismic Data to Enable Future Discoveries September 18-19, 2019 Albuquerque, New Mexico

“…The emerging understanding of the importance of volcano-tectonic earthquakes for forecasting eruptions (White and McCausland, 2016) points to the need for better catalogs of volcano-related and unrelated seismicity, especially where populations are at risk from explosive volcanism, lahars, tsunamis, and similar hazards. Despite the large number of submarine volcanoes, submarine eruptions had remained largely undetected until new tools were developed (e.g., Tepp et al, 2019). Historical records provide a means to obtain a longer, and consistent database required to constrain hazards to shipping and to understand fundamental Earth processes.…”