Evidence from acoustic imaging for submarine volcanic activity in 2012 off the west coast of El Hierro (Canary Islands, Spain)

Abstract

We report precursory geophysical, geodetic, and geochemical signatures of a new submarine volcanic activity observed off the western coast of El Hierro, Canary Islands. Submarine manifestation of this activity has been revealed through acoustic imaging of submarine plumes detected on the 20-kHz chirp parasound subbottom profiler (TOPAS PS18) mounted aboard the Spanish RV Hespérides on June 28, 2012. Five distinct "filament-shaped" acoustic plumes emanating from the flanks of mounds have been recognized at water depth between 64 and 88 m on a submarine platform located NW El Hierro. These plumes were well imaged on TOPAS profiles as "flares" of high acoustic contrast of impedance within the water column. Moreover, visible plumes composed of white rafts floating on the sea surface and sourcing from the location of the submarine plumes were reported by aerial photographs on July 3, 2012, 5 days after acoustic plumes were recorded. In addition, several geophysical and geochemical data support the fact that these submarine vents were preceded by several precursory signatures: (i) a sharp increase of the seismic energy release and the number of daily earthquakes of magnitude ≥2.

Comment on “Evidence from acoustic imaging for submarine volcanic activity in 2012 off the west coast of El Hierro (Canary Islands, Spain)” by Pérez NM, Somoza L, Hernández PA, González de Vallejo L, León R, Sagiya T, Biain A, González FJ, Medialdea T, Barrancos J, Ibáñez J, Sumino H, Nogami K and Romero C [Bull Volcanol (2014) 76:882-896]

“…They present as their main evidence acoustic imaging records, interpreted as showing submarine plumes, and an aerial picture showing white traces on the sea, which are interpreted as pyroclastic material. Pérez et al (2014) state that the superficial deformation, the geochemical changes, the strong seismicity, and what they call Bearthquake tremor^also support their conclusions. Despite the fact that Pérez et al (2014) do not use the word eruption either in the title or in the abstract, in the Discussion section, the authors affirm that the acoustic imaging data and the aerial picture provide sufficient evidence to infer the occurrence of a new submarine pyroclastic eruption and postulate that these plumes were produced by a short-lived eruption involving several jets.…”

“…Pérez et al (2014) state that the superficial deformation, the geochemical changes, the strong seismicity, and what they call Bearthquake tremor^also support their conclusions. Despite the fact that Pérez et al (2014) do not use the word eruption either in the title or in the abstract, in the Discussion section, the authors affirm that the acoustic imaging data and the aerial picture provide sufficient evidence to infer the occurrence of a new submarine pyroclastic eruption and postulate that these plumes were produced by a short-lived eruption involving several jets. We have critically reviewed the content of that article and conclude that the data (some of which is inexactly interpreted or not correctly georeferenced) do not support the existence of a second eruption on the Island of El Hierro.…”

“…Pérez et al (2014) reported five Bfilament-shaped^acoustic signals emanating from the flanks of mounds in the western coast of El Hierro, well imaged in only one parametric TOPAS profile as Bflares^of high acoustic contrast of impedance within the water column. The authors interpreted this acoustic imaging as submarine plumes caused by volcanic material and gas bubbles, detected on the 0.5-5-kHz chirp parametric subbottom profiler (TOPAS PS18) with a primary pulse at 18 kHz.…”

“…The authors interpreted this acoustic imaging as submarine plumes caused by volcanic material and gas bubbles, detected on the 0.5-5-kHz chirp parametric subbottom profiler (TOPAS PS18) with a primary pulse at 18 kHz. However, this assessment is quite speculative since Pérez et al (2014) do not provide any in situ analysis of the physical-chemical properties of the whole water column by a CTD-carousel as temperature, salinity, transmittance, pH, C T , A T , H 2 S, etc., completely necessary in order to prove the real nature of these signals. In March 2013, VULCANO0313 cruise was carried out, in the context of the VULCANO project (CTM2012-36317) on board R/V Ramón Margalef from the Spanish Institute of Oceanography.…”

“…In March 2013, VULCANO0313 cruise was carried out, in the context of the VULCANO project (CTM2012-36317) on board R/V Ramón Margalef from the Spanish Institute of Oceanography. The ship was equipped with a multibeam echosounder EM710, a CTD Seabird 911 Plus with a 24-l carrousel and the same model of the chirp parametric echosounder (TOPAS PS18) used in Pérez et al (2014), which collected multidisciplinary data all around the Island of El Hierro. Our results show not only the presence of very similar acoustic artifacts in the same place where Pérez et al (2014) localized their five acoustic plume-like artifacts, but also 24 more acoustic artifacts (Fig.…”