Underwater records of submarine volcanic activity: El Hierro (Canary Islands 2011–2012) eruption

We present the monitoring of a submarine volcanic eruption that took place near the southernmost emerged land of El Hierro Island (Canary Islands, Spain), from October 2011 to February 2012. Right after the onset of the eruption, in mid-October 2011, we deployed an offshore geophone array for the purpose of monitoring the submarine eruptive activity signals. It acquired continuous data from October 2011 to May 2012, sometime after the end of the eruption. The array consisted of 8 high-frequency, 3-component geophones assembled into a cable string, with 6 m of separation. The geophone string was installed in La Restinga Harbor at a distance of less than 2 km from the volcanic edifice. The dataset acquired with the array is a unique continuous acoustic record of the activity associated with this eruption. We analyzed the continuous signal of the eruptive activity, with special interest in those events reflecting the eruption dynamics. Our results show that the geophone array was recording acoustic waves from a back-azimuth source corresponding to the position of the submarine vent, traveling at a speed of 1510 m/s, compatible with the speed of sound in water. Acoustic data shows a good correlation with the seismic data recorded on land for the case of earthquake occurrence. In addition, it provides relevant information towards the understanding of the eruptive surface activity. Therefore, this methodology can be successfully used in cases of submarine eruptions.