While surface volcanic eruptions are both common and dramatic, by far the greatest volume of volcanic material is erupted on the seafloor, where they have not been observed, and remain poorly understood. Recent direct observations of eruptions at three sites in the western Pacific have provided a very rare glimpse of this type of activity. One site, West Mata in the Lau basin, was instrumented with a number of hydrophones to record acoustic signals (sound) from the eruption that can be used to gain insights into the eruptive process. This project has the aim of analyzing the data from a suite of four instruments to locate the sources of the acoustic signals, understand the sources of volcanic tremor, and correlate the acoustic activity with the production of volcanic ash and debris. Broader impacts include improved understanding of fundamental earth processes, public outreach and education.
As part of a large scale effort to quantify and understand submarine volcanic activity in the southwestern Pacific, we deployed four hydrophones (underwater microphones) and volcanic debris sensors for 5-months off the R/V Revelle in 2009. The sensors were all positioned around a submarine volcano called West Mata. West Mata is 1200 m deep (rising some 2000 off the seafloor) and located 100 km south of American Samoa. West Mata is the deepest actively erupting volcano ever observed, which allowed us to make the first ever soud recordings of a deep-ocean eruption. We found that the volcano generates contiual explosion bursts at it summit vent that are broadband, as well as unique, continuous tones the fluctuate in frequnecy that are likelly produced by small vents or conduits near the summit that were not previously identified. We also were able to closely study the link between volcano explosion activity at the summit and massive landslides down the volcano's flank. Near the end of our 5-month recording period, we observed a giant debris flow that lasted for 2-weeks that was preceeded by the loudest volcanic explosion sequence observed from the summit vent. Understanding this process allows us to better mitigate the volcanic and tsunami hazards posed by underwater volcanoes to nearby coastal and island communities.
