Getting to the bottom of deep sea volcanic activity
Data featured in two new studies provide a step-by-step account of an underwater volcano erupting off the western coast of the U.S. in 2015. The results reveal that deformation patterns of the seafloor, and possibly even tidal activity, can be used to estimate the timing of future eruptions of undersea volcanoes. More than 80% of volcanic activity on Earth happens below water. Sustaining long-term observations of submarine volcanoes, however, and recovering related instruments after an eruption, are challenging, meaning that the activity of these mysterious magma outlets remains largely unexplored. The Axial Seamount, located off the coast of Oregon, erupted in 1998 and 2011, prompting researchers to deploy, in 2014, the Ocean Observatories Initiative Cabled Array, a seven station seismic network to monitor further activity in real time. In the first study in this issue, William Wilcock et al. analyze the seismic activity of an April 2015 Axial Seamount volcanic event, when the newly laid seismic network captured an eruption that culminated in explosive acoustic signals where lava erupted on the seafloor. Prior to the eruption, in the network's first year of operation, the network detected nearly 200,000 local earthquakes, the researchers say. The frequency of minor earthquakes increased from less than 500 per day to roughly 2,000 per day leading up to the eruption on 24 April, 2015. The patterns of these earthquakes corresponded with the tide, with rates of seismicity being about six times greater during the lowest tides than the highest tides, which can be attributed to the faults "unclamping" when the ocean loading is less, the authors say. The strong tidal triggering before the eruption hints at the utility of tidal monitoring to determine stress state of underwater volcanoes, the researchers suggest.
In a second study, Scott Nooner and William Chadwick Jr. describe how they were able to use the same seismic network to predict the 2015 Axial Seamount eruption based on patterns of seafloor deformation – which provide insights into subsurface magma movements. In their analysis, they used additional instruments on the Ocean Observatories Initiative Cabled Array, which captured data related to the 2011 Axial Seamount eruption as well. Leading up to that eruption, there was a distinct increase in the inflation of the magma reservoir below the Axial Seamount, the data show. Based on these measurements, Nooner and Chadwick predicted that if the magma inflation rate remained the same over the next few years, the next eruption of this undersea volcano would occur in 2018. However, the inflation rate of the reservoir was significantly higher following the 2011 eruption. Thus, the authors adjusted their prediction in early fall of 2014, estimating that the next eruption would occur sometime in 2015. Given that their prediction was correct, with the Axial Seamount erupting in late April 2015, the results suggest that monitoring magma pools underneath the Axial Seamount can help predict when future undersea eruptions will occur.
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