Forecasting the Next Eruption at Axial Seamount Based on an
Inflation-Predictable Pattern of Deformation
Abstract
Axial Seamount is the most active submarine volcano in the NE Pacific
Ocean, and is monitored by instruments connected to a cabled observatory
(the US Ocean Observatories Initiative Cabled Array), supplemented by
autonomous battery-powered instruments on the seafloor (at
~1500 m depth). Axial is a basaltic hot spot volcano
superimposed on the Juan de Fuca spreading ridge, giving it a robust and
apparently continuous magma supply. It has had three effusive eruptions
in the last 21 years: in 1998, 2011, and 2015. Deformation measurements
have been conducted at Axial Seamount since the late 1980’s with bottom
pressure recorders (BPRs) that can detect vertical movements of the
seafloor with a resolution of ~1 cm. This monitoring has
produced a 22+ year time-series including co-eruption rapid deflation
events of 2.5-3.2 meters, separated by continuous gradual inter-eruption
inflation at variable rates between 15-80 cm/yr. The overall pattern
appears to be inflation-predictable, with eruptions triggered at or near
a critical level of inflation. Using this pattern, the 2015 eruption was
successfully forecast within a one-year time window, 7 months in
advance. As of December 2019, Axial Seamount has re-inflated 1.98 m
(~78%) of the 2.54 m it deflated during the 2015
eruption. We are exploring several methods to forecast the next
eruption, including daily extrapolation of the average rate of inflation
from OOI BPR data during the last 3 months forward in time until it
intersects the threshold reached before the 2015 eruption. Using this
method with the difference in inflation between two OOI BPR instruments
located 3.5 km apart removes noise from tidal residuals and
oceanographic signals that are common to both instruments. This method
suggests the next eruption is likely between 2020 and 2024. However,
this simple method is complicated by uncertainties in the next inflation
threshold (the volcano inflated 20 cm higher before the 2015 eruption
compared to 2011), changes in the rate of inflation with time, and by
intermittent pauses in the inflation (and seismicity) observed since
2015 that have lasted from a week to several months.