|Characteristics of deformation:|
Since the eruption in 1998, deformation at Axial Seamount has been monitored using bottom pressure recorders (BPRs) and mobile pressure recorders (MPRs).
Between 1998 and 2004, the rate of inflation was highest in the months immediately after the eruption (20 cm/month) and has since declined to a steady rate of 15 cm/month. Uplift in the caldera has been observed at a rate of 22 cm/year relative to a point outside the caldera. Assuming continuous uplift since the 1998 eruption, these observations suggest that the centre of the caldera has re-inflated about 1.5 m, thus recovering almost 50% of the 3.2 m subsidence that was measured during the 1998 eruption. This inflation rate was used to calculate a magma supply rate of 14 x 10^6 m³/year. If this recurrence continues, it also suggests a recurrence interval of ~16 years between eruptions at Axial Seamount, assuming that it will be ready to erupt again when it has re-inflated to 1998 levels. (Chadwick et al., 2006).
Data between 2004 to 2007 indicate steady inflation of 12.7 cm/year at the caldera centre. The spatial pattern of uplift is consistent with magma storage in a shallow reservoir underlying the caldera at a depth of 3.5 km, and the current uplift rate implies that magma is being supplied to the volcano at a rate of 7.5×10^6 m³/year. However, the supply rate immediately after the eruption in 1998 was significantly higher, and the temporal pattern of uplift at Axial caldera appears to be governed by at least two processes occurring on very different time scales. The high uplift rates immediately following the 1998 eruption are interpreted to be due to either an influx from one or more small satellite magma bodies or as the result of viscoelastic relaxation and/or poroelastic behavior of the crust surrounding the shallow magma chamber. The current lower uplift rate is interpreted as being due to a steady long term magma supply from the mantle. This two component uplift pattern has not been observed on land volcanoes, suggesting that magma supply/storage processes beneath this ridge axis volcano differ from volcanoes on land (including Iceland). It is possible to forecast that the next eruption at Axial Seamount is likely to occur by about 2020, when most of the 3 m of deflation that occurred during the 1998 eruption will have been recovered. (Nooner et al., 2009).
Continuous measurements of ocean bottom pressure document the deflation–inflation cycle of Axial Seamount between 1998 and 2011. The volcano inflation rate, caused by the intrusion of magma, is found to have gradually increased in the months leading up to the 2011 eruption. Sudden uplift occurred 40–55 minutes before the onset of eruption, which is interpreted as a precursor event. Based on ground deformation measurements through the entire eruption cycle at Axial Seamount, it is suggested that another eruption could occur as early as 2018. It is proposed that the long-term eruptive cycle of Axial Seamount could be more predictable compared with its subaerial counterparts. This is because the volcano receives a relatively steady supply of magma through the Cobb hotspot and because it is located on thin oceanic crust at a spreading plate boundary. (Chadwick et al., 2012).
|Reference(s):||Chadwick, W.W., Nooner, S.L., Zumberge, M.A., Embley, R.W. and Fox, C.G., 2006. Vertical deformation monitoring at Axial Seamount since its 1998 eruption using deep-sea pressure sensors. Journal of Volcanology and Geothermal Research, 150(1), pp.313-327.|
|Chadwick Jr, W.W., Nooner, S.L., Butterfield, D.A. and Lilley, M.D., 2012. Seafloor deformation and forecasts of the April 2011 eruption at Axial Seamount. Nature Geoscience, 5(7), pp.474-477.|