Modeling the Long-term Deformation Field at Erebus volcano, Antarctica using 20 years of GPS Observations

Erebus volcano, Antarctica, has hosted a convecting phonolite lava lake for over 50 years. Associated Strombolian eruptions from the lake and surrounding vents typically occur daily and rarely eject bombs onto the crater rim. Geochemical, volcanological, and geophysical studies examined degassing from the lava lake, the eruptive history, and the structure of the magmatic system. Processes driving the short and long-term deformation of the volcano, are however, largely unconstrained.

GPS observations have been collected for over 20 years at Erebus by UNAVCO on behalf of the former Mount Erebus Volcano Observatory (MEVO). Prior to that the Transantarctic Mountains Deformation (TamDEF) project collected limited campaign observations. We have examined data from 10 continuous GPS stations and 10 campaign GPS stations. The position time series generated for these data suggest a variety of deformation mechanisms have impacted the stations. We observe long-term, long-wavelength subsidence of the network suggesting a loading related process, and a small summit-crater subnet shows horizontal motion toward the eruptive vent perhaps resulting from volcanic deformation. Two models are examined to understand the observations. We simulate surface displacements due to long-term loading and growth of the volcanic edifice over the past 20 ka. The GPS data constrains the rheologic parameter values of the model: a 10 km thick elastic layer overlying visco-elastic material. The load is constrained by the average eruption rate of 4km³ / 1000 years distributed over the summit caldera. A χ² test helps determine parameter values that best explain observations with the modeled displacements at the existing GPS stations. Second, we use a deflating volcanic source models to explain the horizontal velocities. The model results constrain the physical characteristics of Erebus and contribute to the understanding of its volcanic history. We reproduce horizontal velocities and location of a shallow volcanic source comparable to seismic observations.