| Summary: | Erebus volcano is Antarctica’s most active volcano. Inside the 200 m-deep Inner Crater is a convecting phonolitic lava lake that has been stable for 50 years. Eruptive activity is characterized by small Strombolian explosions from the lava lake and adjacent vents, which occasionally eject lava bombs onto the crater rim. Global Navigation Satellite System (GNSS) stations have been used to observe Erebus deformation for 24 years, first in campaign mode and since the mid-2000s with seven continuous stations. Seismic activity at Erebus has been observed with a short-period seismic network since 1980 and broadband seismometers since 2003. Seismic surveys, such as the 2007-2008 TOMO Erebus experiment, have been used to densify these observations. Here, we use seismic and geodetic observations to analyze Erebus deformation from 10s of minutes to decadal time scales. Tilt derived from the broadband seismic data shows no notable deformation prior to Strombolian explosions, indicating hydrostatic adjustments of the magma column to rising gas slugs in the lava lake-conduit system. The GNSS data show long-term subsidence of Ross Island, consistent with a response of the lithosphere to Erebus loading over the last 20 ka as suggested by modeling. We also discover multi-year inflation and deflation cycles of the summit area in the GNSS data that we link to dynamics of the shallow magmatic system. The most recent inflation event lasted from November 2020 until March 2022. Based on prior inflation periods, this might herald an increase in the number and size of Strombolian eruptions.
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