In the time that InSAR data has been available over Alutu (1997-2000, 2004-2010) two periods of uplift, followed by periods of gradual subsidence, have been observed (Biggs et al., 2011). The deformation throughout each period had a circular pattern, which was centred over the volcano. Firstly, 15 cm of uplift between December 2003 and August 2004 was observed. Gradual subsidence of 4.7 cm followed this, lasting 400 days, which could be fit by a simple exponential decay with a 200-300 day decay constant. The second phase of inflation (9.9 cm) was in July 2008 and lasted 150 days. In December 2008 this inflation ended, and gradual subsidence of 4.3 cm continued over the remaining 750 days of data. At this point the subsidence looked to continue. Throughout this period the magnitude of the inflation was greater than deflation, and so an overall inflation over this period is apparent. The time series of inflation and deflation show that these ground motions are not linear (Biggs et al., 2011).
The deformation patterns at Alutu have been fit best by a penny shaped crack at a depth of 0.5-2.5 km, with a radius of 3-10 km. It has been suggested that the deformation can be explained by magma-driven uplift and hydrothermal field activity, and that the subsequent subsidence is associated with hydrothermal activity alone (Biggs et al., 2011).