InSAR measurements show that the caldera floor of Aniakchak volcano has subsided. The rate of subsidence decreased from ~12 mm/yr during 1992 – 2000 to ~8 mm/yr during 2000 – 2005 and ~6 mm/yr during 2005 – 2010. The deformation is modelled by a point source at shallow depth (2 – 4 km). Evidence from melt inclusions show that this is equal to preeruptive magma storage depths at the volcano. Subsidence may therefore be due to crystallisation or fluid loss from a shallow magma body. Another possible cause is a decrease in pore fluid pressure due to cooling or fluid loss from the hydrothermal system.