Interferograms covering the volcano show two regions of subsidence. The first is location on the southeastern flank of the volcano with deformation occuring at rates of ~0.5 cm/yr. This deformation is modelled by a point source at <1 km depth and is thought to originate from cooling and degassing of magma intruded during eruptions in 1987 and 1996.  A second region of subsidence at rates of ~1 mm/yr is seen on the lower southwestern flank. This is in a region of lava flows thought to originate from the 1963 eruption, and subsidence is therefore attributed to thermoelastic constraction of lava flows.