During the 1991 – 1992 eruption of Westdahl, interferograms spanning 21 – 30 November 1991 indicate ~6 cm of subsidence attributed to magma withdrawl from a shallow reservoir. This is modelled as a point source with volume decrease of 0.03 ± 0.01 km³ at 5 – 7 km depth beneath the summit area.
Between 1992 – 2000 and 2003 – 2010, interferograms show inflation of the volcano at a decreasing rate, with maximum displacements of ~3 cm/yr. The source of deformation is thought to be the same as coeruptive subsidence in 1991 and is modelled as a point source at 6 km depth. In total 0.06 km³ of magma is thought to have accumulated between 1992 – 2010. The magma flow rate is though to be governed by the pressure gradient between a deeper source region and the reservoir.