Papandayan is fortunate enough to be the site of a large and well-established network of seven GPS stations, and campaign surveys monitoring deformation of the volcano first began in 1998, carried out by the Department of Geodetic Engineering, Institute of Technology, Bandung. A 2006 paper by Abidin et al summarises seven such surveys over a period of five years, including the recent eruption which occurred November-December 2002.
During ‘normal’ periods of activity at the site (i.e. before the eruption), the ground deformation observed at the site was minimal, typically on the order of several millimetres to 1-2cm per year, though in the year prior to the eruption a larger signal of horizontal expansion was noted across the volcanic crater. In the months leading up to the November 2002 explosion, ‘significant’ inflation of tens of centimetres was observed around the crater, with the largest displacement of 30cm occurring at station DPN0, 500m from the vent.
During the eruption itself, deformation on the edifice was considerably more erratic; conflicting signals of inflation and deflation were observed at adjacent stations, sometimes changing within the space of a single day. The authors attribute this to a fluctuating pressure source at depth, with inflation being linked to a relatively shallower source and vice versa; however, as data could only be safely collected from two stations during this period, this hypothesis could not be verified.
Following the eruption, a comparison of readings taken between August 2002 and June 2003 showed a general inflation of the site of between 10-20cm, with the majority of the displacement being focused around the crater site.