Though not the direct subject of the study, Ungaran volcano was included in Kuehn et al’s land subsidence survey of the city of Semarang in Sumatra. This study used the Stable Points Network (SPN) technique to measure ground displacement – the SPN technique is a relatively modern synthetic aperture radar-based method, which utilises backscattering objects on the ground surface to measure displacement with millimetre-scale accuracy. The survey was performed using images acquired between 2002 and 2006, and covers an area of approximately 375km².
Over the four years of observation, the northeastern flank of Ungaran exhibited significant subsidence, at a rate of approximately 1cm/yr. The deformation increases with distance from the volcanic edifice, and takes the form of a roughly cylindrical depression. A comparison with geological surveys of the area confirms the presence of a collapse ring fault structure, to which the authors attribute the ground displacement.