The recognition of geophysical precursors to volcanic activity is a primary challenge in volcano monitoring. That challenge was successfully met by scientists at the Icelandic Meteorological Office (IMO) before the 1 November 2004 eruption of Grímsvötn, a subglacial volcano beneath the Vatnajökull ice cap,Iceland (Figure 1).

Seismic and geodetic precursors were properly recognized, leading to a timely eruption forecast and warning announcements. During the eruption, IMO's monitoring capability was greatly expanded by employing geophysical and meteorological observation tools, which enabled real-time hazard assessment.