From the latest bulletin released by the Pasto volcano observatory of INGEOMINAS, 19 January 2008:

The activity of the volcano has changed: Level II (eruption likely within days or weeks). On the basis of the constant monitoring and analysis of the activity carried out by the Galeras Volcano Observatory of INGEOMINAS in Pasto, it is clear that in the last few hours the seismic activity of the volcano has been declining steadily in terms of frequency and energy. This activity is associated with a gradual degassing process such as usually occurs after an explosive eruptive event as took place on January 17.

Volcanologists at Galeras see this eruption as notable for its suddenness, according to a report in El País (Cali). The LP seismic events being monitored at Galeras gave no indication that an eruption was imminent:

If something made this eruption of Galeras different from past eruptive processes, it was the suddenness with which it occurred. On this occasion, according to Martha Calvache, deputy director of Geological Hazard at Ingeominas, the signals which usually precede an eruption were not recorded at their usual levels, such the occurrence of tornillo earthquakes … [She] observed that in a previous episode of alert, between November 2006 and March 2007, more than 350 movements of this type were recorded by the Pasto Volcano Observatory. The director of the agency, Diego Gomez, added that to be precise nine of the last eleven explosive eruptions of Galeras were preceded by tornillo earthquakes. On this occasion, only five earthquakes of this type preceded the strongest eruption of Galeras in the last twenty years, leaving no time to regulate the level of alert, which went straight to the maximum level.

El País also reports that President Alvaro Uribe visited Pasto yesterday and announced an allocation of $60 million to fund the resettlement of 8,000 people, presently occupying 3,000 at-risk properties around the volcano which, in the Colombian government’s view, should be abandoned. It seems, however, that locals are reluctant to evacuate: according to an Associated Press report, only 100 of the 8,000 residents ordered to evacuate when the eruption began actually left. El País puts the total slightly higher: ‘The eight thousand inhabitants in the zone of highest threat, located in rural districts of the municipalities of Pasto, Nariño and La Florida, ignored an order to vacate their premises, and only 10% of them transferred to community shelters’.

Information
Smithsonian Institution Global Volcanism Program - summary information for Galeras (1501-08=)
Portal Corporativo de INGEOMINAS - Instituto Colombiano de Geología y Minería
Observatorio Vulcanológico y Sismológico de Pasto - Pasto volcanological observatory main page

News
El Galeras sigue ‘acompañado’ - El País, 19 January 2008 (Spanish)
Few persuaded to flee Colombia volcano - Associated Press, 18 January 2008