2004-2010 eruptions

Frequent small ash and gas explosions took place during 2006-2010.
More intense periods of activity were recorded in Dec 2004, Nov 2005 - February 2006. Small phreatic explosions causing minor ash fall were noted on 6 March and 23 April 2006.
Another episode of phreatic explosions began on 18 May and continued until 27 May 2006.
Climbers at the summit on 10 November 2006. aw fresh ejecta from explosions during the previous days.
On 22 June 2008, a moderate explosion generated a gas-and-ash plume causing minor ash fall in 16 km distance SW. A series of explosions occurred on 11 July, and again on 22 November 2008.
An explosion on 6 September 2009 generated a small 200 m high ash plume, and one on 14 Sep reached 350 m.
On 9 June 2010, the Washington VAAC reported a well-defined ash plume drifting about 115 km WNW and originating most likely from San Cristobal.

1997 eruption

An eruption began at San Cristóbal volcano during the night of 19-20 May 1997. The eruption had been preceded by 2 weeks of intense seismic activity and elevated SO2 emission. A series of ash explosions occurred, producing plumes rising up to 800 m. On 20 May explosions were sometimes nearly continuous for few minutes, and then stopped for minutes or even hours.
One explosion on 22 May could be heard in 3 km distance.
Field work on 23 May revealed that the inner pit crater of the inner crater cone had grown considerably and a new a new 4 m wide vent was observed at the SW end of its floor, at a location where there had been high-temperature fumaroles (600 deg C) previously.
The activity produced a layer of light gray ash on the W flank of the mountain. Activity calmed down towards the end of May, but isolated eruptions occurred throughout June and July.
Source: Smithsonian / GVP monthly reports