The latest monthly bulletin of Costa Rica's volcano observatory OBSICORI published a more detailed summary of Poás' activity during February summarized as follows:
The ultra-acid crater lake had a greenish-gray color with sporadic convection cells visible in the central part carrying sulfur in suspension. Lake temperature were measured at 44° C, which is a value significantly lower than those measured during most of 2009-2011. The pH value of the lake water was measured at 0.01, slightly "less" acidic than during November 2011 (pH -0.4). [less]

Am 23. Februar wachte Einwohner in Guachipelin (11 km SW) auf um Explosion zwischen 0400 und 0430 Ortszeit zu hören. Seismische Aufzeichnungen zeigte Signale typisch für Explosionen zur gleichen Zeit, obwohl andere Bewohner in anderen Bereichen nicht, jede Eruption hören.
Ähnliche seismische Signale gefunden auf 19 Feb 00:16 und 20 Feb 00:46 lokaler Zeit, was darauf hindeutet, dass auch kleinere Explosionen dann aufgetreten ist. [less]

(Nachricht von J Duarte, Vulkan Monitoring Team, OVSICORI-UNA) [less]

The eruption was first noticed by park rangers and local residents.
During the previous day, numerous rumblings could be heard from the mountain. According to OVSICORI-UNA, the eruption started between 3:10 and 3:20 pm and produced an ash plume from a vent on the southeast flank of the main crater in an area known as "La Quemada". [less]

This decompression event released ash that was carried by the wind at least up to Tres Rios (27km SW from the vent). As a consequence the Comisión Nacional de Emergencias and the Turrialba Volcano National Park's administration declared a yellow alert and closed the access, which is still the case on January 17th. [less]

Gas-and-steam plumes rose from the lava dome.
(Smithsonian / USGS Weekly Volcanic Activity Report 28 December-3 January 2012) [less]