POST-ERUPTIVE CHANGES OF SANTA ANA VOLCANO CRATER LAKE: NOVEMBER 2005 – NOVEMBER 2008

We report visual observations performed using photographies taken from rim of the Southeastern part of the crater of Santa Ana Volcano during 2005 to 2008. The lake inside of the crater has presented reductions in volume, a small eruption and changes in color. In most cases this changes were preceded by an increment in seismic activity and emissions of CO2 at the monitored fault. During this time, three distinct periods have been observed.

Phase I, November 2005 to April 2006, after the Santa Ana volcano eruption of October 1, 2005, a highly evaporated lake appeared and the crater showed large fumarolic emissions from the southwestern part of the crater lake. During this phase, periods of bubbling of gases was observed at the center of the lake. In addition, the color of the water changed from green aqua to lemon. On April 20, 2006, the volume of the lake had been reduced to about 30% of its normal volume.

Phase II, May 2006 to August 2007. From May to December 2006, the lakes recovers its normal level and the water lake color is dark green. In February 2007, the lake changes color again to a green aqua, turning to a gray color in March of that year as the lake evaporated almost completely to only 4% of the original volume on April 24, this day, between 12:50 and 2:30 pm several small explosions were observed, one reaching 40 m in high. In August 18 and 19, 2007, the lake has evaporated almost completely. During the two periods when the lake dried (April 2006 and August 2007), the CO2 efflux along the Southeastern fault increased from 31 g/m2day to 196 and 176 g/m2day respectively (Barahona et al, this meeting).

Phase III, September 2007 to November 2008. From September 2007 to November 2008, the lake recovers its volume partially. During 2008 does not present evaporation periods where the lake evaporate almost completely. These observations at Santa Ana volcano crater lake show that the magma source emplaced at a shallow depth is releasing heat and gases to the lake changing its physical-chemical conditions and producing periods of evaporation and water volume recovering as the input of heat and gases, as well as the meteoric input, changes with the system activity. The changes in color are probably related to changes in mineral stability and precipitation of different minerals as the pH, temperature, and redox potential of the water changes due to the input of heat and gases.