CHANGES IN SOIL CO2 FLUX AND TEMPERATURE AT IZALCO VOLCANO

Izalco volcano is a stratovolcano located at west part of El Salvador, composed of basaltic rocks. This volcano started to form in the eighteen century with its first eruption in 1770, and the last one in 1966. In the last 8 years, CO2 flux and soil temperature measurements have been done. The purpose of these studies was to establish a base line of these two parameters during the periods of low volcanic activity.

A low increase in gas emission was visible many kilometers away from the crater during the period of October-December 2005. This period correspond to the post-eruption stage of the neighboring Santa Ana volcano, who erupted last time in October 1st 2005. In May 2006, July 2007 and January 2008 CO2 flux measurements were performed in Izalco volcano. In 2006, 53 points were measured around the principal crater. 28 points were sampled in 2007 around the principal crater as well. In January 2008 the measurements were distributed in an area inside the principal crater, and 51 points were sampled. The maximum values obtained in these surveys were 477, 530 and 649 g/m2d respectively. These results are one order of magnitude higher than the values measured by Salazar et al. (2004) in May 2001. In that study, the authors reported a maximum value of 15 g/m2d (Salazar et al., 2004).

According to the CO2 flux measurements performed in January 2008, three populations were observed in the measurements. The first group had a maximum value of 18.5 g/m2d, the second one 97.3 g/m2d, and the third one a maximum value of 649.3 g/m2d with an average value of 44.4 g/m2d. The soil temperature measurements allowed to identify conductive areas (T < 70 oC ) in the north-east sector, and convective areas(T > 80 oC) in north-east and south-east sectors. In general, the survey in this area shows a soil temperature maximum of 88 oC, and a minimum of 21 oC. This temperature interval is quite similar in the last 3 field campaigns. The fact that there are no changes in the soil temperature while the gas flux is increasing could be related to the predominant atmospheric buffer of the temperature in the summit area of the volcano. However, the moderate increase in soil CO2 efflux suggests a possible higher release of gases from the deep magmatic source in this volcano. The constant monitoring of these parameters will permit to detect short term warnings prior to future eruptive events.