firma Térmica y geoquímica del Volcán Poás, cosT a rica (marZo 2009)

We report results from a multidisciplinary campaign conducted at Poas volcano (Costa Rica) in March 2009. Thermal imagery of the fumaroles sited on the north side of the pyroclastic cone revealed mean apparent tem - peratures ranging between 25 and 40°C with a maximum apparent temperature of 80°C. The crater lake surface was characterised by mean apparent temperatures varying between 30 and 35°C and a maximum recorded value of 48°C. Thermal profiles across the lake surface revealed steady temperatures and thus thorough convective mixing. The overall mean SO 2 flux emitted from the crater was 76 Mg d -1 , with approximately equal contributions from both the pyroclastic cone and the lake. Analysis of gas composition using active, open-path FTIR spectroscopy indicated molar ratios of H 2 O/SO 2 = 151, CO 2 /SO 2 = 1.56, SO 2 /HCl > 40, and SO 2 /HF > 200 for the lake emission. The plume was also sampled using filter packs. Ion chromatographic analysis revealed the presence of abundant K + and SO 4 2- , with small amounts of Ca 2+ , Cl - , and Mg 2+ . This provides a detailed picture of lake surface temperature characteristics and of gas flux and com- position of the plume emitted from Poas. The results are consistent with the typical non-eruptive state of this volcano.

我们报告了2009年3月在波阿斯火山（哥斯达黎加）开展的一项多学科活动的结果。位于火山碎屑锥北侧的喷气孔的热成像显示，平均表观温度在25℃到40℃之间，最高表观温度为80℃。火山口湖表面的特征是平均表观温度在30℃到35℃之间，记录到的最高值为48℃。湖面的热剖面显示温度稳定，因此存在充分的对流混合。火山口排放的二氧化硫总平均通量为76毫克/天，火山碎屑锥和湖泊的贡献大致相等。使用主动式开放光路傅里叶变换红外光谱对气体成分进行分析表明，湖泊排放的水/二氧化硫摩尔比为151，二氧化碳/二氧化硫为1.56，二氧化硫/氯化氢>40，二氧化硫/氟化氢>200。还使用滤膜包对烟羽进行了采样。离子色谱分析显示存在大量的钾离子和硫酸根离子，以及少量的钙离子、氯离子和镁离子。这提供了波阿斯湖表面温度特征以及烟羽气体通量和成分的详细情况。这些结果与该火山的典型非喷发状态相符。