Gas emissions and crustal deformation from the Krýsuvík high temperature geothermal system, Iceland

The Krýsuvík volcanic system is located on the oblique spreading Reykjanes Peninsula, SW Iceland. Since early 2009 the region has been undergoing episodes of localized ground uplift and subsidence. From April–November 2013, we operated near-real time monitoring of gas emissions in Krýsuvík, using a Multi-component Gas Analyzer System (Multi-GAS), collecting data on gas composition from a fumarole (H2O, CO2, SO2, H2S). The dataset in this study, comprises a near-continuous gas composition time series, the quantification of diffuse CO2 gas flux, analytical results for direct samples of dry gas, seismic records, and GPS data. Gas emissions from the Krýsuvík geothermal system were examined and compared with crustal deformation and seismicity. The gas emissions from the Krýsuvík system are H2O-dominated, with CO2 as the most abundant dry gas species, followed by smaller concentrations of H2S. The average subsurface equilibrium temperature was calculated as 278 °C. This is consistent with previous observations made through sporadic spot sampling campaigns. In addition, the semi-continuous Multi-GAS dataset reveals higher variations in gas composition than previously reported by spot sampling. The diffuse soil CO2 flux is found to be variable between the three studied degassing areas in Krýsuvík, ranging from 10.9–70.9 T/day, with the highest flux in Hveradalir where the Multi-GAS station is located. The total flux is estimated as 101 T/day. Comparison between Multi-GAS and geophysical data shows that peaks of H2O-rich emissions appears to follow crustal movements. Coinciding with the H2O-rich peaks, SO2 is detected in minor amounts (~0.6 ppmv), allowing for calculations of H2O/SO2, CO2/SO2 and H2S/SO2 ratios. This is the first time SO2 has been detected in the Krýsuvík area. The large variations in H2O/CO2 and H2O/H2S ratios are considered to reflect variable degassing activity in the fumarole. The activity of the fumarole appears less intense during intervals of low or no recorded seismic events. The H2O/CO2 and H2O/H2S ratios are lower, presumably due to H2O condensation affecting the steam jet before reaching the Multi-GAS inlet tube.

克里斯武维克火山系统位于冰岛西南部雷克雅内斯半岛的斜向扩张区域。自2009年初以来，该地区经历了局部地面隆起和下沉的过程。2013年4月至11月，我们在克里斯武维克使用多组分气体分析仪系统（Multi - GAS）对气体排放进行了近实时监测，收集了来自一个喷气孔的气体成分数据（水、二氧化碳、二氧化硫、硫化氢）。本研究中的数据集包括一个近乎连续的气体成分时间序列、扩散二氧化碳气体通量的量化、干燥气体直接样本的分析结果、地震记录以及全球定位系统数据。对克里斯武维克地热系统的气体排放进行了检测，并与地壳变形和地震活动进行了比较。 克里斯武维克系统的气体排放以水为主，二氧化碳是最丰富的干燥气体种类，其次是浓度较低的硫化氢。计算得出的平均地下平衡温度为278°C。这与之前通过零星的定点采样活动所做的观测结果一致。此外，半连续的多组分气体分析仪系统数据集显示，气体成分的变化比之前定点采样所报告的更大。 在克里斯武维克所研究的三个排气区域之间，扩散土壤二氧化碳通量有所不同，范围在10.9 - 70.9吨/天之间，在多组分气体分析仪系统监测站所在的赫瓦拉迪利尔通量最高。总通量估计为101吨/天。 多组分气体分析仪系统数据和地球物理数据之间的比较表明，富水排放的峰值似乎与地壳运动相关。在富水峰值出现的同时，检测到少量的二氧化硫（约0.6 ppmv），从而可以计算出水/二氧化硫、二氧化碳/二氧化硫和硫化氢/二氧化硫的比率。这是首次在克里斯武维克地区检测到二氧化硫。 水/二氧化碳和水/硫化氢比率的巨大变化被认为反映了喷气孔中排气活动的变化。在地震事件记录较少或没有记录的时间段内，喷气孔的活动似乎不太强烈。水/二氧化碳和水/硫化氢比率较低，可能是由于在到达多组分气体分析仪系统入口管之前，水的凝结影响了蒸汽喷射。