Diffuse Emission of Hydrogen from Poás Volcano, Costa Rica, America Central

We report the results of four soil H2 surveys carried out in 2000–2003 at Poa´s volcano, Costa Rica, to investigate the soil H2 distribution and evaluate the diffuse H2 emission as a potential surveillance tool for Poa´s volcano. Soil gas H2 contents showed a wide range of concentration from 0.2 to 7,059 ppmV during the four surveys. Maps of soil gas H2 based on Sequential Gaussian Simulation showed low H2 concentration values in the soil atmosphere (<0.7 ppmV) for most of the study area, whereas high soil gas H2 values were observed inside the active crater of Poa´s. A significant increase in soil gas H2 concentration was observed inside the active crater during 2001 and 2002 with respect to year 2000, followed by a decrease in 2003. The observed spatial and temporal variations of soil H2 concentration have been well correlated with seismicity, microgravimetry and fumarolic chemistry changes which occurred during this study. These observations evidence changes in the shallow magmatic-hydrothermal system of Poa´s, and it might be related to a potential magmatic intrusion during the period 1998–2004. Therefore, monitoring diffuse H2 emission of Poa´s has become an important geochemical tool for the monitoring of its volcanic activity.