Continuous H2O, CO2, 222Rn and temperature measurements on Merapi Volcano, Indonesia

A set of analytical instruments, consisting of a gas chromatograph for water and carbon dioxide, an alpha scintillation counter to measure radon and a temperature sensor, was especially designed and constructed to monitor volcanic gases and was successfully operated over weeks in the high temperature fumaroles at the summit of Merapi Volcano, Indonesia. The analytical unit runs automatically and is remote controlled through a radio-link. Over a period of several weeks, concentrations of H2O and CO2 were measured every 35 min and Rn activity was monitored at about 90-min intervals. The fumarole temperatures were continuously recorded every minute from July 2000 to the end of January 2001. The composition and temperature of the gas emitted at Merapi Volcano show significant variations. Due to a regular stronger degassing of the magma, concentrations of CO2 increase periodically while H2O concentrations decrease. On the other hand, Rn activity rises with increasing atmospheric pressure and higher water concentrations. After intensive rainfall, infiltration of cold meteoric water into the volcanic edifice possibly causes an increase in the concentration of water vapour and a decrease in the temperature of the gases in the fumarole. Several seismic events recorded at Merapi correlate with gas temperature.