Abstract
Turrialba Volcano, located in Central-Southern Costa Rica, has been characterized, since the last period of eruptive activity in 1884-1886, by a weak and discontinuous fumarolic activity in the western area of its summit. During the 1998-2002 period, fumaroles discharging from central and West craters were collected for chemical analyses of major and trace gas compounds, 13C/12C in CO2 and 18O/16O and D/H (in one fumarolic condensate), isotopic ratios. Geophysical measurements (seismic activity and ground deformation), monitored in the same period, were compared to geochemical data to define the status of the volcanic system. Chemical and isotopic characteristics of fumaroles of Turrialba Volcano seem to be related to interaction processes between a magmatic source and a shallower hydrothermal aquifer. Since February 1997, seismicity at Turrialba Volcano gradually increased, while since August 2001 new fumaroles start to discharge from a new fracture system located in the area between central and West craters. Since September 2001, strong compositional changes of gas discharges have been recorded at central crater. These occurrences are possibly due to variations in the permeability of the conduit system feeding the fumaroles. Heat pulse episodes from a magmatic source have possibly caused the increase of vapour pressure at depth and, consequently, favoured the uprising of the magmatic fluids toward the surface. The observed evolution of chemical and physical parameters suggests that to forecast a possible renewal of the volcanic activity in the near future a full program of both geochemical and geophysical surveillance must be provided at Turrialba Volcano.
Highlights
Turrialba (10.03N, 83.77E) is an active stratovolcano belonging to the Holocene «Cordillera Central» volcanic belt and is located at about 35 and 15 km from the towns of San José and Carta-In the present study, the results of a geochemical monitoring carried out from 1998 to 2002Franco Tassi, Orlando Vaselli, Vilma Barboza, Erick Fernandez and Eliecer Duarte on the fumaroles of the summit craters are described and discussed
N2/Ar ratios of all the samples are higher than that in the air (83), suggesting a non-atmospheric origin for N2, probably partly released from subducted sedimentary material, as commonly observed for gases collected in areas of convergent active tectonics (Giggenbach, 1996), He relative contents seem to differ sensitively from the typical volcanic arc gas compositions (Sano and Wakita, 1985; Sano et al, 1987)
The described behaviour of the volcanic system is not necessarily related to an incipient resumption of eruptive activity at Turrialba Volcano, that would eventually be preceded by further changes in gas chemistry, ground deformation and seismic signals
Summary
Turrialba (10.03N, 83.77E) is an active stratovolcano belonging to the Holocene «Cordillera Central» volcanic belt and is located at about 35 and 15 km from the towns of San José and Carta-In the present study, the results of a geochemical monitoring carried out from 1998 to 2002Franco Tassi, Orlando Vaselli, Vilma Barboza, Erick Fernandez and Eliecer Duarte on the fumaroles of the summit craters are described and discussed. Turrialba is a composite stratovolcano (3,325 meters a.s.l.) and belongs to the Cordillera central where two more active volcanoes with historical eruptions are present: Irazu and Poàs. This volcanic range includes Platanar, Congo and Barva volcanoes. Historic eruptive activity of Turrialba dates back to 1723, 1847, 1853, 1855, 1861 and 1864-1866 (Castillo, 1984). They were probably small phreatic eruptive events, but very little is currently known about these volcanic activities. Turrialba summit presently hosts three NESW oriented craters: East, central and West
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