Istituto di Geoscienze e Georisorse     
Marini L., Agostini A., Cioni R., Guidi M., Leon O. Guagua Pichincha volcano, Ecuador: fluid geochemistry in volcanic surveillance. In: Journal of Volcanology and Geothermal Research, vol. 46 pp. 21 - 35. Elsevier, 1991.
The densely populated matropolitan area of Quito is located on the slopes of active Guaga Pichicha volcano at only 10 km from the crater. Recently, the Italian ministry of Foreign Affaiers sponsored a project for the mitagation of volcanic hazard in this area. The geochemical model of zone for use in volcanic surveillance. According to this geochemical model, a hydrothermal aquifer (T=200-240C), fed both by meteoric waters and by fluids released by magma body, lies at shallow levels beneath Guaga Pichicha crater. The crater fumaroles are essentially fed by steam boiled off from the hydrothermal aquifer. The high flow rate fumaroles located in dome area show significant SO2 content, wigh suggest a relatively high contribution of magmatic fluids in the zone of aquifer feeding them. The absence of SO2 in fumarolic dicharges near the southern crater wall indicates instead that the magmatic fluids disssolve entirely into the aquifer here. The hot springs located at the western end of the crater represent the lateral dicharge of the hydrothermal aquifer. On the basis of this model, it is likely that an increment in the flux of both the magmatic fluids and the heat from a magma body produces an increase, albeit small, of the pressure-temperature conditions of the hydrothermal system and conseguent changes in the flow rate and the fluids chemistry in the fumarolic vents. In particular, total sulphur and possibly hydrochloric acid may increase in the all the vents and sulphur dioxide may appear in the other fumarolic discharges. The varying thermodynamic conditions in the hydrothermal aquifer can be evaluated on the basis of the equilibria among carbon species and the hydrogen. Only minor delayed changes are expected in the physical-chemical characteristics of the spring located at the western end of the crater
URL: http://https://www.journals.elsevier.com/journal-of-volcanology-and-geothermal-research/
Subject Ecuador
Guagua Pichincha volcano
fluids chemistry
chemical thermometers
volcanic surveillance

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