April Flowers for redOrbit.com – Your Universe Online
Underneath volcanoes, water and fire coexist to generate “hydrothermal” systems. These systems are complex “steam engines” that produce white smoke – fumaroles – sometimes observed at the surface. A new study, led by the Institut de Recherche pour le Developpement (IRD), demonstrates why these hydrothermal reservoirs are not always found under volcanic peaks.
The volcanologists conducted their study at the Ticsani and Ubinas volcanoes in Peru. For some structures, such as these, fumarole resurgences occur more than 6 miles from the top of the dome. The research team developed a numerical model that showed the position of the hydrothermal systems depends on regional topography, which may significantly deviate subsurface flows.
The majority of active volcanoes have an internal hydrothermal system. These systems develop from the infiltration of rainwater that acidifies, heats up, boils and is partly vaporized as it comes into contact with the magma. Changes in volcanic activity are reflected in the variations of movement and volume of these liquids or gases. Sometimes during an eruption, magma breaks up in contact with the hydrothermal system causing an explosive type eruption. Hydrothermal activity such as this may also contribute to destabilizing the volcanic edifice in the long term, by altering the rocks. The position of the hydrothermal activity also indicates the permeability of the volcanic rocks – one of the key parameters of the physical processes at work within volcanoes. Being able to locate this activity precisely in the sub-soil helps volcanologists better estimate the permeability.
For scientists to gain a better understanding, and greater ability to predict the behavior of volcanoes, it is essential to accurately locate these hydrothermal systems, which are not always located at the top. This is the case with Ticsani and Ubinas. The team located the hydrothermal resurgence more than 6 miles downstream from each volcano. They noted that only a few events are observed in the hollow of the crater. By measuring the soil temperature – up to 98.6 degrees F at the surface of Ticsani, and hot springs – from 48 to 201 F – and the electrical potential created by the movement of fluids in the sub-soil, the team was able to develop a numerical model to explain the asymmetric distribution of hydrothermal fluids.
Peaking at 17,742 and 18,608 feet respectively, Ticsani and Ubinas have an atypical profile. The formations are characterized by a significant difference in altitude between their upstream and downstream sides. The influence of the regional topography on the position of the hydrothermal system is displayed in the numerical simulations – the considerable altitudinal gradient observed is able to significantly divert the flow of thermal water, shifting groundwater several kilometers in relation to the volcanic cone.
Two of the most active volcanoes in Peru, the Ubinas and Ticsani are located near the second largest Peruvian metropolitan area, Arequipa – which has nearly 1 million inhabitants – and the city of Moquegua. This study will help other scientists locate the hydrothermal activity beneath the volcanoes and to characterize the permanent boiling in their belly. The results will also contribute to better monitoring of the volcanoes and better management of eruption events.
Findings are published in the journal Earth and Planetary Science Letters.
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