The CO2 output from the Sperchios Basin area (central Greece): the role of hidden degassing from streams

The Sperchios Basin is an actively spreading rift area with deeply rooted extensional faults and also a site of quaternary volcanic activity. Such geologic conditions favoured the formation of many hydrothermal systems, whose surface expressions are among the biggest thermal springs of the whole Greece. Degassing of deeply derived geogenic CO2 is highlighted by strong bubbling within the main pools of the springs. Flux measurements were made in the Thermopyles spring with the floating chamber method and results showed that bubbling gases in the spring release about 1 ton/day of CO2. The outgoing stream has a flow of more than 250 l/s of water rich in CO2 (about 16 mmol/l). Although no bubbling is visible along the stream, after 300 m, the CO2 content decreases to 2 mmol/l, indicating an intense CO2 degassing. This was quantified in more than 10 tons/day, suggesting that most of the degassing is not visible. Output estimations at the close by thermal springs of Psoroneria and Ypatis have not been made yet, but considering that the bubbling in their pools and the water outflow rates are similar, the CO2 emitted will be of the same order of magnitude. Further contributions from the Sperchios area may come from the Kamena Vourla springs and from diffuse soil degassing. To sum up, the best estimate of the total CO2 output of the studied area is in the order of many tens of tons/day. Such output is comparable to that of the single active volcanic systems along the South Aegean Volcanic Arc (Sousaki, Methana, Milos, Santorini, Kos and Nisyros) and it highlights the importance of hidden degassing along CO2-oversaturated streams.