Thermal anomalies associated with shallow gas hydrates in the K-2 mud volcano, Lake Baikal
Résumé
Thermal measurements and hydrate mapping in the vicinity of the K-2 mud volcano in Lake Baikal have revealed a particular type of association of thermal anoma- lies (29-121 mW m-2) near hydrate-forming layers. De- tailed coring within K-2 showed that hydrates are restricted to two distinct zones at sub-bottom depths exceed- ing 70-300 cm. Temperature data from stations with hydrate recovery and degassing features all display low thermal gradients. Otherwise, the thermal gradients within the mud volcano are generally increased. These findings imply a more complicated thermal regime than often assumed for mud volcanoes, with important roles for both fluids and hydrates. The coexistence of neighbouring low and high thermal anomalies is interpreted to result from discharging and recharging fluid activity, rather than hydrate thermody- namics. It is suggested that hydrates play a key role in controlling the fluid circulation pattern at an early stage. At a later stage, the inflow of undersaturated lake water would favour the dissolution of structure I hydrates and the forma- tion of structure II hydrates, the latter having been observed on top of structure I hydrates in the K-2 mud volcano.