Hidden tuff rings: a new target for water resource prospecting in volcanicrocks. The case of the well field of Vourzac (Deves, French Massif Central).

Several independent and abundant springs are located in the valley of Vourz ac. The geological context is a phreatomagmatic tuff-ring overlaid by a Str ombolian cone, the two being interbedded in the Deves basaltic plateau. The tuff ring acts as a radial drainpipe system, which collects water at its p eriphery and drives it to the central part of the ring. The springs are at the intersection of the drainpipe with the talweg of the Vourzac valley. Th e basaltic plateaus, frequently associated with maars, could often contain such hidden tuff rings. Their detection could be useful to locate and explo it confined aquifers. (C) 2001 Academic des sciences / Editions scientifiqu es et medicales Elsevier SAS.