HR: 1330h
AN: H42F-1151    [PDF]
TI: Fluid-rock interaction at Las Ca\~{n}adas aquifer, Tenerife, Canary Islands
AU: * Marrero, R
EM: rayco@iter.rcanaria.es
AF: Environmental Research Division, ITER, Granadilla, Tenerife, Granadilla, 38611 Spain
AU: L\'{o}pez, D
EM:
AF: Department of Geological Scienses,, Ohio University, Athens, 45701 United States
AU: P\'{e}rez, N
EM:
AF: Environmental Research Division, ITER, Granadilla, Tenerife, Granadilla, 38611 Spain
AB: Las Ca\~{n}adas caldera, located at the central part of Tenerife, Canary Islands, is a large volcanic depression (16 $\times$ 9 km). The caldera is opened to the sea at the north side and filled by continuous layers of lava flows and fall deposits. These volcanic deposits form a good hydrogeological trap which is the largest ground water reserve of the island. In comparison, the basement of the caldera has low permeability. Numerous galleries (horizontal drains) intercept the Las Ca\~{n}adas aquifer. During the last century, this aquifer has been overexploited depleting the water table as well as the water quality. The Teide-Pico Viejo volcanic complex is located at the margin of the caldera. The ascent of deep magmatic gases (e.g. $CO_{2}$) confers aggressiveness to the waters causing rock dissolution and alteration. The aim of this work is to study water-rock interactions in Las Ca\~{n}adas aquifer. Chemical diagrams showing the relative composition of Mg, Ca, Na and K as described by Giggenbach (1988) indicate that the waters discharged by the galleries correspond to the process of rock dissolution and evolution towards full rock-fluid equilibrium. The lower contents in Ca and Mg are found in the galleries which reach more deeply the north flank of the Teide Volcano, suggesting mineral precipitation and heating in this zone. Geochemical modeling of fluid-rock interactions using Chiller (Reed and Spycher, 1984) show that the gases discharged at Teide summit cannot generate the water compositions observed at Las Ca\~{n}adas. These gases represent the separated phase of a condensation process within the volcanic edifice. Modeling of the gas-enriched Las Ca\~{n}adas waters from the recharge zone with phonolitic rocks from the caldera show that the galleries waters correspond to the dissolution of 1 to 7 g of rock$\div$liter of water and a relatively shallow circulation. The simulations suggest that waters have not encountered the $\sim$ $250\deg$C temperature region suggested by the gas geothermometers. This behavior suggests that the heat source in this system is deep as suggested by geophysical studies.
UR: http://iter.es
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2003 Fall Meeting