New geodetic monitoring system in the volcanic island of Tenerife, Canaries, Spain. Combination of InSAR and GPS techniques

Even though volcanic activity in Tenerife is characterized by the fact that eruptions do not normally occur more than once in the same volcanic edifice, geodetic monitoring has mainly focused on the Las Cañadas Caldera, where a geodetic micronetwork and a levelling profile are located. A sensitivity test of this geodetic network showed a clear need to extend it to cover the full island for volcano monitoring purposes. This conclusion, together with the detection of two unexpected movements on the island using InSAR that were beyond the scope of the traditional geodetic network, prompted the authors to design and observe a GPS network covering the whole of Tenerife. The network was monitored in August 2000. The results obtained were accurate to 1 cm, and confirm the deformation in the Pinar de Chı́o zone, but are not definitive enough to confirm the displacements detected to the south of the village of Garachico. Furthermore, new cases of possible subsidence have been detected in areas where InSAR could not be used to measure deformation due to low coherence. Future observations will be necessary for further validation and to study the time evolution of the displacements, and supplementary research must be conducted to determine the possible causes, in particular if they are connected with the water pumping operations performed on the island. One important result is that a new geodetic monitoring system based on two complementary techniques, InSAR and GPS, has been set up on Tenerife island. This is the first time that the whole surface of any of the volcanic Canary Islands has been covered with a single network. This research has displayed the need for further similar studies in the Canary Islands, at least on the islands which pose a greater risk of volcanic reactivation.