Geodetic methods for detecting volcanic unrest: a theoretical approach

In this paper we study the application of different geodetic techniques to volcanic activity monitoring, using theoretical analysis. This methodology is very useful for obtaining an idea of the most appropriate land efficient ) monitoring method, mainly when there are no records of geodetic changes p revious to volcanic activity. The analysis takes into account the crustal s tructure of the area, its geology, and its known volcanic activity to estim ate the de-formation and gravity changes that might precede eruptions. The deformation model used includes the existing gravity field and vertical cha nges in the crustal properties. Both factors can have a considerable effect on computed deformation and gravity changes. Topography should be consider ed when there is a steep slope (greater than 10 degrees). The case study of Teide stratovolcano (Tenerife, Canary Islands), for which no deformation o r gravity changes are available, is used as a test. To avoid considering to pography, we worked at the lowest level of Las Canadas and examined a small er area than the whole caldera or island. Therefore, the results are only a first approach to the most adequate geodetic monitoring system. The method ology can also be applied to active areas where volcanic risk is not associ ated with a stratovolcano but instead with monogenetic scattered centers, e specially when sites must be chosen in terms of detection efficiency or exi sting facilities. The Canary Islands provide a good example of this type of active volcanic areas, and we apply our model to the island of Lanzarote t o evaluate the efficiency of the monitoring system installed at the existin g geodynamic station. On this island togography is not important. The resul ts of our study show clearly that the most appropriate geodetic volcano mon itoring system is not the same for all different volcanic zones and types, and the particular properties of each volcano/zone. must be taken into acco unt when designing each system.