Monitoring crustal movements and sea level in Lanzarote

Abstract

The Institute of Astronomy and Geodesy is measuring sea level variations in Lanzarote Island by two automated tide gauges of precision since 1993. In order to obtain "real" sea level variations a permanent GPS station has been installed near the tide gauges. The goal of this GPS station is to measurement vertical crustal movements in order to obtain absolute sea level variations removing these movements from tide gauge data. A vertical tie with high accuracy between the reference point of the pillar where the GPS antenna is installed and the tide gauges bench marks is absolutely necessary. We have carried out this altimetric link yearly since year 2000. Methods of repeated geometric and trigonometric levelling of very short tracts have been used due to the great level difference existent. The control of the local stability of the pillar where the GPS antenna has been established, is carried out by a micro-geodetic control network building around it. This network of 13 benchmarks has been regularly observed by classic and GPS geodetic techniques in years 2000, 2001, 2002, 2003 and 2004. The data of these campaigns have been processed by different types of adjustments in the same reference system. The precision of the measurements and the reliability of the networks have been calculated. In this work the results obtained, the evaluation of the altimetric links and levelling campaigns, and the comparison of the levels of different measurements are presented.