SELF-POTENTIAL SIGNALS CAUSED BY ERUPTIONS OF THE GALERAS VOLCANO-COLOMBIA.

The National Institute of Geology and Mining, INGEOMINAS -- Colombia, and the Federal Institute for Geosciences and Natural Resources, BGR -- Germany, perform since 1997 as a joint venture multi-parameter measurements at the Galeras volcano, in the southwest of Colombia. Since the end of 1998 the Multi-parameter Station at Galeras (Estación Multiparámetro del Galeras -- EMG) includes the continuous monitoring of electromagnetic variations. The electromagnetic (EM) station is located at the north-eastern foot walls of the central cone inside the caldera. During almost six years of electromagnetic monitoring, the data did not show significant variations of the electromagnetic field, which could be related to the volcanic activity. In July 2004 a new active period of Galeras began with two strong ash emissions. During both emissions strong self potential-(SP) signals were recorded lasting for several hours. The present paper will present the data which could give some indications on the movements of liquids during ash emissions. [ABSTRACT FROM AUTHOR]