Spatial and temporal magnetic anomalies of Colima volcano, western Mexico

Abstract

Colima volcano has erupted frequently in historic times. Present activity includes the episodic growth of a lava dome within the summit crater. Total magnetic field at stations spaced every 0.5 km along a 35 km long transect was measured across the eastern flank and the summit, between Atenquique and El Playón, from April 27, 1995 to May 16, 1996. Three distinct sectors were recognized. (1) The Nevado de Colima debris avalanche and volcanic conglomerates of the Atenquique Formation, between stations 10 and 23 km, characterized by low-amplitude, low-frequency anomalies and no temporal changes. (2) Andesitic lavas and breccias between stations 23 and 35 km, characterized by low-frequency anomalies with superimposed high-frequency anomalies of varying amplitude, and low-amplitude temporal changes. (3) Between stations 35 and 45 km, characterized by low-frequency, high-amplitude anomalies and large-amplitude temporal variations, across the summit and avalanche caldera, in andesitic lavas and breccias. Modeling indicates that source bodies may extend several hundred meters deep, depending on the variation of magnetic properties with depth. Temporal variations in the magnetization within the volcano may be caused by temperature changes. Magnetization/demagnetization beneath the summit may be associated with the eruptive activity. Potential mechanisms for heating/cooling processes may include magma movement, an active hydrothermal system with strong fumarolic activity and groundwater interactions. A 1500-2500 nT composite magnetic low was found at the present cone summit and the avalanche caldera. Temporal changes superimposed over the high-amplitude, low-frequency magnetic anomalies, are associated with the ongoing volcanic activity.