Geology of the Ahuachapan Area, Western El Salvador, Central America

Abstract

The Ahuachapan area lies in Western El Salvador between the town of Ahuachapan and the Guatemalan border. It is within an E-W trending graben which transgresses the entire republic and which is believed to have formed from the collapse of a geanticline at the end of the Pliocene. Quaternary volcanism along the margins and within the graben largely filled it with volcanic debris, consisting of flat-lying tuffs, agglomerates and lavas. The sequence in the area, beginning with the oldest, is: ancient agglomerate, laminar andesite, massive andesite, blue ignimbrite, gray agglomerate, lower brown tuff, pink ignimbrite, gray ignimbrite, pumice and upper brown tuff. The thickness of these rocks attains a maximum of 425 meters. The strata are disrupted by a number of northeast-trending normal faults. Volcanic activity is still in progress at various centers in the region.