Eruption History

The origin and evolution of the Ilopango caldera is discussed by Williams and Meyer-Abich (1953 and 1955), however a detailed description of the Islas Quemadas dome extrusion in 1879-1880 is found in Meyer-Abich (1956).

On December 20-21st, 1879, a heightened seismic activity, including 600-800 tremors recorded until December 31st, marked the beginning of dome extrusion.On this date seismic activity ceased. The level of the lake rose to a maximum of 1.22 m from normal on January 11th 1880.

The outflow river, Desague increased its discharge, eroding up to 10 m of its original surface resulting in a continual lowering of the level of the lake. On January 20th the first spines of the dome reached the lake surface, which was preceded and followed by large steam explosions, producing a 500-700 m high steam column. The level of the lake continued to decrease, reaching a height 9.27 m lower than normal on March 6th. Activity ended at the end of the month.

Presently there are only five small islands that rise a few meters above lake level. No activity is evident at the surface, however local fishermen mention that every now and then fish die in large quantities and a sulfuric smell is noticeable.