Ages of 5.3 to 1.6 mya have been estimated via potassium-argon dating of the andesite lavas and subvolcanic rocks. An age of 5.3±1.9 mya on lavas in the northern part of the volcanic complex is the oldest obtained date. Other dating has resulted in ages of 3.9±1.3 mya for Pico Laco's dome, 3.8±0.9 mya for lavas beneath San Vicente Bayo, 3.7±0.9 mya for a lava front next to Laco Norte, 2.6±0.6 for Crystales Grandes, 2.1±0.4 for Hueso Chico, and 1.6±0.5 for Volcano 5009. Cordon de Puntas Negras has younger dates. Another date from Pico Laco is 2.0±0.3 mya; one study suggested four separate episodes of volcano development. Later alteration included hydrothermal alteration and glacial erosion; the former has left bleached rocks and exhalation deposits. Some minor metasomatic alteration occurred at the contact sites between andesites and iron-containing rocks.:684 Hydrothermal alteration has also been described for lower portions of the volcanic pile and probably occurred because of gases escaping from intruded magma. Moraines found west of El Laco were generated by glaciation both on El Laco and Puntas Negras. Surface exposure dating has indicated ages of 226 and 287 ka for some ice-affected lavas. Further, andesitic volcanism in neighbouring volcanoes has blanketed El Laco.:684 Reports exist of continuing fumarolic activity and hot springs with the deposition of clay and other minerals.