Quilotoa is a water filled caldera and the most western volcano in the ecuadorian andes the 3 kilometers 2 mi wide caldera was formed by the collapse of this dacite volcano following a catastrophic vei 6 eruption about 800 years ago which produced pyroclastic flows and lahars that reached the pacific ocean and spread an airborne deposit of volcanic ash throughout the northern andes this last eruption followed a dormancy period of 14 000 years and is known as the 1280 plinian eruption