Quilotoa is a water-filled crater lake and the most western volcano in the Ecuadorian Andes. The 3-kilometre (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. The caldera has since accumulated a 250-metre-deep (820 ft) crater lake, which has a greenish color as a result of dissolved minerals. Fumaroles are found on the lake floor and hot springs occur on the eastern flank of the volcano.