Sangay (also known as Macas, Sanagay, or Sangai) is an active stratovolcano in central Ecuador. It is the most active volcano in Ecuador, despite erupting only four times in recorded history, because the eruption that started in 1934 is still ongoing. It exhibits mostly strombolian activity. Geologically, Sangay marks the southern boundary of the Northern Volcanic Zone, and its position straddling two major pieces of crust accounts for its high level of activity. Sangay's approximately 500,000-year-old history is one of instability; two previous versions of the mountain were destroyed in massive flank collapses, evidence of which still litters its surroundings today.