At first, it was assumed that caldera collapse took place during the 1600 event, as accounts of the eruption stated that the volcano was obliterated to its foundation; later investigation suggested otherwise. Normally very large volcanic eruptions are accompanied by the formation of a caldera, but exceptions do exist. This might reflect either the regional tectonics or the absence of a shallow magma chamber, which prevented the collapse of the chamber from reaching the surface; most of the magma erupted in 1600 originated at of depth. Some collapse structures did nevertheless form at Huaynaputina, in the form of two not readily recognizable circular areas within the amphitheatre and around the three vents, probably when the magmatic system depressurized during the eruption. Additionally, part of the northern flank of the amphitheatre collapsed during the eruption, with some of the debris falling into the Río Tambo canyon.