 Processes such as fractional crystallization, magma mixing and the absorption of crustal material by developing magmas have been invoked to explain the formation of the magmas of both Ampato and Sabancaya.Estimating the rate of magma production at Ampato is difficult owing to the uncertainties in determining the volume of the edifice and the duration of repose times between eruptions; on average it appears to be .This rate does not consider "spurt"-like behaviour; volcano growth in fits and spurts has been observed at many other volcanic arc volcanoes.