Pyroclastic flows ran down the slopes of the volcano, entered the Río Tambo valley and formed dams on the river, probably mainly at the mouth of the Quebrada Aguas Blancas; one of the two dammed lakes was about long. When the dams failed, the lakes released hot water with floating pumice and debris down the Río Tambo. The deposits permanently altered the course of the river. The volume of the ignimbrites has been estimated to be about , excluding the ash that was erupted during this stage. The pyroclastic flows along with pumice falls covered an area of about .