Pyroclastic flows from Alpehué have been dated to 2,960-2,780 years before present. The Alpehué unit was emplaced during a large Plinian eruption, which generated a eruption column and ejected about of pumice falls; layers of tephra identified in a bog of South Georgia away as well as in an ice core at Siple Dome in Antarctica and dated to about 980 BCE may be a product of the Alpehué eruption. Alpehué tephra has been used as a tephrochronology tool. Pyroclastic flows from the eruption melted the caldera ice sheet, forming lahars that propagated northwest away from Sollipulli. Ignimbrites from this eruption cover surfaces of at least around Sollipulli, their volume has been estimated to be about . They are brown to grey in colour and unwelded with the exception of part of the ignimbrite that is emplaced within the Alpehué crater. The eruption reached a level of 5 on the volcanic explosivity index.