Scars at elevations of on the edifice have been the origin of mudflows ; the largest is known as Estación flow and covers much of the southern and western foot of San Pedro to distances of ; the debris apron reaches the Loa River and San Pedro River . These mudflows occurred between 110,000 – 36,000 years ago and they filled the river bed of the Loa , while the impact on the San Pedro River was much more minor . Hot avalanche deposits or pyroclastic flows are also found on the volcano ; the largest of which covers large parts of the edifice and has a total volume of approximately . These deposits contain prismatic jointed blocks and poorly sorted pumice , with their thickness ranging from a thick layer to scattered rocks . Their formation was probably due to the steep incline of San Pedro 's slopes which tended to destabilize lava bodies high on the edifice , similar to regular landslides . At least one Plinian fall deposit is known from San Pedro ; the size of the deposit indicates that it was as large as the AD 79 eruption of Vesuvius in Italy . This Plinian eruption was accompanied by the formation of an ignimbrite that covers much of the southern , southwestern and western slopes of San Pedro and reaches thicknesses of . It has a volume of and is called the El Encanto ignimbrite . There is evidence of a large sector collapse on San Pedro , which removed the northwestern flank of the volcano and formed a large debris avalanche deposit . This avalanche deposit covers a surface area of and its front is high in the Pampa de la Avestruz . The debris flow formed by the sector collapse does not have many of the typical hummock-like hills of volcanic sector collapse deposits and instead features grooves and radial ridges . Such flank collapse occurred notably on Mount St. Helens during its eruption in 1980 . A high scarp west of the eastern summit was left by the collapse of San Pedro ; otherwise much of the evidence was buried by later volcanic activity . As with the mudflows , the steep slopes of San Pedro probably facilitated the onset of the sector collapse , which descended over an elevation difference of about
AD 79 eruption
Eruption of Mount Vesuvius in 79
San Pedro (Chile volcano)