pyroclastic flow activity, and lava domes in the summit region are of Pleistocene age. The long-term growth rate of Ojos del Salado amounts to . Radiometric dating has yielded ages of 1.53 ± 0.13, 1.2 ± 0.3 million and less than one million years ago for rocks in the northwestern part of Ojos del Salado, 1.08 ± 0.09 million years for flows underlying the summit, 1.08 ± 0.04 million years for the northern flank of Ojos del Salado, 700,000±50,000 for its western flank, 450,000±60,000 for El Muerto, 340,000 ± 190,000 years for the summit rocks, and 230,000±40,000 years for El Fraile. Lava flows and a lava dome on the northern flank have yielded ages of 100,000 ± 17,000 and 35,000 years, respectively. The "El Quemado Ignimbrite" may be either 200,000 or less than 50,000 years old. The youngest dates reported are 30,000 years ago. Holocene and historical activity The volcano produced lava flows during the Holocene, which cover an area of , as well as pumice deposits at Laguna Verde and elongated fractures in the summit region. A rhyodacitic eruption was dated with tephrochronology to have occurred 750 ± 250 CE. Many volcanic rocks have a fresh appearance but there is no clear evidence of recent activity. There are no confirmed historical eruptions and the volcano is presently inactive. In November 1993, observers witnessed ash and steam columns on two separate days but no deformation of the volcano was observed by satellites during this occasion. An ash cloud observed on the June 13, 2015, and which led to a warnings about volcanic ash to aircraft turned out to be wind-blown volcanic ash in the Fiambala valley. Hazards There is no information on volcanic hazards at Ojos del Salado and volcanic hazards in the Central Volcanic Zone are poorly reconnoitered, but a 2018 presentation at the University of Auckland ranked it 14th of 38 Argentine volcanoes and the Chilean geological agency SERNAGEOMIN 75th out of 92, thus as a very low risk volcano. The latter has published hazard maps for the Chilean part of the volcano. Future eruptions would most likely produce lava domes, lava flows and minor explosive activity, and the presence of ice on the mountain makes it a potential source for lahars. Effects would most likely be limited to the direct surroundings of the volcano, such as highway . Fumarolic activity There are fumaroles that emit sulfurous smokes.