Cerro Porquesa, Mountain summit in Tarapacá Region, Chile.

Cerro Porquesa is a rhyodacite lava dome in the Andes, about 800 metres (2,600 ft) above its base, with an oval outline of 1.5 by 3 kilometres (0.93 by 1.86 mi). It was formed in at least three eruption stages, each contributing two or three lobes, and is accompanied by block-and-ash flows and lava flows. Two volcanic cones have been reported. The summit reaches 5,155 metres (16,913 ft) above sea level.

Cerro Porquesa is a rhyodacite lava dome of Pliocene/Pleistocene age, built in at least three eruption stages, each adding about two or three lobes. Three dates from the domes give 0.63±0.63 mya, less than 1 mya and 1.1±0.4 mya. A rhyolitic ignimbrite in a southern valley, about 2 m thick, was dated 0.73±0.16 and 0.63 +0.92/-0.63 mya by potassium-argon dating on biotite. The complex was probably active after 280,000 years ago but not in the Holocene, and faults offset some ignimbrites.

The name Cerro Porquesa comes from Aymara. The dome sits in the Pica gap, a stretch of the Andes where no volcanic activity younger than 2 million years is found and where lead isotope ratios in the rocks become less radiogenic from south to north; Porquesa has intermediate ratios.

The summit stands at 5,155 m, about 800 m above its base, in the largely uninhabited Pica gap of Tarapacá, roughly 1,500 km north of Santiago. Approach from the Salar del Huasco side, where the Quebrada de Piga rises on the dome's slopes. The terrain is open bushland with no settlements nearby, so carry all supplies and allow for acclimatisation.

The Quebrada de Piga, a ravine that feeds into the Salar del Huasco, begins on the slopes of Cerro Porquesa. The dome's rhyolitic ignimbrite, about 2 metres thick, fills a valley on the south side of the complex and has been dated by potassium-argon analysis of biotite to roughly 0.63 to 0.73 million years ago.