Hualca Hualca is a 6,025-metre-high (19,767 ft) extinct volcano in the Andes of southern Peru. It is part of the Peruvian segment of the Central Volcanic Zone, one of several volcanic belts in the Andes. It lies about 70 kilometres (43 mi) northwest of Arequipa and is part of a north–south chain that includes the volcanoes Ampato and Sabancaya, the latter of which has been active historically. The mountain is important to the towns of Cabanaconde and Pinchollo, whose inhabitants viewed it as their source of water and used to carry out religious ceremonies to guarantee continuing water supply.

Hualca Hualca features a wide amphitheatre-like structure on the northern flank, created by a gigantic landslide during the Pleistocene. After the collapse, renewed volcanic activity built a new summit and several lava dome complexes within the collapse scar. After cessation of volcanic activity, glaciers eroded the volcano and formed multiple moraines. The present-day volcano is covered by glaciers, and during the last glacial maximum, glaciers advanced to low altitudes. There are hot springs and geysers north of the mountain, and the magma chambers of Sabancaya are located below Hualca Hualca.

Hualca Hualca is in the Caylloma Province of southern Peru, 70 kilometres (43 mi) northwest from Arequipa. Directly north of the volcano is the Colca Valley, an important tourism destination and agricultural area which has been settled since before Inca times. The towns of Cabanaconde and Pinchollo lie at the northern foot of Hualca Hualca; other settlements in the area are Madrigal, Lari, Maca, Achoma and Ichupampa. Several roads run around the volcano; one goes to the Hornillo viewpoint on the northeastern flank. Canals and dams collect water flowing from the mountain and convey it to fields at Cabanaconde and west of Sabancaya volcano. Other infrastructure on the mountain consists of homesteads mainly on its western flank and equipment of Peru's volcano monitoring service. Hualca Hualca can be climbed in a few days from Pinchollo by the north side, and is not considered challenging from a mountaineering perspective.

Hualca Hualca is a heavily eroded stratovolcano. A 14-kilometre-wide (8.7 mi) ragged semicircular ridge surrounds a 1,600-metre-deep (5,200 ft) amphitheatre with 700–1,000-metre-high (2,300–3,300 ft) cliffs; the 6,025-metre-high (19,767 ft) summit is on the southeastern part of the ridge. The amphitheatre opens north to the Colca Valley at an elevation of about 3,500 metres (11,500 ft). The scar was formed by a gigantic landslide that removed a volume of about 1.3 cubic kilometres (0.31 cu mi) from the edifice. Within the scar are several volcanic structures consisting of lava domes and lava flows, including 5,310-metre-high (17,420 ft) Nevado de Puye close to the summit, 5,190-metre-high (17,030 ft) Cerro Ahuashune farther west, and a 4,400-metre-high (14,400 ft) volcanic structure with the "Mirador Cruz del Condor" viewpoint to the north. Between Ahuashune and Mirador Cruz del Condor is a lake, and there are cold water springs. Valleys, such as the Huayuray valley due north of the summit and the Hualca-Hualca at the western margin of the amphitheatre, run through the amphitheatre heading north; they are used as irrigation water sources.

The mountain towers above the Colca Valley with irregular slopes. Elsewhere around the perimeter of Hualca Hualca, it and its neighbours rise about 2 kilometres (1.2 mi) above the Altiplano highland. Valleys on its outer slopes include the Mollebaya to the east, Pujro Huayjo to the southwest and Mucurca to the west. Moraines and glacial sediments cover the western slopes of Hualca Hualca, while lava flows of Sabancaya onlap the southern slopes. The edifice is 25 kilometres (16 mi) wide. Surfaces on the volcano are frequently covered by debris and moraine rocks, and Sabancaya has deposited tephra on the land south of Hualca Hualca. At the western foot of Hualca Hualca is Laguna Mucurca.

Volcanism in South America occurs in four distinct zones along its western coast in the Andes: the Northern Volcanic Zone, the Central Volcanic Zone (CVZ), the Southern Volcanic Zone and the Austral Volcanic Zone. The volcanoes of Peru and the Central Andes belong to the CVZ, which includes more than 50 calderas, composite volcanoes and monogenetic volcanic fields that erupted during the Quaternary. In Peru they include (from north to south) Auquihuato, Sara Sara, Coropuna, Mismi, Hualca Hualca-Sabancaya-Ampato, Chachani, Misti, Ubinas, Huaynaputina, Ticsani, Tutupaca, Yucamane and Casiri. The volcanism of the Central Andes is caused by the northeastward subduction of the Nazca Plate under the South American Plate, at a rate of about 4.6 centimetres per year (1.8 in/year).

Hualca Hualca and its neighbours to the south Sabancaya and Ampato form the Ampato volcanic complex. With an area of about 630 square kilometres (240 sq mi) it is one of the largest volcanic complexes of the Central Andes. Hualca Hualca is the oldest volcano of the complex. Ampato began erupting 450,000 years ago and formed a summit dome 20,000–10,000 years ago. Sabancaya has been active during the Holocene and in historical time, and is the second-most active volcano in Peru.

The rock formations in the area are subdivided into five groups: the Paleozoic intrusive rocks that crop out in the Colca Valley; sedimentary rocks of the Yura Group in the Colca Valley; Oligocene–Miocene volcanic rocks of the Terraza Group, north of the Colca River; Pliocene ignimbrites of the Barroso Group around Hualca Hualca; and the Quaternary sediments of the Colca Group in the collapse scar of the volcano and the Colca Valley. Rocks in the Ampato volcanic complex form the Ampato Group. Some sources regard Hualca Hualca or the entire Ampato volcanic complex as members of the Barroso Group. The rocks underlying the Ampato volcanic complex consist of the Sencca Formation, which is between 1.4 and 4.9 million years old.