Hualca Hualca is a 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 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.
Geography and geomorphology
Hualca Hualca is in the Caylloma Province of southern Peru, 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 ragged semicircular ridge surrounds a amphitheatre with cliffs; the summit is on the southeastern part of the ridge. The amphitheatre opens north to the Colca Valley at an elevation of about . The scar was formed by a gigantic landslide that removed a volume of about from the edifice. Within the scar are several volcanic structures consisting of lava domes and lava flows, including Nevado de Puye close to the summit, Cerro Ahuashune farther west, and a 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 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 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.
Geology
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 .
Hualca Hualca and its neighbours to the south Sabancaya and Ampato form the Ampato volcanic complex. With an area of about 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.
Most of the volcano is formed by lava flows, which are stacked more than high. Numerous fault zones cross the northern sector of Hualca Hualca; from north to south these are the Chachas-Cabanaconde-Patapampa Fault System, Solarpampa-Puye Puye-Pillo Fault System and Pungo-Hornillo Fault System. Many show evidence of neotectonic activity, and some have produced earthquakes in recent times or undergone aseismic creep. There are three clusters of shallow seismic activity at Hualca Hualca, where volcano-tectonic processes cause earthquakes. Spontaneous potential analysis has found evidence of two buried structures in the northern part of Hualca Hualca, which might be buried calderas. Magnetotelluric analysis has identified various zones of high and low electrical conductivity under Hualca Hualca.
Composition
The composition of Hualca Hualca's rocks ranges from andesite-trachyandesite to dacite-trachydacite, and define a potassium-rich calc-alkaline rock suite similar to that of the other volcanoes in the Ampato volcanic complex. Phenocrysts consist of amphibole, biotite, plagioclase and pyroxene. The magmas that built Hualca Hualca formed when the mantle wedge, metasomatised during subduction, melted; the magmas underwent fractional crystallization before erupting at the surface. Minor geochemical differences between the rocks of the three Ampato complex volcanoes may reflect differences in magma generation processes. Hydrothermal manifestations are often accompanied by the deposition of minerals; for example, geysers at Pinchollo have emplaced various sulfate minerals.
Climate and life
Above an elevation of , annual temperatures range from . There is no temperature data from Hualca Hualca, but data from Chachani implies stable temperatures year-round. Annual precipitation is about , decreasing at lower elevations. During December–March, the Intertropical Convergence Zone reaches the mountain and draws moisture from the Amazon, as part of the South American Summer Monsoon (Pacific Ocean-derived moisture is trapped beneath a temperature inversion at an elevation of and cannot reach Hualca Hualca). This is the wet season, during which most of the annual precipitation falls. April to November is the dry season. The mountain is snow-covered year-round. Precipitation on Hualca Hualca may constitute a source of groundwater and recharge the hydrothermal system. El Niño-Southern Oscillation events cause temperatures to increase and precipitation to decrease.
Below an elevation of there is herbaceous vegetation, dominated by Festuca and Stipa but also featuring cacti, Peruvian feather grass and other pioneer plant species. Above that altitude, cushion plants such as Azorella compacta replace the herbs until elevation, where most vegetation disappears except for lichens and mosses. Peat bogs grow in valleys on the southern side of Hualca Hualca in places where precipitation water and meltwater accumulate. They are classified as "bofedales". Between elevations of , the land is used for pasture of alpaca, cattle, llama and sheep. Animals include insects and birds like the Andean condor.
During the Late Pleistocene, temperatures in the Peruvian Andes were up to lower, and episodes of increased precipitation led to the formation of giant lakes in the Altiplano ("Lake Tauca") and (possibly) to the growth of glaciers. In recent decades, temperatures have been increasing at a rate of about per decade. The warming has been blamed for the drying of springs and more irregular meltwater flows.
Glaciation
Past glaciations have left moraines down to altitudes of around the entire volcano. Moraine tongues form complex and well-preserved structures; they are particularly well-developed on the eastern flank of the volcano and in the Huayuray valley, where they reach lengths of and heights of . Other glacial landforms are striated/polished surfaces, glacial overdeepenings, glacial valleys, inactive cirques and outwash plains. During the Last Glacial Maximum, the Ampato volcanoes featured an ice cap with an area of about .
The timing of glaciation in the Peruvian Andes is complex, with evidence of glacial advances at Hualca Hualca both during the last glacial maximum and the "Tauca" and "Coipasa" periods. The advances produced several generations of moraines, and eroded older moraines. Cosmogenic isotope dating has yielded ages of 17,000–16,000 and 12,000 years ago for glacial advances at Hualca Hualca, implying that glacier retreat at Hualca Hualca occurred later than at other Central Andean volcanoes. Final glacier retreat occurred at the beginning of the Holocene; two advances in the Huayuray valley have been attributed to the Little Ice Age. The moraines at Hualca Hualca have been used to reconstruct equilibrium line altitude and temperature changes during the glaciation.
Glaciers persist around the summit in active cirques, and there is permanent snow cover on the subsidiary peaks. There are crevasses and seracs. Rock glaciers occur in numerous locations around the mountain. The glaciers are retreating; the Huayuray glacier lost half its surface area between 1955 and 2000 and a further near-halving occurred between 2000 and 2008; the Ampato volcanic complex might lose all of its glaciers by 2065, threatening water supplies in the region.
Eruption history
Hualca Hualca was active during the Pliocene and Pleistocene. It formed in several stages, with initial activity producing andesitic to dacitic-trachydacitic lava flows that build the main edifice and crop out in the collapse scar. Dates ranging from 1.07±0.3 million years ago to 610,000±10,000 years ago have been obtained from this unit. Hydrothermal alteration and volcanic activity weakened the mountain until collapse, which did not occur during an eruption but may have been triggered by an earthquake. The first collapse removed the central sector of the volcano; subsequent activity rebuilt the summit and spilled lava flows over the northeastern flank without filling in the entire scar.