A number of other volcanoes are found in the region, such as Aguas Calientes, Cordon de Puntas Negras and the giant La Pacana caldera.

[16] Volcanic centres include calderas and associated large ignimbrites, lava domes and stratovolcanoes;[22] among the better-researched volcanoes are Galan, Nevados de Payachata, Ollague, Purico Complex, San Pedro–San Pablo, La Pacana, Tata Sabaya and Tumisa.

[31] Also fumarolically active are: Sabancaya, El Misti, Ubinas, Tacora, Isluga, Irruputuncu, Olca, Ollague, San Pedro, Putana and Lastarria.

[27] The andesitic-dacitic Aguas Calientes is located 5 kilometres (3.1 mi) east of Lascar; it may have formed a lava flow close to the summit during the Holocene.

[41] Miocene–Quaternary volcanic centres in the neighbourhood include Cerro Negro in the north, Acamarachi northeast, Tumisa southwest, and the Cordon de Puntas Negras in the south,[42] which Lascar is sometimes considered to be part of.

[43] Tumisa, to the south of Lascar, was active between 2.5 and 0.4 million years ago,[44] is composed of dacite and surrounded by pyroclastic flow deposits.

[45] These lava domes are about 5 million years old,[52] and are composed of dacite and smaller amounts of pyroxene andesite,[50] along with rhyolite and visible minerals including biotite and hornblende.

[45] An eruption 16,700 years ago from Corona deposited tephra containing biotite and quartz in Laguna Lejía and generated a rhyodacitic lava flow.

The large eruption gave rise to a pyroclastic flow that extended 27 kilometres (17 mi) westward and contained breccia and various magmas.

[72] Traces of glacial action are found on the older parts of Lascar at altitudes above 4,600 metres (15,100 ft) and include meltwater gorges, striated rock surfaces, and U-shaped valleys.

Other minerals include anhydrite,[58] augite, plagioclase[34] which is also the dominant phenocryst phase in Lascar rocks,[80] apatite, ilmenite, magnetite, olivine, orthopyroxene, phyrrotite, quartz, rhyolite in the groundmass, and spinel in inclusions.

[71] Additional component minerals found at Lascar include anorthite, augite bordering on diopside, bronzite, fassaite, forsterite, hypersthene, pigeonite and more.

Minerals encountered in xenoliths include andradite, anhydrite, anorthite, apatite, biotite, calcite, diopside, fassaite, garnet, gypsum, ilmenite, magnetite, monazite, orthopyroxene, perovskite, plagioclase, prehnite, quartz, sphene, thorite, wilkeite, wollastonite and zircon.

[97] Lascar emits plumes of gas and white clouds of condensed water vapor,[30] mostly through many hundreds of fumarolic vents, which are chiefly located in the active crater.

[108] Trace elements include arsenic, boron and titanium, with smaller amounts of barium, chromium, copper, lead, strontium and zinc.

[116][117] In 2005, Lascar was the third-largest source of volcanic sulfur dioxide in the world among continuously active volcanoes, behind Etna in Italy and Bagana in Papua-New Guinea.

[135] Lascar rests atop the Atana ignimbrite, a rhyodacitic sheet which was erupted by La Pacana caldera 4.5–3.7 million years ago.

The western edifice generated a complex of lava domes (stage II),[54] which was probably surrounded by a horseshoe-shaped crater open to the west.

[145] An alternative theory posits that the Piedras Grandes unit formed when an ice cap on Lascar interacted with a block and ash flow erupted by Aguas Calientes.

[71] A major Plinian eruption occurred 26,450 ± 500 years ago,[147] releasing 10–15 cubic kilometres (2.4–3.6 cu mi) of ejecta, both volcanic ash and pyroclastic flows.

The deposits left contain both andesite and dacite,[54] with phenocrysts consisting of apatite, augite, biotite, iron-titanium oxides, orthopyroxene and plagioclase in a rhyolite matrix.

[91] The Soncor deposit was subsequently affected by glaciation[71] and the stage I edifice by a debris avalanche,[40] which was radiocarbon dated at 22,310 +2,700/−2000 years ago in the Quebrada de Chaile.

[166] The deposits left by this erosional period contain no clear evidence of stage III activity; indeed Lascar was probably inactive between 14,000 and 10,500 years ago.

However, an eruption of the Cerro Corona lava dome occurred during this period,[64] and activity of stage III did not commence earlier than 22,300 years ago.

[139] Landsat images taken during this time indicate that a lava lake may have existed in the central crater,[173] generating a plume of volcanic gases and, in September 1986, a vulcanian eruption happened and dropped ash in Salta, Argentina.

[46] Noticeable erosion occurred in the areas over which pyroclastic flows had passed, forming abrasion surfaces and removing loose detritus from the ground.

[184] Ash fall in Tucuman and Santiago del Estero was intense enough that traffic ground to a halt,[208] and air travel was impacted internationally.

[252] Past eruptions caused ash fall in Argentina and disruption of air travel[254] and could have major effects in the Salta Province in case of renewed activity.

[255] In 1982,[256] the town of Talabre was moved for safety reasons[53] stemming from flooding and volcanic activity,[256] and ballistic blocks ejected by the volcano are a threat to mountaineers and scientists working on Lascar.

[262] Volcanic activity at Lascar affects neighbouring ecosystems such as the Aguas Calientes crater lake and Laguna Lejia; flamingos disappeared from the latter after the 1993 eruption and did not return until 2007.