from the summit. In 1997, a surface area of was reported. Between 1986 and 2016 the mountain lost over three quarters of its ice cap, and the remaining ice field broke up into several ice bodies. Moraines at elevations of above sea level testify to the occurrence of more extensive glaciation during the last ice age between 25,000 and 17,000 years before present; these moraines have diverted some lava flows. Younger moraines are found at higher altitudes, above sea level, and may have formed between 13,000 and 10,000 years ago, shortly after the beginning of the Holocene. Earthquake activity has allowed the identification of a candidate magma reservoir beneath Pampa Sepina northeast of Sabancaya about away from the summit. Between 1992 and 1996 this area inflated at a depth of below sea level, indicating that the magma supply system of Sabancaya may not be centered directly below the volcano. Indeed, a phase of ground uplift at Hualca Hualca volcano and earthquake swarms in 1990 and later seismic activity under Hualca Hualca could indicate that the magma chamber of Sabancaya is actually under the neighbouring volcano, a not uncommon phenomenon at volcanoes. Geology The tectonic conditions in the region have not been constant over time; at various times the plates approached each other at higher speed, and this led to a compressional tectonic regimen. In the Western Cordillera however, tensional faulting facilitated the occurrence of voluminous volcanism. This faulting is still underway and produces earthquakes in the area. The basement of the volcano is formed by Precambrian rocks, which are overlaid by various sediments and volcanic formations of Mesozoic and Cenozoic age. Especially during the Neogene, the supply of volcanic material was high and dominated the region, forming a volcanic "foot"; the present volcanoes are constructed on this volcanic "foot". This "foot" is made out of an ignimbrite plateau that drops down south. The "foot" beneath Ampato, Hualca Hualca and Sabancaya has been dated 2.2 ±0.15 million years ago, while a lava flow beneath the first and the last of these is about 0.8 ±0.04 million years old. Composition Fresh volcanites of Sabancaya consist of porphyritic andesite and dacite which form a potassium-rich calc-alkaline suite similar to other volcanoes in southern Peru; the andesites occasionally appear as fine-grained enclaves. The rocks are not very vesicular and contain a moderate amount of phenocrysts. Minerals encountered in both phenocrysts and groundmass are amphibole,