Sangay (also known as Macas, Sanagay, or Sangai) is an active stratovolcano in central Ecuador. It exhibits mostly strombolian activity. Geologically, Sangay marks the southern boundary of the Northern Volcanic Zone, and its position straddling two major pieces of crust accounts for its high level of activity. Sangay's approximately 500,000-year-old history is one of instability; two previous versions of the mountain were destroyed in massive flank collapses, evidence of which still litters its surroundings today. Due to its remoteness, Sangay hosts a significant biological community with fauna such as the mountain tapir, giant otter, Andean cock-of-the-rock and king vulture. Since 1979, its ecological community has been protected as part of the Sangay National Park. Although climbing the mountain is hampered by its remoteness, poor weather conditions, river flooding, and the danger of falling ejecta, the volcano is regularly summited, a feat first achieved by Robert T. Moore in 1929.
History Folklore sourced from native people in the region compared Sangay to a lighthouse surrounded by a sea, which represented the dense jungle. The density of the jungle caused people to lose their way, but seeing ash and steam emissions from the volcano would help orient travelers along their way. Scientists have interpreted folklore like this as evidence of frequent and long-lasting eruptive activity at Sangay. In January 2024, archaeologists announced the discovery of archaeological sites on the east side of the volcano known as the Upano Valley sites. It is estimated that this cluster of urban settlements were inhabited between about 500 BCE to sometime between 300 and 600 CE. Altogether the cities may have reached a population between 15,000 and 100,000 people. They were surrounded by agricultural fields that archaeologist Stéphen Rostain speculates may have been particularly productive because their proximity to Sangay. Seventeen additional archaeological sites had been located prior to the 2024 announcement including potential monuments. An estimated 30,000 people lived in the region before Spanish occupation began in 1534. The Spanish prospected for gold on and around the volcano through the 16th and 17th Centuries and settled the area but expeditions undertaken in the 19th Century noted no inhabitants nearby. Modern development of the eastern side of the volcano began in the early 20th Century. The volcano and lands surrounding it were placed in a National Wildlife Reserve by the Ecuadorian government in 1975. This became Sangay National Park in 1979, which was expanded in 1992. The United Nations added it to their list of World Heritage Sites in 1983. From 1992 to 2005, poaching and human development led the UN to consider the site as being endangered but removed this status in 2005. The modern native inhabitants of the region primarily consist of Quechua people. The name Sangay comes from the Quechuan languages and is translated as "the frightener."
Geography Sangay is on the eastern edge of the Andes Mountains in central Ecuador about 160 km (99 mi) south of Quito and 20 km (12 mi) east of Riobamba. It lies within Sangay National Park. Two nearby volcanoes, Tungurahua and El Altar, are also located within the national park. The three volcanoes reach exceed 5,000 m (16,000 ft) above sea level with El Altar being the tallest. The principal rivers draining Sangay are the Llushin, Palora, and the Upano, each of which have numerous smaller tributaries on the middle and upper slopes. Flash flooding from significant rainfall is frequent and erosion is a problem despite thick forests. Rivers drain east into the Amazon Basin. Topography is dominated by volcanic and glacial features. Hanging valleys from prior glaciation feature numerous waterfalls and lakes.
Climate Sangay reaches high enough to enjoy snow cover on its upper slopes despite its location near the Equator. It is disputed whether or not the volcano has a glacier though ice and snowfields are present. The snow line in this part of South America lies approximately 4,800 m (15,700 ft) above sea level. The mountain environment leads to significant changes in precipitation across short distances. Prevailing winds are out of the east, causing rainfall to be greatest to the east where moisture is sourced from the Amazon rainforest. Observed rainfall averages from 4,827 mm (190.0 in) per year at Pastaza to the northeast of the volcano to 423 mm (16.7 in) at Riobamba just 20 km (12 mi) west of the summit in the rain shadow. Orographic lift and the Intertropical Convergence Zone are major factors in precipitation values. Annual temperatures see little variability but diurnal changes in temperature can be wide in more arid portions of the mountain's slopes. Higher elevations never rise above 0 °C (32 °F). Climate change threatens the snowpack and the high altitude grasslands.
Geology
Regional setting
Lying at the eastern edge of the Andean cordillera, Sangay was formed by volcanic processes associated with the subduction of the Nazca Plate under the South American Plate at the Peru–Chile Trench. It is the southernmost volcano in the Northern Volcanic Zone, a subgroup of Andean volcanoes whose northern limit is Nevado del Ruiz in Colombia. The next active volcano in the chain, Sabancaya, is in Peru, 1,600 km (990 mi) to the south. Sangay is above a seismogenic tectonic slab about 130 km (80 mi) beneath Sabancaya, reflecting a sharp difference in the thermal character of the subducted oceanic crust, between older rock beneath southern Ecuador and Peru (dated more than 32 million years old), and younger rock under northern Ecuador and Colombia (dated less than 22 million years old). The older southern rock is more thermally stable than the northern rock, and to this is attributed the long break in volcanic activity in the Andes; Sangay occupies a position at the boundary between these two bodies, accounting for its high level of activity.
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