Misti

Misti is a prominent stratovolcano located in the southern Peruvian Andes. It rises sharply above Arequipa, the second-largest city in Peru.

This volcano is part of the Andean Central Volcanic Zone, or CVZ. The CVZ is a large volcanic belt stretching through southern Peru, Bolivia, northern Argentina, and Chile. Misti is a young, symmetrical cone with slopes measuring about 30 degrees. It is a significant landmark because it is visible from the Pacific Ocean.

The mountain was built through a specific geological process involving four distinct stages. During each stage, lava flows and domes built up the mountain's structure. This was followed by a summit collapse that created a bowl-shaped depression. These cycles of growth and collapse repeated four times to form the current cone. The volcano sits atop an older, eroded stratovolcano known as Misti 1. Its surface is covered by a large fan of volcanic debris. This debris covers an area of 150 square kilometers around the volcano.

The summit of Misti features two nested craters. The outer crater is wide and deep, with a gap in its southwestern rim. The inner crater sits in the southeastern part of the outer crater. This inner crater cuts through layers of ash and scoria. It also cuts through historical lava domes. Inside this inner crater, there is an active lava plug or dome. This dome has a cracked, boulder-strewn surface. It also contains sulphur deposits and active fumaroles, which are vents that emit volcanic gases.

Geologically, Misti is driven by the movement of tectonic plates. The Nazca Plate subducts beneath the South American Plate at a rate of about 6 centimeters per year. This process, called subduction, is responsible for the volcanism in the CVZ. As the Nazca Plate descends, it releases fluids into the mantle. These fluids chemically modify the mantle to generate melt. Most volcanoes in this region produce potassium-rich andesitic magmas. This magma is created through fractional crystallization and the absorption of crustal rocks.

History shows that Misti has been active for a very long time. Over the past 50,000 years, many intense explosive eruptions have occurred. These eruptions spread tephra, which are rocks fragmented by volcanic activity. The last two major eruptions happened 2,000 years ago and between 1440 and 1470 AD.

The Inca people recognized the volcano as a threat. During the 15th-century eruption, they performed human sacrifices on the mountain. The mummies found on Misti represent the largest known Inca human sacrifices. The name "Misti" may come from Quechua, meaning "mixed," "mestizo," or "white." This likely refers to the snow that covers the summit.

Misti is considered one of the most dangerous volcanoes in the world. This danger is due to its proximity to Arequipa. The city has a population exceeding one million people. Some northeastern suburbs have even expanded onto the volcano's slopes. If Misti erupts, narrow valleys could channel mudflows or hot volcanic debris toward the city. These flows could also damage vital infrastructure, such as hydropower plants. Even a moderate eruption could cover most of the city in volcanic ash. Many dams, such as the Aguada Blanca Dam, sit near the volcano's northern side.

Scientific interest in Misti has grown significantly over the years. In 1893, Professor Solon Irving Bailey installed a weather station on the summit. This was once the highest continuously inhabited location on Earth. It allowed researchers to study the human body at high altitudes. Today, the Peruvian Geological, Mining and Metallurgical Institute (INGEMMET) monitors the volcano. They operate a volcano observatory in Arequipa to keep the public safe. They also publish hazard maps and run public awareness campaigns. This monitoring helps manage the risks posed by this massive Andean peak.