Stratovolcano

[1] Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and explosive eruptions.

[13] Stratovolcanoes also occur in some other geological settings, for example as a result of intraplate volcanism on oceanic islands far from plate boundaries.

The magma then rises through the crust, incorporating silica-rich crustal rock, leading to a final intermediate composition.

[20] In recorded history, explosive eruptions at subduction zone (convergent-boundary) volcanoes have posed the greatest hazard to civilizations.

[26] As a consequence, the tremendous internal pressures of the trapped volcanic gases remain and intermingle in the pasty magma.

Most deaths were caused by pyroclastic flows and lahars, deadly hazards that often accompany explosive eruptions of subduction-zone stratovolcanoes.

[25] Pyroclastic flows are swift, avalanche-like, ground-sweeping, incandescent mixtures of hot volcanic debris, fine ash, fragmented lava, and superheated gases that can travel at speeds over 150 km/h (90 mph).

[25] During March and April 1982, El Chichón in the State of Chiapas in southeastern Mexico, erupted 3 times, causing the worst volcanic disaster in that country's history and killied more than 2,000 people in pyroclastic flows.

On 15 June, Mount Pinatubo erupted and caused an ash cloud to shoot 40 km (25 mi) into the air.

It produced large pyroclastic surges and lahar floods that caused a lot of damage to the surrounding area.

[25] Mount Pinatubo, located in Central Luzon just 90 km (56 mi) west-northwest of Manila, had been dormant for six centuries before the 1991 eruption.

[27] The volcanic ash cloud consisted of 22 million tons of SO2 which combined with water droplets to create sulfuric acid.

It completely smothered the nearby ancient cities of Pompeii and Herculaneum with thick deposits of pyroclastic surges and pumice ranging from 6–7 meters deep.

[29] Mount Vesuvius is recognized as one of the most dangerous of the world's volcanoes, due to its capacity for powerful explosive eruptions coupled with the high population density of the surrounding Metropolitan Naples area (totaling about 3.6 million inhabitants).

[30] In addition to potentially affecting the climate, volcanic ash clouds from explosive eruptions pose a serious hazard to aviation.

[31] For example, during the 1982 eruption of Galunggung in Java, British Airways Flight 9 flew into the ash cloud, causing it to sustain temporary engine failure and structural damage.

[35] Lava flows can bury homes and farms in thick volcanic rock which greatly reduces property value.

Nyiragongo, near Lake Kivu in central Africa, is very dangerous because its magma has an unusually low silica content, making it much less viscous than other stratovolcanoes.

[40] In the 1985 eruption of Nevado del Ruiz in Colombia, Pyroclastic surges melted snow and ice atop the 5,321 m (17,457 ft) high Andean volcano.

It is known for its pungent egg smell and role in ozone depletion and has the potential to cause acid rain downwind of an eruption.

The SO2 in this cloud combined with water (both of volcanic and atmospheric origin) and formed sulfuric acid, blocking a portion of the sunlight from reaching the troposphere.

[43] An eruption the size of Mount Pinatubo affected the weather for a few years; with warmer winters and cooler summers observed.

The eruption caused crop failures, food shortages, and floods that killed over 100,000 people across Europe, Asia, and North America.