Geog 4

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Nevado del Ruiz

A stratovolcano, composed of many layers of lava alternating with hardened volcanic ash and other pyroclastic rocks.

Has been active for 2 million years, with three major eruption periods. Usually creating 'Plinian Eruptions', which produces swift moving currents of hot gas and rock (pyroclastic flows).

These eruptions often cause massive lahars, where hot gas and lava melts the snow caps.

In 1985 such eruoption produced an enormous lahar that burned and detsroyed the town of Amero, causing an estimated 25,000 deaths. The deadliest lahar in history.

Similar incidents occured in 1595 and 1845. The large glaciers covering the summit also pose threat to 500,000 people. Altough they continue to retreat.

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Mount Vesuvius

Vesuvius is part of the companian volcanic arc, a line of volcanoes that formed over the subduction zone created by the convergence of the African and Eurasian plate.

The subduction zone stretches the length of the Italian peninsula and also the source of Mount Etna.

Under Vesuvius, the lower part of the subducting slab has torn and detached forming a slab window, making Vesuvius rocks chemically different. 

Vesuvius is a cone partially encircled by the steep rim of the summit caldera caused by the collapse of a higher structure. It is considered one of the most dangerous volcanoes due to the density of Napoli.

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Yellowstone lies over a hotpost where light, hot, molten mantle rock rises towards the surface. The caldera was formed when the massive magma chamber was emptied during a massive eruption, causing the walls to drop and block the vents.

Over the past 18 million years or so, this hotspot has generated a succession of violent eruptions and less violent floods of basaltic lava. Together these eruptions have helped create the eastern part of the Snake river plain from a once-mountainous region.

At least a dozen of these eruptions were so massive that they are classified as supereruptions. Volcanic eruptions sometimes empty their stores of magma so swiftly that they cause the overlying land to collapse into the emptied magma chamber, forming a geographic depression called a caldera.

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