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What is a Stratovolcano?

Pyroclastic flows, lava domes, and cinder cones sometimes characterize stratovolcanoes. Usually, these types of volcanoes erupt explosively and violently, sometimes completely blowing their tops!

Pyroclastic flows don't really look much like "flowing" eruptions. They look more like big explosions, complete with billowing clouds. What happens during a pyroclastic flow is enormous volumes of extremely hot gases, ash, and rocks rush down the side of a volcano, like an avalanche of sorts.

Lava domes are rounded mounds that were built when super thick magma that was too thick to flow squeezed up through a volcanic vent and cooled as it reached the air. Kinda like toothpaste does when you squeeze it through the tube opening and leave the cap off so that it dries.

Some of the most powerful and destructive volcanoes in human history have been stratovolcanoes. They can send cubic miles of rock and ash into the atmosphere in an extremely violent series of eruptions known as a plinian-type eruption. The build up of extreme - really extreme - pressure beneath the surface from gases trapped in the magma trying to escape eventually breaks loose in a violent paroxysm, liberating enormous volumes of overlying rock, steam and ash into the atmosphere. With some historically famous and cataclysmic volcanoes, the build up of pressure beneath the crust of the volcano was so extremely intense that the entire volcanic mountain blew up, leaving just the root of the original mountain remaining.

Here are some classic examples of these awesome explosions...

Krakatoa
In 1883 this volcanic island in the Sunda Strait experienced a series of extremely violent eruptions that sent ash over 50 miles up into the atmosphere and whose explosions could be heard 2,200 miles away. 36,000 people lost their lives on the nearby islands of Java and Sumatra when enormous tsunamis generated by the tremendous release of energy from the eruptions swept over the island. The eruptions ejected so much material from the interior of the volcano that when the eruptions were over, there was just a crescent-shaped fragment of the original island remaining. It completely blew itself up.

Tambora

In 1815 this Indonesian volcano erupted in a series of extremely violent explosions that are said to be the largest in recorded history. Ash was thrown 50 km into the atmosphere and global temperatures around the world fell an average of 3°C. Although it doesn't sound like much of a drop, in the higher latitudes the effect of the ash in the atmosphere cooled summer temperatures so much 1815 became known as the year without a summer.

Tambora is an island in the Southeast Pacific Ocean. This and many other volcanoes are found in this Island chain where the Pacific Plate is subducting beneath the Indian plate. Quite possibly the largest volcanic eruption to occur in recorded history, Tambora ejected so much material when it erupted that the top of the volcano caved in, forming this enormous caldera, visible from space.

If the eruptions of a stratovolcano continue long enough to evacuate enough earth from beneath the surface, the entire top of the mountain can completely collapse into the empty chamber below, leaving a caldera. Although a caldera is usually what happens after a stratovolcano blows its top or spills all its guts, there is another extremely powerful type of volcanic eruption that truly qualifies as an Extreme Volcano.