F2-4 Composite Volcano or Stratovolcano
The structure of a composite or stratovolcano.

A composite volcano, also known as a stratovolcano, is a steep-sided, often symmetrical cone composed of alternating layers of lava flows, ash, and other volcanic material. Material ejected during a volcanic eruption is known as pyroclastic material. Pyroclastic materials can range in size from very small particles of ash [less than 2 mm (less than 1/10 of an inch) in diameter] to large blocks of rock as big as cars or even houses. It is the alternating layers of lava and pyroclastic materials that leads to the name composite volcano.

Word Link
Pyroclastic: First used in 1887, this adjective is formed by combining the word pyro meaning fire with the word clastic, meaning rock fragment.

Composite volcanoes have steeper slopes than shield volcanoes. The lower slope ranges between 6–10°, but the slope angle rises sharply up to 30° near the top of the volcano. The steep upper slope is due to the highly viscous lava from this type of eruption. This thick lava does not usually travel far down the slope before it solidifies.



Mt. Baker in Washington is a good example of the typical shape of a composite volcano with its steep sides.
Did You Know?
The largest volcanic eruption in recorded history occurred on April 1815 when Mt. Tambora erupted on the Indonesian island of Sumbawa. Approximately 71,000 people died as a result of the eruption of this composite volcano.

Composite volcanoes represent the picture that most people have in their mind when they think of volcanoes. These volcanoes can be quite explosive because of their highly viscous magma with relatively high concentrations of gas. Mt. Rainier in the U.S., and Mt. Fuji in Japan are two fairly well known examples of composite volcanoes.