Volcano Composite Stratovolcano — free printable diagram

What a composite volcano diagram shows

A composite volcano, also called a stratovolcano, is the steep-sided cone most people picture when they think of a volcano. The name describes how it is built: in layers, alternating between lava and ash from successive eruptions. Its shape and its explosive eruptions both come from one property of its lava — it is thick and sticky, so it does not flow far before it sets.

Also called

A stratovolcano

Shape

Tall, steep-sided, symmetrical cone

Built from

Alternating layers of lava and ash

Lava

Thick and sticky (viscous), rich in silica

Eruptions

Explosive, and less frequent than at a shield volcano

Features labelled

Magma chamber, main vent, crater, side vents, layers

Found at

Destructive plate margins, where one plate subducts beneath another

• "Composite" and "strato" both mean built in layers. Each eruption adds a layer of lava or a layer of ash, and the alternating bands are what the cross-section is drawn to show.
• Thick lava cannot travel far before it cools and solidifies, so the material piles up close to the vent. That is what gives the volcano its steep sides and height.
• The same thickness traps gas inside the magma. Pressure builds until it is released suddenly, which is why eruptions are violent and can produce ash clouds and fast-moving pyroclastic flows.
• Compare it with a shield volcano, which is the standard contrast: runny basaltic lava that flows a long way, producing a broad, gently sloping dome and much less explosive eruptions.
• Composite volcanoes form where an oceanic plate is subducted. Water and sediment carried down with the plate change the chemistry of the magma produced, which is why the lava is silica-rich in the first place.
• They can stay dormant for long periods between eruptions, which is one reason large populations end up living on their fertile slopes.