Which volcano type is formed by alternating layers of lava and ash?

Which volcano type is formed by alternating layers of lava and ash?

• A. Shield volcano
• B. Caldera
• C. Lava dome
• D. Strato volcano/ Composite volcano

Answer: (D)

The idea here is that some volcanoes build up from alternating eruptions of lava and volcanic ash, leaving distinct rock layers each time. When lava erupts and flows, it hardens into solid rock, and in later eruptions ash and other tephra settle to form separate layers. Over many cycles, these alternating lava and ash layers create a tall, steep-sided cone known as a stratovolcano, or composite volcano. In contrast, shield volcanoes are built mainly from broad, gently sloping flows of low-viscosity lava with little layering; lava domes form from viscous lava that piles up near the vent into a dome without multiple layers; and calderas are large craters produced by the collapse of the magma chamber after an eruption, not by layered construction.

The idea here is that some volcanoes build up from alternating eruptions of lava and volcanic ash, leaving distinct rock layers each time. When lava erupts and flows, it hardens into solid rock, and in later eruptions ash and other tephra settle to form separate layers. Over many cycles, these alternating lava and ash layers create a tall, steep-sided cone known as a stratovolcano, or composite volcano. In contrast, shield volcanoes are built mainly from broad, gently sloping flows of low-viscosity lava with little layering; lava domes form from viscous lava that piles up near the vent into a dome without multiple layers; and calderas are large craters produced by the collapse of the magma chamber after an eruption, not by layered construction.