Lessons 9-12 Notes Lesson 9: Volcanoes Lesson 11: Volcanoes Create New Landforms L12: Viscosity of Lava

Lesson 9: Introducing Volcanoes

What is a volcano? A landform, usually conical, produced by accumulations of erupted material around a vent, or opening, in the surface of the earth, through which gas and erupted material pass. The erupted material can include flowing lava, fragmented rock, and airborne rock/dust.

When does a volcano occur? A volcanic eruption occurs when pressure from the gases trapped within magma is released with enough force to cause the magma to break through the earth’s surface. Gases, lava, and/or rock fragments shoot up through the vent, sometimes explosively, and spill over its edges.

Question: Where do volcanoes occur? Answer: Volcanoes can occur along plate boundaries. Volcanic mountains form along a plate boundary where an oceanic plate subducts beneath a continental plate. – The sinking plate melts, sending magma up to the earth’s surface, where the volcanic mountain is formed. Chains of volcanic mountains also occur along mid-ocean ridges where magma emerges and oceanic crust is formed.

Question: Where do volcanoes occur? Answer: Volcanoes can occur within a plate. Areas beneath a volcano within a plate are known as hot spots. Eruptions from oceanic hot spots (within oceanic crust) are characterized by “runny” (less viscous) lava that spreads out for miles. Iceland is an example of this. Hot spots under continental crust (like Yellowstone National Park) have more viscous lava. – These hot spots also have a high amount of dissolved gas. As the magma rises, it releases gas/pressure, which leads to enormous, explosive eruptions.