Section 2: Volcanic Activity Chapter 2: Volcanoes

How magma reaches Earth’s surface Liquid magma is less dense than the surrounding solid material, so it flows upward into any cracks in the rock above During a volcanic eruption, the gasses dissolved in magma rush out, carrying the magma with them

Inside a volcano

Characteristics of magma The force of volcanic eruption depends partly on the amount of gas dissolved in magma Other important factors that affect an eruption: How thick or thin the magma is, the temperature and its silica content. More silica= higher viscosity (thicker) Less silica= lower viscosity (thinner)

Types of volcanic eruptions The silica content of magma helps to determine whether the volcanic eruption is quiet or explosive High viscosity (thick) causes an Explosive eruption Low viscosity (thin) causes a Quiet eruption A volcano erupts quietly if its lava flows easily Two types of lava produced by quiet eruptions Pahoehoe -fast moving, hot lava (Low viscosity) Aa -slow moving, cooler lava (High viscosity)

Pahoehoe Aa

Magma rises through the lithosphere because it is less dense and it is rising through the solid rock. As the magma materials rise, the rock cracks and magma goes through. Both quiet and explosive eruptions can cause damage far from the crater’s rim.

3 Stages of a Volcano Active - it will erupt or is erupting Dormant - there is a possibility that it will erupt (may not be for a long time) Extinct - it will not erupt

Other types of volcanic activity Hot spring: forms when groundwater heated by nearby magma, rises to the surface and collects in a natural pool Pressure can build and cause a geyser- a fountain of water and steam that erupts from the ground Geothermal Energy: a clean, reliable energy source caused when water is heated by magma

Geyser Hot Spring