Section 2: Volcanic Activity

Chapter 2: Volcanoes

How magma reaches Earth’s surfaceLiquid 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 magmaThe 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 eruptionsThe 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 easilyTwo 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 VolcanoActive - 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 activityHot spring: forms when groundwater

heated by nearby magma, rises to the surface and collects in a natural poolPressure 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