Volcanic Activity

How Magma Reaches the Surface Magma rises because magma is less dense than the surrounding solid material. It will rise until it reaches the surface or becomes trapped beneath layer of rock.

A Volcano Erupts A volcano erupts when an opening develops in weak rock on the surface. During a volcanic eruption, the gases dissolved in magma rush out, carrying the magma with them. Inside a Volcano: Magma Chamber – The pocket beneath a volcano where magma collects

, The magma moves through the pipe, a long tube in the ground that connects the magma chamber to Earth’s surface. Vent - an opening in the volcano where gases and molten rock leave. Lava flow – The area covered by lava as it pours out of a vent. Crater – A bowl-shaped area that may form at the top of a volcano around the volcano’s central vent.

Characteristics of Magma Gas content, how thick or thin the magma is, temperature and silica contents are important factors as to the force of a volcanic eruptions. The amount of silica in magma helps to determine how easily the magma flows. Silica is formed from the elements oxygen and silicon and is abundant in the crust and mantle. The more silica content in magma the thicker the magma.

Types of Volcanic Eruptions Silica content determines whether the volcanic eruption is quiet or explosive. Quiet Eruption: A volcano erupts quietly if its magma flows easily. Quiet eruptions produce two types of lava: Pahoehoe – fast-moving, hot lava aa – cooler, slower moving lava

Explosive Eruptions: If magma is thick and sticky, a volcano will erupt explosively. The explosion will break the lava into fragments that quickly cool and harden into pieces of different size called Tephra. Smallest pieces are called ash (fine, rocky particles as small as a grain of sand), cinders are pebble-sized particles and bombs are larger pieces that range in size from a baseball to a car.

Stages of a Volcano Active – a volcano that is erupting or has shown signs that it may erupt. Dormant – sleeping and may become active in the future. Extinct – a volcano that is unlikely to erupt again.

Other Types of Volcanic Activity Hot Spring – forms when groundwater heated by a nearby body of magma rises to the surface and collects in a natural pool. Geyser – a fountain of water and steam that erupts form the ground. Geothermal Energy – water heated by magma that provides a clean, reliable energy source.

Monitoring Volcanoes Geologists have been somewhat successful in predicting eruptions. They use the same devices that are used to monitor earthquakes (tiltmeters, laser-ranging devices, etc.). Geologist will also monitor the small earthquakes that normally accompany a volcano.

Volcano Hazards Although quiet eruptions and explosive eruptions involve different volcano hazards, both types of eruptions can cause damage far from the crater’s rim. Volcanic ash can bury entire towns, damage crops, and car engines. Eruptions can also cause landslides and avalanches.