CH 6 Prentice Hall p CH 6 Prentice Hall p Volcanoes & Plate Tectonics

Characteristics of Magma The force of an eruption depends partly on the amount of gases dissolved in the magma. The temperature and the silica content are also important factors. – Temp- partially determines whether it is thick or fluid. (Hotter- the more fluid it is.)

Characteristics of Magma Silica- a material found in magma composed of the elements silica and oxygen. (The more silica- the thicker the magma.) High Silica- light colored lava – Rhyolite an extrusive igneous rock – Pumice spaces left in the rock by gases bubbling out. – Obsidian- cools very quickly giving a glassy texture. Low Silica- dark colored rocks – Basalt dark colored extrusive igneous rock

Types of Volcanic Eruptions A volcano’s magma influences how the volcano erupts. The silica content helps determine whether the volcanic eruption is quiet or explosive.

Quiet Eruptions Magma flows easily. Dissolved gases in the magma bubble out easily. Thin runny lava oozes from the vent and flows. Examples Iceland and Hawaii

aa Cooler, slow moving lava. Forms jagged chunks of lava.

Pahoehoe Fast moving, hot lava. Surface of lava looks like a solid mass of wrinkles, billows and ropelike coils.

Explosive Eruptions Magma is thick and sticky. Thick magma builds up in the pipe, plugging it like a cork in a bottle. Pressure builds up due to the gases in the magma until the volcano explodes. The gases push the magma out with incredible force.

Explosive Eruptions Fragments: Volcanic Ash – fine, rocky, grain of sand sized particles. Cinders- – pebble sized particles Bombs- – large pieces of rock (baseball to the size of a car) Pyroclastic Flow Occurs when an explosive eruption hurls out ash, cinders and bombs as well as gases. (400mph, 1,800˚F)

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.

Other types of Volcanic Activity Geyser- A fountain of water and steam that erupts from the ground. – Forms due to rising hot water and steam that become trapped underground in a narrow crack. – Builds up pressure until it sprays out of the ground.

Other types of Volcanic Activity Geothermal Energy- A clean, reliable energy source provided by water heated by magma. Hot water can be piped into homes. Used as a source of electricity – Steam is piped into a turbine that spins and generates electricity.

Monitoring Volcanoes Geologists are more successful with predicting a volcanic eruption. Changes around a volcano shows signs of an eruption and allow for a short warning time. – Monitor a volcano with: Tiltmeters and Laser ranging devices to see ground changes due to shifting magma. Monitor escaping gases and water level in a volcano's crater lake.

Monitoring Volcanoes – Monitor a volcano with: Check the temperature of the ground water to see if the magma is heating it. Monitor the many small earthquakes triggered by magma moving from the chamber to the pipe. – Unable to predict the strength of the eruption

Volcano Hazards Time between eruptions can span hundreds of years. (Dormant Volcano) – People may be unaware of the danger. – Mt. St Helens 123 years.

Volcano Hazards Quiet Eruptions: – Lava flows- set fire and bury everything in their path. Explosive Eruptions: – Hot clouds of volcanic gases, cinders and bombs Pyroclastic Flow

Volcano Hazards Volcanic Ash: – Bury towns, damage crops, and clog car engines. – Wet ash is heavy and can cause roofs to collapse. Plane engines can fail if pulled into the engine. Lahar: – A mud flow of caused by melted snow. Carries ash, trees and rocks.

Volcano Hazards Pompeii