Volcanoes

1. Volcanoes Forces Inside the Earth

2. What is a volcano? • A volcano is a weak spot in the crust where molten material, or magma, comes to the surface. • when magma reaches the surface, it is called lava • After lava has cooled, it forms solid rock, building up Earth’s surface

3. Plate Boundaries The Ring of Fire is formed by many volcanoes that rim the Pacific Ocean. Why do volcanic belts form along Earth’s boundaries? Huge pieces of crust are diverging or converging, often fractures in the crust allow magma to reach the surface.

4. Divergent and Convergent • form along mid-ocean ridges. • form along rift valley • Form where oceanic and continental crust meet or where two oceanic plate collide. • An island arc is formed by volcanoes along a deep ocean trench • Can also form under continents

5. Hot Spots • An area where material from deep within the mantle rises and then melts, forming magma.

6. Properties of Magma Physical Properties Chemical Properties Any property that produces a change in the composition of matter. Ability to burn, combine or react with other substances • Any characteristic of a substance that can be observed or measured without changing the composition of the substance. • Density, hardness, melting point, boiling point, whether it is magnetic

7. Viscosity of Magma • Viscosity is the resistance of a liquid to flow. • The greater the viscosity, the slower the flow • ex. honey • Liquids have different viscosities because of the particles that make them up. • Viscosity of magma depends on the silica content and temperature • Silica is made of silicon and oxygen • more silica, the higher viscosity, slow moving, cools to rhyolite • less silica, the lower the viscosity, faster moving, cools to basalt

8. Temperature- Ranges from 750° C to 1175° C pahoehoe aa Slow moving Cooler High viscosity Rough surface, jagged lava chunks • Fast moving • Hot • Low viscosity • Solid mass of wrinkles

9. Magma Reaches the Surface • Inside a volcano • Magma chamber- a pocket where the magma collects under the volcano • Pipe- a long tube in the ground that connects the magma chamber to the Earth’s surface • Vent- the opening where molten rock and gas leave the volcano • Lava flow- area covered by lava as it pours out of the vent • Crater- bowl-shaped area that may form at the top of a volcano around the central vent

10. A Volcanic Eruption • What pushes magma to the surface? • The force of the expanding gases push magma from the magma chamber through the pipe until it flows or explodes out of the vent. • Quiet eruptions • low-silica, magma bubbles out gently, oozes quietly from the vent • Explosive Eruptions • high-silica, builds up pressure and explodes • breaks lava into fragments that cool and harden into pieces of different sizes; from volcanic ash to pebble sized to larger pieces called bombs • Pyroclastic flow occurs when an explosive eruption hurls out a mixture of hot gases, ash, cinders, and bombs • Obsidian and pumice forms

11. Mount St Helens

12. Life Cycle of a Volcano • Geologist use the terms active, dormant, or extinct • Active or live volcano is erupting or showing signs of erupting in the near future • Dormant volcano is like a sleeping bear, to be awakened in the future to become active • Extinct is a dead volcano unlikely to erupt again

13. Volcanic eruptions create landforms made of lava, ash, and other materials. • Shield volcano- form when thin layers of lava pour out of a vent and harden on top of previous layers building a wide, gently sloping mountain. • Cinder cone volcano- high viscosity lava with ash, cinders, and bombs build up around the vent in a steep, cone-shaped hill or small mountain.

14. Composite volcano- tall, cone shaped mountains in which layers of lava alternate with layers of ash formed by lava flow alternating with explosive eruptions of ash, cinder, and bombs. • Lava plateaus-instead of forming mountains, some eruptions of lava form high level area. • Thin, runny lava travels far before it cools and solidifies. • This happens again and again and after millions of years, plateaus form.

15. Caldera- a huge hole left by a volcanic mountain

16. Which is Which?

17. Why would anyone want to live near an active volcano? • To take advantage of the fertile volcanic soil. • When the volcanic ash breaks down, it releases potassium, phosphorus, and other substances plants need to grow. • This creates some of the richest soils in the world.

18. Features formed by magma include volcanic necks, dikes, sill, batholiths, and dome mountains. • A volcanic neck forms when magma hardens around a volcanic pipe. • Magma that forces itself into rock layer and hardens becomes a • Dike, slanted though bedrock • Sill, horizontal through bedrock

19. Batholiths-a mass of rock formed when a large body of magma cools inside the crust. Dome Mountains- forms when uplift pushes a batholith toward the surface.

20. Geothermal Activity • “geo” means EARTH • “therme” means HEAT • hot spring- a natural pool of water heated by a nearby body of magma • geysers- a fountain of water and steam that erupts from the ground as pressure builds