Presentation Transcript

1. Volcanoes

2. Volcanoes A volcano is a weak spot in the crust where molten material, or magma, comes to the surface. Volcanic belts form along the boundaries of Earth’s plates.

3. Ring of Fire – a major volcanic belt that rims the Pacific Ocean.

4. Volcanoes and Plate Boundaries Volcanoes often form where two oceanic plates collide or where an oceanic plate collides with a continental plate. In both situations, an oceanic plate sinks through a trench.

5. Rock above the plate melts to form magma, which then erupts to the surface as lava.

6. Hot Spot Volcanoes A volcano forms above a hot spot when magma erupts through the crust and reaches the surface.

7. Magma Reaches Earth’s Surface When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent.

8. Volcanic Eruptions Within the last 150 years, major volcanic eruptions have greatly affected the land and people around them.

9. Effusive Eruption An effusive eruption happens when lava flows out and over the land. The shape of the lava and how fast it moves is determined by the minerals that it is made up of.

10. Plinian Eruptions Plinian eruptions are the strongest eruptions. Gases and tephra are sent up to 11 miles into the atmosphere. Tephra is material produced by volcanic eruptions.

11. Strombolian Eruptions In Strombolian eruptions molten basaltic rock is thrown upward in strands from one vent. The eruptions come every few minutes and are caused by bursts of gases

12. Eruption Cloud Clouds of tephra and gases from an eruptions spreads across the sky for hundreds of miles.

13. Phreatic Eruptions Phreatic eruptions are steam and debris from the inside of a volcano. Magma heats up water below the surface and causes it to boil. When enough pressure builds up, the steam blows the top off of the volcano.  

14. Volcanian Eruption This type of eruptions explodes new volcanic material out of the volcano. This is a kind of explosive eruption that only happens if the pressure inside the volcano is extreme.

15. Landforms From Lava and Ash Volcanic eruptions create landforms made of lava, ash, and other materials. These landforms include composite volcanoes, shield volcanoes, cinder cone volcanoes, and lava plateaus.

16. Shield Volcano • the eruption is quiet • gently sloping • consist of basaltic lava flows

17. Cinder Cone Volcano • the eruption is explosive • steep-sloped • consist of fragmental lava

18. Composite Volcano • the eruptions alternate between quiet and explosive • build into steep towering mountains • consists of layers of lava which cover and protect layers • of loose materials • sometimes called stratovolcanoes

19. Lava Plateau A lave plateau is a plateau that is formed by lava during a volcanic eruption.

20. Caldera A caldera forms when an volcano’s magma chamber empties and the roof of the chamber collapses. The result is a large, bowl-shaped caldera.

21. Landforms From Magma Features formed by magma include volcanic necks, dikes, and sills, as well as batholiths and dome mountains.

22. Volcanic Neck A volcanic neck is a cylindrical-shaped landform standing above the surface created by magma solidifying in the vent of a volcano. This is Devil’s Tower in Wyoming.

23. Dikes A volcanic dike is a sheet which transports magma parallel to the ground.

24. Sills A volcanic sill is a sheet of magma which is parallel to the surrounding rock. Sills store magma compared to dikes which transport magma.

25. Batholiths A batholith is a mass of rock formed when a large body of magma cools inside the crust. Several large batholiths form the core of mountain ranges in western North America. Half Dome in Yosemite National Park, California, is part of the Sierra Nevada batholith.

26. Volcanoes in the U.S. Active volcanoes in the U.S. are found mainly in Hawaii, Alaska, California, Oregon and Washington.

27. Forecasting Volcanic Eruptions Volcanoes are difficult to forecast because they can cause so many different disasters themselves. The volcanic gases that come with a volcanic explosion mixes with the ash and clouds formed by the eruption and acid rain may fall in your area.  Volcano eruptions throw objects and debris during strong eruptions. Poisonous gases, lava, and ash are all major events during volcanic eruptions.  

28. Famous U.S. Volcanoes • Mount St. Helens in Washington – last erupted in 1980 killing 57 people • Mauna Loa in Hawaii – the largest volcano on our planet and also one of the most active volcano on our planet. It erupts quite often is and is constantly monitored for its next eruption

29. Resources • http://library.thinkquest.org/CR0212082/ndvol.htm • http://www.fema.gov/kids/volcano.htm • http://belmont.sd62.bc.ca/teacher/geology12/photos/volcanoes/features.htm • Prentice Hall, Inc.