Volcanoes

1. Volcanoes

2. Volcano • A vent in the crust of the earth or another planet from which usually molten or hot rock and steam issue or a hill or mountain composed wholly or in part of the ejected material

3. Why do volcanoes erupt? • Magma • Thick flowing substance from some slowly melting rocks that is deep within the Earth because it is so hot. • Magma Chambers • Where magma rises and collects because it is lighter than the solid rock around it.

4. Why do volcanoes erupt? • Vents • The opening at the earth's surface through which the magma eventually pushes forth. • Fissures • Elongated fractures or cracks on the slopes of a volcano where magma also flows out. Fissure eruptions typically produce liquid flows.

5. Why do volcanoes erupt? • Lava • The magma that comes through the vents and fissures from an eruption. • Some volcanic eruptions are explosive and others are not. • How explosive an eruption is depends on how runny or sticky the magma is. • If magma is thin and runny, gases can escape easily from it. When this type of magma erupts, it flows out of the volcano. • Lava flows rarely kill people, because they move slowly enough for people to get out of their way. • Lava flows, however, can cause considerable destruction to buildings in their path.

6. Why do volcanoes erupt?

7. Why do volcanoes erupt? • Tephra • The pieces of magma that blasts into the air in a violent explosion from thick and sticky magma. • Tephra can range in size from tiny particles of ash to house-size boulders. • Ash • Fine particles of pulverized rock blown from an explosion vent. Measuring less than 1/10 inch in diameter

8. Why do volcanoes erupt?

9. Why do volcanoes erupt? • Explosive volcanic eruptions can be dangerous and deadly. • They can blast out clouds of hot tephra from the side or top of a volcano. These fiery clouds race down mountainsides destroying almost everything in their path. • Ash erupted into the sky falls back to Earth like powdery snow, but snow that won't melt. If thick enough, blankets of ash can suffocate plants, animals, and humans. • When hot volcanic materials mix with water from streams or melted snow and ice, mudflows form. Mudflows have buried entire communities located near erupting volcanoes.

10. Where Do Volcanoes Erupt? • subduction zone • When plates push together, one plate slides beneath the other. • Some of the rock on the overlying plate melts and forms magma that can move upward and erupt at the Earth's surface..

11. Where Do Volcanoes Erupt? • Rift zones • Where plates are moving apart and magma comes to the surface and erupts. • Hotspots - This is where volcanoes occur in the middle of plates where magma melts through the plate and erupts.

12. Why Do Volcanoes Grow? • Stratovolcanoes • Volcanoes that build from eruptions of lava and tephra that pile up in layers, or strata, much like layers of cake and frosting. These volcanoes form symmetrical cones with steep sides.

13. Why Do Volcanoes Grow?

14. Why Do Volcanoes Grow? • Cinder cones • These are volcanoes that build from erupting lava that breaks into small pieces as it blasts into the air. • As the lava pieces fall back to the ground, they cool and harden into cinders that pile up around the volcano's vent. • Cinder cones are very small cone-shaped volcanoes.

15. Why Do Volcanoes Grow?

16. Why Do Volcanoes Grow? • Shield volcanoes • These volcanoes form from eruptions of flowing lava. • The lava spreads out and builds up volcanoes with broad, gently sloping sides. • The shape resembles a warrior's shield.

17. Why Do Volcanoes Grow?

18. Information Thanks Mainly To… • http://interactive2.usgs.gov/learningweb/teachers/volcanoes.htm