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8 -2
Volcanoes form over thousands of years as magma is forced onto the Earth's surface from underground magma chambers, dries, and hardens. Most volcanoes share features like vents where lava is released and lava tubes through which lava travels. Volcanoes occur at boundaries where tectonic plates meet or move apart, and at hot spots deep in the Earth. There are three main types of volcanoes - shield volcanoes which form wide, gentle slopes from non-explosive eruptions, cinder cone volcanoes which are steep and form from explosive eruptions, and composite volcanoes which can erupt explosively or gently.
8 -2
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- 2. How do volcanoeswork? • Magma is forced onto Earth’s surface. • It dries and hardens, this happens many times over thousands of years. • Eventually a mountain called a volcano is formed.
- 4. Parts of aVolcano • Most volcanoes share a specific set of features. • The magma that feeds the eruptions pools deep underground in a structure called a magma chamber. • At Earth’s surface, lava is released through openings called vents. • Flowing lava in the interior travels through long, pipelike structures known as lava tubes.
- 5. Where do mostvolcanoes occur? • Volcanoes occur at both divergent and convergent boundaries and also at hot spots.
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- 7. Types of volcanoes • Shield volcano: usually form at hot spots, from non explosive eruptions • Cinder cone volcano: form from explosive eruptions, very steep. • Composite volcano: form from both explosive and non explosive eruptions.
- 8. Shield volcano •Form from many layers of “runny” lava. • Very wide, not to steep. • Biggest type of volcanoes • Tallest mountain in the world is Mauna Kea (measures from sea floor to top) • non explosive eruptions
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- 10. Cinder cone volcano • Smallest type of volcano • Most common • Made from pyroclastic material (material shot out of a volcano) • Form a large crater • Explosive!
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- 12. Composite volcano: •Eruptions alternate between explosive and non-explosive. • Sometimes they have runny lava layers, other times the have pyroclastic materials form layers. • Have a wide base and steep sides. • Have a crater • Mount Fuji
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- 14. 2 Types oferuptions • Explosive: volcanoes that build enough pressure to blow its top, sending pyroclastic material into the air. • Non explosive: Build only enough pressure to allow lava to run down its sides.
- 15. Non explosive eruption • Mafic: refers to rocks and magma rich in iron and magnesium. • This type of lava that is very runny. • As magma nears the surface there is little pressure, causing gasses escape easily. • Magma low in Silica have quiet eruptions
- 16. Explosive eruptions •Felsic: means magma with high silica and feldspar content. • Felsic magma traps water and gas bubbles, which leads to lots of pressure. • Silica acts like a cork • Explosive eruptions are caused by a build up of high pressure. • Convergent zones contain lots of water, therefore have explosive eruptions.
- 17. Pyroclastic materials •Material that is thrown into the air during an explosion. • Volcanic bombs: large blobs of magma that harden in the air. • Lapilli: pebble size rocks • Volcanic ash: tiny powder like material
- 19. Four types oflava • Aa: lava that is thick and sharp • Pahoehoe: lava that forms thin crust and wrinkles • Pillow lava: lava that erupts under water, has a round shape • Blocky lava: cooler, lava that does not travel far from eruption, jagged when it dries.
- 20. Aa • lavathat is thick and sharp
- 21. Pahoehoe: • lavathat forms thin crust and wrinkles
- 22. Pillow lava •lava that erupts under water, has a round shape
- 23. Blocky lava •cooler, lava that does not travel far from eruption, jagged when it dries.