4. What is a Volcano? Opening in the Earth’s surface where magma escapes volcano Vulcano island off Sicily, The word volcano is derived from the name of Vulcano island off Sicily, which was named after Vulcan the Roman God of Fire

5. What is Volcanism? Volcanism Volcanism describes all the processes associated with the discharge of magma, hot fluids and gases

6. Magma or Lava magma Molten rock below the surface of the Earth that rises in volcanic vents is known as magma lava After it erupts from a volcano it is called lava

7. Magma Commonly contains some crystals, fragments of surrounding (un-melted) rocks, and dissolved gases, but it is primarily a liquid composed principally of oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, potassium, titanium, and manganese

8. LAVA Red hot when it pours or blasts out of a vent but soon changes to dark red, gray, black, or some other color as it cools and solidifies. Very hot, gas-rich lava containing abundant iron and magnesium is fluid and flows like hot tar, whereas cooler, gas-poor lava high in silicon, sodium, and potassium flows sluggishly, like thick honey in some cases or in others like pasty, blocky masses

9. List any contributions made by Volcanoes 1.Played a key role in forming and modifying the planet 2.More than 80 percent of the Earth's surface--above and below sea level--is of volcanic origin

10. Contributions 3.Gaseous emissions from volcanic vents over hundreds of millions of years formed the Earth's earliest oceans and atmosphere 4.Volcanic eruptions have produced mountains, plateaus, and plains, which subsequent erosion and weathering have sculpted into majestic landscapes and formed fertile soils

11. Where do most volcanoes form? PLATE BOUNDRIES

13. MAP LEGEND World map plate boundaries (blue lines), the distribution of recent earthquakes (yellow dots) active volcanoes (red triangles) Courtesy of NASA

14. Review Tectonic plates are composed of huge pieces of the lithosphere, (earth’s crust) that are driven by convection currents in the mantle. 3 types of plate boundaries; Convergent, Divergent and Transform

15. Divergent Volcanism Occurs at mid-oceanic ridges As the plates are pulled apart pillows of lava form new ocean floor Non explosive with large amounts of lava About 2/3 of volcanism occurs underwater @ divergent boundries

16. Convergent Volcanism Oceanic-oceanic subduction zone Produce a line of volcanoes parallel to the oceanic trench, The chain of volcanoes is called an island arc For Example the Aleutian Island chain

17. Convergent Volcanism Oceanic-continental subduction zone Belt of volcanoes will be generated on continental crust The belt is then called a volcanic arc Characterized by explosive eruptions For Example the U.S. Pacific northwest, and the Andes of South America and the most volcanically active belt on Earth is known as the Ring of Fire

18. 452 active and dormant volcanoes

19. Hot Spots Hot spots: Regions inside a plate with active volcanism Unlike other volcanoes, not created at plate boundaries, created within the plate interiors For Example The Hawaiian Islands

21. ANY QUESTIONS?