Volcanoes

1. Volcanoes

2. Volcanoes • Lesson Essential Question: How can the type and eruptive style of a volcano be determined based on gas pressure and viscosity of magma?

3. Volcano ? • A volcano is a opening in the earth’s surface that erupts lava, gases, and ash. • Lava- melted rock( magma) that cools on the earth’s surface. • Most active volcano - Kilauea, Hawaii • Iceland

4. How do volcanoes form • Deep inside the Earth, heat and pressure changes cause rock to melt forming liquid rock or magma. • Magma is less dense than the rock around it, so it is forced slowly toward Earth’s surface. • After millions of years , magma reaches the Earth’s surface and flows out as(lava) at an opening called a vent. • On the earth’s surface the lava quickly cools and solidifies forming layers of igneous(fire) rock around the vent. • The steep-walled depression around a volcanoes vent is called the crater.

6. Elements in the Earth’s Crust

7. Check-in Question • What is magma? • Melted rock found beneath the earth’s surface. • Specifically: Magma is a complex mixture that contains partly melted mineral crystals, dissolved gases, and water. What causes magma to form? • Heat caused by friction at subduction radioactive decay

8. Volcanoes – where do they occur? • Divergent Plate Boundary • Mid Ocean Ridges • Rift – a long, deep crack in the earths surface • Iceland-the result of volcanic and rift eruptions which rose above sea level. • East African Rift

9. Spreading ridges As plates move apart new material is erupted to fill the gap Divergent Boundaries

13. Effects of Eruptions • Lava flows destroy everything in its path • Falling volcanic ash can collapse buildings and cause lung disease. • Sulfurous gas from the volcano mixes with water vapor to produce acid rain killing vegetation and polluting lakes and streams • Volcanic ash and debris resulting from an eruption is called a pyroclastic flow. • Bits of rock and solidified lava dropped from the air is called tephra.

15. Volcanic Ash

16. Pyroclastic Flow- hot gases and ash

20. Volcanic Aerosols – Gas, ash, etc. that get into the atmosphere and block out the sun

22. Lahar – a mudslide caused by a volcano erupting

23. Effects of Eruptions

24. Other Volcano Locations • Convergent Plate Boundary • one plate slides beneath another plate (subduction zone – water vaporizes, rock melts producing volcanoes) ex. Andes Mountains in South America ex. Soufriere Hills Volcano on the island of Montserrat in the Caribbean Ocean

25. Convergent Boundary

28. Volcano locations continued • Intraplate Boundary • some areas at the boundary between earth’s mantle and core are unusually hot. Hot rock at these areas is forced toward the crust where it melt to form a hot spot. • Hawaiian Islands sits a top a hot spot under the Pacific Plate. • The volcanoes that rise above water form the HI. • Yellowstone National Park, Wyoming

29. Earth Science Read and Review Assignment • Read pages 330-335 • On a piece of paper for turn –in: • Answer the reading check question on page:332. • Answer the Section Review Self Check questions 1-5 on page 335.

31. Volcanic Eruptions • Two factors control whether an eruption will be explosive or quiet. 1. Amount of Trapped Gases and Water Vapor • Silica content of the magma.

32. Volcanic Eruptions continued 2. Composition of Magma Silica-mineral composed of silicon and oxygen. Silica Rich-explosive Silica Poor-quiet high viscosity low viscosity Light color Dark color

33. Quiet Eruptions • Magma that is relatively low in silica is called basaltic magma. • It’s fluid and produces quiet non-violent eruptions. • Basaltic magma allows trapped gases to easily escape into the atmosphere • It pours from volcanic vents and runs down the sides of volcanoes. (ex. Hawaiian Islands)

35. Explosive Eruptions • Silica rich or granitic magma produces explosive eruptions (Soufriere Hills Volcano) • Silica-rich granitic magma is thick and the gases trapped inside causes pressure to build up. • When the explosion occurs gases expand rapidly carry lava and debris with it.

37. Tephra-bits of rock or solid lava in the air that falls to the ground.

38. Explosive Eruptions contu’d • Between silica rich and poor magma is an intermediate type lava called andesiticmagma which forms at convergent boundaries. • This type of magma erupts more violently than basaltic type magma. • In 1883, Krakatau, a volcanic island in the SundraStraits exploded with such force it was heard 2500 miles away and produced a giant Tsunami which killed more than 36,000 people.

39. Lava Flows • Hawaiian Island lava flows -quiet • Pahoehoe –a fluid basaltic lava that forms a rope like structure when it cools. • aa lava- a cooler, stiffer ,slow moving pahoehoe lava. • Pillow Lava oozes out of cracks in the ocean floor. Most common type of lava on earth. • Visualizing Lava- page 338

41. Forms of Volcanoes – The shape/type of volcano is a result of what comes out (mainly the type of lava)

42. Forms of Volcanoes Shield Volcano is a broad, gently sloping volcano formed by the quiet eruptions of basaltic lava. ex. Hawaiian Islands

45. Forms of Volcanoes cont’ud • Cinder Cone Volcano is a steep-sided, loosely packed volcano formed from tephra. • Tephra varies in size from volcanic ash, to cinders, larger rocks called bombs and blocks. ex. Paricutin, Mexico What find of eruption would form a cinder cone volcano?

48. Forms of Volcanoes contu’d • Composite volcanoes are formed by alternating explosive and quiet eruptions that produce layers of tephra and lava. (ex. Mt. Rainer, Mt. Shasta, Mt. St. Helen) Soufriere Hills on Montserrat in the Caribbean Located at convergent plate boundaries Lab-Identifying Types of Volcanoes(Page 342 & 344)