1. Santiaguito Volcano 2009

2. Bellringer# 31 Read “Volcanoes and Humans” page 747 Answer the question in your journal.

3. Chapter 21 S.2 Volcanoes Volcanic eruptions are windows to the Earth’s interior. They eject lava, therefore they provide opportunities to observe the processes that occur deep beneath the Earth’s surface. Izalco volcano, El Salvador

4. What is a volcano exactly? A volcano is an opening in Earth’s crust through which magma has reached Earth’s surface. crust: an opening in the surface of Earth through which volcanic material passes

5. Mount St. Helens May 18, 1980

6. Kilauea in Hawaii 2008

7. Factors Affecting Eruptions The primary factors that determine whether a volcano erupts violently or quietly include: – Magma composition (what it is made of) – Magma temperature – The amount of dissolved gases in the magma

8. Viscosity Viscosity is a substance’s resistance to flow. – Magma from an explosive eruption is going to be thousands of times more viscous than magma that is extruding quietly. Magma that has been heated flows more easily. Viscosity of lava depends on its silica content. – Rhyolitic lavas are very viscous and do not flow easily. – Basaltic lavas are more fluid. (less silica)

9. Dissolved Gases These gases trapped in magma provide the force to eject molten rock from the vent. Vent- an opening to the surface. When magma move towards the surface, the pressure is reduced and dissolved gases are released suddenly. Highly viscous magmas slow the movement of expanding gases. – Gases collect in bubbles and pockets that increase in size and cause eruptions like Mount St. Helens.

10. Volcanic Material Lava is not the only material extruded from volcanoes. – Broken rock – Lava bombs – Fine ash – Dust All volcanic eruptions emit large quantities of gas.

11. Lava Flows Basaltic lavas flow at a rate of 10-30 meters per hour. (low silica) The movement of rhyolitic lava is too slow to be visiable. (lots of silica) Hawaii 2008

13. Gases Magmas contain dissolved gases. They are held in the molten rock by confining pressure. (just like soda) When the pressure is reduced, the gases begin to escape. The gases in volcanoes have helped form the atmosphere. Hawaiian eruption example: – 70% water vapor, 15% carbon dioxide, 5% nitrogen, 5% sulfur, and small amounts of chlorine, hydrogen and argon.

14. Pyroclastic Material Pyroclastic material is the name given to particles produced by volcanic eruptions. The fragmanets ejected during eruptions range in size from very fine dust and volcanic ash to pieces that weigh several tons. Santiaguito Volcano 2009

15. Anatomy of a Volcano Begins- when a fissure or crack forms and then magma comes out of the fissure. Repeated eruptions and long periods of inactivity build the volcano. Crater- a steep walled depression at the summit.

16. VOLCANIC STRUCTURE The central opening is called a vent. There is usually only one vent but there can be several smaller vents. (secondary cones) The shape of a volcanic structure will vary according to the nature of the eruption and the magma type

17. Types of Volcanoes The three main volcanic types are : – Shield volcanoes – Cinder cones – Composite cones

18. Shield Volcano Produced by the accumulation of fluid basaltic lavas. Shape: broad slightly domed, resembles a warrior’s shield. Most form out of the deep ocean floor to form islands. Ex: Hawaiian Islands and Iceland Largest on Earth Mauna Loa Hawaii

19. Cinder Cone Made from ejected fragments the size of cinders, harden in the air. (pyroclastic) Result from gas rich basaltic magma. Shape: steep sides Only erupts once. Erupts for weeks or a few years. Magma solidifies when it is over. Size: small 30-300 meters Ex: SP Crater in AZ, Mount Etna Capulin Volcano, New Mexico Sunset Crater, Arizona

20. Composite Cone Earth’s most beautiful and dangerous Also called a stratovolcano. Most are around the Pacific Ocean Made of lava and pyroclastic material Tallest volcanoes Shape: steep summit, sloping flanks Ex: Fujiyama in Japan, Mount Shasta in CA, Mount Rainier, Washington 2005 Mount Shasta, California

21. Dangers of Composite Cones Pyroclastic flows, hot gases, glowing ash, large rock fragments. The flow can race down the slope at 200km per hour. Mudflows called lahars happen when the debris becomes saturated with water. – Rain or ice melting Lahars can happen with out an eruption.

22. Mount St. Helens erupted often between 1980 and 1986. An explosive eruption on March 19, 1982, sent pumice and ash 9 miles (14 kilometers) into the air, and resulted in a lahar (the dark deposit on the snow) flowing from the crater into the North Fork Toutle River valley. Part of the lahar entered Spirit Lake (lower left corner) but most of the flow went west down the Toutle River, eventually reaching the Cowlitz River, 50 miles (80 kilometers) downstream.

23. Mount St. Helens erupted often between 1980 and 1986. An explosive eruption on March 19, 1982, sent pumice and ash 9 miles (14 kilometers) into the air, and resulted in a lahar (the dark deposit on the snow) flowing from the crater into the North Fork Toutle River valley. Part of the lahar entered Spirit Lake (lower left corner) but most of the flow went west down the Toutle River, eventually reaching the Cowlitz River, 50 miles (80 kilometers) downstream. USGS Photograph taken on March 21, 1982, by Tom Casadevall.

24. Other Volcanic Landforms Calders- a large depressionin a volcano. They form two ways. – The collapse of the top of a composite volcano after a violent eruption – The collapse of the top of a shield volcano after the magma chamber is drained. Ex: Mount Mazama erupted to form Crater Lake, Oregon.

25. Over 6,000 years ago Mount Mazama erupted. Before the explosion the mountain was 12,000 feet high; when it was over it had been replaced by a 1,900- foot deep crater. Crater Lake, famed for its intense blue waters, was made a National Park in 1902. Volcanic activity occurred some time after the Mount Mazama explosion, creating Wizard Island in the middle of the lake. Crater Lake is the world's seventh deepest lake. At it's greatest depth it measures 1,932 feet

26. Necks and Pipes- most volcanoes are fed magma through conduits, called pipes connecting a magma chamber to the surface. Form because of erosion of cinder cones. A neck is what is left over. Best known pipes are the diamond bearing pipes of S. Africa Ship Rock, New Mexico Diamonds are formed in the Earth's mantle, and are brought up to the surface in the volcanic rock called kimberlite.

27. Lava Plateaus The greatest amount of volcanic material comes from fissures. No cone is formed. The lava flows over a wide area of land. Ex: Columbia Plateau 1.6 km thick Basalt lava flows exposed in canyons hundreds of feet deep occur throughout the Snake River Plain and Columbia Plateau. Large landslides tend to form where the basalts are underlain by unconsolidated sediments.

29. Top 10 More than 800 active volcanoes in the world. There was no way to understand why volcanoes are located where they are before the 1960s. Scientists understand now because of the plate tectonic theory. 1.Mount Mazama/Crater Lake, Oregon 2.Mount Etna, Sicily 3.Mount Vesuvius, Italy 4.Mount Tambora, Indonesia 5.Mount Krakatau, Indonesia 6.Mount Pelee, Martinique 7.Parícutin, Mexico 8.Mount St. Helens, Washington 9.Nevada del Ruiz, Colombia 10.Mount Pinatubo, Philippines Paricutin, Mexico 2008

30. Where do Volcanoes Occur? Most volcanoes occur at convergent plate boundaries. – 75% of the active volcanoes on Earth are located in an area known as the Ring of Fire. – The Ring of Fire is located along the edges of the Pacific ocean, where oceanic tectonic plates are colliding with continental plates.

31. Underwater volcanoes occur at divergent plate boundaries. – As plates move apart at divergent boundaries, magma rises to fill the gap. – This magma creates the volcanic mountains that form ocean ridges. – Iceland is a volcanic island on the Mid-Atlantic ridge that is growing outward in opposite directions.

32. Volcanoes occur at hotspots. – Some volcanoes occur in the middle of plates. – Mantle plumes are mushroom shaped trails of hot rock that rise from deep inside the mantle, melt as they rise, and erupt from volcanoes at hot spots at the surface. – The plumes remain in the same place as the tectonic plate moves, creating a trail of volcanoes. – The Hawaiian Islands are an example of this type of volcanic activity. (intraplate volcanism)

33. Homework Chapter 21 Section 2 Review Questions Page 746 Do #1-8 You do not have to write the question.