2. Volcanoes are Hot Stuff

3. Volcanoes I. Volcano: An opening in the earth's crust through which magma flows out as lava Magma that comes to surface orignates from the ‘zone of weakness’ in the mantle (zone of weakness is at the base of the plates)Magma that comes to surface orignates from the ‘zone of weakness’ in the mantle (zone of weakness is at the base of the plates) The plates put pressure on a zone and forces magma up through cracks and openingsThe plates put pressure on a zone and forces magma up through cracks and openings

4. Volcanoes Most volcanoes are near plate boundaries, where earthquakes occur. Exception – Hawaiian islands, in the Pacific Ocean ‘Ring of Fire’ –Hot spots form when hot magma from below earth’s crust rises to the surface

5. II. Structure Dormant: volcano quiet or inactive. Ex: Mt. St. Helen’s was dormant for 100 years Extinct: Volcano that has not erupted within historic times. (man was here and recorded) Ex: Mt. Lassen in California until 1913 Active: Volcano that has erupted & smoke often

6. II. Structure of Volcanoes Crater: is the opening at the top of the volcano Lava settles back down into the crus and a solid cap or plug forms in the crater Vent is the channel through which the magma travels

7. II. Structures of Volcanoes Caldera: A very large crater located at the top of the volcano Laccolith: mass of hardened magma that is dome shaped (magma moves between layers causing bulge) Batholith: large mass of igneous rock (hardened magma) below earth’s surface

8. II. Structures of Volcanoes Dikes: magma fills and hardens in vertical cracks Sill: a structure of hardened magma between horizontal layers of rock Stock: small mass of hardened magma below the earth’s surface

9. III. Three main types of Volcanoes Classified by shape of cone (how lava flows out) Cone: Pile of material that collects around the opening

10. III. Three main types of Volcanoes 1. Shield Cone: Lava runs out quietly from the opening and forms gently sloping sides, almost flat, quiet eruptions 2. Cinder Cone: An explosive type of eruption and is built up by layers of ash and cinders. (steeper sloped sides than sheild) 3. Composite Cone: Both explosive and quiet eruptions. Alternating layers of cinders & lava.flows, (like cake & icing)

11. Shield Volcano

12. Cinder Cone Volcanoes

13. Cinder Cone Volcano

14. Strato or Composite Volcano

16. IV. Volcanic Eruptions A. Eruptions depend on….. –1. If the vent is blocked or open –2. The length of the vent. (long vents release gases at high speeds)

17. B. Four Basic Kind of Eruptions 1. Quiet eruption with watery lava flow  Magma is thin  Magma contains little gas  Thin lava flows out in a steady stream 2. Quiet eruption with thick lava flow  Magma contains little gas  Thick lava forms huge dome

18. B. Four Basic Kind of Eruptions 3. Active Eruption –Thin magma with large amounts of gas –Gas escapes – causes hot magma to shoot out 4. Explosive eruption –Magma thick with large amounts of gas –Magma hardens before leaving the vent (blocked) –Trapped gas under high pressure –Sudden release - explosion

19. V. Types of Materials A. Lava –Pahoe hoe – hot, thin, and fast flowing. Wrinkled surface –Aa – cooler and thicker Rough, block – like surface Jagged, hurts to walk on (‘ah – ah’) –Pillow lava: forms on ocean floor

20. V. Types of Materials B. Gases –Water vapor – dissolved water in magma –Carbon monoxide, sulfur dioxide, & hydrogen sulfide –More gasses trapped and cannot escape, so pressure builds up and volcano explodes

21. V. Types of Materials C. Pieces of rock (pyroclastic material) –Volcanic dust – smallest, 2 mm or less –Ash – fragments, sand sized –Cinders – sent out by eruptions, several cm across –Bombs – 1 meter across –Blocks – weighing several tons

22. Pyroclastic Material: Explosive Fragments ejected from a volcano: volcanic bombs volcanic ash volcanic blocks

23. VI. Volcanoes and Man A. Wiped out civilizations (landscapes) B. Predicting eruptions –Mild earthquake activity around the volcano –Plug inside the crater may steam and swell Problems 1.Can cause climate change (blocking sun with ash) 2.Damage property & people Benefits 1.Ashes spread & creates rich soil 2.Hot Springs in Iceland for power 3.Colorful sunsets for several years 4.Pumice use for polishing

24. Mt. Vesuvius in Pompeii, Italy