VOLCANOES

1. VOLCANOES

2. Volcanoes around the World

3. Factors Affecting Eruptions 10.1 The Nature of Volcanic Eruptions  Factors that determine an eruption • Composition Details on next slide • Temperature • Dissolved gases  Viscosity • Viscosity is the measure of a material's resistance to flow.

4. Comparison of ash plumes Mt. St Helens was a relatively small eruption compared to prehistoric eruptions

5. 10.1The Nature of Volcanic Eruptions  Factors Affecting Viscosity - Temperature (hotter magmas are less viscous) - Composition (silica content) More silica—high viscosity, thicker 2. Low silica—less viscous, more fluid

6. Factors Affecting Eruptions 10.1 The Nature of Volcanic Eruptions • Viscous (thicker) magma produces a more violent eruption.

7. 10.1 The Nature of Volcanic Eruptions • Dissolved gases • Mainly water vapor and carbon dioxide More trapped gas = Greater Eruption • Avent is an opening in the surface of Earth through which molten rock and gases are released. • Provide the force to extrude lava

8. Volcanic Material 10.1 The Nature of Volcanic Eruptions • Lava Flows • Basaltic lavas are more fluid. • Types of lava -Pahoehoe lava (resembles braids in ropes) • Aa lava (rough, jagged blocks)

9. Mayon Volcano, Philippines

10. Volcanic Material 10.1The Nature of Volcanic Eruptions • Pyroclastic materials-fragments ejected during eruptions Includes dust, ash, and rock • Range in size from very fine dust and ash to pieces that weigh several tons. Yes – write this down- names only!!! - Ash and dust — fine, glassy fragments - Pumice— frothy, air-filled lava - Lapilli— walnut-sized particles - Cinders— pea-sized particles - Blocks — hardened lava (large) - Bombs— ejected as hot lava (large)

11. Types of Volcanoes 10.1 The Nature of Volcanic Eruptions • Anatomy of a Volcano • A volcano is a mountain formed of lava and/or pyroclastic material. • A crateris the depression at the summit/top of a volcano • A conduit carries gas-rich magma to the surface.

12. Magma - Very fluid & the lava can flow great distances – rich in Fe & Mg Eruptions are usually mild & can occur several times Ex. Mauna Loa, HI Types of Volcanoes – 3 main Types 10.1 The Nature of Volcanic Eruptions • Shield Volcanoes • Broad, gently sloping volcanoes, usually the largest built from basaltic lavas, shaped like a shield

13. Cinder Cones • Cinder Cones - Ex. Paricutin, Mexico • Small steep sloped volcanoes built primarily of pyroclastic material ejected from a single vent. • Magma: gas rich in basaltic lava, ejects lava • fragments – mostly cinders - Eruption: typically a single eruption lasting a few weeks to a few years

14. 10.1The Nature of Volcanic Eruptions • Composite Cones (a.k.a. Stratovolcano) • Steep sides w/ alternating layers of ash, cinder, and lava - Magma: Thick magma contains trapped gases, very viscous, silica rich - Eruptions alternate between flows and explosions (cinder & ash) & pyroclastics Most violent Ex. Mt. Shasta, CA Mt. St. Helens, WA

15. Mount St. Helens Before and After the May 18, 1980, Eruption

16. Size Comparisons of Volcanoes

17. Different types of volcanoes

18. Other Volcanic Landforms 10.1The Nature of Volcanic Eruptions • Calderasare large depressions in volcanoes. • Nearly circular • Formed by collapse of the vent • Lava Plateaus • Fluid basaltic lava extruded from crustal fractures called fissures.

19. Plutons 10.2 Intrusive Igneous Activity • Plutonsare intrusive igneous structures that result from the cooling and hardening of magma beneath the surface of Earth.

20. Plutons Sill 10.2 Intrusive Igneous Activity • Sills and laccoliths are plutons that form when magma is intruded close to the surface. - Sills resemble buried lava flows and may exhibit columnar joints. Store magma. - Laccoliths are lens-shaped masses that arch overlying strata upward. Transport magma.

21. Plutons 10.2 Intrusive Igneous Activity • Batholiths arelarge masses of igneous rock that formed when magma intruded at depth, became crystallized, and subsequently was exposed by erosion. Ex) Mount Rushmore • An intrusive igneous body must have a surface exposure greater than 100 square kilometers to be considered abatholith.

22. Origin of Magma 10.2 Intrusive Igneous Activity • Magma originates when rock located in the lithosphere partially melts.

23. 10.2 Intrusive Igneous Activity • The geothermal gradient— Earth’s natural temperature is not sufficient to melt rock in lithosphere • Additional heat is generated by: - friction in subduction zones - rocks heated during subduction - rising, hot mantle rocks

24. 10.3 Plate Tectonics and Igneous Activity Lava

25. Where Do Volcanoes Occur? • Mostly occur at plate boundaries • Convergent plate boundaries: 75% of active volcanoes • Ex: Ring of Fire • Divergent plate boundaries: as plates move apart, magma rises to fill the space - Ex: Iceland, Mid-Atlantic Ridge

26. Convergent Plate Boundaries 10.3Plate Tectonics and Igneous Activity • Ocean-Ocean • Forms volcanic island arcs in an ocean Ex. Aleutian Islands • Ocean-Continent • Forms continental volcanic arcs Ex. Andes Mountains

27. Divergent Plate Boundaries 10.3Plate Tectonics and Igneous Activity • The greatest volume of volcanic rock is produced along the oceanic ridge system. Ex. Mid-Atlantic ridge • Lithosphere pulls apart. • Partial melting occurs • Oceanic Ridges form

28. Intraplate Igneous Activity 10.3Plate Tectonics and Igneous Activity • Intraplate volcanism occurs within a tectonic plate away from plate boundaries. • Occurs when hotter than normal mantle material called a mantle plume rises to the surface. • Forms localized volcanic regions called hot spots. • Ex. Hawaiian Islands (Kilauea) & Columbia Plateau.

29. 10 Most Active Volcanoes