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Class Announcements

Class Announcements. Term Break extra credit option due Friday at class time. Sign up today to attend a Papago Park extra credit field trip (worth 20 points). Options: Wed., April 16: 10-11AM or 4-5 PM Thurs., April 17: 10-11AM or 2-3 PM. Today’s Lecture: Chapter 9 Volcanic activity.

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Class Announcements

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  1. Class Announcements Term Break extra credit option due Friday at class time. Sign up today to attend a Papago Park extra credit field trip (worth 20 points). Options: Wed., April 16: 10-11AM or 4-5 PM Thurs., April 17: 10-11AM or 2-3 PM

  2. Today’s Lecture: Chapter 9 Volcanic activity Class presentations: Mexican Volcanoes - Shawn Brown Dissolved gases, silica content and explosiveness of eruptions Silicic volcanoes Intermediate volcanoes

  3. lava • gases • pyroclastics Materials extruded during an eruption 2. Materials extruded during an eruption Magmas contain dissolved gases, held in by pressure! 1-6% by weight, Mostly water vapor Gases (volatiles) gases expand causing lava and volcanic rock to explode Magma rises to surface & pressure rapidly drops

  4. Fig. 09.08 Stephen Marshak

  5. Nature of volcanic eruptions Importance of gas in eruptions Expanding gas provides the force to fragment and violently expel molten rock & ash.

  6. lava • gas • pyroclastics Materials extruded during an eruption 2. Materials extruded during an eruption Expanding gases pulverize rock, forming ash. Violent escape hurls ash, blocks of rock and blobs of magma into the air above the volcano Pyroclastic materials

  7. Silica-rich magmas produce explosive eruptions. • Violent volcanic eruptions produce: • rock fragments • finely fragmented ash • molten bombs • large angular blocks These accumulate to form: pyroclastic volcanic rocks

  8. Three basic general volcano types: a. Shield volcanoes b. Cinder cones c. Composite cones • Composed of • pyroclastics • Small, steep sided • cones • Sometimes have • associated flows

  9. Cerro Negro Nicaragua

  10. San Francisco Volcanic Field, AZ

  11. Sunset crater, AZ

  12. Types of Volcanoes a. Shield volcanoes b. Cinder cones c. Composite cones • Symmetrical form • Intermediate size • Alternating lava flows • & pyroclastic deposits

  13. Mt. Fuji, Japan Composite volcanoes erupt pyroclastics and lava in ~ equal Proportions. Mt. Mayon, Philippines

  14. Intermediate and silicic volcanism Most found above subduction zones. Subduction zones

  15. Andes

  16. Mt. Shasta, CA

  17. Mt. Fujiyama, Japan

  18. Fig. 09.05a Stratospheric haze Rising column W. W. Norton Collapsing column Falling lapilli Nuée ardente Features of Explosive Volcanic Eruptions

  19. Hot ash clouds are denser than air and may collapse and rush down volcanic slopes at high speeds forming a nuee ardente (fiery cloud) or ash-flow. Pyroclastic flows

  20. Fig. 09.01a Stephen Marshak

  21. Fig. 09.01b Stephen Marshak

  22. Body cast of Pompeii victim. A mold was formed when hot ash congealed around body, burning it away to leave a mold.

  23. lava • gas • pyroclastics Materials extruded during an eruption 2. Materials extruded during an eruption If hot ash is erupted onto snow, or a lake, or if once deposited, ash becomes saturated by rain, volcanic mudflows may form. These are highly fluid mixtures of water, ash and rock that travel downslope at very high speed, burying whatever is in their path. Volcanic mudflows or “lahars”

  24. Fig. 09.07 U.S. Geological Survey Mount Saint Helens Mudflow

  25. Volcanic hazards map for Mount Rainier WA

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