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Volcanoes p.p. --one to use
 

Volcanoes p.p. --one to use

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    Volcanoes p.p. --one to use Volcanoes p.p. --one to use Presentation Transcript

    • Introduction to volcanoesVolcano: an opening in the earth’s surface through which lava, hot gases, and rock fragments erupt
    • Origin of Volcanoes1. Magma 50-100 miles below the earth’s surface slowly begins to rise to the surface2. As the magma rises it melts gaps in the surrounding rock3. As more magma rises a large reservoir forms as close as 2 miles below the surface (magma chamber)
    • Origin of Volcanoes4. Pressure from the surrounding rock causes the magma to blast or melt a conduit (channel) to the surface where magma erupts onto the surface through a vent (opening)
    • Origin of Volcanoes5. The magma, now called lava, builds up at the vent forming a volcano
    • Origin of Volcanoes6. Often the volcano sides will be higher than the vent forming a depression called a crater
    • Crater:
    • Caldera: an unusually large crater or the remains when the cone collapses into its own magma chamber
    • Anatomy of a VolcanoCone: the above ground structure built from lava and/or tephra
    • Conduit: the path that magma takes from the magma chamber to the vent
    • Magma Chamber: the reservoir located under the volcano where magma collects and becomes the supply of magma/lava to build the volcano
    • Parasitic Cone: a smaller secondary volcano built on the side of or near the main volcano, but sharing the same conduit to the magma chamber
    • Fumarole: a secondary vent that emits only gases
    • Fissure: a long fissure (crack) from which lava flows
    • Vent: opening of the volcano, through which lava, ash and gases flow
    • Take a minute tolabel the parts onthe diagram (not all parts are shown)
    • Crater Ash Cloud/Gases VentParasitic Cone Lava Flow conduit mantle Magma chamber
    • Lava— There are 3 kinds:
    • Pahoehoe lava: Hot, thin, fast flowing harden with a relatively smooth surface Often has a ropy or wrinkled appearance
    • Pahoehoe lava:
    • Aa lava:• Cooler, thicker, slow moving• Hardens with a rough, jagged, sharp edge surface
    • Pillow Lava: Lava suddenly cooled by water shows sack-like segments (stuffed pillows)
    • Can you identify the kindsof lava from the pictures? Circle your choice.
    • Tephra (pyroclastic, rock fragments) Volcanic Dust: Smallest particles and carried by atmosphere circulation
    • Volcanic Ash: 0.25-0.5 cm diameter Generally settles out within miles of the cone but can be carried greater distances by stronger winds. Forms a mudflow when mixed with water
    • Bomb: Smaller bombs (gravel, pea size) are called cinders. Walnut size bombs are called lapilli. Larger fragments up to 4+ feet in diameter are called bombs.
    • Lahar (mudflow): mixture of ash, eroded land, and water flowing down river valleys
    • Lahar (mudflow):
    • Gases: water vapor, carbon dioxide, nitrogen, sulfur dioxide, hydrogen sulfide, chlorine
    • Locations of VolcanoesDivergent Boundaries: As the plate move long cracks (rifts) form and lava builds up forming volcanoes.
    •  If the boundary is on the ocean floor, volcanoes can grow tall enough to break the surface of the ocean and become islands (Iceland)
    • Convergent Boundaries: Places where plates are moving toward each other forming a subduction zone. One plate melts under the other and the magma moves upward to form volcanoes.
    •  Example: Pacific Ring of Fire
    •  Example: Cascade Volcanoes
    • Hot Spots Magma that may originate in the mantle or outer core will move upward, breaking the surface and forming a volcano, they are independent of plate boundaries and a chain of volcanoes may form as the plate moves across a hot spot.
    • Hot Spots (Examples: Hawaiian Islands and Yellowstone National Park)
    • Types of Volcanic Eruptions Two factors determine the type of eruption: Amount of water vapor & other gases in the magma The chemical composition of the magma
    • Explosive Eruptions Trapped gases under high pressure will violently explode when the magma reaches the lower pressure of the surface. Has granitic magma is very thick and plugs the vent causing the pressure to build until it blows violently out the vent The high water content of the magma produces more water vapor which when mixed in granitic magma produces explosive eruptions
    • Explosive EruptionsMt. Pinatubo Mont serrat Mt. St. Helens
    • Quiet Eruptions Low pressure gas Has basaltic magma (is more fluid and will flow instead of explode) And has low water content
    • Types of Volcano MountainsCinder Cones: Small base, steep-sided, loosely consolidated Up to 1000 feet tall Life span of a few years Commonly built from gravel size lava rock fragments call cinders Has violent eruptions, dangerous when close.
    • Types of Volcano MountainsCinder Cones:
    •  High pressure gas bubbles cause thick lava to explode into the air; lava begins to cool as it rises and falls, becoming very sticky When lava hits the ground it sticks rather than flows This builds a steep cone with a small base
    • Sketch a Cinder Cone Volcano:
    • Types of Volcano MountainsShield Volcanoes: Large base, gentle slope, lava rock layers A few miles wide Life span of a million years or more The lava is hot, thin, very fluid, often basaltic. Example: Hawaiian Islands
    • Take a look at these examples:http://www.volcano.si.edu/world/tpgallery.cfm?category=Shield%20Volcanoes The Mauna Loa volcano in Hawaii— the largest volcano on Earth—has the broad expanse characteristic of shield volcanoes. It spreads across half the island of Hawaii. Shield volcano on Mars; Taken from space
    • Shield Volcanoes Mauna Kea
    • Sketch a sheild Volcano:
    • Types of Volcano MountainsComposite (strato) Volcanoes: Large mountain volcano often snow capped, a few miles high Life span of million years or more Have alternating eruptions of tephra (air- borne) and lava. The tephra adds height to the volcano and the lava cements the tephra together and adds to the base. Found mostly in subduction zones and have violent eruptions.Examples: Mt Rainier, Mt Fuji, Mt Kilimanjaro
    • Composite (strato) Volcanoes: (Make a Flip-Book) Mt. FujiMt. Rainier Mt. Kilimanjaro
    • Sketch a composite Volcano:
    • Volcano Activity Levels (Stages)Active (awake): Has erupted within recent time and can erupt again at any time.Pre-eruption activities:  Increase in earthquake activity under the cone  increase in temperature of cone,  melting of ice/snow in the crater  swelling of the cone  steam eruptions  minor ash eruptions
    • Mt St. Helens
    • Dormant (sleeping): No eruption within recent times, but there is record of past eruptions Can become active and erupt again after a “wake up” period Example: Mt. Rainier
    • Extinct: No eruption within recorded history Not expected to ever erupt againExample: Mount Mazama (Crater Lake)
    • Crater Lake
    • Mount Rainier • The most dangerous volcano in the US • The danger is mostly from lahars traveling down river valleys at a speed of 25mph and destroying everything in its path • 100,000 people live on the solidified mudflows of previous eruptions
    • Mount Rainier • The mountain is dangerously unstable, a tall, steep heap of loose rock held together by the force of gravity and a cubic mile of glacier ice that could be melted or shaken loose • Lahar flows average every 500 years and have gone as far as the Puget Sound lowlands (1 in 7 chance of it happening during your lifetime) • Mount Rainier has erupted 4 times in the last 4000 years with the last eruption 200 years ago
    • VolcanoVideos• http://video.nationalgeographic.com/video/player/ environment/environment-natural- disasters/volcanoes/volcano-eruptions.html• http://video.nationalgeographic.com/video/player/ environment/environment-natural- disasters/volcanoes/volcano-lava.html• http://video.nationalgeographic.com/video/player/ environment/environment-natural- disasters/volcanoes/volcano-eruptions.html