Chapter 5: Volcanoes How does a volcano erupt? BrainPop: http://www.brainpop.com/science/earthsystem/volcanoes/
1: Volcanoes and Plate Tectonics Where Are Volcanoes Found on Earth s Surface?
Volcano A mountain that forms in Earth s crust when molten material, or magma, reaches the surface. Magma: Molten mixture of rock-forming substances, gases, and water from the mantle. (beneath the surface) Lava: Magma that reaches Earth s surface. (on the surface)
Volcanoes and Plate Boundaries Volcanic belts form along the boundaries of Earth s plates. Divergent boundaries Convergent boundaries
Divergent Boundaries Move apart Mid-ocean ridges Rift valleys
Converging Boundaries Convergent (come together) Volcanoes can form where two oceanic plates collide: Older, denser plate sinks into the mantle creating a deep-ocean trench Due to the water entering the mantle, the mantle partially melts Magma rises up and breaks through the ocean floor creating a volcano
Ring of Fire Major belt of volcanoes Around the border of the Pacific Ocean
Island Arc String of islands (from the collision of two oceanic plates) Examples: Japan, New Zealand, Aleutians, and Caribbean islands http://esminfo.prenhall.com/science/geoanimations/animations/35_volcanicact.html
Hot Spots Area where material from deep inside the Earth s mantle rises through the crust and melts to form magma. Plates move over hot spots Example: Yellowstone National Park
What Happens When a Volcano Erupts? What Are the Stages of Volcanic Activity?
INSIDE A VOLCANO Open to page 139 in your textbook. Fill in Figure 1 as we go! Magma chamber: The pocket beneath a volcano where magma collects. Magma chamber
Pipe: Inside a Volcano A long tube through which magma moves from the magma chamber to Earth s surface. Pipe
Vent: Inside a Volcano The opening through which molten rock and gas leave a volcano. Central vent Side vent
Inside a Volcano Lava flow: The area covered by lava as it pours out of a volcano s vent. Lava flow
Inside a Volcano Crater: A bowl-shaped area that forms around a volcano s central opening. Crater
Inside a Volcano Central vent Crater Side vent Lava flow Pipe Magma chamber
What Happens When a Volcano Erupts? What Are the Stages of Volcanic Activity?
A Volcanic Eruption When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent. Quiet Explosive
Quiet Eruptions Magma is hot Low in silica (forms from elements oxygen and silicon) Thin magma Runny magma Example: Hawaiian Islands
Quiet Eruptions = Different Types of Lava Pahoehoe: from fast-moving, hot lava that is thin and runny; looks like ropelike coils Aa: from lava that is cooler and thicker (slower); rough surface consisting of jagged lava chunks
Explosive Eruptions High in silica Thick Sticky Gases build up pressure (explosive) Example: Mount St. Helens
Chunks Thrown in the Air Smallest: ash (dust-sized) Medium: cinders (pebble-sized) Large: bombs (size of golf ball to size of car)
Volcano Hazards Lava: set fire and bury Pyroclastic flow: mixture of hot gases, ash (small specks of dust), cinders, and bombs (large chunks) that flow down the sides of a volcano (occur during an explosive eruption) Landslide: mud, melted snow and rock
Stages of Volcanic Activity Active: Live; is erupting or has shown signs that it may erupt in the near future Dormant: Sleeping; expected to erupt in the future Extinct: Dead; Unlikely to ever erupt again
Warnings of a Possible Eruption Tiltmeter: detects slight surface changes in elevation and tilt caused by magma moving underground Monitor gases escaping from the volcano Monitor the many small earthquakes that occur around a volcano before an eruption Rising temperatures in underground water
1. Which has more silica an explosive or a quiet volcano? -Explosive 2. What are golf-ball to car-sized particles shooting out of a volcano called? -Bombs 3. A volcano that may erupt sometime in the future is known as. -Dormant
3: Volcanic Landforms What Landforms Do Lava and Ash Create? What Landforms Does Magma Create?
What Landforms Do Lava and Ash Create? Calderas Shield Volcanoes Cinder Cone Volcanoes Composite Volcanoes Lava Plateaus
Caldera The hole left when a volcano collapses (a lake can form, filling the hole) http://dli.taftcollege.edu/streams/geography/animations/caldera.html
Cinder Cone Volcanoes Steep, cone-shaped hill or small mountain High silica (thick, sticky) Explosive Example: Paricutin (Mexico, 1943)
Composite Volcanoes Tall, cone-shaped mountains in which layers of lava alternate with layers of ash Silica content varies (lava flows and explosive eruptions) Example: Mt. Fuji (Japan) and Mount St. Helens (Washington)
Shield Volcanoes Gentle sloping mountain from lava flow Hot spot volcanoes are usually shield volcanoes Example: Mauna Loa (Hawaii)
Lava Plateaus Lava flows out of long cracks Over time runny lava builds up a high, level area (called a plateau) Example: Columbia Plateau (Washington, Oregon, and Idaho)
Cinder Cone Landforms Composite (Stratovolcano) Shield Lava Plateau
What Landforms Does Magma Create? Volcanic necks Dikes Sills Dome mountains Batholiths
Formed when magma hardened in an ancient volcano s pipe. Later, soft rock around the pipe wore away, exposing the harder rock inside Volcanic Neck
Dikes and Sills Dike: Magma that forces itself vertically across rock layers and hardens Sill: Magma that squeezes between horizontal rock layers hardens to form a sill.
Dome Mountains Forms when uplift pushes a large body of hardened magma toward the surface Example: Black Hills (South Dakota)
Batholiths A mass of rock formed when a large body of magma cools inside the crust. Half-Dome in Yosemite Natl. Park
The Big Question How does a volcano erupt?