Chapter 9 Earth Science

 Shield Volcanoes – built of layers of lava released from repeated nonexplosive eruption.  The runny lava spreads out over a wide area.  The layers of lava create a volcano that has gently sloping sides.

 Mauna Kea, Hawaii – the shield volcano shown below is the tallest mountain on Earth when measured from the bottom to it’s peak, including Mount Everest.

 Cinder cone volcanoes – Cone shaped volcano with steeps sides made of pyroclastic material.  Pyroclastic material forms steep slopes.  Small and usually erupt for only a short time.  Often erode easily because the pyroclastic material is not cemented together.

 Stratovolcanoes – have broad bases and sides that get steeper toward the top.  Form from explosive eruptions of pyroclastic material followed by quieter flows of lava.

 Crater – funnel-shaped pit found around the central vent at the top of many volcanoes.  When eruption stops, lava drains back underground making a larger collapsed crater.  Next eruption may blast it away creating a larger and deeper crater.

 Caldera – a large, semicircular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink.  Much larger than a crater.

 Lava Plateau – a wide, flat landform that results from repeated nonexplosive eruptions of lava that spread over a larger area.  Formed from seepage of magma from long cracks or rifts.  Lava can pour out for millions of years and spread over huge areas.

 Volcanoes – are areas of Earth’s surface through which magma and volcanic gases pass.  Explosion of a volcanic eruption can turn an entire mountain into a billowing cloud of ash and rock in a matter of seconds.  Help form fertile land.  Create some of the largest mountains on earth.

 Magma – melted rock below the Earth’s surface.  Lava – Melted rock above the Earth’s surface.

 Flows of lava are calm.  Releases huge amounts of lava.  Vast areas of the Earth’s surface, are covered with lava from non-explosive eruptions such as Hawaii.

 Pahoehoe lava flows – sheet like lava flows that result in continuous surfaces.  Flow smoothly  Move forwards in tongues or lobes and are characterized by a glassy, plastic skin.

 Aa – lava pours out quickly and forms a brittle crust.  The crust is torn into jagged pieces as molten lava continues to flow underneath.  Got its name because of the painful experience of walking barefoot across the jagged surfaces.  Associated with lava fountaining.

 Lava Fountaining – spraying of lava into the air pulsing with the pressure of escaping gases.

 Pillow lava – forms when lava erupts underwater.  Lava forms rounded lumps that are the shape of pillows.

 Blocky Lava – cool, stiff lava that does not travel far from the erupting vent.  Normally forms jumbled heaps of sharp-edged chunks.  Get it’s shape from oozing from a volcano.

 If the water content of magma is high, an explosive eruption is more likely.  Underground the water and magma are under extreme pressures.  When water and magma rise to the top the gases expand rapidly, an explosion can result.  Sometime so rapid a water floating version of lava called Pumice is formed.

 Magma that has a high silica content will tend to cause explosive eruptions.  Silica-rich magma has a stiff consistency.  Flows slowly and hardens in a volcano’s vents plugging the vents.

 The more that is trapped in a volcano the more explosive it will be due to the rapid rate in which the gas escapes from the volcano.

 Pyroclastic material - forms when magma is blasted into the air and hardens.  Volcano’s eruptions may alternate between lava and pyroclastic eruptions.

 Pyroclastic Flow – produced when enormous amounts of hot ash, dust, and gases are ejected from a volcano.  Can move downhill at 200km/h.  Center of the flow can exceed 700 C.

 Volcanic Bombs – large blobs of magma that harden in the air.  The shape of the bomb was caused by the magma spinning through the air as it cooled.

 Lapilli – pebblelike bits of magma that hardened before they hit the ground.  Means “little stones”

 Volcanic Ash – forms when the gases in stiff magma expand rapidly and the walls of the gas bubbles explode into tiny, glasslike silvers.  Makes up most of the pyroclastic material in an eruption.  Problems  Health-Ex: Respiratory, skin, and eye  Environment-Ex: Acid Rain, Contaminated water and Plants damage  Climate- Block Sunlight and Add to Greenhouse  Transportation-Ex: Air travel, damage cars and Roads

 1815, Mount Tambora blanketed most of Indonesia in darkness for more than 3 days.  12,000 people died directly from the explosion.  80,000 people died from the resulting hunger and disease.

 Volcanic ash and gases spread throughout the atmosphere, they can block enough sunlight to cause global temperature to drop.

 1815, Mount Tambora blanketed most of Indonesia in darkness for more than 3 days.  12,000 people died directly from the explosion.  80,000 people died from the resulting hunger and disease.

 Volcanic ash and gases spread throughout the atmosphere, they can block enough sunlight to cause global temperature to drop.

Convergent Plate Boundaries  The basic connection between plate tectonics and volcanism is that plate motions provide the mechanisms by which mantle rocks melt to generate magma. Rising magma can form continental volcanic arcs (Andes Mountains).  Ocean-Ocean  Ocean-Continent Rising magma can form volcanic island arcs in an ocean (Aleutian Islands).

 Two Major Belts  Circum-Pacific (Pacific Ring of Fire)  Cascade Range in USA  Mount Pinatuba in Philippines  Mediterranean Belt  Mount Etna in Italy  Mount Vesuvius in Italy

Divergent Plate Boundaries  The greatest volume of volcanic rock is produced along the oceanic ridge system. Less pressure on underlying rocks Lithosphere pulls apart. Large quantities of fluid basaltic magma are produced. Partial melting occurs

 Rift Zones  Most occur under water along ocean ridges  Results in new ocean floor (seafloor spreading)  Mid-Atlantic Ridge  Part above sea level  Example Iceland

Intraplate Igneous Activity  Intraplate volcanism is igneous activity that occurs within a tectonic plate away from plate boundaries. The activity forms localized volcanic regions called hot spots. Most intraplate volcanism occurs where a mass of hotter than normal mantle material called a mantle plume rises toward the surface. Examples include the Hawaiian Islands and the Columbia Plateau.

 Mantle plumes are areas of hot, upwelling mantle.  A hot spot develops above the plume. Magma generated by the hot spot rises through the rigid plates of the lithosphere and produces active volcanoes at the Earth's surface.Magmahot spotlithosphere  As oceanic volcanoes move away from the hot spot, they cool and subside, producing older islands, atolls, and seamounts.  As continental volcanoes move away from the hot spot, they cool, subside, and become extinct. extinct

 One of the most famous hot spots on Earth are the Hawaiian Islands.  The oldest islands found in the Hawaiian Island chain consist of mostly dead volcanoes. These volcanoes were active millions of years ago, but the moving crust of the ocean floor has carried them away the hot spot that feed the volcanoes.  The newest island is the big island, which today has two active volcanoes. These volcanoes are feed by the same hot spot that used to feed the dead volcanoes on older islands.  Millions of years from now, it is likely that additional islands will form over the same hot spot, as the Earth’s crust carries the big island away from the hot spot it know sits on.

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  Example: Mt. Rainier

Extinct:  No eruption within recorded history  Not expected to ever erupt again Example: Mount Mazama (Crater Lake)