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Lava Video  Volcanoes are weak spots in the crusts where molten material, or magma, comes to the surface.  When magma reaches the surface it is called.

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Presentation on theme: "Lava Video  Volcanoes are weak spots in the crusts where molten material, or magma, comes to the surface.  When magma reaches the surface it is called."— Presentation transcript:


2 Lava Video

3  Volcanoes are weak spots in the crusts where molten material, or magma, comes to the surface.  When magma reaches the surface it is called lava.  The lava released during volcanic activity builds up Earth’s surface, it is a constructive force.

4  There are about 600 active volcanoes on land, many more lie beneath the sea.  Most volcanoes occur along volcanic belts which lie along plate boundaries.  Most volcanoes occur along diverging plate boundaries, such as the mid-oceanic ridge.  The biggest volcanic belt is the Ring of Fire that lies along the edges of the Pacific Ocean.

5  Many volcanoes occur on islands, near plate boundaries where two oceanic plates collide.  When the magma breaks through the ocean floor it creates volcanoes.  The resulting volcanoes create a string of islands called island arcs.  Examples of island arcs are Japan, New Zealand, Indonesia, and the Caribbean Islands.  Birth of a Volcano Birth of a Volcano

6  Some volcanoes result from hot spots in Earth’s mantle.  A hot spot is an area where magma from deep within the mantle melts through the crust like a blow torch.  Hot spots often lie in the middle of plates far from any plate boundaries.  A hot spot volcano in the ocean floor can gradually form a series of volcanic mountains. (HAWAII)  Hot spots can also form under the continents. (YELLOW STONE NATIONAL PARK) Last volcanic eruption there occurred 75,000 year ago.  Under Water Hot Spots Under Water Hot Spots

7  Lava begins as magma in the earth’s mantle.  Because magma is less dense than the surrounding solid material, magma flows upward into any cracks in the rock above.  Magma rises until it reaches the surface, or until it becomes trapped beneath layers of rock.  All materials go from areas of high pressure to areas of low pressure. Magma reacts in the same way.

8  During a volcanic eruption, the gases dissolved in magma rush out, carrying the magma with them.  Picture to the right is Mount St. Helens.

9  Beneath a volcano magma collects in a pocket called a Magma Chamber.  The magma moves through a Pipe, a long tube in the ground that connects the magma chamber to the Earth’s surface.  The volcanoes Vent is the point on the surface where magma leaves the volcanoes pipe.  Lava can collect in the Crater the bowl shaped area that forms around the volcanoes vent.

10  Some types of magma are thick and flow very slowly. Other types of magma are fluid and flow almost as easily as water.  The hotter the magma, the more fluid it is.  The amount of silica in magma also helps determine how easily magma flows. Silica is a material formed the from the elements of oxygen and silicon. The more silica magma contains the thicker it is.  Obsidian is high in silica

11  A volcano erupts quietly if its magma flows easily.  Thin, runny lava oozes quietly from the vent.  Quiet eruptions produce two different types of lava known as “pahoehoe” which is lava that flows like a solid mass of wrinkles, billows, and chunks.  The second type of lava is called “aa.” Which translated means “painful to walk on.”

12  If a volcanoes magma is thick and sticky, a volcano erupts explosively.  The thick magma does not flow out of the crater and down the mountain. Instead it slowly builds up in the volcano’s pipe, like putting your finger over a garden hose.  Dissolved gases cannot escape from the thick magma. The trapped gases build up pressure until they explode.

13  Explosive volcanoes create volcanic ash, cinders, and large pieces of lava called bombs.  These bombs can be as big as cars.  Pyroclastic flows occur when an explosive eruption hurls out ash, cinders, and bombs.  Pyroclastic flows are quick they can travel between 100 and 200 mph. You will be cooked if you are around one of these.  Pyroclastic Flow Video Pyroclastic Flow Video

14  During a quiet eruption, lava flows pour from vents, setting fire to and then burying everything in their path.  During an explosive eruption, a volcano can throw out hot, burning clouds of volcanic gases as well as cinders and bombs.  Volcanic ash can bury entire towns, damage crops, and collapse the roofs of homes.

15  The activity of a volcano may last from less than a decade to more than 10 million years.  An active, or live, volcano is one that is erupting or has shown signs that it may erupt in the near future.  A dormant, or sleeping, volcano may be awaken in the future and become active. (Mt. Taranaki-New Zealand Pictured to the right)  An extinct, or dead, volcano is unlikely to erupt again.  Dating Lava Flows Dating Lava Flows

16  Hot springs and geysers are two examples of volcanic activity that do not involve the eruption of lava.  These features may occur in any volcanic area-even around an extinct volcano.  A hot spring forms when groundwater heated by a nearby body of magma rises to the surface and collects into a natural pool.  Japanese Macaque is relaxing in a hot spring to the right in a cold winter day

17  Sometimes, rising hot water and steam become trapped underground in a narrow crack. Pressure builds until the mixture suddenly sprays above the surface as a geyser.  A geyser is a fountain of water and steam that erupts from the ground.

18  Rock and other materials formed from lava create a variety of landforms including shield volcanoes, composite volcanoes, cinder cone volcanoes, calderas and lava plateaus.

19  At some places on Earth’s surface, thick layers of lava pour out of a vent and harden on top of previous layers.  Such lava flows gradually build a wide, gently sloping mountain called a shield volcano.

20  Cinder Cone Volcanoes are steep, cone shaped hills or mountains.  If a volcanoes lava is thick and stiff, it may produce ash, cinders, and bombs.  These materials pile up around the vent in a steep, cone shaped pile.

21  Sometimes, lava flows alternate with explosive eruptions of ash, cinder, and bombs.  This creates a Composite Volcano which are generally tall, cone shaped mountains in which layers of lava alternate with layers of ash.  Example is Mount Fuji or Mount St. Helens.

22  Enormous eruptions may empty the main vent and the magma chamber beneath the volcano.  The mountain becomes a hollow shell with nothing to support it. This hollow shell is known as a Caldera.  Crater Lake is pictured to the right

23  Instead of forming mountains, some eruptions of lava form high, level areas called Lava Plateaus.  This is usually caused by thin, runny lava traveling far before cooling and solidifying.

24  Before an eruption, magma moves into the area beneath the volcano and collects in a magma chamber, or reservoir. As it comes closer to the surface, the magma releases gases.  These events can offer valuable clues about the likelihood of an eruption.  For example, the movement of magma produces small earthquakes and vibrations (seismicity).

25  Magma gathering in a chamber causes slight swelling of the volcano's slopes. Gases released near the volcano can be measured for changes in quantity and makeup.  A number of tools can be used to record these warning signs. Seismographs can detect small earthquakes, while tiltmeters and geodimeters can measure the subtle swelling of a volcano. Correlation spectrometers (COSPECS) can measure amounts of sulfur dioxide--a telltale gas that is released in increasing quantities before an eruption.

26  Lava Sampling Video in Hawaii Lava Sampling Video in Hawaii  Dating Lava Flows in Hawaii Dating Lava Flows in Hawaii  Mount Pinatubo Prediction Mount Pinatubo Prediction  Mount Pinatubo Aftermath Mount Pinatubo Aftermath

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