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Distribution of volcanoes in the world . A.M.F NAZRIN, Dept. of Natural Resources, Sabaragamuwa University Of Srilanka .


Volcano?????...... Vesuvius , Krakatoa , Fujiyama , and Mount St. Helens .........What are these names? These are the names of some well-known volcanoes. Most people have never seen a real volcano but have learned about them through movies or books.

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Volcanoes are a type of landforms produced by extrusive igneous activity and are mountains built of lava and/or tephra .

Geographic distribution of volcanoes:

Geographic distribution of volcanoes Indonesia / Ice land and arctic Ocean / Hawaii and the Pacific ocean / Japan Taiwan and Marianas

How many volcanoes are there?:

How many volcanoes are there? There are more than 1500 active volcanoes on the Earth. We currently know of 80 or more which are under the oceans. Active volcanoes in the U.S. are found mainly in Hawaii, Alaska, California, Oregon and Washington. ACTIVE VOLCANO - An active volcano is one that erupts regularly.

What is the largest active volcano?:

What is the largest active volcano? The world's largest, active volcano is Mauna Loa in Hawaii , 13,677 feet above sea level and taller than Mount Everest.

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Volcanoes are not scattered randomly on the Earth’s surface. They occur in belts in some areas and are absent from others. Earth’s major volcanoes

What does distribute the volcanoes in this pattern? :

What does distribute the volcanoes in this pattern? Why do they occur in belts in some areas and are absent from others?


World map showing plate boundaries (blue lines ), the distribution of recent earthquakes (yellow dots) and active volcanoes (red triangles ). Courtesy of NASA.

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. Most occur along tectonic plate boundaries. Location of the Earth's major volcanoes

What are these “plates”?:

What are these “plates”? Planet earth, which we live is a thin skin of solid crust and the rigid uppermost mantle making up Earth's lithosphere.

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. The lithosphere is broken up into slabs that geologists call lithospheric plates or tectonic plates that are in motion. (1960) This is the theory of plate tectonics and is important to geology as the theory of relativity is to physics, the atomic theory to chemistry, or evolution to biology.

The major plates of the world.:

The major plates of the world.

There are usually seven or eight "major" plates and dozens of smaller plates.:

There are usually seven or eight "major" plates and dozens of smaller plates. Major plates African Plate Antarctic Plate Indo-Australian Plate , sometimes subdivided into: Indian Plate Australian Plate Eurasian Plate North American Plate South American Plate Pacific Plate Minor plates Arabian Plate Caribbean Plate Juan de Fuca Plate Cocos Plate Nazca Plate Philippine Sea Plate Scotia Plate

Plate boundaries?:

Plate boundaries? The basic idea of plate tectonics is that earth’s surface is divided in to a few large thick plates that move slowly and change in size. The regions along the boundaries of plates are geologically active areas characterized by earth’s quacks and volcanoes. Tectonic plates interact with one another in three basic ways, creating three different types of plate boundaries.

Volcanism at plate boundaries.:

Volcanism at plate boundaries. Divergent plate boundary Convergent plate boundary Transform plate boundary

Divergent plate boundaries:

Are initiated when a single plate is split in to two and diverge from one another. Divergent plate boundaries

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As the plate fragments move apart molten rock material rises from the asthenosphere. Under water eruptions such as these produce elongated groups of undersea volcanoes, called mid-oceanic ridges. Eg: Iceland and Mid- Atlantic ridge.

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Mid oceanic ridges of the world

Convergent plate boundaries:

Convergent plate boundaries Plates move toward each other and less-dense plate will override the denser plate. By the character of the plates involved, this is divided into 3 types. Ocean-Continent convergence. Ocean-Ocean convergence. Continent-Continent convergence.

Ocean-continent convergence.:

Ocean-continent convergence. Oceanic plate bends beneath the continental plate and sinks along what is known as a subduction zone , a zone where oceanic plate descends into the mantle. The magma is less dense than the overlying solid rock. Therefore, the magma created along the subduction zone works it’s way upward and erupts as volcanoes.

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E.g:The entire Pacific ocean basin is surrounded by chains of active volcanoes often called the “Ring of fire”. Andes mountain range ;Nazca plate is subducting beneath the south American plate cascade range of Washington ; Juan de Fuca plate is subducting beneath the north American plate.

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What is the Ring of Fire? Pacific Ocean. The Ring of Fire has 452 volcanoes and is home to over 50% of the world's active and dormant volcanoes. Ninety percent of the world's earthquakes and 81% of the world's largest earthquakes occur along the Ring of Fire.

Ocean-Ocean convergence.:

Ocean-Ocean convergence. If both plates are oceanic the denser plate will subduct beneath the less-dense plate. The resulting mountain belt is called a volcanic island arc E.g.: Aleutian islands in Alaska , Islands of Indonesia and Sumatra

Continent-Continent Convergence:

Continent-Continent Convergence Continental lithosphere is much less dense tan the mantle below and neither plates subducts. They buckle and deform significant vertical uplifts. E.g.: Himalayan mountain belt and mount. Everest.

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Mountain building occurs as the continental crust is folded and faulted Earthquakes occur as two continents collide NO volcanic activity Continent-Continent Convergent Plate Boundary

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Transform boundaries Occurs where two plates slide horizontally past each other. This boundary is not involved in volcanism but in earthquakes. E.g.: Alpine fault of New Zealand , The San Andreas fault in California

What about Hawaiian chain? Yellowstone? Iceland?:

What about Hawaiian chain? Yellowstone? Iceland? They are not situated in plate boundaries.

Hotspot-produced volcanoes.:

Hotspot-produced volcanoes. Mantle plumes and Hot spots The convection process in the asthenosphere occurs in the form of mantle plumes. Plumes form “hot spots” of active volcanism at earth’s surface(mid plates)

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