Volcanoes and plate tectonics

1. Volcanoes and plate tectonics Lava Video

2. Volcanoes, magma, and lava • 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.

3. Location of volcanoes • 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.

4. Island arc’s • 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

5. Hot spot volcanoes • 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

6. Where Does Lava Come From • 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.

7. Volcanic Eruption • During a volcanic eruption, the gases dissolved in magma rush out, carrying the magma with them. • Picture to the right is Mount St. Helens.

8. Inside a volcano • 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.

9. Lava Consistency • 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

10. Quiet eruptions • 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.”

11. Explosive Eruptions • 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.

12. Pyroclastic flow • 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

13. Volcanic Damages • 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.

14. Stages of a volcanoes life • 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

15. Hot Springs • 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

16. Geysers • 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.

17. Landforms from lava and ash • Rock and other materials formed from lava create a variety of landforms including shield volcanoes, composite volcanoes, cinder cone volcanoes, calderas and lava plateaus.

18. Shield volcanoes • 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.

19. Cinder cone volcanoes • 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.

20. Composite volcanoes • 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.

21. Calderas • 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

22. Lava Plateaus • 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.

23. Predicting volcanic Eruptions • 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).

24. Predicting volcanic Eruptions • 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.

25. Volcano Videos • Lava Sampling Video in Hawaii • Dating Lava Flows in Hawaii • Mount Pinatubo Prediction • Mount Pinatubo Aftermath