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Dear Students, Today in class you will learn all about volcanoes. :) Please carefully read the attached power point and answer the questions on your "Volcanoes Notes" page. (I have numbered the pages- 104a and 104b.) Note: Volcanoes will not be on the next quiz, but we still need to learn about them. :) We will have an activity to do about volcanoes in the near future. Reminders: Our quiz over fossils will be on Friday 1/17. It will cover sections 6-1, 6-2, and 6-4. HW: Read P. 152-155 of ther textbook and complete the graphic organizer ("Uniformitarianism" by Monday.). Make sure that everything is completed and glued into your composition notebook for Monday. I will come around and check notebooks and make sure you are keeping up with them on Monday. You will receive a homework grade for your efforts. Make me proud! :)You may update your table of contents now:100 Fossil Foldable101 Fossils Checkup102 Uniformitarianism103 Fossils WS104a-b Volcanoes Notes
1. Brainpop • Before you start on this Power Point, watch the Brainpop about Volcanoes and take the “Graded Quiz”. • www.brainpop.com • User name: webbbridge • Password: wbms
The word volcano comes from name of the roman god of fire, Vulcan. Vulcan, Roman God of Fire
A volcano is a place on the surface where molten rock, gases and pyroclastic debris erupt through weak spots in the earth's crust. Volcanoes vary quite a bit in their structure - some are cracks in the earth's crust where lava erupts, and some are domes, shields, or mountain-like structures with a crater at the summit. 2. What is a Volcano?
Magma is a molten mixture of rock forming substances (liquid rock), gases, and water vapor inside the Earth. When it reaches the surface it is called lava. It forms igneous rock when it cools. 4. Reshapes the surface by adding to land, creating mountains and islands. 3. Magma or Lava?
5. Location of Volcanoes • Most occur on diverging plate boundaries or in subduction zones at converging boundaries. • About 600 active volcanoes on land, and more under the ocean.
Underwater rift valleys where new crust is being created from lava pouring out of cracks in the ocean floor. Only in a few places like Iceland and the Azores do they rise above the ocean surface. Divergent Boundaries Worlds longest mountain range is the Mid-Atlantic Ridge Mid-ocean Ridges
Mid-Ocean Ridges The Mid-Atlantic Ridge is not the world’s only mid ocean ridge! Look at all of the other ones.
Subduction can cause a series of volcanoes parallel to the plate boundary. • This creates mountain ranges like the Andes and volcanoes in the Pacific Northwest. • At sea they create island arcs like Japan.
6. The Ring of Fire • A large number of volcanoes lie directly on tectonic plate boundaries. In fact, the plate boundaries surrounding the Pacific Ocean have so many volcanoes that the area is called the Ring of Fire.
7. Hot Spots Hot spots are volcanically active places on the Earth’s surface that are far from plate boundaries. More rarely, volcanoes are found in the middle of plates. Most of these volcanoes occur within oceanic plates. The Yellowstone volcano is doubly rare, because it is found in the middle of a continental plate. This map shows selected hotspots throughout the world. It is believed that more than 100 such hotspots have been active during the past 10 million years
Can occur in the middle of plates. The plate moves over a stationary hot spot. A chain of islands is formed over millions of years as the plate drifts over the hot spot. Hot Spot Volcanoes
Magma rises because it is less dense than the surrounding solid material. It will rise to the surface unless it is trapped beneath layers of rock. 8. Magma and the Earth’s Surface
When a volcano erupts, the dissolved gases (carbon dioxide and water vapor mainly) rush to the surface, carrying the magma with it, At the surface the magma becomes lava. A Volcano Erupts
A large underground pocket formed by the rising magma. Magma Chamber Pipe
Sometimes lava will exit from cracks in the side of a volcano. Side Vent
Narrow, almost vertical crack in the crust that carries the magma to the surface. Note: The “pipe” is sometimes called a “vent”. Pipe
Bowl shaped area that forms around the vent. Crater Lake in Oregan was formed when Mount Mazama blew its top some 8,000 years ago. Crater
The river of lava that gravity causes to flow down the side of a volcano Lava Flow
Is the resistance a liquid has to flowing. Honey has a high viscosity as it pours very slowly. Water has a low viscosity as it pours quickly. 9. Viscosity
Magma • Silica in Magma • The two most abundant elements in earth's crust and mantle are oxygen and silicon. These two elements combine to form the molecule called silica. (Note that silicon is an element, while silica is a molecule). The formula for silica is: • SiO2 Magma with a low silica content = runny lava (low viscosity). These are quiet eruptions (non-explosive). Magma with high silica content = thick lava (high viscosity). These are explosive eruptions.
11. IMPORTANT:**The higher the silica content of a magma, the higher the viscosity(thickness) and more explosive the eruption will be.** HIGH LOW Composite Volcano Cinder Cone Volcano Shield Volcano *Also, the more dissolved gases a volcano has, the more explosive the eruption. Silica content Viscosity Violence of eruption
Type of eruption is determined by the amount of gas and the viscosity of the magma. Low pressure gas and low viscosity magma will ooze out, forming shield volcanoes. 12. Quiet Eruptions
Thick magma can plug the volcano pipe like a cork. The pressure can build until it suddenly explodes. The higher the gas content the larger the explosion. 12. Explosive Eruptions
Rock fragments thrown into the air are called tephra. They are classified by size. Dust is the smallest, followed by ash. Larger pieces are called lapilli, which means “little stones.” Also called cinders. Bombs/blocks: The largest tephra thrown from a volcano can be the size of a car or small building. Bombs cool on the way down. Volcanic Material
Very deadly cloud of ash, gas, dust, and other tephra that rushes down the sides of a volcano at speeds of nearly 200-km/hr. Temperature can exceed 700°C. Pyroclastic Flows
One that is currently erupting or may erupt in the very near future. Sakurajima is one of the most active volcanoes on Earth. Since 764 AD eleven eruptions have caused fatalities. The largest historic eruption was in 1471-1476 and caused an unknown number of deaths, probably from pyroclastic flows. An eruption in 1779 caused 153 deaths from tsunami and tephra. Evacuation of the island in 1914 prevent a larger death toll from that eruption. The current eruptive activity began in 1955. 13.Active Volcanoes
Sleeping volcano. Expected to erupt again in the future. Can be thousands of years between eruptions. Dormant Volcanoes
A dead volcano, not considered likely to ever erupt again. Extinct Volcanoes
14. There are 3 basic types of volcanoes • Shield • Cinder Cone • Composite (also called strato volcanoes)
Shield Volcanoes • Built by repeated lava flows from quiet (non-explosive)eruptions. • Builds up a gently sloping volcanic mountain. • Lava is very runny and spreads out over a large area. • Very large. • Ex: Hawaiian Islands
Erupt explosively, forming, the cinders pile up around the vent. This forms steep, cone shaped volcanoes. Tend to be very small. Ex: Paricutin in Mexico Cinder Cone Volcanoes
Also called stratovolcanoes Most common type Has alternating layers of ash and lava. Form from explosive eruptions of pyroclastic material followed by quieter eruptions of lava. (It’s kind of a cross between shield and cinder cone volcanoes.) Ex: Japan’s Mt. Fuji. In the United States: Mt. Ranier in Washington state, and Mt. St. Helens. Composite Volcanoes
More info about Types of Volcanoes • http://www.ruf.rice.edu/~leeman/volcanotype_poster.gif
When magma cools it hardens to solid rock. Igneous rock is usually fairly hard, so when the softer rock and soil around it erodes, these landforms are exposed to view. Landforms from Magma
When the magma in the volcano pipe hardens it forms a volcanic neck. It looks like a giant tooth sticking out of the ground when the softer rock around it erodes away. Volcanic Necks
Magma that forces itself across rock layers is called a dike. Tend to be vertical Dikes
Magma that squeezes between layers of rock before hardening forms sills. Usually horizontal Sills
Very large rock masses that form the core of some mountain ranges. Occurs when a large amount of magma cools below the surface. Stone Mountain in Georgia Batholiths
Volcanoes and Climate Change The explosion of Mount Tambora in 1815 blanketed most of Indonesia in darkness for three days. It is estimated that 12,000 people died directly from the explosion and 80,000 people died from the resulting hunger and disease. The global effects of the eruption were not felt until the next year, however. During large-scale eruptions, enormous amounts of volcanic ash and gases are ejected into the upper atmosphere. As volcanic ash and gases spread throughout the atmosphere, they can block enough sunlight to cause global temperatures to drop. The Tambora eruption affected the global climate enough to cause food shortages in North America and Europe. Later, come back to this slide and read about it here to see why 1816 was called “The Year with No Summer” (Note: do this only when you are finished with your notes). http://www.britannica.com/EBchecked/topic/581878/Mount-Tambora
Volcanic ash caused global temperatures to fall by over 1.2 degrees Celsius . Acted as a “sun filter.” Weather patterns were chaotic for years and temperatures did not return to normal until 1888. In the US 1816 was the “Year without Summer,” as frost in May and snow in June destroyed the crops in New England. Caused famine and death from disease throughout the world. The Year Without Summer
Mount Pinatubo • More recently, the eruption of Mount Pinatubo, June 15, 1991, caused average global temperatures to drop by as much as 0.5°C. Although this may seem insignificant, such a shift can disrupt climates all over the world.
The eruption column of Mount Pinatubo on June 12, 1991, three days before the climactic eruption.
Case Studies- Volcanic Eruptions in History • Visit the National Geographic Website. Click on the “Case Studies” tab. Write down each of the volcanic eruptions and facts about each one. (Do this on the next page of your composition notebook). • http://environment.nationalgeographic.com/environment/natural-disasters/forces-of-nature/
