Reading Pre" Ww ere are most of Earth's volcanoes found? ‘* How do hot spot volcanoes form? * volcano * magma © Ring of Fire island arc * hot spot Asking Questions Before you read, preview the red headings. In a graphic organizer like the one below, ask a where, what, or how question for each heading. As you read, write the Fs to your questions. Volcanoes and Plate Tectonics Question Answer Where are Most volcanoes volcanoes, are found along found? plate boundaries. Volcanoes and Plate Tectonics aurre yeaa tc Lab zone’ Where Are Volcanoes Found on Earth’s Surface? rth’s Active Volcanoes on page 83, What s? What other symbol, 1. Look at the map of Ea! symbols are used to represent volcanoe are shown on the map? 2. Do the locations of the volcanoes form a pattern? Do the volcanoes seem related to any other features on Earth's surface? Think About It g Hypotheses Develop a hypothesis to explain where Earth's volcanoes are located In 2002, Mount Etna erupted in glowing fountains and rivers molten rock. Located on the island of Sicily in the Mediterra nean Sea, Mount Etna is Europe’s largest volcano. Over the ls 2,500 years, it has erupted often. The ancient Greeks believe that Mount Etna was one home of Hephaestus, the Greek god 0! fire. Beneath the volcano was the forge where Hephaestus made beautiful metal objects for the other Greek gods. The eruption of a volcano is among the most awe-inspiring events on Earth. A volcano is a weak spot in the crust molten material, or magma, comes to the surface. Magma is? molten mixture of roc forming substances, gases, 2 from the mantle. When magma reaches the surface, itis call? lava. After lava has cooled, it forms solid rock. Lava relea# during volcanic activity builds up Earth’s surfac Ficure 17 Lava Flow on Mount Etna A lava flow from Mount Etna in Sicily almost buried this small building.GR entry Volcanoes and Plate Boundai There are about 600 active volcanoes on land. Many more lie beneath the sea, where it is difficult for scientists to observe and map them. Figure 18 shows the location of some of Earth’s major volcanoes. Notice how volcanoes occur in belts that extend across continents and oceans. One major volcanic belt is the Ring of Fire, formed by the many volcanoes that rim the Pacific Ocean. . Volcanic belts form along the boundaries of Earth’s plates, At plate boundaries, huge pieces of the crust diverge (pull apart) or converge (push together). As a result, the crust often fractures, allowing magma to reach the surface. Most vol- canoes form along diverging plate boundaries such as mid- ocean ridges and along converging plate boundaries where subduction takes place. For example, Mount Etna formed near the boundary of the Eurasian and African plates. Diverging Boundaries Volcanoes form along the mid- ‘ocean ridges, which mark diverging plate boundaries. Recall that ridges are Jong, underwater mountain ranges that some- times have a rift valley down their center, Along the rift valley, lava pours out of cracks in the ocean floor, gradually building new mountains. Volcanoes also form along diverging plate boundaries on land. For example, there are several large volca~ noes along the Great Rift Valley in East Africa, Figure 18 Many of Earth’s volcanoes are located along the boundaries of ‘tectonic plates. The Ring of Fire is a belt of volcanoes that circles the Pacific Ocean. Observing What other regions have a large number of volcanoes? (Go @nline For: More on volcanoes Visit: PHSchool.com ‘Web Code: cfd-1031 Chapter 6 # 205Ficure 19 Volcanoes at Converging Boundaries Volcanoes often form where two oceanic plates collide or where an oceanic plate collides with a continental plate. In both situations, an oceanic plate sinks beneath a trench. Rock above the plate melts to form magma, which then erupts to the surface as lava. 206 + Converging Boundaries Many volcanoes form near con verging plate boundaries where oceanic plates return to 4, mantle. Volcanoes may form where two oceanic plates colIj or where an oceanic plate collides with a continental pla Figure 19 shows how converging plates produce volcanoes Many volcanoes occur near boundaries where two oceanic plates collide. Through subduction, the older, denser plate sinks beneath a deep-ocean trench into the mantle. Some of the rock above the subducting plate melts and forms magma Because the magma is less dense than the surrounding rock, it rises toward the surface, Eventually, the magma breaks through the ocean floor, creating volcanoes. The resulting volcanoes create a string of islands called an island arc. The curve of an island arc echoes the curve of its deep-ocean trench. Major island arcs include Japan, New Zealand, Indonesia, the Philippines, the Aleutians, and the Caribbean islands. Volcanoes also occur where an oceanic plate is subducted beneath a continental plate. Collisions of this type produc the volcanoes of the Andes Mountains in South America and the volcanoes of the Pacific Northwest in the United States. 9) How did the volcanoes in the Andes Gcrecipoine ) Mountains form? Mid-ocean ridge Key EE Fate movement EE subduction"ta Hot Spot in a Box 1. Fill a plastic box half full of cold water. This represents the mantle. 2. Mix red food coloring with hot water in a small, narrow-necked bottle to represent magma, Ficure 20 Hot Spot Volcanoes Eventually, the Pacific plate’s 3. Hold your finger over the movement will carry the island of mouth of the bottle as you Hawaii away from the hot spot. place the bottle in the Inferring Which island on the map center of the box. The formed first mouth of the bottle must be under water. Hot Spot Volcanoes 4, Float a flat piece of plastic 1c 2 » foam on the water above Some volcanoes result from “hot spots” in Earth’s mantle. A the bottle to model a hot spot is an area where material from deep within the mantle tectonic plate rises and then melts, forming magma. A volcano forms above | 5. Take your finger off the ahot spot when magma erupts through the crust and reaches bottle and observe what happens to the “magma.” the surface. Some hot spot volcanoes lie in the middle of plates Making Models Move the far from any plate boundaries. Other hot spots occur on or near plate boundaries. plastic foam slowly along A hot spot in the ocean floor can gradually forma series of | \wner“yne srtosers ee volcanic mountains. For example, the Hawaiian Islands | goes this model a hot spot formed one by one over millions of years as the Pacific plate | volcano? drifted over a hot spot. Hot spots can also form under the con- tinents, Yellowstone National Park in Wyoming marks a hot spot under the North American plate. Section (4 Assessment §@ Target Reading Skill Asking Questions Work with a partner to check the answers in your graphic organizer. |Brochure Asa travel agent, Reviewing Key Concepts 5 1, a. Defining What is a volcano? earns atc Gceay b. Reviewing Where are most volcanoes located? _ cruise that Mika volcanoes in the Relating Cause and Effect What causes volcanoes to eee ESA TYG form at a diverging plate boundary? RSLRGEN ys Wl 2. a, Defining What is a hot spot? Hat yates Ral cup see: b, Summarizing How does a hot spot volcano form? | where they did. volcanoes formed © Predicting What features form as an oceanic plate PRDBOSIEY 8 orci oiotnagys moves across a hot spot? Chapter 6 # 207