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Geohazards: Volcanoes and Earthquakes 5 GEOHAZARDS: 14 Volcanoes and Earthquakes Chapter Outline 14.1 About Volcanoes 14.2 Pele’s Power: Volcanic Hazards reproduction 14.3 Tectonic Hazards: Faults and Earthquakes 14.4 Unstable Crust: Seismic Waves 14.5 Geographic Perspectives: The World’s Deadliest Volcano unauthorized No 2014. Freeman H. W. © Mount Nyiragongo is a volcano located in Virunga 30° N National Park in the Democratic Republic of the Congo. 15° AFRICA Mount Nyiragongo has a molten lake of lava in the crater of its summit, obscured here by steam. Mount 0° Nyiragongo Nyiragongo’s lava is unusually runny, flowing downslope at speeds up to 100 km/h (62 mph). The volcano has 15° twice sent lava streams down into nearby villages and ATLANTIC OCEAN 30° S into the city of Goma. (© Last Refuge/Robert Harding Picture Library/Age 15° W 0° 15° 30° E 45° E Fotostock Inc.) 2 Gervais_c14_002-035v7.0.1_pv6.0.1.indd 2 4/17/14 12:31 PM LIVING PHYSICAL GEOGRAPHY What is a tsunami? Why do some volcanoes explode violently? What causes earthquakes? What was the “Year without a Summer”? reproduction unauthorized No 2014. Freeman H. W. © To learn more about this type of volcano, turn to Section 14.1. 3 Gervais_c14_002-035v7.0.1_pv6.0.1.indd 3 4/17/14 12:31 PM 4 PART III • TECTONIC SYSTEMS: BUILDING THE LITHOSPHERE THE BIG PICTURE Earth’s hot interior and its moving crust create volcanoes and earthquakes. These phenomena shape the surface of the crust and present hazards for people. LEARNING GOALS After reading this chapter, you will be able to: 14.1 ¥ Describe three main types of volcanoes and major landforms associated with each. 14.2 ¥ Explain the hazards volcanoes pose and which geographic areas are most at risk. 14.3 ¥ Explain what causes earthquakes. 14.4 ¥ Describe the types of seismic waves produced by earthquakes, how earthquakes are ranked, and what can be done to reduce our vulnerability to earthquakes. 14.5 ¥ Assess the potential links between large volcanic eruptions, Earth’s physical systems, and people. THE HUMAN SPHERE: Deadly Ocean Wavesreproduction JUST BEFORE 8:00 A.M. ON DECEMBER 26, 2004, the seafloor off the coast of the island of Sumatra, in Indonesia, was thrust upward 5 m (16 ft) in a magnitude 9.1 earthquake. This earthquake was the third stron- gest in recorded history. The movement of the seafloor heaved an estimated 30 km3 (7.2 mi3) of seawater upward, creating a series of waves that radiated across the Indian Ocean. Such large ocean waves triggered tsunami unauthorized A large ocean wave triggered by an earthquake or other natural disturbance of the ocean floor are called tsunamis. by an earthquake or other In the open ocean, the waves traveledNo at nearly the speed of a jetliner natural disturbance. What is a tsunami?* (800 km/h or 500 mph), but they went largely undetected because they had a geohazard A hazard posed to people by wavelength (the distance between wave crests) of hundreds of kilometers. Thus, the thousands of boats in the physical Earth. the Indian Ocean did not detect2014. the waves as they passed underneath. As the waves approached shallow water, however, the wave- lengths decreased and the height of the waves grew up to 15 m FIGURE 14.1 Banda Aceh. A French military helicopter surveys the destruction in Banda Aceh, Indonesia, on January 14, (50 ft) high in some regions. Some coastal areas even experienced 2005. The 2004 tsunami surged across theFreeman crowded city at about 30 m (100 ft) waves. The waves devastated coastal areas along the 60 km/h (35 mph), far faster than a person can run. About 170,000 Indian Ocean, particularly in regions nearest the earthquake. Most people died in Banda Aceh on the day ofH. the tsunami. (© Joel Saget/ of the city of Banda Aceh, on Sumatra (Figure 14.1), was destroyed. AFP/Getty Images) W. In response to this catastrophe, the Indian Ocean Tsunami © Warning System, similar to one already active in the Pacific Ocean, Video was developed and activated in June of 2006. Cell-phone users can Tsunami warning system access a free app that is connected to the detection system and http://qrs.ly/a83w0pv provides real-time data and warnings. It is hoped that with this system in place, another catastrophic loss of life can be avoided. This chapter focuses on geologic hazards, or geo- hazards: hazards presented to people by the physical China Earth. Examples of geohazards include volcanic erup- India Thailand tions, earthquakes, and tsunamis. We first examine 15° N Vietnam BAY OF Cambodia volcano types as well as the behavior of volcanoes BENGAL Malaysia and the hazards they present. We next explore earth- 0° Banda Aceh quakes and the dangers they pose for people. Finally, INDIAN Indonesia OCEAN we take a look at the global reach of large volcanic 90° E 105° E 120° E *Answers to the Living Physical Geography questions are found on page 000. eruptions and their effects on human societies. Gervais_c14_002-035v7.0.1_pv6.0.1.indd 4 4/17/14 12:31 PM CHAPTER 14 • GEOHAZARDS: VOLCANOES AND EARTHQUAKES 5 14.1 About Volcanoes Three Types of Volcanoes active volcano A volcano that has erupted ¥ Describe three main types of volcanoes Volcanoes are surface landforms created by ac- during the last 10,000 years and major landforms associated with each. cumulations of the materials they emit over time. and is likely to erupt again. Although they take on many shapes and sizes, extinct volcano Volcanoes shape Earth’s crust. They can pour cubic most volcanoes can be categorized as either A volcano that has not erupted kilometers of lava onto Earth’s surface to build new stratovolcanoes, shield volcanoes, or cinder for tens of thousands of years islands and landmasses. They form beautiful snow- cones. and can never erupt again. capped peaks that have inspired humans for gen- A stratovolcano, or composite volcano, is a large, stratovolcano erations, and they provide nutrient-rich soils that potentially explosive, cone-shaped volcano com- (or composite volcano) A plants thrive in. Volcanoes can also be extremely posed of alternating layers of lava and pyroclasts. large, potentially explosive cone-shaped volcano dangerous and cause catastrophic loss of human Pyroclasts, or pyroclastic materials, encompass composed of alternating life. any fragmented solid material that is ejected from layers of lava and pyroclast. Active volcanoes—those that have erupted in a volcano. Pyroclasts range in size from ash—pul- pyroclast the last 10,000 years and could erupt again—pose verized rock particles and solidified droplets of Any fragment of solid material the greatest danger to human life. Volcanoes that lava that form a fine powder—to large boulders. that is ejected from a volcano, have not erupted for 10,000 years or more, but could Stratovolcanoes are the most conspicuous type of ranging in size from ash to awaken again, are considered dormant or inactive. volcano. Their cones can tower over landscapes, large boulders. An extinct volcano is one that has not erupted for as shown in Figure 14.2. ash (volcanic) tens of thousands of years and can never erupt A shield volcano is a broad, domed volcano Fine volcanic powder again. formed from many layers of fluid basaltic lava consisting of pulverized rock reproduction particles and solidified droplets of lava. shield volcano A broad, domed volcano formed from many layers of basaltic lava. FIGURE 14.2 A stratovolcano: Mount Fuji. (A) The interior structure of a stratovolcano consists of a central vent, surrounded by alternating layers of lava flows and pyroclasts. The solidified lava holds the pyroclastic material together, allowing stratovolcanoes to develop steepunauthorized slopes. Magma travels up from the reservoir (magma chamber) beneath the volcano through the vent, and to the summit crater. (B) Mount Fuji, an active stratovolcano, has a symmetrical conical profile typical Noof stratovolcanoes. It reaches a height of 3,775 m (12,387 ft). (B. © Takeshi.K/Flickr/Getty Images) Animation 2014. Stratovolcano formation Pyroclasts http://qrs.ly/s93vzwq Russia FreemanCrater Mongolia 45° N H. Lava SEA OF JAPAN Layers of lava China W. and pyroclasts Mount Fuji, 30° N © Japan Vent Taiwan 120° E 135° E Magma chamber A B Gervais_c14_002-035v7.0.1_pv6.0.1.indd 5 4/17/14 12:31 PM 6 PART III • TECTONIC SYSTEMS: BUILDING THE LITHOSPHERE FIGURE 14.3 (A) Shield volcanoes are built of layers of basaltic lava Animation Shield volcanoes: Hawai'i. Shield volcano flows. There are no alternating layers of pyroclasts like those found in stratovolcanoes. (B) Mauna Kea, on formation Hawai'i, has a typical shield volcano profile. The island of Hawai'i, formed on a hot spot (see Section 12.4), is http://qrs.ly/yd3vzwr made up of five shield volcanoes that have joined together. Mauna Kea is the highest, standing at 4,207 m (13,803 ft). (B. © Peter French/Design Pics/Corbis) Central vent Flank eruption Lava flow PACIFIC OCEAN 20° N Mauna Kea, Hawai'i Magma chamber Basalt layers A B 155° W reproduction cinder cone (Figure 14.3). Shield volcanoes are much larger Most cinder cones are less than 400 m (1,300 ft) A small, cone-shaped volcano than stratovolcanoes. In fact, they are so large that high, and they are roughly symmetrical. They are consisting of pyroclasts that they can be difficult to identify as volcanoes from roughly symmetrical. Many cinder cones erupt for settle at the angle of repose. the ground. Instead, they look like a broad, gently a few decades or less, then become extinct. Structurally, angle of repose sloped horizon.
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