Exam_final review Eath Science review part 3.pptx

Earth science review

1. Exam Review

2. Copyright © McGraw-Hill Education The Causes of Weather What is meteorology? Weather versus climate Short-term variations in atmospheric phenomena that interact and affect the environment and life on Earth are called weather . Climate is the long-term average of variations in weather for a particular area.

3. Copyright © McGraw-Hill Education The Causes of Weather Heating Earth’s Surface Imbalanced heating One reason that temperatures may vary from location to location at a certain time of year is that Earth’s axis of rotation is tilted relative to the plane of Earth’s orbit.

4. Copyright © McGraw-Hill Education The Causes of Weather Heating Earth’s Surface Imbalanced heating Solar radiation is unequal partly due to the changing angle of incidence of the sunlight. The greater the area covered by solar radiation, the smaller the amount of heat per unit of area.

5. Copyright © McGraw-Hill Education The Causes of Weather Heating Earth’s Surface Thermal energy redistribution The constant movement of air redistributes thermal energy around the world. Weather—from thunderstorms to large-scale weather systems—is part of the constant redistribution of Earth’s thermal energy.

6. Copyright © McGraw-Hill Education The Causes of Weather Air Masses An air mass is a large volume of air that has the same characteristics, such as humidity and temperature, as its source region. A source region is the area over which an air mass forms.

7. Copyright © McGraw-Hill Education The Causes of Weather Air Masses Types of air masses The origins of maritime tropical air are tropical bodies of water. The southwestern United States and Mexico are the source regions of continental tropical air , which is hot and dry, especially in summer.

8. Copyright © McGraw-Hill Education The Causes of Weather Air Masses Types of air masses Maritime polar air masses form over the cold waters of the North Atlantic and North Pacific. Continental polar air masses form over the interior of Canada and Alaska, and carry frigid air southward in the winter. Earth’s ice- and snow-covered surfaces above 60° N latitude in Siberia and the Arctic Basin are the source regions of arctic air masses .

9. Copyright © McGraw-Hill Education The Causes of Weather Air Masses Air mass modification When an air mass travels over land or water that has characteristics different from those of its source region, the air mass can acquire some of the characteristics of that land or water and undergo modification.

10. Copyright © McGraw-Hill Education The Causes of Weather Air Masses Air mass modification As the cold, continental polar air moves over the warmer Great Lakes, the air gains thermal energy and moisture. This modified air cools as it is uplifted and produces lake-effect snows.

11. Weather Systems Copyright © McGraw-Hill Education Global Wind Systems The directions of Earth’s winds are influenced by Earth’s rotation. This Coriolis effect results in fluids and objects moving in an apparent curved path rather than a straight line.

12. Copyright © McGraw-Hill Education Weather Systems Global Wind Systems The directions of Earth’s wind systems, such as the polar easterlies and the trade winds, vary with the latitudes in which they occur.

13. Copyright © McGraw-Hill Education Weather Systems Global Wind Systems Polar easterlies The polar easterlies are the wind zones between 60° N latitude and the north pole, and 60° S latitude and the south pole.

14. Copyright © McGraw-Hill Education Weather Systems Global Wind Systems Prevailing westerlies The prevailing westerlies are the wind systems on Earth located between latitudes 30° N and 60° N, and 30° S and 60° S.

15. Copyright © McGraw-Hill Education Weather Systems Global Wind Systems Trade winds Between latitudes 30° N and 30° S are two circulation belts of wind known as the trade winds . Near latitudes 30° N and 30° S, the sinking air associated with the trade winds creates an area of high pressure. This results in a belt of weak surface winds called the horse latitudes.

16. Copyright © McGraw-Hill Education Weather Systems Global Wind Systems Trade winds Trade winds from the North and the South meet and join near the equator. The air is forced upward, which creates an area of low pressure. This process, called convergence, can occur on a small or large scale. Near the equator, it occurs over a large area called the intertropical convergence zone (ITCZ).

17. Copyright © McGraw-Hill Education Weather Systems Jet Streams A large temperature gradient in upper-level air combined with the Coriolis effect results in strong westerly winds called jet streams. A jet stream is a narrow band of fast, high-altitude, westerly wind.

18. Copyright © McGraw-Hill Education Weather Systems Jet Streams Weather in the middle latitudes is strongly influenced by fast-moving, high-altitude jet streams.

19. Copyright © McGraw-Hill Education Weather Systems Jet Streams Types of jet streams The major jet streams, called the polar jet streams , separate the polar easterlies from the prevailing westerlies. The minor jet streams are the subtropical jet streams . They occur where the trade winds meet the prevailing westerlies.

20. Copyright © McGraw-Hill Education Weather Systems Fronts A collision of two air masses forms a front —a narrow region between two air masses of different densities.

21. Copyright © McGraw-Hill Education Weather Systems Fronts Cold front When cold, dense air displaces warm air, it forces the warm air, which is less dense, up along a steep slope. This type of collision is called a cold front.

22. Copyright © McGraw-Hill Education Weather Systems Fronts Warm front Advancing warm air displaces cold air along a warm front. A warm front develops a gradual boundary slope.

23. Copyright © McGraw-Hill Education Weather Systems Fronts Stationary front When two air masses meet but neither advances, the boundary between them stalls. This stationary front frequently occurs between two modified air masses that have small temperature and pressure gradients between them.

24. Copyright © McGraw-Hill Education Weather Systems Fronts Occluded front Sometimes, a cold air mass moves so rapidly that it overtakes a warm front and forces the warm air upward. As the warm air is lifted, the advancing cold air mass collides with another cold air mass that was in front of the warm air. This is called an occluded front.

25. Copyright © McGraw-Hill Education Weather Systems Pressure Systems Sinking or rising air, combined with the Coriolis effect, results in the formation of rotating high- and low-pressure systems in the atmosphere.

26. Copyright © McGraw-Hill Education Weather Systems Pressure Systems In the northern hemisphere, winds move counterclockwise around a low-pressure center, and clockwise around a high-pressure center. Low-pressure center High-pressure center

27. Gathering Weather Data Copyright © McGraw-Hill Education Data from Earth’s Surface Two important factors in weather forecasting are the accuracy of the data and the amount of available data .

28. Copyright © McGraw-Hill Education Gathering Weather Data Data from Earth’s Surface Temperature and air pressure A thermometer measures temperature using either the Fahrenheit or Celsius scale.

29. Copyright © McGraw-Hill Education Gathering Weather Data Data from Earth’s Surface Temperature and air pressure A barometer measures air pressure.

30. Copyright © McGraw-Hill Education Gathering Weather Data Data from Earth’s Surface Wind speed and relative humidity An anemometer measures wind speed..

31. Copyright © McGraw-Hill Education Gathering Weather Data Data from Earth’s Surface Wind speed and relative humidity . A hygrometer measures relative humidity.

32. Copyright © McGraw-Hill Education Gathering Weather Data Data from Earth’s Surface Automated Surface Observing System The Automated Surface Observing System (ASOS) gathers data in a consistent manner, 24 hours a day, every day. It provides essential weather data for aviation, weather forecasting, and weather-related research.

33. Copyright © McGraw-Hill Education Gathering Weather Data Data from the Upper Atmosphere The instrument used for gathering upper-atmosphere data is a radiosonde . A radiosonde’s sensors measure the air’s temperature, pressure, and humidity.

34. Copyright © McGraw-Hill Education Gathering Weather Data Weather Observation Systems Weather radar The Doppler effect is the change in pitch or frequency that occurs due to the relative motion of a wave, such as sound or light, as it comes toward or goes away from an observer.

35. Copyright © McGraw-Hill Education Gathering Weather Data Weather Observation Systems Weather radar Analysis of Doppler radar data can be used to determine the speed at which precipitation moves toward or away from a radar station.

36. Copyright © McGraw-Hill Education Gathering Weather Data Weather Observation Systems Weather satellites Some weather satellites use infrared imagery to make observations at night. Objects radiate thermal energy at slightly different frequencies. Infrared imagery detects these different frequencies, which enables meteorologists to map either cloud cover or surface temperatures.

37. Copyright © McGraw-Hill Education Gathering Weather Data Weather Observation Systems Weather satellites Another type of satellite imagery that is useful in weather analysis and forecasting is called water-vapor imagery . Water-vapor imagery is a valuable tool for weather analysis and prediction because it shows moisture in the atmosphere, not just cloud patterns.

38. Copyright © McGraw-Hill Education Weather Analysis and Prediction Surface Weather Analysis Plotting station model data To plot data nationwide and globally, meteorologists use lines that connect points of equal or constant values.

39. Copyright © McGraw-Hill Education Weather Analysis and Prediction Surface Weather Analysis Plotting station model data Lines of equal pressure are called isobars . Lines of equal temperature are called isotherms .

40. Copyright © McGraw-Hill Education Weather Analysis and Prediction Surface Weather Analysis Interpreting station model data The weather map shows isobars and air pressure data for the continental United States.

41. Copyright © McGraw-Hill Education Weather Analysis and Prediction Surface Weather Analysis Interpreting station model data Using isobars, isotherms, and station model data, meteorologists can analyze current weather conditions for a particular location.

42. Copyright © McGraw-Hill Education Weather Analysis and Prediction Types of Forecasts Digital forecasts A digital forecast is created by applying physical principles and mathematics to atmospheric variables and then making a prediction about how these variables will change over time.

43. Copyright © McGraw-Hill Education Weather Analysis and Prediction Types of Forecasts Analog forecasts An analog forecast is based on a comparison of current weather patterns to similar weather patterns from the past.

44. Copyright © McGraw-Hill Education Weather Analysis and Prediction Short-Term Forecasts The most accurate and detailed forecasts are short term because weather systems change directions, speeds, and intensities over time.

45. Copyright © McGraw-Hill Education Weather Analysis and Prediction Long-Term Forecasts Because it is impossible for computers to model every variable that affects the weather at a given time and place, all long-term forecasts are less reliable than short-term forecasts.

46. Defining Climate Copyright © McGraw-Hill Education Annual Averages and Variations Climatology is the study of Earth’s climate and the factors that affect past, present, and future climatic changes. Climate describes the long-term weather patterns of an area.

47. Copyright © McGraw-Hill Education Defining Climate Annual Averages and Variations Normals The data used to describe an area’s climate include daily high and low temperatures, amounts of rainfall, wind speed and direction, humidity, and air pressure. The data are averaged on a monthly or annual basis for a period of at least 30 years to determine the normals , which are the standard values for a location.

48. Copyright © McGraw-Hill Education Defining Climate Causes of Climate Latitude Latitude has a great effect on climate. The amount of solar radiation received on Earth decreases from the equator to the poles.

49. Copyright © McGraw-Hill Education Defining Climate Causes of Climate Topographic effects Orographic lifting leads to rain on the windward side of a mountain. The leeward side is usually dry and warm. Water heats up and cools down more slowly than land.

50. Copyright © McGraw-Hill Education Defining Climate Causes of Climate Air masses Air masses affect regional climates by transporting the temperature and humidity of their source regions.

51. Copyright © McGraw-Hill Education Climate Classification Köppen Classification System These graphs show temperature and precipitation for two different climates—a desert in Reno, Nevada, and a tropical rain forest in New Guinea.

52. Copyright © McGraw-Hill Education Climate Classification Köppen Classification System Tropical climates Year-round high temperatures characterize tropical climates. In tropical wet climates, high temperatures are accompanied by up to 600 cm of rain each year. Tropical regions are almost continually under the influence of maritime tropical air. These areas have distinct dry winter seasons as a result of the occasional influx of dry continental air masses.

53. Copyright © McGraw-Hill Education Climate Classification Köppen Classification System Dry climates Dry climates, which cover about 30 percent of Earth’s land area, make up the largest climatic zone. In these climates, continental tropical air dominates, precipitation is low, and vegetation is scarce. There are two subtypes of dry climates: arid regions, called deserts, and semiarid regions, called semideserts.

54. Copyright © McGraw-Hill Education Climate Classification Köppen Classification System Mild climates Mild climates can be classified into three subtypes: humid subtropical climates, marine west-coast climates, and Mediterranean climates. The marine west-coast climates are dominated by the constant inland flow of air off the ocean.

55. Copyright © McGraw-Hill Education Climate Classification Köppen Classification System Continental climates Continental climates are classified into three subtypes: warm summer climates, cool summer climates, and subarctic climates. These zones experience rapid and sometimes violent changes in weather, including severe thunderstorms or tornadoes.

56. Copyright © McGraw-Hill Education Climate Classification Köppen Classification System Polar climates To the north of the subarctic climate lies one of the polar climates—the tundra. The tundra is known for its low temperatures. There are no trees in the tundra and precipitation is generally low.

57. Copyright © McGraw-Hill Education Climate Classification Microclimates Heat islands Many concrete buildings and large expanses of asphalt can create a heat island, where the climate is warmer than in surrounding rural areas.

58. Climatic Changes Copyright © McGraw-Hill Education Long-Term Climatic Changes Ice ages The most recent ice age, as shown here by the extent of its glaciers, ended only about 10,000 years ago. Average global temperatures decreased by an estimated 5°C

59. Copyright © McGraw-Hill Education Climatic Changes Short-Term Climatic Changes While an ice age may last for several million years, other climatic changes occur over much shorter time periods. Seasons are short-term periods of climatic change caused by regular variations in daylight, temperature, and weather patterns.

60. Copyright © McGraw-Hill Education Climatic Changes Short-Term Climatic Changes El Niño Under normal conditions, trade winds and ocean currents move warm water west across the Pacific Ocean.

61. Copyright © McGraw-Hill Education Climatic Changes Short-Term Climatic Changes El Niño During El Niño, warm water surges back toward South America, changing weather patterns.

62. Copyright © McGraw-Hill Education Climatic Changes Natural Causes of Climatic Changes Solar activity The Maunder minimum is the term used to describe the period of low numbers of sunspots, from 1645 to 1716. This period closely corresponds to an unusually cold climatic episode called the Little Ice Age.

63. Copyright © McGraw-Hill Education Climatic Changes Natural Causes of Climatic Changes Earth’s orbit Scientists hypothesize that a more elliptical orbit around the Sun could produce significant changes in Earth’s climate.

64. Copyright © McGraw-Hill Education Climatic Changes Natural Causes of Climatic Changes Earth’s tilt If the angle of the tilt of Earth’s axis decreased, there would be less temperature contrast between summer and winter.

65. Copyright © McGraw-Hill Education Climatic Changes Natural Causes of Climatic Changes Earth’s wobble Earth’s wobble determines the timing of the seasons. When the axis points toward the star Vega in 13,000 years, the northern hemisphere will experience summer during the time now associated with winter.

66. Copyright © McGraw-Hill Education Climatic Changes Natural Causes of Climatic Changes Volcanic activity Climatic changes can also be triggered by the immense quantities of dust-sized particles, called aerosols, that are released into the atmosphere during major volcanic eruptions. Volcanic dust can remain suspended in the atmosphere for several years, blocking incoming solar radiation and thus lowering global temperatures.

67. Impact of Human Activities Copyright © McGraw-Hill Education Influence on the Atmosphere The greenhouse effect The process of absorption and radiation of energy in the atmosphere results in the greenhouse effect —the natural heating of Earth’s surface caused by certain atmospheric gases called greenhouse gases. An increase in the amount of atmospheric greenhouse gases, particularly carbon dioxide and methane , would theoretically result in increased absorption of energy in the atmosphere. This can lead to a rise in global temperatures, known as global warming .

68. Copyright © McGraw-Hill Education Impact of Human Activities Global Warming Burning fossil fuels One of the main sources of atmospheric carbon dioxide from humans is from the burning of fossil fuels including coal, oil, and natural gas. Burning fossil fuels also releases other greenhouse gases, such as methane and nitrous oxide, into the atmosphere.

69. Copyright © McGraw-Hill Education Impact of Human Activities Global Warming Deforestation Deforestation—the mass removal of trees—also plays a role in increasing levels of atmospheric carbon dioxide. When trees are cut down, photosynthesis is reduced, and more carbon dioxide remains in the atmosphere.

70. Copyright © McGraw-Hill Education Impact of Human Activities Global Warming Environmental efforts Individuals can reduce the amount of carbon dioxide emitted to the atmosphere by conserving energy, which reduces fossil fuel consumption.

71. Drifting Continents Copyright © McGraw-Hill Education Early Observations With the exception of events such as earthquakes, volcanic eruptions, and landslides, most of Earth’s surface appears to remain relatively unchanged during the course of a human lifetime.

72. Drifting Continents Copyright © McGraw-Hill Education Early Observations In the late 1500s, Abraham Ortelius , a Dutch cartographer, noticed the apparent fit of continents on either side of the Atlantic Ocean. He proposed that North America and South America had been separated from Europe and Africa by earthquakes and floods.

73. Drifting Continents Copyright © McGraw-Hill Education Early Observations The first time that the idea of moving continents was proposed as a scientific hypothesis was in the early 1900s. In 1912, German meteorologist Alfred Wegener presented his ideas about continental movement to the scientific community.

74. Copyright © McGraw-Hill Education Drifting Continents Continental Drift Wegener developed a hypothesis that he called continental drift . He proposed that Earth’s continents had once been joined in a single landmass, a supercontinent called Pangaea , that broke apart about 200 mya and sent the continents adrift.

75. Copyright © McGraw-Hill Education Drifting Continents Continental Drift Evidence from rock formations Wegener observed that many layers of rocks in the Appalachian Mountains in the United States were identical to layers of rocks in similar mountains in Greenland and Europe. These similar groups of rocks, older than 200 million years, supported Wegener’s idea that the continents had once been joined.

76. Copyright © McGraw-Hill Education Drifting Continents Continental Drift Evidence from fossils Wegener gathered evidence of the existence of Pangaea from fossils. Similar fossils of animals and plants that once lived on or near land had been found on widely separated continents.

77. Copyright © McGraw-Hill Education Drifting Continents Continental Drift Climatic evidence Wegener argued that because Glossopteris grew in temperate climates, the places where the fossils had been found had been closer to the equator. This led him to conclude that the rocks containing these fossil ferns had once been joined.

78. Copyright © McGraw-Hill Education Drifting Continents Continental Drift Climatic evidence Glacial deposits nearly 300 million years old on several continents led Wegener to propose that these landmasses might have once been joined and covered with ice. The extent of the ice is shown in white.

79. Copyright © McGraw-Hill Education Drifting Continents A Rejected Notion Although Wegener had compiled an impressive collection of data, the hypothesis of continental drift was not accepted by the scientific community. Two unanswered questions : What forces could cause the movement? How continents could move through solids? It was not until the early 1960s , when new technology revealed more evidence about how continents move, that scientists began to reconsider Wegener’s ideas.

80. Volcanoes Copyright © McGraw-Hill Education Zones of Volcanism Volcanism describes all the processes associated with the discharge of magma, hot fluids, and gases .

81. Volcanoes Copyright © McGraw-Hill Education Zones of Volcanism Most volcanoes form at plate boundaries. The majority form at convergent boundaries and divergent boundaries.

82. Volcanoes Copyright © McGraw-Hill Education Zones of Volcanism Convergent volcanism In an oceanic-continental subduction zone, the denser oceanic plate slides under the continental plate into the hot mantle. Parts of the mantle above the subducting plate melt and magma rises, eventually leading to the formation of a volcano.

83. Volcanoes Copyright © McGraw-Hill Education Zones of Volcanism Two major belts The volcanoes associated with convergent plate boundaries form two major belts. The larger belt, the Circum-Pacific Belt, is also called the Pacific Ring of Fire. The outline of the belt corresponds to the outline of the Pacific Plate.

84. Volcanoes Copyright © McGraw-Hill Education Zones of Volcanism Two major belts The smaller belt is the Mediterranean Belt. Its general outlines correspond to the boundaries between the Eurasian, African, and Arabian plates.

85. Copyright © McGraw-Hill Education Volcanoes Zones of Volcanism Divergent volcanism Eruptions at divergent boundaries tend to be nonexplosive . At the divergent boundary on the ocean floor, eruptions often form huge piles of lava called pillow lava .

86. Copyright © McGraw-Hill Education Volcanoes Zones of Volcanism Hot spots Some volcanoes form far from plate boundaries over hot spots. A hot spot is an unusually hot area in Earth’s mantle where high-temperature plumes of mantle material rise toward the surface.

87. Copyright © McGraw-Hill Education Volcanoes Zones of Volcanism Hot spots Flood basalts form when lava flows out of long cracks in Earth’s crust. These cracks are called fissures . The Columbia River basalts, located in the northwestern United States, were formed this way.

88. Copyright © McGraw-Hill Education Volcanoes Anatomy of a Volcano Lava reaches the surface by traveling through a tubelike structure called a conduit . The lava then emerges through an opening called a vent .

89. Copyright © McGraw-Hill Education Volcanoes Anatomy of a Volcano Over time, layers of solidified lava can accumulate to form a mountain known as a volcano. At the top of a volcano, around the vent, is a bowl-shaped depression called a crater . Volcanic craters are usually less than 1 km in diameter. Larger depressions, called calderas , can be up to 100 km in diameter.

90. Copyright © McGraw-Hill Education Volcanoes Types of Volcanoes Shield volcanoes A shield volcano is a mountain with broad, gently sloping sides and a nearly circular base. Shield volcanoes form when layers of lava accumulate during nonexplosive eruptions. They are the largest type of volcano.

91. Copyright © McGraw-Hill Education Volcanoes Types of Volcanoes Cinder cones When eruptions eject small pieces of lava into the air, cinder cones form as this material, called tephra, falls back to Earth and piles up around the vent. Cinder cones have steep sides and are the smallest type of volcano.

92. Copyright © McGraw-Hill Education Volcanoes Types of Volcanoes Composite volcanoes Composite volcanoes are formed of layers of ash and hardened chunks of lava from violent eruptions alternating with layers of lava that oozed downslope before solidifying. These volcanoes are generally cone-shaped with concave slopes.

93. Eruptions Copyright © McGraw-Hill Education Making Magma A volcano’s explosivity depends on the composition of the magma. Lava from an eruption can be thin and runny or thick and lumpy.

94. Eruptions Copyright © McGraw-Hill Education Making Magma Temperature Depending on their composition, most rocks begin to melt at temperatures between 800°C and 1200°C. In addition to temperature, pressure and the presence of water and dissolved gases also affect the formation of magma.

95. Eruptions Copyright © McGraw-Hill Education Making Magma Pressure Pressure increases with depth because of the weight of overlying rocks. As pressure increases, the temperature at which a substance melts also increases, which explains why most of the rocks in Earth’s lower crust and upper mantle do not melt.

96. Eruptions Copyright © McGraw-Hill Education Composition of Magma The composition of magma determines a volcano’s explosivity, which is how it erupts and how its lava flows. Understanding the factors that determine the behavior of magma can aid scientists in predicting the eruptive style of volcanoes.

97. Eruptions Copyright © McGraw-Hill Education Composition of Magma Dissolved gases In general, as the amount of gases in magma increases, the magma’s explosivity also increases. Important gases in magma are water vapor, carbon dioxide, sulfur dioxide, and hydrogen sulfide.

98. Eruptions Copyright © McGraw-Hill Education Composition of Magma Viscosity The physical property that describes a material’s resistance to flow is called viscosity . Temperature and silica content affect the viscosity of a magma.

99. Copyright © McGraw-Hill Education Eruptions Types of Magma Basaltic magma When rock in the upper mantle melts, basaltic magma typically forms. Basaltic magma contains less than 50 percent silica. Its low silica content produces low-viscosity magma. The resulting volcano is characterized by quiet eruptions.

100. Copyright © McGraw-Hill Education Eruptions Types of Magma Andesitic magma Andesitic magma is 50 to 60 percent silica and is found along oceanic-continental subduction zones. The source material for this magma can be either oceanic crust or oceanic sediments.

101. Copyright © McGraw-Hill Education Eruptions Types of Magma Andesitic magma The higher silica content of Andesitic magma results in a magma that has intermediate viscosity. Thus, the volcanoes it fuels are said to have intermediate explosivity.

102. Copyright © McGraw-Hill Education Eruptions Types of Magma Rhyolitic magma High viscosity, along with the large volume of gas trapped within rhyolitic magma, makes the volcanoes fueled by this magma very explosive.

103. Copyright © McGraw-Hill Education Eruptions Visualizing Eruptions As magma rises due to plate tectonics and hot spots, it mixes with Earth’s crust. This mixing causes differences in the temperature , silica content, and gas content of magma as it reaches Earth’s surface. These properties of magma determine how volcanoes erupt.

104. Copyright © McGraw-Hill Education Eruptions Explosive Eruptions When lava is too viscous to flow freely from the vent, pressure builds up in the lava until the volcano explodes, throwing lava and rock into the air. The erupted materials are called tephra .

105. Copyright © McGraw-Hill Education Eruptions Pyroclastic Flows Violent volcanic eruptions can send clouds of ash and other tephra down a slope at speeds of about 80 km/h. Rapidly moving clouds of tephra mixed with hot, suffocating gases are called pyroclastic flows .

106. Copyright © McGraw-Hill Education Eruptions Pyroclastic Flows In 1902, a pyroclastic flow from Mount Pelée on the island of Martinique in the Caribbean Sea was so powerful that it destroyed the entire town of St. Pierre in only a few minutes.

107. Intrusive Activity Copyright © McGraw-Hill Education Plutons Most of Earth’s volcanism happens below the surface because not all magma emerges at the surface. Before it gets to the surface, rising magma can interact with the crust in several ways.

108. Intrusive Activity Copyright © McGraw-Hill Education Plutons Plutons are intrusive igneous rock bodies, formed through mountain-building processes and oceanic-oceanic collisions. They can be exposed at Earth’s surface due to uplift and erosion and are classified based on their size, shape, and relationship to surrounding rocks.

109. Intrusive Activity Copyright © McGraw-Hill Education Plutons Batholiths and stocks Batholiths , the largest plutons, are irregularly shaped masses of coarse-grained igneous rocks that cover at least 100 km 2 and take millions of years to form. Batholiths are common in the interior of mountains.

110. Intrusive Activity Copyright © McGraw-Hill Education Plutons Batholiths and stocks Irregularly shaped plutons that are similar to batholiths but smaller in size are called stocks . Both batholiths and stocks cut across older rocks and generally form 5 to 30 km beneath Earth’s surface.

111. Intrusive Activity Copyright © McGraw-Hill Education Plutons Laccoliths A laccolith is a lens-shaped pluton with a round top and flat bottom. Compared to batholiths and stocks, laccoliths are relatively small; at most, they are 16 km wide.

112. Intrusive Activity Copyright © McGraw-Hill Education Plutons Sills A sill forms when magma intrudes parallel to layers of rock. Because it takes great amounts of force to lift entire layers of rock, most sills form relatively close to the surface.

113. Intrusive Activity Copyright © McGraw-Hill Education Plutons Dikes A dike is a pluton that cuts across preexisting rocks and often forms when magma invades cracks in surrounding rock bodies. A volcanic neck occurs when the magma in a volcano conduit solidifies. Dikes are often associated with the conduit but do not always form the neck.

114. Intrusive Activity Copyright © McGraw-Hill Education Plutons Dikes The coarse-grained texture of most sills and dikes suggests that they formed deep in Earth’s crust, where magma cooled slowly enough for large mineral grains to develop. Dikes and sills with a fine-grained texture formed closer to the surface where many crystals began growing at the same time.

115. Intrusive Activity Copyright © McGraw-Hill Education Plutons and Tectonics Scientists think that some of the collisions along continental-continental convergent plate boundaries might have forced continental crust down into the upper mantle where it melted, intruded into the overlying rocks, and eventually cooled to form batholiths.

116. Intrusive Activity Copyright © McGraw-Hill Education Plutons and Tectonics Plutons are also thought to form as a result of oceanic plate convergence. When an oceanic plate converges with another plate, water from the subducted plate causes the overlying mantle to melt. Plutons often form when the melted material rises but does not erupt at the surface.