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L_0082 | staying safe in earthquakes | T_0834 | Buildings must be specially built to withstand earthquakes. Skyscrapers and other large structures built on soft ground must be anchored to bedrock. Sometimes that bedrock is hundreds of meters below the ground surface! | text | null |
L_0082 | staying safe in earthquakes | T_0835 | Building materials need to be both strong and flexible. Small structures, like houses, should bend and sway. Wood and steel bend. Brick, stone, and adobe are brittle and will break. Larger buildings must sway, but not so much that they touch nearby buildings. Counterweights and diagonal steel beams can hold down sway. Buildings need strong, flexible connections where the walls meet the foundation. Earthquake-safe buildings are well connected (Figure Steel or wood can be added to older buildings to reinforce a buildings structure and its connections (Figure 7.42). Elevated freeways and bridges can also be reinforced so that they do not collapse. Important structures must be designed to survive intact. | text | null |
L_0082 | staying safe in earthquakes | T_0836 | One of the biggest problems caused by earthquakes is fire. Fires start because earthquakes rupture gas and electrical lines. Water mains may break. This makes it difficult to fight the fires. The shapes of pipes can make a big difference. Straight pipes will break in a quake. Zigzag pipes bend and flex when the ground shakes. In San Francisco, water and gas pipelines are separated by valves. Areas can be isolated if one segment breaks. | text | null |
L_0082 | staying safe in earthquakes | T_0837 | Strong, sturdy structures are expensive to build. Communities must decide how safe to make their buildings. They must weigh how great the hazard is, what different building strategies will cost, and how much risk they are willing to take. | text | null |
L_0082 | staying safe in earthquakes | T_0838 | If you live in an earthquake zone, there are many things you can do to protect yourself. You must protect your home. Your household must be ready to live independently for a few days. It may take emergency services that long to get to everyone. Before an Earthquake: Make sure the floor, walls, roof, and foundation are all well attached to each other. Have an engineer evaluate your house for structural integrity. Bracket or brace brick chimneys to the roof. Be sure that heavy objects are not stored in high places. Move them to low places so that they do not fall. Secure water heaters all around and at the top and bottom. Bolt heavy furniture onto walls with bolts, screws, or strap hinges. Replace halogen and incandescent light bulbs with fluorescent bulbs to lessen fire risk. Check to see that gas lines are made of flexible material so they do not rupture. Any equipment that uses gas should be well secured. Everyone in the household should know how to shut off the gas line. A wrench should be placed nearby for doing so. Prepare an earthquake kit with at least three days supply of water and food. Include a radio and batteries. Place flashlights all over the house so there is always one available. Place one in the glove box of your car. Keep several fire extinguishers around the house to fight any small fires that break out. Be sure to have a first aid kit. Everyone in the household who is capable should know basic first aid and CPR. Plan in advance how you will evacuate your property and where you will go. Do not plan on driving, as roadways will likely be damaged. During the Earthquake: If you are in a building, drop to the ground, get beneath a sturdy table or desk, cover your head, and hold on. Stay away from windows and mirrors since glass can break and fall on you. Stay away from large furniture that may fall on you. If the building is structurally unsound, get outside as fast as possible. Run into an open area away from buildings and power lines that may fall on you. If you are in a car, stay in the car and stay away from structures that might collapse like overpasses, bridges, or buildings. After the Earthquake: Be aware that aftershocks are likely. Avoid dangerous areas, like hillsides, that may experience a landslide. Turn off water, gas lines, and power to your home. Use your phone only if there is an emergency. Many people with urgent needs will be trying to get through to emergency services. Be prepared to wait for help or instructions. Assist others as necessary. | text | null |
L_0083 | volcanic activity | T_0839 | Volcanoes rise where magma forms underground. Volcanoes are found at convergent plate boundaries and at hotspots. Volcanic activity is found at divergent plate boundaries. The map in Figure 8.1 shows where volcanoes are located. | text | null |
L_0083 | volcanic activity | T_0840 | There is a lot of volcanic activity at divergent plate boundaries in the oceans. As the plates pull away from each other, they create deep fissures. Molten lava erupts through these cracks. The East Pacific Rise is a divergent plate boundary in the Pacific Ocean (Figure 8.2). The Mid-Atlantic Ridge is a divergent plate boundary in the Atlantic Ocean. Continents can also rift apart. When mantle gets close enough to the surface, volcanoes form. Eventually, a rift valley will create a new mid-ocean ridge. | text | null |
L_0083 | volcanic activity | T_0841 | Lots of volcanoes form along subduction plate boundaries. The edges of the Pacific Plate are a long subduction boundary. Lines of volcanoes can form at subduction zones on oceanic or continental crust. Japan is an example of a volcanic arc on oceanic crust. The Cascade Range and Andes Mountains are volcanic arcs on continental crust. | text | null |
L_0083 | volcanic activity | T_0842 | Some volcanoes form over active hot spots. Scientists count about 50 hot spots on the Earth. Hot spots may be in the middle of a tectonic plate. Hot spots lie directly above a column of hot rock called a mantle plume. Mantle plumes continuously bring magma up from the mantle towards the crust (Figure 8.3). As the tectonic plates move above a hot spot, they form a chain of volcanoes. The islands of Hawaii formed over a hot spot in the middle of the Pacific plate. The Hawaii hot spot has been active for tens of millions of years. The volcanoes of the Hawaiian Islands formed at this hot spot. Older volcanoes that formed at the hot spot have eroded below sea level. These are called the Emperor Seamounts. Loihi seamount is currently active beneath the water southeast of the Big Island of Hawaii. One day the volcano will rise above sea level and join the volcanoes of the island or create a new island (Figure 8.4). Hot spots may also be active at plate boundaries. This is especially common at mid-ocean ridges. Iceland is formed by a hot spot along the Mid-Atlantic Ridge. Hot spots are found within continents, but not as commonly as within oceans. The Yellowstone hot spot is a famous example of a continental hot spot. | text | null |
L_0083 | volcanic activity | T_0842 | Some volcanoes form over active hot spots. Scientists count about 50 hot spots on the Earth. Hot spots may be in the middle of a tectonic plate. Hot spots lie directly above a column of hot rock called a mantle plume. Mantle plumes continuously bring magma up from the mantle towards the crust (Figure 8.3). As the tectonic plates move above a hot spot, they form a chain of volcanoes. The islands of Hawaii formed over a hot spot in the middle of the Pacific plate. The Hawaii hot spot has been active for tens of millions of years. The volcanoes of the Hawaiian Islands formed at this hot spot. Older volcanoes that formed at the hot spot have eroded below sea level. These are called the Emperor Seamounts. Loihi seamount is currently active beneath the water southeast of the Big Island of Hawaii. One day the volcano will rise above sea level and join the volcanoes of the island or create a new island (Figure 8.4). Hot spots may also be active at plate boundaries. This is especially common at mid-ocean ridges. Iceland is formed by a hot spot along the Mid-Atlantic Ridge. Hot spots are found within continents, but not as commonly as within oceans. The Yellowstone hot spot is a famous example of a continental hot spot. | text | null |
L_0084 | volcanic eruptions | T_0843 | All volcanoes share the same basic features. First, mantle rock melts. The molten rock collects in magma chambers that can be 160 kilometers (100 miles) beneath the surface. As the rock heats, it expands. The hot rock is less dense than the surrounding rock. The magma rises toward the surface through cracks in the crust. A volcanic eruption occurs when the magma reaches the surface. Lava can reach the surface gently or explosively. | text | null |
L_0084 | volcanic eruptions | T_0844 | Eruptions can be explosive or non-explosive. Only rarely do gentle and explosive eruptions happen in the same volcano. | text | null |
L_0084 | volcanic eruptions | T_0845 | An explosive eruption produces huge clouds of volcanic ash. Chunks of the volcano fly high into the atmosphere. Explosive eruptions can be 10,000 times as powerful as an atomic bomb (Figure 8.6). Hot magma beneath the surface mixes with water. This forms gases. The gas pressure grows until it must be released. The volcano erupts in an enormous explosion. Ash and particles shoot many kilometers into the sky. The material may form a mushroom cloud, just like a nuclear explosion. Hot fragments of rock, called pyroclasts, fly up into the air at very high speeds. The pyroclasts cool in the atmosphere. Some ash may stay in the atmosphere for years. The ash may block out sunlight. This changes weather patterns and affects the temperature of the Earth. For a year or two after a large eruption, sunsets may be especially beautiful worldwide. Volcanic gases can form poisonous, invisible clouds. The poisonous gases may be toxic close to the eruption. The gases may cause environmental problems like acid rain and ozone destruction. Mt St. Helens was not a very large eruption for the Cascades. Mt. Mazama blew itself apart in an eruption about 42 times more powerful than Mount St. Helens in 1980. Today all that remains of that huge stratovolcano is Crater Lake (Figure 8.18). | text | null |
L_0084 | volcanic eruptions | T_0846 | Some volcanic eruptions are non-explosive (Figure 8.7). This happens when there is little or no gas. The lava is thin, fluid and runny. It flows over the ground like a river. People generally have a lot of warning before a lava flow like this reaches them, so non-explosive eruptions are much less deadly. They may still be destructive to property, though. Even when we know that a lava flow is approaching, there are few ways of stopping it! | text | null |
L_0084 | volcanic eruptions | T_0847 | Great volcanic explosions and glowing red rivers of lava are fascinating. All igneous rock comes from magma or lava. Remember that magma is molten rock that is below Earths surface. Lava is molten rock at Earths surface. | text | null |
L_0084 | volcanic eruptions | T_0848 | Magma forms deep beneath the Earths surface. Rock melts below the surface under tremendous pressure and high temperatures. Molten rock flows like taffy or hot wax. Most magmas are formed at temperatures between 600o C and 1300o C (Figure 8.8). Magma collects in magma chambers beneath Earths surface. Magma chambers are located where the heat and pressure are great enough to melt rock. These locations are at divergent or convergent plate boundaries or at hotpots. The chemistry of a magma determines the type of igneous rock it forms. The chemistry also determines how the magma moves. Thicker magmas tend to stay below the surface or erupt explosively. When magma is fluid and runny, it often reaches the surface by flowing out in rivers of lava. | text | null |
L_0084 | volcanic eruptions | T_0849 | The way lava flows depends on what it is made of. Thick lava doesnt flow easily. It may block the vent of a volcano. If the lava traps a lot of gas, the pressure builds up. After the pressure becomes greater and greater, the volcano finally explodes. Ash and pyroclasts shoot up into the air. Pumice, with small holes in solid rock, shows where gas bubbles were when the rock was still molten. Fluid lava flows down mountainsides. The rock that the flow becomes depends on which type of lava it is and where it cools. The three types of flows are aa, pahoehoe, and pillow lava. Aa Lava Aa lava is the thickest of the non-explosive lavas. Aa forms a thick and brittle crust, which is torn into rough, rubbly pieces. The solidified surface is angular, jagged and sharp. Aa can spread over large areas as the lava continues to flow underneath. Pahoehoe Lava Pahoehoe lava is thinner than aa, and flows more readily. Its surface looks more wrinkly and smooth. Pahoehoe lava flows in a series of lobes that form strange twisted shapes and natural rock sculptures (Figure 8.9). Pahoehoe lava can form lava tubes. The outer layer of the lava flow cools and solidifies. The inner part of the flow remains fluid. The fluid lava flows through and leaves behind a tube (Figure 8.10). Pillow Lava Pillow lava is created from lava that enters the water. The volcanic vent may be underwater. The lava may flow over land and enter the water (Figure 8.11). Once in the water, the lava cools very quickly. The lava forms round rocks that resemble pillows. Pillow lava is particularly common along mid-ocean ridges. | text | null |
L_0084 | volcanic eruptions | T_0849 | The way lava flows depends on what it is made of. Thick lava doesnt flow easily. It may block the vent of a volcano. If the lava traps a lot of gas, the pressure builds up. After the pressure becomes greater and greater, the volcano finally explodes. Ash and pyroclasts shoot up into the air. Pumice, with small holes in solid rock, shows where gas bubbles were when the rock was still molten. Fluid lava flows down mountainsides. The rock that the flow becomes depends on which type of lava it is and where it cools. The three types of flows are aa, pahoehoe, and pillow lava. Aa Lava Aa lava is the thickest of the non-explosive lavas. Aa forms a thick and brittle crust, which is torn into rough, rubbly pieces. The solidified surface is angular, jagged and sharp. Aa can spread over large areas as the lava continues to flow underneath. Pahoehoe Lava Pahoehoe lava is thinner than aa, and flows more readily. Its surface looks more wrinkly and smooth. Pahoehoe lava flows in a series of lobes that form strange twisted shapes and natural rock sculptures (Figure 8.9). Pahoehoe lava can form lava tubes. The outer layer of the lava flow cools and solidifies. The inner part of the flow remains fluid. The fluid lava flows through and leaves behind a tube (Figure 8.10). Pillow Lava Pillow lava is created from lava that enters the water. The volcanic vent may be underwater. The lava may flow over land and enter the water (Figure 8.11). Once in the water, the lava cools very quickly. The lava forms round rocks that resemble pillows. Pillow lava is particularly common along mid-ocean ridges. | text | null |
L_0084 | volcanic eruptions | T_0849 | The way lava flows depends on what it is made of. Thick lava doesnt flow easily. It may block the vent of a volcano. If the lava traps a lot of gas, the pressure builds up. After the pressure becomes greater and greater, the volcano finally explodes. Ash and pyroclasts shoot up into the air. Pumice, with small holes in solid rock, shows where gas bubbles were when the rock was still molten. Fluid lava flows down mountainsides. The rock that the flow becomes depends on which type of lava it is and where it cools. The three types of flows are aa, pahoehoe, and pillow lava. Aa Lava Aa lava is the thickest of the non-explosive lavas. Aa forms a thick and brittle crust, which is torn into rough, rubbly pieces. The solidified surface is angular, jagged and sharp. Aa can spread over large areas as the lava continues to flow underneath. Pahoehoe Lava Pahoehoe lava is thinner than aa, and flows more readily. Its surface looks more wrinkly and smooth. Pahoehoe lava flows in a series of lobes that form strange twisted shapes and natural rock sculptures (Figure 8.9). Pahoehoe lava can form lava tubes. The outer layer of the lava flow cools and solidifies. The inner part of the flow remains fluid. The fluid lava flows through and leaves behind a tube (Figure 8.10). Pillow Lava Pillow lava is created from lava that enters the water. The volcanic vent may be underwater. The lava may flow over land and enter the water (Figure 8.11). Once in the water, the lava cools very quickly. The lava forms round rocks that resemble pillows. Pillow lava is particularly common along mid-ocean ridges. | text | null |
L_0084 | volcanic eruptions | T_0849 | The way lava flows depends on what it is made of. Thick lava doesnt flow easily. It may block the vent of a volcano. If the lava traps a lot of gas, the pressure builds up. After the pressure becomes greater and greater, the volcano finally explodes. Ash and pyroclasts shoot up into the air. Pumice, with small holes in solid rock, shows where gas bubbles were when the rock was still molten. Fluid lava flows down mountainsides. The rock that the flow becomes depends on which type of lava it is and where it cools. The three types of flows are aa, pahoehoe, and pillow lava. Aa Lava Aa lava is the thickest of the non-explosive lavas. Aa forms a thick and brittle crust, which is torn into rough, rubbly pieces. The solidified surface is angular, jagged and sharp. Aa can spread over large areas as the lava continues to flow underneath. Pahoehoe Lava Pahoehoe lava is thinner than aa, and flows more readily. Its surface looks more wrinkly and smooth. Pahoehoe lava flows in a series of lobes that form strange twisted shapes and natural rock sculptures (Figure 8.9). Pahoehoe lava can form lava tubes. The outer layer of the lava flow cools and solidifies. The inner part of the flow remains fluid. The fluid lava flows through and leaves behind a tube (Figure 8.10). Pillow Lava Pillow lava is created from lava that enters the water. The volcanic vent may be underwater. The lava may flow over land and enter the water (Figure 8.11). Once in the water, the lava cools very quickly. The lava forms round rocks that resemble pillows. Pillow lava is particularly common along mid-ocean ridges. | text | null |
L_0084 | volcanic eruptions | T_0850 | Volcanic eruptions can be devastating, particularly to the people who live close to volcanoes. Volcanologists study volcanoes to be able to predict when a volcano will erupt. Many changes happen when a volcano is about to erupt. | text | null |
L_0084 | volcanic eruptions | T_0851 | Scientists study a volcanos history to try to predict when it will next erupt. They want to know how long it has been since it last erupted. They also want to know the time span between its previous eruptions. Volcanoes can be active, dormant, or extinct (Figure 8.12). An active volcano may be currently erupting. Alter- natively, it may be showing signs that it will erupt in the near future. A dormant volcano no longer shows signs of activity. But it has erupted in recent history and will probably erupt again. An extinct volcano is one that has not erupted in recent history. Scientists think that it will probably not erupt again. Scientists watch both active and dormant volcanoes closely for signs that show they might erupt. | text | null |
L_0084 | volcanic eruptions | T_0852 | Earthquakes may take place every day near a volcano. But before an eruption the number and size of earthquakes increases. This is the result of magma pushing upward into the magma chamber. This motion causes stresses on neighboring rock to build up. Eventually the ground shakes. A continuous string of earthquakes may indicate that a volcano is about to erupt. Scientists use seismographs to record the length and strength of each earthquake. | text | null |
L_0084 | volcanic eruptions | T_0853 | All that magma and gas pushing upwards can make the volcanos slope begin to swell. Ground swelling may change the shape of a volcano or cause rock falls and landslides. Most of the time, the ground tilting is not visible. Scientists detect it by using tiltmeters, which are instruments that measure the angle of the slope of a volcano. | text | null |
L_0084 | volcanic eruptions | T_0854 | Scientists measure the gases that escape from a volcano to predict eruptions. Gases like sulfur dioxide (SO2 ), carbon dioxide (CO2 ), hydrochloric acid (HCl), and water vapor can be measured at the site. Gases may also be measured from satellites. The amounts of gases and the ratios of gases are calculated to help predict eruptions. | text | null |
L_0084 | volcanic eruptions | T_0855 | Satellites can be used to monitor more than just gases (Figure 8.13). Satellites can look for high temperature spots or areas where the volcano surface is changing. This allows scientists to detect changes accurately and safely. | text | null |
L_0084 | volcanic eruptions | T_0856 | No scientist or government agency wants to announce an eruption and then be wrong. There is a very real cost and disruption to society during a large-scale evacuation. If the scientists are wrong, people would be less likely to evacuate the next time scientists predicted an eruption. But if scientists predict an eruption that does take place it could save many lives. | text | null |
L_0085 | types of volcanoes | T_0857 | A composite volcano forms the tall cone shape you usually think of when you think of a volcano. Shield volcanoes are huge, gently sloping volcanoes. Cinder cones are small, cone-shaped volcanoes. | text | null |
L_0085 | types of volcanoes | T_0858 | Figure 8.14 shows Mt. Fuji, a classic example of a composite volcano. Composite volcanoes have broad bases and steep sides. These volcanoes usually have a large crater at the top. The crater was created during the volcanos last eruption. Composite volcanoes are also called stratovolcanoes. This is because they are formed by alternating layers (strata) of magma and ash (Figure 8.15). The magma that creates composite volcanoes tends to be thick. The steep sides form because the lava cannot flow too far from the vent. The thick magma may also create explosive eruptions. Ash and pyroclasts erupt into the air. Much of this material falls back down near the vent. This creates the steep sides of stratovolcanoes. Composite volcanoes are common along convergent plate boundaries. When a tectonic plate subducts, it melts. This creates the thick magma needed for these eruptions. The Pacific Ring of Fire is dotted by composite volcanoes. | text | null |
L_0085 | types of volcanoes | T_0858 | Figure 8.14 shows Mt. Fuji, a classic example of a composite volcano. Composite volcanoes have broad bases and steep sides. These volcanoes usually have a large crater at the top. The crater was created during the volcanos last eruption. Composite volcanoes are also called stratovolcanoes. This is because they are formed by alternating layers (strata) of magma and ash (Figure 8.15). The magma that creates composite volcanoes tends to be thick. The steep sides form because the lava cannot flow too far from the vent. The thick magma may also create explosive eruptions. Ash and pyroclasts erupt into the air. Much of this material falls back down near the vent. This creates the steep sides of stratovolcanoes. Composite volcanoes are common along convergent plate boundaries. When a tectonic plate subducts, it melts. This creates the thick magma needed for these eruptions. The Pacific Ring of Fire is dotted by composite volcanoes. | text | null |
L_0085 | types of volcanoes | T_0859 | Shield volcanoes look like a huge ancient warriors shield laid down. Figure 8.16 shows the Kilaeua Volcano. A shield volcano has a very wide base. It is much flatter on the top than a composite volcano. The lava that creates shield volcanoes is reltively thin. The thin lava spreads out. This builds a large, flat volcano layer by layer. Shield volcanoes are very large. For example, the Mauna Loa Volcano has a diameter of more than 112 kilometers (70 miles). The volcano forms a significant part of the island of Hawaii. The top of nearby Mauna Kea Volcano is more than ten kilometers (6 miles) from its base on the seafloor. Shield volcanoes often form along divergent plate boundaries. They also form at hot spots, like Hawaii. Shield volcano eruptions are non-explosive. | text | null |
L_0085 | types of volcanoes | T_0860 | Cinder cones are the smallest and most common type of volcano. Cinder cones have steep sides like composite volcanoes. But they are much smaller, rarely reaching even 300 meters in height. Cinder cones usually have a crater at the summit. Cinder cones are composed of small fragments of rock, called cinders. The cinders are piled on top of one another. These volcanoes usually do not produce streams of lava. Cinder cones often form near larger volcanoes. Most composite and shield volcanoes have nearby cinder cones. Cinder cones usually build up very rapidly. They only erupt for a short time. Many only produce one eruption. For this reason, cinder cones do not reach the sizes of stratovolcanoes or shield volcanoes (Figure 8.17). | text | null |
L_0085 | types of volcanoes | T_0861 | During a massive eruption all of the material may be ejected from a magma changer. Without support, the mountain above the empty chamber may collapse. This produces a huge caldera. Calderas are generally round, bowl-shaped formations like the picture in Figure 8.18. | text | null |
L_0085 | types of volcanoes | T_0862 | Supervolcanoes are the most dangerous type of volcano. During an eruption, enormous amounts of ash are thrown into the atmosphere. The ash encircles the globe. This blocks the Sun and lowers the temperature of the entire planet. The result is a volcanic winter. A supervolcano eruption took place at Lake Toba in northern Sumatra about 75,000 years ago (Figure 8.19). This was the largest eruption in the past 25 million years. As much as 2,800 cubic kilometers of material was ejected into the atmosphere. The result was a 6- to 10-year volcanic winter. Some scientists think that only 10,000 humans survived worldwide. The numbers of other mammals also plummeted. The most recent supervolcano eruption was in New Zealand. The eruption was less than 2000 years ago. For a supervolcano eruption it was small, about 100 cubic kilometers of material. A much larger super eruption in Colorado produced over 5,000 cubic kilometers of material. That eruption was 28 million years ago. It was 5000 times larger than the 1980 Mount St. Helens eruption. The largest potentially active supervolcano in North America is Yellowstone. The caldera has had three super eruptions at 2.1 million, 1.3 million and 640,000 years ago. The floor of the Yellowstone caldera is slowly rising upwards. Another eruption is very likely but no one knows when. The cause of supervolcano eruptions is being debated. Enormous magma chambers are filled with super hot magma. This enormous eruption leaves a huge hole. The ground collapses and creates a caldera. | text | null |
L_0085 | types of volcanoes | T_0862 | Supervolcanoes are the most dangerous type of volcano. During an eruption, enormous amounts of ash are thrown into the atmosphere. The ash encircles the globe. This blocks the Sun and lowers the temperature of the entire planet. The result is a volcanic winter. A supervolcano eruption took place at Lake Toba in northern Sumatra about 75,000 years ago (Figure 8.19). This was the largest eruption in the past 25 million years. As much as 2,800 cubic kilometers of material was ejected into the atmosphere. The result was a 6- to 10-year volcanic winter. Some scientists think that only 10,000 humans survived worldwide. The numbers of other mammals also plummeted. The most recent supervolcano eruption was in New Zealand. The eruption was less than 2000 years ago. For a supervolcano eruption it was small, about 100 cubic kilometers of material. A much larger super eruption in Colorado produced over 5,000 cubic kilometers of material. That eruption was 28 million years ago. It was 5000 times larger than the 1980 Mount St. Helens eruption. The largest potentially active supervolcano in North America is Yellowstone. The caldera has had three super eruptions at 2.1 million, 1.3 million and 640,000 years ago. The floor of the Yellowstone caldera is slowly rising upwards. Another eruption is very likely but no one knows when. The cause of supervolcano eruptions is being debated. Enormous magma chambers are filled with super hot magma. This enormous eruption leaves a huge hole. The ground collapses and creates a caldera. | text | null |
L_0085 | types of volcanoes | T_0862 | Supervolcanoes are the most dangerous type of volcano. During an eruption, enormous amounts of ash are thrown into the atmosphere. The ash encircles the globe. This blocks the Sun and lowers the temperature of the entire planet. The result is a volcanic winter. A supervolcano eruption took place at Lake Toba in northern Sumatra about 75,000 years ago (Figure 8.19). This was the largest eruption in the past 25 million years. As much as 2,800 cubic kilometers of material was ejected into the atmosphere. The result was a 6- to 10-year volcanic winter. Some scientists think that only 10,000 humans survived worldwide. The numbers of other mammals also plummeted. The most recent supervolcano eruption was in New Zealand. The eruption was less than 2000 years ago. For a supervolcano eruption it was small, about 100 cubic kilometers of material. A much larger super eruption in Colorado produced over 5,000 cubic kilometers of material. That eruption was 28 million years ago. It was 5000 times larger than the 1980 Mount St. Helens eruption. The largest potentially active supervolcano in North America is Yellowstone. The caldera has had three super eruptions at 2.1 million, 1.3 million and 640,000 years ago. The floor of the Yellowstone caldera is slowly rising upwards. Another eruption is very likely but no one knows when. The cause of supervolcano eruptions is being debated. Enormous magma chambers are filled with super hot magma. This enormous eruption leaves a huge hole. The ground collapses and creates a caldera. | text | null |
L_0088 | soils | T_0882 | We can think about soil as a living resource. Soil is an ecosystem all by itself! Soil is a complex mixture of different materials. Some of them are inorganic. Inorganic materials are made from non-living substances like pebbles and sand. Soil also contains bits of organic materials from plants and animals. In general, about half of the soil is made of pieces of rock and minerals. The other half is organic materials. In the spaces of soil are millions of living organisms. These include earthworms, ants, bacteria, and fungi. In some soils, the organic portion is entirely missing. This is true of desert sand. At the other extreme, a soil may be completely organic. Peat, found in a bog or swamp, is totally organic soil. Organic materials are necessary for a soil to be fertile. The organic portion provides the nutrients needed for strong plant growth. | text | null |
L_0088 | soils | T_0883 | Soil formation requires weathering. Where there is less weathering, soils are thinner. However, soluble minerals may be present. Where there is intense weathering, soils may be thick. Minerals and nutrients would have been washed out. Soil development takes a very long time. It may take hundreds or even thousands of years to form the fertile upper layer of soil. Soil scientists estimate that in the very best soil forming conditions, soil forms at a rate of about 1mm/year. In poor conditions, it may take thousands of years! How well soil forms and what type of soil forms depends on many factors. These include climate, the original rock type, the slope, the amount of time, and biological activity. | text | null |
L_0088 | soils | T_0884 | Climate is the most important factor in soil formation. The climate of a region is the result of its temperature and rainfall. We can identify different climates by the plants that grow there (Figure 9.6). Given enough time, a climate will produce a particular type of soil. The original rock type does not matter. The same rock type will form a different soil type in each different climate. Rainfall Rainfall in an area is important because it influences the rate of weathering. More rain means that more rainwater passes through the soil. The rainwater reacts chemically with the particles. The top layers of soil are in contact with the freshest water, so reactions are greatest there. High rainfall increases the amount of rock that experiences chemical reactions. High rainfall may also carry material away. This means that new surfaces are exposed. This increases the rate of weathering. Temperature The temperature of a region is the other important part of climate. The rate of chemical reactions increases with higher temperatures. The rate doubles for every 10 C increase in temperature. Plants and bacteria grow and multiply faster in warmer areas. | text | null |
L_0088 | soils | T_0885 | Soil formation increases with time. The longer the amount of time that soil remains in a particular area, the greater the degree of alteration. The warmer the temperatures, the more rainfall, and the greater the amount of time, the thicker the soils will become. | text | null |
L_0088 | soils | T_0886 | The original rock is the source of the inorganic portion of the soil. Mechanical weathering breaks rock into smaller pieces. Chemical reactions change the rocks minerals. A transported soil forms from materials brought in from somewhere else. These soils form from sediments that were transported into the area and deposited. The rate of soil formation is faster for transported materials because they have already been weathered. A soil is a residual soil when it forms in place. Only about one third of the soils in the United States form this way. The material comes from the underlying bedrock. Residual soils form over many years since it takes a long time for solid rock to become soil. First, cracks break up the bedrock. This may happen due to ice wedging. Weathering breaks up the rock even more. Then plants, such as lichens or grasses, become established. They cause further weathering. As more time passes and more layers of material weather, the soil develops. | text | null |
L_0088 | soils | T_0887 | Biological activity produces the organic material in soil. Humus forms from the remains of plants and animals. It is an extremely important part of the soil. Humus coats the mineral grains. It binds them together into clumps that hold the soil together. This gives the soil its structure. Soils with high humus are better able to hold water. Soils rich with organic materials hold nutrients better and are more fertile. These soils are more easily farmed. The color of soil indicates its fertility. Black or dark brown soils are rich in nitrogen and contain a high percentage of organic materials. Soils that are nitrogen poor and low in organic material might be gray, yellow, or red. | text | null |
L_0088 | soils | T_0888 | The inorganic part of soil is made of different amounts of different size particles. This affects the characteristics of a soil. Water flows through soil more easily if the spaces between the particles are large enough and well connected. Sandy or silty soils are light soils because they drain water. Soils rich in clay are heavier. Clay particles allow only very small spaces between them, so clay-rich soils tend to hold water. Clay-rich soils are heavier and hold together more tightly. A soil that contains a mixture of grain sizes is called a loam. Soil scientists measure the percentage of sand, silt, and clay in soil. They plot this information on a triangular diagram, with each type of particle at one corner (Figure 9.7). The soil type is determined by where the soil falls on the diagram. At the top, the soil is clay rich. On the left corner, the soil is sandy. On the right corner, the soil is silty. | text | null |
L_0088 | soils | T_0889 | Soil develops over time and forms soil horizons. Soil horizons are different layers of soil with depth. The most weathering occurs in the top layer. This layer is most exposed to weather! It is where fresh water comes into contact with the soil. Each layer lower is weathered just a little bit less than the layer above. As water moves down through the layers, it is able to do less work to change the soil. If you dig a deep hole in the ground, you may see each of the different layers of soil. All together, the layers are a soil profile. Each horizon has its own set of characteristics (Figure 9.8). In the simplest soil profile, a soil has three horizons. | text | null |
L_0088 | soils | T_0890 | The first horizon is the A horizon. It is more commonly called the topsoil. The topsoil is usually the darkest layer of the soil. It is the layer with the most organic material. Humus forms from all the plant and animal debris that falls to or grows on the ground. The topsoil is also the region with the most biological activity. Many organisms live within this layer. Plant roots stretch down into this layer. The roots help to hold the topsoil in place. Topsoil usually does not have very small particles like clay. Clay-sized particles are carried to lower layers as water seeps down into the ground. Many minerals dissolve in the fresh water that moves through the topsoil. These minerals are carried down to the lower layers of soil. | text | null |
L_0088 | soils | T_0891 | Below the topsoil is the B horizon. This is also called the subsoil. Soluble minerals and clays accumulate in the subsoil. Because it has less organic material, this layer is lighter brown in color than topsoil. It also holds more water due to the presence of iron and clay. There is less organic material in this layer. | text | null |
L_0088 | soils | T_0892 | The next layer down is the C horizon. This layer is made of partially altered bedrock. There is evidence of weathering in this layer. Still, it is possible to identify the original rock type from which this soil formed (Figure Not all climate regions develop soils. Arid regions are poor at soil development. Not all regions develop the same soil horizons. Some areas develop as many as five or six distinct layers. Others develop only a few. | text | null |
L_0088 | soils | T_0893 | For soil scientists, there are thousands of types of soil! Soil scientists put soils into very specific groups with certain characteristics. Each soil type has its own name. Lets consider a much simpler model, with just three types of soil. These types are based on climate. Just remember that there are many more than just these three types. | text | null |
L_0088 | soils | T_0894 | One important type of soil forms in a deciduous forest. In these forests, trees lose their leaves each winter. Deciduous trees need lots of rain at least 65 cm of rainfall per year. Deciduous forests are common in the temperate, eastern United States. The type of soil found in a deciduous forest is a pedalfer (Figure 9.10). This type of soil is usually dark brown or black in color and very fertile. | text | null |
L_0088 | soils | T_0895 | Pedocal soil forms where grasses and brush are common (Figure 9.11). The climate is drier, with less than 65 cm of rain per year. With less rain, there is less chemical weathering. There is less organic material and the soils are slightly less fertile. | text | null |
L_0088 | soils | T_0896 | A third important type of soil is laterite. Laterite forms in tropical areas. Temperatures are warm and rain falls every day (Figure 9.12). So much rain falls that chemical weathering is intense. All soluble minerals are washed from the soil. Plant nutrients get leached or carried away. There is practically no humus. Laterite soils are often red in color from the iron oxides. If laterites are exposed to the Sun, they bake as hard as a brick. | text | null |
L_0088 | soils | T_0897 | Soil is a renewable resource. But it is only renewable if we take care of it. Natural events can degrade soil. These events include droughts, floods, insect plagues, or diseases that damage soil ecosystems. Human activities can also degrade soil. There are many ways in which people neglect or abuse this important resource. | text | null |
L_0088 | soils | T_0898 | People remove a lot of vegetation. They log forests or prepare the land for farming or construction. Even just walking or riding your bike over the same place can kill the grass. But plants help to hold the soil in place (Figure faster than it is forming. In these locations, soil is a non-renewable resource. Soils may also remain in place but become degraded. Soil is contaminated if too much salt accumulates. Soil can also be contaminated by pollutants. | text | null |
L_0088 | soils | T_0899 | There are many ways to protect soil. We can add organic material like manure or compost. This increases the soils fertility. Increased fertility improves the soils ability to hold water and nutrients. Inorganic fertilizers also increase fertility. These fertilizers are less expensive than natural fertilizers, but they do not provide the same long term benefits. Careful farming helps to keep up soil quality each season. One way is to plant different crops each year. Another is to alternate the crops planted in each row of the field. These techniques preserve and replenish soil nutrients. Planting nutrient rich cover crops helps the soil. Planting trees as windbreaks, plowing along contours of a field, or building terraces into steeper slopes all help to hold soil in place (Figure 9.14). No-till or low-till farming disturbs the ground as little as possible during planting. | text | null |
L_0097 | avoiding soil loss | T_0935 | Bad farming practices and a return to normal rainfall levels after an unusually wet period led to the Dust Bowl. In some regions more than 75% of the topsoil blew away. This is the most extreme example of soil erosion the United States has ever seen. Still, in many areas of the world, the rate of soil erosion is many times greater than the rate at which it is forming. Drought, insect plagues, or outbreaks of disease are natural cycles of events that can negatively impact ecosystems and the soil, but there are also many ways in which humans neglect or abuse this important resource. Soils can also be contaminated if too much salt accumulates in the soil or where pollutants sink into the ground. One harmful practice is removing the vegetation that helps to hold soil in place. Sometimes just walking or riding your bike over the same place will kill the grass that normally grows there. Land is also deliberately cleared or deforested for wood. The loose soils then may be carried away by wind or running water. A farmer and his sons walk through a dust storm in Cimarron County, Oklahoma in 1936. Click image to the left or use the URL below. URL: | text | null |
L_0097 | avoiding soil loss | T_0936 | Soil is only a renewable resource if it is carefully managed. There are many practices that can protect and preserve soil resources. | text | null |
L_0097 | avoiding soil loss | T_0937 | Adding organic material to the soil in the form of plant or animal waste, such as compost or manure, increases the fertility of the soil and improves its ability to hold on to water and nutrients (Figure 1.2). Inorganic fertilizer can also temporarily increase the fertility of a soil and may be less expensive or time consuming, but it does not provide the same long-term improvements as organic materials. | text | null |
L_0097 | avoiding soil loss | T_0938 | Soil is a natural resource that is vitally important for sustaining natural habitats and for growing food. Although soil is a renewable resource, it is renewed slowly, taking hundreds or thousands of years for a good fertile soil to develop. Organic material can be added to soil to help increase its fertility. Most of the best land for farming is already being cultivated. With human populations continuing to grow, it is extremely important to protect our soil resources. Agricultural practices such as rotating crops, alternating the types of crops planted in each row, and planting nutrient-rich cover crops all help to keep soil more fertile as it is used season after season. Planting trees as windbreaks, plowing along contours of the field, or building terraces into steeper slopes will all help to hold soil in place (Figure 1.3). No-till or low-tillage farming helps to keep soil in place by disturbing the ground as little as possible when planting. Steep slopes can be terraced to make level planting areas and decrease surface water runoff and erosion. The rate of topsoil loss in the United States and other developed countries has decreased recently as better farming practices have been adopted. Unfortunately, in developing nations, soil is often not protected. Table 1.1 shows some steps that we can take to prevent erosion. Some are things that can be done by farmers or developers. Others are things that individual homeowners or community members can implement locally. Source of Erosion Strategies for Prevention Leave leaf litter on the ground in the winter. Grow cover crops, special crops grown in the winter to cover the soil. Plant tall trees around fields to buffer the effects of wind. Drive tractors as little as possible. Use drip irrigation that puts small amounts of water in the ground frequently. Avoid watering crops with sprinklers that make big water drops on the ground. Keep fields as flat as possible to avoid soil erod- ing down hill. Grazing Animals Move animals throughout the year, so they dont consume all the vegetation in one spot. Keep animals away from stream banks, where hills are especially prone to erosion. Logging and Mining Reduce the amount of land that is logged and mined. Reduce the number of roads that are built to access logging areas. Avoid logging and mining on steep lands. Cut only small areas at one time and quickly replant logged areas with new seedlings. Development Reduce the amount of land area that is developed into urban areas, parking lots, etc. Keep as much green space in cities as possible, such as parks or strips where plants can grow. Invest in and use new technologies for parking lots that make them permeable to water in order to reduce runoff of water. Recreational Activities Avoid using off-road vehicles on hilly lands. Stay on designated trails. Avoid building on steep hills. Grade surrounding land to distribute water rather than collecting it in one place. Where water collects, drain to creeks and rivers. Landscape with plants that minimize erosion. Click image to the left or use the URL below. URL: | text | null |
L_0097 | avoiding soil loss | T_0938 | Soil is a natural resource that is vitally important for sustaining natural habitats and for growing food. Although soil is a renewable resource, it is renewed slowly, taking hundreds or thousands of years for a good fertile soil to develop. Organic material can be added to soil to help increase its fertility. Most of the best land for farming is already being cultivated. With human populations continuing to grow, it is extremely important to protect our soil resources. Agricultural practices such as rotating crops, alternating the types of crops planted in each row, and planting nutrient-rich cover crops all help to keep soil more fertile as it is used season after season. Planting trees as windbreaks, plowing along contours of the field, or building terraces into steeper slopes will all help to hold soil in place (Figure 1.3). No-till or low-tillage farming helps to keep soil in place by disturbing the ground as little as possible when planting. Steep slopes can be terraced to make level planting areas and decrease surface water runoff and erosion. The rate of topsoil loss in the United States and other developed countries has decreased recently as better farming practices have been adopted. Unfortunately, in developing nations, soil is often not protected. Table 1.1 shows some steps that we can take to prevent erosion. Some are things that can be done by farmers or developers. Others are things that individual homeowners or community members can implement locally. Source of Erosion Strategies for Prevention Leave leaf litter on the ground in the winter. Grow cover crops, special crops grown in the winter to cover the soil. Plant tall trees around fields to buffer the effects of wind. Drive tractors as little as possible. Use drip irrigation that puts small amounts of water in the ground frequently. Avoid watering crops with sprinklers that make big water drops on the ground. Keep fields as flat as possible to avoid soil erod- ing down hill. Grazing Animals Move animals throughout the year, so they dont consume all the vegetation in one spot. Keep animals away from stream banks, where hills are especially prone to erosion. Logging and Mining Reduce the amount of land that is logged and mined. Reduce the number of roads that are built to access logging areas. Avoid logging and mining on steep lands. Cut only small areas at one time and quickly replant logged areas with new seedlings. Development Reduce the amount of land area that is developed into urban areas, parking lots, etc. Keep as much green space in cities as possible, such as parks or strips where plants can grow. Invest in and use new technologies for parking lots that make them permeable to water in order to reduce runoff of water. Recreational Activities Avoid using off-road vehicles on hilly lands. Stay on designated trails. Avoid building on steep hills. Grade surrounding land to distribute water rather than collecting it in one place. Where water collects, drain to creeks and rivers. Landscape with plants that minimize erosion. Click image to the left or use the URL below. URL: | text | null |
L_0105 | cenozoic plate tectonics | T_0971 | The Cenozoic began around 65.5 million years ago and continues today. Although it accounts for only about 1.5% of the Earths total history, as the most recent era it is the one scientists know the most about. Much of what has been discussed elsewhere in CK-12 Earth Science Concepts For High School describes the geological situation of the Cenozoic. A few highlights are mentioned here. | text | null |
L_0105 | cenozoic plate tectonics | T_0972 | The paleogeography of the era was very much like it is today. Early in the Cenozoic, blocks of crust uplifted to form the Rocky Mountains, which were later eroded away and then uplifted again. Subduction off of the Pacific Northwest formed the Cascades volcanic arc. The Basin and Range province that centers on Nevada is where crust is being pulled apart. | text | null |
L_0105 | cenozoic plate tectonics | T_0973 | The San Andreas Fault has grown where the Pacific and North American plates meet. The plate tectonic evolution of that plate boundary is complex and interesting (Figure 1.1). The Farallon Plate was subducting beneath the North American Plate 30 Ma. By 20 Ma the Pacific Plate and East Pacific Rise spreading center had started to subduct, splitting the Farallon Plate into two smaller plates. Transform motion where the Pacific and North American plates meet formed the San Andreas Fault. The fault moved inland and at present small sea floor spreading basins along with the transform motion of the San Andreas are splitting Baja California from mainland Mexico. This figure shows the evolution of the San Andreas Fault zone from 30 million years ago (bottom) to present (top). Although most plate tectonic activity involves continents moving apart, smaller regions are coming together. Africa collided with Eurasia to create the Alps. India crashed into Asia to form the Himalayas. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0105 | cenozoic plate tectonics | T_0974 | As the continents moved apart, climate began to cool. When Australia and Antarctica separated, the Antarctic Circumpolar Current could then move the frigid water around Antarctica and spread it more widely around the planet. Antarctica drifted over the south polar region and the continent began to grow a permanent ice cap in the Oligocene. The climate warmed in the early Miocene but then began to cool again in the late Miocene and Pliocene when glaciers began to form. During the Pleistocene ice ages, which began 2.6 million years ago, glaciers advanced and retreated four times (Figure 1.2). During the retreats, the climate was often warmer than it is today. Glacial ice at its maximum during the Pleistocene. These continental ice sheets were extremely thick, like the Antarctic ice cap is today. The Pleistocene ice ages guided the evolution of life in the Cenozoic, including the evolution of humans. | text | null |
L_0108 | chemical weathering | T_0981 | Chemical weathering is the other important type of weathering. Chemical weathering may change the size of pieces of rock materials, but definitely changes the composition. So one type of mineral changes into a different mineral. Chemical weathering works through chemical reactions that cause changes in the minerals. | text | null |
L_0108 | chemical weathering | T_0982 | Most minerals form at high pressure or high temperatures deep in the crust, or sometimes in the mantle. When these rocks are uplifed onto Earths surface, they are at very low temperatures and pressures. This is a very different environment from the one in which they formed and the minerals are no longer stable. In chemical weathering, minerals that were stable inside the crust must change to minerals that are stable at Earths surface. | text | null |
L_0108 | chemical weathering | T_0983 | Remember that the most common minerals in Earths crust are the silicate minerals. Many silicate minerals form in igneous or metamorphic rocks. The minerals that form at the highest temperatures and pressures are the least stable at the surface. Clay is stable at the surface and chemical weathering converts many minerals to clay (Figure 1.1). There are many types of chemical weathering because there are many agents of chemical weathering. Deforestation in Brazil reveals the under- lying clay-rich soil. | text | null |
L_0108 | chemical weathering | T_0984 | A water molecule has a very simple chemical formula, H2 O, two hydrogen atoms bonded to one oxygen atom. But water is pretty remarkable in terms of all the things it can do. Remember that water is a polar molecule. The positive side of the molecule attracts negative ions and the negative side attracts positive ions. So water molecules separate the ions from their compounds and surround them. Water can completely dissolve some minerals, such as salt. Weathered rock in Walnut Canyon near Flagstaff, Arizona. Hydrolysis is the name of the chemical reaction between a chemical compound and water. When this reaction takes place, water dissolves ions from the mineral and carries them away. These elements have been leached. Through hydrolysis, a mineral such as potassium feldspar is leached of potassium and changed into a clay mineral. Clay minerals are more stable at the Earths surface. | text | null |
L_0108 | chemical weathering | T_0985 | Carbon dioxide (CO2 ) combines with water as raindrops fall through the atmosphere. This makes a weak acid, called carbonic acid. Carbonic acid is a very common in nature, where it works to dissolve rock. Pollutants, such as sulfur and nitrogen from fossil fuel burning, create sulfuric and nitric acid. Sulfuric and nitric acids are the two main components of acid rain, which accelerates chemical weathering (Figure 1.3). Acid rain is discussed in the chapter Human Impacts on Earths Systems. This statue at Washington Square Arch in New York City exhibits damage from acid rain. | text | null |
L_0108 | chemical weathering | T_0986 | Oxidation is a chemical reaction that takes place when oxygen reacts with another element. Oxygen is very strongly chemically reactive. The most familiar type of oxidation is when iron reacts with oxygen to create rust (Figure 1.4). Minerals that are rich in iron break down as the iron oxidizes and forms new compounds. Iron oxide produces the red color in soils. | text | null |
L_0108 | chemical weathering | T_0987 | Now that you know what chemical weathering is, can you think of some other ways chemical weathering might occur? Chemical weathering can also be contributed to by plants and animals. As plant roots take in soluble ions as nutrients, certain elements are exchanged. Plant roots and bacterial decay use carbon dioxide in the process of respiration. | text | null |
L_0108 | chemical weathering | T_0988 | Mechanical weathering increases the rate of chemical weathering. As rock breaks into smaller pieces, the surface area of the pieces increases Figure 1.5. With more surfaces exposed, there are more surfaces on which chemical weathering can occur. Mechanical weathering may increase the rate of chemical weathering. Click image to the left or use the URL below. URL: | text | null |
L_0112 | clouds | T_1006 | Humidity is the amount of water vapor in the air in a particular spot. We usually use the term to mean relative humidity, the percentage of water vapor a certain volume of air is holding relative to the maximum amount it can contain. If the humidity today is 80%, it means that the air contains 80% of the total amount of water it can hold at that temperature. What will happen if the humidity increases to more than 100%? The excess water condenses and forms precipitation. Since warm air can hold more water vapor than cool air, raising or lowering temperature can change airs relative humidity (Figure 1.1). The temperature at which air becomes saturated with water is called the airs dew point. This term makes sense, because water condenses from the air as dew if the air cools down overnight and reaches 100% humidity. This diagram shows the amount of water air can hold at different temperatures. The temperatures are given in degrees Cel- sius. | text | null |
L_0112 | clouds | T_1007 | Water vapor is not visible unless it condenses to become a cloud. Water vapor condenses around a nucleus, such as dust, smoke, or a salt crystal. This forms a tiny liquid droplet. Billions of these water droplets together make a cloud. | text | null |
L_0112 | clouds | T_1008 | Clouds form when air reaches its dew point. This can happen in two ways: (1) Air temperature stays the same but humidity increases. This is common in locations that are warm and humid. (2) Humidity remains the same, but temperature decreases. When the air cools enough to reach 100% humidity, water droplets form. Air cools when it comes into contact with a cold surface or when it rises. Rising air creates clouds when it has been warmed at or near the ground level and then is pushed up over a mountain or mountain range or is thrust over a mass of cold, dense air. Click image to the left or use the URL below. URL: | text | null |
L_0112 | clouds | T_1009 | Clouds have a big influence on weather: by preventing solar radiation from reaching the ground. by absorbing warmth that is re-emitted from the ground. as the source of precipitation. When there are no clouds, there is less insulation. As a result, cloudless days can be extremely hot, and cloudless nights can be very cold. For this reason, cloudy days tend to have a lower range of temperatures than clear days. | text | null |
L_0112 | clouds | T_1010 | Clouds are classified in several ways. The most common classification used today divides clouds into four separate cloud groups, which are determined by their altitude (Figure 1.2). The four cloud types and where they are found in the atmosphere. High clouds form from ice crystals where the air is extremely cold and can hold little water vapor. Cirrus, cirrostratus, and cirrocumulus are all names of high clouds. Middle clouds, including altocumulus and altostratus clouds, may be made of water droplets, ice crystals or both, depending on the air temperatures. Thick and broad altostratus clouds are gray or blue-gray. They often cover the entire sky and usually mean a large storm, bearing a lot of precipitation, is coming. Low clouds are nearly all water droplets. Stratus, stratocumulus, and nimbostratus clouds are common low clouds. Nimbostratus clouds are thick and dark. They bring steady rain or snow. Vertical clouds, clouds with the prefix "cumulo-," grow vertically instead of horizontally and have their bases at low altitude and their tops at high or middle altitude. Clouds grow vertically when strong air currents are rising upward. Precipitating clouds are nimbus clouds. | text | null |
L_0112 | clouds | T_1011 | Fog (Figure 1.3) is a cloud located at or near the ground . When humid air near the ground cools below its dew point, fog is formed. Each type of fog forms in a different way. Radiation fog forms at night when skies are clear and the relative humidity is high. As the ground cools, the bottom layer of air cools below its dew point. Tule fog is an extreme form of radiation fog found in some regions. San Francisco, California, is famous for its summertime advection fog. Warm, moist Pacific Ocean air blows over the cold California current and cools below its dew point. Sea breezes bring the fog onshore. Steam fog appears in autumn when cool air moves over a warm lake. Water evaporates from the lake surface and condenses as it cools, appearing like steam. Warm humid air travels up a hillside and cools below its dew point to create upslope fog. (a) Tule fog in the Central Valley of California. (b) Advection fog in San Francisco. (c) Steam fog over a lake. (d) Upslope fog in Terespolis city, Rio de Janeiro State, Brazil. Fog levels are declining along the California coast as climate warms. The change in fog may have big ecological changes for the state. Click image to the left or use the URL below. URL: | text | null |
L_0117 | composition of the atmosphere | T_1027 | Several properties of the atmosphere change with altitude, but the composition of the natural gases does not. The proportions of gases in the atmosphere are everywhere the same, with one exception. At about 20 km to 40 km above the surface, there is a greater concentration of ozone molecules than in other portions of the atmosphere. This is called the ozone layer. | text | null |
L_0117 | composition of the atmosphere | T_1028 | Nitrogen and oxygen together make up 99% of the planets atmosphere. Nitrogen makes up the bulk of the atmosphere, but is not involved in geological or biological processes in its gaseous form. Nitrogen fixing is described in the chapter Life on Earth. Oxygen is extremely important because it is needed by animals for respiration. The rest of the gases are minor components but sometimes are very important (Figure 1.1). Nitrogen and oxygen make up 99% of the atmosphere; carbon dioxide is a very important minor component. | text | null |
L_0117 | composition of the atmosphere | T_1029 | Humidity is the amount of water vapor in the air. Humidity varies from place to place and season to season. This fact is obvious if you compare a summer day in Atlanta, Georgia, where humidity is high, with a winter day in Phoenix, Arizona, where humidity is low. When the air is very humid, it feels heavy or sticky. Dry air usually feels more comfortable. When humidity is high, water vapor makes up only about 4% of the atmosphere. Where around the globe is mean atmospheric water vapor higher and where is it lower (Figure 1.2)? Why? Higher humidity is found around the equatorial regions because air temperatures are higher and warm air can hold more moisture than cooler air. Of course, humidity is lower near the polar regions because air temperature is lower. | text | null |
L_0117 | composition of the atmosphere | T_1030 | Remember that greenhouse gases trap heat in the atmosphere. Important natural greenhouse gases include carbon dioxide, methane, water vapor, and ozone. CFCs and some other man-made compounds are also greenhouse gases. | text | null |
L_0117 | composition of the atmosphere | T_1031 | Some of what is in the atmosphere is not gas. Particles of dust, soil, fecal matter, metals, salt, smoke, ash, and other solids make up a small percentage of the atmosphere and are called particulates. Particles provide starting points (or nuclei) for water vapor to condense on and form raindrops. Some particles are pollutants. Click image to the left or use the URL below. URL: | text | null |
L_0122 | dark matter | T_1041 | The things we observe in space are objects that emit some type of electromagnetic radiation. However, scientists think that matter that emits light makes up only a small part of the matter in the universe. The rest of the matter, about 80%, is dark matter. Dark matter emits no electromagnetic radiation, so we cant observe it directly. However, astronomers know that dark matter exists because its gravity affects the motion of objects around it. When astronomers measure how spiral galaxies rotate, they find that the outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than they can see. Gravitational lensing occurs when light is bent from a very distant bright source around a super-massive object (Figure 1.1). To explain strong gravitational lensing, more matter than is observed must be present. With so little to go on, astronomers dont really know much about the nature of dark matter. One possibility is that it could just be ordinary matter that does not emit radiation in objects such as black holes, neutron stars, and brown dwarfs objects larger than Jupiter but smaller than the smallest stars. But astronomers cannot find enough of these types of objects, which they have named MACHOs (massive astrophyiscal compact halo object), to account for all the dark matter, so they are thought to be only a small part of the total. Another possibility is that the dark matter is very different from the ordinary matter we see. Some appear to be particles that have gravity, but dont otherwise appear to interact with other particles. Scientists call these theoretical particles WIMPs, which stands for Weakly Interactive Massive Particles. Most scientists who study dark matter think that the dark matter in the universe is a combination of MACHOs and some type of exotic matter, such as WIMPs. Researching dark matter is an active area of scientific research, and astronomers knowledge about dark matter is changing rapidly. | text | null |
L_0122 | dark matter | T_1042 | Astronomers who study the expansion of the universe are interested in knowing the rate of that expansion. Is the rate fast enough to overcome the attractive pull of gravity? If yes, then the universe will expand forever, although the expansion will slow down over time. If no, then the universe would someday start to contract, and eventually get squeezed together in a big crunch, the opposite of the Big Bang. Recently, astronomers have made a discovery that answers that question: the rate at which the universe is expanding is actually increasing. In other words, the universe is expanding faster now than ever before, and in the future it will expand even faster. So now astronomers think that the universe will keep expanding forever. But it also proposes a perplexing new question: what is causing the expansion of the universe to accelerate? One possible hypothesis involves a new, hypothetical form of energy called dark energy (Figure 1.2). Some scientists think that dark energy makes up as much as 71% of the total energy content of the universe. Today matter makes up a small percentage of the universe, but at the start of the universe it made up much more. Where did dark energy, if it even exists, come from? Other scientists have other hypotheses about why the universe is continuing to expand; the causes of the universes expansion is another unanswered question that scientists are researching. Click image to the left or use the URL below. URL: | text | null |
L_0122 | dark matter | T_1043 | Meet one of the three winners of the 2011 Nobel Prize in Physics, Lawrence Berkeley Lab astrophysicist Saul Perlmutter. He explains how dark energy, which makes up 70 percent of the universe, is causing our universe to expand. Click image to the left or use the URL below. URL: | text | null |
L_0129 | divergent plate boundaries | T_1057 | Were on a new trip now. We will start in Mexico, in the region surrounding the Gulf of California, where a divergent plate boundary is rifting Baja California and mainland Mexico apart. Then we will move up into California, where plates on both sides of a transform boundary are sliding past each other. Finally well end up off of the Pacific Northwest, where a divergent plate boundary is very near a subduction zone just offshore. In the Figure 1.1 a red bar where seafloor spreading is taking place. A long black line is a transform fault and a black line with hatch marks is a trench where subduction is taking place. Notice how one type of plate boundary transitions into another. | text | null |
L_0129 | divergent plate boundaries | T_1058 | A divergent plate boundary on land rips apart continents (Figure 1.2). In continental rifting, magma rises beneath the continent, causing it to become thinner, break, and ultimately split apart. New ocean crust erupts in the void, ultimately creating an ocean between continents. On either side of the ocean are now two different lithospheric plates. This is how continents split apart. These features are well displayed in the East African Rift, where rifting has begun, and in the Red Sea, where water is filling up the basin created by seafloor spreading. The Atlantic Ocean is the final stage, where rifting is now separating two plates of oceanic crust. | text | null |
L_0129 | divergent plate boundaries | T_1059 | Baja California is a state in Mexico just south of California. In the Figure 1.3, Baja California is the long, skinny land mass on the left. You can see that the Pacific Ocean is growing in between Baja California and mainland Mexico. This body of water is called the Gulf of California or, more romantically, the Sea of Cortez. Baja is on the Pacific Plate and the rest of Mexico is on the North American Plate. Extension is causing the two plates to move apart and will eventually break Baja and the westernmost part of California off of North America. The Gulf of California will expand into a larger sea. Rifting has caused volcanic activity on the Baja California peninsula as seen in the Figure 1.4. Can you relate what is happening at this plate boundary to what happened when Pangaea broke apart? | text | null |
L_0130 | divergent plate boundaries in the oceans | T_1060 | Iceland provides us with a fabulous view of a mid-ocean ridge above sea level (Figure 1.1) As you can see, where plates diverge at a mid-ocean ridge is a rift valley that marks the boundary between the two plates. Basalt lava erupts into that rift valley and forms new seafloor. Seafloor on one side of the rift is part of one plate and seafloor on the other side is part of another plate. Leif the Lucky Bridge straddles the divergent plate boundary. Look back at the photo at the top. You may think that the rock on the left side of the valley looks pretty much like the rock on the right side. Thats true - its all basalt and it even all has the same magnetic polarity. The rocks on both sides are extremely young. Whats different is that the rock one side of the bridge is the youngest rock of the North American Plate while the rock on the other side is the youngest rock on the Eurasian plate. This is a block diagram of a divergent plate boundary. Remember that most of these are on the seafloor and only in Iceland do we get such a good view of a divergent plate boundary in the ocean. | text | null |
L_0130 | divergent plate boundaries in the oceans | T_1061 | Remember that the mid-ocean ridge is where hot mantle material upwells in a convection cell. The upwelling mantle melts due to pressure release to form lava. Lava flows at the surface cool rapidly to become basalt, but deeper in the crust, magma cools more slowly to form gabbro. The entire ridge system is made up of igneous rock that is either extrusive or intrusive. The seafloor is also igneous rock with some sediment that has fallen onto it. Earthquakes are common at mid-ocean ridges since the movement of magma and oceanic crust results in crustal shaking. Click image to the left or use the URL below. URL: | text | null |
L_0134 | earthquake characteristics | T_1080 | An earthquake is sudden ground movement caused by the sudden release of energy stored in rocks. Earthquakes happen when so much stress builds up in the rocks that the rocks rupture. The energy is transmitted by seismic waves. Earthquakes can be so small they go completely unnoticed, or so large that it can take years for a region to recover. | text | null |
L_0134 | earthquake characteristics | T_1081 | The description of how earthquakes occur is called elastic rebound theory (Figure 1.1). Elastic rebound theory. Stresses build on both sides of a fault, causing the rocks to deform plastically (Time 2). When the stresses become too great, the rocks break and end up in a different location (Time 3). This releases the built up energy and creates an earthquake. Click image to the left or use the URL below. URL: | text | null |
L_0134 | earthquake characteristics | T_1082 | In an earthquake, the initial point where the rocks rupture in the crust is called the focus. The epicenter is the point on the land surface that is directly above the focus (Figure 1.2). In the vertical cross section of crust, there are two features labeled - the focus and the epicenter, which is directly above the focus. Click image to the left or use the URL below. URL: | text | null |
L_0135 | earthquake damage | T_1083 | We know that earthquakes kill lots of people. However, the ground shaking almost never kills people, and the ground does not swallow someone up. Fatalities depend somewhat on an earthquakes size and the type of ground people inhabit. But much of what determines the number of fatalities depends on the quality of structures. People are killed when structures fall on them. More damage is done and more people are killed by the fires that follow an earthquake than the earthquake itself. | text | null |
L_0135 | earthquake damage | T_1084 | Population density. The magnitude 9.2 Great Alaska Earthquake, near Anchorage, of 1964 resulted in only 131 deaths. At the time few people lived in the area (Figure 1.1). Not size. Only about 2,000 people died in the 1960 Great Chilean earthquake, the largest earthquake ever recorded. The Indian Ocean earthquake of 2004 was one of the largest ever, but most of the 230,000 fatalities were caused by the tsunami, not the earthquake itself. Ground type. Solid bedrock vibrates less than soft sediments, so there is less damage on bedrock. Sediments that are saturated with water undergo liquefaction and become like quicksand (Figure 1.2). Soil on a hillside may become a landslide. Liquefaction of sediments in Mexico City caused the collapse of many buildings in the 1985 earthquake. | text | null |
L_0135 | earthquake damage | T_1084 | Population density. The magnitude 9.2 Great Alaska Earthquake, near Anchorage, of 1964 resulted in only 131 deaths. At the time few people lived in the area (Figure 1.1). Not size. Only about 2,000 people died in the 1960 Great Chilean earthquake, the largest earthquake ever recorded. The Indian Ocean earthquake of 2004 was one of the largest ever, but most of the 230,000 fatalities were caused by the tsunami, not the earthquake itself. Ground type. Solid bedrock vibrates less than soft sediments, so there is less damage on bedrock. Sediments that are saturated with water undergo liquefaction and become like quicksand (Figure 1.2). Soil on a hillside may become a landslide. Liquefaction of sediments in Mexico City caused the collapse of many buildings in the 1985 earthquake. | text | null |
L_0135 | earthquake damage | T_1085 | In earthquake-prone areas, city planners try to reduce hazards. For example, in the San Francisco Bay Area, maps show how much shaking is expected for different ground types (Figure 1.3). This allows planners to locate new hospitals and schools more safely. The expected Modified Mercalli Intensity Scale for an earthquake of magnitude 7.1 on the northern portion of the Hayward Fault. Click image to the left or use the URL below. URL: | text | null |
L_0136 | earthquake safe structures | T_1086 | New construction can be made safer in many ways: Skyscrapers and other large structures built on soft ground must be anchored to bedrock, even if it lies hundreds of meters below the ground surface. The correct building materials must be used. Houses should bend and sway. Wood and steel are better than brick, stone, and adobe, which are brittle and will break. Larger buildings must sway, but not so much that they touch nearby buildings. Counterweights and diagonal steel beams are used to hold down sway. Large buildings can be placed on rollers so that they move with the ground. Buildings may be placed on layers of steel and rubber to absorb the shock of the waves. Connections, such as where the walls meet the foundation, must be made strong. In a multi-story building, the first story must be well supported (Figure 1.1). The first floor of this San Francisco build- ing is collapsing after the 1989 Loma Pri- eta earthquake. | text | null |
L_0136 | earthquake safe structures | T_1087 | To make older buildings more earthquake safe, retrofitting with steel or wood can reinforce a buildings structure and its connections. Elevated freeways and bridges can also be retrofitted so that they do not collapse. Steel trusses were built diagonally and horizontally across windows to retrofit a building at Stanford University in Palo Alto, California. The San Andreas Fault passes just west of the university. | text | null |
L_0136 | earthquake safe structures | T_1088 | Fires often cause more damage than the earthquake. Fires start because seismic waves rupture gas and electrical lines, and breaks in water mains make it difficult to fight the fires (Figure 1.3). Builders zigzag pipes so that they bend and flex when the ground shakes. In San Francisco, water and gas pipelines are separated by valves so that areas can be isolated if one segment breaks. | text | null |
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