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L_0210 | intraplate earthquakes | T_1337 | In August 2011 the eastern seaboard of the U.S. was rocked by a magnitude 5.8 earthquake. While not huge, most of the residents had never experienced a quake and many didnt know what it was. Some people thought the shaking might have been the result of a terrorist attack. This region is no longer part of an active plate boundary. But if you went back in time to the late Paleozoic, you would find the region being uplifted into the ancestral Appalachian mountains as continent-continent convergence brought Pangaea together. The Piedmont Seismic Zone is an area of several hundred million year-old faults that sometimes reactivate. | text | null |
L_0210 | intraplate earthquakes | T_1338 | In 1812, a magnitude 7.5 earthquake struck near New Madrid, Missouri. The earthquake was strongly felt over approximately 50,000 square miles and altered the course of the Mississippi River. Because very few people lived there at the time, only 20 people died. Many more people live there today (Figure 1.1). A similar earthquake today would undoubtedly kill many people and cause a great deal of property damage. Like the Piedmont Seismic Zone, the New Madrid Seismic Zone is a set of reactivated faults. These faults are left from the rifting apart of the supercontinent Rodinia about 750 million years ago. The plates did not rift apart here but left a weakness in the lithosphere that makes the region vulnerable to earthquakes. Click image to the left or use the URL below. URL: | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1349 | Gravity shapes the Earths surface by moving weathered material from a higher place to a lower one. This occurs in a variety of ways and at a variety of rates, including sudden, dramatic events as well as slow, steady movements that happen over long periods of time. The force of gravity is constant and it is changing the Earths surface right now. | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1350 | Erosion by gravity is called mass wasting. Mass wasting can be slow and virtually imperceptible, or rapid, massive, and deadly. Weathered material may fall away from a cliff because there is nothing to keep it in place. Rocks that fall to the base of a cliff make a talus slope. Sometimes as one rock falls, it hits another rock, which hits another rock, and begins a landslide. | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1351 | Landslides are the most dramatic, sudden, and dangerous examples of Earth materials moved by gravity. Landslides are sudden falls of rock; by contrast, avalanches are sudden falls of snow. When large amounts of rock suddenly break loose from a cliff or mountainside, they move quickly and with tremendous force (Figure 1.1). Air trapped under the falling rocks acts as a cushion that keeps the rock from slowing down. Landslides can move as fast as 200 to 300 km/hour. This landslide in California in 2008 blocked Highway 140. Landslides are exceptionally destructive. Homes may be destroyed as hillsides collapse. Landslides can even bury entire villages. Landslides may create lakes when the rocky material dams a stream. If a landslide flows into a lake or bay, they can trigger a tsunami. Landslides often occur on steep slopes in dry or semi-arid climates. The California coastline, with its steep cliffs and years of drought punctuated by seasons of abundant rainfall, is prone to landslides. | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1352 | Added water creates natural hazards produced by gravity (Figure 1.2). On hillsides with soils rich in clay, little rain, and not much vegetation to hold the soil in place, a time of high precipitation will create a mudflow. Mudflows follow river channels, washing out bridges, trees, and homes that are in their path. A lahar is mudflow that flows down a composite volcano (Figure 1.3). Ash mixes with snow and ice melted by the eruption to produce hot, fast-moving flows. The lahar caused by the eruption of Nevado del Ruiz in Columbia in 1985 killed more than 23,000 people. | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1353 | Less dramatic types of downslope movement move Earth materials slowly down a hillside. Slump moves materials as a large block along a curved surface (Figure 1.4). Slumps often happen when a slope is undercut, with no support for the overlying materials, or when too much weight is added to an unstable slope. Mudflows are common in southern California. A lahar is a mudflow that forms from vol- canic ash and debris. Slump material moves as a whole unit, leaving behind a crescent shaped scar. The trunks of these trees near Mineral King, California, were bent by snow creeping downhill when the trees were saplings. Click image to the left or use the URL below. URL: | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1353 | Less dramatic types of downslope movement move Earth materials slowly down a hillside. Slump moves materials as a large block along a curved surface (Figure 1.4). Slumps often happen when a slope is undercut, with no support for the overlying materials, or when too much weight is added to an unstable slope. Mudflows are common in southern California. A lahar is a mudflow that forms from vol- canic ash and debris. Slump material moves as a whole unit, leaving behind a crescent shaped scar. The trunks of these trees near Mineral King, California, were bent by snow creeping downhill when the trees were saplings. Click image to the left or use the URL below. URL: | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1353 | Less dramatic types of downslope movement move Earth materials slowly down a hillside. Slump moves materials as a large block along a curved surface (Figure 1.4). Slumps often happen when a slope is undercut, with no support for the overlying materials, or when too much weight is added to an unstable slope. Mudflows are common in southern California. A lahar is a mudflow that forms from vol- canic ash and debris. Slump material moves as a whole unit, leaving behind a crescent shaped scar. The trunks of these trees near Mineral King, California, were bent by snow creeping downhill when the trees were saplings. Click image to the left or use the URL below. URL: | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1353 | Less dramatic types of downslope movement move Earth materials slowly down a hillside. Slump moves materials as a large block along a curved surface (Figure 1.4). Slumps often happen when a slope is undercut, with no support for the overlying materials, or when too much weight is added to an unstable slope. Mudflows are common in southern California. A lahar is a mudflow that forms from vol- canic ash and debris. Slump material moves as a whole unit, leaving behind a crescent shaped scar. The trunks of these trees near Mineral King, California, were bent by snow creeping downhill when the trees were saplings. Click image to the left or use the URL below. URL: | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1354 | There are several factors that increase the chance that a landslide will occur. Some of these we can prevent and some we cannot. | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1355 | A little bit of water helps to hold grains of sand or soil together. For example, you can build a larger sand castle with slightly wet sand than with dry sand. However, too much water causes the sand to flow quickly away. Rapid snow melt or rainfall adds extra water to the soil, which increases the weight of the slope and makes sediment grains lose contact with each other, allowing flow. | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1356 | Layers of weak rock, such as clay, also allow more landslides. Wet clay is very slippery, which provides an easy surface for materials to slide over. | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1357 | If people dig into the base of a slope to create a road or a homesite, the slope may become unstable and move downhill. This is particularly dangerous when the underlying rock layers slope towards the area. When construction workers cut into slopes for homes or roads, they must stabilize the slope to help prevent a landslide (Figure 1.6). Tree roots or even grasses can bind soil together. It is also a good idea to provide drainage so that the slope does not become saturated with water. | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1358 | An earthquake, volcanic eruption, or even just a truck going by can shake unstable ground loose and cause a slide. Skiers and hikers may disturb the snow they travel over and set off an avalanche. | text | null |
L_0214 | landforms from erosion and deposition by gravity | T_1359 | Landslides cause $1 billion to $2 billion damage in the United States each year and are responsible for traumatic and sudden loss of life and homes in many areas of the world. Some at-risk communities have developed landslide warning systems. Around San Francisco Bay, the National Weather Service and the U.S. Geological Survey use rain gauges to monitor soil moisture. If soil becomes saturated, the weather service issues a warning. Earthquakes, which may occur on Californias abundant faults, can also trigger landslides. To be safe from landslides: Be aware of your surroundings and notice changes in the natural world. Look for cracks or bulges in hillsides, tilting of decks or patios, or leaning poles or fences when rainfall is heavy. Sticking windows and doors can indicate ground movement as soil pushes slowly against a house and knocks windows and doors out of alignment. Look for landslide scars because landslides are most likely to happen where they have occurred before. Plant vegetation and trees on the hillside around your home to help hold soil in place. Help to keep a slope stable by building retaining walls. Installing good drainage in a hillside may keep the soil from getting saturated. Hillside properties in the San Francisco Bay Area and elsewhere may be prone to damage from landslides. Geologists are studying the warning signs and progress of local landslides to help reduce risks and give people adequate warnings of these looming threats. | text | null |
L_0218 | lithosphere and asthenosphere | T_1370 | The lithosphere is composed of both the crust and the portion of the upper mantle that behaves as a brittle, rigid solid. The lithosphere is the outermost mechanical layer, which behaves as a brittle, rigid solid. The lithosphere is about 100 kilometers thick. How are crust and lithosphere different from each other? The definition of the lithosphere is based on how Earth materials behave, so it includes the crust and the uppermost mantle, which are both brittle. Since it is rigid and brittle, when stresses act on the lithosphere, it breaks. This is what we experience as an earthquake. Although we sometimes refer to Earths plates as being plates of crust, the plates are actually made of lithosphere. Much more about Earths plates follows in the chapter "Plate Tectonics." | text | null |
L_0218 | lithosphere and asthenosphere | T_1371 | The asthenosphere is solid upper mantle material that is so hot that it behaves plastically and can flow. The lithosphere rides on the asthenosphere. | text | null |
L_0220 | locating earthquake epicenters | T_1380 | Here are the steps to finding an earthquake epicenter using three seismograms: 1. Determine the epicenter distance from three different seismographs. The longer the time between the arrival of the P-wave and S-wave, the farther away is the epicenter. So the difference in the P- and S-wave arrival times determines the distance between the epicenter and a seismometer. 2. Draw a circle with a radius equal to the distance from the epicenter for that seismograph. The epicenter is somewhere along that circle. Do this for three locations. Using data from two seismographs, the two circles will intercept at two points. A third circle will intercept the other two circles at a single point. This point is the earthquake epicenter (Figure 1.1). Of course, its been a long time since scientists drew circles to locate an earthquake epicenter. This is all done digitally now. but its a great way to learn the basics of how locating an epicenter works. Three circles drawn from three seismic stations each equal to the radius from the station to the epicenter of the quake will intercept at the actual epicenter. Click image to the left or use the URL below. URL: | text | null |
L_0223 | magma composition at volcanoes | T_1392 | There are as many types of volcanic eruptions as there are eruptions. Actually more since an eruption can change character as it progresses. Each volcanic eruption is unique, differing in size, style, and composition of erupted material. One key to what makes the eruption unique is the chemical composition of the magma that feeds a volcano, which determines (1) the eruption style, (2) the type of volcanic cone that forms, and (3) the composition of rocks that are found at the volcano. Different minerals within a rock melt at different temperatures. The amount of partial melting and the composition of the original rock determine the composition of the magma. The words that describe composition of igneous rocks also describe magma composition. Mafic magmas are low in silica and contain more dark, magnesium- and iron-rich mafic minerals, such as olivine and pyroxene. Felsic magmas are higher in silica and contain lighter colored minerals such as quartz and orthoclase feldspar. The higher the amount of silica in the magma, the higher is its viscosity. Viscosity is a liquids resistance to flow. Viscosity determines what the magma will do. Mafic magma is not viscous and will flow easily to the surface. Felsic magma is viscous and does not flow easily. Most felsic magma will stay deeper in the crust and will cool to form igneous intrusive rocks such as granite and granodiorite. If felsic magma rises into a magma chamber, it may be too viscous to move, so it gets stuck. Dissolved gases become trapped by thick magma. The magma churns in the chamber and the pressure builds. Magma collects in magma chambers in the crust at 160 kilometers (100 miles) beneath the surface. Click image to the left or use the URL below. URL: | text | null |
L_0228 | materials humans use | T_1407 | People depend on natural resources for just about everything that keeps us fed and sheltered, as well as for the things that keep us entertained. Every person in the United States uses about 20,000 kilograms (40,000 pounds) of minerals every year for a wide range of products, such as cell phones, TVs, jewelry, and cars. Table 1.1 shows some common objects, the materials they are made from, and whether they are renewable or non-renewable. Common Object Natural Resources Used Cars 15 different metals, such as iron, lead, and chromium to make the body. Precious metals like gold, silver, and platinum. Gems like diamonds, rubies, emer- alds, turquoise. Jewelry Are These Resources Renewable or Non-Renewable? Non-renewable Non-renewable Common Object Natural Resources Used Electronic Appliances (TVs, com- puters, DVD players, cell phones, etc.) Clothing Many different metals, like copper, mercury, gold. Food Bottled Water Gasoline Household Electricity Paper Houses Soil to grow fibers such as cotton. Sunlight for the plants to grow. Animals for fur and leather. Soil to grow plants. Wildlife and agricultural animals. Water from streams or springs. Petroleum products to make plastic bottles. Petroleum drilled from wells. Coal, natural gas, solar power, wind power, hydroelectric power. Trees; Sunlight Soil. Trees for timber. Rocks and minerals for construc- tion materials, for example, granite, gravel, sand. Are These Resources Renewable or Non-Renewable? Non-renewable Renewable Renewable Non-renewable and Renewable Non-renewable Non-renewable and Renewable Renewable Non-renewable and Renewable 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_0234 | mesozoic plate tectonics | T_1424 | As heat builds up beneath a supercontinent, continental rifting begins. Basaltic lavas fill in the rift and eventually lead to seafloor spreading and the formation of a new ocean basin. This basalt province is where Africa is splitting apart and generating basalt lava. | text | null |
L_0234 | mesozoic plate tectonics | T_1425 | At the end of the Paleozoic there was one continent and one ocean. When Pangaea began to break apart about 180 million years ago, the Panthalassa Ocean separated into the individual but interconnected oceans that we see today on Earth. The Atlantic Ocean basin formed as Pangaea split apart. The seafloor spreading that pushed Africa and South America apart is continuing to enlarge the Atlantic Ocean (Figure 1.1). As the continents moved apart there was an intense period of plate tectonic activity. Seafloor spreading was so vig- orous that the mid-ocean ridge buoyed upwards and displaced so much water that there was a marine transgression. Later in the Mesozoic those seas regressed and then transgressed again. | text | null |
L_0234 | mesozoic plate tectonics | T_1426 | The moving continents collided with island arcs and microcontinents so that mountain ranges accreted onto the continents edges. The subduction of the oceanic Farallon plate beneath western North America during the late In the Afar Region of Ethiopia, Africa is splitting apart. Three plates are pulling away from a central point. Jurassic and early Cretaceous produced igneous intrusions and other structures. The intrusions have since been uplifted so that they are exposed in the Sierra Nevada Mountains (Figure 1.2). The snow-covered Sierra Nevada is seen striking SE to NW across the eastern third of the image. The mountain range is a line of uplifted batholiths from Mesozoic subduction. Click image to the left or use the URL below. URL: | text | null |
L_0234 | mesozoic plate tectonics | T_1426 | The moving continents collided with island arcs and microcontinents so that mountain ranges accreted onto the continents edges. The subduction of the oceanic Farallon plate beneath western North America during the late In the Afar Region of Ethiopia, Africa is splitting apart. Three plates are pulling away from a central point. Jurassic and early Cretaceous produced igneous intrusions and other structures. The intrusions have since been uplifted so that they are exposed in the Sierra Nevada Mountains (Figure 1.2). The snow-covered Sierra Nevada is seen striking SE to NW across the eastern third of the image. The mountain range is a line of uplifted batholiths from Mesozoic subduction. Click image to the left or use the URL below. URL: | text | null |
L_0235 | metabolism and replication | T_1427 | Organic molecules must also carry out the chemical work of cells; that is, their metabolism. Chemical reactions in a living organism allow that organism to live in its environment, grow, and reproduce. Metabolism gets energy from other sources and creates structures needed in cells. The chemical reactions occur in a sequence of steps known as metabolic pathways. The metabolic pathways are very similar between unicellular bacteria that have been around for billions of years and the most complex life forms on Earth today. This means that they evolved very early in Earths history. | text | null |
L_0235 | metabolism and replication | T_1428 | Living cells need organic molecules, known as nucleic acids, to store genetic information and pass it to the next generation. Deoxyribonucleic acid (DNA) is the nucleic acid that carries information for nearly all living cells today and did for most of Earths history. Ribonucleic acid (RNA) delivers genetic instructions to the location in a cell where protein is synthesized. | text | null |
L_0235 | metabolism and replication | T_1429 | Many scientists think that RNA was the first replicator. Since RNA catalyzes protein synthesis, most scientists think that RNA came before proteins. RNA can also encode genetic instructions and carry it to daughter cells, such as DNA. The idea that RNA is the most primitive organic molecule is called the RNA world hypothesis, referring to the possibility that the RNA is more ancient than DNA. RNA can pass along genetic instructions as DNA can, and some RNA can carry out chemical reactions like proteins can. Click image to the left or use the URL below. URL: Pieces of many scenarios can be put together to come up with a plausible suggestion for how life began. Click image to the left or use the URL below. URL: | text | null |
L_0241 | mineral formation | T_1441 | Minerals form in a variety of ways: crystallization from magma precipitation from ions in solution biological activity a change to a more stable state as in metamorphism precipitation from vapor | text | null |
L_0241 | mineral formation | T_1442 | Imagine a rock that becomes so hot it melts. Many minerals start out in liquids that are hot enough to melt rocks. Magma is melted rock inside Earth, a molten mixture of substances that can be hotter than 1,000 C. Magma cools slowly inside Earth, which gives mineral crystals time to grow large enough to be seen clearly (Figure 1.1). Granite is rock that forms from slowly cooled magma, containing the minerals quartz (clear), plagioclase feldspar (shiny white), potassium feldspar (pink), and bi- otite (black). When magma erupts onto Earths surface, it is called lava. Lava cools much more rapidly than magma. Crystals do not have time to form and are very small. The chemical composition between minerals that form rapidly or slowly is often the same, only their size differs. Existing rocks may be heated enough so that the molecules are released from their structure and can move around. The molecules may match up with different molecules to form new minerals as the rock cools. This occurs during metamorphism, which will be discussed in the "Metamorphic Rocks" concept. | text | null |
L_0241 | mineral formation | T_1443 | Water on Earth, such as the water in the oceans, contains chemical elements mixed into a solution. Various processes can cause these elements to combine to form solid mineral deposits. | text | null |
L_0241 | mineral formation | T_1444 | When water evaporates, it leaves behind a solid precipitate of minerals, as shown in Figure 1.2. When the water in glass A evaporates, the dissolved mineral particles are left behind. Water can only hold a certain amount of dissolved minerals and salts. When the amount is too great to stay dissolved in the water, the particles come together to form mineral solids, which sink. Halite easily precipitates out of water, as does calcite. Some lakes, such as Mono Lake in California (Figure 1.3) or The Great Salt Lake in Utah, contain many mineral precipitates. Tufa towers form when calcium-rich spring water at the bottom of Mono Lake bubbles up into the alkaline lake. The tufa towers appear when lake level drops. | text | null |
L_0241 | mineral formation | T_1444 | When water evaporates, it leaves behind a solid precipitate of minerals, as shown in Figure 1.2. When the water in glass A evaporates, the dissolved mineral particles are left behind. Water can only hold a certain amount of dissolved minerals and salts. When the amount is too great to stay dissolved in the water, the particles come together to form mineral solids, which sink. Halite easily precipitates out of water, as does calcite. Some lakes, such as Mono Lake in California (Figure 1.3) or The Great Salt Lake in Utah, contain many mineral precipitates. Tufa towers form when calcium-rich spring water at the bottom of Mono Lake bubbles up into the alkaline lake. The tufa towers appear when lake level drops. | text | null |
L_0241 | mineral formation | T_1445 | Magma heats nearby underground water, which reacts with the rocks around it to pick up dissolved particles. As the water flows through open spaces in the rock and cools, it deposits solid minerals. The mineral deposits that form when a mineral fills cracks in rocks are called veins (Figure 1.4). Quartz veins formed in this rock. When minerals are deposited in open spaces, large crystals form (Figure 1.5). Amethyst formed when large crystals grew in open spaces inside the rock. These special rocks are called geodes. | text | null |
L_0241 | mineral formation | T_1445 | Magma heats nearby underground water, which reacts with the rocks around it to pick up dissolved particles. As the water flows through open spaces in the rock and cools, it deposits solid minerals. The mineral deposits that form when a mineral fills cracks in rocks are called veins (Figure 1.4). Quartz veins formed in this rock. When minerals are deposited in open spaces, large crystals form (Figure 1.5). Amethyst formed when large crystals grew in open spaces inside the rock. These special rocks are called geodes. | text | null |
L_0241 | mineral formation | T_1446 | In the last several years, many incredible discoveries have been made exploring how minerals behave under high pressure, like rocks experience inside the Earth. If a mineral is placed in a special machine and then squeezed, eventually it may convert into a different mineral. Ice is a classic example of a material that undergoes solid-solid "phase transitions" as pressure and/or temperature is changed. A "phase diagram" is a graph which plots the stability of phases of a compound as a function of pressure and temperature. A phase diagram for water (ice) is included in the Figure 1.6. The phase diagram is split up into 3 main areas for the solid crystalline phase (ice), the liquid phase (water), and the gas phase (water vapor). Notice that increasing pressure lowers the freezing point and raises the boiling point of water. What does that do to the stability conditions of the liquid phase? A sample phase diagram for water. Click image to the left or use the URL below. URL: | text | null |
L_0242 | mineral groups | T_1447 | Minerals are divided into groups based on chemical composition. Most minerals fit into one of eight mineral groups. | text | null |
L_0242 | mineral groups | T_1448 | The roughly 1,000 silicate minerals make up over 90% of Earths crust. Silicates are by far the largest mineral group. Feldspar and quartz are the two most common silicate minerals. Both are extremely common rock-forming minerals. The basic building block for all silicate minerals is the silica tetrahedron, which is illustrated in Figure 1.1. To create the wide variety of silicate minerals, this pyramid-shaped structure is often bound to other elements, such as calcium, iron, and magnesium. Silica tetrahedrons combine together in six different ways to create different types of silicates (Figure 1.2). Tetrahe- drons can stand alone, form connected circles called rings, link into single and double chains, form large flat sheets of pyramids, or join in three dimensions. One silicon atom bonds to four oxygen atoms to form a silica tetrahedron. The different ways that silica tetrahedrons can join together cause these two minerals to look very different. | text | null |
L_0242 | mineral groups | T_1448 | The roughly 1,000 silicate minerals make up over 90% of Earths crust. Silicates are by far the largest mineral group. Feldspar and quartz are the two most common silicate minerals. Both are extremely common rock-forming minerals. The basic building block for all silicate minerals is the silica tetrahedron, which is illustrated in Figure 1.1. To create the wide variety of silicate minerals, this pyramid-shaped structure is often bound to other elements, such as calcium, iron, and magnesium. Silica tetrahedrons combine together in six different ways to create different types of silicates (Figure 1.2). Tetrahe- drons can stand alone, form connected circles called rings, link into single and double chains, form large flat sheets of pyramids, or join in three dimensions. One silicon atom bonds to four oxygen atoms to form a silica tetrahedron. The different ways that silica tetrahedrons can join together cause these two minerals to look very different. | text | null |
L_0242 | mineral groups | T_1449 | Native elements contain atoms of only one type of element. Only a small number of minerals are found in this category. Some of the minerals in this group are rare and valuable. Gold (Figure 1.3), silver, sulfur, and diamond are examples of native elements. | text | null |
L_0242 | mineral groups | T_1450 | The basic carbonate structure is one carbon atom bonded to three oxygen atoms. Carbonates consists of some cation (like C, Fe, Cu, Mg, Ba, Sr, Pb) bonded to a carbonate molecule. Calcite (CaCO3 ) is the most common carbonate mineral (Figure 1.4). Calcite. | text | null |
L_0242 | mineral groups | T_1451 | Halide minerals are salts that form when salt water evaporates. Halite is a halide mineral, but table salt (see Figure bond with various metallic atoms to make halide minerals. All halides are ionic minerals, which means that they are typically soluble in water. Two carbonate minerals: (a) deep blue azurite and (b) opaque green malachite. Azurite and malachite are carbonates that contain copper instead of calcium. Beautiful halite crystal. | text | null |
L_0242 | mineral groups | T_1451 | Halide minerals are salts that form when salt water evaporates. Halite is a halide mineral, but table salt (see Figure bond with various metallic atoms to make halide minerals. All halides are ionic minerals, which means that they are typically soluble in water. Two carbonate minerals: (a) deep blue azurite and (b) opaque green malachite. Azurite and malachite are carbonates that contain copper instead of calcium. Beautiful halite crystal. | text | null |
L_0242 | mineral groups | T_1452 | Oxides contain one or two metal elements combined with oxygen. Many important metal ores are oxides. Hematite (Fe2 O3 ), with two iron atoms to three oxygen atoms, and magnetite (Fe3 O4 ) (Figure 1.7), with three iron atoms to four oxygen atoms, are both iron oxides. Magnetite is one of the most distinctive oxides since it is magnetic. | text | null |
L_0242 | mineral groups | T_1453 | Phosphate minerals are similar in atomic structure to the silicate minerals. In the phosphates, phosphorus bonds to oxygen to form a tetrahedron. As a mineral group they arent particularly common or important rock-forming minerals, but they are important for you and I. Apatite (Figure 1.8) is a phosphate (Ca5 (PO4 )3 (F,OH)) and is one of the major components of human bone! | text | null |
L_0242 | mineral groups | T_1454 | Sulfate minerals contain sulfur atoms bonded to four oxygen atoms, just like silicates and phosphates. Like halides, they form where salt water evaporates. The most common sulfate mineral is probably gypsum (CaSO4 (OH)2 ) (Figure 1.9). Some gigantic 11-meter gypsum crystals have been found (See opening image). That is about as long as a school bus! Gypsum. | text | null |
L_0242 | mineral groups | T_1455 | Sulfides are formed when metallic elements combine with sulfur in the absence of oxygen. Pyrite (Figure 1.10) (FeS2 ) is a common sulfide mineral colloquially known as "fools gold" because it has a golden metallic looking mineral. There are three easy ways to discriminate real gold from fools gold: real gold is extremely dense, real gold does not grow into perfect cubes, as pyrite commonly does, and pyrite smells like rotten eggs (because of the sulfur). Click image to the left or use the URL below. URL: | text | null |
L_0243 | mineral identification | T_1456 | There are a multitude of laboratory and field techniques for identifying minerals. While a mineralogist might use a high-powered microscope to identify some minerals, or even techniques like x-ray diffraction, most are recognizable using physical properties. The most common field techniques put the observer in the shoes of a detective, whose goal it is to determine, by process of elimination, what the mineral in question is. The process of elimination usually includes observing things like color, hardness, smell, solubility in acid, streak, striations and/or cleavage. Check out the mineral in the opening image. What is the minerals color? What is its shape? Are the individual crystals shiny or dull? Are there lines (striations) running across the minerals? In this concept, the properties used to identify minerals are described in more detail. | text | null |
L_0243 | mineral identification | T_1458 | Color may be the first feature you notice about a mineral, but color is not often important for mineral identification. For example, quartz can be colorless, purple (amethyst), or a variety of other colors depending on chemical impurities Figure 1.1. | text | null |
L_0243 | mineral identification | T_1459 | Streak is the color of a minerals powder, which often is not the same color as the mineral itself. Many minerals, such as the quartz in the Figure 1.1, do not have streak. Hematite is an example of a mineral that displays a certain color in hand sample (typically black to steel gray, sometimes reddish), and a different streak color (red/brown). | text | null |
L_0243 | mineral identification | T_1460 | Luster describes the reflection of light off a minerals surface. Mineralogists have special terms to describe luster. One simple way to classify luster is based on whether the mineral is metallic or non-metallic. Minerals that are opaque and shiny, such as pyrite, have a metallic luster. Minerals such as quartz have a non-metallic luster. Different types of non-metallic luster are described in Table 1.1. Luster Adamantine Earthy Pearly Resinous Silky Vitreous Appearance Sparkly Dull, clay-like Pearl-like Like resins, such as tree sap Soft-looking with long fibers Glassy The streak of hematite across an unglazed porcelain plate is red-brown. | text | null |
L_0243 | mineral identification | T_1461 | Density describes how much matter is in a certain amount of space: density = mass/volume. Mass is a measure of the amount of matter in an object. The amount of space an object takes up is described by its volume. The density of an object depends on its mass and its volume. For example, the water in a drinking glass has the same density as the water in the same volume of a swimming pool. Gold has a density of about 19 g/cm3 ; pyrite has a density of about 5 g/cm3 - thats another way to tell pyrite from gold. Quartz is even less dense than pyrite and has a density of 2.7 g/cm3 . The specific gravity of a substance compares its density to that of water. Substances that are more dense have higher specific gravity. | text | null |
L_0243 | mineral identification | T_1462 | Hardness is a measure of whether a mineral will scratch or be scratched. Mohs Hardness Scale, shown in Table Hardness 1 2 3 4 5 6 7 8 Mineral Talc Gypsum Calcite Fluorite Apatite Feldspar Quartz Topaz Hardness 9 10 Mineral Corundum Diamond With a Mohs scale, anyone can test an unknown mineral for its hardness. Imagine you have an unknown mineral. You find that it can scratch fluorite or even apatite, but feldspar scratches it. You know then that the minerals hardness is between 5 and 6. Note that no other mineral can scratch diamond. | text | null |
L_0243 | mineral identification | T_1463 | Breaking a mineral breaks its chemical bonds. Since some bonds are weaker than other bonds, each type of mineral is likely to break where the bonds between the atoms are weaker. For that reason, minerals break apart in characteristic ways. Cleavage is the tendency of a mineral to break along certain planes to make smooth surfaces. Halite (Figure 1.3) breaks between layers of sodium and chlorine to form cubes with smooth surfaces. Mica has cleavage in one direction and forms sheets (Figure 1.4). Minerals can cleave into polygons. Magnetite forms octahedrons (Figure 1.5). One reason gemstones are beautiful is that the cleavage planes make an attractive crystal shape with smooth faces. Fracture is a break in a mineral that is not along a cleavage plane. Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral. Minerals may have characteristic fractures (Figure 1.6). Metals usually fracture into jagged edges. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, form smooth curved surfaces when they fracture. Sheets of mica. | text | null |
L_0243 | mineral identification | T_1463 | Breaking a mineral breaks its chemical bonds. Since some bonds are weaker than other bonds, each type of mineral is likely to break where the bonds between the atoms are weaker. For that reason, minerals break apart in characteristic ways. Cleavage is the tendency of a mineral to break along certain planes to make smooth surfaces. Halite (Figure 1.3) breaks between layers of sodium and chlorine to form cubes with smooth surfaces. Mica has cleavage in one direction and forms sheets (Figure 1.4). Minerals can cleave into polygons. Magnetite forms octahedrons (Figure 1.5). One reason gemstones are beautiful is that the cleavage planes make an attractive crystal shape with smooth faces. Fracture is a break in a mineral that is not along a cleavage plane. Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral. Minerals may have characteristic fractures (Figure 1.6). Metals usually fracture into jagged edges. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, form smooth curved surfaces when they fracture. Sheets of mica. | text | null |
L_0243 | mineral identification | T_1463 | Breaking a mineral breaks its chemical bonds. Since some bonds are weaker than other bonds, each type of mineral is likely to break where the bonds between the atoms are weaker. For that reason, minerals break apart in characteristic ways. Cleavage is the tendency of a mineral to break along certain planes to make smooth surfaces. Halite (Figure 1.3) breaks between layers of sodium and chlorine to form cubes with smooth surfaces. Mica has cleavage in one direction and forms sheets (Figure 1.4). Minerals can cleave into polygons. Magnetite forms octahedrons (Figure 1.5). One reason gemstones are beautiful is that the cleavage planes make an attractive crystal shape with smooth faces. Fracture is a break in a mineral that is not along a cleavage plane. Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral. Minerals may have characteristic fractures (Figure 1.6). Metals usually fracture into jagged edges. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, form smooth curved surfaces when they fracture. Sheets of mica. | text | null |
L_0243 | mineral identification | T_1464 | Some minerals have other unique properties, some of which are listed in Table 1.3. Can you name a unique property that would allow you to instantly identify a mineral thats been described quite a bit in this concept? (Hint: It is most likely found on your dinner table.) Chrysotile has splintery fracture. Property Fluorescence Magnetism Radioactivity Reactivity Smell Taste Description Mineral glows under ultraviolet light Mineral is attracted to a magnet Mineral gives off radiation that can be measured with Geiger counter Bubbles form when mineral is ex- posed to a weak acid Some minerals have a distinctive smell Some minerals taste salty Example of Mineral Fluorite Magnetite Uraninite Calcite Sulfur (smells like rotten eggs) Halite | text | null |
L_0244 | minerals | T_1465 | Minerals are everywhere! Scientists have identified more than 4,000 minerals in Earths crust, although the bulk of the planet is composed of just a few. A mineral possesses the following qualities: It must be solid. It must be crystalline, meaning it has a repeating arrangement of atoms. It must be naturally occurring. It must be inorganic. It must have a specific chemical composition. Minerals can be identified by their physical properties, such as hardness, color, luster (shininess), and odor. The most common laboratory technique used to identify a mineral is X-ray diffraction (XRD), a technique that involves shining an X-ray light on a sample, and observing how the light exiting the sample is bent. XRD is not useful in the field, however. The definition of a mineral is more restricted than you might think at first. For example, glass is made of sand, which is rich in the mineral quartz. But glass is not a mineral, because it is not crystalline. Instead, glass has a random assemblage of molecules. What about steel? Steel is made by mixing different metal minerals like iron, cobalt, chromium, vanadium, and molybdenum, but steel is not a mineral because it is made by humans and therefore is not naturally occurring. However, almost any rock you pick up is composed of minerals. Below we explore the qualities of minerals in more detail. | text | null |
L_0244 | minerals | T_1466 | Minerals are "crystalline" solids. A crystal is a solid in which the atoms are arranged in a regular, repeating pattern. Notice that in Figure 1.1 the green and purple spheres, representing sodium and chlorine, form a repeating pattern. In this case, they alternate in all directions. Sodium ions (purple balls) bond with chlo- ride ions (green balls) to make table salt (halite). All of the grains of salt that are in a salt shaker have this crystalline structure. | text | null |
L_0244 | minerals | T_1467 | Organic substances are the carbon-based compounds made by living creatures and include proteins, carbohydrates, and oils. Inorganic substances have a structure that is not characteristic of living bodies. Coal is made of plant and animal remains. Is it a mineral? Coal is a classified as a sedimentary rock, but is not a mineral. | text | null |
L_0244 | minerals | T_1468 | Minerals are made by natural processes, those that occur in or on Earth. A diamond created deep in Earths crust is a mineral, but a diamond made in a laboratory by humans is not. Be careful about buying a laboratory-made diamond for jewelry. It may look pretty, but its not a diamond and is not technically a mineral. | text | null |
L_0244 | minerals | T_1469 | Nearly all (98.5%) of Earths crust is made up of only eight elements - oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium - and these are the elements that make up most minerals. All minerals have a specific chemical composition. The mineral silver is made up of only silver atoms and diamond is made only of carbon atoms, but most minerals are made up of chemical compounds. Each mineral has its own chemical formula. Table salt (also known as halite), pictured in Figure 1.1, is NaCl (sodium chloride). Quartz is always made of two oxygen atoms (red) bonded to a silicon atom (grey), represented by the chemical formula SiO2 (Figure 1.2). Quartz is made of two oxygen atoms (red) bonded to a silicon atom (grey). In nature, things are rarely as simple as in the lab, and so it should not come as a surprise that some minerals have a range of chemical compositions. One important example in Earth science is olivine, which always has silicon and oxygen as well as some iron and magnesium, (Mg, Fe)2 SiO4 . | text | null |
L_0244 | minerals | T_1470 | Some minerals can be identified with little more than the naked eye. We do this by examining the physical properties of the mineral in question, which include: Color: the color of the mineral. Streak: the color of the minerals powder (this is often different from the color of the whole mineral). Luster: shininess. Density: mass per volume, typically reported in "specific gravity," which is the density relative to water. Cleavage: the minerals tendency to break along planes of weakness. Fracture: the pattern in which a mineral breaks. Hardness: which minerals it can scratch and which minerals can scratch it. How physical properties are used to identify minerals is described in the concept "Mineral Identification." 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_0247 | mountain building | T_1476 | Converging plates create the worlds largest mountain ranges. Each combination of plate types continent- continent, continent-ocean, and ocean-ocean creates mountains. | text | null |
L_0247 | mountain building | T_1477 | Two converging continental plates smash upwards to create gigantic mountain ranges (Figure 1.1). Stresses from this uplift cause folds, reverse faults, and thrust faults, which allow the crust to rise upwards. As was stated previously there is currently no mountain range of this type in the western U.S., but we can find one where India is pushing into Eurasia. (a) The worlds highest mountain range, the Himalayas, is growing from the colli- sion between the Indian and the Eurasian plates. (b) The crumpling of the Indian and Eurasian plates of continental crust creates the Himalayas. | text | null |
L_0247 | mountain building | T_1478 | Subduction of oceanic lithosphere at convergent plate boundaries also builds mountain ranges. This happens on continental crust, as in the Andes Mountains (Figure 1.2), or on oceanic crust, as with the Aleutian Islands, which we visited earlier. The Cascades Mountains of the western U.S. are also created this way. The Andes Mountains are a chain of con- tinental arc volcanoes that build up as the Nazca Plate subducts beneath the South American Plate. | text | null |
L_0247 | mountain building | T_1479 | Amazingly, even divergence can create mountain ranges. When tensional stresses pull crust apart, it breaks into blocks that slide up and drop down along normal faults. The result is alternating mountains and valleys, known as a basin-and-range (Figure 1.3). In basin-and-range, some blocks are uplifted to form ranges, known as horsts, and some are down-dropped to form basins, known as grabens. (a) Horsts and grabens. (b) Mountains in Nevada are of classic basin-and-range form. 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_0267 | plate tectonics through earth history | T_1550 | First, lets review plate tectonics theory. Plate tectonics theory explains why: Earths geography has changed over time and continues to change today. some places are prone to earthquakes while others are not. certain regions may have deadly, mild, or no volcanic eruptions. mountain ranges are located where they are. many ore deposits are located where they are. living and fossil species are found where they are. Plate tectonic motions affect Earths rock cycle, climate, and the evolution of life. | text | null |
L_0267 | plate tectonics through earth history | T_1551 | Remember that Wegener used the similarity of the mountains on the west and east sides of the Atlantic as evidence for his continental drift hypothesis. Those mountains rose at the convergent plate boundaries where the continents were smashing together to create Pangaea. As Pangaea came together about 300 million years ago, the continents were separated by an ocean where the Atlantic is now. The proto-Atlantic ocean shrank as the Pacific Ocean grew. The Appalachian mountains of eastern North America formed at a convergent plate boundary as Pangaea came together (Figure 1.1). About 200 million years ago, the they were probably as high as the Himalayas, but they have been weathered and eroded significantly since the breakup of Pangaea. Pangaea has been breaking apart since about 250 million years ago. Divergent plate boundaries formed within the continents to cause them to rift apart. The continents are still moving apart, since the Pacific is shrinking as the Atlantic is growing. If the continents continue in their current directions, they will come together to create a supercontinent on the other side of the planet in around 200 million years. If you go back before Pangaea there were earlier supercontinents, such as Rodinia, which existed 750 million to 1.1 billion years ago, and Columbia, at 1.5 to 1.8 billion years ago. This supercontinent cycle is responsible for most of the geologic features that we see and many more that are long gone (Figure 1.2). Scientists think that the creation and breakup of a supercontinent takes place about every 500 million years. The supercontinent before Pangaea was Rodinia. A new continent will form as the Pacific ocean disappears. Click image to the left or use the URL below. URL: | text | null |
L_0267 | plate tectonics through earth history | T_1551 | Remember that Wegener used the similarity of the mountains on the west and east sides of the Atlantic as evidence for his continental drift hypothesis. Those mountains rose at the convergent plate boundaries where the continents were smashing together to create Pangaea. As Pangaea came together about 300 million years ago, the continents were separated by an ocean where the Atlantic is now. The proto-Atlantic ocean shrank as the Pacific Ocean grew. The Appalachian mountains of eastern North America formed at a convergent plate boundary as Pangaea came together (Figure 1.1). About 200 million years ago, the they were probably as high as the Himalayas, but they have been weathered and eroded significantly since the breakup of Pangaea. Pangaea has been breaking apart since about 250 million years ago. Divergent plate boundaries formed within the continents to cause them to rift apart. The continents are still moving apart, since the Pacific is shrinking as the Atlantic is growing. If the continents continue in their current directions, they will come together to create a supercontinent on the other side of the planet in around 200 million years. If you go back before Pangaea there were earlier supercontinents, such as Rodinia, which existed 750 million to 1.1 billion years ago, and Columbia, at 1.5 to 1.8 billion years ago. This supercontinent cycle is responsible for most of the geologic features that we see and many more that are long gone (Figure 1.2). Scientists think that the creation and breakup of a supercontinent takes place about every 500 million years. The supercontinent before Pangaea was Rodinia. A new continent will form as the Pacific ocean disappears. Click image to the left or use the URL below. URL: | text | null |
L_0272 | precipitation | T_1563 | Precipitation (Figure 1.1) is an extremely important part of weather. Water vapor condenses and usually falls to create precipitation. | text | null |
L_0272 | precipitation | T_1564 | Some precipitation forms in place. Dew forms when moist air cools below its dew point on a cold surface. Frost is dew that forms when the air temperature is below freezing. | text | null |
L_0272 | precipitation | T_1565 | The most common precipitation comes from clouds. Rain or snow droplets grow as they ride air currents in a cloud and collect other droplets (Figure 1.2). They fall when they become heavy enough to escape from the rising air currents that hold them up in the cloud. One million cloud droplets will combine to make only one rain drop! If temperatures are cold, the droplet will hit the ground as snow. (a) Dew on a flower. (b) Hoar frost. (a) Rain falls from clouds when the temperature is fairly warm. (b) Snow storm in Helsinki, Finland. Other less common types of precipitation are sleet (Figure 1.3). Sleet is rain that becomes ice as it hits a layer of freezing air near the ground. If a frigid raindrop freezes on the frigid ground, it forms glaze. Hail forms in cumulonimbus clouds with strong updrafts. An ice particle travels until it finally becomes too heavy and it drops. (a) Sleet. (b) Glaze. (c) Hail. This large hail stone is about 6 cm (2.5 inches) in diameter. Click image to the left or use the URL below. URL: | text | null |
L_0272 | precipitation | T_1565 | The most common precipitation comes from clouds. Rain or snow droplets grow as they ride air currents in a cloud and collect other droplets (Figure 1.2). They fall when they become heavy enough to escape from the rising air currents that hold them up in the cloud. One million cloud droplets will combine to make only one rain drop! If temperatures are cold, the droplet will hit the ground as snow. (a) Dew on a flower. (b) Hoar frost. (a) Rain falls from clouds when the temperature is fairly warm. (b) Snow storm in Helsinki, Finland. Other less common types of precipitation are sleet (Figure 1.3). Sleet is rain that becomes ice as it hits a layer of freezing air near the ground. If a frigid raindrop freezes on the frigid ground, it forms glaze. Hail forms in cumulonimbus clouds with strong updrafts. An ice particle travels until it finally becomes too heavy and it drops. (a) Sleet. (b) Glaze. (c) Hail. This large hail stone is about 6 cm (2.5 inches) in diameter. Click image to the left or use the URL below. URL: | text | null |
L_0272 | precipitation | T_1565 | The most common precipitation comes from clouds. Rain or snow droplets grow as they ride air currents in a cloud and collect other droplets (Figure 1.2). They fall when they become heavy enough to escape from the rising air currents that hold them up in the cloud. One million cloud droplets will combine to make only one rain drop! If temperatures are cold, the droplet will hit the ground as snow. (a) Dew on a flower. (b) Hoar frost. (a) Rain falls from clouds when the temperature is fairly warm. (b) Snow storm in Helsinki, Finland. Other less common types of precipitation are sleet (Figure 1.3). Sleet is rain that becomes ice as it hits a layer of freezing air near the ground. If a frigid raindrop freezes on the frigid ground, it forms glaze. Hail forms in cumulonimbus clouds with strong updrafts. An ice particle travels until it finally becomes too heavy and it drops. (a) Sleet. (b) Glaze. (c) Hail. This large hail stone is about 6 cm (2.5 inches) in diameter. Click image to the left or use the URL below. URL: | text | null |
L_0273 | predicting earthquakes | T_1566 | Scientists are a long way from being able to predict earthquakes. A good prediction must be detailed and accurate. Where will the earthquake occur? When will it occur? What will be the magnitude of the quake? With a good prediction authorities could get people to evacuate. An unnecessary evacuation is expensive and causes people not to believe authorities the next time an evacuation is ordered. | text | null |
L_0273 | predicting earthquakes | T_1567 | Where an earthquake will occur is the easiest feature to predict. How would you predict this? Scientists know that earthquakes take place at plate boundaries and tend to happen where theyve occurred before (Figure 1.1). Fault segments behave consistently. A segment with frequent small earthquakes or one with infrequent huge earthquakes will likely do the same thing in the future. The probabilities of earthquakes striking along various faults in the San Francisco area between 2003 (when the work was done) and 2032. | text | null |
L_0273 | predicting earthquakes | T_1568 | When an earthquake will occur is much more difficult to predict. Since stress on a fault builds up at the same rate over time, earthquakes should occur at regular intervals (Figure 1.2). But so far scientists cannot predict when quakes will occur even to within a few years. Click image to the left or use the URL below. URL: Around Parkfield, California, an earth- quake of magnitude 6.0 or higher occurs about every 22 years. So seismologists predicted that one would strike in 1993, but that quake came in 2004 - 11 years late. Click image to the left or use the URL below. URL: | text | null |
L_0273 | predicting earthquakes | T_1569 | Signs sometimes come before a large earthquake. Small quakes, called foreshocks, sometimes occur a few seconds to a few weeks before a major quake. However, many earthquakes do not have foreshocks, and small earthquakes are not necessarily followed by a large earthquake. Ground tilting, caused by the buildup of stress in the rocks, may precede a large earthquake, but not always. Water levels in wells fluctuate as water moves into or out of fractures before an earthquake. This is also an uncertain predictor of large earthquakes. The relative arrival times of P-waves and S-waves also decreases just before an earthquake occurs. Folklore tells of animals behaving erratically just before an earthquake. Mostly, these anecdotes are told after the earthquake. If indeed animals sense danger from earthquakes or tsunami, scientists do not know what it is they could be sensing, but they would like to find out. Earthquake prediction is very difficult and not very successful, but scientists are looking for a variety of clues in a variety of locations and to try to advance the field. | text | null |
L_0274 | predicting volcanic eruptions | T_1570 | Many pieces of evidence can mean that a volcano is about to erupt, but the time and magnitude of the eruption are difficult to pin down. This evidence includes the history of previous volcanic activity, earthquakes, slope deformation, and gas emissions. | text | null |
L_0274 | predicting volcanic eruptions | T_1571 | A volcanos history how long since its last eruption and the time span between its previous eruptions is a good first step to predicting eruptions. Active and dormant volcanoes are heavily monitored, especially in populated areas. | text | null |
L_0274 | predicting volcanic eruptions | T_1572 | Moving magma shakes the ground, so the number and size of earthquakes increases before an eruption. A volcano that is about to erupt may produce a sequence of earthquakes. Scientists use seismographs that record the length and strength of each earthquake to try to determine if an eruption is imminent. | text | null |
L_0274 | predicting volcanic eruptions | T_1573 | Magma and gas can push the volcanos slope upward. Most ground deformation is subtle and can only be detected by tiltmeters, which are instruments that measure the angle of the slope of a volcano. But ground swelling may sometimes create huge changes in the shape of a volcano. Mount St. Helens grew a bulge on its north side before its 1980 eruption. Ground swelling may also increase rock falls and landslides. | text | null |
L_0274 | predicting volcanic eruptions | T_1574 | Gases may be able to escape a volcano before magma reaches the surface. Scientists measure gas emissions in vents on or around the volcano. Gases, such as sulfur dioxide (SO2 ), carbon dioxide (CO2 ), hydrochloric acid (HCl), and even water vapor can be measured at the site (Figure 1.1) or, in some cases, from a distance using satellites. The amounts of gases and their ratios are calculated to help predict eruptions. Scientists monitoring gas emissions at Mount St. Helens. | text | null |
L_0274 | predicting volcanic eruptions | T_1575 | Some gases can be monitored using satellite technology (Figure 1.2). Satellites also monitor temperature readings and deformation. As technology improves, scientists are better able to detect changes in a volcano accurately and safely. | text | null |
L_0274 | predicting volcanic eruptions | T_1576 | Since volcanologists are usually uncertain about an eruption, officials may not know whether to require an evac- uation. If people are evacuated and the eruption doesnt happen, the people will be displeased and less likely to evacuate the next time there is a threat of an eruption. The costs of disrupting business are great. However, scientists continue to work to improve the accuracy of their predictions. 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_0295 | scales that represent earthquake magnitude | T_1648 | People have always tried to quantify the size of and damage done by earthquakes. Since early in the 20th century, there have been three methods. What are the strengths and weaknesses of each? | text | null |
L_0295 | scales that represent earthquake magnitude | T_1649 | Earthquakes are described in terms of what nearby residents felt and the damage that was done to nearby structures. What factors would go into determining the damage that was done and what the residents felt in a region? | text | null |
L_0295 | scales that represent earthquake magnitude | T_1650 | Developed in 1935 by Charles Richter, this scale uses a seismometer to measure the magnitude of the largest jolt of energy released by an earthquake. | text | null |
L_0295 | scales that represent earthquake magnitude | T_1651 | This scale measures the total energy released by an earthquake. Moment magnitude is calculated from the area of the fault that is ruptured and the distance the ground moved along the fault. | text | null |
L_0295 | scales that represent earthquake magnitude | T_1652 | The Richter scale and the moment magnitude scale are logarithmic scales. The amplitude of the largest wave increases ten times from one integer to the next. An increase in one integer means that thirty times more energy was released. These two scales often give very similar measurements. How does the amplitude of the largest seismic wave of a magnitude 5 earthquake compare with the largest wave of a magnitude 4 earthquake? How does it compare with a magnitude 3 quake? The amplitude of the largest seismic wave of a magnitude 5 quake is 10 times that of a magnitude 4 quake and 100 times that of a magnitude 3 quake. How does an increase in two integers on the moment magnitude scale compare in terms of the amount of energy released? Two integers equals a 900-fold increase in released energy. | text | null |
L_0295 | scales that represent earthquake magnitude | T_1653 | Which scale do you think is best? With the Richter scale, a single sharp jolt measures higher than a very long intense earthquake that releases more energy. The moment magnitude scale more accurately reflects the energy released and the damage caused. Most seismologists now use the moment magnitude scale. The way scientists measure earthquake intensity and the two most common scales, Richter and moment magnitude, are described in the video below. Click image to the left or use the URL below. URL: | text | null |
L_0307 | soil characteristics | T_1688 | Soil is a complex mixture of different materials. About half of most soils are inorganic materials, such as the products of weathered rock, including pebbles, sand, silt, and clay particles. About half of all soils are organic materials, formed from the partial breakdown and decomposition of plants and animals. The organic materials are necessary for a soil to be fertile. The organic portion provides the nutrients, such as nitrogen, needed for strong plant growth. In between the solid pieces, there are tiny spaces filled with air and water. Within the soil layer, important reactions between solid rock, liquid water, air, and living things take place. In some soils, the organic portion could be missing, as in desert sand. Or a soil could be completely organic, such as the materials that make up peat in a bog or swamp (Figure 1.1). | text | null |
L_0307 | soil characteristics | T_1689 | The inorganic portion of soil is made of many different size particles, and these different size particles are present in different proportions. The combination of these two factors determines some of the properties of the soil. A permeable soil allows water to flow through it easily because the spaces between the inorganic particles are large and well connected. Sandy or silty soils are considered "light" soils because they are permeable, water-draining types of soils. Soils that have lots of very small spaces are water-holding soils. For example, when clay is present in a soil, the soil is heavier, holds together more tightly, and holds water. When a soil contains a mixture of grain sizes, the soil is called a loam (Figure 1.2). A loam field. | text | null |
L_0307 | soil characteristics | T_1689 | The inorganic portion of soil is made of many different size particles, and these different size particles are present in different proportions. The combination of these two factors determines some of the properties of the soil. A permeable soil allows water to flow through it easily because the spaces between the inorganic particles are large and well connected. Sandy or silty soils are considered "light" soils because they are permeable, water-draining types of soils. Soils that have lots of very small spaces are water-holding soils. For example, when clay is present in a soil, the soil is heavier, holds together more tightly, and holds water. When a soil contains a mixture of grain sizes, the soil is called a loam (Figure 1.2). A loam field. | text | null |
L_0307 | soil characteristics | T_1690 | When soil scientists want to precisely determine soil type, they measure the percentage of sand, silt, and clay. They plot this information on a triangular diagram, with each size particle at one corner (Figure 1.3). The soil type can then be determined from the location on the diagram. At the top, a soil would be clay; at the left corner, it would be sand; at the right corner, it would be silt. Soils in the lower middle with less than 50% clay are loams. Soil types by particle size. | text | null |
L_0307 | soil characteristics | T_1691 | Soil is an ecosystem unto itself. In the spaces of soil, there are thousands or even millions of living organisms. Those organisms could include earthworms, ants, bacteria, or fungi (Figure 1.4). | text | null |
L_0308 | soil erosion | T_1692 | The agents of soil erosion are the same as the agents of all types of erosion: water, wind, ice, or gravity. Running water is the leading cause of soil erosion, because water is abundant and has a lot of power. Wind is also a leading cause of soil erosion because wind can pick up soil and blow it far away. Activities that remove vegetation, disturb the ground, or allow the ground to dry are activities that increase erosion. What are some human activities that increase the likelihood that soil will be eroded? | text | null |
L_0308 | soil erosion | T_1693 | Agriculture is probably the most significant activity that accelerates soil erosion because of the amount of land that is farmed and how much farming practices disturb the ground (Figure 1.1). Farmers remove native vegetation and then plow the land to plant new seeds. Because most crops grow only in spring and summer, the land lies fallow during the winter. Of course, winter is also the stormy season in many locations, so wind and rain are available to wash soil away. Tractor tires make deep grooves, which are natural pathways for water. Fine soil is blown away by wind. The soil that is most likely to erode is the nutrient-rich topsoil, which degrades the farmland. (a) The bare areas of farmland are especially vulnerable to erosion. (b) Slash-and-burn agriculture leaves land open for soil erosion and is one of the leading causes of soil erosion in the world. | text | null |
L_0308 | soil erosion | T_1694 | Grazing animals (Figure 1.2) wander over large areas of pasture or natural grasslands eating grasses and shrubs. Grazers expose soil by removing the plant cover for an area. They also churn up the ground with their hooves. If too many animals graze the same land area, the animals hooves pull plants out by their roots. A land is overgrazed if too many animals are living there. Grazing animals can cause erosion if they are allowed to overgraze and remove too much or all of the vegetation in a pasture. | text | null |
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