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Chapter 2: Plate Tectonics The goals and objectives of this chapter are to: Understand the internal structure of the earth Compare and contrast the science behind the theory of continental drift and the theory of plate tectonics Explain the various types of tectonic plate boundaries and their geologic effects Structure of the Earth This is a file from the Wikimedia Commons. The most powerful forces on the planet are earthquakes and volcanoes. On December 26, 2004, the second most powerful earthquake in the last 100 years occurred off the coast of Indonesia creating a massive tsunami. Several volcanoes also erupted shortly afterward in the local region. By the end of the day, over 240,000 people had died. It is possible that the earthquake occurred because another one in Iran a year earlier, killing over 20,000 people, weakened the Asian fault. In October 2005, a powerful earthquake in Kashmir, India killed over 80,000 people. And just before 5 p.m. January 12, 2010, a magnitude 7.0 earthquake devastated the Caribbean nation of Haiti, leaving more than 250,000 dead, 300,000 wounded and more than one million people homeless. On March 11, 2011, Japan was rocked by a magnitude 9.0 earthquake followed by a devastating tsunami that killed over 30,000 people. So why do earthquakes and volcanoes occur? Is there a direct relationship between the two? In order to understand earthquakes and volcanoes, you have to understand the grander theory called Plate Tectonics. The earth consists of three layers: an inner and outer core, the mantle, and two types of crust. The earth's core consists of two parts: a liquid outer core and a solid inner core, both made of iron and nickel from the early make-up of the planet where the temperatures can range from 8,600 degrees to 9,600 degrees Fahrenheit. The next and largest layer is called the mantle, which makes up two-thirds of Earth's mass. The mantle is actually called a plastic solid, which means it has the ability to flow very slowly. Heat from the earth's core causes the mantle to convect, like water over a stove but much slower, and it is the mantle's convection that is the driving force of plate tectonics. The surface layer of the earth is called the crust and it makes up only 1 percent of Earth's mass. The crust is subdivided into two components: oceanic and continental crust. Again referring back to the image on the right, note that the oceanic crust is only about 3 miles thick, but is slightly more dense than continental crust. Most of this oceanic rock is called basalt and is a dark, dense rock. Continental crust is much thicker than oceanic crust (averages between 20 to 25 miles thick), but is actually slightly less dense than oceanic crust. The main type of rock on continents is called granite. So if these two types of crust were to collide into each other, what do you think would happen to the oceanic crust? As a whole, notice that the crust is lighter than the mantle. It is sometimes said that the crust "floats" on the mantle like an iceberg in water and that is not too far from the truth and is called isostacy. Finally, the crust is the coldest, most rigid, and brittle layer with lots of folds and fractures. Editor’s note/Poem: I found this poem online that was written by Amanda Paul for a science project. I think that it does a great job of describing plate tectonics and how it affects earthquakes and volcanoes as well as how the plates shift and move. Tectonic Plates Over the earth, the continents glide Attached to things called plates, they slide They crawl throughout this world, wide And mountains form as they collide The world, born much long before Plates will spread the ocean floor Atlantic large, Pacific small Across the earth, they shift us all A bonded crust and lithosphere The centimeters grow per year This layer moves, in plates it breaks And as they slip, they cause earthquakes Across whole world, a perpetual motion Along all the faults in the land and the ocean Across the mantle these plates float Slowly, like a raft or boat When the lithosphere is weak, Erupting molten rock will leak Volcanoes spew the magma, hot Out of the mantle, the lava is shot Over the globe, the continents glide They crawl throughout this world, wide Attached to things called plates, they slide Volcanoes form when they collide They move transforming and diverging Creating mountains and converging Moving at their slowpoke rates That’s what they are: Tectonic plates Continental Drift Image copyright: (USGS) under Public Domain. In the early 1900s, a climatologist named Alfred Wegener proposed a hypothesis that at one time all of the continents were once together, creating a super-continent called Pangea, which later broke apart intoGondwanaland and Laurasia and finally the continents today. Over many years Wegner accumulated a lot of evidence to support his theory called continental drift. First, he noticed on world maps that the continents looked like large pieces of a world puzzle that could be put together to form a massive super-continent. Later he found similar plant and animal fossils on different continents separated by thousands of miles of oceans. He questioned how plants could and land species travel thousands of miles across the ocean to get to other continents; unless at one time all the continents were once together. Wegener also found climate evidence such as glaciation in the Sahara Desert and tropical fossils in Antarctica. Ultimately, Alfred Wegener believed that the crust was not as rigid as others believed, but actually flowed somehow. Yet he could not come up with a reason why the continents would move. Editors note/Youtube video: This is a link to a video about Pangea and plate tectonics. It is a video from Bill Nye where he uses corn syrup and a camp stove to illustrate how the continents are moving. https://youtu.be/lJiAUvB1vEU Plate Tectonics Because Alfred Wegener could not propose a reason why continents would move, most of the scientific community never believed him before he died. It wasn't until the 1960s, during the Cold War, did technology finally catch up with Wegener's hypothesis. The United States military developed sonar as a way to look for Soviet submarines and in the process they discovered the largest mountain range in the world in the middle of the Atlantic Ocean, later called the mid-Atlantic ridge. Editor’s note/Newspaper article: In the December 2010 issue of the University of Bergen newspaper there is information about new species being discovered at the northern end of the Mid Atlantic ridge. There is also information about species migrating to this area of the ridge and then adapting to the area. As more research was done to better understand the ocean floor, scientists discovered that the polar direction of magnetized rocks would reverse or flip symmetrical from the mid-Atlantic ridge, called paleomagnetism. At one point all the rocks are pointing toward magnetic north, followed by pointing toward magnetic south in the distant past, then magnetic north and so forth on equal sides of the mid-Atlantic ridge like a mirror image of each other. This proved that the earth's magnetic field has flipped several times throughout earth's history. Further research found that the youngest oceanic rocks exist near ocean ridges like the mid-Atlantic ridge and get older away from it. All this evidence, including the data collected by Alfred Wegner's for this theory of continental drift, was put together to form the theory of plate tectonics. The theory states that the earth is made of several tectonic plates along with several smaller plates. Each tectonic plate consists of oceanic and continental crust. Scientists now realize that new oceanic rock is forming at these mid-oceanic ridges creating large mountain ranges. When this molten rock along the ridges rises to the Earth’s surface, the iron within them quickly points toward magnetic north (or magnetic south if the polarity has reversed) much like a compass before cooling into rock. Image copyright: United States Geologic Survey licensed as Public Domain. licensed as Public Domain. Image copyright: Creative Commons But if new oceanic rock is forming, and the earth is not growing, oceanic rock must be destroyed somewhere else. We now realize this occurs along the boundaries between lighter continental crust and denser oceanic crust. When the two collide, the heavier oceanic rock subducts underneath the lighter continental crust in a process called subduction. As the oceanic rock subducts downward, it can get locked up building large amounts of energy. Once the energy is too strong, the rock snaps free releasing that energy, called an earthquake. If the crust subducts deep enough, it may begin to melt into molten rock called magma. Magma is less dense than solid rock, so the magma rises to the surface to create volcanoes. So there is a direct relationship between earthquakes and volcanoes. In fact, the Ring of Fire in the Pacific Ocean consists of several subduction zones and is where 90 percent of all earthquakes and volcanoes occur. Tectonic Plate Boundaries There are three major types of tectonic plate boundares: convergent, divergent, and transform. Let's first look at convergent plate boundaries, which can be broken down into three subcategories. Recall that oceanic crust is denser than continental rock like granite. Thus when two tectonic plates collide, the denser oceanic crust will subduct underneath the lighter continental crust. If the subducting rock becomes stuck, vast amounts of energy builds up. But once the pressure and energy is too great, the rock will rupture creating powerful earthquakes. As the subducted material sinks further, it will begin to melt under great heat and pressure, becoming less dense as it melts, and rise up as magma to form dangerous composite volcanoes. Mountain ranges created by oceanic-tocontinental convergence are the Andes mountains in South America, the Cascades in the western United States, and the Ring of Fire in the Pacific Ocean. Below is a Google Earth image showing a series of oceanic-to-oceanic subduction zones within the Pacific Ring of Fire. You can visibly see the subduciton zones that create the volcanic and powerful Aleutian Islands and the converging subduction plates that make of volcanic islands of Japan. With oceanic-to-oceanic convergence, the heavier of the two will subduct down beneath the other. Just like continental-to-oceanic convergence, this plate boundary can generate powerful earthquakes and volcanoes; but instead of volcanoes on land, volcanic islands form such as Japan, the Aleutian Islands of Alaska, and Indonesia. The great earthquake in Indonesia in 2004, which produced the devastating tsunami, was created by this process along with the 2011 earthquake and tsunami in Japan. When two continental plates converge, instead of subduction, the two similar tectonic plates will buckle up to create large mountain ranges like a massive car pile-up. This is called continental-tocontinental convergence, and geologically creates intense folding and faulting rather than volcanic activity. Examples of mountain ranges created by this process are the Himalayan Mountains (taken from the International Space Station) as India is colliding with Asia, the Alps in Europe, and the Appalachian mountains in the United States as the North American plate collided with the African plate when Pangea was forming. The Kashmir India earthquake of 2005 that killed over 80,000 people occurred because of this process. And most recently, the 2008 earthquake in China which killed nearly 85,000 people before the Summer Olympics was because of this tectonic force. Editor’s note/Personal findings: I read an article about the formation of the Himalayan Mountains in Asia and how it was all started 225 million years ago when the Indian plate began moving northward towards the Eurasia plate. They finally collided 50 million years ago and in the time since the mountain range has grown to over 9 km in height. The most interesting part is that they are still growing at a rate of 10km in a million years. That would double their height in a million years but they are being offset because the Eurasia plate is now spreading out rather than moving up. It was really interesting to think that the world’s tallest peak is still growing. When convection within the mantel causes two tectonic plates move away from each other, or when a tectonic plate tears itself apart, divergent boundaries can form. As divergence occurs, shallow earthquakes can occur along with volcanoes along the rift areas. When the process begins, a valley will develop such as the Great Rift Valley in Africa. Over time that valley can fill up with water creating linear lakes. If divergence continues, a sea can form like the Red Sea and finally an ocean like the Atlantic Ocean. Check out the eastern half of Africa and notice the lakes that look linear. Eastern Africa is tearing apart from these linear lakes, to the Great Rift Valley, and up to the Red Sea. Notice how the Red Sea looks like it could be put back together again. The ultimate divergent boundary is the Atlantic Ocean, which began when Pangea broke apart. Below are two satellite images using Google Earth, both focusing on parts of Africa. On the left you can see rift valleys that have filled in with water to form linear lakes. On the right in northern Africa, you can see the Red Sea with a rift valley in the center, which use to be a linear lake that grew into a sea. If the Red Sea continues to grow, it could form an ocean similar to the Atlantic Ocean with the mid-Atlantic Ridge. Transform boundaries occurs when two tectonic plates slide (or grind) past parallel to each other. The most famous transform boundary is the San Andreas Fault where the Pacific plate (that Los Angeles and Hawaii are on) is grinding past the North American plate (that San Francisco and the rest of the United States is on) at the rate of 3 inches a year. Recently, geologists have stated that San Francisco should expect another disastrous earthquake in the next 30 years. Another important transform boundary is the North Anatolian Fault in Turkey. This powerful fault last ruptured in 1999 in Izmit, Turkey which killed 17,000 people in 48 seconds. Comparison of the San Andreas Fault, CA and the North Anatolian Fault in Turkey. Both are located along transform boundaries. Image States Geologic Survey (USGS). Below is an interesting video from National Geographic called Colliding Continents. It takes a hypothetical situation of humans coming back to Earth in the distant future and uses the idea of Plate Tectonics to understand the past. CREATE A Chapter 3: Earthquakes Earthquakes are serious natural hazards that affect people across the globe, sometimes at long distances from where the quakes occur. They are especially dangerous because seismologists, the scientists who study earthquakes, cannot predict them in time for evacuations or other precautions. Your goals in this module should be to: understand how scientists measure and compare earthquakes. be familiar with processes that take place in an earthquake such as faulting, tectonic creep, and seismic waves. know which global regions are most at risk for earthquakes and shy they are at risk. know and understand the effects of earthquakes, including shaking, ground rupture, and liquefaction, as well as how earthquakes are linked to other natural hazards such as landslides, fires, and tsunamis. know the important natural service functions of earthquakes. know how human beings interact with and affect the earthquake hazard. understand how we can minimize seismic risk, and recognize adjustments we can make to protect ourselves. 3.1 Earthquake Basics Image copyright: United Nations Development Programme, licensed as Creative Commons Public Domain. An earthquake is a sudden motion or trembling in the earth caused by the abrupt release of slowly accumulated energy. All earthquakes occur along a fault, which is a fracture in the earth's crust where tectonic movement occurs. Where the actual break occurred along the fault is called the focus (also called the hypocenter) and the epicenter is the point on the Earth's surface that lies directly above the focus and is where the strongest shockwave is normally felt. Click here to watch a brief video on earthquakes. Recall that all around the planet, tectonic plates are moving because of convection in the mantle. Tectonic plates are also composed of two types of crust, oceanic and continental. The oceanic crust, which is made mostly of basalt is more dense than continental crust that is made of granite. When these tectonic plates come in contact, the denser oceanic crust subducts below the continental crust. Now sometimes when two tectonic plate come in contact they become stuck. As the rocks begin to bend or strain under tectonic forces, large amounts of energy - called strain - builds. When the stress becomes too great for the rocks to hold, segments may suddenly snap, releasing large amounts of energy. This is called the elastic rebound theory. Movement along a fault can occur vertically or horizontally. The greatest horizontal displacement was 21 feet along the San Andreas Fault in the Great San Francisco Quake of 1906. Imagine in an instant being moved 21 feet horizontally! The greatest maximum vertical displacement used to be the Alaskan earthquake in 1964. The vertical displacement was 33 feet! But on December 26, 2004 a 9.1 underwater earthquake occurred in Indonesia. It had a vertical displacement of 60 feet over 800 miles long! Imaging being thrown 60 feet instantly and that it occurred for 800 miles. The compression caused by the oceanic-oceanic convergence actually sped up the earth's rotation 2.676 millionths of a second and shifted the axis 1 inch! It produced a massive tsunami traveling 500 mph. Over 240,000 died from the earthquake and tsunami; one in three were children. The image below if of an earthquake in Pakistan that killed 80,000. 3.2 Types of Earthquakes There are several types of faults that earthquakes occur on, which are dependent on whether the fault is occurring because of convergent, divergent, or transform tectonic plate forcing. Geologists use old mining terms to distinguish between different types of faults. Think of a minor walking down into the earth along a fault line. The ground the miner is walking on is called the footwall. If the minor needs to hand their lantern, the ceiling is called the hanging-wall. 3.3 Measuring Seismic Activity Strike-slip faults (A) occur along transform boundaries where tectonic plates are moving horizontal or parallel to each other. Deformation of rivers, roads, fences, etc. can occur if they cross over these fault lines. Examples of strike-slip faults are the San Andreas Fault in the United States and the North Anatolian Fault in Turkey. Normal faults (B) are common along divergent plate boundaries. As extensional forces occur, the footwall is forced upward, while the hanging wall slides downward. This can create a series of valleys (called a graben) and mountains (called a horst). Examples of mountain ranges and valleys created by normal faulting are theGrand Tetons, the Basin and Range in the western United States, and the Wasatch Front in Utah. Reverse faults (C) are caused by compressional forces as tectonic plates collide together forcing one plate to rise above another. Using the mining terminology, movement along a reverse fault would cause the hangingwall to rise up and the footwall to drop lower. The angle of a reverse fault is about 45 degrees, but if the angle of the fault is steeper than 45 degrees it is called a thrust fault. When two plates collide, intense folding and faulting can occur. Examples of where reverse and thrust faults occur are where convergent boundaries are common such as: the Northern Rocky Mountains, the Alps, Himalayas, and the Appalachian mountains. Image copyright: United States Geologic Survey, licen Commons Public Domain. Seismologists record seismic waves using a seismograph. When a rupture occurs within the earth, energy is released from the focus in all directions and the seismograph will record the magnitude of the energy. There are three types of seismic waves: P-waves, S-waves, and Surface waves. Primary waves, also called P-waves, are compressional waves and are the first to be felt by seismographs and individuals because they travel the fastest (about 3.7 miles per second). To visualize a P-wave, think of stretching a slinky and letting it go. You would be able to actually see the compression occurring within the slinky. The second type of seismic wave is called a secondary wave or S-wave. They reach the seismograph second because they travel slower than P-waves and travel in a side-to-side manner. Imaging pulling a slinky and shaking one end side to side. You would be able to see the side-to-side movement travel up the slinky. P-waves and Swaves together are called body waves because they travel through the earth rather than on the surface. Surface waves are the last seismic waves to reach an area, create the greatest ground motion, and are the most destructive because they are the slowest and move in a rolling manner. Image copyright: United Creative Co 3.4 Locating Seismic Activity Editor’s Note/Map: This is a map I found that shows the earthquake hazard levels for the United States. I added this because the Wasatch front has the same level of earthquake risk as the areas along the San Andreas Fault in California. Image copyright: United States Geologic Survey, licensed as Creative Commons Public Domain. In order to determine the location of an earthquake, seismologists must measure the interval distance of P-waves and S-waves released during the rupture. P-waves travel faster than S-waves, thus scientists calculate the time difference between both waves to determine a perimeter of the epicenter. But the epicenter could be anywhere within that perimeter. Therefore, scientists must use a minimum of three seismic readings from different seismograph stations in order to determine the exact location of the epicenter. 3.5 Classifying Earthquakes Image copyright: Licensed as Creative Commons Public Domain. There are two basic ways to measure the strength and destructive power of an earthquake. The first is called the Richter scale. Based on a range from 1 (weakest) to 10 (strongest), the Richter scale measures the magnitude (energy released) by an earthquake. The scale is logarithmic meaning that every whole number increase in magnitude is 10 times more ground shaking and 30 times more energy released. Example: a magnitude 7.0 earthquake has ground shaking 10 times more than a 6.0 and 30 times more energy released. A magnitude 8.0 earthquake has ground shaking 100 times more than a 6.0 and 900 times more energy released. The December 26, 2004 Indonesian earthquake had a magnitude of 9.1. It should be noted that for the strongest earthquakes, the Richter Scale is no longer used. Instead, the Moment Magnitude Scaleis used, though it is very similar to the Richter Scale. The Richter Scale and Moment Magnitude Scale provide quantitative information of the energy released from an earthquake. The Modified Mercalli Intensity Scale (shown below) is more qualitative and focuses on the actual damage caused by the earthquake and its impact on human lives and property. The scale has 12 categories ranging from I (felt by very few people) to XII (total destruction). Each category is based on a description of how people felt or perceived the earthquake. The major problem with the Modified Mercalli Intensity Scale is that ground damage is relative to location. The scale can be influenced by the types of rocks underneath, if the ground is mostly bedrock, loose sediment, or even landfill, how well buildings are built, and how far away the people and buildings are from the epicenter. The farther away from the epicenter, the weaker the earthquake will feel. So the Modified Mercalli Intensity Scale is great to determine ground damage and how the earthquake affected people, but does not tell you how much energy was actually released from the rupture. Because of the access to the Internet, the United States Geologic Survey (USGS) allows you to email them if you just felt and earthquake. They take this information and create a map similar to the Modified Mercalli maps, but call it a shake map. To view real-time shake maps from the USGS, click here. For a list of recent earthquakes in Utah along with shake maps, check out the Seismology Departmentat the University of Utah. Editor’s Note/Website url: While looking for information about elastic rebound theory I stumbled upon the usgs earthquake website. This website allows you to not only report earthquakes but also to see recent earthquake activity worldwide. One thing that caught my attention was how many earthquakes occur around Japan and Indonesia. Also I saw that there was a 5.0 earthquake near Challis Idaho just 120 miles ene of where I was born and grew up. That was weird to think about that there is earthquake activity so near to where I know. http://earthquake.usgs.gov/ Image copyright: United States Geologic Sur Public Doma One final note, with the recent popularity of smart phones and the iTouch, there are several apps now available in relation to natural disasters. In terms of earthquakes, a highly popular app in Apple's iTunes is called QuakeWatch. There are probably similar apps for other smart phone devises. 3.6 Earthquake Hazards Image copyright: United Nations Development Program, licensed as Creative Commons Public Domain. Earthquakes do not kill people; falling buildings and highways kill people. History has taught us the importance of building codes to create safer buildings. Many of the massive death tolls reported by earthquakes are caused by poorly built buildings rather than the earthquake itself. In general, buildings or structures built out of brick, stone, mud, or reinforced concrete fair poorly in large earthquakes because there is very little flexibility in the structures as the ground shakes. The best types of buildings to be in are those built of wood because of there flexibility; the house may not be habitable after the earthquake, but they won't crumble or collapse on people. Buildings with weak floors or basement garages are also susceptible to collapsing. There are several techniques engineers have developed to help buildings withstand the destructive power of earthquakes. Many buildings are being built or retrofitted with diagonal braces that can withstand the ground motions caused by an earthquake. Tall buildings also tend to sway at different frequencies them to slam into each other during an earthquake. If engineers know how much a building will sway, they can determine how far apart buildings must be built. Finally, engineers are placing rubber pads at the base of newly built and retrofitted buildings that act as shock absorbers. Liquefaction can occur when earthquakes rupture in regions with loose sediment and high water tables. As the ground shakes, the high water table rises to the surface which softens and destabilizes the surface causing structures to break off their foundations or fall over. Liquefaction has occurred in Mexico City in 1985, San Francisco 1989, Anchorage, Alaska 1964, Kobe Japan in 1995 and will occur in Salt Lake City. Editor’s note/Historical Article: In 1912 there was an earthquake centered in New Madrid, MO that was so powerful that there were reports of the Mississippi river flowing backwards for a time. There are findings that the area has a 90 percent chance for a 6 or 7 magnitude quake in the next 50 years. This would affect areas with high water tables and the potential for liquefaction. The city of Memphis, TN is one place where the damage would be extremely significant if this occurs. This is due to the city being situated over an aquafer and right on the Mississippi river. The previous quake was strong enough to be felt in Boston so it would be bad if nearby major population areas were unprepared. The city of Memphis is also a very low income area so it could be a situation similar to Haiti but not as bad only because there would be less people there. Image copyright: This work is in the public domain in that between 1923 and 1977 and without a c Click here to see a map of liquefaction potential and ground shaking within Salt Lake County. (You can also look at maps for Tooele, Cache, Davis, Weber and Utah Counties.) For those who live in the Salt Lake valley, notice how the liquefaction potential is greatest along the Jordan River and near the Great Salt Lake. Any ideas why? It has to do with the fact the water table is highest near those areas. So when an earthquake occurs and the ground begins to shake, the water will rise and destabilize the ground. In these maps, the reds and purples represent the areas of greatest liquefaction potential from a magnitude 7.0 earthquake. Earthquakes can also destabilize steep slopes causing them to slip and fail. These landslides tend to occur where the ground is mostly loose sandy soil with a high water table. Fires are also another serious hazard created by earthquakes as our infrastructure collapses and electrical and gas lines break. The treat of fires will also increase as emergency crews have a hard time maneuvering through the debris. There are two simple things individuals can do to reduce their risk of a fire: first is to have a wrench attached to their outside gas line. If you smell gas at your house, quickly turn off the gas. But if you do not smell gas, do not turn it off; doing so may prevent you from having heating in your house in the winter and it may be months before it gets turned back on. Second, make sure your water heater is attached to your house. A simple $20 bracket wrapped around your water heater and bolted into your house may prevent it from falling over and breaking its gas line. Another interesting effect of powerful earthquakes is island creation. In September 2013, a moderately powerful earthquake off the coast of Pakistan created a 200 foot wide, 60 foot tall island. It won't last long because ocean waves will erode it back down, but it's an interesting and rare effect of earthquakes. Click here to learn more. 3.7 Human-Induced Earthquakes Can humans create earthquakes? Maybe not intentionally, but the answer is yes and here is why. If a water reservoir is built on top of an active fault line, the water may actually lubricate the fault and weaken the stress built up within it. This may either create a series of small earthquakes or potentially create a large earthquake. Also the shear weight of the reservoir's water can weaken the bedrock causing it to fracture. Then the obvious concern is if the dam fails. Earthquakes can also be generated if humans inject other fluids into a fault such as sewage or chemical waste. Finally, nuclear explosions can trigger earthquakes. In fact, one way to determine if a nation has tested a nuclear bomb is by monitoring the earthquakes and energy released by the explosion. Editor’s note/Personal Note: In the last year Oklahoma has been hit by over 580 earthquakes of greater magnitude than 3.0 in 2014 after only having about 100 in 2013. There are multiple reports linking this to the increase of fracking in the state. This is where wastewater and other liquids are injected into the ground to remove the natural gas and oil found in bedrock. This has a social impact because there is the massive employment that the oil industry provides to the area but there is also the issue of what we are doing to the area. There are similar findings in other states that have seen an increase in fracking operations. There needs to be more regulations and care taken when things are done that affects the balance in an area. 3.8 Earthquake Prepardeness Everywhere in the world has disasters, so nowhere is safe. But everyone should be prepared for the type of disasters their region experiences. Everyone should have a 72 hour kit prepared in your car and house. Recently the Federal Emergency Management Agency (FEMA) stated that citizens should prepare a 5-day kit in case federal, state, and local agencies can not reach you. Learn more how you can prepare at Ready.gov. Here are a few more items you should think about with disaster preparedness. Each member in your family should also know where to meet in case of a disaster. The number one reason why people end up in the hospital after an earthquake is glass in their feet. Having a pair of old shoes under your bed can greatly reduce that probability. Know how to shut off your gas line if you smell gas in your house. If it requires a wrench to shut off, always have one next to the line for quick shutoff. You will know if you have a gas leak because the gas companies place a chemical in the gas that will smell like rotten eggs. Also make sure your water heater is attached to your house. If your water heater falls over and the gas line breaks, your house can catch fire. If you and your family are safe, take care of others in need. Finally for those interested, look into getting CERT certified as a first responder. Chapter 4: Volcanoes Where Volcanoes Are Located Google Earth image of Japan and the oceanic-to-oceanic subduction zones. VOLCANOES ALONG CONVERGENT PLATE BOUNDARIES Volcanoes are a vibrant manifestation of plate tectonics processes. Volcanoes are common along convergent and divergent plate boundaries, but are also found within lithospheric plates away from plate boundaries. Wherever mantle is able to melt, volcanoes may be the result. Volcanoes erupt because mantle rock melts. The first stage in creating a volcano is when mantle rock begins to melt because of extremely high temperatures, lithospheric pressure lowers, or water is added. Along subducting plate boundaries, the crust heats up as it sinks into the mantle. Also, ocean water is mixed in with the sediments lying on top of the subducting plate. This water lowers the melting point of the mantle material, which increases melting. Volcanoes at convergent plate boundaries are found all along the Pacific Ocean basin, primarily at the edges of the Pacific, Cocos, and Nazca plates. Large earthquakes are extremely common along convergent plate boundaries. Since the Pacific Ocean is rimmed by convergent and transform boundaries, about 80% of all earthquakes strike around the Pacific Ocean basin and is why the region is called the Ring of Fire. A description of the Pacific Ring of Fire along western North America is below: Subduction at the Middle American Trench creates volcanoes in Central America. The San Andreas Fault is a transform boundary. Subduction of the Juan de Fuca plate beneath the North American plate creates the Cascade volcanoes like Mount St. Helens, Mount Rainer, Mount Hood and more. Subduction of the Pacific plate beneath the North American plate in the north creates the long chain of the Aleutian Islands volcanoes near Alaska. This incredible explosive eruption of Mount Vesuvius in Italy in A.D. 79 is an example of a composite volcano that forms as the result of a convergent plate boundary. Editor’s note/Personal writing: One thing that I think of when I hear of Mount Vesuvius I think of the roman mythology of volcanos. The word for volcano comes from the roman god Vulcan who was the god of fire and also smithing/metalworking. He was associated with both destruction as well as life very much like a volcano is a destructive force but also a means of renewal for areas. Another thing that I find interesting is that he is the god of forging and a byproduct of volcanic eruptions is precious metals and we get most of our stronger elements from molten rock escaping through the crust. VOLCANOES ALONG DIVERGENT PLATE BOUNDARIES Why does melting occur at divergent plate boundaries? Hot mantle rock rises where the plates are moving apart. This releases pressure on the mantle, which lowers its melting temperature allowing lava to erupt through long cracks or fissures. Scientists have captured incredible footage of "Deepest Ocean Eruption Ever Filmed" and other undersea volcanoes erupt at mid-ocean ridges, such as the Mid-Atlantic ridge, where seafloor spreading creates new seafloor in the rift valleys. Where a hotspot is located along the ridge, such as at Iceland, volcanoes grow high enough to create islands. Eruptions are found at divergent plate boundaries as continents break apart such as the East African Rift between the African and Arabian plates and the Great Basin and Range in the western United States. But those volcanoes of the ladder are now extinct. For some dramatic time-lapsed photography of a volcanic eruption on Iceland, click here. Iceland (image on the right) is a hot spot volcano and the surface manifestation of the mid-Atlantic ridge. VOLCANIC HOTSPOTS Although most volcanoes are found at convergent or divergent plate boundaries, intraplate volcanoes are found in the middle of a tectonic plate. The Hawaiian Islands are the exposed peaks of a great chain of volcanoes that lie on the Pacific plate. These islands are in the middle of the Pacific plate. The youngest island sits directly above a column of hot rock called a mantle plume. As the plume rises through the mantle, pressure is released and mantle melts to create a hotspot. Earth is home to about 50 known hot spots. Most of these are in the oceans because they are better able to penetrate oceanic lithosphere to create volcanoes. The hotspots that are known beneath continents are extremely large, such as Yellowstone. The video on the right is of the hot spot beneath Hawaii, the origin of the voluminous lava produced by the shield volcano Kilauea. There are several key indicators to determine a hot spot from island arc volcanoes. At island arcs, the volcanoes are all about the same age. By contrast, at hotspots the volcanoes are youngest at one end of the chain and oldest at the other. Magma Composition In 1980, Mount St. Helens blew up in the costliest and deadliest volcanic eruption in United States history. The eruption killed 57 people, destroyed 250 homes and swept away 47 bridges. Mount St. Helens today still has minor earthquakes and eruptions, and now has a horseshoe-shaped crater with a lava dome inside. The dome is formed of viscous lava that oozes into place. It should first be noted that magma is molten material inside the earth, whereas lava is molten material on the surface of the earth. The reason for the distinction is because lava can cool quickly from the air and solidify into rock rapidly, whereas magma may never reach the earth's surface. Volcanoes do not always erupt in the same way. 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 rocks melt at different temperatures and the amount of partial melting and the composition of the original rock determine the composition of the magma. Magma collects in magma chambers in the crust at 160 kilometers (100 miles) beneath the surface of a volcano. 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 liquid’s 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 and so it gets stuck. Dissolved gases become trapped by thick magma and the magma chamber begins to build pressure. EXPLOSIVE ERUPTIONS The type of magma in the chamber determines the type of volcanic eruption. A large explosive eruption creates even more devastation than the force of the atom bomb dropped on Nagasaki at the end of World War II in which more than 40,000 people died. A large explosive volcanic eruption is 10,000 times as powerful. Felsic magmas erupt explosively because of hot, gas-rich magma churning within its chamber. The pressure becomes so great that the magma eventually breaks the seal and explodes, just like when a cork is released from a bottle of champagne. Magma, rock, and ash burst upward in an enormous explosion creating volcanic ash called tephra. It should be noted that when looked under a microscope, the volcanic “ash” is actual microscopic shards of glass. That is why it is so dangerous to inhale the air following an eruption. Scorching hot tephra, ash, and gas may speed down the volcano’s slopes at 700 km/h (450 mph) as a pyroclastic flow. Pyroclastic flows knock down everything in their path. The temperature inside a pyroclastic flow may be as high as 1,000oC (1,800 degrees F). Prior to the Mount St. Helens eruption in 1980, the Lassen Peak eruption on May 22, 1915, was the most recent Cascades eruption. A column of ash and gas shot 30,000 feet into the air. This triggered a high-speed pyroclastic flow, which melted snow and created a volcanic mudflow known as a lahar. Lassen Peak currently has geothermal activity and could erupt explosively again. Mt. Shasta, the other active volcano in California, erupts every 600 to 800 years. An eruption would most likely create a large pyroclastic flow, and probably a lahar. Of course, Mt. Shasta could explode and collapse like Mt. Mazama in Oregon. Volcanic gases can form poisonous and invisible clouds in the atmosphere that could contribute to environmental problems such as acid rain and ozone destruction. Particles of dust and ash may stay in the atmosphere for years, disrupting weather patterns and blocking sunlight. EFFUSIVE ERUPTIONS Mafic magma creates gentler effusive eruptions. Although the pressure builds enough for the magma to erupt, it does not erupt with the same explosive force as felsic magma. People can usually be evacuated before an effusive eruption, so they are much less deadly. Magma pushes toward the surface through fissures and reaches the surface through volcanic vents. Click here to view a lava stream within the vent of a Hawaiian volcano using a thermal camera. Low-viscosity lava flows down mountainsides. Differences in composition and where the lavas erupt result in lava types like a ropy form pahoehoe and a chunky form called aa. Although effusive eruptions rarely kill anyone, they can be destructive. Even when people know that a lava flow is approaching, there is not much anyone can do to stop it from destroying a building, road, or infrastructure. Pahoehoe lava Predicting Volcanic Eruptions Volcanologists attempt to forecast volcanic eruptions, but this has proven to be nearly as difficult as predicting an earthquake. 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. HISTORY OF VOLCANIC ACTIVITY A volcano’s history, how long since its last eruption and the time span between its previous eruptions, is a good first step to predicting eruptions. If the volcano is considered active, it is currently erupting or shows signs of erupting soon. A dormant volcano means there is no current activity, but it has erupted recently. Finally, an extinct volcano means there is no activity and will probably not erupt again. Active and dormant volcanoes are heavily monitored, especially in populated areas. EARTHQUAKES 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. Magma and gas can push the volcano’s 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 rockfalls and landslides. GAS EMISSIONS 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 or, in some cases, from a distance using satellites. The amounts of gases and their ratios are calculated to help predict eruptions. REMOTE MONITORING Some gases can be monitored using satellite technology. Satellites also monitor temperature readings and deformation. As technology improves, scientists are better able to detect changes in a volcano accurately and safely. Since volcanologists are usually uncertain about an eruption, officials may not know whether to require an evacuation. If people are evacuated and the eruption doesn’t 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. Types of Volcanoes A volcano is a vent through which molten rock and gas escape from a magma chamber and they can differ in height, shape, and slope steepness. Some volcanoes are tall cones and others are just cracks in the ground. As you might expect, the shape of a volcano is related to the composition of its magma. COMPOSITE VOLCANOES Composite volcanoes are some of the most dangerous volcanoes on the planet. They tend to occur along oceanic-to-oceanic or oceanic-to-continental boundaries because of subduction zones. They tend to be made of felsic to intermediate rock and the viscosity of the lava means that eruptions tend to be explosive. The viscous lava cannot travel far down the sides of the volcano before it solidifies, which creates the steep slopes of a composite volcano. Viscosity also causes some eruptions to explode as ash and small rocks. The volcano is constructed layer by layer, as ash and lava solidify, one upon the other and are sometimes called stratovolcanoes or andesite volcanoes. The result is the classic cone shape of composite volcanoes. Examples of composite volcanoes include Mount St. Helens, Mount Rainer, Mount Shasta, Mount Hood, and Mount Pinatubo. Here's a great time-lapse of Mount St. Helens from NASA's Earth Observatory from 1979 to 2013. Editor’s Note/Photo: Here is a picture of a volcanic eruption of the Villarica volcano in Chile. This happened at 3am and no one was hurt because they followed the warnings of geologists who told them an eruption was imminent. Sometimes composite volcanoes and other violent volcanoes can erupt so violently that they sometimes collapse in on themselves or actually blow themselves up to produce calderas. One of the most powerful volcanoes in the world - Yellowstone- is a massive caldera that has collapsed several times. Sometimes these calderas can fill up with water to produce beautiful lakes such as Mount Mazama (Crater Lake), in Oregon. SHIELD VOLCANOES Shield volcanoes get their name from their shape. Although shield volcanoes are not steep, they may be very large. In fact, Mauna Loa, Hawaii is the tallest mountain in the world. From sea level, Mount Everest is the tallest, but when you consider from the ocean floor to the top of the island, Mauna Loa wins. Shield volcanoes are common at spreading centers or intraplate hot spots. The lava that creates shield volcanoes is fluid and flows easily and creates the shield shape. Shield volcanoes are built by many layers over time and the layers are usually of very similar composition. The low viscosity also means that shield eruptions are non-explosive. Eruptions tend to be mild in comparison to other volcanoes, but lava flows can destroy property and vegetation. The low viscosity magma can flow not only on the surface as lava, but also underground in lava tubes. The most well known shield volcano is Hawaii. There are two types of lava flows, pahoehoe which is a ropy type of lava that flows easily (low viscosity). The other type is called aa and is a blocky type of lava and has a higher viscosity and does not like to flow well. The following is a short video on Hawaii, an example of a shield volcano. CINDER CONES Cinder cones are the most common type of volcano. A cinder cone has a cone shape, but is much smaller than a composite volcano. Cinder cones rarely reach 300 meters in height but they have steep sides. Cinder cones grow rapidly, usually from a single eruption cycle. Cinder cones are composed of small fragments of rock, such as pumice, piled on top of one another. The rock shoots up in the air and doesn’t fall far from the vent. The exact composition of a cinder cone depends on the composition of the lava ejected from the volcano. Cinder cones usually have a crater at the summit. Cinder cones are often found near larger volcanoes. SUPERVOLCANOES Supervolcano eruptions are extremely rare in Earth history. It’s a good thing because they are unimaginably large. A supervolcano must erupt more than 1,000 cubic km (240 cubic miles) of material, compared with 1.2 km3 for Mount St. Helens or 25 km3 for Mount Pinatubo, a large eruption in the Philippines in 1991. Not surprisingly, supervolcanoes are the most dangerous type of volcano. Supervolcanoes are a fairly new idea in volcanology. The exact cause of supervolcano eruptions is still debated, however, scientists think that a very large magma chamber erupts entirely in one catastrophic explosion. This creates a huge hole or caldera into which the surface collapses. The largest supervolcano in North America is beneath Yellowstone National Park in Wyoming. Yellowstone sits above a hotspot that has erupted catastrophically three times: 2.1 million, 1.3 million, and 640,000 years ago. Yellowstone has produced many smaller (but still enormous) eruptions more recently. Fortunately, current activity at Yellowstone is limited to the region’s famous geysers. Long Valley Caldera, south of Mono Lake in California, is the second largest supervolcano in North America. Long Valley had an extremely hot and explosive rhyolite explosion about 700,000 years ago. An earthquake swarm in 1980 alerted geologists to the possibility of a future eruption, but the quakes have since calmed down. A supervolcano could change life on Earth as we know it. Ash could block sunlight so much that photosynthesis would be reduced and global temperatures would plummet. Volcanic eruptions could have contributed to some of the mass extinctions in our planet’s history. No one knows when the next super eruption will be. Volcanic Landforms and Geothermal Activity VOLCANIC LANDFORMS AND VENTS Volcanoes are associated with many types of landforms. The landforms vary with the composition of the magma that created them. Hot springs and geysers are also examples of surface features related to volcanic activity. The most obvious landforms created by lava are volcanoes, most commonly as cinder cones, composite volcanoes, and shield volcanoes or eruptions that take place through fissures. The eruptions that created the entire ocean floor are essentially fissure eruptions. Magma intrusions ALSO can create landforms. The image on the right is of Shiprock in New Mexico, which is the neck of an old volcano that has eroded away Lava dome inside Mount St. Helen's crater. LAVA DOMES When lava is viscous, it flows slowly. If there is not enough magma or enough pressure to create an explosive eruption, the magma may form a lava dome. But because the viscosity of the magma is so thick, the lava does not flow far from the vent. Lava flows often make mounds right in the middle of craters at the top of volcanoes. LAVA PLATEAUS AND LAND A lava plateau forms when large amounts of fluid lava flows over an extensive area. When the lava solidifies, it creates a large, flat surface of igneous rock. Lava creates new land as it solidifies on the coast or emerges from beneath the water. Over time the eruptions can create whole islands. The Hawaiian Islands are formed from shield volcano eruptions that have grown over the last 5 million years. HOT SPRINGS AND GEYSERS Water sometimes comes into contact with hot rock. The water may emerge at the surface as either a hot spring or a geyser. Water heated below ground that rises through a crack to the surface creates a hot spring. The water in hot springs may reach temperatures in the hundreds of degrees Celsius beneath the surface, although most hot springs are much cooler. Hazards and Benefits of Volcanic Activity There are several hazards that volcanic activity can produce. Eruption clouds occur when massive quantities of ash is ejected into the atmosphere where it can reach heights of 50,000 feet. Eruption clouds have proven to be very dangerous for aviation jets because the ash can shut down the engines. The ash cloud can also be very hazardous in terms of air pollution. Editor’s note/Photos: These are some of the photos taken of the Mt. St. Helens landslide and eruption in 1980. These were taken by Keith Ronnholm ten miles northeast of the volcano. They show the eruption cloud at the moment of explosion. Lahars are volcanic mudflows. Lahars are very dangerous because they do not require a volcanic eruption yet can travel hundreds of miles. All that is required is loose pyroclastic material on the volcano that mixes with precipitation or melting snow. Lava flows are layers of molten rock that flow over the surface, later cooling and solidifying. Lava bombs are large chunks of pyroclastic material ejected from a volcano. Larger pyroclastic material is called blocks. Pyroclastic flows are some of the most dangerous hazards caused by composite volcanoes. Pyroclastic flows are superheated clouds of pyroclastic material (e.g. hot rock and tephra) ranging in size from small rocks to the size of houses that are over 1,000 degrees F traveling down a mountain at speeds up to 100 mph. Tephra (or volcanic ash) is fine particles of pyroclastic material that can be carried thousands of miles away by prevailing winds. Regions hundreds of miles away could suffer collapsed buildings is the falling ash accumulates enough. Tephra can also cool the entire planet if enough is ejected into the atmosphere. Poisonous gases such as carbon dioxide, carbon monoxide, and sulfur dioxide can travel down a volcano and asphyxiate (suffocating) wildlife and humans. In 1986, an invisible cloud of carbon dioxide traveled down a volcano in Africa asphyxiating 1,742 people and 3,000 cattle. There are actually many benefits to volcanic activity. One of the major benefits is the fact that volcanic activity can create very fertile soil for agriculture. The problem is that many civilizations developed near volcanoes for this reason - with sometimes deadly effects. Volcanic activity can also create many mineral resources such as gold, sliver, nickel, copper, and lead. Volcanic rock is often used for landscaping, tile, and cement. Some of the most amazing landscapes are near volcanoes. This is because volcanic activity builds land creating breathtaking scenery. So volcanoes are economically vital for many regions because of the recreational activity and tourism they bring. Editor’s note/Tourism video: This is a link to a tourism video for Hawaii. In the video the park ranger talks about some of the volcanoes in the park as well as some of the experiences people can have there. She mentions some of the local folklore about the volcanos as well as what happens now. There is a part where she talks about how the volcano is part of the process of rebirth for the island and that all the vegetation is there only because of the volcanos. It is really cool to think that something that can be so destructive can also help to create new ecosystems and life. http://www.gohawaii.com/stories/stories.html?video=11 Finally, a new but important trend is geothermal power. The heat generated by volcanoes can create electricity to power civilization. Geothermal power is a completely renewable resource free of pollution and energy dependency on fossil fuels. Iceland - the surface manifestation of the midAtlantic ridge - has a goal of powering the entire nation on geothermal energy. Geothermal energy is also being used in California, Kilauea, Hawaii, and now Utah. Chapter 5: Mass Wasting Editor’s note/Personal experience: The below picture is of the Bingham Canyon mine slide. At the time I was working as a security guard and emt at the Kennecott smelter. I remember how many people were worried about the slow down at the mine that was caused by the slide. I also had a friend who worked in the smelter so he was worried about being able to keep his job. There were hundreds of employees who took early retirement to help reduce layoffs but there were also about 2100 employees asked to take paid leave and vacation time as well. This was a time of great worry even for me and my coworkers even though we were not directly employed by Kennecott. This shows the impact that natural disasters can have on the lives of people even when there is no casualties in the immediate event. Weathering Weathering is the process that changes solid rock into sediments. With weathering, rock is disintegrated into smaller pieces. Once these sediments are separated from the rocks, erosion is the process that moves the sediments away from it's original position. The four forces of erosion are water, wind, glaciers, and gravity. Water is responsible for most erosion. Water can move most sizes of sediments, depending on the strength of the force. Wind moves sandsized and smaller pieces of rock through the air. Glaciers move all sizes of sediments, from extremely large boulders to the tiniest fragments. Gravity moves broken pieces of rock, large or small, downslope. These forces of erosion will be covered later. While plate tectonics forces work to build huge mountains and other landscapes, the forces of weathering and mass wasting gradually wear those rocks and landscapes away, called denudation. Together with erosion, tall mountains turn into hills and even plains. The Appalachian Mountains along the east coast of North America were once as tall as the Himalayas. No human being can watch for millions of years as mountains are built, nor can anyone watch as those same mountains gradually are worn away. But imagine a new sidewalk or road. The new road is smooth and even. Over hundreds of years, it will completely disappear, but what happens over one year? What changes would you see? What forces of weathering wear down that road, or rocks or mountains over time? MECHANICAL WEATHERING Mechanical weathering, also called physical weathering, breaks rock into smaller pieces. These smaller pieces are just like the bigger rock, just smaller. That means the rock has changed physically without changing its composition. The smaller pieces have the same minerals, in just the same proportions as the original rock. There are many ways that rocks can be broken apart into smaller pieces. Ice wedging, also called freeze-thaw weathering, is the main form of mechanical weathering in any climate that regularly cycles above and below the freezing point. Ice wedging works quickly, breaking apart rocks in areas with temperatures that cycle above and below freezing in the day and night, and also that cycle above and below freezing with the seasons. Ice wedging breaks apart so much rock that large piles of broken rock are seen at the base of a hillside called talus. Ice wedging is common in Earth’s Polar Regions and mid latitudes, and also at higher elevations, such as in the mountains. Abrasion is another form of mechanical weathering. In abrasion, one rock bumps against another rock. Gravity causes abrasion as a rock tumbles down a mountainside or cliff. Moving water causes abrasion as particles in the water collide and bump against one another. Strong winds carrying pieces of sand can sandblast surfaces. Ice in glaciers carries many bits and pieces of rock. Rocks embedded at the bottom of the glacier scrape against the rocks below. Abrasion makes rocks with sharp or jagged edges smooth and round. If you have ever collected beach glass or cobbles from a stream, you have witnessed the work of abrasion. Now that you know what mechanical weathering is, can you think of other ways it could happen? Plants and animals can do the work of mechanical weathering. This could happen slowly as a plant’s roots grow into a crack or fracture in rock and gradually grow larger, wedging open the crack. Burrowing animals can also break apart rock as they dig for food or to make living spaces for themselves. Mechanical weathering increases the rate of chemical weathering. As rock breaks into smaller pieces, the surface area of the pieces increases. With more surfaces exposed, there are more surfaces on which chemical weathering can occur. CHEMICAL WEATHERING Chemical weathering is the other important type of weathering. Chemical weathering is different from mechanical weathering because the rock changes, not just in size of pieces, but in composition. That is, one type of mineral changes into a different mineral. Chemical weathering works through chemical reactions that cause changes in the minerals. Most minerals form at high pressure or high temperatures deep in the crust, or sometimes in the mantle. When these rocks reach the Earth’s surface, they are now 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 Earth’s surface. Remember that the most common minerals in Earth’s crust are the silicate minerals. Many silicate minerals form in igneous or metamorphic rocks deep within the earth. 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. There are many types of chemical weathering because there are many agents of chemical weathering. Water is the most important agent of chemical weathering. Two other important agents of chemical weathering are carbon dioxide and oxygen. CHEMICAL WEATHERING BY WATER A water molecule has a very simple chemical formula, H2O, two hydrogen atoms bonded to one oxygen atom. But water is pretty remarkable in terms of all the things it can do. 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. 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 undergone leaching. 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 Earth’s surface. CHEMICAL WEATHERING BY CARBON DIOXIDE 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 accelerate chemical weathering. Editor’s Note/Picture: Here is a picture I found that shows the formation of acid rain and the problems it causes. Part of the picture references the weathering it causes but also the affects it has on crops and pollution of waterways. CHEMICAL WEATHERING BY OXYGEN 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. Minerals that are rich in iron break down as the iron oxidizes and forms new compounds. Iron oxide produces the red color in soils. 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. Influences on Weathering ROCK AND MINERAL TYPE Weathering rates depend on several factors. These include the composition of the rock and the minerals it contains as well as the climate of a region. Different rock types weather at different rates. Certain types of rock are very resistant to weathering. Igneous rocks, especially intrusive igneous rocks such as granite, weather slowly because it is hard for water to penetrate them. Other types of rock, such as limestone, are easily weathered because they dissolve in weak acids. Rocks that resist weathering remain at the surface and form ridges or hills. Devil’s Tower in Wyoming is an igneous rock from beneath a volcano. As the surrounding less resistant rocks were worn away, the resistant center of the volcano remained behind. Different minerals also weather at different rates. Some minerals in a rock might completely dissolve in water, but the more resistant minerals remain. In this case, the rock’s surface becomes pitted and rough. When a less resistant mineral dissolves, more resistant mineral grains are released from the rock. CLIMATE A region’s climate strongly influences weathering. Climate is determined by the temperature of a region plus the amount of precipitation it receives. Climate is weather averaged over a long period of time. Chemical weathering increases as: Temperature increases: Chemical reactions proceed more rapidly at higher temperatures. For each 10 degrees C increase in average temperature, the rate of chemical reactions doubles. Precipitation increases: More water allows more chemical reactions. Since water participates in both mechanical and chemical weathering, more water strongly increases weathering. So how do different climates influence weathering? A cold, dry climate will produce the lowest rate of weathering. A warm, wet climate will produce the highest rate of weathering. The warmer a climate is, the more types of vegetation it will have and the greater the rate of biological weathering. This happens because plants and bacteria grow and multiply faster in warmer temperatures. Factors that Influence Mass Wasting Once rock material has been broken down into smaller, unstable pieces by weathering, the material has the potential to move downslope called mass wasting (also called a landslide). Before looking into the various types of landslides, the factors that influence them must be examined. STEEPNESS OF SLOPE There are several factors that influence mass wasting, but ultimately it is a battle between friction and gravity. If the friction on a rock is stronger than gravity for a particular slope, the rock material will likely stay. But if gravity is stronger, the slope will fail. The steeper the slope, the stronger the friction or rock strength must be to resist downslope motion. The steepest angle a slope can be before the ground will slide is about 35 degrees, called the angle of repose. Many times we will cut through a slope to make room for a road or other forms of development. So to help prevent the slope from sliding along these cut areas, retaining walls must be build. More on this later. COMPOSITION OF SLOPE MATERIAL Another factor that determines mass wasting is the slope's material. Mass wasting is more prone on slopes that contain clay and shale. Without going into great detail here, the shape and composition of individual clay particles can absorb water and prevent water from peculating through the ground. A layer of clay on a slope can prevent water from filtering through the slope. Instead, the water stays near the surface and saturates the ground. This can cause the surface layers to lose friction and slide. WEIGHT AND FRICTION OF SLOPE A third factor that influences whether a slope will fail is the load or weight of that slope. Adding weight to a weakened slope can obviously cause it to slide easier, especially on steep slopes. This added weight tends to occur by building on top of weak slopes, increasing the steepness of the slope, or over-saturating the slope. Friction has been mentioned as a factor several times already, but there are a few more things must be said here. As already noted, as long as the friction along the slope is stronger than gravity, the ground is unlikely to slide. But if that friction is weakened, slope fail becomes more likely. There are several other ways friction can be reduced along a slope: wildfires, removal of vegetation, or adding too much water. Gravity is probably the ultimate driving force of mass wasting. The force of gravity pulls all things on the planet toward the center of the Earth. Without gravity, mass wasting would not occur. But unlike many of the other factors, humans have no influence or control on gravity. REGIONAL CLIMATE CONDITIONS A region's climate can also determine the likelihood of a landslide. Climate is based on temperature and precipitation. Mass wasting is prone in the spring-time when snowmelt, water saturation, and runoff is greatest. Also the type of climate will help determine the type of mass wasting. Humid climates tend to have slides, where water- saturated slopes fail and fall. Drier climates tend to have rocks that fall; especially early spring. Canyons and places prone to wildfires tend to have debris flows. WATER CONTENT WITHIN SLOPES The amount of water in the soil is a major factor in the stability of a slope. When you build a sand castle, water is needed to build the walls and towers. That is because water has surface tension and is attracted to each other. This allows you to build towers greater than the angle of repose. So a little water can actually prevent slopes from sliding. But too much water lubricates the individual grains of sediment decreasing friction between each grain, so the possibility of mass wasting increases. The increase of water within the soils can come from over watering, pipe or swimming pool leaks, or prolonged stormy weather. In Utah and many mountainous regions, spring runoff of snow melt increases the water content within the soil. The following is a video from the USGS of the La Conchita, California landslide in 2005. Notice how well it flows down the mountainside. There are two reasons why this landslide occurred. First, this slide occurred on the same slope as a previous landslide in 1995. But the 2005 slide was also influenced by the fact that above is an orchard that was over-watering the vineyards and over-saturated the soil. Finally, gravity is the driving force of mass wasting. The force of gravity pulls all things on the planet toward the center of the Earth. But unlike many of the other factors, humans have no influence or control on gravity. For more information on what causes landslides in Utah, click here. Types of Mass Wasting ROCK FALL A rock fall are the fastest of all landslide types and occurs when a rock falls through the air until it comes to rest on the ground - not too complicated. In Utah, they are common in the spring and fall because of what is called freeze-thaw weathering. In the daytime, temperatures in the spring and fall tend to be above freezing, which allows liquid water to enter cracks within rocks. At night, the temperatures cool below freezing and the water within the rocks freezes and expands which causes the rock to break more. The following morning, the ice will melt and go deeper within the crack to refreeze later that night. This freeze-thaw action over time can cause rocks to break off and fall to the ground. The debris the accumulates at the base of these steep slopes is called talus. But rock falls can also occur when heavy precipitation is falling on a steep slope, causing the rocks to lose friction and fall. The YouTube video on the right is a rock fall captured in Taiwan in late August 2013, following heavy precipitation in the region. ROTATIONAL SLIDES Rotational slides occur when the landslide occurs in a curved manner concave to the sky. When this type of slide occurs, the upper surface of the slide tilts backwards toward the original slope and the lower surface moves away from the slope. They are common when the soil tends to be deep in clay or soft sediment deposits. The video on the right is a large landslide again in Taiwan in early September 2013 following every rainfall. Needless to say, they were having a bad few days in the region. TRANSLATIONAL SLIDES Rather than rotating, a translational slide occurs when slope failure occurs parallel to the slope. Often times the slope failure occurs on soil composed of clay or shale, or along old fault lines, or previous slide areas. What makes translational slides dangerous is that they tend to flow faster and travel farther than rotational slides. The most expensive translational slide in U.S. history actually occurred in Thistle, Utah in 1983. The Utah Geologic Survey also provides a Google Earth file that looks at the Thistle landslide. DEBRIS FLOWS Debris flows are one of the most common, but most dangerous of the various types of landslides because of their speed and consistency. Debris flows tend to be a mixture of rock and water with two to three times the density of flooding streams. That density allows debris flows strip away the land and pick up objects as large as school buses. Debris flows are most common at the mouth of canyons along alluvial fans. Lets first explain an alluvial fan. When floods occur within the mouth of a canyon, either because of intense thunderstorms or snow melt, the erosive power of the water can pick up sediment and boulders - a debris flow. Now once the debris flow reaches the mouth of a canyon, the sediment gets deposited in a fan-shaped delta called an alluvial fan. The problem is that people like to live along alluvial fans because of their scenic view on the canyon. Another influence of debris flows is wildfires. When a wildfire strips an area of its vegetation, the bare soil is easily eroded away in either a thunderstorm or snow melt creating these debris flows. Because of Utah's topography and tendency to wildfires, debris flows are quite common. Editor’s Note/News article: Since we live in Utah I decided to add a news article from august 2014 about the landslide in North Salt Lake. I was working with a woman at the time that lived in North Salt Lake so she was very concerned about what was going on. She was fine but she knew some of the people affected by the slide. http://www.nbcnews.com/news/weather/utah-mudslide-destroys-home-north-salt-lakecity-n173071 Image source: This image is in the public domain because it contains materials that originally came from the United States Geological Survey, an agency of the United States Department of the Interior. VOLCANIC MASS WASTING Lahars were mentioned in the module on volcanoes, but in essence they are volcanic landslides. Recall that volcanoes eject pyroclastic material ranging is size from ash to boulders. Now there tends to be two ways lahars occur. One is if a thunderstorm precipitates large amounts of moisture on the pyroclastic material and the pyroclastics flow downslope. The other option is if a volcano is snow-capped and the heat from the volcano causes some of the snow to melt and mix with the pyroclastic material. What makes lahars so dangerous is that they have the consistency of concrete and can travel hundreds of miles. Limiting Mass Wasting Potential DRAINAGE CONTROLS Ultimately preventing mass wasting is impossible because gravity will always exist, but smarter development can help minimize the risk and hazards. One component in landslide mitigation is basic drainage control of water. Recall that water can cause slopes to lose their friction as water lubricates individual grains of soil. And if you cut a slope and put a retaining wall for support, you may be preventing the water from filtering through. Thus you will often find drains at the base of retaining walls that allow underground water to within the slopes to drain out. SLOPE GRADE AND SUPPORT 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. Ultimately preventing landslides is impossible because gravity will always exist. But smarter development can help minimize the risk and hazards created by landslides. One component in landslide mitigation is basic drainage control of water. Recall that water can cause slopes to lose their friction as water lubricates individual grains of soil. And if you cut a slope and put a retaining wall for support, you may be preventing the water from filtering through. Thus you will often find drains at the base of retaining walls that allow underground water to within the slopes to drain out. Slope support is one of most common types of mitigation for potential mass wasting. As mentioned above, a retaining wall can be built to support a steep slope. Next, the retaining wall must be anchored to the bedrock within the slope to hold the wall to the slope. Another type of slope support is simply planting vegetation. The roots of vegetation tend to grab and hold soil in place, so by planting various types of plants and trees can be a simple and cheap way to stabilize a slope. For more on what homeowners can do to minimize your risk to landslides in Utah, click here. Subsidence Subsidence occurs when loose, water saturated sediment begins to compact causing the ground surface to collapse. Now there are two types of subsidence. SLOW SUBSIDENCE Slow subsidence occurs when the water within the sediment is slowly squeezed out because of overlying weight. There are several examples of slow subsidence, but the best one is Venice, Italy. Venice was built at sea level on the now submerged delta of the Brenta River. The city is sinking because of the overlying weight of the city and pumping of ground water. The problem now is that sea levels are rising as glaciers melt and water expands due to global warming. An example of slow subsidence in the U.S. includes New Orleans, Louisiana. As we all know from Hurricane Katrina, the Mississippi River has a vast network of levees that prevent the massive river from flooding - most of the time. But by preventing the spring-time flooding, we are preventing the river from depositing sediment onto the land. Instead, the sediment is being transported to the Gulf of Mexico creating the massive Mississippi delta. Below is a Landsat satellite image from NASA of this delta. FAST SUBSIDENCE Fast subsidence occurs when naturally acidic water begins to dissolve limestone rock to forma a network of water-filled underground caverns. But if droughts or pumping of ground water reduces the water table below the level of the caves, they caverns collapse creating surface sinkholes. A dramatic example of fast subsidence occurred in Guatemala City in 2007 when a massive sinkhole formed 300 feet deep. As noted above, the underground region surrounding Guatemala is composed of limestone that and a vast underground network of caverns. It is believed that the water table has been dropping in the region and thus draining the caves. Afterward the caves cannot support the overlying weight and collapse in. Editor’s note/Picture: I decided to add a picture of the sinkhole that occurred in 2007 in Guatemala. It almost doesn’t look real to me. It almost looks bottomless in some images. Prevention and Awareness DRAINAGE CONTROLS Ultimately preventing landslides is impossible because gravity will always exist. But smarter development can help minimize the risk and hazards created by landslides. One component in landslide mitigation is basic drainage control of water. Recall that water can cause slopes to lose their friction as water lubricates individual grains of soil. And if you cut a slope and put a retaining wall for support, you may be preventing the water from filtering through. Thus you will often find drains at the base of retaining walls that allow underground water to within the slopes to drain out. SLOPE GRADE AND SUPPORT 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. Ultimately preventing landslides is impossible because gravity will always exist. But smarter development can help minimize the risk and hazards created by landslides. One component in landslide mitigation is basic drainage control of water. Recall that water can cause slopes to lose their friction as water lubricates individual grains of soil. And if you cut a slope and put a retaining wall for support, you may be preventing the water from filtering through. Thus you will often find drains at the base of retaining walls that allow underground water to within the slopes to drain out. Slope support is one of most common types of mitigation for potential landslides. As mentioned above, a retaining wall can be built to support a steep slope. Next, the retaining wall must be anchored to the bedrock within the slope to hold the wall to the slope. Another type of slope support is simply planting vegetation. The roots of vegetation tend to grab and hold soil in place, so by planting various types of plants and trees can be a simple and cheap way to stabilize a slope. 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. 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. For more on what homeowners can do to minimize your risk to landslides in Utah, click here. Editor’s note/Song link: After searching for things on landslides and mass wasting and finding mostly links to Fleetwood Mac I have decided for fun to add a link to a youtube video of the song Landslide. https://www.youtube.com/watch?v=6yY4bNCx9TY Chapter 6: Tsunamis Editor’s note/Painting: This is one of the iconic Japanese paintings of a Tsunami. I decided to add this because it shows that in this particular region tsunamis are a common occurrence and something people there have incorporated into their everyday life as well as something that causes such devastation. What is a Tsunami? Most people never thought much about tsunamis until the cataclysmic event that occurred on December 26, 2004 in Indonesia. Tsunami actually is a Japanese term that means "harbor wave". There are four major ways tsunamis form: underwater earthquakes, volcanic eruptions, landslides, or extraterrestrial impacts such as asteroids. These four seismic events will be looked at in greater detail in a minute. The formation of a tsunami by these catastrophic events is called tsunami initiation. Now once a tsunami is generated, it will travel outward in a circular radius from the tsunami epicenter at speeds of 500 mph! But the height of each wave crest in the deep ocean is only 2-3 feet, thus large ships never feel tsunamis in the deep ocean. It's important to stop here and briefly discuss the physics of energy traveling through water. First, a wave of water is called a wave - that was easy! Next, the distance between two wave peaks or heights is called a wavelength. The time it takes one wavelength (distance between two wave peaks) to pass a given position is called the frequency. Thus, waves with long wavelengths have low frequencies because it takes a long time for the wave to cross a given point. Waves that have short wavelengths have high frequencies. Have you ever watched an object floating in water as a wave passes by it? Let's say it’s a stick in the ocean. Now when that wave passes by, the stick does not travel with the wave; rather the stick bops up and down but stays relatively in the same place. That is because the water does not travel with the wave's energy; rather the energy passes through the water causing the water to travel in a circle (which appears as an up, slightly forward, down, and backward motion). The depth of the circular size of motion generated by waves is half the distance from each wave crest. Thus if the distance from one wave crest to the next wave crest is one mile, the depth of the water's circular motion is half a mile. This is important because tsunamis have very long wavelengths, thus their depths reach the ocean floor. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. Click on the image to view the source. It was noted above that out in the deep ocean, the height of a tsunami is only a few feet high with very long wavelengths. This is because in the deep water, the amplitude of the waves is very small and the wavelengths quite large for anyone on a boat to notice. But as the tsunami approaches the shoreline, it begins to slow down and grow taller because the friction between the oscillating tsunami waves comes into more contact with the rising elevation of the sea floor. This friction causes the wave's amplitude to grow, the wavelength shorten (distance between each successive tsunami wave), and the frequency becomes shorter causing the energy of the tsunami to make the wave grow taller. The height of a tsunami is called the run-up. Thus when a tsunami reaches shore, it may have slowed to 30-40 mph, but dramatically higher. The size of the run-up is determined by the distance between the tsunami epicenter and the shoreline, the energy released by the tsunami initiation, and the steepness of the continental slope. Tsunamis are also not a large, single wave coming ashore, rather they are a series of powerful, rippling waves called atsunami train. As the waves approach shore, the shoreline oftentimes disappears as the water is pulled back into the ocean to build up the waves. Many people find this strange event enticing and go onto the beach to see the fish flapping on the newly bare ground. But this is a false sense of security and within minutes the series of waves comes crashing ashore. Often times there can be up to ten individual tsunami waves and the most powerful ones may be the second or third wave. So if you see the water along the coastline disappear, you need to quickly gather your family and friends and head to higher ground. Creating a Tsunami EARTHQUAKES Most tsunamis occur because of powerful, subduction zone such as the Ring of Fire. Thus, most tsunamis are generated by reverse fault or thrust fault earthquakes along subduction zones because of the amount of water displaced by these events. But not all reverse fault earthquakes can initiate tsunamis. The minimum magnitude of an earthquake needed to create a tsunami is a 7.5; the Asian tsunami of 2004 was generated by a M 9.1 thrust fault along an oceanic-to-oceanic subduction zone. Strike-slip faults along transform boundaries do not generate tsunamis because their parallel movement does not displace enough water. The potential for a tsunami striking the United States is very high for a variety of reasons. One is because of the oceanic-to-continental subduction zone in the northwestern states of Washington, Oregon, and northern California. Recall from previous modules that this subduction zone not only generates earthquakes, but has produced the major volcanoes of the region such as Mount St. Helens, Mt. Rainer, and Mt. Shasta. Research show that ever few hundred years the region experiences a M 9.0 earthquake generating a major tsunami that would reach coastal cities within 20 minutes. Obviously there would be no time to evacuate the people in time. VOLCANOES Less common, but still a force to consider are large, violent, composite volcanoes. There are a couple of ways a volcano can generate a tsunami. Sometimes just the energy released by the volcano along with the pyroclastic flow can initiate a tsunami. Other times, a violent eruption can cause a portion of a volcano's slope to slide off into the ocean. The most dangerous way would be if a volcano explodes or collapses to generate a caldera in the ocean. There are some real-world examples of these occurring. In 1883 on the volcanic island of Krakatau (image on the right), a violent eruption occurred producing a tsunami that killed 35,000 people and destroyed two-thirds of the island. It is believed a massive pyroclastic flow slammed into the ocean producing a massive tsunami. Ultimately the eruption was so violent that the island collapsed to produce a massive caldera of the former island. A concern today is the volcanic islands off western Africa called the Canary Islands. Scientists are concerned with an unstable slope on the western side of one of the volcanic islands. Their concern is that a major eruption could cause a portion of the slope to slide off into the Atlantic Ocean, generating a massive tsunami. Within 9 hours - traveling at 500 mph - this tsunami would reach the eastern United States with a run-up of nearly 150 feet! Last, but not least, is the major island of Hawaii - Mauna Loa. Scientific studies of the former volcanic islands that use to be over this hot spot show that shield volcanoes tend to grow fastest just before they move off the hot spot. Mauna Loa is the most active volcano in the world and is about to move off the hot spot. In fact, a new volcanic island is beginning to form underwater just east of the main island. Studies are showing that the increased activity and lava flows can destabilize portions of the slopes as more weight is added. Field works has discovered that Mauna Loa has had over 60 giant debris avalanches that slide into the Pacific Ocean. These slides tend to be 10-20 miles long and could ultimately generate a tsunami 900 feet high! LANDSLIDES Large scale landslides can also displace large amounts of water to generate massive tsunamis. But often times, it’s a volcanic eruption or earthquake that generates the landslide, which creates a tsunami. One concern for the United States is an underwater landslide - called a submarine landslide - off the eastern coast of the continental shelf can displace enough water to generate a 20 foot tsunami and reach the nation within 20 minutes. The largest landslide ever recorded in human history happened in Lituya Bay, Alaska. A magnitude 7.0 earthquake along the Denali Fault generated a massive rock fall into the bay, which produced a 1,700 foot tsunami! But the bay contained most of the energy and thus a major catastrophe was averted. But the concern is another such event occurring in Glacier Bay, Alaska which is a major tourist attraction for cruise lines. Lituya Bay a few weeks after the 1958 tsunami. The areas of destroyed forest along the shorelines are clearly recognizable as the light a rimming the bay. A fishing boat anchored in the cove at lower left was carried over the spit in the foreground; a boat under way near the e was sunk; and a third boat, anchored near the lower right, rode out the wave. Photo by D.J. Miller, United States Geological Survey ASTEROID IMPACTS The rarest, but most lethal tsunami would be generated by an asteroid or comet impact. If an asteroid were to make it through the earth's atmosphere, there is a 70 percent chance it would land in the ocean. For example, an asteroid striking the Atlantic Ocean could produce a tsunami that would cover over half of the nation. All coastal cities around the world would also be destroyed. And with 90 percent of all humans living near a large body of water, well you see the impact! As most of you are aware, the last asteroid impact in the ocean occurred 65 million years ago and produced a tsunami half a mile high. Editor’s Note/Movie clip: Here is a youtube video from the movie Deep Impact where the asteroid hits the pla The size of the tsunami would be so large that just like in the movie buildings would be decimated and the surg would be immense. I do like how it showed how the water recedes before the wave hits. It actually shows just would happen if it hit the Atlantic ocean. https://www.youtube.com/watch?v=fl0USo6q1js Coastal Impacts There are a variety of coastal vulnerabilities caused by tsunamis. As noted in previous modules, there are two types of effects of tsunamis (and all disasters). The primary effects are pretty straight forward. Areas at most risk of tsunamis are highly populated coastal regions such as major cities. And if the tsunami occurs during high tide, the fingers of destruction will reach farther inland. Most of the deaths from the Asian tsunami of 2004 were from flooding and the actual debris within the water. Other primary effects include coastal erosion and the destruction of ecosystems. The following are aerial photographs of tsunamis from National Geographic. The secondary effects of tsunamis are less obvious. These include contaminated water sources, disease outbreaks, chemical pollution, homelessness, and economic loss. Sometimes the secondary effects are worse than the primary effects because all the new attention occurs with the primary effects, but very little attention is on the region after a few months. The Great East Japan Earthquake of 2011 was the most documented natural disaster in human history. Click here to view some amazing aerial imagery of this catastrophic event. 6.4 Mitigation Against Tsunamis People and ecosystems are quite resilient to natural disasters, but a lot must be done to prevent massive death and destruction to begin with. After a deadly tsunami in Hawaii in the 1950s, the United States developed the Pacific Tsunami Warning Center. If a M 7.5 earthquake occurs somewhere in the Ring of Fire, a tsunami watch is released by NOAA indicating that a seismic event just occurred that could have generated a tsunami. Out in the Pacific Ocean, a system of instruments on the ocean floor and buoys monitor the Pacific Ocean for tsunamis. If the system detects a tsunami, a signal is sent to satellites, which is then sent to coastal areas and a tsunami warning is announced. Another mitigation measure is tsunami run-up maps. A tsunami run-up map indicates how far a tsunami will travel inland based on the continental shelf and strength of the tsunami. By understanding where and how far a tsunami will travel inland, government agencies can determine proper zoning and building codes. Before the Asian tsunami of 2004, the United States had tsunami run-up maps of Indonesia but were considered classified. Indonesia, being a poorer nation, did not have run-up maps for their own nation. After the catastrophic event, the U.S. military saw how destabilizing this was to the nation and decided to release this information from the run-up maps to the region. Editor Notes/Ancient warning: In a small town in Japan there was a very early warning system in place that was centuries old. It was a stone marker that read "High dwellings are the peace and harmony of our descendants, remember the calamity of the great tsunamis. Do not build any homes below this point." The people of this little village were kept safe because they listened to the marker and got above the line indicated. This shows that we need to learn from the disasters of the past and at times the simplest warning is the best. Other ways the impacts of tsunamis can be minimized include: Strong building codes and zoning policies that are enforced by local officials Planting and protecting existing natural barriers such as vegetation and coastal areas Proper education of how to prepare and what to do during and after a tsunami Recent Tsunami Catastrophes Image of the first incoming tsunami wave off the coast of Thailand. The video on the left is about the magnitude 9.1 earthquake and tsunami near Indonesia, called the Sumatra-Andaman Earthquake, in the Indian Ocean on December 26, 2004 that killed over 200,000 people. The earthquake occurred along a oceanic-to-oceanic subduction zone and created a fault scarp 60 feet high for nearly 800 miles. The video on the right is about the Great East Japan Earthquake of 2011. There a magnitude 9.0 earthquake along an oceanic-to-oceanic subduction zone generated a powerful tsunami that killed the most documented natural disaster event in human history. Editor’s Note/Photographs: I found an article online that shows some of the areas hit by the 2004 tsunami and how they have been rebuilt. The article is at the link here http://www.dailymail.co.uk/news/article-2867055/Indonesia-rebuilds-stunning-series-imagescountry-risen-ashes-tsunami-decade-on.html but here are some of the pictures I found the most dramatic.