Composite volcanoes, also called strato volcanoes, are formed by alternating layers of lava and rock fragments. This is the reason they are called composite. Strato-volcanoes often form impressive, snow-capped peaks which are often exceeding 2500m in height, 1000sq.km in surface, and 400km3 in volume. Between eruptions they are often so quiet they seem extinct. To witness the start of a great eruption requires luck or very careful surveillance. Composite volcanoes usually erupt in an explosive way. This is usually caused by viscous magma. When very viscous magma rises to the surface, it usually clogs the craterpipe, and gas in the craterpipe gets locked up. Therefore, the pressure will increase resulting in an explosive eruption. Although strato-volcanoes are usually large and conical, we can distinguish different shapes of them: concave (like Agua), pyramidal (like Stromboli), convex-concave (like Vesuvius), helmet-shaped (like Mount Rainier), collapse caldera (like Graciosa), nested (like El Piton in Teide), multiple summits (like Shasta), elongated along a fissure (like Hekla). Strato-volcanoes are constructed along subduction zones. Examples of composite volcanoes include Mount Hood, Mount Rainier, Mount Shield volcanoes are huge in size. They are built by many layers of runny lava flows. Lava spills out of a central vent or group of vents. A broad shaped, gently sloping cone is formed. This is caused by the very fluid, basaltic lava which can't be piled up into steep mounds. Shield volcanoes may be produced by hot spots which lay far away from the edges of tectonic plates. Shields also occur along the mid-oceanic ridge, where sea-floor spreading is in progress and along subduction related volcanic arcs. The eruptions of shield volcanoes are characterized by low-explosivity lava-fountaining that forms cinder cones and spatter cones at the vent. Famous shield volcanoes can be found for example in Hawaii (e.g. A cinder cone is a steep conical hill formed above a vent. Cinder cones are among the most common volcanic landforms found in the world. They aren't famous as their eruptions usually don't cause any loss of life. Cinder cones are chiefly formed by Strombolian eruptions. The cones usually grow up in groups and they often occur on the flanks of strato volcanoes and shield volcanoes. Cinder cones are built from lava fragments called cinders. The lava fragments are ejected from a single vent and accumulate around the vent when they fall back to earth. Cinder cones grow rapidly and soon approach their maximum size. They rarely exceed 250m in height and 500m in diameter. The shape of a cinder cone can be modified during its (short) life. When the position of the vent alters, aligned, twin or secant cones develop. Nested,buried or breached cones are formed when the power of the eruption varies. A great example of a cinder cone is Paricutín in Mexico.
Spatter Cone. - When hot erupting lava contains just enough explosive gas to prevent the formation of a lava flow, but not enough to shatter it into small fragments the lava is torn by expanding gases into fluid hot clots, ranging in size from 1cm to 50cm across, called spatter. When the spatter falls back to Earth the clots weld themselves together and solidify forming steep-sided accumulations. These accumulations focused on an individual vent are called spatter cones.

Complex volcanoes- In fact all volcanoes could be complex volcanoes since all of them are made up of multiple flows, ash layers, domes, cones, etc. in varying amounts. However, when we call a volcano a complex volcano it is because we mean the "system" of those volcanoes is not "simple". Caldera complexes for instance have often got a large caldera with many subsidiary vents and deposits, some of which could be considered "volcanoes" in their own right.

Fissure volcanoes have no central crater at all. Instead,giant cracks open in the ground and expel vast quantities of lava.
This lava spreads far and wide to form huge poolsthat can cover almost everything around. When these pools of lava cool and solidify, the surfaceremains mostly flat. Since the source cracks are usually buried, there is often nothing "volcano-like" to see - only a flat plain. A fissure eruption occured at the Los Pilasvolcano in Nicaragua in 1952.

Lava domes
Volcanic or lava domes are formed by relatively small, bulbous masses of lava too viscous to flow any great distance; consequently, on extrusion, the lava piles over and around its vent. A dome grows largely by expansion from within. As it grows its outer surface cools and hardens, then shatters, spilling loose fragments down its sides. Some domes form craggy knobs or spines over the volcanic vent, whereas others form short, steep-sided lava flows known as “coulees.”
Volcanic domes commonly occur within the craters or on the flanks of large composite volcanoes. The nearly circular Novarupta Dome that formed during the 1912 eruption of Katmai Volcano, Alaska, measures 800 feet across and 200 feet high. The internal structure of this dome—defined by layering of lava fanning upward and outward from the center—indicates that it grew largely by expansion from within. Mont Pelée in Martinique, Lesser Antilles, and Lassen Peak and Mono domes in California are examples of lava domes. An extremely destructive eruption accompanied the growth of a dome at Mont Pelée in 1902. The coastal town of St. Pierre, about 4 miles downslope to the south, was demolished and nearly 30,000 inhabitants were killed by an incandescent, high-velocity ash flow and associated hot gases and volcanic dust
. Three Types of Rocks That Form When Lava Cools
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Balsatic Lava
There are three different types of basaltic lava flow. This lava typically flows from spatter cones, scoria cones, fissure systems and shield volcanoes. The different types of flow will produce different surface structures. Pahoehoe lava can have a ropy, billowy or smooth surface. As the lava cools it becomes less fluid and acts like a plastic substance. These lavas are the first to come out of volcanoes. A'a flows are thicker than pahoehoe lavas and move faster. At the front of the flow is a lot of rubble.
Silica Lava-The amount of silica also is used to classify different lava. Basaltic lava has low levels of silica at levels under 52 percent. Andesitic lava contains between 52 and 63 percent silica. Rhyolitic lava contains more than 63 percent silica. The rate of flow is based on the silica content as lavas with low silica have lower viscosity and will flow faster. Lava with higher contents of silica will flow very slowly.
Alkaline Lava-Some lava also can be classified based on the alkaline content. The alkaline content refers to the amount of sodium oxide and potassium oxide. Lava types with mild levels of alkaline include alkali basalt, trachyandesite, trachybasalt, comendite and trachyte. Lava that contains high levels of alkaline compounds include tephrite, tephriphonolite, phonolite and tephrite. Alkaline lavas are typically found near oceanic and continental settings.
Unusual Lavas-Several lavas exist that are unusual and rarely found. Carbonatites contain more than 50 percent carbonite and less than 10 percent silica. There are only 330 sites around the world that contain carbonatites lava. These types of lava erupt at temperatures between 500 and 600 degrees Celsius, a low temperature for volcanic eruptions. Komatites is found in South Africa along the Komati River. This type of lava has more than 18 percent magnesium oxide and a low silica content of between 40 to 45 percent. These are the oldest types of lava as there are no modern lava flows. The youngest komatites lava is 90 million years old.

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Pahoehoe lava is usually the first kind of lava to erupt from a volcano. The lava that flows from Pahoehoe flows is very viscous, that means that it is thin and liquid. It has a smooth surface that dries pretty quickly and becomes thicker and flows more slowly than the still hot lava below the surface. As the surface of the flow dries, it turn black and becomes crusty. The top crust is not safe to walk on because it is weak and can collapse.
A'a lava flows have a rough surface made up of broken blocks of lava. These broken pieces of lava are called clinkers. It looks like little lava spines are sticking up from the lava as it moves. The lava is like paste because it is so thick and the clinkers travel on top of the lava flow. Below the top layer of the lava flow there is a core of slow viscous lava. The clinkers are burried by the front of the lava flow as the lava moves.
A lava flow is a molten river of melted rock. Lava flows do not come from explosive eruptions, but they just pour out of the top of a vent slowly. Lava flows burn and destroy everything in their paths. How fast lava flows depends on what the lava is made up, how steep the ground is, how much lava is flowing from the vent, and how wide the flow is. Basalt flows are thin enough to flow quickly for a long distance. Lava flows made up of andesite move very slowl and is called viscous because it is very thick. Viscous lava flows so slowly that lava domes can form over the mouth of a vent
When large amounts of lava pour into a crater a lake of lava is made. Once the lava that has collected in the crater has cooled and dried it is still called a lava lake
Pillow lava forms when lava pours into the ocean. The lava cools fast and makes a ball. As the lava continues to flow it forces an opening in the crust of the pillow and more flows out to form another pillow shape. Pillow lava is made from basalt lava flows that reaches a source of water. Sometimes scientists find pillow lava strings on the land. That helps them to know that an area of land was under water in the past.
A lava fountain is a large amount of lava that is thrown up into the air when gas bubbles expand in the melted rock. Most lava fountains range in height from 30 to 300 feet. Sometimes the fountain can be as tall as 1,500 feet tall.
Lava fountains erupt inside lava lakes, along a fissure, isolated vents or from lava tubes. 1. San Diego State University, Department of Geology - http://www.geology.sdsu.edu/how_volcanoes_work/Lavaflows.html Last visited 3-7-03

The movement of tectonic plates results in their inevitable convergence in some places. The types of convergence include consuming, where one plate passes under another (subduction), collisional, where both crumple and maintain pressure against each other, and transform, where the plate margins slip against one another.

Consuming plate margins, where one plate is subducted beneath the other, results in melting of some of the subducted plate at depth. Some of that magma rises to the surface of the other plate, forming volcanoes. The ongoing collison of the plates produces earthquakes, particularly when the motion between the plates is temporarily stopped by one plate becoming jammed. Whenm motion begins, it is usually associated with a major earthquake. Volcanoes also produce local earthquakes, due to motion along associated faults, and due to explosive activity within the magma chamber.

Collisional plates, where both continue to push against one another without being subducted, create large mountain ranges such as the Himalayas. These are associated with earthquakes because of the pressures and crumpling taking place. However, they are not associated with volcanoes, as magma is not being produced by the collisional process.

Transcurrent collision results in two plates sliding against one another (e.g. San Andreas Fault). This is certain to cause earthquakes, particularly when plates temporarily become jammed. As no magma is generated, volcanoes are unlikely here. the tectonic plates are the actual plates that make up the less-than-firm crust of the earth. These plates float on the magma layer of moltan rock underneth them. When they move and rub together, the vibrations are earthquakes. When the magma pushes up between the plates or in a weak point in a single plate it creates a volcano.
Volcanoes are formed because of the movements of plate tectonic

* When the environment becomes less valuable or damaged, environmental degradation is said to occur. There are many forms of environmental degradation. When habitats are destroyed, biodiversity is lost, or natural resources are depleted, the environment is hurt. Environmental degradation can occur naturally, or through human processes. The largest areas of concern at present are the loss of rain forests, air pollution and smog, ozone depletion, and the destruction of the marine environment. Pollution is occurring all over the world and poisoning the planet's oceans. Even in remote areas, the effects of marine degradation are obvious. In some areas, the natural environment has been exposed to hazardous waste. In other places, major disasters such as oil spills have ruined the local environment. Environmental degradation is a process through which the natural environment is compromised in some way, reducing biological diversity and the general health of the environment. This process can be entirely natural in origin, or it can be accelerated or caused by human activities. Many international organizations recognize environmental degradation as one of the major threats facing the planet, since humans have only been given one Earth to work with, and if the environment becomes irreparably compromised, it could mean the end of human existence. There are a number of ways in which environmental degradation can work. In a classic case, resources simply become depleted. Air, water, and soil are all resources which are vulnerable to depletion through overuse, as are natural resources like minerals and oil deposits. Habitat pressures which force animals into a small area can also contribute to resource depletion, as the animals consume a high volume of material in a small area.
Pollution is another cause of environmental degradation. When the environment becomes polluted, it means that toxic substances have rendered it unhealthy. Pollution can come from a variety of sources, including vehicle emissions, agricultural runoff, accidental chemical release from factories, and poorly-managed harvesting of natural resources. In some cases, pollution may be reversible with costly environmental remediation measures, and in other instances, it may take decades or even centuries for the environment to cope with the pollution.
Consumption overpopulation occurs when each individual in a population consumes too large a share of resources, resulting in pollution, environmental degradation, and resource depletion.
Many affluent, highly developed nations, including the U.S., suffer from consumption overpopulation. Highly developed nations represent 20% of the world’s population, yet they consume considerably more than half of its resources.
Fossil fuels are burned in order to meet the high demands of nations suffering from consumption overpopulation. Increased consumption puts a higher demand on fossil fuels in order to produce more materials. Global warming is a consequence of air pollution by fossil fuel-burning industries, including energy and transport systems, and of land clearing and certain other air pollutants, including methane gases produced by grazing animals such as cattle and sheep, nitrous oxides and CFC's.
Scientists increasingly agree that the earth's atmosphere is becoming warmer. A long-term rise in the global climate could cause sea levels to rise around the world and bring a number of other adverse consequences. Reliance on fossil fuels as an energy source and the widespread destruction and burning of forests are chiefly responsible for the carbon emissions that lie behind global warming.
Spaceship earth-One of the really nice things about living on earth is all of the stuff we don't have to worry about. We don't have to worry about running out of oxygen. There is always plenty of water somewhere on the planet. And where the soils and climate are right, we can find or grow ample food for ourselves. In short, the earth functions as a massive life-support system for over six billion humans as well as the trillions of other life forms that share the planet with us. How does our planetary life-support system work? There is no real mystery to the broad outlines of the story (although scientists continue to refine our understanding of various bits): the requirements for human life are provided by organisms and their interactions with the non-living environment. Energy from the sun powers the food webs and the water cycle and all parts of the system are interconnected. Outputs from one part of the system are inputs for another part. This linked output-input setup is often called feedback, and feedback is what keeps the system from careening out of bounds like a soccer ball. For earth, out of bounds might mean runaway global climate change (such as ice ages), or catastrophic loss of important species leading to the collapse of vital ecosystems, or wildly unusual extreme weather patterns and the consequent loss of life and property. This lesson is entitled Spaceship Earth to reinforce the idea that our planet is–in reality–like a spaceship hurtling through space on a long-duration mission. There is no resupply from outside sources. Recycling is as much a part of the natural order of things as is the sunrise everyday. Pollution occurs when there are outputs that cannot be used as inputs for something else. Pollution is harmful and can be downright dangerous. The connections between parts of the natural system are imperative to its normal operation. By actively thinking through what it takes to keep people alive on a spaceship, the students will come to understand more fully what it takes to keep people alive on this planet.
Sustainable earth
The earth is sustainable, just like the human body heals itself, as soon as it gets damaged. Or as soon as people damage it. But sometimes, that healing of its balance can be a bit rough. Clean water is essential for life, but most people in the developed world don't think much about the water they use for drinking, food preparation, and sanitation. In developing nations, however, the search for safe drinking water can be a daily crisis. Millions of people die each year, most of them children, from largely preventable diseases caused by a lack of access to clean water and proper sanitation.
Serious Challenges About 5,000 children die each day due to preventable diarrheal diseases such as cholera and dysentery, which spread when people use contaminated water for drinking or cooking. A lack of water for personal hygiene leads to the spread of totally preventable ailments like trachoma, which has blinded some six million people.Water woes also trap many low-income families in a cycle of poverty and poor education—and the poorest suffer most from lack of access to water. People who spend much of their time in ill health, caring for sick children, or laboriously collecting water at distances averaging 3.75 miles (6 kilometers) a day are denied educational and economic opportunities to better their lives.
The Path to Solutions The silver lining, Postel noted, is that many opportunities exist to use the water we do have more productively. Change begins with more efficient management of water resources.
"Seventy percent of all the water we use globally is for agriculture, so that's where we first have to become a lot more efficient through methods like drip irrigation and growing crops that are more suitable to the local climate," Postel said. "We still have too few incentives for farmers to use water more efficiently. Farmers are good businesspeople; they respond to incentives that affect their bottom line." The United National General Assembly has recognized "the right to safe and clean drinking water and sanitation as a human right that is essential for the full enjoyment of life and all human rights." Making that right become a universal reality, and providing each person on the planet with affordable access to the 20 to 50 liters of daily water required to sustain life, is a clear goal for the decades ahead.