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Changes in the Air Some volcanoes erupt quietly; others violently shoot gas, steam and ash into the air. After a volcano erupts, gases are released into the atmosphere. These gases include water vapor as well as carbon dioxide, sulfur dioxide, hydrogen sulfide, carbon monoxide, hydrogen gas and methane. All of these gases can form acid rain in high concentrations. Incorporated in the mass of gases expelled from a volcano exist tiny rock particles called tephra. Tephra particles can adhere to gas particles and be carried for great distances according to the U.S. Geological Survey. The immediate effect of high concentrations of gas in the air result in closure of the airspace above and around the volcano to air traffic. Over time, upper level winds can carry volcanic gases around the world.Ash particles impede air traffic as well as create immense breathing difficulties for people living near an erupting volcano. After a volcano, these 2-mm or smaller ash particles fly through the air, coating everything near the volcano. Ash particles can form a layer just like snow but it's much harder to remove. Combined with water, the ash becomes a mud-like mass. The Federal Aviation Administration monitors volcano eruptions to prevent planes from traveling in areas with possible ash particles in the air due to the dangers of loss of visibility and possible engine failure. Ash particle clouds also rise into the atmosphere for transportation with the prevailing winds, making their existence dangerous to any aircraft flying in the vicinity. Changes to the Landscape Every volcano makes a change to the landscape of the earth after an eruption. Volcanoes build new earth with every eruption, spewing hot lava from deep inside the earth onto the much cooler surface. After a volcano erupts, the magma flows down the sides of the volcano, reaching a point where it cools enough to stop flowing. As the flow progresses, everything in the lava's path is consumed. Plants, animals, buildings, roads, and trees are burned completely. Lava flows cool over time and form new rock. Wind, rain, and water after lava flows with weathering to break down lava and turn it into soil. When a volcano expels high volumes of ash, this coats the surface of the land around a volcano. This creates a dangerous condition of unstable earth with a thick layer of ash coating the sides of mountains and hillsides. Lahars are violent mudslides that result of waterlogged ash rushing down the sides of a mountain. These dangerous mudslides carry ash, rock, and debris, obliterating everything in its path. Changes to the Water Rivers and streams near erupting volcanoes suffer the effects of ash, hot gases and lava. After a volcano erupts, the debris expelled by the volcano affects waterways in a number of ways. Streams and rivers form a very basic part of the hydrologic cycle to disperse water through a drainage basin toward the sea. Volcanoes disrupt this process by blocking stream and river bed flows, re-routing courses, and contaminating the water supply with dangerous gases and particles. Fine ash can be carried away easily by water, but it takes time to restore a waterway after an eruption. Effects on Plants and Animals Like humans, animals can survive with little permanent effect resulting from ash deposition--as long as the ash isn't too hot and doesn't cover their source of food. The greatest threat from a volcano comes from damage to the environment. Ash quickly contaminates water, a necessity for any animal. Without access to an untainted water supply, many wild animals move to safer areas. Fish are extremely susceptible to a change in water quality. Volcanic eruptions often result in complete kills in streams and rivers near volcanoes. Ash contaminates the water, and burned or dead trees don't provide enough shade along these rivers to keep water temperatures down. High sediment content in the water prevents proper feeding, movement and reproduction. Birds naturally have difficulty flying in areas with ash clouds. Hot gases are deadly to birds as well. Plants and trees suffer from the effects of heat generated by the eruption and deposition of ash and sediments. However, unburned trees recover and usually continue growing after ash is washed off the tree itself. According to the U.S. Geological Survey, the increased amount of erosion possible with ash and tephra depositions creates slower re-vegetation of any damaged areas. Tephra contains potassium and phosphorus that are valuable nutrients for rich, fertile soil. Weathering helps release these nutrients into the soil, creating the prime environment for renewed growth of native plants and trees.

A tsunami is a series of waves generated in an ocean or other body of water by a disturbance such as an earthquake, landslide, volcanic eruption, or meteorite impact. The picture at the left shows how an earthquake can generate a tsunami in the overlying water.

Causes of earthquakes If seen broadly we can say that earthquakes are caused due to two major reasons. The first reason is the eruption of volcanoes, which are sudden, and as is known volcanoes are seat of inner disturbance and can effect the plates which is the second cause of earthquakes. Earthquakes are caused due to disturbance in the movement of plates, which again can be caused due to various reasons like under crust waves or cracks in the plates. Plate Tectonic Theory The outer layer of the earth is divided into many sections known as plates, which are floating on the molten magma beneath the earth’s crust. Now the movement of these plates is determined by the convection current in the molten magma. The heat makes these plates rise and vice versa. Therefore after intervals there are plates that get submerged in the molten magma and there plates that rise upwards and at times even new crust is formed from the molten magma which in turn forms a new plate until it connects itself with the already existing ones. At times these plates and can be pushed up to form mountains and hills and the movement is so slow that it is really hard to comprehend that there is any movement at all. The movement and the results come out to be visible suddenly. Now these plates are the bases on which the continents stand and when these plates move the continents also move. Most of the earthquakes occur on the edges of the plates where a plate is under one or across. This movement disrupts the balance and position of all plates, which leads to tremors, which are called earthquakes.

The causes of landslides are usually related to instabilities in slopes. It is usually possible to identify one or more landslide causes and one landslide trigger. The difference between these two concepts is subtle but important. The landslide causes are the reasons that a landslide occurred in that location and at that time. Landslide causes are listed in the following table, and include geological factors, morphological factors, physical factors and factors associated with human activity. Causes may be considered to be factors that made the slope vulnerable to failure, that predispose the slope to becoming unstable. The trigger is the single event that finally initiated the landslide. Thus, causes combine to make a slope vulnerable to failure, and the trigger finally initiates the movement. Landslides can have many causes but can only have one trigger as shown in the next figure. Usually, it is relatively easy to determine the trigger after the landslide has occurred (although it is generally very difficult to determine the exact nature of landslide triggers ahead of a movement event). Occasionally, even after detailed investigations, no trigger can be determined - this was the case in the large Mount Cook landslide in New Zealand 1991. It is unclear as to whether the lack of a trigger in such cases is the result of some unknown process acting within the landslide, or whether there was in fact a trigger, but it cannot be determined. Perhaps this is because the trigger was in fact a slow but steady decrease in material strength associated with the weathering of the rock - at some point the material becomes so weak that failure must occur. Hence the trigger is the weathering process, but this is not detectable externally. In most cases we think of a trigger as an external stimulus that induces an immediate or near-immediate response in the slope, in this case in the form of the movement of the landslide. Generally this movement is induced either because the stresses in the slope are altered, perhaps by increasing shear stress or decreasing the effective normal stress, or by reducing the resistance to the movement perhaps by decreasing the shear strength of the materials within the landslide.

When two oceanic tectonic plates converge, one is subducted or pulled under, the other. This convergent activity allows for magma from the earth's core to erupt at the point of contact. The cooled erupted lava and debris build up over time. When the pile of debris and lava build up high enough, land is formed above sea level. This land is called an island. Often, these island volcanoes stay active, continuously growing.

The Ring of Fire, also known as the Circum-Pacific Belt, is a string of islands with active volcanoes in the Pacific Ocean. This geographical region is the most active volcanic and seismic zone in the world, and corresponds with oceanic-continental convergence of multiple tectonic plates.