A natural disaster is a major adverse event resulting from natural processes of the Earth. A natural disaster can cause loss of life or damage property, leaves some economic damage in its wake, the severity of which depends on the affected population's resilience, or ability to recover and on the infrastructure available. An adverse event will not rise to the level of a disaster if it occurs in an area without vulnerable population. In a vulnerable area, such as Nepal during the 2015 earthquake, an earthquake can have disastrous consequences and leave lasting damage, which can require years to repair. A landslide is described as an outward and downward slope movement of an abundance of slope-forming materials including rock, artificial, or a combination of these things. During World War I, an estimated 40,000 to 80,000 soldiers died as a result of avalanches during the mountain campaign in the Alps at the Austrian-Italian front. Many of the avalanches were caused by artillery fire. An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves.
At the Earth's surface, earthquakes manifest themselves by vibration and sometimes displacement of the ground. Earthquakes are caused by slippage within geological faults; the underground point of origin of the earthquake is called the seismic focus. The point directly above the focus on the surface is called the epicenter. Earthquakes by themselves kill people or wildlife, it is the secondary events that they trigger such as building collapse, fires and volcanoes. Many of these could be avoided by better construction, safety systems, early warning and planning; when natural erosion, human mining or underground excavation makes the ground too weak to support the structures built on it, the ground can collapse and produce a sinkhole. For example, the 2010 Guatemala City sinkhole which killed fifteen people was caused when heavy rain from Tropical Storm Agatha, diverted by leaking pipes into a pumice bedrock, led to the sudden collapse of the ground beneath a factory building. Volcanoes can cause widespread consequent disaster in several ways.
The effects include the volcanic eruption itself that may cause harm following the explosion of the volcano or falling rocks. Secondly, lava may be produced during the eruption of a volcano, so as it leaves the volcano the lava destroys many buildings and animals due to its extreme heat. Thirdly, volcanic ash meaning the cooled ash, may form a cloud, settle thickly in nearby locations; when mixed with water this forms a concrete-like material. In sufficient quantities, ash may cause roofs to collapse under its weight but small quantities will harm humans if inhaled. Since the ash has the consistency of ground glass, it causes abrasion damage to moving parts such as engines; the main killer of humans in the immediate surroundings of a volcanic eruption is the pyroclastic flows, which consist of a cloud of hot volcanic ash which builds up in the air above the volcano and rushes down the slopes when the eruption no longer supports the lifting of the gases. It is believed. A lahar is landslide; the 1953 Tangiwai disaster was caused by a lahar, as was the 1985 Armero tragedy in which the town of Armero was buried and an estimated 23,000 people were killed.
Volcanoes rated at 8 on the Volcanic Explosivity Index are known as supervolcanoes. According to the Toba catastrophe theory, 75,000 to 80,000 years ago a supervolcanic eruption at what is now Lake Toba in Sumatra reduced the human population to 10,000 or 1,000 breeding pairs, creating a bottleneck in human evolution, killed three-quarters of all plant life in the northern hemisphere. However, there is considerable debate regarding the veracity of this theory; the main danger from a supervolcano is the immense cloud of ash, which has a disastrous global effect on climate and temperature for many years. A violent and destructive change either in the quality of Earth's water or in the distribution or movement of water on land below the surface or in the atmosphere. A flood is an overflow of water that'submerges' land; the EU Floods Directive defines a flood as a temporary covering the land with water, not covered by water. In the sense of'flowing water', the word may be applied to the inflow of the tides.
Flooding may result from the volume of water within a body of water, such as a river or lake, which overflows, causing some of the water to escape its usual boundaries. While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, it is not a significant flood unless the water covers land used by man, like a village, city or other inhabited area, expanses of farmland, etc. A tsunami known as a seismic sea wave or as a tidal wave, is a series of waves in a water body caused by the displacement of a large volume of water in an ocean or a large lake. Tsunamis can be caused by undersea earthquakes such as the 2004 Boxing Day tsunami, or by landslides such as the one in 1958 at Lituya Bay, Alaska, or by volcanic eruptions such as the ancient eruption of Santorini. On March 11, 2011, a tsunami occurred near Fukushima and spread through the Pacific Ocean. A limnic eruption occurs when a gas CO2 erupts from deep lake water, posing the threat of suffocating wildlife and humans.
Such an eruption may cause tsunamis in the la
Andersonville National Historic Site
The Andersonville National Historic Site, located near Andersonville, preserves the former Camp Sumter, a Confederate prisoner-of-war camp during the final twelve months of the American Civil War. Most of the site lies in southwestern Macon County, adjacent to the east side of the town of Andersonville; as well as the former prison, the site contains the Andersonville National Cemetery and the National Prisoner of War Museum. The prison was made in February 1864 and served to April 1865; the site was commanded by Captain Henry Wirz, tried and executed after the war for war crimes. It was overcrowded to four times its capacity, with an inadequate water supply, inadequate food rations, unsanitary conditions. Of the 45,000 Union prisoners held at Camp Sumter during the war, nearly 13,000 died; the chief causes of death were scurvy and dysentery. The prison, which opened in February 1864 covered about 16.5 acres of land enclosed by a 15-foot high stockade. In June 1864, it was enlarged to 26.5 acres.
The stockade was rectangular, of dimensions 1,620 feet by 779 feet. There were two entrances on the west side of the stockade, known as "north entrance" and "south entrance". Robert H. Kellogg, sergeant major in the 16th Regiment Connecticut Volunteers, described his entry as a prisoner into the prison camp, May 2, 1864: As we entered the place, a spectacle met our eyes that froze our blood with horror, made our hearts fail within us. Before us were forms that had once been erect. Many of our men, in the heat and intensity of their feeling, exclaimed with earnestness. "Can this be hell?" "God protect us!" and all thought that he alone could bring them out alive from so terrible a place. In the center of the whole was a swamp, occupying about three or four acres of the narrowed limits, a part of this marshy place had been used by the prisoners as a sink, excrement covered the ground, the scent arising from, suffocating; the ground allotted to our ninety was near the edge of this plague-spot, how we were to live through the warm summer weather in the midst of such fearful surroundings, was more than we cared to think of just then.
Further descriptions of the camp can be found in the diary of Ransom Chadwick, a member of the 85th New York Infantry Regiment. Chadwick and his regimental mates were taken to the Andersonville Prison, arriving on April 30, 1864. An extensive and detailed diary was kept by John L. Ransom of his time as a prisoner at Andersonville. Father Peter Whelan arrived on 16 June 1864 to muster the resources of the Catholic church and help provide relief to the prisoners. At Andersonville, a light fence known as "the dead line" was erected 19 feet inside the stockade wall, it demarcated a no-man's land that kept prisoners away from the stockade wall, made of rough-hewn logs about 16 feet high and stakes driven into the ground. Anyone crossing or touching this "dead line" was shot without warning by sentries in the pigeon roosts. At this stage of the war, Andersonville Prison was undersupplied with food. By 1864, not only civilians living within the Confederacy but the soldiers of the Confederate Army itself were struggling to obtain sufficient quantities of food.
The shortage of fare was suffered by prisoners and Confederate personnel alike within the fort, but the prisoners received less than the guards, who unlike their captives did not become emaciated or suffer from scurvy. The latter was a major cause of the camp's high mortality rate, as well as dysentery and typhoid fever, which were the result of filthy living conditions and poor sanitation; when sufficient quantities of supplies were available, they were of poor quality and inadequately prepared. There were no new outfits given to prisoners, whose own clothing was falling to pieces. In some cases, garments were taken from the dead. John McElroy, a prisoner at Andersonville, recalled "Before one was cold his clothes would be appropriated and divided, I have seen many sharp fights between contesting claimants."Although the prison was surrounded by forest little wood was allowed to the prisoners for warmth or cooking. This, along with the lack of utensils, made it impossible for the prisoners to cook the meagre food rations they received, which consisted of poorly milled cornflour.
During the summer of 1864, Union prisoners suffered from hunger and disease. Within seven months, about a third had died from scurvy. In 1864, the Confederate Surgeon General asked Joseph Jones, an expert on infectious disease, to investigate the high mortality rate at the camp, he concluded that it was due to "scorbutic dysentery". In 2010, the historian Drisdelle said that hookworm disease, a condition not recognized or known during the Civil War, was the major cause of much of the fatalities amongst the prisoners; the water supply from Stockade Creek became polluted when too many Union prisoners were housed by the Confederate authorities within the prison walls. Part of the creek was used as a sink, the men were forced to wash themselves in the creek. At the time of the Civil War, the concept of a prisoner of
East Point, Georgia
East Point is a suburban city located southwest of Atlanta in Fulton County, United States. As of the 2010 census, the city had a population of 33,712; the city name is derived from being at the opposite end of the former Atlanta & West Point Railroad from West Point. The name "East Point" derives from the fact that this is the terminus of the Atlanta & West Point Railroad in the east; this settlement was founded as a railroad terminus with 16 families in 1870, but grew after it became an inviting place for industry to develop. Soon it boasted the railway, two gristmills, a government distillery located on Connally Drive. One of the earliest buildings was the factory of the White Hickory Manufacturing Company, built by B. M. Blount and L. M. Hill. By 1880 the town had two churches, a common school, a steam-cotton gin, a sawmill, a post office, a telegraph office and its own newspaper weekly, The Plow Boy. East Point ranked as a grain and cotton-growing center. With its pleasant upland climate and proximity to the railway, it was a popular summer resort for people from the city of Atlanta.
In 1884 the first telephone rang in East Point, in 1887 the city received its first charter. In 1890 a major portion of property along East Point Avenue was subdivided and developed, opening the way for more homes, more churches, more people, more places of employment. By 1892 Main Street was completed, despite protests from a few progress-shy early settlers who maintained that one major thoroughfare, Newnan Road, was more than sufficient. By the start of the 20th century, the adolescent town was poised to grow into the city it would become. In late 2015 and early 2016, some scenes for the Netflix series Stranger Things were filmed at the exterior of the First Baptist Church; the city has a city council-city manager form of government, with a professional city manager hired by the council. The manager is approved by the eight-member city council, headed by the mayor; the city is divided into each electing two city council members. In the late 20th century, East Point suffered a loss of jobs due to railroad and industrial restructuring.
In the first quarter of the 21st century, its economy has expanded, new businesses and residences have been developed around the city. The new Camp Creek Marketplace, for example, boasts 718,590 sq. ft. of retail space, with new businesses moving in regularly. Several Fortune 500 companies call it home. In December 2007, the city's newest multiplex opened; the National Archives regional repository for data collected by the U. S. Census was located in the Colonial Hills area of East Point, it was moved to a new facility in nearby Morrow. The Federal Bureau of Prisons Southeast Region Office is in East Point. MARTA heavy rail subway and bus lines serve the city; the East Point Historic Civic Block consists of three significant buildings and one memorial park in downtown East Point. It is located within the parameters of East Point Street, Linwood Avenue, Church Street, West Cleveland Avenue; the City Hall, City Auditorium, New Deal Library, Victory Park make up the Civic Block, which since 2011 has been the focus of both redevelopment interest and historic preservation efforts.
East Point is served by Sumner Park, Sykes Park, Brookdale Park, Grayson Field, Jefferson Park, John Milner Park and Chris Stacks Field. The city boasts of producing several notable athletes, among them Reggie Rutland, Jonas Jennings, Nick Rogers, Bill Thorn, Donald Adams, John Milner and Jay Hudson; when the Dick Lane Velodrome was built in 1974, it was one of only two in the United States. Named after a longtime City Council member, the Velodrome was inspired by a facility seen by a group of residents and city officials who visited the Munich Olympics in 1972; the Velodrome is a 1/5 mile and 36° banked concrete track for bicycle racing, set in Sumner park in a residential part of historic East Point. Dick Lane is the only velodrome in the world with a green space that contains a large oak tree and a creek running through the in-field, it is located eight miles south of downtown Atlanta. The City of East Point owns the velodrome and has a long-term partnership with the East Point Velodrome Association to manage it.
The EPVA is a 100% volunteer-based 5013 nonprofit organization dedicated to the rehabilitation and growth of the Dick Lane Velodrome. The EPVA conducts Youth Service Activities for children at no cost to the state; these activities include the Bicycle Little League, summer camps, bicycle safety clinics. In addition to raising bicycle safety awareness, these programs promote physical health and wellness and individual growth through the sport, positive alternatives to drugs and gangs; these pioneering grass-root programs are intended to build the base of competitive cycling in the U. S. EPVA hosts three professional-level events annually, held in May and September. East Point is located at 33°40′34″N 84°27′05″W, it is bordered to the north and west by the city of Atlanta, to the southeast by Hapeville, to the south by College Park. Downtown Atlanta is 7 miles northeast of the center of East Point. According to the United States Census Bureau, East Point has a total area of 14.7 square miles, of which 0.02 square miles, or 0.12%, is water.
As of the census of 2000, there were 39,595 people, 14,553 household
American Civil War
The American Civil War was a war fought in the United States from 1861 to 1865, between the North and the South. The Civil War is the most studied and written about episode in U. S. history. As a result of the long-standing controversy over the enslavement of black people, war broke out in April 1861 when secessionist forces attacked Fort Sumter in South Carolina shortly after Abraham Lincoln had been inaugurated as the President of the United States; the loyalists of the Union in the North proclaimed support for the Constitution. They faced secessionists of the Confederate States in the South, who advocated for states' rights to uphold slavery. Among the 34 U. S. states in February 1861, secessionist partisans in seven Southern slave states declared state secessions from the country and unveiled their defiant formation of a Confederate States of America in rebellion against the U. S. Constitutional government; the Confederacy grew to control over half the territory in eleven states, it claimed the additional states of Kentucky and Missouri by assertions from exiled native secessionists without territory or population.
These were given full representation in the Confederate Congress throughout the Civil War. The two remaining slave holding states of Delaware and Maryland were invited to join the Confederacy, but nothing substantial developed; the Confederate States was never diplomatically recognized by the government of the United States or by that of any foreign country. The states that remained loyal to the U. S. were known as the Union. The Union and the Confederacy raised volunteer and conscription armies that fought in the South over the course of four years. Intense combat left 620,000 to 750,000 people dead, more than the number of U. S. military deaths in all other wars combined. The war ended when General Robert E. Lee surrendered to General Ulysses S. Grant at the Battle of Appomattox Court House. Confederate generals throughout the southern states followed suit. Much of the South's infrastructure was destroyed the transportation systems; the Confederacy collapsed, slavery was abolished, four million black slaves were freed.
During the Reconstruction Era that followed the war, national unity was restored, the national government expanded its power, civil rights were granted to freed black slaves through amendments to the Constitution and federal legislation. In the 1860 presidential election, led by Abraham Lincoln, supported banning slavery in all the U. S. territories. The Southern states viewed this as a violation of their constitutional rights and as the first step in a grander Republican plan to abolish slavery; the three pro-Union candidates together received an overwhelming 82% majority of the votes cast nationally: Republican Lincoln's votes centered in the north, Democrat Stephen A. Douglas' votes were distributed nationally and Constitutional Unionist John Bell's votes centered in Tennessee and Virginia; the Republican Party, dominant in the North, secured a plurality of the popular votes and a majority of the electoral votes nationally. He was the first Republican Party candidate to win the presidency.
However, before his inauguration, seven slave states with cotton-based economies declared secession and formed the Confederacy. The first six to declare secession had the highest proportions of slaves in their populations, with an average of 49 percent. Of those states whose legislatures resolved for secession, the first seven voted with split majorities for unionist candidates Douglas and Bell, or with sizable minorities for those unionists. Of these, only Texas held a referendum on secession. Eight remaining slave states continued to reject calls for secession. Outgoing Democratic President James Buchanan and the incoming Republicans rejected secession as illegal. Lincoln's March 4, 1861, inaugural address declared that his administration would not initiate a civil war. Speaking directly to the "Southern States", he attempted to calm their fears of any threats to slavery, reaffirming, "I have no purpose, directly or indirectly to interfere with the institution of slavery in the United States where it exists.
I believe I have no lawful right to do so, I have no inclination to do so." After Confederate forces seized numerous federal forts within territory claimed by the Confederacy, efforts at compromise failed and both sides prepared for war. The Confederates assumed that European countries were so dependent on "King Cotton" that they would intervene, but none did, none recognized the new Confederate States of America. Hostilities began on April 1861, when Confederate forces fired upon Fort Sumter. While in the Western Theater the Union made significant permanent gains, in the Eastern Theater, the battle was inconclusive during 1861–1862. In September 1862, Lincoln issued the Emancipation Proclamation, which made ending slavery a war goal. To the west, by summer 1862 the Union destroyed the Confederate river navy much of its western armies, seized New Orleans; the successful 1863 Union siege of Vicksburg split the Confederacy in two at the Mississippi River. In 1863, Robert E. Lee's Confederate incursion north ended at the Battle of Gettysburg.
Western successes led to Ulysses S. Grant's command of all Union armies in 1864. Inflicting an ever-tightening naval blockade of Confederate ports, the Union marshaled the resources and manpower to attack the Confederacy from all directions, leading to the fall of Atlanta to William T. Sherman and his march to th
ACF River Basin
The ACF River Basin is the drainage basin, or watershed, of the Apalachicola River, Chattahoochee River, Flint River, in the Southeastern United States. This area is alternatively known as the Apalachicola Basin and is listed by the United States Geological Survey as basin HUC 031300, as well as sub-region HUC 0313, it is located in the South Atlantic-Gulf Water Resource Region, listed as HUC 03. The basin is further sub-divided into 14 sub-basins; the ACF River Basin begins in the mountains of northeast Georgia, drains much of metro Atlanta, most of west Georgia and southwest Georgia and adjoining counties of southeast Alabama, before it splits the central part of the Florida Panhandle and flows into the Gulf of Mexico at Apalachicola Bay, near Apalachicola, Florida. It drains an area of 20,355 square miles. Most of the northern half of the basin abuts the Eastern Continental Divide on the east, the ACT River Basin to the west; these states and Alabama have been involved in a water-use dispute for two decades, known as the Tri-state water dispute.
Georgia has lobbied the United States Congress to end navigation on the Appalachicola and lower Chattahoochee, to conserve more water during droughts. Keeping the two rivers at a navigable depth during these times requires large releases from dams upstream, sending potential drinking water downstream for shipping, dropping lakes to levels dangerous to boaters. Other ecological conservation and economic concerns include protecting harvests of oysters in Apalachicola Bay, which require a large enough flow of fresh water to prevent excessive saltwater intrusion from the Gulf. Numerous endangered and imperiled species occur in the basin, including many endemic mussels The cost of dredging silt, much of it from uncontrolled growth across metro Atlanta's fine red clay soil, has been called wasteful to float so little ship traffic. U. S. Army Corps of Engineers: ACF Basin website Florida DEP: Apalachicola River Watershed
Soil mechanics is a branch of soil physics and applied mechanics that describes the behavior of soils. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids and particles but soil may contain organic solids and other matter. Along with rock mechanics, soil mechanics provides the theoretical basis for analysis in geotechnical engineering, a subdiscipline of civil engineering, engineering geology, a subdiscipline of geology. Soil mechanics is used to analyze the deformations of and flow of fluids within natural and man-made structures that are supported on or made of soil, or structures that are buried in soils. Example applications are building and bridge foundations, retaining walls and buried pipeline systems. Principles of soil mechanics are used in related disciplines such as engineering geology, geophysical engineering, coastal engineering, agricultural engineering and soil physics; this article describes the genesis and composition of soil, the distinction between pore water pressure and inter-granular effective stress, capillary action of fluids in the soil pore spaces, soil classification and permeability, time dependent change of volume due to squeezing water out of tiny pore spaces known as consolidation, shear strength and stiffness of soils.
The shear strength of soils is derived from friction between the particles and interlocking, which are sensitive to the effective stress. The article concludes with some examples of applications of the principles of soil mechanics such as slope stability, lateral earth pressure on retaining walls, bearing capacity of foundations; the primary mechanism of soil creation is the weathering of rock. All rock types may be broken down into small particles to create soil. Weathering mechanisms are physical weathering, chemical weathering, biological weathering Human activities such as excavation and waste disposal, may create soil. Over geologic time buried soils may be altered by pressure and temperature to become metamorphic or sedimentary rock, if melted and solidified again, they would complete the geologic cycle by becoming igneous rock. Physical weathering includes temperature effects and thaw of water in cracks, wind and other mechanisms. Chemical weathering includes dissolution of matter composing a rock and precipitation in the form of another mineral.
Clay minerals, for example can be formed by weathering of feldspar, the most common mineral present in igneous rock. The most common mineral constituent of silt and sand is quartz called silica, which has the chemical name silicon dioxide; the reason that feldspar is most common in rocks but silica is more prevalent in soils is that feldspar is much more soluble than silica. Silt and Gravel are little pieces of broken rocks. According to the Unified Soil Classification System, silt particle sizes are in the range of 0.002 mm to 0.075 mm and sand particles have sizes in the range of 0.075 mm to 4.75 mm. Gravel particles are broken pieces of rock in the size range 4.75 mm to 100 mm. Particles larger than gravel are called boulders. Soil deposits are affected by the mechanism of deposition to their location. Soils that are not transported are called residual soils—they exist at the same location as the rock from which they were generated. Decomposed granite is a common example of a residual soil.
The common mechanisms of transport are the actions of gravity, ice and wind. Wind blown soils include dune loess. Water carries particles of different size depending on the speed of the water, thus soils transported by water are graded according to their size. Silt and clay may settle out in a lake, gravel and sand collect at the bottom of a river bed. Wind blown soil deposits tend to be sorted according to their grain size. Erosion at the base of glaciers is powerful enough to pick up large rocks and boulders as well as soil. Gravity on its own may carry particles down from the top of a mountain to make a pile of soil and boulders at the base; the mechanism of transport has a major effect on the particle shape. For example, low velocity grinding in a river bed will produce rounded particles. Freshly fractured colluvium particles have a angular shape. Silts and gravels are classified by their size, hence they may consist of a variety of minerals. Owing to the stability of quartz compared to other rock minerals, quartz is the most common constituent of sand and silt.
Mica, feldspar are other common minerals present in sands and silts. The mineral constituents of gravel may be more similar to that of the parent rock; the common clay minerals are montmorillonite or smectite and kaolinite or kaolin. These minerals tend to form in sheet or plate like structures, with length ranging between 10−7 m and 4x10−6 m and thickness ranging between 10−9 m and 2x10−6 m, they have a large specific surface area; the specific surface area is defined as the ratio of the surface area of particles to the mass of the particles. Clay minerals have specific surface areas in the range of 10 to 1,000 square meters per gram of solid. Due to the large surface area available for chemical and van der Waals interaction, the mechanical behavior of clay minerals is sensitive to the amount of pore fluid available and the type and amount of dissolved ions in the pore fluid. To
A wetland is a distinct ecosystem, inundated by water, either permanently or seasonally, where oxygen-free processes prevail. The primary factor that distinguishes wetlands from other land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique hydric soil. Wetlands play a number of functions, including water purification, water storage, processing of carbon and other nutrients, stabilization of shorelines, support of plants and animals. Wetlands are considered the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal life. Whether any individual wetland performs these functions, the degree to which it performs them, depends on characteristics of that wetland and the lands and waters near it. Methods for assessing these functions, wetland ecological health, general wetland condition have been developed in many regions and have contributed to wetland conservation by raising public awareness of the functions and the ecosystem services some wetlands provide.
Wetlands occur on every continent. The main wetland types are swamp, marsh and fen. Many peatlands are wetlands; the water in wetlands is either brackish, or saltwater. Wetlands can be non-tidal; the largest wetlands include the Amazon River basin, the West Siberian Plain, the Pantanal in South America, the Sundarbans in the Ganges-Brahmaputra delta. The UN Millennium Ecosystem Assessment determined that environmental degradation is more prominent within wetland systems than any other ecosystem on Earth. Constructed wetlands are used to treat municipal and industrial wastewater as well as stormwater runoff, they may play a role in water-sensitive urban design. A patch of land that develops pools of water after a rain storm would not be considered a "wetland" though the land is wet. Wetlands have unique characteristics: they are distinguished from other water bodies or landforms based on their water level and on the types of plants that live within them. Wetlands are characterized as having a water table that stands at or near the land surface for a long enough period each year to support aquatic plants.
A more concise definition is a community composed of hydric soil and hydrophytes. Wetlands have been described as ecotones, providing a transition between dry land and water bodies. Mitsch and Gosselink write that wetlands exist "...at the interface between terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet dependent on both."In environmental decision-making, there are subsets of definitions that are agreed upon to make regulatory and policy decisions. A wetland is "an ecosystem that arises when inundation by water produces soils dominated by anaerobic and aerobic processes, which, in turn, forces the biota rooted plants, to adapt to flooding." There are four main kinds of wetlands – marsh, swamp and fen. Some experts recognize wet meadows and aquatic ecosystems as additional wetland types; the largest wetlands in the world include the swamp forests of the Amazon and the peatlands of Siberia. Under the Ramsar international wetland conservation treaty, wetlands are defined as follows: Article 1.1: "...wetlands are areas of marsh, peatland or water, whether natural or artificial, permanent or temporary, with water, static or flowing, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres."
Article 2.1: " may incorporate riparian and coastal zones adjacent to the wetlands, islands or bodies of marine water deeper than six metres at low tide lying within the wetlands." Although the general definition given above applies around the world, each county and region tends to have its own definition for legal purposes. In the United States, wetlands are defined as "those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, that under normal circumstances do support, a prevalence of vegetation adapted for life in saturated soil conditions. Wetlands include swamps, marshes and similar areas"; this definition has been used in the enforcement of the Clean Water Act. Some US states, such as Massachusetts and New York, have separate definitions that may differ from the federal government's. In the United States Code, the term wetland is defined "as land that has a predominance of hydric soils, is inundated or saturated by surface or groundwater at a frequency and duration sufficient to support a prevalence of hydrophytic vegetation adapted for life in saturated soil conditions and under normal circumstances supports a prevalence of such vegetation."
Related to this legal definitions, the term "normal circumstances" are conditions expected to occur during the wet portion of the growing season under normal climatic conditions, in the absence of significant disturbance. It is not uncommon for a wetland to be dry for long portions of the growing season. Wetlands can be dry during the dry season and abnormally dry periods during the wet season, but under normal environmental conditions the soils in a wetland will be saturated to the surface or inundated such that the soils become anaerobic, those conditions will persist through the wet portion of the growing season; the most important factor producing wetlands is flooding. The duration of flooding or prolonged soil saturation by groundwater determines whether the resulting wetland has aquatic, marsh or swamp vegetation