Library of Alexandria
The Great Library of Alexandria in Alexandria, was one of the largest and most significant libraries of the ancient world. The Library was part of a larger research institution called the Mouseion, dedicated to the Muses, the nine goddesses of the arts; the idea of a universal library in Alexandria may have been proposed by Demetrius of Phalerum, an exiled Athenian statesman living in Alexandria, to Ptolemy I Soter, who may have established plans for the Library, but the Library itself was not built until the reign of his son Ptolemy II Philadelphus. The Library acquired a large number of papyrus scrolls, due to the Ptolemaic kings' aggressive and well-funded policies for procuring texts, it is unknown how many such scrolls were housed at any given time, but estimates range from 40,000 to 400,000 at its height. Alexandria came to be regarded as the capital of knowledge and learning, in part because of the Great Library. Many important and influential scholars worked at the Library during the third and second centuries BC, among many others: Zenodotus of Ephesus, who worked towards standardizing the texts of the Homeric poems.
During the reign of Ptolemy III Euergetes, a daughter library was established in the Serapeum, a temple to the Greco-Egyptian god Serapis. Despite the widespread modern belief that the Library was "burned" once and cataclysmically destroyed, the Library declined over the course of several centuries, starting with the purging of intellectuals from Alexandria in 145 BC during the reign of Ptolemy VIII Physcon, which resulted in Aristarchus of Samothrace, the head librarian, resigning from his position and exiling himself to Cyprus. Many other scholars, including Dionysius Thrax and Apollodorus of Athens, fled to other cities, where they continued teaching and conducting scholarship; the Library, or part of its collection, was accidentally burned by Julius Caesar during his civil war in 48 BC, but it is unclear how much was destroyed and it seems to have either survived or been rebuilt shortly thereafter. The Library dwindled during the Roman Period, due to lack of support, its membership appears to have ceased by the 260s AD.
Between 270 and 275 AD, the city of Alexandria saw a rebellion and an imperial counterattack that destroyed whatever remained of the Library, if it still existed at that time. The daughter library of the Serapeum may have survived after the main Library's destruction; the Serapeum was vandalized and demolished in 391 AD under a decree issued by Coptic Christian Pope Theophilus of Alexandria, but it does not seem to have housed books at the time and was used as a gathering place for Neoplatonist philosophers following the teachings of Iamblichus. The Library of Alexandria was not the first library of its kind. A long tradition of libraries existed in the ancient Near East; the earliest recorded archive of written materials comes from the ancient Sumerian city-state of Uruk in around 3400 BC, when writing had only just begun to develop. Scholarly curation of literary texts began in around 2500 BC; the kingdoms and empires of the ancient Near East had long traditions of book collecting. The ancient Hittites and Assyrians had massive archives containing records written in many different languages.
The most famous library of the ancient Near East was the Library of Ashurbanipal in Nineveh, founded in the seventh century BC by the Assyrian king Ashurbanipal. A large library existed in Babylon during the reign of Nebuchadnezzar II. In Greece, the Athenian tyrant Peisistratos was said to have founded the first major public library in the sixth century BC, it was out of this mixed heritage of both Greek and Near Eastern book collections that the idea for the Library of Alexandria was born. The Macedonian kings who succeeded Alexander the Great as rulers of the Near East wanted to promote Hellenistic culture and learning throughout the known world. Historian Roy MacLeod calls this "a programme of cultural imperialism"; these rulers therefore had a vested interest to collect and compile information from both the Greeks and from the far more ancient kingdoms of the Near East. Libraries enhanced a city's prestige, attracted scholars, provided practical assistance in matters of ruling and governing the kingdom.
For these reasons, every major Hellenistic urban center would have a royal library. The Library of Alexandria, was unprecedented due to the scope and scale of the Ptolemies' ambitions; the Library was one of the largest and most significant libraries of the ancient world, but details about it are a mixture of history and legend. The earliest known surviving source of information on the founding of the Library of Alexandria is the pseudepigraphic Letter of Aristeas, composed between c. 180 and c. 145 BC. The Letter of Aristeas claims that the Library was founded during
Munich is the capital and most populous city of Bavaria, the second most populous German federal state. With a population of around 1.5 million, it is the third-largest city in Germany, after Berlin and Hamburg, as well as the 12th-largest city in the European Union. The city's metropolitan region is home to 6 million people. Straddling the banks of the River Isar north of the Bavarian Alps, it is the seat of the Bavarian administrative region of Upper Bavaria, while being the most densely populated municipality in Germany. Munich is the second-largest city in the Bavarian dialect area, after the Austrian capital of Vienna; the city is a global centre of art, technology, publishing, innovation, education and tourism and enjoys a high standard and quality of living, reaching first in Germany and third worldwide according to the 2018 Mercer survey, being rated the world's most liveable city by the Monocle's Quality of Life Survey 2018. According to the Globalization and World Rankings Research Institute Munich is considered an alpha-world city, as of 2015.
Munich is a major international center of engineering, science and research, exemplified by the presence of two research universities, a multitude of scientific institutions in the city and its surroundings, world class technology and science museums like the Deutsches Museum and BMW Museum.. Munich houses many multinational companies and its economy is based on high tech, the service sector and creative industries, as well as IT, biotechnology and electronics among many others; the name of the city is derived from the Old/Middle High German term Munichen, meaning "by the monks". It derives from the monks of the Benedictine order, who ran a monastery at the place, to become the Old Town of Munich. Munich was first mentioned in 1158. Catholic Munich resisted the Reformation and was a political point of divergence during the resulting Thirty Years' War, but remained physically untouched despite an occupation by the Protestant Swedes. Once Bavaria was established as a sovereign kingdom in 1806, it became a major European centre of arts, architecture and science.
In 1918, during the German Revolution, the ruling house of Wittelsbach, which had governed Bavaria since 1180, was forced to abdicate in Munich and a short-lived socialist republic was declared. In the 1920s, Munich became home to several political factions, among them the NSDAP; the first attempt of the Nazi movement to take over the German government in 1923 with the Beer Hall Putsch was stopped by the Bavarian police in Munich with gunfire. After the Nazis' rise to power, Munich was declared their "Capital of the Movement". During World War II, Munich was bombed and more than 50% of the entire city and up to 90% of the historic centre were destroyed. After the end of postwar American occupation in 1949, there was a great increase in population and economic power during the years of Wirtschaftswunder, or "economic miracle". Unlike many other German cities which were bombed, Munich restored most of its traditional cityscape and hosted the 1972 Summer Olympics; the 1980s brought strong economic growth, high-tech industries and scientific institutions, population growth.
The city is home to major corporations like BMW, Siemens, MAN, Linde and MunichRE. Munich is home to many universities and theatres, its numerous architectural attractions, sports events and its annual Oktoberfest attract considerable tourism. Munich is one of the fastest growing cities in Germany, it is a top-ranked destination for expatriate location. Munich hosts more than 530,000 people of foreign background; the first known settlement in the area was of Benedictine monks on the Salt road. The foundation date is not considered the year 1158, the date the city was first mentioned in a document; the document was signed in Augsburg. By the Guelph Henry the Lion, Duke of Saxony and Bavaria, had built a toll bridge over the river Isar next to the monk settlement and on the salt route, but as part of the archaeological excavations at Marienhof in advance of the expansion of the S-Bahn from 2012 shards of vessels from the eleventh century were found, which prove again that the settlement Munich must be older than their first documentary mention from 1158.
In 1175 Munich received city fortification. In 1180 with the trial of Henry the Lion, Otto I Wittelsbach became Duke of Bavaria, Munich was handed to the Bishop of Freising. In 1240, Munich was transferred to Otto II Wittelsbach and in 1255, when the Duchy of Bavaria was split in two, Munich became the ducal residence of Upper Bavaria. Duke Louis IV, a native of Munich, was elected German king in 1314 and crowned as Holy Roman Emperor in 1328, he strengthened the city's position by granting it the salt monopoly, thus assuring it of additional income. In the late 15th century, Munich underwent a revival of gothic arts: the Old Town Hall was enlarged, Munich's largest gothic church – the Frauenkirche – now a cathedral, was constructed in only 20 years, starting in 1468; when Bavaria was reunited in 1506, Munich became its capital. The arts and politics became influenced by the court. During the 16th century, Munich was a centre of the German counter reformation, of renaissance arts. Duke Wilhelm V commissioned the Jesuit Michaelskirche, which became a centre for the counter-reform
The Zaca Fire was a massive wildfire that began burning in the San Rafael Mountains, northeast of the Santa Ynez Valley in Santa Barbara County, California. It was the single largest wildfire of the 2007 California wildfire season; the fire started on July 4, 2007, by August 31, it had burned over 240,207 acres, making it California's second largest fire in recorded history at that time after the Cedar Fire of 2003. As of 2018, it is California's sixth-largest fire in recorded history; the fire was contained on September 4, 2007, with the fire being brought under control on October 29, 2007. On July 4, 2007, at 10:53 AM PDT, the Zaca Fire was started as a result of sparks from a grinding machine on private property, being used to repair a water pipe; the Zaca Fire continued reaching 240,207 acres in August. By August 12, progress was being made on the fire through the combined efforts of firefighters and aircraft. Firefighters were able to turn the direction of the fire away from the Paradise Road community.
The Zaca Fire neared containment on September 2. On September 4, 2007, the fire had cost $117 million to fight, was 100% contained. Hotspots within the fire perimeter continued to burn for over another month, until the Zaca Fire was brought under control on October 29, 2007. Of the 43 non-fatal injuries 2 occurred; the fire had burned away from populated areas in steep and rugged areas of the San Rafael Mountains in the Los Padres National Forest and the Santa Ynez River Recreation Area. It only destroyed one Forest Service outbuilding, its impacts on the environment and area water resources are not yet known. Many trails and campgrounds in the Dick Smith Wilderness were destroyed. Since a number of them have been rebuilt. October 2017 California wildfires Witch Fire December 2017 California wildfires Thomas Fire CDF—California Dept. Forestry: Maps of the Zaca Fire California Fire News: daily coverage of the "Zaca Fire" wildland fire including fire perimeter maps, photos - Over 100 pages labeled "Zaca Fire" Associated Press: "Giant fire in Los Padres forest to cross into Ventura County" Los Angeles Times - "Santa Barbara fire flares anew" Santa Maria Times - "Zaca Fire takes unexpected turn".
Southern California's Worst Brush Fires
Lübeck is a city in Schleswig-Holstein, northern Germany, one of the major ports of Germany. On the river Trave, it was the leading city of the Hanseatic League, because of its extensive Brick Gothic architecture, it is listed by UNESCO as a World Heritage Site. In 2015, it had a population of 218,523; the old part of Lübeck is on an island enclosed by the Trave. The Elbe–Lübeck Canal connects the Trave with the Elbe River. Another important river near the town centre is the Wakenitz. Autobahn 1 connects Lübeck with Denmark. Travemünde is a sea ferry port on the coast of the Baltic Sea. Lübeck Hauptbahnhof links Lübeck to a number of railway lines, notably the line to Hamburg. Humans settled in the area around what today is Lübeck after the last Ice Age ended about 9700 BCE. Several Neolithic dolmens can be found in the area. Around AD 700, Slavic peoples started moving into the eastern parts of Holstein, an area settled by Germanic inhabitants who had moved on in the Migration Period. Charlemagne, whose efforts to Christianise the area were opposed by the Germanic Saxons, expelled many of the Saxons and brought in Polabian Slavs allies.
Liubice was founded on the banks of the River Trave about four kilometers north of the present-day city-center of Lübeck. In the 10th century it became the most important settlement of the Obotrite confederacy and a castle was built. In 1128 the pagan Rani from Rügen razed Liubice. In 1143 Adolf II, Count of Schauenburg and Holstein, founded the modern town as a German settlement on the river island of Bucu, he built a new castle, first mentioned by the chronicler Helmold as existing in 1147. Adolf had to cede the castle to the Duke of Saxony, Henry the Lion, in 1158. After Henry's fall from power in 1181 the town became an Imperial city for eight years. Emperor Barbarossa ordained. With the council dominated by merchants, pragmatic trade interests shaped Lübeck's politics for centuries; the council survived into the 19th century. The town and castle changed ownership for a period afterwards and formed part of the Duchy of Saxony until 1192, of the County of Holstein until 1217, of the kingdom of Denmark until the Battle of Bornhöved in 1227.
Around 1200 the port became the main point of departure for colonists leaving for the Baltic territories conquered by the Livonian Order and by the Teutonic Order. In 1226 Emperor Frederick II elevated the town to the status of an Imperial Free City, by which it became the Free City of Lübeck. In the 14th century Lübeck became the "Queen of the Hanseatic League", being by far the largest and most powerful member of that medieval trade organization. In 1375 Emperor Charles IV named Lübeck one of the five "Glories of the Empire", a title shared with Venice, Rome and Florence. Several conflicts about trading privileges resulted in fighting between Lübeck and Denmark and Norway – with varying outcome. While Lübeck and the Hanseatic League prevailed in conflicts in 1435 and 1512, Lübeck lost when it became involved in the Count's Feud, a civil war that raged in Denmark from 1534 to 1536. Lübeck joined the pro-Lutheran Schmalkaldic League of the mid-16th century. After its defeat in the Count's Feud, Lübeck's power declined.
The city remained neutral in the Thirty Years' War of 1618–1648, but the combination of the devastation from the decades-long war and the new transatlantic orientation of European trade caused the Hanseatic League – and thus Lübeck with it – to decline in importance. However after the de facto disbanding of the Hanseatic League in 1669, Lübeck still remained an important trading town on the Baltic Sea. Franz Tunder was the organist in the Marienkirche, it was part of the tradition in this Lutheran congregation that the organist would pass on the duty in a dynastic marriage. In 1668, his daughter Anna Margarethe married the great Danish-German composer Dieterich Buxtehude, the organist at the Marienkirche in Lübeck until at least 1703; some of the greatest composers of the day came to the church to hear his renowned playing. In the course of the war of the Fourth Coalition against Napoleon, troops under Bernadotte occupied the neutral Lübeck after a battle against Blücher on 6 November 1806. Under the Continental System, the State bank went into bankruptcy.
In 1811, the French Empire formally annexed Lübeck as part of France. The writer Thomas Mann was a member of the Mann family of Lübeck merchants, his well-known 1901 novel Buddenbrooks made readers in Germany familiar with the manner of life and mores of the 19th Century Lübeck bourgeoisie. In 1937, the Nazis passed the so-called Greater Hamburg Act, which merged the city of Lübeck with Prussia. During World War II, Lübeck became the first German city to suffer substantial Royal Air Force bombing; the attack of 28 March 1942 created a firestorm. This raid destroyed large parts of the built-up area. Germany operated a POW camp for officers, Oflag X-C, near the city from 1940 until April 1945; the British Second Army occupied it without resistance. On 3 May 1945 one of the biggest disasters in naval history occurred in the Bay of Lübeck when RAF bombers sank three ships: the SS Cap Arcona, the SS Deutschland, the SS Thielbek – which, unknown to them, were packed with concentr
Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition. Fire is hot because the conversion of the weak double bond in molecular oxygen, O2, to the stronger bonds in the combustion products carbon dioxide and water releases energy. At a certain point in the combustion reaction, called the ignition point, flames are produced; the flame is the visible portion of the fire. Flames consist of carbon dioxide, water vapor and nitrogen. If hot enough, the gases may become ionized to produce plasma. Depending on the substances alight, any impurities outside, the color of the flame and the fire's intensity will be different. Fire in its most common form can result in conflagration, which has the potential to cause physical damage through burning. Fire is an important process; the positive effects of fire include maintaining various ecological systems.
The negative effects of fire include hazard to life and property, atmospheric pollution, water contamination. If fire removes protective vegetation, heavy rainfall may lead to an increase in soil erosion by water; when vegetation is burned, the nitrogen it contains is released into the atmosphere, unlike elements such as potassium and phosphorus which remain in the ash and are recycled into the soil. This loss of nitrogen caused by a fire produces a long-term reduction in the fertility of the soil, which only recovers as nitrogen is "fixed" from the atmosphere by lightning and by leguminous plants such as clover. Fire has been used by humans in rituals, in agriculture for clearing land, for cooking, generating heat and light, for signaling, propulsion purposes, forging, incineration of waste, as a weapon or mode of destruction. Fires start when a flammable or a combustible material, in combination with a sufficient quantity of an oxidizer such as oxygen gas or another oxygen-rich compound, is exposed to a source of heat or ambient temperature above the flash point for the fuel/oxidizer mix, is able to sustain a rate of rapid oxidation that produces a chain reaction.
This is called the fire tetrahedron. Fire can not exist in the right proportions. For example, a flammable liquid will start burning only if the fuel and oxygen are in the right proportions; some fuel-oxygen mixes may require a catalyst, a substance, not consumed, when added, in any chemical reaction during combustion, but which enables the reactants to combust more readily. Once ignited, a chain reaction must take place whereby fires can sustain their own heat by the further release of heat energy in the process of combustion and may propagate, provided there is a continuous supply of an oxidizer and fuel. If the oxidizer is oxygen from the surrounding air, the presence of a force of gravity, or of some similar force caused by acceleration, is necessary to produce convection, which removes combustion products and brings a supply of oxygen to the fire. Without gravity, a fire surrounds itself with its own combustion products and non-oxidizing gases from the air, which exclude oxygen and extinguish the fire.
Because of this, the risk of fire in a spacecraft is small. This does not apply. Fire can be extinguished by removing any one of the elements of the fire tetrahedron. Consider a natural gas flame, such as from a stove-top burner; the fire can be extinguished by any of the following: turning off the gas supply, which removes the fuel source. In contrast, fire is intensified by increasing the overall rate of combustion. Methods to do this include balancing the input of fuel and oxidizer to stoichiometric proportions, increasing fuel and oxidizer input in this balanced mix, increasing the ambient temperature so the fire's own heat is better able to sustain combustion, or providing a catalyst, a non-reactant medium in which the fuel and oxidizer can more react. A flame is a mixture of reacting gases and solids emitting visible and sometimes ultraviolet light, the frequency spectrum of which depends on the chemical composition of the burning material and intermediate reaction products. In many cases, such as the burning of organic matter, for example wood, or the incomplete combustion of gas, incandescent solid particles called soot produce the familiar red-orange glow of "fire".
This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single-wavelength radiation from various electron transitions in the excited molecules formed in the flame. Oxygen is involved, but hydrogen burning in chlorine produces a flame, producing hydrogen chloride. Other possible combinations producing flames, amongst many, are fluorine and hydrogen, hydrazine and nitrogen tetroxide. Hydrogen and hydrazine/UDMH flames are
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a reactive nonmetal, an oxidizing agent that forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up half of the Earth's crust. Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids and fats, as do the major constituent inorganic compounds of animal shells and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide.
Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of thus a pollutant. Oxygen was isolated by Michael Sendivogius before 1604, but it is believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, Joseph Priestley in Wiltshire, in 1774. Priority is given for Priestley because his work was published first. Priestley, called oxygen "dephlogisticated air", did not recognize it as a chemical element; the name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and characterized the role it plays in combustion. Common uses of oxygen include production of steel and textiles, brazing and cutting of steels and other metals, rocket propellant, oxygen therapy, life support systems in aircraft, submarines and diving.
One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration. In the late 17th century, Robert Boyle proved. English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
From this he surmised that nitroaereus is consumed in both combustion. Mayow observed that antimony increased in weight when heated, inferred that the nitroaereus must have combined with it, he thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke, Ole Borch, Mikhail Lomonosov, Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element; this may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts.
One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. Combustible materials that leave little residue, such as wood or coal, were thought to be made of phlogiston. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea. Polish alchemist and physician Michael Sendivogius in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti described a substance contained in air, referring to it as'cibus vitae', this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by the thermal decomposition of potassium nitrate. In Bugaj’s view, the isolation of oxygen and the proper association of the substance to that part of air, required for life, lends sufficient weight to the discovery of oxygen by Sendivogius.
A wildfire or wildland fire is a fire in an area of combustible vegetation occurring in rural areas. Depending on the type of vegetation present, a wildfire can be classified more as a brush fire, desert fire, forest fire, grass fire, hill fire, peat fire, vegetation fire, or veld fire. Fossil charcoal indicates that wildfires began soon after the appearance of terrestrial plants 420 million years ago. Wildfire's occurrence throughout the history of terrestrial life invites conjecture that fire must have had pronounced evolutionary effects on most ecosystems' flora and fauna. Earth is an intrinsically flammable planet owing to its cover of carbon-rich vegetation, seasonally dry climates, atmospheric oxygen, widespread lightning and volcanic ignitions. Wildfires can be characterized in terms of the cause of ignition, their physical properties, the combustible material present, the effect of weather on the fire. Wildfires can cause damage to property and human life, although occurring wildfires may have beneficial effects on native vegetation and ecosystems that have evolved with fire.
High-severity wildfire creates complex early seral forest habitat, which has higher species richness and diversity than unburned old forest. Many plant species depend on the effects of fire for reproduction. Wildfires in ecosystems where wildfire is uncommon or where non-native vegetation has encroached may have negative ecological effects. Wildfire behavior and severity result from a combination of factors such as available fuels, physical setting, weather. Analyses of historical meteorological data and national fire records in western North America show the primacy of climate in driving large regional fires via wet periods that create substantial fuels, or drought and warming that extend conducive fire weather. Strategies for wildfire prevention and suppression have varied over the years. One common and inexpensive technique is controlled burning: intentionally igniting smaller fires to minimize the amount of flammable material available for a potential wildfire. Vegetation may be burned periodically to maintain high species diversity and limit the accumulation of plants and other debris that may serve as fuel.
Wildland fire use is the cheapest and most ecologically appropriate policy for many forests. Fuels may be removed by logging, but fuels treatments and thinning have no effect on severe fire behavior when under extreme weather conditions. Wildfire itself is "the most effective treatment for reducing a fire's rate of spread, fireline intensity, flame length, heat per unit of area", according to Jan Van Wagtendonk, a biologist at the Yellowstone Field Station. Building codes in fire-prone areas require that structures be built of flame-resistant materials and a defensible space be maintained by clearing flammable materials within a prescribed distance from the structure. Three major natural causes of wildfire ignitions exist: dry climate lightning volcanic eruptionThe most common direct human causes of wildfire ignition include arson, discarded cigarettes, power-lines arcs, sparks from equipment. Ignition of wildland fires via contact with hot rifle-bullet fragments is possible under the right conditions.
Wildfires can be started in communities experiencing shifting cultivation, where land is cleared and farmed until the soil loses fertility, slash and burn clearing. Forested areas cleared by logging encourage the dominance of flammable grasses, abandoned logging roads overgrown by vegetation may act as fire corridors. Annual grassland fires in southern Vietnam stem in part from the destruction of forested areas by US military herbicides and mechanical land-clearing and -burning operations during the Vietnam War; the most common cause of wildfires varies throughout the world. In Canada and northwest China, lightning operates as the major source of ignition. In other parts of the world, human involvement is a major contributor. In Africa, Central America, Mexico, New Zealand, South America, Southeast Asia, wildfires can be attributed to human activities such as agriculture, animal husbandry, land-conversion burning. In China and in the Mediterranean Basin, human carelessness is a major cause of wildfires.
In the United States and Australia, the source of wildfires can be traced both to lightning strikes and to human activities. Coal seam fires burn in the thousands around the world, such as those in Burning Mountain, New South Wales, they can flare up unexpectedly and ignite nearby flammable material. The spread of wildfires varies based on the flammable material present, its vertical arrangement and moisture content, weather conditions. Fuel arrangement and density is governed in part by topography, as land shape determines factors such as available sunlight and water for plant growth. Overall, fire types can be characterized by their fuels as follows: Ground fires are fed by subterranean roots and other buried organic matter; this fuel type is susceptible to ignition due to spotting. Ground fires burn by smoldering, can burn for days to months, such as peat fires in Kalimantan and Eastern Sumatra, which resulted from a riceland creation project that unintentionally drained and dried the peat.
Crawling or surface fires are fueled by low-lying vegetation on the forest floor such as leaf and timber litter, debris and low-lying shrubbery. This kind of fire burns at a lower temperature than crown fires and may spread