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Carbonyl Sulfide

Carbonyl sulfide

Carbonyl sulfide is a colourless gas with an unpleasant smell. The chemical formula is OCS or COS and the molecule consists of a carbonyl group with the carbon atom also double bonded to a sulfur atom. Carbonyl sulfide is the major sulfur compound naturally present in the atmosphere at 0.5 (± 0.05) ppb and is an important part of the global sulfur cycle. It is also present in foodstuffs such as cheese and prepared vegetables of the cabbage family. OSC is naturally present in grains and seeds in the range of 0.05-0.1 mg kg-1. Carbonyl sulfide is a component of volcanic gasses and gasses emitted by deep sea vents. This compound is found to catalyze the formation of peptides from amino acids. This finding is an extention of the Miller-Urey experiment and it is suggested that carbonyl sulfide played a significant role in the origin of life . Carbonyl sulfide forms in the atmosphere as a result of sulfur emissions. In one study the tracking of carbonyl sulfide in Antarctica ice cores gives a detailed picture of OCS concentrations from 1640 to the present day separating anthropogenic and non-anthropogenic sulfur sources. Carbonyl sulfide is transported into the stratospheric sulfate layer where it is oxidized to sulfuric acid. Carbonyl sulfide is a potential fumigant and a replacement for methyl bromide and phosphine. Carbonyl sulfide is also an interstellar molecule.

External links


- [http://www.scripps.edu/newsandviews/e_20041011/ghadiri.html Carbonyl sulfide and origins of life]
- [http://www.cmdl.noaa.gov/hotitems/cos.html Carbonyl sulfide in ice cores]
- [http://mbao.org/altmet00/86wright.pdf Carbonyl sulfide as a potential fumigant]
- [http://ptcl.chem.ox.ac.uk/MSDS/CA/carbonyl_sulfide.html Carbonyl sulfide MSDS]
- [http://amsglossary.allenpress.com/glossary/search?id=carbonyl-sulfide1 Carbonyl sulfide in the atmosphere]

References

# Carbonyl Sulfide–Mediated Prebiotic Formation of Peptides Luke Leman, Leslie Orgel, M. Reza Ghadiri Science October 8, 2004 # The possible importance of COS for the sulfate layer of the stratosphere. Paul Crutzen Geophys. Res. Lett., 3, 73–76. 1976 Category:Inorganic carbon compounds Category:Oxides Category:Sulfides

Template:Chembox simple organic



Chemical formula

A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. It identifies each type of chemical element by its element symbol and identifies the number of atoms of such element to be found in each discrete molecule of that compound. The number of atoms (if greater than one) is indicated as a subscript. For non-molecular substances the subscripts indicate the ratio of elements in the empirical formula. Chemical formula used for a series of compounds that differ from each other by a constant unit is called general formula. Such a series is called the homologous series, while its members are called homologs.

Elements

In organic chemistry most compounds consist of the following five chemical elements:
- C carbon
- H hydrogen
- N nitrogen
- O oxygen
- S sulfur For other element symbols see list of elements by symbol.

Molecular and structural formulas

For example methane, a simple molecule consisting of one carbon atom bonded to four hydrogen atoms has the chemical formula: : CH4 and glucose with six carbon atoms, twelve hydrogen atoms and six oxygen atoms has the chemical formula: : C6H12O6. A chemical formula may also supply information about the types and spatial arrangement of bonds in the chemical, though it does not necessarily specify the exact isomer. For example ethane consists of two carbon atoms single-bonded to each other, each having three hydrogen atoms bonded to it. Its chemical formula can be rendered as CH3CH3. If there were a double bond between the carbon atoms (and thus each carbon only had two hydrogens), the chemical formula may be written: CH2CH2, and the fact that there is a double bond between the carbons is assumed. However, a more explicit and correct method is to write H2C:CH2 or H2C=CH2. The two dots or lines indicate that a double bond connects the atoms on either side of them. A triple bond may be expressed with three dots or lines, and if there may be ambiguity, a single dot or line may be used to indicate a single bond. Molecules with multiple functional groups that are the same may be expressed in the following way: (CH3)3CH. However, this implies a different structure from other molecules that can be formed using the same atoms (isomers). The formula (CH3)3CH implies a chain of three carbon atoms, with the middle carbon atom bonded to another carbon: Carbon chain and the remaining bonds on the carbons all leading to hydrogen atoms. However, the same number of atoms (10 hydrogens and 4 carbons, or C4H10) may be used to make a straight chain: CH3CH2CH2CH3. The alkene 2-butene has two isomers which the chemical formula CH3CH=CHCH3 does not identify. The relative position of the two methyl groups must be indicated by additional notation denoting whether the methyl groups are on the same side of the double bond (cis or Z) or on the opposite sides from each other.(trans or E)

Polymers

For polymers, parentheses are placed around the repeating unit. For example, a hydrocarbon molecule that is described as: CH3(CH2)50CH3, is a molecule with 50 repeating units. If the number of repeating units is unknown or variable, the letter n may be used to indicate this: CH3(CH2)nCH3.

Ions

For ions, the charge on a particular atom may be denoted with a right-hand superscript. For example Na+, or Cu2+. The total charge on a charged molecule or a polyatomic ion may also be shown in this way. For example: hydronium, H3O+ or sulfate, SO42-.

Isotopes

Although isotopes are more relevant to nuclear chemistry or stable isotope chemistry than to conventional chemistry, different isotopes may be indicated with a left-hand superscript in a chemical formula. For example, the phosphate ion containing radioactive phosphorus-32 is 32PO43-. Also a study involving stable isotope ratios might include 18O:16O. A left-hand subscript is sometimes used to indicate redundantly, for convenience, the atomic number.

Empirical formula

In chemistry, the empirical formula of a chemical is a simple expression of the relative number of each type of atom or ratio of the elements in it. Empirical formulas are the standard for ionic compounds, such as CaCl2, and for macromolecules, such as SiO2. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The term empirical refers to the process of elemental analysis, a technique of analytical chemistry used to determine the relative percent composition of a pure chemical substance by element. For example, hexane could have a chemical formula of CH3CH2CH2CH2CH2CH3, implying that it has a straight chain structure, 6 carbon atoms, and 14 hydrogen atoms. However the empirical formula for the same molecule would be C3H7.

See also


- Periodic table
- Element symbol Category:Chemical nomenclature Category:Notation als:Summenformel ja:化学式 th:สูตรเคมี

Carbonyl

In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (e.g., nickel carbonyl); in this situation, carbon is triple-bonded to oxygen. A carbonyl group characterizes the following types of compounds (and a representation of the full group, where -CO means a C=O group):
- aldehyde- (R-CHO)
- ketone- (R-CO-R1)
- carboxylic acid- (R-COOH)
- ester- (R-CO-O-R1)
- amide- (R-CO-NH2 or R-CO-NHR1 or R-CO-NR1R2)
- enone- R2-C=CR−CO−R
- acyl chloride- (R-CO-Cl)
- anhydride- (R-CO-O-CO-R)

Reactivity

Oxygen is more electronegative than carbon, and thus pulls electron density away from carbon to increase the bond's polarity. Therefore, the carbonyl carbon becomes electrophilic, and thus more reactive with nucleophiles. Carbonyl groups can be reduced by reaction with hydride reagents such as NaBH4 and LiAlH4, and by organometallic reagents such as organolithium reagents and Grignard reagents. Other important reactions include:
- Wolff-Kishner Reduction
- Clemmensen reduction
- Conversion into thioacetals
- Hydration to hemiacetals and hemiketals, and then to acetals and ketals
- Reaction with ammonia and primary amines to form imines
- Reaction with hydroxylamines to form oximes
- Reaction with cyanide to form cyanohydrins

α,β-unsaturated carbonyl compounds

α,β-unsaturated carbonyl compounds are an important class of carbonyl compounds with the general structure Cβ=Cα-C=0. In these compounds the carbonyl group is conjugated with an alkene (hence the adjective unsaturated), from which they derive special properties. Examples of unsaturated carbonyls are acrolein, mesityl oxide, acrylic acid and maleic acid. Unsaturated carbonyls can be prepared in the laboratory in an aldol reaction and in the perkin reaction. The carbonyl group, be it an aldehyde or acid, draws electrons away from the alkene and the alkene group in unsaturated carbonyls are therefore deactived towards an electrophile such as bromine or hydrochloric acid. As a general rule with unsymmetric electrophiles hydrogen attaches itself at the α position in an electrophilic addition. On the other hand, these compounds are activated towards nucleophiles in nucleophilic conjugate addition.

Spectroscopy


- IR spectroscopy: the C=O double bond absorbs infrared light at wavenumbers between approximately 1680–1750 cm-1. This absorption is known as the "carbonyl stretch" when displayed on an infrared absorption spectrum.
- Nuclear magnetic resonance: the C=O double-bond exhibits different resonances depending on surrounding atoms.
- Mass spectrometry

See also


- ketone
- aldehyde
- ester
- amide
- anhydride
- organic chemistry

References


- William Reusch. (2004) [http://www.cem.msu.edu/~reusch/VirtualText/aldket1.htm Aldehydes and Ketones] Retrieved 23 May 2005.
- ILPI. (2005) [http://www.ilpi.com/msds/ref/anhydride.html The MSDS Hyperglossary- Anhydride].

Further Reading


- L.G. Wade, Jr. [http://www.amazon.com/exec/obidos/tg/detail/-/013033832X/qid=1116901319/sr=8-1/ref=pd_csp_1/002-6183595-6998447?v=glance&s=books&n=507846 Organic Chemistry, 5th ed.] Prentice Hall, 2002. ISBN 013033832X
- The Frostburg State University Chemistry Department. [http://www.chemhelper.com/ Organic Chemistry Help] (2000).
- Advanced Chemistry Development, Inc. [http://www.acdlabs.com/iupac/nomenclature IUPAC Nomenclature of Organic Chemistry] (1997).
- William Reusch. [http://www.cem.msu.edu/~reusch/VirtualText/intro1.htm VirtualText of Organic Chemistry] (2004). Category:Functional groups ja:カルボニル基

Ppb

Parts-per notation is a measure of concentration that is used where low levels of concentration are significant. These types of measurement units are also known as mixing ratios. This is often used to denote the relative abundance of trace elements in the Earth's crust, trace elements in forensics or other analyses, or levels of pollutants in the environment.

Types of Parts-per notations


- Parts per hundred (denoted by '%' and very rarely 'pph') - denotes one particle of a given substance for every 99 other particles. This is the common percent. 1 part in 102.
- Parts per thousand (denoted by '‰' [the permille symbol], and occasionally 'ppt') denotes one particle of a given substance for every 999 other particles. This is roughly equivalent to one drop of ink in a cup of water, or one second per 17 minutes. 'Parts per thousand' is often used to record the salinity of seawater. 1 part in 103.
- Parts per million ('ppm') denotes one particle of a given substance for every 999,999 other particles. This is roughly equivalent to one drop of ink in a 40 gallon drum of water, or one second per 280 hours. 1 part in 106.
- Parts per billion ('ppb') denotes one particle of a given substance for every 999,999,999 other particles. This is roughly equivalent to one drop of ink in a canal lock full of water, or one second per 32 years. 1 part in 109.
- Parts per trillion ('ppt') denotes one particle of a given substance for every 999,999,999,999 other particles. This is roughly equivalent to one drop of ink in an Olympic-sized swimming pool, or one second every 320 centuries. 1 part in 1012.
- Parts per quadrillion ('ppq') denotes one particle of a given substance for every 999,999,999,999,999 other particles. This is roughly equivalent to a drop of ink in a medium-sized lake, or one second every 32,000 millennia. There are no known analytical techniques that can measure with this degree of accuracy; nevertheless, it is still used in some mathematical models of toxicology and epidemiology. 1 part in 1015.

Caveats

Of all the pp- variants, ppm is by far the one in most common usage; ppb is also sparingly used, while the others are little more than a curiosity. Although 'ppt' is usually used to denote 'parts per trillion', it is also on occasion used to denote 'parts per thousand'. If there is any chance of ambiguity, one should describe the abbreviation in full. Users of ppb and beyond should be aware of the intercultural issues of the Long and short scales and the potential for misunderstandings. It is a term with several variants in meaning, so the meaning should be made clear if this term is used. In particular, the ratio can be expressed in terms of particles as above, volume (used in particular for gases) or mass. The usage is generally quite fixed inside most specific branches of science, leading some researchers to believe that their own usage (mass/mass, volume/volume or others) is the only correct one. This, in turn, leads them not to specify their usage in their research, and others may therefore misinterpret their results. For example, electrochemists often use volume/volume, while chemical engineers use mass/mass. Many academic papers of otherwise excellent level fail to specify their usage of the part-per notation.

Examples of parts per notation

The metric system is the most convenient way to express this since metric units go by steps of ten, hundred and thousand. For example, a milligram is a thousandth of a gram and a gram is a thousandth of a kilogram. Thus, a milligram is a thousandth of a thousandth, or a millionth of a kilogram. A milligram is one part per million of a kilogram thus, one part per million (ppm) by mass is the same as one milligram per kilogram. Just as part per million is abbreviated as ppm, a milligram per kilogram has its own symbolic form -- mg/kg, which unlike ppm is unambiguous.
- By mass:
  - one milligram in a kilogram is 1 ppm by mass.
  - one milligram in a metric tonne is 1 ppb by mass.
- By volume:
  - one millilitre (or cubic centimetre) in a cubic metre (or kilolitre) is 1 ppm by volume. For most gases (those behaving much like an ideal gas) this is numerically equivalent to µmol/mol on the basis of molecules (not atoms). See Avogadro's law.
- By mass/volume ratio for dilute aqueous solutions (ppm w/v or ppm m/v):
  - 1 litre (L) of water has mass of approximately 1 kg1, so 1 milligram per litre (mg/L) is, loosely speaking, 1 ppm, for small concentrations in a water solution2.
- By number of particles or moles:
  - one micromole per mole can also be called 1 ppm.
  - one nanomole per mole is 1 ppb.
  - one picomole per mole is 1 ppt.

Use

Examples of situations where parts per million are an appropriate measure include:
- relative abundances of trace elements in the earth's crust
- concentrations of pollutants in the environment

Inexact analogues


- one square centimeter in 1000 square feet is about .95 ppm
- one two-parent, two-child family in a city of about 4 million people is roughly 1 ppm
- one CD in the 1.57-million disc3 FreeDB catalogue is nearly 2/3 ppm

NIST caution

According to the U.S. National Institute of Standards and Technology (NIST) Guide for the Use of the International System of Units (SI), "the language-dependent terms part per million, part per billion, and part per trillion ... are not acceptable for use with the SI to express the values of quantities." NIST's [http://physics.nist.gov/Pubs/SP811/sec07.html#7.10.3 Guide for the Use of the International System of Units (SI)] has examples of alternative expressions. Acceptable SI units are: 1 millimole/mole = 1 part per thousand 1 micromole/mole = 1 part per million 1 nanomole/mole = 1 part per billion 1 picomole/mole = 1 part per trillion

Notes

#Exactly one kg of pure water at maximum density (~4°C) and standard pressure was the definition of a litre from 1901 to 1964; today the litre is defined as exactly 1 dm³, the distinction being whether it is calibrated to the [http://www.sizes.com/units/kilogram.htm international standard kilogram] or the [http://www.sizes.com/units/meter.htm international standard meter], which are defined without reference to one another. #Properly speaking it is approximately 1 ppm by mass or by weight in solution. When solids dissolve, they can increase or decrease the total volume they occupy, and even increase or decrease the total volume of the solution. Adding 1 ppm by weight will rarely produce a solution that is 1 ppm by volume to the same precision. The notation ppm w/v or ppm m/v demonstrates the exact nature of the ratio and is therefore the most precise. #The definition given above is that parts per notation refers to numbers of particles (equivalent to moles), but the parts per notation can also be used by mass or volume. Those using the notation need to state their usage to avoid confusion. #In atmospheric chemistry the parts per notation is commonly expressed with a v following, such as ppmv (or ppvm is some usages), to indicate parts per million by volume. In gases ppmv is equivalent to ppm by particles (Avogadro's law). This works fine for gases, but may have problems with cloud droplets and smoke or other atmospheric particulate matter. Category:Mathematical terminology Category:Analytical chemistry Category:Environmental chemistry Category:Units of density ko:Ppm ja:Ppm

Cheese

Cheese is a solid food made from the curdled milk of cows, goats, sheep, or other mammals. The milk is curdled using some combination of rennet (or rennet substitutes) and acidification. Bacteria acidify the milk and play a role in defining the texture and flavor of most cheeses. Some cheeses also feature molds, either on the outer rind or throughout. There are hundreds of types of cheese. Different styles and flavors of cheese are the result of using different species of bacteria and molds, different levels of milk fat, variations in length of aging, differing processing treatments (cheddaring, pulling, brining, mold wash) and different breeds of cows, sheep, or other mammals. Other factors include animal diet and the addition of flavoring agents such as herbs, spices, or wood smoke. Whether or not the milk is pasteurized may also affect the flavor. For a few cheeses, the milk is curdled by adding acids such as vinegar or lemon juice. Most cheeses, however, are acidified to a lesser degree by bacteria, which turn milk sugars into lactic acid, followed by the addition of rennet to complete the curdling. Rennet is an enzyme traditionally obtained from the stomach lining of young cattle, but now also laboratory produced. Substitute "vegetable rennets" have been extracted from various species of the Cynara thistle family. In some societies, stored cheese is a hedge against famine and a good travel food. It is valuable for its portability, long life, and high content of fat, protein, calcium, and phosphorus. Cheese is lighter-weight, more compact, and has a longer shelf life than the milk from which it is made. Cheesemakers can place themselves near the center of a dairy region and benefit from fresher milk, lower milk prices, and lower shipping costs. Cheese's substantial storage life lets a cheesemaker sell when prices are high or money is needed. Some markets even pay more for "aged" cheeses, exactly the opposite case from conventional milk production. Cheeses are eaten raw or cooked, alone or with other ingredients. As they are heated, most cheeses melt and brown. Some cheeses, like raclette, melt smoothly; many others can be coaxed into doing so in the presence of acids or starch. Fondue, with wine providing the acidity, is a good example of a smoothly-melted cheese dish. Other cheeses turn elastic and stringy when they melt, a quality that can be enjoyed in dishes like pizza and Welsh rarebit. Some cheeses melt unevenly, their fats separating as they heat, while a few acid-curdled cheeses, including halloumi, paneer and ricotta, do not melt at all and can become firmer when cooked.

History

Cheese is an ancient food whose origins may predate recorded history. Probably discovered in Central Asia or the Middle East, cheesemaking spread to Europe and had become a sophisticated enterprise by Roman times. As Rome's influence receded, local cheesemaking techniques diverged from one another and each region became home to specific types of cheese. This diversity reached its peak in the early industrial age and has declined somewhat since then due to mechanization and economic factors.

Origins

The exact origins of cheesemaking are unknown, and estimates range from around 8000 BCE (when sheep were domesticated) to around 3000 BCE. Credit for the discovery most likely goes to nomadic Turkic tribes in Central Asia, around the same time that they developed yogurt, or to people in the Middle East. A common tale about the discovery of cheese tells of an Arab nomad carrying milk across the desert in a container made from an animal's stomach, only to discover the milk had separated into curd and whey by the rennet from the stomach. Folktales aside, cheese likely began as a way of preserving soured and curdled milk through pressing and salting, with rennet introduced later— perhaps when someone noticed that cheese made in an animal stomach produced more solid and better-textured curds. The earliest archaeological evidence of cheesemaking has been found in Egyptian tomb murals, dating to about 2300 BCE. The earliest cheeses would likely have been quite sour and salty, similar in texture to rustic cottage cheese or feta. From the Middle East, basic cheesemaking found its way into Europe, where cooler climates meant less aggressive salting was needed for preservation. With moderate salt and acidity, the cheese became a suitable environment for a variety of beneficial microbes and molds, which are what give aged cheeses their pronounced and interesting flavors.

Classical times

Ancient Greek mythology credited Aristaeus with the discovery of cheese. Homer's Odyssey (8th century BCE) describes the Cyclops making and storing sheeps' and goats' milk cheese. From Samuel Butler's translation: :We soon reached his cave, but he was out shepherding, so we went inside and took stock of all that we could see. His cheese-racks were loaded with cheeses, and he had more lambs and kids than his pens could hold... :When he had so done he sat down and milked his ewes and goats, all in due course, and then let each of them have her own young. He curdled half the milk and set it aside in wicker strainers... By Roman times, cheese was an everyday food and cheesemaking a mature art, not very different from what it is today. Columella's De Re Rustica (circa 65 CE) details a cheesemaking process involving rennet coagulation, pressing of the curd, salting, and aging. Pliny's Natural History (77 CE) devotes a chapter (xi. 97) to describing the diversity of cheeses enjoyed by Romans of the early Empire. He stated that the best cheeses came from the villages near Nîmes, but did not keep long and had to be eaten fresh. Cheeses of the Alps and Apennines were remarkable for their variety then as now. A Ligurian cheese was noted for being made mostly from sheeps' milk, and some cheeses produced nearby were stated to weigh as much as a thousand pounds each. Goats' milk cheese was a recent taste in Rome, improved over the "medicinal taste" of Gaul's similar cheeses by smoking. Of cheeses from overseas, Pliny preferred those of Bithynia in Asia Minor.

Post-classical Europe

Rome spread a uniform set of cheesemaking techniques throughout much of Europe, and introduced cheesemaking to areas without a previous history of it. As Rome declined and long-distance trade collapsed, cheese in Europe diversified further, with various locales developing their own distinctive cheesemaking traditions and products. France and Italy are the nations with the most diversity in locally made cheeses— today with approximately 400 each. (A French proverb says there is a different French cheese for every day of the year, and Charles de Gaulle once asked "how can you govern a country in which there are 246 kinds of cheese?") Still, the advancement of the cheese art in Europe was slow during the centuries after Rome's fall. Many of the cheeses we know best today were first recorded in the late Middle Ages or after— cheeses like cheddar around 1500 CE, Parmesan in 1597, Gouda in 1697, and Camembert in 1791. In 1546, John Heywood wrote in Proverbes that "the moon is made of a greene cheese." (Greene refers here not to the color, as many now think, but to being new or unaged.) Variations on this sentiment were long repeated. Although some people assumed that this was a serious belief in the era before space exploration, it is more likely that Heywood was indulging in nonsense.

Modern era

The first factory for the industrial production of cheese opened in Switzerland in 1815, but it was in the United States where large-scale production first found real success. Credit usually goes to Jesse Williams, a dairy farmer from Rome, New York, who in 1851 started making cheese in an assembly-line fashion using the milk from neighboring farms. Within decades hundreds of such dairy associations existed. The 1860s saw the beginnings of mass-produced rennet, and by the turn of the century scientists were producing pure microbial cultures. Before then, bacteria in cheesemaking had come from the environment or from recycling an earlier batch's whey; the pure cultures meant a more standardized cheese could be produced. Factory-made cheese overtook traditional cheesemaking in the World War II era, and factories have been the source of most cheese in America and Europe ever since. Today, Americans buy more processed cheese than "real", factory-made or not. Worldwide, cheese is a major agricultural product. According to the Food and Agricultural Organization of the United Nations, over 18 million metric tons of cheese was produced worldwide in 2004. This is more than the yearly production of coffee beans, tea leaves, cocoa beans and tobacco combined.

Cultural attitudes

Cheese is rarely found in East Asian dishes, as dairy products in general are rare. However, East Asian sentiment against cheese is not universal. Cheese made from yaks' (chhurpi) or mares' milk is common on the Asian steppes, and cheese is used in India, where paneer curries are popular. Even in China, cheese consumption is increasing, with annual sales more than doubling from 1996 to 2003 (to a still quite-small 30 million U.S. dollars a year). Certain kinds of Chinese preserved bean curd are sometimes misleadingly referred to in English as "Chinese cheese", due to their strong flavor. Strict followers of the dietary laws of Judaism and Islam must avoid most hard cheeses, which are made with rennet from animals not slaughtered in a manner adhering to kosher or halal laws. Both faiths allow cheese made with vegetable-based rennet or with rennet made from animals that were processed in a kosher or halal manner. Many less-orthodox Jews also believe that rennet undergoes enough processing to change its nature entirely, and do not consider it to ever violate kosher law. (See Cheese and kashrut.) As cheese is a dairy food under kosher rules it cannot be eaten in the same meal with any meat. Many vegetarians avoid any cheese made from animal-based rennet. Most widely available vegetarian cheeses are made using rennet produced by fermentation of the fungus Mucor miehei. Vegans and other dairy-avoiding vegetarians cannot eat real cheese at all, but some vegetable-based substitute cheeses (usually soy based) are available. Even in cultures with long cheese traditions, it is not unusual to find people who perceive cheese — especially pungent-smelling or mold-bearing varieties such as Limburger or Roquefort — as unappetizing, unpalatable, or disgusting. Food-science writer Harold McGee proposes that cheese is such an acquired taste because it is produced through a process of controlled spoilage and many of the odor and flavor molecules in an aged cheese are the same found in rotten foods. McGee notes "An aversion to the odor of decay has the obvious biological value of steering us away from possible food poisoning, so it's no wonder that an animal food that gives off whiffs of shoes and soil and the stable takes some getting used to."

Types of cheese

No one categorization scheme can capture all the diversity of the world's cheeses. These are some commonly used classifications. spoilage

Fresh

For these simplest cheeses, milk is curdled and drained, with little other processing. Examples include Cottage cheese, Romanian Caş, Neufchâtel (the model for American-style cream cheese), and fresh goats' milk chèvre. Such cheeses are soft and spreadable, with a mild taste. Fresh cheeses without additional preservatives can spoil in a matter of days. Whey cheeses are fresh cheeses made from the whey discarded while producing other cheeses. Ricotta, Romanian Urda and Norwegian Geitost are examples. Traditional Mozzarella also falls into the fresh cheese category. Fresh curds are stretched and kneaded in hot water to form a ball of Mozzarella, which in southern Italy is usually eaten within a few hours of being made. Other firm fresh cheeses include paneer and queso fresco.

Distinctively aged

Soft-ripened cheeses such as Brie and Camembert are made by allowing white Penicillium candida or P. camemberti mold to grow on the outside of a soft cheese for a few days or weeks. The mold forms a white crust and contributes to the smooth, runny, or gooey textures and more intense flavors of these aged cheeses. Goats' milk cheeses are often treated in a similar manner, sometimes with white molds and sometimes with blue. Blue-mold cheeses like Roquefort, Gorgonzola, and Stilton are produced by inoculating loosely pressed curds with Penicillium roqueforti or Penicillium glaucum molds. The mold grows within the cheese as it ages. These cheeses have distinct blue veins and, often, assertive flavors. Their texture can be soft or firm. Washed-rind cheeses are periodically bathed in a saltwater brine as they age, making their surfaces amenable to a class of bacteria (the reddish-orange "smear bacteria") which impart pungent (some say "stinky") odors and distinctive flavors. Washed-rind cheeses can be soft (Limburger), semi-hard (Muenster), or hard (Appenzeller).

Other categories

Categorizing cheeses by firmness is a common but inexact practice. The lines between "soft", "semi-soft", "semi-hard", and "hard" are arbitrary, and many types of cheese are made in softer or firmer variations. Harder cheeses have a lower moisture content than softer cheeses. They are generally packed into molds under more pressure and aged for a longer time. The familiar cheddar is one of a family of semi-hard or hard cheeses (including Cheshire and Gloucester) whose curd is cut, gently heated, piled, and stirred before being pressed into forms. Colby and Monterey Jack are similar but milder cheeses; their curd is rinsed before it is pressed, washing away some acidity and calcium. A similar curd-washing takes place when making the Dutch cheeses Edam and Gouda. Swiss-style cheeses like Emmental and Gruyère are generally quite firm. The same bacteria that give Emmental its holes contribute to their aromatic and sharp flavors. The hardest cheeses — "grating cheeses" such as Parmesan, Pecorino, and Romano — are quite firmly packed into large forms and aged for months or years. Processed cheese is made from traditional cheese and emulsifiers, often with the addition of milk, more salt, preservatives, and food coloring. It is inexpensive, consistent, and melts smoothly. This is the most-consumed category of cheese in the United States. The most familiar processed cheese may be pre-sliced mild yellow American Cheese or Velveeta. Many other varieties exist, including Easy Cheese, a Kraft Foods brand sold in a spray can.

Health and nutrition

Kraft Foods.]] In general, cheese supplies a great deal of calcium, protein, and phosphorus. A 30 gram (one ounce) serving of cheddar cheese contains about seven grams of protein and 200 milligrams of calcium. Nutritionally, cheese is essentially concentrated milk: it takes about 200 grams (seven ounces) of milk to provide that much protein, and 150 grams to equal the calcium. Cheese shares milk's nutritional disadvantages as well. The Center for Science in the Public Interest condemns cheese as America's number one source of saturated fat, adding that the average American ate 30 pounds (13.6 kg) of cheese in the year 2000, up from 11 pounds (5 kg) in 1970. Their recommendation is to limit full-fat cheese consumption to two ounces (60 grams) a week. Whether cheese's highly saturated fat actually leads to an increased risk of heart disease is called into question when considering France and Greece, which lead the world in cheese eating (more than 14 ounces (400 grams) a week per person, or over 45 pounds (20 kg) a year) yet have relatively low rates of heart disease. A number of food safety agencies around the world have warned of the risks of raw-milk cheeses. The U.S. Food and Drug Administration states that soft raw-milk cheeses can cause "serious infectious diseases including listeriosis, brucellosis, salmonellosis and tuberculosis". It is U.S. law since 1944 that all raw-milk cheeses (including imports since 1951) must be aged at least 60 days. Australia has a wide ban on raw-milk cheeses as well, though in recent years exceptions have been made for Swiss Gruyère, Emmental and Sbrinz, and for French Roquefort. Some say these worries are overblown, pointing out that pasteurization of the milk used to make cheese does not ensure its safety in any case. This is supported by statistics showing that in Europe (where young raw-milk cheeses are still legal in some countries), most cheese-related food poisoning incidents were traced to pasteurized cheeses. Some studies claim to show that cheeses including Cheddar, Mozzarella, Swiss and American can help to prevent tooth decay. Several mechanisms for this protection have been proposed:
- The calcium, protein, and phosphorus in cheese may act to protect tooth enamel.
- Cheese increases saliva flow, washing away acids and sugars.
- Cheese may have an antibacterial effect in the mouth. Cheese is often avoided by those who are lactose intolerant, but ripened cheeses like Cheddar contain only about 5% of the lactose found in whole milk, and aged cheeses contain almost none. Some people suffer reactions to amines found in cheese, particularly histamine and tyramine. Some aged cheeses contain significant concentrations of these amines, which can trigger symptoms mimicking an allergic reaction: headaches, rashes, and blood pressure elevations.

Making cheese

:Main article: Home cheesemaking

Curdling

The only strictly required step in making any sort of cheese is separating the milk into solid curds and liquid whey. Usually this is done by acidifying the milk and adding rennet. The acidification is accomplished directly by the addition of an acid like vinegar in a few cases (paneer, queso fresco), but usually starter bacteria are employed instead. These starter bacteria convert milk sugars into lactic acid. The same bacteria (and the enzymes they produce) also play a large role in the eventual flavor of aged cheeses. Most cheeses are made with starter bacteria from the Lactococci, Lactobacilli, or Streptococci families. Swiss starter cultures also include Propionibacter shermani, which produces carbon dioxide gas bubbles during aging, giving Swiss cheese or Emmentaler its holes. Some fresh cheeses are curdled only by acidity, but most cheeses also use rennet. Rennet sets the cheese into a strong and rubbery gel compared to the fragile curds produced by acidic coagulation alone. It also allows curdling at a lower acidity—important because flavor-making bacteria are inhibited in high-acidity environments. In general, softer, smaller, fresher cheeses are curdled with a greater proportion of acid to rennet than harder, larger, longer-aged varieties.

Curd processing

At this point, the cheese has set into a very moist gel. Some soft cheeses are now essentially complete: they are drained, salted, and packaged. For most of the rest, the curd is cut into small cubes. This allows water to drain from the individual pieces of curd. Some hard cheeses are then heated to temperatures in the range of 35°C–55°C (100°F–130°F). This forces more whey from the cut curd. It also changes the taste of the finished cheese, affecting both the bacterial culture and the milk chemistry. Cheeses that are heated to the higher temperatures are usually made with thermophilic starter bacteria which survive this step—either lactobacilli or streptococci. Salt has a number of roles in cheese besides adding a salty flavor. It preserves cheese from spoiling, draws moisture from the curd, and firms up a cheese’s texture in an interaction with its proteins. Some cheeses are salted from the outside with dry salt or brine washes. Most cheeses have the salt mixed directly into the curds. A number of other techniques can be employed to influence the cheese's final texture and flavor. Some examples:
- Stretching: (Mozzarella, Provolone) The curd is stretched and kneaded in hot water, developing a stringy, fibrous body.
- Cheddaring: (Cheddar, other English cheeses) The cut curd is repeatedly piled up, pushing more moisture away. The curd is also mixed (or milled) for a long period of time, taking the sharp edges off the cut curd pieces and influencing the final product's texture.
- Washing: (Edam, Gouda, Colby) The curd is washed in warm water, lowering its acidity and making for a milder-tasting cheese. Most cheeses achieve their final shape when the curds are pressed into a mold or form. The harder the cheese, the more pressure is applied. The pressure drives out moisture — the molds are designed to allow water to escape — and unifies the curds into a single solid body.

Aging

A newborn cheese is usually salty yet bland in flavor and, for harder varieties, rubbery in texture. These qualities are sometimes enjoyed—cheese curds are eaten on their own—but usually cheeses are left to rest under carefully controlled conditions. This aging period (also called ripening, or, from the French, affinage) can last from a few days to several years. As a cheese ages, microbes and enzymes transform its texture and intensify its flavor. This transformation is largely a result of the breakdown of casein proteins and milkfat into a complex mix of amino acids, amines, and fatty acids. fatty acidSome cheeses have additional bacteria or molds intentionally introduced to them before or during aging. In traditional cheesemaking, these microbes might be already present in the air of the aging room; they are simply allowed to settle and grow on the stored cheeses. More often today, prepared cultures are used, giving more consistent results and putting fewer constraints on the environment where the cheese ages. For the blue cheeses (Roquefort, Stilton, Gorgonzola), Penicillium mold is introduced to the curd before molding. During aging, the blue molds (P. roqueforti or P. glaucum ) grow in the small fissures in the cheese, imparting a sharp flavor and aroma. The same molds are also grown on the surface of some aged goat cheeses. The soft cheeses Brie and Camembert, among others, get a surface growth of other Penicillium species, white-colored P. candidum or P. camemberti. The surface mold contributes to the interior texture and flavor of these small cheeses. Some cheeses are periodically washed in a saltwater brine during their ripening. Not only does the brine carry flavors into the cheese (it might be seasoned with spices or wine), but the salty environment may nurture the growth of the Brevibacterium linens bacteria, which can impart a very pronounced odor (Limburger) and interesting flavor. The same bacteria can also have some impact on cheeses that are simply ripened in humid conditions, like Camembert. Large populations of these "smear bacteria" show up as a sticky orange-red layer on some brine-washed cheeses.

Cheese in language

Throughout the history of the English language, the word cheese has been chese (in Middle English) and cīese or cēse (in Old English). Similar words are shared by other West Germanic languages — Frisian tsiis, Dutch kaas, German Käse, Old High German chāsi — all of which probably come from the reconstructed West-Germanic root
- kasjus, which in turn is an early borrowing from Latin. The Latin word caseus — from which are derived the Spanish queso, Portuguese queijo, Romanian caş and Italian cacio — and the Celtic root which gives the Irish cáis and the Welsh caws are also related. This whole group of words is probably derived from the proto-Indo-European root
- kwat-, which means "to ferment, become sour". When the Romans began to make hard cheeses for their legionaries' supplies, a new word started to be used: formaticum, from caseus formatus, or "molded cheese". It is from this word that we get the French fromage, Italian formaggio, Breton fourmaj and Provençal furmo. Cheese itself is occasionally employed in a sense that means "molded" or "formed". Head cheese uses the word in this sense. In modern English slang, something "cheesy" is kitsch, cheap, inauthentic, or of poor quality. One can also be "cheesed off"— unhappy or annoyed. Such negative connotations might derive from a ripe cheese's sometimes-unpleasant odor. Almost certainly the odor explains the use of "cutting the cheese" as a euphemism for flatulence. A more upbeat slang use is seen in "the big cheese", an expression referring to the most important person in a group, the "big shot" or "head honcho". This use of the word probably derived not from the word cheese, but from the Persian or Hindi word chiz, meaning a thing. A more whimsical bit of American and Canadian slang refers to school buses as "cheese wagons", a reference to school bus yellow. People getting their photo taken are often encouraged to "say cheese!", as the word "cheese" contains the phoneme /i/, a long vowel which requires the lips to be stretched in the appearance of a smile. People from Wisconsin and the Netherlands, both centers of cheese production, have been called cheeseheads. This nickname has been embraced by Wisconsin sports fans — especially fans of the Green Bay Packers or Wisconsin Badgers — who are now seen in the stands sporting plastic or foam hats in the shape of giant cheese wedges.

Notes

# Quoted in Newsweek, October 1, 1962 according to The Columbia Dictionary of Quotations (Columbia University Press, 1993 ISBN 0-2310719-4-9 p 345). Numbers besides 246 are often cited in very similar quotes; whether these are misquotes or whether de Gaulle repeated the same quote with different numbers is unclear. # . [http://www.ebs.hw.ac.uk/SDA/publshr.html Full text], [http://www.ebs.hw.ac.uk/SDA/cheese1.html Chapter with cheese timetable]. # Cecil Adams (1999). [http://www.straightdope.com/classics/a990723a.html Straight Dope: How did the moon=green cheese myth start?]. Retrieved October 15, 2005. # . p 54. "In the United States, the market for process cheese [...] is now larger than the market for 'natural' cheese, which itself is almost exclusively factory-made." # [http://www.globalpolicy.org/globaliz/cultural/2003/1211chinacheese.htm Full text] # Toronto Public Health. [http://www.toronto.ca/health/nm_faq_halal_foods.htm Frequently Asked Questions about Halal Foods]. Retrieved October 15, 2005. # McGee p 58, "Why Some People Can't Stand Cheese." # Nutritional data from [http://www.cnn.com/FOOD/resources/food.for.thought/dairy/compare.dairy.html CNN Interactive]. Retrieved October 20, 2004. # Center for Science in the Public Interest (2001). [http://www.cspinet.org/new/cheese.html Don't Say Cheese]. Retrieved October 15, 2005. # McGee, p 67. McGee supports both this contention and that more food poisonings in Europe are caused by pasteurized cheeses than raw-milk. # [http://www.consumeraffairs.com/news04/2005/fda_cheese.html FDA Warns About Soft Cheese Health Risk]. Retrieved October 15, 2005. # Chris Mercer (2005). [http://www.ap-foodtechnology.com/news/ng.asp?id=62799-fsanz-roquefort-speciality-cheese Australia lifts Roquefort cheese safety ban]. Retrieved October 22, 2005. # Janet Fletcher. [http://www.specialtyfood.com/do/news/ViewNewsArticle?id=1841 The Myths About Raw-Milk Cheese]. Retrieved October 15, 2005. # National Dairy Council. [http://www.nationaldairycouncil.org/NationalDairyCouncil/Nutrition/Products/cheesePage6.htm Specific Health Benefits of Cheese]. Retrieved October 15, 2005. # [http://www.ilovecheese.com/lactose_intolerant_faqs.asp Lactose Intolerance FAQs] from the American Dairy Association. Retrieved October 15, 2005. # Michael Quinion (2000). [http://www.worldwidewords.org/qa/qa-big1.htm World Wide Words: Big Cheese]. Retrieved October 15, 2005. # Straight Dope Staff Report (2005). [http://www.straightdope.com/mailbag/msaycheese.html Why do photographers ask you to say "cheese"?]. Retrieved October 15, 2005.

References


-
- pp 51-63, "Cheese"
- James Mellgren (2003). [http://www.gourmetretailer.com/gourmetretailer/magazine/article_display.jsp?vnu_content_id=1911696 2003 Specialty Cheese Manual, Part II: Knowing the Family of Cheese]. Retrieved October 12, 2005.

External links


- [http://www.food-info.net/uk/dairy/cheese-production.htm Production of cheese] — From Food-info.net.
- [http://www.completerecipes.com/cheese1.htm Complete Recipes: Cheese]
- [http://www.foodsci.uoguelph.ca/cheese/welcom.htm University of Guelph Food Science Cheese Site]
- [http://www.elook.org/recipes/appetizer/cheese1.html Cheese Recipes - eLook - Contains a listing of over 1,100 recipes.]
- [http://biology.clc.uc.edu/fankhauser/Cheese/Cheese_course/Cheese_course.htm Cheese Making Illustrated] — Learn the science behind homemade cheese.
- Category:Dairy products ko:치즈 ja:チーズ simple:Cheese

Volcano

:Eruption redirects here. For other meanings of the word eruption, see eruption (disambiguation) A volcano is a geological landform (usually a mountain) where a substance, usually magma (rock of the Earth's interior made molten or liquid by extremely high temperatures along with a reduction in pressure and/or the introduction of water or other volatiles) erupts through the surface of a planet. Although there are numerous volcanoes (some very active) on the solar system's rocky planets and moons, on Earth at least, this phenomenon tends to occur near the boundaries of the continental plates. However, important exceptions exist in hotspot volcanoes. hotspot volcanoes.]] The name "volcano" originates from the name of Vulcan, a god of fire in Roman mythology. The study of volcanoes is called vulcanology (or volcanology in some spellings). Mud volcanoes are formations which are often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes, except when a mud volcano is actually a vent of an igneous volcano. This article describes igneous volcanoes.

Volcano classification

Erupted material

One way of classifying volcanoes is by the type of material erupted, which affects the shape of the volcano. If the erupting magma contains a high percentage (65%) of silica the lava is called felsic or acidic and tends to be highly viscous (not very fluid) and is pushed up in a blob that will solidify relatively quickly. Lassen Peak in California is an example. This type of volcano has a tendency to explode because it retains the volatiles or gases and easily plugs. Mount Pelée on the island of Martinique is another example. If, on the other hand, the magma contains a relatively low percentage of silica, the lava is called mafic or basic and will be very fluid as it erupts, capable of flowing for long distances. Due to the low viscosity the volatiles are able to escape. A good example of a mafic lava flow is the Great flow produced by an eruptive fissure almost in the geographical center of Iceland roughly 8,000 years ago; it flowed to the sea, a distance of 130 kilometers, and covered an area of 800 square km.

Explosivity

The behaviour of volcanoes range from rare collossally explosive events to common cases of long term, gradual and gentle flow of magma. The Volcanic Explosivity Index is an attempt to categorise these into clear types, with low VEI values corresponding to gentle flows and high VEIs indicating a cataclysmic event with severe global consequences.

Shape

Shield volcanoes

Hawaii and Iceland are examples of places where volcanoes extrude huge quantities of lava that gradually build a wide mountain with a shield-like profile. Their lava flows are generally very hot and very fluid, contributing to long flows. The largest lava shield on Earth, Mauna Loa, is 9,000 m tall (it sits on the sea floor), 120 km in diameter and forms part of the Island of Hawai. Olympus Mons is a shield volcano on Mars, and the tallest mountain in the known solar system. Smaller versions of the "lava shield" include the 'lava dome' (tholoid), 'lava cone', and 'lava mound'. Volcanic cones or cinder cones result from eruptions that throw out mostly small pieces of rock that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 300 m high.

Stratovolcanoes or composite volcanoes

These are tall conical mountains composed of both lava flows and ejected material, which form the strata that give rise to the name. Classic examples include Mt. Fuji in Japan and Mount Mayon in the Philippines. Volcanoes on land often take the form of flat cones, as the expulsions build up over the years, or in short-lived volcanic cones, cinder cones.

Supervolcanoes

Supervolcano is the popular term for large volcanoes that usually have a large caldera and can potentially produce devastation on a continental scale and cause major global weather pattern changes. Potential candidates include Yellowstone National Park and Lake Toba, but are hard to identify given that there is no formal definition of the term.

Submarine volcanoes

Submarine volcanoes are common features on certain zones of the ocean floor. Some are active at the present time and, in shallow water, disclose their presence by blasting steam and rock-debris high above the surface of the sea. Many others lie at such great depths that the tremendous weight of the water above them results in high, confining pressure and prevents the formation and explosive release of steam and gases. Even very large, deepwater eruptions may not disturb the ocean surface. Under water, volcanoes often form rather steep pillars and in due time break the ocean surface in new islands.

Active, Dormant, or Extinct?

Supervolcano Volcanoes are usually situated either at the boundaries between tectonic plates or over geology hotspots. Volcanoes may be either dormant (having no activity) or active (near constant expulsion and occasional eruptions), and change state unpredictably. Surprisingly, there is no consensus among volcanologists on how to define an "active" volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespans of humans or even civilizations. For example, many of Earth's volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of activity. Given the long lifespan of such volcanoes, they are very active. By our lifespans, however, they are not. Complicating the definition are volcanoes that become restless but do not actually erupt. Are these volcanoes active? Scientists usually consider a volcano active if it is currently erupting or showing signs of unrest, such as unusual earthquake activity or significant new gas emissions. Many scientists also consider a volcano active if it has erupted in historic time. It is important to note that the span of recorded history differs from region to region; in the Mediterranean, recorded history reaches back more than 3,000 years but in the Pacific Northwest of the United States, it reaches back less than 300 years, and in Hawaii, little more than 200 years. Dormant volcanoes are those that are not currently active (as defined above), but could become restless or erupt again. Extinct volcanoes are those that scientists consider unlikely to erupt again. Whether a volcano is truly extinct is often difficult to determine. Since calderas have lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct. For example, the Yellowstone Caldera (considered a Supervolcano) in Yellowstone National Park is at least 2 million years old and hasn't erupted violently for approximately 640,000 years — although there has been some minor activity as relatively recent as 70,000 years ago. For this reason, scientists do not consider the Yellowstone Caldera as extinct. In fact, because the caldera has frequent earthquakes, a very active geothermal system (i.e., the entirety of the geothermal activity found in Yellowstone National Park), and rapid rates of ground uplift, many scientists consider it to be a very active volcano.

Notable Volcanoes

Volcanoes on Earth

:Main article: List of volcanoes List of volcanoes
- Mount Baker (Washington, USA)
- Cold Bay Volcano (Alaska, USA)
- El Chichon/El Chichonal, (Chiapas, Mexico)
- Citlaltépetl/Pico de Orizaba, (Veracruz/Puebla, Mexico)
- Cotopaxi (Ecuador)
- Mount Fuji (Honshu, Japan)
- Mount Hood (Oregon, USA)
- Mount Erebus (Ross Island, Antarctica)
- Etna (Sicily, Italy)
- Krafla (Iceland)
- Hekla (Iceland)
- Kick-'em-Jenny, (Grenada)
- Kilauea (Hawaii, USA)
- Kluchevskaya (Kamchatka, Russia)
- Krakatoa (Rakata, Indonesia)
- Mauna Kea (Hawaii, USA)
- Mauna Loa (Hawaii, USA)
- El Misti (Arequipa, Peru)
- Novarupta (Alaska, USA)
- Paricutín (Michoacán, Mexico)
- Mount Pinatubo (Luzon Island, Philippines)
- Popocatépetl (Mexico-Puebla state line, Mexico)
- Santorini (Santorini islands, Greece)
- Soufriere Hills volcano, (Montserrat)
- Stromboli (Aeolian Islands, Italy)
- Mount Rainier (Washington, USA)
- Mount Shasta (California, USA)
- Mount St. Helens (Washington, USA)
- Surtsey (Iceland)
- Tambora (Sumbawa, Indonesia)
- Teide (Tenerife, Canary Islands, Spain)
- White Island (Bay of Plenty, New Zealand)
- Mount Vesuvius (Bay of Naples, Italy)

Volcanoes elsewhere in the solar system

Italy, "Mount Olympus") is the tallest known mountain in our solar system, located on the planet Mars.]] The Earth's Moon has no large volcanoes, but does have many volcanic features such as rilles and domes. The planet Venus is believed to be volcanically active, and its surface is 90% basalt, indicating that volcanism plays a major role in shaping its surface. Lava flows are widespread and many of its surface features are attributed to exotic forms of volcanism not present on Earth. Other Venusian phenomena, such as changes in the planet's atmosphere and observations of lightning, have been attributed to ongoing volcanic eruptions. There are several extinct volcanoes on Mars, four of which are vast shield volcanoes far bigger than any on Earth:
- Arsia Mons
- Ascraeus Mons
- Hecates Tholus
- Olympus Mons
- Pavonis Mons These volcanoes have been extinct for many millions of years, but the European Mars Express spacecraft has found evidence that volcanic activity may have occurred on Mars in the recent past as well. Jupiter's moon Io is the most volcanic object in the solar system, due to tidal interaction with Jupiter. It is covered with volcanoes that erupt sulfur, sulfur dioxide and silicate rock, with the result that the moon is constantly being resurfaced. Its lavas are the hottest known anywhere in the solar system, with temperatures exceeding 1800 K (1500 °C). In February 2001, the largest recorded volcanic eruptions in the solar system occurred on Io [http://www2.keck.hawaii.edu/news/archive/eruption/]. See the list of geological features on Io for a list of named volcanoes on the moon. list of geological features on Io In 1989 the Voyager 2 spacecraft observed ice volcanoes (cryovolcanism) on Triton, a moon of Neptune and in 2005 the Cassini-Huygens probe photographed fountains of frozen particles erupting from Saturn's moon Enceladus. The ejecta are believed to consist of liquid nitrogen, dust, or methane compounds. Cassini-Huygens also found evidence of a methane-spewing cryovolcano on the Saturnian moon Titan, which is believed to be a significant source of the methane found in its atmosphere. [http://www.newscientist.com/article.ns?id=dn7489] It is theorized that cryovolcanism may also be present on the Kuiper Belt Object Quaoar.

Volcanology

Volcano formation

Quaoar Like most of the interior of the earth, the movements and dynamics of magma are poorly understood. However, it is known that an eruption usually follows movement of magma upwards into the solid layer (the earth's crust) beneath a volcano and occupying a magma chamber. Eventually, magma in the chamber is forced upwards and flows out across the planet surface as lava, or the rising magma can heat water in the surrounding landform and cause explosive discharges of steam; either this or escaping gases from the magma can produce forceful ejections of rocks, cinders, volcanic glass, and/or volcanic ash also known as tephra. While always displaying powerful forces, eruptions can vary from effusive to extremely explosive. Most volcanoes on the land are formed at destructive plate margins: where oceanic crust is forced below the continental crust because oceanic crust is denser than continental crust. Friction between these moving plates will cause the oceanic crust to melt, and reduced density will force the newly formed magma to rise. As the magma rises through weak areas in the continental crust it may eventually erupt as one or more volcanoes. For example, Mount St. Helens is found inland from the margin between the oceanic Juan de Fuca Plate and the continental North American Plate. North American Plate A volcano generally presents itself to the imagination as a mountain sending forth from its summit great clouds of smoke with vast sheets of flame. The truth is that a volcano seldom emits either smoke or flame, although various combinations of hydrogen, carbon, oxygen, and sulfur do sometimes ignite. What is mistaken for smoke consists of vast volumes of fine dust, mingled with steam and other vapors, chiefly sulfurous. Most of what appears to be flames is the glare from the erupting materials, glowing because of their high temperature; this glare reflects off the clouds of dust and steam, resembling fire. Perhaps the most conspicuous part of a volcano is the crater, a basin of a roughly circular form within which occurs a vent (or vents) from which magma erupts as gases, lava, and ejecta. A crater can be of large dimensions, and sometimes of vast depth. Very large features of this sort are termed calderas. Some volcanoes consist of a crater alone, with scarcely any mountain at all; but in the majority of cases the crater is situated on top of a mountain (the volcano), which can tower to an enormous height. Volcanoes that terminate in a principal crater are usually of a conical form. Volcanic cones are usually smaller features composed of loose ash and cinder, with occasional masses of stone which have been tossed violently into the air by the eruptive forces (and are thus called ejecta). Within the crater of a volcano there may be numerous cones from which vapours are continually issuing, with occasional volleys of ashes and stones. In some volcanoes these cones form lower down the mountain, along rift zones or fractures. When the cone is eroded these rifts or lava filled fractures remain as radial near vertical dikes of volcanic rock. For example the radiating dikes at Shiprock in NW New Mexico.

Tectonic environments of volcanoes

Volcanoes can principally be found in three tectonic environments. New Mexico
Constructive plate margins
These are by far the most common volcanoes on the Earth. They are also the least frequently seen, because most of their activity takes place beneath the surface of the oceans. Along the whole of the oceanic ridge system are irregularly spaced surface eruptions, and more frequent sub-surface intrusions without surface expression. The large majority of these are only known about at surface because of earthquakes as part of the eruptions/ intrusions, or occasionally if passing shipping happens to notice unusually high water temperatures or chemical precipitates in the seawater. In a few places oceanic ridge activity has lead to the volcanoes coming up to the surface - Saint Helena and Tristan da Cunha in the Atlantic Ocean; the Galapagos Islands in the Pacific Ocean, allowing them to be studied in some detail. But most activity takes place in considerable water depths. Iceland is also on a ridge, but has different characteristics than a simple volcano. It could be argued that the volcanoes of the Great Rift Valley system of East Africa are modified constructive margin volcanoes. However the modifications caused by the presence of thick continental crust are very substantial, and the magmas produced are very different from the typically very homogenous MORB (Mid-Ocean Ridge Basalt) that makes up the huge majority of constructive margin volcanoes.
Destructive plate margins
These are the most visible and well-known types of volcanoes on earth, forming above the subduction zones where (oceanic) plates dive into the Earth to their destruction. Their magmas are typically "calc-alkaline" as a result of their origins in the upper parts of altered ocean plate materials, mixed with sediments, and processed through variable thicknesses of more-or-less continental crust. The heavier plate sinks under the lighter one and the friction from the melting plate causes magma to force it's way out through a crack in the crust. Unsurprisingly, their compositions are much more varied than at constructive margins.
Hotspot situations
subduction zones, Iceland]] Hotspots were originally a catch-all for volcanoes that didn't fit into one of the above two categories, but these days this refers to a more specific circumstance - where an isolated plume of hot mantle material intersects the underside of crust (oceanic or continental), leading to a volcanic center that is not obviously connected with a plate margin. The classic example is the Hawaiian chain of volcanoes and seamounts; Yellowstone is cited as another classic example, in this case the intersection is with the underside of continental crust. Iceland is sometimes cited as yet a third classical example, but complicated by the coincidence of a hotspot intersecting an oceanic ridge constructive margin. There are debates about the simple "hotspot" concept, since theorists cannot agree on whether the "hot mantle plumes" originate in the upper mantle or in the lower mantle. Meanwhile, field geologists and petrologists see considerable variation in the detailed chemistry of one hotspot's magmas versus a second hotspot's magmas. On the third hand, high-resolution seismology of different hotspots is yielding different pictures of the deep sub-structure of Hawaii versus Iceland. There is no detailed consensus about how to interpret these varied results, and it seems plausible that eventually several different sub-types of hotspots will be identified.

Predicting eruptions

Science has not yet been able to predict with absolute certainty when a volcanic eruption will take place, but significant progress in judging when one is probable has been made in recent time. Iceland, 1980 at 8:32 a.m. PDT]] Volcanologists use the following to forecast eruptions.

Seismicity

Seismic activity (small earthquakes and tremors) always occurs as volcanoes awaken and prepare to erupt. Some volcanoes normally have continuing low-level seismic activity, but an increase can signify an eruption. The types of earthquakes that occur and where they start and end are also key signs. Volcanic seismicity has three major forms: short-period earthquakes, long-period earthquakes, and harmonic tremor.
- Short-period earthquakes are like normal fault-related earthquakes. They are related to the fracturing of brittle rock as the magma forces its way upward. These short-period earthquakes signify the growth of a magma body near the surface.
- Long-period earthquakes are believed to indicate increased gas pressure in a volcano's "plumbing system." They are similar to the clanging sometimes heard in your home's plumbing system. These oscillations are the equivalent of acoustic vibrations in a chamber, in the context of magma chambers within the volcanic dome. Patterns of seismicity are complex and often difficult to interpret. However, increasing activity is very worrisome, especially if long-period events become dominant and episodes of harmonic tremor appear. In December 2000, scientists at the National Center for Prevention of Disasters in Mexico City predicted an eruption within two days from Popocatépetl, on the outskirts of Mexico City. Their prediction used research done by Dr. Bernard Chouet, a Swiss vulacanologist working at the United States Geological Survey, into increasing long-period oscillations as an indicator of an imminent eruption. The government evacuated tens of thousands of people. Forty eight hours later, bang on time, the volcano erupted spectacularly. It was Popocatépetl's largest eruption for a thousand years and yet no one was hurt.

Gas emissions

United States Geological Survey As magma nears the surface and its pressure decreases, gases escape. This process is much like what happens when you open a bottle of soda and carbon dioxide escapes. Sulfur dioxide is one of the main components of volcanic gases, and increasing amounts of it herald the arrival of more and more magma near the surface. For example, on May 13, 1991, 500 tonnes of sulfur dioxide were released from Mount Pinatubo in the Philippines. On May 28, just two weeks later, sulfur dioxide emissions had increased to 5,000 tonnes, ten times the earlier amount. Mount Pinatubo erupted on June 12, 1991. On several occasions, such as before the Mount Pinatubo eruption, sulfur dioxide emissions have dropped to low levels prior to eruptions. Most scientists believe that this drop in gas levels is caused by the sealing of gas passages by hardened magma. Such an event leads to increased pressure in the volcano's plumbing system and an increased chance of an explosive eruption.

Ground deformation

Swelling of the volcano signals that magma has accumulated near the surface. Scientists monitoring an active volcano will often measure the tilt of the slope and track changes in the rate of swelling. An increased rate of swelling, especially if accompanied by an increase in sulfur dioxide emissions and harmonic tremors is a high probability sign of an impending event.

Effects of volcanoes

There are many different kinds of volcanic activity and eruptions:
- phreatic eruptions (steam)
- explosive eruption of high-silica lava (e.g., rhyolite)
- effusive eruption of low-silica lava (e.g., basalt)
- pyroclastic flows
- lahars (debris flow)
- carbon dioxide emission All of these activities can pose a hazard to humans. Volcanic activity is often accompanied by earthquakes, hot springs, fumaroles, mud pots and geysers. Low-magnitude earthquakes often precede eruptions. The concentrations of different volcanic gases can vary considerably from one volcano to the next. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide. Other principal volcanic gases include hydrogen sulfide, hydrogen chloride, and hydrogen fluoride. A large number of minor and trace gases are also found in volcanic emissions, for example: hydrogen, carbon monoxide, and volatile metal chlorides. carbon monoxide carbon monoxide carbon monoxide Large, explosive volcanic eruptions inject water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen chloride (HCl), hydrogen fluoride (HF) and ash (pulverized rock and pumice) into the stratosphere to heights of 10-20 miles above the Earth's surface. The most significant impacts from these injections come from the conversion of sulfur dioxide to sulfuric acid (H2SO4), which condenses rapidly in the stratosphere to form fine sulfate aerosols. The aerosols increase the reflection of radiation from the Sun back into space and thus cool the Earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere. Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree (Fahrenheit scale) for periods of one to three years. The sulfate aerosols also promote complex chemical reactions on their surfaces that alter chlorine and nitrogen chemical species in the stratosphere. This effect, together with increased stratospheric chlorine levels from chlorofluorocarbon pollution, generates chlorine monoxide (ClO), which destroys ozone (O3). As the aerosols grow and coagulate, they settle down into the upper troposphere where they serve as nuclei for cirrus clouds and further modify the Earth's radiation balance. Most of the hydrogen chloride (HCl) and hydrogen fluoride (HF) are dissolved in water droplets in the eruption cloud and quickly fall to the ground as acid rain. The injected ash also falls rapidly from the stratosphere; most of it is removed within several days to a few weeks. Finally, explosive volcanic eruptions release the greenhouse gas carbon dioxide and thus provide a deep source of carbon for biogeochemical cycles. Gas emissions from volcanoes are a natural contributor to acid rain. Volcanic activity now releases about 130 to 230 teragrams (145 million to 255 million short tons) of carbon dioxide each year. Volcanic eruptions may inject an aerosol of particles and chemicals in the Earth's atmosphere. Large injections may have visual effects and affect global climate through climate forcing.

Past beliefs

Before it was understood that most of the Earth's interior is molten, various explanations existed for volcano behavior. For decades after awareness that compression and radioactive materials may be heat sources, their contributions were specifically discounted. Volcanic action was often attributed to chemical reactions and a thin layer of molten rock near the surface. Jesuit Athanasius Kircher (1602-1680), witnessed eruptions of Aetna and Stromboli, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by the burning of sulfur, bitumen and coal. coal

See also


- Supervolcano
- Iceland hotspot
- Prehistoric volcano
- List of volcanoes
- List of famous volcanic eruption deaths
- Volcanic Explosivity Index
- Black smoker (deep sea vent)
- Magma
- Lava
- Pacific Ring of Fire
- Geomorphology
- Earth science
- Io
- Triton (moon)
- Tsunami
- Top 10 most deadly Volcanic Eruptions
- Haroun Tazieff (famous volcanologist)

References


- Macdonald, Gordon A., and Agatin T. Abbott. (1970). Volcanoes in the Sea. University of Hawaii Press, Honolulu. 441 p.
- Ollier, Cliff. (1988). Volcanoes. Basil Blackwell, Oxford, UK, ISBN 0-631-15664-X (hardback), ISBN 0-631-15977-0 (paperback).

Further reading


- Haraldur Sigurðsson, ed. (1999) Encyclopedia of Volcanoes. Academic Press. ISBN 012643140X. This is a reference aimed at geologists, but many articles are accessible to non-professionals.

External links


- [http://volcanoes.usgs.gov/Products/Pglossary/pglossary.html Glossary of Volcanic Terms from USGS]
- [http://volcano.und.nodak.edu/vwdocs/glossary.html Volcanic and Geologic Terms] from [http://volcano.und.nodak.edu/ Volcano World]
- [http://news.bbc.co.uk/1/hi/sci/tech/3183047.stm Television program (BBC) on the prediction of Popocatepetl's 2000 eruption]
- [http://www.volcano.si.edu Smithsonian Global Volcanism Program]
- [http://www.geology.sdsu.edu/how_volcanoes_work Explore the geologic causes of an eruption]
- [http://science.howstuffworks.com/volcano.htm/printable How Volcanoes Work by Tom Harris]
- [http://www.geology.sdsu.edu/how_volcanoes_work/ How Volcanoes Work] - Educational resource on the science and processes behind volcanoes, intended for university students of geology, volcanology and teachers of earth science.
- [http://www.geonet.org.nz/volcanocam.html Volcano Cam Geonet's live pictures of 4 of New Zealand's volcanoes]
- [http://facweb.bhc.edu/academics/science/harwoodr/GEOL101/Labs/VolcanicMaterials/ Volcanic Materials Identification] Category:Landforms Category:Plate tectonics Category:Volcanology
- Category:Geological hazards Category:Climate forcing agents als:Vulkanismus ms:Gunung berapi ja:火山 simple:Volcano th:ภูเขาไฟ

Deep sea vent

Black smokers are a type of hydrothermal vent found on the ocean floor. Generally hundreds of meters wide, black smokers are formed when superheated water from below the Earth's crust comes through the ocean floor. They are rich in dissolved minerals from the crust, most notably sulfides, which crystallize to create a chimney-like structure around the vent. When the superheated water in the vent comes in contact with the frigid ocean water, many minerals are precipitated, creating the distinctive black color. The metal sulfides that are deposited can become massive sulfide ore deposits in time. Black smokers were first discovered in 1977 around the Galápagos Islands by the National Oceanic and Atmospheric Administration. They were observed using a small submersible vehicle called Alvin. Today, black smokers are known to exist in the Atlantic and Pacific Oceans, at an average depth of 2100 meters. The temperature of the water they vent can reach 400 °C, but does not boil due to the high pressure it is under at that depth. The water is also extremely acidic, often having a pH value as low as 2.8 — approximately that of vinegar.

Black smoker ecosystem

vinegar Although life is very sparse at these depths, black smokers are the center of entire ecosystems. Sunlight is nonexistent, so many organisms — such as archaea and extremophiles — must convert the heat, methane, and sulfur compounds provided by black smokers into energy through a process called chemosynthesis. In turn, more complex life forms like clams and tubeworms feed on these organisms. The organisms at the base of the food chain also deposit minerals into the base of the black smoker, thus completing the life cycle. A bacterium that uses photosynthesis has been found living near a black smoker off the coast of Mexico. At a depth of 2,500 m, no sunlight penetrates the waters. Instead, the bacterium, part of the Green sulfur bacteria family, use the faint glow from the black smoker for photosynthesis making