Stags Leap District AVA
The Stags Leap District AVA is an American Viticultural Area located within the Napa Valley AVA 6 miles north of the city of Napa, California. The Stags Leap District was the first appellation to be designated an AVA based on the unique terroir characteristics of its soil; the soil of this region include loam and clay sediments from the Napa River and volcanic soil deposits left over from erosion of the Vaca Mountains. Like many Napa Valley AVAs, Stags Leap District is known for its Cabernet Sauvignon. In 1976 at the Judgment of Paris wine tasting, the 1973 Stag's Leap Wine Cellars Cabernet from the area that would become this AVA won first place in the red wine category, beating out classified Bordeaux estates. Today, the Stags Leap District is home to twenty different wineries. Grapes were planted in the area that would become the Stags Leap District as early as the 1870s, with the first winery in the area being founded in 1878. Nathan Fay planted the first Cabernet Sauvignon in the area in 1961, on land that would be purchased by Warren Winiarski for Stag's Leap Wine Cellars.
One of the leading forces in the region is Stags Leap District Winery Association which aims to promote the wines of the AVA and host an annual day-long event called Vineyard to Vintner which allows consumers the opportunity to interact with wineries and taste the regions wine. The following wineries are members: Baldacci Family Vineyards Chimney Rock Winery Cliff Lede Vineyards Clos Du Val Griffin Vineyards Hartwell Vineyards Ilsley Vineyards Pine Ridge Vineyards Regusci Winery Shafer Vineyards Silverado Vineyards Robert Sinskey Vineyards Stags' Leap Winery Stag's Leap Wine Cellars Steltzner Vineyards Taylor Family Vineyards Odette Estate Winery
Chardonnay
Chardonnay is a green-skinned grape variety used in the production of white wine. The variety originated in the Burgundy wine region of eastern France, but is now grown wherever wine is produced, from England to New Zealand. For new and developing wine regions, growing Chardonnay is seen as a "rite of passage" and an easy entry into the international wine market; the Chardonnay grape itself is neutral, with many of the flavors associated with the wine being derived from such influences as terroir and oak. It is vinified in many different styles, from the lean, crisply mineral wines of Chablis, France, to New World wines with oak and tropical fruit flavors. In cool climates, Chardonnay wine tends to be medium to light body with noticeable acidity and flavors of green plum and pear. In warmer locations, the flavors become more citrus and melon, while in warm locations, more fig and tropical fruit notes such as banana and mango come out. Wines that have gone through malolactic fermentation tend to have softer acidity and fruit flavors with buttery mouthfeel and hazelnut notes.
Chardonnay is an important component of many sparkling wines around the world, including Champagne and Franciacorta in Italy. Chardonnay's popularity peaked in the late 1980s gave way to a backlash among those wine connoisseurs who saw the grape as a leading negative component of the globalization of wine. Nonetheless, it is one of the most planted grape varieties, with 210,000 hectares worldwide, second only to Airén among white wine grapes and fifth among all wine grapes. For much of its history, a connection was assumed between Pinot blanc. In addition to being found in the same region of France for centuries, ampelographers noted that the leaves of each plant have near-identical shape and structure. Pierre Galet disagreed with this assessment, believing that Chardonnay was not related to any other major grape variety. Viticulturalists Maynard Amerine and Harold Olmo proposed a descendency from a wild Vitis vinifera vine, a step removed from white Muscat. Chardonnay's true origins were further obscured by vineyard owners in Lebanon and Syria, who claimed that the grape's ancestry could be traced to the Middle East, from where it was introduced to Europe by returning Crusaders, though little external evidence supports that theory.
Another theory stated. Modern DNA fingerprinting research at University of California, now suggests that Chardonnay is the result of a cross between the Pinot noir and Gouais blanc grape varieties; the Romans are thought to have brought Gouais blanc from Croatia, it was cultivated by peasants in eastern France. The Pinot of the French aristocracy grew in close proximity to the Gouais blanc, giving both grapes ample opportunity to interbreed. Since the two parents were genetically distant, many of the crosses showed hybrid vigour and were selected for further propagation; these "successful" crosses included Chardonnay and siblings such as Aligoté, Aubin vert, Bachet noir, Franc Noir de la-Haute-Saône, Gamay Blanc Gloriod, Gamay noir, Knipperlé, Roublot and Dameron. As of 2006, 34 clonal varieties of Chardonnay could be found in vineyards throughout France, most of which were developed at the University of Burgundy in Dijon; the so-called "Dijon clones" are bred for their adaptive attributes, with vineyard owners planting the clonal variety best suited to their terroir and which will produce the characteristics that they are seeking in the wine.
Examples include the lower-yielding clones'Dijon-76','95' and'96' that produce more flavor-concentrated clusters.'Dijon-77' and'809' produce more aromatic wines with a "grapey" perfume, while'Dijon-75','78','121','124','125' and'277' are more vigorous and higher-yielding clones. New World varieties include the'Mendoza' clone, which produced some of the early California Chardonnays. The'Mendoza' clone is prone to develop millerandage known as "hens and chicks", where the berries develop unevenly. In places such as Oregon, the use of newer Dijon clones has had some success in those regions of the Willamette Valley with climates similar to that of Burgundy. Chardonnay has served as parent to several French-American hybrid grapes, as well as crossings with other V. vinifera varieties. Examples include the hybrid Chardonel, a Chardonnay and Seyval blanc cross produced in 1953 at the New York State Agricultural Experiment Station. Mutations of the Chardonnay grape include the rare pink-berried'Chardonnay Rose'.
Chardonnay Blanc Musqué is found around the Mâconnais village of Clessé and sometimes confused with the'Dijon-166' clone planted in South Africa, which yields Muscat-like aromas. In the 1930s, Chardonnay was crossed with a Seibel grape to create the hybrid grape Ravat blanc. Chardonnay has a wide-ranging reputation for relative ease of cultivation and ability to adapt to different conditions; the grape is "malleable", in that it reflects and takes on the impression of its terroir and winemaker. It is a vigorous vine, with extensive leaf cover which can inhibit the energy and nutrient uptake of its grape clusters. Vineyard managers counteract this with aggressive canopy management; when Chardonnay vines are planted densely, they are forced to compete for resources and funnel energy into their grape clusters. In certain conditions, the vines can be v
Mediterranean climate
A Mediterranean climate or dry summer climate is characterized by rainy winters and dry summers, with less than 40 mm of precipitation for at least three summer months. While the climate receives its name from the Mediterranean Basin, these are located on the western coasts of continents, between 30 and 45 degrees north and south of the equator between oceanic climates towards the poles, semi-arid and arid climates towards the equator. In essence, due to the seasonal shift of the subtropical high-pressure belts with the apparent movement of the Sun, a Mediterranean climate is an intermediate type between these other climates, with winters warmer and drier than oceanic climates and summers imitating sunny weather in semi-arid and arid climates; the resulting vegetation of Mediterranean climates are the garrigue or maquis in the Mediterranean Basin, the chaparral in California, the fynbos in South Africa, the mallee in Australia, the matorral in Chile. Areas with this climate are where the so-called "Mediterranean trinity" of agricultural products have traditionally developed: wheat and olive.
Most large, historic cities of the Mediterranean basin lie within Mediterranean climatic zones, including Algiers, Beirut, İzmir, Marseille, Rome and Valencia. Examples of major cities with Mediterranean climates that lie outside of the historic Mediterranean basin include major examples as Adelaide, Cape Town, Dushanbe, Los Angeles, Perth, San Francisco and Victoria. Under the Köppen climate classification, "hot dry-summer" climates and "cool dry-summer" climates are referred to as "Mediterranean". Under the Köppen climate system, the first letter indicates the climate group. Temperate climates or "C" zones have an average temperature above 0 °C, but below 18 °C, in their coolest months; the second letter indicates the precipitation pattern. Köppen has defined a dry summer month as a month with less than 30 mm of precipitation and with less than one-third that of the wettest winter month. Some, use a 40 mm level; the third letter indicates the degree of summer heat: "a" represents an average temperature in the warmest month above 22 °C, while "b" indicates the average temperature in the warmest month below 22 °C.
Under the Köppen classification, dry-summer climates occur on the western sides of continents. Csb zones in the Köppen system include areas not associated with Mediterranean climates but with Oceanic climates, such as much of the Pacific Northwest, much of southern Chile, parts of west-central Argentina, parts of New Zealand. Additional highland areas in the subtropics meet Cs requirements, though they, are not associated with Mediterranean climates, as do a number of oceanic islands such as Madeira, the Juan Fernández Islands, the western part of the Canary Islands, the eastern part of the Azores. Under Trewartha's modified Köppen climate classification, the two major requirements for a Cs climate are revised. Under Trewartha's system, at least eight months must have average temperatures of 10 °C or higher, the average annual precipitation must not exceed 900 mm. Thus, under this system, many Csb zones in the Köppen system become Do, the rare Csc zones become Eo, with only the classic dry-summer to warm winter, low annual rainfall locations included in the Mediterranean type climate.
During summer, regions of Mediterranean climate are influenced by cold ocean currents which keep the weather in the region dry and pleasant. Similar to desert climates, in many Mediterranean climates there is a strong diurnal character to daily temperatures in the warm summer months due to strong heating during the day from sunlight and rapid cooling at night. In winter, Mediterranean climate zones are no longer influenced by the cold ocean currents and therefore warmer water settles near land and causes clouds to form and rainfall becomes much more likely; as a result, areas with this climate receive all of their precipitation during their winter and spring seasons, may go anywhere from 3 to 6 months during the summer without having any significant precipitation. In the lower latitudes, precipitation decreases in both the winter and summer because they are closer to the Horse latitudes, thus bringing smaller amounts of rain. Toward the polar latitudes, total moisture increases; the rainfall tends to be more evenly distributed throughout the year in Southern Europe, while in the Eastern Mediterranean and in Southern California the summer is nearly or dry.
In places where evapotranspiration is higher, steppe climates tend to prevail, but still follow the weather pattern of the Mediterranean climate. The majority of the regions with Mediterranean climates have mild winters and warm summers; however winter and summer temperatures can vary between different regions with a Mediterranean climate. For instance, in the case of winters and Los Angeles experience mild temperatures in the winter, with frost and snowfall unknown, whereas Tashkent has colder winters with annual frosts and snowfall. Or to consider summer, Athens experiences rather high temperatures in that season. In contrast, San Francisco has cool summers with daily highs around 21 °C due to
Judgment of Paris (wine)
The Paris Wine Tasting of 1976—known as the Judgment of Paris—was a wine competition organized in Paris on 24 May 1976 by Steven Spurrier, a British wine merchant, in which French judges carried out two blind tasting comparisons: one of top-quality Chardonnays and another of red wines. A Californian wine rated best in each category, which caused surprise as France was regarded as being the foremost producer of the world's best wines. Spurrier believed that the California wines would not win; the event's informal name. Red wines White wines The eleven judges were: Blind tasting was performed and the judges were asked to grade each wine out of 20 points. No specific grading framework was given, leaving the judges free to grade according to their own criteria. Rankings of the wines preferred by individual judges were done based on the grades they individually attributed. An overall ranking of the wines preferred by the jury was established in averaging the sum of each judge's individual grades. However, grades of Patricia Gallagher and Steven Spurrier were not taken into account, thus counting only grades of French judges.
California Cabernet Sauvignon vs. Bordeaux. In alphabetical order of judges; the original grades are shown. Pierre Brejoux Original grades: out of 20 points. Claude Dubois-Millot Original grades: out of 20 points. Michel Dovaz Original grades: out of 20 points. Patricia Gallagher Original grades: out of 20 points. Odette Kahn Original grades: out of 20 points. Raymond Oliver Original grades: out of 20 points. Steven Spurrier Original grades: out of 20 points. Pierre Tari Original grades: out of 20 points. Christian Vanneque Original grades: out of 20 points. Aubert de Villaine Original grades: out of 20 points. Jean-Claude Vrinat Original grades: out of 20 points. Average Original grades: out of 20 points. California Chardonnays vs. Burgundy Chardonnays Average Original grades: out of 20 points. Criticism of the event suggested that wine tastings lacked scientific validity due to the subjectivity of taste in human beings. Indeed, the organizer of the competition, Steven Spurrier, said, "The results of a blind tasting cannot be predicted and will not be reproduced the next day by the same panel tasting the same wines."
In one case it was reported that a "side-by-side chart of best-to-worst rankings of 18 wines by a roster of experienced tasters showed about as much consistency as a table of random numbers." Without calling into question the abilities of the tasters, scientific concerns have been raised about the methodology used by individual judges as well as the validity of any statistical interpretation. The heterogeneity of the grades given by individual judges was seen as a consequence of the lack of a common grading system among tasters, the data sample was deemed too small for meaningful statistical interpretation. Steven Spurrier, the organizer of the tasting, acknowledged in Decanter in August 1996 that he tallied the winners by "adding the judges' marks and dividing this by nine." Orley Ashenfelter and Richard E. Quandt analyzed the results of all 11 judges instead of only 9 and proposed a different ranking, they stated that only the scores of the first two wines in their ranking were statistically valid, that the seven other wines could not be differentiated statistically.
USA Stag's Leap Wine Cellars'73 France Montrose'70 France Mouton'70 France Haut Brion'70 USA Ridge Monte Bello'71 USA Heitz Martha's'70 France Leoville-las-cases'71 USA Freemark Abbey'69 USA Mayacamas'71 USA Clos du Val'72 Some critics argued that French red wines would age better than the California reds, so this was tested. The San Francisco Wine Tasting of 1978 was conducted 20 months after the Paris Wine Tasting of 1976. Steven Spurrier flew in from Paris to participate in the evaluations, which were held at the Vintners Club. On January 11, 1978, evaluators blind-tasted. USA – 1974 Chalone Winery USA – 1973 Chateau Montelena USA – 1973 Spring Mountain Vineyard France – 1972 Puligny-Montrachet Les Pucelles Domaine Leflaive. Ranking lower were Meursault Charmes Roulot 1973, Beaune Clos des Mouches Joseph Drouhin 1973, Batard-Montrachet Ramonet-Prudhon 1973. On January 12, 1978, evaluators blind-tasted. USA – 1973 Stag's Leap Wine Cellars USA – 1970 Heitz Wine Cellars Martha's vineyard USA – 1971 Ridge Vineyards Monte Bello France – 1970 Château Mouton Rothschild.
Ranking lower were Château Montrose 1970, Château Haut-Brion 1970, Château Leoville Las Cases 1971. Two tastings were conducted by the French Culinary Institute on the tenth anniversary of the original Paris Wine Tasting. White wines were not evaluated in the belief. Steven Spurrier, who organized the original 1976 wine competition, assisted in the anniversary tasting. Eight judges blind tasted nine of the ten wines evaluated; the evaluation resulted in the following ranking ResultsRank Wine USA – Clos Du Val Winery 1972 USA – Ridge Vineyards Monte Bello France – Château Montrose France – Château Leoville Las Cases 1971 France – Château Mouton Rothschild 1970 USA – Stag's Leap Wine Cellars 1973 USA – Heitz Wine Cellars 1970 USA – Mayacamas Vineyards 1971 France – Château Haut-Brion Four of the judges were experts from Wine Spectator and two were outsiders. All tasted the wines blind. ResultsRank Wine USA – Heitz Wine Cellars 1970 USA – Mayacamas Vineyards 1971 USA – Ridge Vineyards Mont
Sauvignon blanc
Sauvignon blanc is a green-skinned grape variety that originates from the Bordeaux region of France. The grape most gets its name from the French words sauvage and blanc due to its early origins as an indigenous grape in South West France, it is a descendant of Savagnin. Sauvignon blanc is planted in many of the world's wine regions, producing a crisp and refreshing white varietal wine; the grape is a component of the famous dessert wines from Sauternes and Barsac. Sauvignon blanc is cultivated in France, Romania, Australia, New Zealand, South Africa, the states of Washington and California in the US; some New World Sauvignon blancs from California, may be called "Fumé Blanc", a marketing term coined by Robert Mondavi in reference to Pouilly-Fumé. Depending on the climate, the flavor can range from aggressively grassy to sweetly tropical. In cooler climates, the grape has a tendency to produce wines with noticeable acidity and "green flavors" of grass, green bell peppers and nettles with some tropical fruit and floral notes.
In warmer climates, it can develop more tropical fruit notes but risk losing a lot of aromatics from over-ripeness, leaving only slight grapefruit and tree fruit notes. Wine experts have used the phrase "crisp and fresh" as a favorable description of Sauvignon blanc from the Loire Valley and New Zealand. Sauvignon blanc, when chilled, pairs well with fish or cheese chèvre, it is known as one of the few wines that can pair well with sushi. Along with Riesling, Sauvignon blanc was one of the first fine wines to be bottled with a screwcap in commercial quantities by New Zealand producers; the wine is consumed young, as it does not benefit from aging, as varietal Sauvignon blancs tend to develop vegetal aromas reminiscent of peas and asparagus with extended aging. Dry and sweet white Bordeaux, including oak-aged examples from Pessac-Léognan and Graves, as well as some Loire wines from Pouilly-Fumé and Sancerre are some of the few examples of Sauvignon blancs with aging potential; the first Friday in May is International Sauvignon Blanc Day.
The Sauvignon blanc grape traces its origins to western France in the Loire Valley and Bordeaux Regions. As noted above, it is not clear. Ongoing research suggests, it has been associated with the Carmenere family. At some point in the 18th century, the vine paired with Cabernet Franc to parent the Cabernet Sauvignon vine in Bordeaux. In the 19th century, plantings in Bordeaux were interspersed with Sauvignon vert as well as the Sauvignon blanc pink mutation Sauvignon gris. Prior to the phylloxera epidemic, the insect plague which devastated French vineyards in the 19th century, these interspersed cuttings were transported to Chile where the field blends are still common today. Despite the similarity in names, Sauvignon blanc has no known relation to the Sauvignon rosé mutation found in the Loire Valley of France; the first cuttings of Sauvignon blanc were brought to California by Charles Wetmore, founder of Cresta Blanca Winery, in the 1880s. These cuttings came from the Sauternes vineyards of Château d'Yquem.
The plantings produced well in Livermore Valley. The wine acquired the alias of "Fumé Blanc" in California by promotion of Robert Mondavi in 1968; the grape was first introduced to New Zealand in the 1970s as an experimental planting to be blended with Müller-Thurgau. The Sauvignon blanc vine buds late but ripens early, which allows it to perform well in sunny climates when not exposed to overwhelming heat. In warm regions such as South Africa and California, the grape flourishes in cooler climate appellations such as the Alexander Valley area. In areas where the vine is subjected to high heat, the grape will become over-ripe and produce wines with dull flavors and flat acidity. Rising global temperatures have caused farmers to harvest the grapes earlier than they have in the past; the grape originated in the regions of Bordeaux and the Loire Valley. Plantings in California, Australia and South Africa are extensive, Sauvignon blanc is increasing in popularity as white wine drinkers seek alternatives to Chardonnay.
The grape can be found in Italy and Central Europe. In France, Sauvignon blanc is grown in the maritime climate of Bordeaux as well as the continental climate of the Loire Valley; the climates of these areas are favorable in slowing the ripening on the vine, allowing the grape more time to develop a balance between its acidity and sugar levels. This balance is important in the development of the intensity of the wine's aromas. Winemakers in France pay careful attention to the terroir characteristics of the soil and the different elements that it can impart to the wine; the chalk and Kimmeridgean marl of Sancerre and Pouilly produces wines of richness and complexity while areas with more compact chalk soils produces wines with more finesse and perfume. The gravel soil found near the Loire River and its tributaries impart spicy and mineral flavors while in Bordeaux, the wines have a fruitier personality. Vines planted in flint tend to produce the longest lasting wines. Pouilly Fumé originate from the town of Pouilly-sur-Loire, located directly across the Loire River from the commune of Sancerre.
The soil here is flinty with deposits of limestone which the locals believed imparted a smoky, gun flint flavor
Los Carneros AVA
Los Carneros AVA is an American Viticultural Area which includes parts of both Sonoma and Napa counties in California, U. S. A.. It is located north of San Pablo Bay; the proximity to the cool fog and breezes from the bay makes the climate in Los Carneros cooler and more moderate than the wine regions further north in Napa Valley and Sonoma Valley. The cooler climate has made Los Carneros attractive for the cultivation of cooler climate varietals like Pinot noir and Chardonnay. Many of the grapes grown in Los Carneros are used for sparkling wine production. Receiving its AVA status in 1983, the Carneros area was the first wine region in California to be defined by its climate characteristics rather than political boundaries; the default Windows XP "Bliss" background image was photographed here, a few years after the vineyards had been removed following a phylloxera infestation. In the year 1942, wine producer Louis M. Martini purchased the old Stanly Ranch and began a replanting effort. By the 1970s, the Carneros region had more than 1,300 acres of vineyards.
By this time the Carneros region was starting to develop a reputation for the quality of the Chardonnays and Pinot noirs that came from this cool-climate region. This reputation caught the eyes of sparkling wine producers from elsewhere. In the 1970s and continuing to this day, Francis Mahoney of Mahoney Vineyards and Fleur de California in conjunction with UC-Davis have conducted an ongoing series of clonal trials to determine the best Pinot noir grapes for the Carneros region; the 1980s saw a wave of investment and development in Los Carneros by producers such as Domaine Chandon, Domaine Carneros, Gloria Ferrer, Mumm Napa and Codorníu Napa that made Carneros one of the centers of California sparkling wine production. In the late 1980s, phylloxera returned to the Carneros region prompting extensive replanting efforts. In addition to taking advantage of better phylloxera-resistant rootstock, many Carneros producers took the opportunity to plant some of the new French clones of Pinot noir and Chardonnay.
The surging popularity of Chardonnay in the 1980s further stimulated plantings in the Carneros region. By the early 1990s, the region had over 6,000 acres planted; the Carneros region covers 90 square miles located along the low-lying hills of the Mayacamas range as it descends underneath San Francisco Bay. Elevations of most vineyards range from 400 feet in the foothills to near sea level closer to the bay; the official boundaries of the AVA fall into both Napa and Sonoma counties with the largest portion being in Sonoma and entitled to use the Sonoma Valley AVA designation as well. The Napa portion of Los Carneros is entitled to use the Napa Valley AVA designation; the region is moderately cool and windy with marked influences from nearby San Pablo Bay, making it the coolest and windiest AVA in both Napa & Sonoma. Early morning fog is a persistent feature; the soils of the Carneros region are predominantly clay and thin and shallow, providing poor drainage and fertility. The fierce and persistent winds coming off the bay encourages the grapevines to struggle and retain moisture.
While this aids in keeping crop yields small, it can delay the grapes from ripening sufficiently. In vintages with a long, drawn out growing season that allow the grapes to ripen and vivid flavors can develop. Los Carneros is associated with the cool-climate wines such as Chardonnay and Pinot noir, as well as the sparkling wines made from those grapes. Many wineries in Napa & Sonoma use Carneros grapes as a cool-climate blending component. In recent years there has been interest in Merlot and Syrah coming from the warmer areas of the region. In 1996, the first possible plantings of Albarino in the United States were planted in the Carneros region. Carneros Chardonnay is marked by its high acidity that can bring balance to the fatter, rounder Chardonnays produced in the warmer climate areas of Sonoma and Napa. While in the past, chardonnay was put through malolactic fermentation and was given significant oak treatment to soften some of the acidity, the current winemaking style in California emphasizes the fruit.
The style now favors stainless steel and neutral French Oak, while using more than a portion of the wine undergoing malolactic fermentation. Pinot noir from the Carneros is known for its crisp acidity and tight structure and exhibits spicy berry fruit; the Carneros region was one of the early pioneers of cool-climate Pinot noirs in California-long before it became a significant planting in the Russian River, Anderson Valley, Santa Rita Hills and Santa Lucia Highlands AVAs. In recent years there has been a focus by Carneros Pinot noir producers on the changing style of the region's Pinot due, in part, on emerging modern philosophies in winemaking and on clonal selections; the older clones found in Carneros include the Martini and Swan clones which produce wines that are lighter, more elegant with some earthy complexity. They are noted for their distinctive aromas of green herbs and mint; the newer French clones being planted, produce more alcoholic and concentrated wines with black fruit notes.
In August 2008, two light brown apple moths were discovered in the Carneros region close to the Napa County line. The pests lay eggs on grape leaves and the resulting larvae feed on the leaves and fruit clusters, leaving them prone to rot. Thus, their discovery caused concern that parts of the Carneros region may be quarantined just before the busy harvest season. Proposals on how to deal with the vineyard pest have been met with controversy
Volcano
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, gases to escape from a magma chamber below the surface. Earth's volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in its mantle. Therefore, on Earth, volcanoes are found where tectonic plates are diverging or converging, most are found underwater. For example, a mid-oceanic ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can form where there is stretching and thinning of the crust's plates, e.g. in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "plate hypothesis" volcanism. Volcanism away from plate boundaries has been explained as mantle plumes; these so-called "hotspots", for example Hawaii, are postulated to arise from upwelling diapirs with magma from the core–mantle boundary, 3,000 km deep in the Earth.
Volcanoes are not created where two tectonic plates slide past one another. Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. One such hazard is that volcanic ash can be a threat to aircraft, in particular those with jet engines where ash particles can be melted by the high operating temperature. Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere. Volcanic winters have caused catastrophic famines; the word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan, the god of fire in Roman mythology. The study of volcanoes is sometimes spelled vulcanology. At the mid-oceanic ridges, two tectonic plates diverge from one another as new oceanic crust is formed by the cooling and solidifying of hot molten rock; because the crust is thin at these ridges due to the pull of the tectonic plates, the release of pressure leads to adiabatic expansion and the partial melting of the mantle, causing volcanism and creating new oceanic crust.
Most divergent plate boundaries are at the bottom of the oceans. Black smokers are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed. Subduction zones are places where two plates an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges, under the continental plate, forming a deep ocean trench just offshore. In a process called flux melting, water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, thus creating magma; this magma tends to be viscous because of its high silica content, so it does not attain the surface but cools and solidifies at depth. When it does reach the surface, however, a volcano is formed. Typical examples are the volcanoes in the Pacific Ring of Fire. Hotspots are volcanic areas believed to be formed by mantle plumes, which are hypothesized to be columns of hot material rising from the core-mantle boundary in a fixed space that causes large-volume melting.
Because tectonic plates move across them, each volcano becomes dormant and is re-formed as the plate advances over the postulated plume. The Hawaiian Islands are said to have been formed in such a manner; this theory, has been doubted. The most common perception of a volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit; the features of volcanoes are much more complicated and their structure and behavior depends on a number of factors. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have landscape features such as massive plateaus. Vents that issue volcanic material and gases can develop anywhere on the landform and may give rise to smaller cones such as Puʻu ʻŌʻō on a flank of Hawaii's Kīlauea. Other types of volcano include cryovolcanoes on some moons of Jupiter and Neptune. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes except when the mud volcano is a vent of an igneous volcano.
Volcanic fissure vents are linear fractures through which lava emerges. Shield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lava that can flow a great distance from a vent, they do not explode catastrophically. Since low-viscosity magma is low in silica, shield volcanoes are more common in oceanic than continental settings; the Hawaiian volcanic chain is a series of shield cones, they are common in Iceland, as well. Lava domes are built by slow eruptions of viscous lava, they are sometimes formed within the crater of a previous volcanic eruption, as in the case of Mount Saint Helen
