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
Mexico the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States. Covering 2,000,000 square kilometres, the nation is the fifth largest country in the Americas by total area and the 13th largest independent state in the world. With an estimated population of over 120 million people, the country is the eleventh most populous state and the most populous Spanish-speaking state in the world, while being the second most populous nation in Latin America after Brazil. Mexico is a federation comprising 31 states and Mexico City, a special federal entity, the capital city and its most populous city. Other metropolises in the state include Guadalajara, Puebla, Tijuana and León. Pre-Columbian Mexico dates to about 8000 BC and is identified as one of five cradles of civilization and was home to many advanced Mesoamerican civilizations such as the Olmec, Teotihuacan, Zapotec and Aztec before first contact with Europeans. In 1521, the Spanish Empire conquered and colonized the territory from its politically powerful base in Mexico-Tenochtitlan, administered as the viceroyalty of New Spain.
Three centuries the territory became a nation state following its recognition in 1821 after the Mexican War of Independence. The post-independence period was tumultuous, characterized by economic inequality and many contrasting political changes; the Mexican–American War led to a territorial cession of the extant northern territories to the United States. The Pastry War, the Franco-Mexican War, a civil war, two empires, the Porfiriato occurred in the 19th century; the Porfiriato was ended by the start of the Mexican Revolution in 1910, which culminated with the promulgation of the 1917 Constitution and the emergence of the country's current political system as a federal, democratic republic. Mexico has the 11th largest by purchasing power parity; the Mexican economy is linked to those of its 1994 North American Free Trade Agreement partners the United States. In 1994, Mexico became the first Latin American member of the Organisation for Economic Co-operation and Development, it is classified as an upper-middle income country by the World Bank and a newly industrialized country by several analysts.
The country is considered both a regional power and a middle power, is identified as an emerging global power. Due to its rich culture and history, Mexico ranks first in the Americas and seventh in the world for number of UNESCO World Heritage Sites. Mexico is an ecologically megadiverse country, ranking fourth in the world for its biodiversity. Mexico receives a huge number of tourists every year: in 2018, it was the sixth most-visited country in the world, with 39 million international arrivals. Mexico is a member of the United Nations, the World Trade Organization, the G8+5, the G20, the Uniting for Consensus group of the UN, the Pacific Alliance trade bloc. Mēxihco is the Nahuatl term for the heartland of the Aztec Empire, namely the Valley of Mexico and surrounding territories, with its people being known as the Mexica, it is believed to be a toponym for the valley which became the primary ethnonym for the Aztec Triple Alliance as a result, although it could have been the other way around.
In the colonial era, back when Mexico was called New Spain this territory became the Intendency of Mexico and after New Spain achieved independence from the Spanish Empire it came to be known as the State of Mexico with the new country being named after its capital: the City of Mexico, which itself was founded in 1524 on top of the ancient Mexica capital of Mexico-Tenochtitlan. Traditionally, the name Tenochtitlan was thought to come from Nahuatl tetl and nōchtli and is thought to mean "Among the prickly pears rocks". However, one attestation in the late 16th-century manuscript known as "the Bancroft dialogues" suggests the second vowel was short, so that the true etymology remains uncertain; the suffix -co is the Nahuatl locative, making the word a place name. Beyond that, the etymology is uncertain, it has been suggested that it is derived from Mextli or Mēxihtli, a secret name for the god of war and patron of the Mexica, Huitzilopochtli, in which case Mēxihco means "place where Huitzilopochtli lives".
Another hypothesis suggests that Mēxihco derives from a portmanteau of the Nahuatl words for "moon" and navel. This meaning might refer to Tenochtitlan's position in the middle of Lake Texcoco; the system of interconnected lakes, of which Texcoco formed the center, had the form of a rabbit, which the Mesoamericans pareidolically associated with the moon rabbit. Still another hypothesis suggests that the word is derived from Mēctli, the name of the goddess of maguey; the name of the city-state was transliterated to Spanish as México with the phonetic value of the letter x in Medieval Spanish, which represented the voiceless postalveolar fricative. This sound, as well as the voiced postalveolar fricative, represented by a j, evolved into a voiceless velar fricative during the 16th century; this led to the use of the variant Méjico in many publications in Spanish, most notably in Spain, whereas in Mexico and most other Spanish–speaking countries, México was the preferred spelling. In recent years, the Real Academia Española, which regulates the Spanish l
Mulegé is the northernmost municipality of the Mexican state of Baja California Sur. It is the second-largest municipality by area in the country, with an area of 32,092.2 km². In the census of 2010 it had a population of 59,114 inhabitants. Isla Natividad is part of the municipality; the municipal seat is located in Santa Rosalía. There is an initiative to split the municipality into two, with the division along the ridge dividing the current municipality, so that the Pacific side, which includes its largest city, Guerrero Negro, Villa Alberto Andrés Alvarado Arámburo, would be separated from the Gulf of California side, which includes Santa Rosalía and Mulegé. Including the municipal seat of Santa Rosalía, the municipality is subdivided into six delegaciones: Santa Rosalía Bahía Tortugas Guerrero Negro Mulegé San Ignacio Vizcaíno As of 2010, the municipality had a total population of 59,114; the municipality had 979 localities, the largest of which were: Guerrero Negro, Santa Rosalía, Villa Alberto Andrés Alvarado Arámburo, Heroica Mulegé, Bahía Tortugas, classified as urban, San Francisco, Las Margaritas, Bahía Asunción, El Silencio, classified as rural.
2010 census tables: INEGI: Instituto Nacional de Estadística, Geografia e Informática Los 20 Municipios Más Extensos Instituto Nacional Para el Federalismo y el Desarrollo Municipal
Types of volcanic eruptions
Several types of volcanic eruptions—during which lava and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are named after famous volcanoes where that type of behavior has been observed; some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series. There are three different types of eruptions; the most well-observed are magmatic eruptions, which involve the decompression of gas within magma that propels it forward. Phreatomagmatic eruptions are another type of volcanic eruption, driven by the compression of gas within magma, the direct opposite of the process powering magmatic activity; the third eruptive type is the phreatic eruption, driven by the superheating of steam via contact with magma. Within these wide-defining eruptive types are several subtypes; the weakest are Hawaiian and submarine Strombolian, followed by Vulcanian and Surtseyan.
The stronger eruptive types are Pelean eruptions, followed by Plinian eruptions. Subglacial and phreatic eruptions are defined by their eruptive mechanism, vary in strength. An important measure of eruptive strength is Volcanic Explosivity Index, an order of magnitude scale ranging from 0 to 8 that correlates to eruptive types. Volcanic eruptions arise through three main mechanisms: Gas release under decompression causing magmatic eruptions Thermal contraction from chilling on contact with water causing phreatomagmatic eruptions Ejection of entrained particles during steam eruptions causing phreatic eruptionsThere are two types of eruptions in terms of activity, explosive eruptions and effusive eruptions. Explosive eruptions are characterized by gas-driven explosions that propels tephra. Effusive eruptions, are characterized by the outpouring of lava without significant explosive eruption. Volcanic eruptions vary in strength. On the one extreme there are effusive Hawaiian eruptions, which are characterized by lava fountains and fluid lava flows, which are not dangerous.
On the other extreme, Plinian eruptions are large and dangerous explosive events. Volcanoes are not bound to one eruptive style, display many different types, both passive and explosive in the span of a single eruptive cycle. Volcanoes do not always erupt vertically from a single crater near their peak, either; some volcanoes exhibit lateral and fissure eruptions. Notably, many Hawaiian eruptions start from rift zones, some of the strongest Surtseyan eruptions develop along fracture zones. Scientists believed that pulses of magma mixed together in the chamber before climbing upward—a process estimated to take several thousands of years, but Columbia University volcanologists found that the eruption of Costa Rica’s Irazú Volcano in 1963 was triggered by magma that took a nonstop route from the mantle over just a few months. The Volcanic Explosivity Index is a scale, for measuring the strength of eruptions, it is used by the Smithsonian Institution's Global Volcanism Program in assessing the impact of historic and prehistoric lava flows.
It operates in a way similar to the Richter scale for earthquakes, in that each interval in value represents a tenfold increasing in magnitude. The vast majority of volcanic eruptions are of VEIs between 0 and 2. Volcanic eruptions by VEI index Magmatic eruptions produce juvenile clasts during explosive decompression from gas release, they range in intensity from the small lava fountains on Hawaii to catastrophic Ultra-Plinian eruption columns more than 30 km high, bigger than the eruption of Mount Vesuvius in 79 that buried Pompeii. Hawaiian eruptions are a type of volcanic eruption, named after the Hawaiian volcanoes with which this eruptive type is hallmark. Hawaiian eruptions are the calmest types of volcanic events, characterized by the effusive eruption of fluid basalt-type lavas with low gaseous content; the volume of ejected material from Hawaiian eruptions is less than half of that found in other eruptive types. Steady production of small amounts of lava builds up the broad form of a shield volcano.
Eruptions are not centralized at the main summit as with other volcanic types, occur at vents around the summit and from fissure vents radiating out of the center. Hawaiian eruptions begin as a line of vent eruptions along a fissure vent, a so-called "curtain of fire." These die down. Central-vent eruptions, meanwhile take the form of large lava fountains, which can reach heights of hundreds of meters or more; the particles from lava fountains cool in the air before hitting the ground, resulting in the accumulation of cindery scoria fragments. If eruptive rates are high enough, they may form splatter-fed lava flows. Hawaiian eruptions are extremely long lived. Another Hawaiian volcanic feature is the formation of active lava lakes, self-maintaining pools of raw lava with a thin crust of semi-cooled rock. Flows from Hawaiian eruptions are basal
Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they remain as tephra unless hot enough to fuse together into pyroclastic rock or tuff; the distribution of tephra following an eruption involves the largest boulders falling to the ground quickest, therefore closest to the vent, while smaller fragments travel further – ash can travel for thousands of miles circumglobal, as it can stay in the stratosphere for days to weeks following an eruption. When large amounts of tephra accumulate in the atmosphere from massive volcanic eruptions, they can reflect light and heat from the sun back through the atmosphere, in some cases causing the temperature to drop, resulting in a temporary "volcanic winter". Tephra mixed in with precipitation can be acidic and cause acid rain and snowfall. Tephra fragments are classified by size: Ash – particles smaller than 2 mm in diameter Lapilli or volcanic cinders – between 2 and 64 mm in diameter Volcanic bombs or volcanic blocks – larger than 64 mm in diameterThe use of tephra layers, which bear their own unique chemistry and character, as temporal marker horizons in archaeological and geological sites, is known as tephrochronology.
The word "tephra" and "pyroclast" both derive from Greek: τέφρα tephra means "ash", while the word pyroclast is derived from the Greek πῦρ, meaning "fire", κλαστός, meaning "broken in pieces". Media related to Tephra at Wikimedia Commons How Volcanoes Work Volcanic Materials Identification
Volcanoes of east-central Baja California
The volcanoes of east-central Baja California are located on the Baja California Peninsula near the Gulf of California, in the state of Baja California Sur, in Mexico. Baja California is a peninsula in Mexico, bordering the the Gulf of Mexico, it is made up of mountains, some coastal plains. The mountain ranges in Baja California, connected to the Pacific Coast Ranges, extend from the north-eastern to the south-western part of the peninsula. Out of the 24 named ranges, the Sierra de Juárez and the Sierra San Pedro Mártir, the highest range in Baja California, are the two most significant; the slopes of the ranges vary depending on location. Coastal plains are found in the south-west regions on the peninsula. In the center of Baja California, volcanic activity is found near the San Ignacio area; the landscape is a patchwork of lava flows and the hardened remains of pyroclastic flows – hot clouds of volcanic ash and rock fragments that race down the slopes of a volcano like an avalanche. The majority of the rivers and streams in Baja California, such as San Benito, San Miguel and Raymundo, lead back to the Pacific Ocean.
The San Ignacio River, the longest river in the peninsula, leads to the Ballenas Bay. In general, Baja California's climate is hot and desert; the north and the south receive much more rain than the central regions, which only receive a small amount of rain in the summer while staying dry. As for the coasts of the peninsula, temperatures on the west are different than those of the east. Due to the cold water coming from the north with the California Current, the west coast is much cooler than the east and south, which stay rather warm in the winter time as well; the arid climate of Baja California limits the amount of vegetation covering the ground and allows the dramatic volcanic features of the landscape to stand out in this natural-color image from the Landsat 7 satellite on October 5, 2000. La Reforma Caldera is a volcano, on the east-central Baja California, it is about 10 km in diameter and at about an elevation of 1,300 m. In the east-central Baja California there are several volcanoes and this one lies east of the Tres Vírgenes volcano and SE of El Aguajito.
There are several things that distinguishes the differences between these volcanoes and one of the things are the type of volcano it is and the kind of rocks it contains. La Reformas other aspect that makes it distinguishable is the outer rim it has; the rim is made up of rocks. The dark colored rocks that make up the outer rim of the volcano is made out of fluid lava. La Reforma is a caldera volcano, one of the most dangerous types of volcanoes: if it collapses it forms in a way where it collapses into an empty magma chamber forming something that looks like a crater. A caldera volcano is one of the most dangerous for the fact that the eruptions are huge of about 100–1,000 km3 of material and has been known as the super volcanic eruptions due to the size of the explosions. La Reformas last huge explosive was recorded about 10,000 years ago, it has been recorded that the eruptions have consisted of ash and pumice falls, pumice flows, pantellerite tuffs. The "Tres Vírgenes", a line of three connected volcanoes, collectively known by that name, are west of La Reforma Caldera.
The Tres Vírgenes lie along the NE-SW eastern Gulf of California with a tectonic setting of rift zones, that are more than 25 km deep within the continental crust, continue towards active seafloor spreading. La Vírgen, in the southwest, El Azufre in the center, El Viejo in the northeast and considering its name, is the oldest lowest peak. La Vírgen is the youngest andesitic stratovolcano of all three. While it has the highest peak, it has a large amount of dacite lava domes; as well as flanks that have a lava flow, thus causing it to be an andesitic volcano. Considering La Vírgen is the youngest volcano, it has had a complex long list of volcanic eruptions, it has a history of pumice eruptions and explosive eruptions consisting of pyroclastic flows and andesitic lava flows. The volcanoes get younger from northeast to southwest, they consist of stratovolcanoes, lava domes, pyroclastic cones. These types of volcanoes form several rock types, some major ones are: andesite, basaltic andesite, dacite rocks.
Dacitic lava domes and flows are composed inside El Azufre. Unlike other volcanoes in Baja California, the Tres Vírgenes are known for some of the largest stratovolcanoes, meaning that they have layers of erupting products that continue to pile up. While they are some of the largest, the last time one of the volcanoes was active was in 1746, with a possible eruption in 1857; the evidence for the 1746 eruption came from a Spanish priest, who at the time was on a navigation in the Gulf of California. In his report, it was said that there was an ash plume from the effusive eruption, while no tephra deposits have been discovered, there is evidence of andesitic lava flow that could have came from the 1746 eruption; as as 6,500 years ago, La Vírgen experienced a Plinian eruption – a huge, explosive event that produces an enormous column of volcanic rock fragments and gas that reaches into the stratosphere. The eruption produced a column that reached at least 18 kilometers into the air and deposited ash and rock fragments over 500 square kilometers.
In stages of the eruption, pyroclastic flows and lahars from El Azufre Volcano paved the plain to the north all the way to the Gulf of California. El Aguajito Caldera known as "Santa Ana Caldera", is located northeast of
Croats or Croatians are a nation and South Slavic ethnic group native to Croatia. Croats live in Croatia and Bosnia and Herzegovina, but are recognized minorities in such countries as Austria, the Czech Republic, Hungary, Montenegro, Serbia and Slovenia. Due to political and economic reasons, many Croats migrated to North and South America as well as Australia and New Zealand, establishing a diaspora in the aftermath of World War II, with grassroots assistance from earlier communities and the Roman Catholic Church. Croats are Roman Catholics; the Croatian language is official in Croatia and Bosnia and Herzegovina, as well as in the European Union, is a recognised minority language within Croatian autochthonous communities and minorities in Montenegro, Italy and Serbia. Evidence is rather scarce for the period between the 7th and 8th centuries, CE. Archaeological evidence shows population continuity in coastal Istria. In contrast, much of the Dinaric hinterland appears to have been depopulated, as all hilltop settlements, from Noricum to Dardania, were abandoned in the early 7th century.
Although the dating of the earliest Slavic settlements is still disputed, there is a hiatus of a century. The origin and nature of the Slavic migrations remain controversial, all available evidence points to the nearby Danubian and Carpathian regions; the ethnonym "Croat" is first attested in the charter of Duke Trpimir. Much uncertainty revolves around the exact circumstances of their appearance given the scarcity of literary sources during the 7th and 8th century "Dark Ages". Traditionally, scholarship has placed the arrival of the Croats in the 7th century on the basis of the Byzantine document De Administrando Imperio; as such, the arrival of the Croats was seen as a second wave of Slavic migrations, which liberated Dalmatia from Avar hegemony. However, as early as the 1970s, scholars questioned the reliability of Porphyrogenitus' work, written as it was in the 10th century. Rather than being an accurate historical account, De Administrando Imperio more reflects the political situation during the 10th century.
It served as Byzantine propaganda praising Emperor Heraclius for repopulating the Balkans with Croats, who were seen by the Byzantines as tributary peoples living on what had always been'Roman land'. Scholars have hypothesized the name Croat may be Iranian, thus suggesting that the Croatians were a Sarmatian tribe from the Pontic region who were part of a larger movement at the same time that the Slavs were moving toward the Adriatic; the major basis for this connection was the perceived similarity between Hrvat and inscriptions from the Tanais dated to the 2nd and 3rd centuries CE, mentioning the name Khoroathos. Similar arguments have been made for an alleged Gothic-Croat link. Whilst there is indeed possible evidence of population continuity between Gothic and Croatian times in parts of Dalmatia, the idea of a Gothic origin of Croats was more rooted in 20th century Ustaše political aspirations than historical reality. Contemporary scholarship views the rise of "Croats" as an autochthonous, Dalmatian response to the demise of the Avar khanate and the encroachment of Frankish and Byzantine Empires into northern Dalmatia.
They appear to have been based around Klis, down to the Cetina and south of Liburnia. Here, concentrations of the "Old Croat culture" abound, marked by some wealthy warrior burials dating to the 9th century CE. Other, distinct polities existed near the Croat duchy; these included the Guduscans, the Narentines and the Sorabi who ruled some other eastern parts of ex-Roman "Dalmatia". Prominent in the territory of future Croatia was the polity of Prince Liutevid, who ruled the territories between the Drava and Sava rivers, centred from his fort at Sisak. Although Duke Liutevid and his people are seen as a "Pannonian Croats", he is, due to the lack of "evidence that they had a sense of Croat identity" referred to as dux Pannoniae Inferioris, or a Slav, by contemporary sources. However, the Croats became the dominant local power in northern Dalmatia, absorbing Liburnia and expanding their name by conquest and prestige. In the south, while having periods of independence, the Naretines "merged" with Croats under control of Croatian Kings.
With such expansion, Croatia soon became dominant power and absorb other polities between Frankish and Byzantine empire. Although the Chronicle of the Priest of Duklja has been dismissed as an unreliable record, the mentioned "Red Croatia" suggests that Croatian clans and families might have settled as far south as Duklja/Zeta and city of Drač in today's Albania; the lands which constitute modern Croatia fell under three major geographic-politic zones during the Middle Ages, which were influenced by powerful neighbour Empires – notably the Byzantines, the Avars and Magyars and Bulgars. Each vied for control of the Northwest Balkan regions. Two independent Slavic dukedoms emerged sometime during the 9th century: the Croat Duchy and Principality of Lower Pannonia. Having been under Avar control, lower Pannonia became a march of the Carolingian Empire around 800. Aided by Vojnomir in 796, the first named Slavic Duke of Pannonia, the Franks wrested control of