Colombia the Republic of Colombia, is a sovereign state situated in the northwest of South America, with territories in Central America. Colombia shares a border to the northwest with Panama, to the east with Venezuela and Brazil and to the south with Ecuador and Peru, it shares its maritime limits with Costa Rica, Honduras, Jamaica and the Dominican Republic. Colombia is a unitary, constitutional republic comprising thirty-two departments, with the capital in Bogota. Colombia has been inhabited by various indigenous peoples since 12,000 BCE, including the Muisca and the Tairona, along with the Inca Empire that expanded to the southwest of the country; the Spanish arrived in 1499 and by the mid-16th century conquered and colonized much of the region, establishing the New Kingdom of Granada, with Santafé de Bogotá as its capital. Independence from Spain was achieved in 1819, but by 1830 the "Gran Colombia" Federation was dissolved, with what is now Colombia and Panama emerging as the Republic of New Granada.
The new nation experimented with federalism as the Granadine Confederation, the United States of Colombia, before the Republic of Colombia was declared in 1886. Panama seceded in 1903. Beginning in the 1960s, the country suffered from an asymmetric low-intensity armed conflict and rampant political violence, both of which escalated in the 1990s. Since 2005, there has been significant improvement in security and rule of law. Colombia is one of the most ethnically and linguistically diverse countries in the world, with its rich cultural heritage reflecting influences by indigenous peoples, European settlement, forced African migration, immigration from Europe and the Middle East. Urban centres are located in the highlands of the Andes mountains and the Caribbean coast. Colombia is among the world's 17 megadiverse countries, the most densely biodiverse per square kilometer. Colombia is a middle power and regional actor in Latin America, it is part of the CIVETS group of six leading emerging markets and a member of the UN, the WTO, the OAS, the Pacific Alliance, other international organizations.
Colombia's diversified economy is the fourth largest in Latin America, with macroeconomic stability and favorable long-term growth prospects. The name "Colombia" is derived from the last name of Christopher Columbus, it was conceived by the Venezuelan revolutionary Francisco de Miranda as a reference to all the New World, but to those portions under Spanish rule. The name was adopted by the Republic of Colombia of 1819, formed from the territories of the old Viceroyalty of New Granada; when Venezuela and Cundinamarca came to exist as independent states, the former Department of Cundinamarca adopted the name "Republic of New Granada". New Granada changed its name in 1858 to the Granadine Confederation. In 1863 the name was again changed, this time to United States of Colombia, before adopting its present name – the Republic of Colombia – in 1886. To refer to this country, the Colombian government uses the terms Colombia and República de Colombia. Owing to its location, the present territory of Colombia was a corridor of early human migration from Mesoamerica and the Caribbean to the Andes and Amazon basin.
The oldest archaeological finds are from the Pubenza and El Totumo sites in the Magdalena Valley 100 kilometres southwest of Bogotá. These sites date from the Paleoindian period. At Puerto Hormiga and other sites, traces from the Archaic Period have been found. Vestiges indicate that there was early occupation in the regions of El Abra and Tequendama in Cundinamarca; the oldest pottery discovered in the Americas, found at San Jacinto, dates to 5000–4000 BCE. Indigenous people inhabited the territory, now Colombia by 12,500 BCE. Nomadic hunter-gatherer tribes at the El Abra, Tibitó and Tequendama sites near present-day Bogotá traded with one another and with other cultures from the Magdalena River Valley. Between 5000 and 1000 BCE, hunter-gatherer tribes transitioned to agrarian societies. Beginning in the 1st millennium BCE, groups of Amerindians including the Muisca, Zenú, Tairona developed the political system of cacicazgos with a pyramidal structure of power headed by caciques; the Muisca inhabited the area of what is now the Departments of Boyacá and Cundinamarca high plateau where they formed the Muisca Confederation.
They farmed maize, potato and cotton, traded gold, blankets, ceramic handicrafts and rock salt with neighboring nations. The Tairona inhabited northern Colombia in the isolated mountain range of Sierra Nevada de Santa Marta; the Quimbaya inhabited regions of the Cauca River Valley between the Western and Central Ranges of the Colombian Andes. Most of the Amerindians practiced agriculture and the social structure of each indigenous community was different; some groups of indigenous people such as the Caribs lived in a state of permanent war, but others had less bellicose attitudes. The Incas expanded their empire onto the southwest part of the country. Alonso de Ojeda reached the Guajira Peninsula in 1499. Spanish explorers, led by Rodrigo de Bastidas, made the first exploration
Peru the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, in the west by the Pacific Ocean. Peru is a megadiverse country with habitats ranging from the arid plains of the Pacific coastal region in the west to the peaks of the Andes mountains vertically extending from the north to the southeast of the country to the tropical Amazon Basin rainforest in the east with the Amazon river. Peruvian territory was home to several ancient cultures. Ranging from the Norte Chico civilization in the 32nd century BC, the oldest civilization in the Americas and one of the five cradles of civilization, to the Inca Empire, the largest state in pre-Columbian America, the territory now including Peru has one of the longest histories of civilization of any country, tracing its heritage back to the 4th millennia BCE; the Spanish Empire conquered the region in the 16th century and established a viceroyalty that encompassed most of its South American colonies, with its capital in Lima.
Peru formally proclaimed independence in 1821, following the military campaigns of José de San Martín and Simón Bolívar, the decisive battle of Ayacucho, Peru secured independence in 1824. In the ensuing years, the country enjoyed relative economic and political stability, which ended shortly before the War of the Pacific with Chile. Throughout the 20th century, Peru endured armed territorial disputes, social unrest, internal conflicts, as well as periods of stability and economic upswing. Alberto Fujimori was elected to the presidency in 1990. Fujimori left the presidency in 2000 and was charged with human rights violations and imprisoned until his pardon by President Pedro Pablo Kuczynski in 2017. After the president's regime, Fujimori's followers, called Fujimoristas, have caused political turmoil for any opposing faction in power causing Pedro Pablo Kuczynski to resign in March 2018; the sovereign state of Peru is a representative democratic republic divided into 25 regions. It is classified as an emerging market with a high level of human development and an upper middle income level with a poverty rate around 19 percent.
It is one of the region's most prosperous economies with an average growth rate of 5.9% and it has one of the world's fastest industrial growth rates at an average of 9.6%. Its main economic activities include mining, manufacturing and fishing; the country forms part of The Pacific Pumas, a political and economic grouping of countries along Latin America's Pacific coast that share common trends of positive growth, stable macroeconomic foundations, improved governance and an openness to global integration. Peru ranks high in social freedom. Peru has a population of 32 million, which includes Amerindians, Europeans and Asians; the main spoken language is Spanish, although a significant number of Peruvians speak Quechua or other native languages. This mixture of cultural traditions has resulted in a wide diversity of expressions in fields such as art, cuisine and music; the name of the country may be derived from Birú, the name of a local ruler who lived near the Bay of San Miguel, Panama City, in the early 16th century.
When his possessions were visited by Spanish explorers in 1522, they were the southernmost part of the New World yet known to Europeans. Thus, when Francisco Pizarro explored the regions farther south, they came to be designated Birú or Perú. An alternative history is provided by the contemporary writer Inca Garcilaso de la Vega, son of an Inca princess and a conquistador, he said the name Birú was that of a common Indian happened upon by the crew of a ship on an exploratory mission for governor Pedro Arias de Ávila, went on to relate more instances of misunderstandings due to the lack of a common language. The Spanish Crown gave the name legal status with the 1529 Capitulación de Toledo, which designated the newly encountered Inca Empire as the province of Peru. Under Spanish rule, the country adopted the denomination Viceroyalty of Peru, which became Republic of Peru after independence; the earliest evidences of human presence in Peruvian territory have been dated to 9,000 BC. Andean societies were based on agriculture, terracing.
Organization relied on reciprocity and redistribution because these societies had no notion of market or money. The oldest known complex society in Peru, the Norte Chico civilization, flourished along the coast of the Pacific Ocean between 3,000 and 1,800 BC; these early developments were followed by archaeological cultures that developed around the coastal and Andean regions throughout Peru. The Cupisnique culture which flourished from around 1000 to 200 BC along what is now Peru's Pacific Coast was an example of early pre-Incan culture; the Chavín culture that developed from 1500 to 300 BC was more of a religious than a political phenomenon, with their religious centre in Chavín de Huantar. After the decline of the Chavin culture around the beginning of the 1st century AD, a series of localized and specialized cultures rose and fell
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and gradually moves away from the ridge. Earlier theories of continental drift postulated; the idea that the seafloor itself moves as it expands from a central axis was proposed by Harry Hess from Princeton University in the 1960s. The theory is well accepted now, the phenomenon is known to be caused by convection currents in the asthenosphere, ductile, or plastic, the brittle lithosphere. Seafloor spreading helps explain continental drift in the theory of plate tectonics; when oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere. The motivating force for seafloor spreading ridges is tectonic plate pull rather than magma pressure, although there is significant magma activity at spreading ridges. At a spreading center, basaltic magma rises up the fractures and cools on the ocean floor to form new seabed. Hydrothermal vents are common at spreading centers.
Older rocks will be found farther away from the spreading zone while younger rocks will be found nearer to the spreading zone. Additionally spreading rates determine if the ridge is fast, intermediate, or slow; as a general rule, fast ridges have spreading rates of more than 9 cm/year. Intermediate ridges have a spreading rate of 5–9 cm/year while slow spreading ridges have a rate less than 5 cm/year. Seafloor spreading occurs at spreading centers, distributed along the crests of mid-ocean ridges. Spreading centers end in overlapping spreading center offsets. A spreading center includes a seismically active plate boundary zone a few kilometers to tens of kilometers wide, a crustal accretion zone within the boundary zone where the ocean crust is youngest, an instantaneous plate boundary - a line within the crustal accretion zone demarcating the two separating plates. Within the crustal accretion zone is a 1-2 km-wide neovolcanic zone. In the general case, seafloor spreading starts as a rift in a continental land mass, similar to the Red Sea-East Africa Rift System today.
The process starts by heating at the base of the continental crust which causes it to become more plastic and less dense. Because less dense objects rise in relation to denser objects, the area being heated becomes a broad dome; as the crust bows upward, fractures occur that grow into rifts. The typical rift system consists of three rift arms at 120-degree angles; these areas can be found in several places across the world today. The separated margins of the continents evolve to form passive margins. Hess' theory was that new seafloor is formed when magma is forced upward toward the surface at a mid-ocean ridge. If spreading continues past the incipient stage described above, two of the rift arms will open while the third arm stops opening and becomes a'failed rift'; as the two active rifts continue to open the continental crust is attenuated as far as it will stretch. At this point basaltic oceanic crust begins to form between the separating continental fragments; when one of the rifts opens into the existing ocean, the rift system is flooded with seawater and becomes a new sea.
The Red Sea is an example of a new arm of the sea. The East African rift was thought to be a "failed" arm, opening somewhat more than the other two arms, but in 2005 the Ethiopian Afar Geophysical Lithospheric Experiment reported that in the Afar region, September 2005, a 60 km fissure opened as wide as eight meters. During this period of initial flooding the new sea is sensitive to changes in eustasy; as a result, the new sea will evaporate several times before the elevation of the rift valley has been lowered to the point that the sea becomes stable. During this period of evaporation large evaporite deposits will be made in the rift valley; these deposits have the potential to become hydrocarbon seals and are of particular interest to petroleum geologists. Seafloor spreading can stop during the process, but if it continues to the point that the continent is severed a new ocean basin is created; the Red Sea has not yet split Arabia from Africa, but a similar feature can be found on the other side of Africa that has broken free.
South America once fit into the area of the Niger Delta. The Niger River has formed in the failed rift arm of the triple junction; as new seafloor forms and spreads apart from the mid-ocean ridge it cools over time. Older seafloor is, colder than new seafloor, older oceanic basins deeper than new oceanic basins due to isostasy. If the diameter of the earth remains constant despite the production of new crust, a mechanism must exist by which crust is destroyed; the destruction of oceanic crust occurs at subduction zones where oceanic crust is forced under either continental crust or oceanic crust. Today, the Atlantic basin is spreading at the Mid-Atlantic Ridge. Only a small portion of the oceanic crust produced in the Atlantic is subducted. However, the plates making up the Pacific Ocean are experiencing subduction along many of their boundaries which causes the volcanic activity in what has been termed the Ring of Fire of the Pacific Ocean; the Pacific is home to one of the world's most active spreading centers with spreading rates of up to 13 cm/yr.
The Mid-Atlantic Ridge is a "textbook" slow-spreading center, while the East Pacific Rise is used as an example of fast spreading. Spreading centers at slow and in
The Chile Rise or Chile Ridge is an oceanic ridge, a tectonic divergent plate boundary between the Nazca and Antarctic plates. Its eastern end is the Chile Triple Junction where the Chile Rise is being subducted below the South American Plate in the Peru–Chile Trench, it runs westward to a triple point south of the Juan Fernández Microplate where it intersects the East Pacific Rise. The Chile Rise subducts near Taitao Peninsula where Taitao ophiolite and other geolical features are associated to the interactions at the triple junction
Magma is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, evidence of magmatism has been discovered on other terrestrial planets and some natural satellites. Besides molten rock, magma may contain suspended crystals and gas bubbles. Magma is produced by melting of the mantle and/or the crust at various tectonic settings, including subduction zones, continental rift zones, mid-ocean ridges and hotspots. Mantle and crustal melts migrate upwards through the crust where they are thought to be stored in magma chambers or trans-crustal crystal-rich mush zones. During their storage in the crust, magma compositions may be modified by fractional crystallization, contamination with crustal melts, magma mixing, degassing. Following their ascent through the crust, magmas may feed a volcano or solidify underground to form an intrusion. While the study of magma has relied on observing magma in the form of lava flows, magma has been encountered in situ three times during geothermal drilling projects—twice in Iceland, once in Hawaii.
Most magmatic liquids are rich in silica. Silicate melts are composed of silicon, aluminium, magnesium, calcium and potassium; the physical behaviours of melts depend upon their atomic structures as well as upon temperature and pressure and composition. Viscosity is a key melt property in understanding the behaviour of magmas. More silica-rich melts are more polymerized, with more linkage of silica tetrahedra, so are more viscous. Dissolution of water drastically reduces melt viscosity. Higher-temperature melts are less viscous. Speaking, more mafic magmas, such as those that form basalt, are hotter and less viscous than more silica-rich magmas, such as those that form rhyolite. Low viscosity leads to less explosive eruptions. Characteristics of several different magma types are as follows: Ultramafic SiO2 < 45% Fe–Mg > 8% up to 32%MgO Temperature: up to 1500°C Viscosity: Very Low Eruptive behavior: gentle or explosive Distribution: divergent plate boundaries, hot spots, convergent plate boundaries.
At any given pressure and for any given composition of rock, a rise in temperature past the solidus will cause melting. Within the solid earth, the temperature of a rock is controlled by the geothermal gradient and the radioactive decay within the rock; the geothermal gradient averages about 25 °C/km with a wide range from a low of 5–10 °C/km within oceanic trenches and subduction zones to 30–80 °C/km under mid-ocean ridges and volcanic arc environments. It is very difficult to change the bulk composition of a large mass of rock, so composition is the basic control on whether a rock will melt at any given temperature and pressure; the composition of a rock may be considered to include volatile phases such as water and carbon dioxide. The presence of volatile phases in a rock under pressure can stabilize a melt fraction; the presence of 0.8% water may reduce the temperature of melting by as much as 100 °C. Conversely, the loss of water and volatiles from a magma may cause it to freeze or solidify.
A major portion of all magma is silica, a compound of silicon and oxygen. Magma contains gases, which expand as the magma rises. Magma, high in silica resists flowing, so expanding gases are trapped in it. Pressure builds up until the gases blast out in a dangerous explosion. Magma, poor in silica flows so gas bubbles move up through it and escape gently. Melting of solid rocks to form magma is controlled by three physical parameters: temperature and composition; the most common mechanisms of magma generation in the mantle are decompression melting and lowering of the solidus. Mechanisms are discussed further in the entry for igneous rock; when rocks melt, they do so and because most rocks are made of several minerals, which all have different melting points. As a rock melts, for example, its volume changes; when enough rock is melted, the small globules of melt soften the rock. Under pressure within the earth, as little as a fraction of a percent of partial melting may be sufficient to cause melt to be squeezed from its source.
Melts can stay in place long enough to melt to 20% or 35%, but rocks are melted in excess of 50%, because the melted rock mass becomes a crystal-and-melt mush tha
1960 Valdivia earthquake
The 1960 Valdivia earthquake or the Great Chilean earthquake of 22 May is the most powerful earthquake recorded. Various studies have placed it at 9.4–9.6 on the moment magnitude scale. It occurred in the afternoon, lasted 10 minutes; the resulting tsunami affected southern Chile, Japan, the Philippines, eastern New Zealand, southeast Australia and the Aleutian Islands. The epicenter of this megathrust earthquake was near Lumaco 570 kilometres south of Santiago, with Valdivia being the most affected city; the tremor caused localised tsunamis that battered the Chilean coast, with waves up to 25 metres. The main tsunami raced across Hawaii. Waves as high as 10.7 metres were recorded 10,000 kilometres from the epicenter, as far away as Japan and the Philippines. The death toll and monetary losses arising from this widespread disaster are not certain. Various estimates of the total number of fatalities from the earthquake and tsunamis have been published, ranging between 1,000 and 7,000 killed. Different sources have estimated the monetary cost ranged from US$400 million to 800 million.
The 1960 Chilean earthquakes were a sequence of strong earthquakes that affected Chile between 21 May and 6 June 1960, centered in the Araucanía, Aysén, Bío Bío Regions of the country. The first three quakes, all registering in the planet's top 10 by magnitude for 1960, are grouped together as the 1960 Concepción earthquakes; the first of these was the 8.1 Mw Concepción earthquake at 06:02 UTC-4 on 21 May 1960. Its epicenter was near Curanilahue. Telecommunications to southern Chile were cut off and President Jorge Alessandri cancelled the traditional ceremony of the Battle of Iquique memorial holiday to oversee the emergency assistance efforts; the second and third Concepción earthquakes occurred the next day at 06:32 UTC-4 and 14:55 UTC-4 on May 22. These earthquakes formed a southward migrating foreshock sequence to the main Valdivia shock, which occurred just 15 minutes after the third event; the earthquake interrupted and ended Lota's coal miners march on Concepción as they demanded higher salaries.
The Valdivia earthquake occurred at 15:11 UTC-4 on 22 May, affected all of Chile between Talca and Chiloé Island, more than 400,000 square kilometres. Coastal villages, such as Toltén, were struck. At Corral, the main port of Valdivia, the water level rose 4 m. At 16:20 UTC-4, a wave of 8 m struck the Chilean coast between Concepción and Chiloé. Another wave measuring 10 m was reported ten minutes later. Hundreds of people were reported dead by the time the tsunami struck. One ship, starting at the mouth of Valdivia River, sank after being moved 1.5 km backward and forward in the river. A number of Spanish-colonial fortifications were destroyed. Soil subsidence destroyed buildings, deepened local rivers, created wetlands in places like the Río Cruces and Chorocomayo, a new aquatic park north of the city. Extensive areas of the city were flooded; the electricity and water systems of Valdivia were destroyed. Witnesses reported underground water flowing up through the soil. Despite the heavy rains of 21 May, the city was without a water supply.
The river turned brown with sediment from landslides and was full of floating debris, including entire houses. The lack of potable water became a serious problem in one of Chile's rainiest regions; the earthquake did not strike all the territory with the same strength. The two most affected areas were Valdivia and Puerto Octay, near the northwest corner of Llanquihue Lake. Puerto Octay was the center of a north-south elliptical area in the Central Valley, where the intensity was at the highest outside the Valdivia Basin. East of Puerto Octay, in a hotel in Todos los Santos Lake, stacked plates were reported to have remained in place. Excepting poor building sites, the zone of Mercalli scales intensities of VII or more all lay west of the Andes in a strip running from Lota southwards; the area of intensities of VII or more did not penetrate into the Central Valley in north of Lleulleu Lake and south of Castro. Two days after the earthquake Cordón Caulle, a volcanic vent close to Puyehue volcano, erupted.
Other volcanoes may have erupted, but none were recorded due to the lack of communication in Chile at the time. The low death toll in Chile is explained in part by the low population density in the region, by building practices that took into account the area's high geological activity; the earthquake was a megathrust earthquake resulting from the release of mechanical stress between the subducting Nazca Plate and the South American Plate, on the Peru–Chile Trench. The focus was shallow at 33 km, considering that earthquakes in northern Chile and Argentina may reach depths of 70 km. Subduction zones are known to produce the strongest earthquakes on earth, as their particular structure allows more stress to build up before energy is released. Geophysicists consider it a matter of time before this earthquake will be surpassed in magnitude by another; the earthquake's rupture zone was 800 km long. Rupture velocity, the speed at which a rupture front expands across the surface of the fault, has been estimated as 3.5 km per second
In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents produce rifts which become rift valleys. Most active divergent plate boundaries exist as mid-oceanic ridges. Divergent boundaries form volcanic islands which occur when the plates move apart to produce gaps which molten lava rises to fill. Current research indicates that complex convection within the Earth's mantle allows material to rise to the base of the lithosphere beneath each divergent plate boundary; this supplies the area with vast amounts of heat and a reduction in pressure that melts rock from the asthenosphere beneath the rift area forming large flood basalt or lava flows. Each eruption occurs in only a part of the plate boundary at any one time, but when it does occur, it fills in the opening gap as the two opposing plates move away from each other. Over millions of years, tectonic plates may move many hundreds of kilometers away from both sides of a divergent plate boundary.
Because of this, rocks closest to a boundary are younger than rocks further away on the same plate. At divergent boundaries, two plates move away from each other and the space that this creates is filled with new crustal material sourced from molten magma that forms below; the origin of new divergent boundaries at triple junctions is sometimes thought to be associated with the phenomenon known as hotspots. Here, exceedingly large convective cells bring large quantities of hot asthenospheric material near the surface and the kinetic energy is thought to be sufficient to break apart the lithosphere; the hot spot which may have initiated the Mid-Atlantic Ridge system underlies Iceland, widening at a rate of a few centimeters per year. Divergent boundaries are typified in the oceanic lithosphere by the rifts of the oceanic ridge system, including the Mid-Atlantic Ridge and the East Pacific Rise, in the continental lithosphere by rift valleys such as the famous East African Great Rift Valley. Divergent boundaries can create massive fault zones in the oceanic ridge system.
Spreading is not uniform, so where spreading rates of adjacent ridge blocks are different, massive transform faults occur. These are many bearing names, that are a major source of submarine earthquakes. A sea floor map will show a rather strange pattern of blocky structures that are separated by linear features perpendicular to the ridge axis. If one views the sea floor between the fracture zones as conveyor belts carrying the ridge on each side of the rift away from the spreading center the action becomes clear. Crest depths of the old ridges, parallel to the current spreading center, will be older and deeper.... It is at mid-ocean ridges that one of the key pieces of evidence forcing acceptance of the seafloor spreading hypothesis was found. Airborne geomagnetic surveys showed a strange pattern of symmetrical magnetic reversals on opposite sides of ridge centers; the pattern was far too regular to be coincidental as the widths of the opposing bands were too matched. Scientists had been studying polar reversals and the link was made by Lawrence W. Morley, Frederick John Vine and Drummond Hoyle Matthews in the Morley–Vine–Matthews hypothesis.
The magnetic banding directly corresponds with the Earth's polar reversals. This was confirmed by measuring the ages of the rocks within each band; the banding furnishes a map in space of both spreading rate and polar reversals. Mid-Atlantic Ridge Red Sea Rift Baikal Rift Zone East African Rift East Pacific Rise Gakkel Ridge Galapagos Rise Explorer Ridge Juan de Fuca Ridge Pacific-Antarctic Ridge West Antarctic Rift Great Rift Valley Convergent boundary Transform boundary Seafloor spreading – A process at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and gradually moves away from the ridge Continental drift – The movement of the Earth's continents relative to each other Subduction zone – A geological process at convergent tectonic plate boundaries where one plate moves under the other