The Cruces River ( Spanish : Río Cruces ) is a river in south-central Chile . Río Cruces originates from hills near the Villarica volcano and flows then in south-west direction. The southern and final part of the river flows in a south-south-west direction following the eastern flank of Cordillera de Oncol . At the latitude of the city of Valdivia it is crossed by Río Cruces Bridge next to its outflow into Valdivia River .
120-409: The 1960 Valdivia earthquake caused c. 2 m of subsidence around Valdivia. As a result of this, a large area of former pastures and cultivated fields around the lower course of Cruces River was permanently flooded. Over the years the new wetlands were colonized chiefly by Egeria densa ( Spanish : luchecillo ). Egeria densa and other aquatic plants created a rich aquatic ecosystem that attracted
240-505: A reflexive verb . The lower plate itself is the subject. It subducts, in the sense of retreat, or removes itself, and while doing so, is the "subducting plate". Moreover, the word slab is specifically attached to the "subducting plate", even though in English the upper plate is just as much of a slab. The upper plate is left hanging, so to speak. To express it geology must switch to a different verb, typically to override . The upper plate,
360-427: A " creative destruction " for farmers of Southern Chile. A large area of former pastures and cultivated fields around the lower course of Cruces River was permanently flooded as a result of c. 2 m of subsidence caused by the earthquake. Over the years the new wetlands were colonized chiefly by Egeria densa ( Spanish : luchecillo ). Egeria densa and other plants created a rich aquatic ecosystem that attracted
480-400: A 5.5 km-long fissure on 135° heading where 21 individual vents have been found. These vents produced an output of about 0.25 km DRE both in form of lava flows and tephra . The eruption ended on 22 July 59 days later. As a result of an evacuation plan, there were no reported human deaths associated with the eruption. The levels of material damage were relatively low despite
600-406: A few km for young lithosphere created at mid-ocean ridges to around 100 km (62 mi) for the oldest oceanic lithosphere. Continental lithosphere is up to 200 km (120 mi) thick. The lithosphere is relatively cold and rigid compared with the underlying asthenosphere , and so tectonic plates move as solid bodies atop the asthenosphere. Individual plates often include both regions of
720-468: A few others. The hospital of Valdivia, built in 1939, suffered major damage and patients had to be evacuated. The United States quickly set up a field hospital following the earthquake. Aided by the United States, a geological survey of Valdivia was done following the earthquake and resulted in the city's first geological map. Mexico built and donated the public school Escuela México after
840-693: A large environmental conflict between citizens of Valdivia and nearby areas and Celulosa Arauco y Constitución , the owner of the pulp mill. A decline of the Egeria densa that swans feed on has been linked to the death and migration of the swans. A 2020 study indicate that whenever the sum of the water discharge of Cruces and Calle-Calle rivers falls below 74 m/s (2,600 cu ft/s) saltwater reaches Valdivia 's water supply site at Cuesta Soto in Calle-Calle River. Such events tend to happen in autumn and are expected to become more frequent in
960-460: A larger portion of Earth's crust to deform in a more brittle fashion than it would in a normal geothermal gradient setting. Because earthquakes can occur only when a rock is deforming in a brittle fashion, subduction zones can cause large earthquakes. If such a quake causes rapid deformation of the sea floor, there is potential for tsunamis . The largest tsunami ever recorded happened due to a mega-thrust earthquake on December 26, 2004 . The earthquake
1080-678: A long-term policy after the earthquake. As a result of the earthquake, an international technological cooperation programme was established in the dairy sector. More specifically, the German and Danish governments helped to create the Centro Tecnológico de la Leche (the Milk Technological Centre) in the Southern University of Chile . The scholar Erik Dahmén believes that the earthquake resulted in
1200-457: A minimum estimate of how far the continent has subducted. The results show at least a minimum of 229 kilometers of subduction of the northern Australian continental plate. Another example may be the continued northward motion of India, which is subducting beneath Asia. The collision between the two continents initiated around 50 my ago, but is still active. Oceanic-Oceanic plate subduction zones comprise roughly 40% of all subduction zone margins on
1320-423: A permanent bird fauna, notably black-necked swans . The protected area of Carlos Anwandter Nature Sanctuary was created in 1981 to protect the ecosystem. A whole neighbourhood of Corral , Corral Bajo was wiped by the tsunami, while the nearby upper area, Corral Alto, suffered the loss of about 20 to 30% of its houses. Among the material loses were a series stilt houses between Corral Bajo and Amargos. After
SECTION 10
#17327764300451440-519: A permanent bird fauna, notably black-necked swans . The protected area of Carlos Anwandter Nature Sanctuary was created in 1981 to protect the ecosystem. Coincident with the opening of the Valdivia Pulp Mill in 2004 there was a sharp decline of the black-necked swan population in the wetlands of the lower course of Cruces River. An estimated 96.4% of the black-necked swan population died or migrated in about six months. The event unleashed
1560-469: A point of no return. Sections of crustal or intraoceanic arc crust greater than 15 km (9.3 mi) in thickness or oceanic plateau greater than 30 km (19 mi) in thickness can disrupt subduction. However, island arcs subducted end-on may cause only local disruption, while an arc arriving parallel to the zone can shut it down. This has happened with the Ontong Java Plateau and
1680-510: A shallow angle, the overriding plate develops a belt of deformation characterized by crustal thickening, mountain building , and metamorphism . Subduction at a steeper angle is characterized by the formation of back-arc basins . According to the theory of plate tectonics , the Earth's lithosphere , its rigid outer shell, is broken into sixteen larger tectonic plates and several smaller plates. These plates are in slow motion, due mostly to
1800-592: A southward migrating foreshock sequence to the main Valdivia shock, which occurred just 15 minutes after the third event. The earthquake interrupted and effectively ended a protest by coal miners from Lota , who were attempting to march to Concepción to demand higher salaries. The Valdivia earthquake occurred at 15:11 UTC-4 on 22 May, and affected all of Chile between Talca and Chiloé Island , more than 400,000 square kilometres (150,000 sq mi). Coastal villages, such as Toltén , were struck. At Corral ,
1920-510: A zone of shortening and crustal thickening in which there may be extensive folding and thrust faulting . If the angle of subduction steepens or rolls back, the upper plate lithosphere will be put in tension instead, often producing a back-arc basin . The arc-trench complex is the surface expression of a much deeper structure. Though not directly accessible, the deeper portions can be studied using geophysics and geochemistry . Subduction zones are defined by an inclined zone of earthquakes ,
2040-418: Is "consumed", which happens the geological moment the lower plate slips under, even though it may persist for some time until its remelting and dissipation. In this conceptual model, plate is continually being used up. The identity of the subject, the consumer, or agent of consumption, is left unstated. Some sources accept this subject-object construct. Geology makes to subduct into an intransitive verb and
2160-499: Is accreted to (scraped off) the continent, resulting in exotic terranes . The collision of this oceanic material causes crustal thickening and mountain-building. The accreted material is often referred to as an accretionary wedge or prism. These accretionary wedges can be associated with ophiolites (uplifted ocean crust consisting of sediments, pillow basalts, sheeted dykes, gabbro, and peridotite). Subduction may also cause orogeny without bringing in oceanic material that accretes to
2280-496: Is characterized by low geothermal gradients and the associated formation of high-pressure low-temperature rocks such as eclogite and blueschist . Likewise, rock assemblages called ophiolites , associated with modern-style subduction, also indicate such conditions. Eclogite xenoliths found in the North China Craton provide evidence that modern-style subduction occurred at least as early as 1.8 Ga ago in
2400-403: Is driven by the temperature difference between the slab and the surrounding asthenosphere, as the colder oceanic lithosphere is, on average, more dense. Sediments and some trapped water are carried downwards by the slab and recycled into the deep mantle. Earth is so far the only planet where subduction is known to occur, and subduction zones are its most important tectonic feature. Subduction
2520-444: Is fairly well understood, the process by which subduction is initiated remains a matter of discussion and continuing study. Subduction can begin spontaneously if the denser oceanic lithosphere can founder and sink beneath the adjacent oceanic or continental lithosphere through vertical forcing only; alternatively, existing plate motions can induce new subduction zones by horizontally forcing the oceanic lithosphere to rupture and sink into
SECTION 20
#17327764300452640-614: Is found behind the Aleutian Trench subduction zone in Alaska. Volcanoes that occur above subduction zones, such as Mount St. Helens , Mount Etna , and Mount Fuji , lie approximately one hundred kilometers from the trench in arcuate chains called volcanic arcs . Plutons, like Half Dome in Yosemite National Park, generally form 10–50 km below the volcanoes within the volcanic arcs and are only visible on
2760-427: Is known as a subduction zone , and its surface expression is known as an arc-trench complex . The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year. Subduction is possible because the cold and rigid oceanic lithosphere is slightly denser than the underlying asthenosphere ,
2880-533: Is located along the Pacific Ring of Fire , a known zone of high seismicity. The earthquake was a megathrust earthquake resulting from the release of mechanical stress between the subducting Nazca plate and South American plate on the Peru–Chile Trench , off the coast of southern Chile. Because of its geography, Chile remains one of the most seismically active countries in the world. The focus of
3000-477: Is more buoyant and as a result will rise into the lithosphere, where it forms large magma chambers called diapirs. Some of the magma will make it to the surface of the crust where it will form volcanoes and, if eruptive on earth's surface, will produce andesitic lava. Magma that remains in the lithosphere long enough will cool and form plutonic rocks such as diorite, granodiorite, and sometimes granite. The arc magmatism occurs one hundred to two hundred kilometers from
3120-411: Is old, goes down the subduction zone. As this happens, metamorphic reactions increase the density of the continental crustal rocks, which leads to less buoyancy. One study of the active Banda arc-continent collision claims that by unstacking the layers of rock that once covered the continental basement, but are now thrust over one another in the orogenic wedge, and measuring how long they are, can provide
3240-723: Is ongoing beneath part of the Andes , causing segmentation of the Andean Volcanic Belt into four zones. The flat-slab subduction in northern Peru and the Norte Chico region of Chile is believed to be the result of the subduction of two buoyant aseismic ridges, the Nazca Ridge and the Juan Fernández Ridge , respectively. Around Taitao Peninsula flat-slab subduction is attributed to the subduction of
3360-404: Is the driving force behind plate tectonics , and without it, plate tectonics could not occur. Oceanic subduction zones are located along 55,000 km (34,000 mi) convergent plate margins, almost equal to the cumulative plate formation rate 60,000 km (37,000 mi) of mid-ocean ridges. Sea water seeps into oceanic lithosphere through fractures and pores, and reacts with minerals in
3480-694: The Aleutian Islands . The epicenter of this megathrust earthquake was near Lumaco , approximately 570 kilometres (350 mi) south of Santiago , with Valdivia being the most affected city. The tremor caused localised tsunamis that severely battered the Chilean coast, with waves up to 25 metres (82 ft). The main tsunami traveled across the Pacific Ocean and devastated Hilo, Hawaii , where waves as high as 10.7 metres (35 ft) were recorded over 10,000 kilometres (6,200 mi) from
3600-528: The Cascade Volcanic Arc , that form along the coast of continents. Island arcs (intraoceanic or primitive arcs) are produced by the subduction of oceanic lithosphere beneath another oceanic lithosphere (ocean-ocean subduction) while continental arcs (Andean arcs) form during the subduction of oceanic lithosphere beneath a continental lithosphere (ocean-continent subduction). An example of a volcanic arc having both island and continental arc sections
3720-711: The Chile Rise , a spreading ridge . The Laramide Orogeny in the Rocky Mountains of the United States is attributed to flat-slab subduction. During this orogeny, a broad volcanic gap appeared at the southwestern margin of North America, and deformation occurred much farther inland; it was during this time that the basement -cored mountain ranges of Colorado, Utah, Wyoming, South Dakota, and New Mexico came into being. The most massive subduction zone earthquakes, so-called "megaquakes", have been found to occur in flat-slab subduction zones. Although stable subduction
Cruces River - Misplaced Pages Continue
3840-561: The Liquiñe-Ofqui Fault . Some of these areas remain sparsely vegetated while others have naturally developed more or less pure stands of Nothofagus dombeyi . These landslides did not cause many fatalities nor significant economic losses because most of the areas were uninhabited, with only minor roads. One landslide caused destruction and alarm following its blockage of the outflow of Riñihue Lake (see below). About 100 km (62 mi) south of Riñihue Lake, landslides in
3960-630: The Paleoproterozoic Era . The eclogite itself was produced by oceanic subduction during the assembly of supercontinents at about 1.9–2.0 Ga. Blueschist is a rock typical for present-day subduction settings. The absence of blueschist older than Neoproterozoic reflects more magnesium-rich compositions of Earth's oceanic crust during that period. These more magnesium-rich rocks metamorphose into greenschist at conditions when modern oceanic crust rocks metamorphose into blueschist. The ancient magnesium-rich rocks mean that Earth's mantle
4080-642: The Valdivia River , sank after being moved 1.5 km (0.93 mi) backward and forward in the river; as of 2005, its mast was still visible from the road to Niebla . Soil subsidence also destroyed buildings, deepened local rivers and created wetlands in such places as 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 totally destroyed. Witnesses reported underground water flowing up through
4200-491: The Vitiaz Trench . Subduction zones host a unique variety of rock types created by the high-pressure, low-temperature conditions a subducting slab encounters during its descent. The metamorphic conditions the slab passes through in this process create and destroy water bearing (hydrous) mineral phases, releasing water into the mantle. This water lowers the melting point of mantle rock, initiating melting. Understanding
4320-533: The Wadati–Benioff zone , that dips away from the trench and extends down below the volcanic arc to the 660-kilometer discontinuity . Subduction zone earthquakes occur at greater depths (up to 600 km (370 mi)) than elsewhere on Earth (typically less than 20 km (12 mi) depth); such deep earthquakes may be driven by deep phase transformations , thermal runaway , or dehydration embrittlement . Seismic tomography shows that some slabs can penetrate
4440-406: The core–mantle boundary . Here the slabs are heated up by the ambient heat and are not detected anymore ~300 Myr after subduction. Orogeny is the process of mountain building. Subducting plates can lead to orogeny by bringing oceanic islands, oceanic plateaus, sediments and passive continental margins to convergent margins. The material often does not subduct with the rest of the plate but instead
4560-411: The lower mantle and sink clear to the core–mantle boundary . Here the residue of the slabs may eventually heat enough to rise back to the surface as mantle plumes . Subduction typically occurs at a moderately steep angle by the time it is beneath the volcanic arc. However, anomalous shallower angles of subduction are known to exist as well as some that are extremely steep. Flat-slab subduction
4680-416: The zeolite , prehnite-pumpellyite, blueschist , and eclogite facies stability zones of subducted oceanic crust. Zeolite and prehnite-pumpellyite facies assemblages may or may not be present, thus the onset of metamorphism may only be marked by blueschist facies conditions. Subducting slabs are composed of basaltic crust topped with pelagic sediments ; however, the pelagic sediments may be accreted onto
4800-457: The 1960 earthquake. Subducting Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second plate, the heavier plate dives beneath the other and sinks into the mantle. A region where this process occurs
4920-433: The 1960s the autumn of 1960 in southern Chile was not particularly dry nor warm. The tsunami that struck the coast of southern Chile destroyed seaside farms, killing numerous livestock and people. Barns and industrial structures were destroyed by the quake. The dairy industry was among the few industries of the affected zone that received subsidies and investment after the earthquake. It received state support through
Cruces River - Misplaced Pages Continue
5040-506: The Alaskan crust. The concept of subduction would play a role in the development of the plate tectonics theory. First geologic attestations of the "subduct" words date to 1970, In ordinary English to subduct , or to subduce (from Latin subducere , "to lead away") are transitive verbs requiring a subject to perform an action on an object not itself, here the lower plate, which has then been subducted ("removed"). The geological term
5160-588: The Alps. The chemistry of the inclusions supports the existence of a carbon-rich fluid in that environment, and additional chemical measurements of lower pressure and temperature facies in the same tectonic complex support a model for carbon dissolution (rather than decarbonation) as a means of carbon transport. Elastic strain caused by plate convergence in subduction zones produces at least three types of earthquakes. These are deep earthquakes, megathrust earthquakes, and outer rise earthquakes. Deep earthquakes happen within
5280-590: The Andes in a strip running from Lota (37° S) southwards. The area of intensities of VII or more did not penetrate into the Central Valley north of Lleulleu Lake (38° S) and south of Castro (42.5° S). Two days after the earthquake Cordón Caulle , a volcanic vent close to Puyehue volcano , erupted. Other volcanoes may also have erupted, but none were recorded because of the lack of communication in Chile at
5400-472: The asthenosphere. Both models can eventually yield self-sustaining subduction zones, as the oceanic crust is metamorphosed at great depth and becomes denser than the surrounding mantle rocks. The compilation of subduction zone initiation events back to 100 Ma suggests horizontally-forced subduction zone initiation for most modern subduction zones, which is supported by results from numerical models and geologic studies. Some analogue modeling shows, however,
5520-486: The city of Valdivia near the coast. As the San Pedro River was blocked, the water level of Riñihue Lake started to rise quickly. Each meter the water level rose was equivalent to 20 million cubic meters, which meant that 480 million cubic meters of water would release into the San Pedro River (easily overpowering its flow capacity of 400 cubic metres (14,000 cu ft) per second if it rose above
5640-622: The coast, mainly the foot of the Chilean Coast Range , and the shores of Llanquihue Lake . A seiche (type of standing wave) of more than 1 meter was observed on Panguipulli Lake following the earthquake. On 22 May, a seiche occurred also in Nahuel Huapi Lake , on the Argentine side of the Andes , more than 200 km away from Valdivia. The wave, most likely produced by an earthquake-triggered sediment slide at
5760-577: The coastal town of Queule , a carabinero reported hundreds of people dead or missing some days after the tsunami. Historians Yoselin Jaramillo and Ismael Basso report that people in Queule decades later know about 50 people to have died because of the earthquake and tsunami. The earthquake triggered numerous landslides , mainly in the steep glacial valleys of the southern Andes . Within the Andes, most landslides occurred on forested mountain slopes around
5880-435: The continent, away from the trench, and has been described in western North America (i.e. Laramide orogeny, and currently in Alaska, South America, and East Asia. The processes described above allow subduction to continue while mountain building happens concurrently, which is in contrast to continent-continent collision orogeny, which often leads to the termination of subduction. Continents are pulled into subduction zones by
6000-506: The crust and mantle to form hydrous minerals (such as serpentine) that store water in their crystal structures. Water is transported into the deep mantle via hydrous minerals in subducting slabs. During subduction, a series of minerals in these slabs such as serpentine can be stable at different pressures within the slab geotherms, and may transport significant amount of water into the Earth's interior. As plates sink and heat up, released fluids can trigger seismicity and induce melting within
6120-579: The crust would be melted and recycled into the Earth's mantle . In 1964, George Plafker researched the Good Friday earthquake in Alaska . He concluded that the cause of the earthquake was a megathrust reaction in the Aleutian Trench , a result of the Alaskan continental crust overlapping the Pacific oceanic crust. This meant that the Pacific crust was being forced downward, or subducted , beneath
SECTION 50
#17327764300456240-597: The crust, megathrust earthquakes on the subduction interface near the trench, and outer rise earthquakes on the subducting lower plate as it bends near the trench. Anomalously deep events are a characteristic of subduction zones, which produce the deepest quakes on the planet. Earthquakes are generally restricted to the shallow, brittle parts of the crust, generally at depths of less than twenty kilometers. However, in subduction zones quakes occur at depths as great as 700 km (430 mi). These quakes define inclined zones of seismicity known as Wadati–Benioff zones which trace
6360-609: The crust, through hotspot magmatism or extensional rifting, would the crust be able to break from its continent and begin subduction. Subduction can continue as long as the oceanic lithosphere moves into the subduction zone. However, the arrival of buoyant continental lithosphere at a subduction zone can result in increased coupling at the trench and cause plate boundary reorganization. The arrival of continental crust results in continental collision or terrane accretion that may disrupt subduction. Continental crust can subduct to depths of 250 km (160 mi) where it can reach
6480-448: The degree of lower plate curvature of the subducting plate in great historical earthquakes such as the 2004 Sumatra-Andaman and the 2011 Tōhoku earthquake, it was determined that the magnitude of earthquakes in subduction zones is inversely proportional to the angle of subduction near the trench, meaning that "the flatter the contact between the two plates, the more likely it is that mega-earthquakes will occur". Outer rise earthquakes on
6600-440: The descending slab. Nine of the ten largest earthquakes of the last 100 years were subduction zone megathrust earthquakes. These included the 1960 Great Chilean earthquake which at M 9.5 was the largest earthquake ever recorded, the 2004 Indian Ocean earthquake and tsunami , and the 2011 Tōhoku earthquake and tsunami . The subduction of cold oceanic lithosphere into the mantle depresses the local geothermal gradient and causes
6720-455: The different regimes present in this setting. The models are as follows: In their 2019 study, Macdonald et al. proposed that arc-continent collision zones and the subsequent obduction of oceanic lithosphere was at least partially responsible for controlling global climate. Their model relies on arc-continent collision in tropical zones, where exposed ophiolites composed mainly of mafic material increase "global weatherability" and result in
6840-492: The earthquake destroyed Valdivia's flood barriers, general land subsidence exposed new areas to flooding. Parts of the botanical garden of the Austral University of Chile that were next to Cau-Cau River and the city's southern outskirts along Route 206 were permanently flooded. The earthquakes damaged an area that had suffered a long period of economic decline, which began with shifts in trade routes due to
6960-454: The earthquake many families in Corral relocated to the neighbourhood of La Aguada. The economy of the coastal town of Queule had during the 1950s developed significantly. Its economy based on fishing, agriculture and industry had grown. Queule was connected by road in 1957 to the rest of the country and the town had developed into a balneario (resort town). This era of prosperity ended with
7080-520: The earthquake was relatively shallow at 33 km (21 mi), considering that earthquakes in northern Chile and Argentina may reach depths of 70 km (43 mi). A 2019 research paper postulates that the Liquiñe-Ofqui fault had a M w 9.07 strike-slip subevent along with the M w 9.37 main thrust sub-event which could help account for how the plate boundary event seemingly "overspent" its tectonic budget. In other words,
7200-563: The earthquake. Valdivia's bridges suffered only minor damage. The damage caused to Calle-Calle Bridge led to its temporary closure after the earthquake, with traffic redirected to Teja Island through Caucau River where people crossed it on boats and, reportedly, also a rudimentary and temporary wooden bridge. Land subsidence in Corral Bay improved navigability as shoal banks, produced earlier by sediments from Madre de Dios and other nearby gold mines, sank and were compacted. As
7320-433: The earthquake. Between two sparsely populated and isolated Andean valleys, the eruption had few eyewitnesses and received little attention by local media, which was preoccupied with the severe and widespread damage and losses caused by the earthquake. The eruption was first noticed and reported as an explosion by the crew of a United States Air Force plane that was heading to Santiago from Puerto Montt . The eruption fed
SECTION 60
#17327764300457440-459: The epicenter. 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 6,000 killed. Different sources have estimated the monetary cost ranged from US$ 400 million to $ 800 million (or US$ 4.1 billion to $ 8.2 billion in 2023, adjusted for inflation). Chile
7560-526: The expansion of railroads in southern Chile and the opening of the Panama Canal in 1914. Unlike Valdivia, Osorno was saved from major destruction. In Osorno only about 20 houses were totally destroyed, although many firewalls and chimneys collapsed. Puerto Montt , a major city today, had in the early 1960s about 49,500 inhabitants. The bulk of the damage in Puerto Montt was located in
7680-547: The fault would have moved as a consequence of the 22 May Valdivia earthquake. Earthquake-induced tsunamis affected southern Chile, Hawaii, Japan, the Philippines, China, eastern New Zealand , southeast Australia, and the Aleutian Islands . Some localized tsunamis severely battered the Chilean coast, with waves up to 25 m (82 ft). The main tsunami crossed the Pacific Ocean at a speed of several hundred km/h and devastated Hilo, Hawaii , killing 61 people. Most of
7800-472: The final, 24-meter-high dam. This potential disaster would have violently flooded all the settlements along the course of the river in less than five hours, with more dire consequences if the dam suddenly broke. About 100,000 people lived in the affected zone. Plans were made to evacuate Valdivia, and many people left. To avoid the destruction of the city, several military units and hundreds of workers from ENDESA , CORFO , and MOP started an effort to control
7920-619: The forearc may include an accretionary wedge of sediments scraped off the subducting slab and accreted to the overriding plate. However, not all arc-trench complexes have an accretionary wedge. Accretionary arcs have a well-developed forearc basin behind the accretionary wedge, while the forearc basin is poorly developed in non-accretionary arcs. Beyond the forearc basin, volcanoes are found in long chains called volcanic arcs . The subducting basalt and sediment are normally rich in hydrous minerals and clays. Additionally, large quantities of water are introduced into cracks and fractures created as
8040-420: The forearc-hanging wall and not subducted. Most metamorphic phase transitions that occur within the subducting slab are prompted by the dehydration of hydrous mineral phases. The breakdown of hydrous mineral phases typically occurs at depths greater than 10 km. Each of these metamorphic facies is marked by the presence of a specific stable mineral assemblage, recording the metamorphic conditions undergone but
8160-509: The future due to a trend of diminished rainfall . Soils around the lower course of the river are trumaos and red clay soils . 39°42′26″S 73°11′51″W / 39.70722°S 73.19750°W / -39.70722; -73.19750 1960 Valdivia earthquake The 1960 Valdivia earthquake and tsunami (Spanish: Terremoto de Valdivia ) or the Great Chilean earthquake ( Gran terremoto de Chile ) on 22 May 1960
8280-491: The high magnitude of the earthquake. Part of the reason behind this was the limited infrastructure development of the region next to the rupture zone. Structures that had been designed to resist earthquakes performed well during the earthquake, chiefly suffering damage when affected by soil subsidence or small fault movements. Houses built by their owners fared badly. In the regions of Maule and Bío Bío , houses built from adobe and masonry proved weak, while from Araucanía to
8400-408: The hot, ductile layer in the upper mantle . Once initiated, stable subduction is driven mostly by the negative buoyancy of the dense subducting lithosphere. The down-going slab sinks into the mantle largely under its own weight. Earthquakes are common along subduction zones, and fluids released by the subducting plate trigger volcanism in the overriding plate. If the subducting plate sinks at
8520-430: The idea of subduction initiation at passive margins is popular, there is no modern day example for this type of subduction nucleation. This is likely due to the strength of the oceanic or transitional crust at the continental passive margins, suggesting that if the crust did not break in its first 20 million years of life, it is unlikely to break in the future under normal sedimentation loads. Only with additional weaking of
8640-398: The incident. As of 2000, the remnants of Canelo were still visible. Santiago , another ship anchored at Corral at the time of the quake, managed to leave Corral in a bad state but was wrecked off the coast of Mocha Island on 24 May. The schooner La Milagrosa departed from Queule on 22 May to load a cargo of Fitzroya wood shingles in a small port south of Corral. La Milagrosa
8760-663: The lake bottom, killed two people and destroyed a pier in San Carlos de Bariloche city. During the Great Chilean earthquake, several landslides west of Tralcán Mountain blocked the outflow of Riñihue Lake . Riñihue Lake is the lowest of the Seven Lakes chain and receives a constant inflow from the Enco River . The blocked San Pedro River , which drains the lake, passes through several towns before reaching
8880-511: The lake. Twenty-seven bulldozers were put into service, but they had severe difficulties moving in the mud near the dams, so dykes had to be constructed with shovels from June onwards. The work was not restricted to the lake; drainages from other parts of the Seven Lakes were dammed to minimize additional flow into Riñihue Lake. These dams were removed later, with the exception of Calafquén Lake , which still retains its dam. By 23 June,
9000-574: The lower plate occur when normal faults oceanward of the subduction zone are activated by flexure of the plate as it bends into the subduction zone. The 2009 Samoa earthquake is an example of this type of event. Displacement of the sea floor caused by this event generated a six-meter tsunami in nearby Samoa. Seismic tomography has helped detect subducted lithospheric slabs deep in the mantle where no earthquakes occur. About one hundred slabs have been described in terms of depth and their timing and location of subduction. The great seismic discontinuities in
9120-474: The lowlands, which absorbed great amounts of energy. Many city blocks with destroyed buildings in the city center remained empty until the 1990s and 2000s, with some of them still used as parking lots . Before the earthquake, some of these blocks had modern concrete buildings built after the Great Valdivia fire of 1909. Around the main city square most buildings collapsed except for Edificio Prales and
9240-468: The main dam had been lowered from 24 to 15 m (79 to 49 ft), allowing 3 billion cubic metres of water to leave the lake gradually, but still with considerable destructive power. The team was led by ENDESA engineer Raúl Sáez . On 24 May, 38 hours after the main shock of the 1960 Valdivia earthquake, the Cordón Caulle volcano erupted. The eruption was believed to have been triggered by
9360-411: The main port of Valdivia, the water level rose 4 m (13 ft) before it began to recede. At 16:20 UTC-4, a wave of 8 m (26 ft) struck the Chilean coast, mainly between Concepción and Chiloé. Another wave measuring 10 m (33 ft) was reported ten minutes later. Hundreds of people were already reported dead by the time the tsunami struck. One ship, Canelo , starting at the mouth of
9480-484: The mantle, at 410 km (250 mi) depth and 670 km (420 mi), are disrupted by the descent of cold slabs in deep subduction zones. Some subducted slabs seem to have difficulty penetrating the major discontinuity that marks the boundary between the upper mantle and lower mantle at a depth of about 670 kilometers. Other subducted oceanic plates have sunk to the core–mantle boundary at 2890 km depth. Generally, slabs decelerate during their descent into
9600-463: The mantle, from typically several cm/yr (up to ~10 cm/yr in some cases) at the subduction zone and in the uppermost mantle, to ~1 cm/yr in the lower mantle. This leads to either folding or stacking of slabs at those depths, visible as thickened slabs in seismic tomography. Below ~1700 km, there might be a limited acceleration of slabs due to lower viscosity as a result of inferred mineral phase changes until they approach and finally stall at
9720-498: The mountains around Golgol River caused the river to dam up; when it burst through the earthen dam, it created a flood down to Puyehue Lake . The Golgol landslides destroyed parts of international Route 215-CH , which connects to Bariloche in Argentina through Cardenal Antonio Samoré Pass . While most landslides clustered around north–south strips in the Andes, other areas that were affected by large numbers of landslides were
9840-418: The neighborhood of Barrio Modelo and the northern part of Bahía Angelmó , where artificial fills subsided. Angelmó and other coastal areas of Puerto Montt were among the few urban areas that suffered "total destruction" by the earthquake. After the earthquake a myth related the unusually warm and clear weather conditions prior to the earthquake to its triggering. When compared with the years that followed in
9960-545: 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 dishes were reported to have remained in place. With the exception of poor building sites, the zone of Mercalli scales intensities of VII or more all lay west of
10080-492: The ocean floor, studied the Mid-Atlantic Ridge and proposed that hot molten rock was added to the crust at the ridge and expanded the seafloor outward. This theory was to become known as seafloor spreading . Since the Earth's circumference has not changed over geologic time, Hess concluded that older seafloor has to be consumed somewhere else, and suggested that this process takes place at oceanic trenches , where
10200-443: The oceanic lithosphere and continental lithosphere. Subduction zones are where cold oceanic lithosphere sinks back into the mantle and is recycled. They are found at convergent plate boundaries, where the heavier oceanic lithosphere of one plate is overridden by the leading edge of another, less-dense plate. The overridden plate (the slab ) sinks at an angle most commonly between 25 and 75 degrees to Earth's surface. This sinking
10320-399: The overriding continent. When the lower plate subducts at a shallow angle underneath a continent (something called "flat-slab subduction"), the subducting plate may have enough traction on the bottom of the continental plate to cause the upper plate to contract by folding, faulting, crustal thickening, and mountain building. Flat-slab subduction causes mountain building and volcanism moving into
10440-404: The planet. The ocean-ocean plate relationship can lead to subduction zones between oceanic and continental plates, therefore highlighting how important it is to understand this subduction setting. Although it is not fully understood what causes the initiation of subduction of an oceanic plate under another oceanic plate, there are three main models put forth by Baitsch-Ghirardello et al. that explain
10560-590: The possibility of spontaneous subduction from inherent density differences between two plates at specific locations like passive margins and along transform faults . There is evidence this has taken place in the Izu-Bonin-Mariana subduction system. Earlier in Earth's history, subduction is likely to have initiated without horizontal forcing due to the lack of relative plate motion, though a proposal by A. Yin suggests that meteorite impacts may have contributed to subduction initiation on early Earth. Though
10680-476: The potential slip in that segment of the plate interface. 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 , and 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
10800-520: The pressures and temperatures necessary for this type of metamorphism are much higher than what is observed in most subduction zones. Frezzoti et al. (2011) propose a different mechanism for carbon transport into the overriding plate via dissolution (release of carbon from carbon-bearing minerals into an aqueous solution) instead of decarbonation. Their evidence comes from the close examination of mineral and fluid inclusions in low-temperature (<600 °C) diamonds and garnets found in an eclogite facies in
10920-467: The previous and current more widely accepted explanation for the earthquake involves the Peru-Chile Trench slipping further than its accumulated slip deficit (the amount of slip available for an earthquake) should allow. The alternative explanation, with two faults slipping nearly simultaneously, could help explain the true mechanism of the earthquake. Subduction zones are known to produce
11040-418: The pull force of subducting lithosphere. Sinking lithosphere at subduction zones are a part of convection cells in the underlying ductile mantle . This process of convection allows heat generated by radioactive decay to escape from the Earth's interior. The lithosphere consists of the outermost light crust plus the uppermost rigid portion of the mantle . Oceanic lithosphere ranges in thickness from just
11160-444: The rocks of the mantle. The mantle-derived magmas (which are initially basaltic in composition) can ultimately reach the Earth's surface, resulting in volcanic eruptions. The chemical composition of the erupting lava depends upon the degree to which the mantle-derived basalt interacts with (melts) Earth's crust or undergoes fractional crystallization . Arc volcanoes tend to produce dangerous eruptions because they are rich in water (from
11280-459: The salvaged remnants of Penco . Canelo was anchored at Corral when the quake struck, filling a cargo of wood and other products destined for northern Chile. The engine of Canelo was warmed up after the earthquake. After hours of drifting around in Corral Bay and Valdivia River, the ship was wrecked and subsequently abandoned by its crew at 1800 local time. Two men on board Canelo died in
11400-436: The sedimentary and volcanic cover is mostly scraped off to form an orogenic wedge. An orogenic wedge is larger than most accretionary wedges due to the volume of material there is to accrete. The continental basement rocks beneath the weak cover suites are strong and mostly cold, and can be underlain by a >200 km thick layer of dense mantle. After shedding the low density cover units, the continental plate, especially if it
11520-450: The sinking oceanic plate they are attached to. Where continents are attached to oceanic plates with no subduction, there is a deep basin that accumulates thick suites of sedimentary and volcanic rocks known as a passive margin. Some passive margins have up to 10 km of sedimentary and volcanic rocks covering the continental crust. As a passive margin is pulled into a subduction zone by the attached and negatively buoyant oceanic lithosphere,
11640-453: The slab and sediments) and tend to be extremely explosive. Krakatoa , Nevado del Ruiz , and Mount Vesuvius are all examples of arc volcanoes. Arcs are also associated with most ore deposits. Beyond the volcanic arc is a back-arc region whose character depends strongly on the angle of subduction of the subducting slab. Where this angle is shallow, the subducting slab drags the overlying continental crust partially with it, which produces
11760-572: 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; measured with the Mercalli scale, tectonically depressed areas suffered heavier damage. The two most affected areas were Valdivia and Puerto Octay , near
11880-632: The south weak houses were mainly those built with inappropriate wood that had decayed over time. It has been estimated that about 40 percent of the houses in Valdivia were destroyed, leaving 20,000 people homeless. The most affected structures were those built of concrete, which in some cases collapsed completely, because they were not built using modern earthquake engineering. Traditional wooden houses fared better; although many were uninhabitable if they did not collapse. Houses built upon elevated areas suffered considerably less damage compared to those on
12000-431: The speed at which a rupture front expands across the surface of the fault, has been estimated as 3.5 km (2.2 mi) per second. The average slip across all 27 Nazca subfaults was estimated to be 11 m , with 25–30 m of slip 200–500 km south of the epicenter on offshore subfaults. While the Valdivia earthquake was extraordinarily large, the 2016 Chiloé earthquake hints that it did not release all
12120-447: The storage of carbon through silicate weathering processes. This storage represents a carbon sink , removing carbon from the atmosphere and resulting in global cooling. Their study correlates several Phanerozoic ophiolite complexes, including active arc-continent subduction, with known global cooling and glaciation periods. This study does not discuss Milankovitch cycles as a driver of global climate cyclicity. Modern-style subduction
12240-481: The stratosphere during violent eruptions can cause rapid cooling of Earth's climate and affect air travel. Arc-magmatism plays a role in Earth's Carbon cycle by releasing subducted carbon through volcanic processes. Older theory states that the carbon from the subducting plate is made available in overlying magmatic systems via decarbonation, where CO 2 is released through silicate-carbonate metamorphism. However, evidence from thermodynamic modeling has shown that
12360-472: 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 (500 mi) long, stretching from Arauco (37° S) to below the Chiloé Archipelago (44° S). Rupture velocity,
12480-399: The subducted plate and in the overlying mantle wedge. This type of melting selectively concentrates volatiles and transports them into the overlying plate. If an eruption occurs, the cycle then returns the volatiles into the oceans and atmosphere. The surface expressions of subduction zones are arc-trench complexes. On the ocean side of the complex, where the subducting plate first approaches
12600-526: The subducting slab bends downward. During the transition from basalt to eclogite, these hydrous materials break down, producing copious quantities of water, which at such great pressure and temperature exists as a supercritical fluid . The supercritical water, which is hot and more buoyant than the surrounding rock, rises into the overlying mantle, where it lowers the melting temperature of the mantle rock, generating magma via flux melting . The magmas, in turn, rise as diapirs because they are less dense than
12720-509: The subducting slab. Transitions between facies cause hydrous minerals to dehydrate at certain pressure-temperature conditions and can therefore be tracked to melting events in the mantle beneath a volcanic arc. Two kinds of arcs are generally observed on Earth: island arcs that form on the oceanic lithosphere (for example, the Mariana and the Tonga island arcs), and continental arcs such as
12840-446: The subduction zone, there is often an outer trench high or outer trench swell . Here the plate shallows slightly before plunging downwards, as a consequence of the rigidity of the plate. The point where the slab begins to plunge downwards is marked by an oceanic trench . Oceanic trenches are the deepest parts of the ocean floor. Beyond the trench is the forearc portion of the overriding plate. Depending on sedimentation rates,
12960-451: The subject, performs the action of overriding the object, the lower plate, which is overridden. Subduction zones are important for several reasons: Subduction zones have also been considered as possible disposal sites for nuclear waste in which the action of subduction itself would carry the material into the planetary mantle , safely away from any possible influence on humanity or the surface environment. However, that method of disposal
13080-454: The surface once the volcanoes have weathered away. The volcanism and plutonism occur as a consequence of the subducting oceanic slab dehydrating as it reaches higher pressures and temperatures. Once the oceanic slab reaches about 100 km in depth, hydrous minerals become unstable and release fluids into the asthenosphere. The fluids act as a flux for the rock within the asthenosphere and cause it to partially melt. The partially melted material
13200-531: The time. The relatively low death toll in Chile (5,700) is explained in part by the low population density in the region, and by building practices that took into account the area's high geological activity. Earthquake lights were reported in Purén . One of the main aftershocks occurred on 6 June in Aysén Region . This magnitude 7.7 earthquake probably occurred along the Liquiñe-Ofqui Fault , meaning that
13320-439: The timing and conditions in which these dehydration reactions occur is key to interpreting mantle melting, volcanic arc magmatism, and the formation of continental crust. A metamorphic facies is characterized by a stable mineral assemblage specific to a pressure-temperature range and specific starting material. Subduction zone metamorphism is characterized by a low temperature, high-ultrahigh pressure metamorphic path through
13440-444: The trench and approximately one hundred kilometers above the subducting slab. Arcs produce about 10% of the total volume of magma produced each year on Earth (approximately 0.75 cubic kilometers), much less than the volume produced at mid-ocean ridges, but they have formed most continental crust . Arc volcanism has the greatest impact on humans because many arc volcanoes lie above sea level and erupt violently. Aerosols injected into
13560-495: The tsunami swell penetrated along Calle-Calle River as far as Huellelhue putting afloat piles of firewood that lay in the fields. After the 21 May Concepción earthquake, people in Ancud sought refuge in boats. A carabinero (police) boat, Gloria , was towing a few of these boats when the second earthquake struck on 22 May. As the sea regressed Gloria became stranded between Cerro Guaiguén and Cochinos Island . The stranded boat
13680-566: The tsunami-related deaths in Japan occurred in the northeast Sanriku region of Honshu . The Chilean coast was devastated by a tsunami from Mocha Island (38° S) to Aysén Region (45° S). Across southern Chile, the tsunami caused huge loss of life, damage to port infrastructure, and the loss of many small boats. Further north, the port of Talcahuano did not suffer any major damage, only some flooding. Some tugboats and small sailboats were stranded on Rocuant Island near Talcahuano. In Valdivia
13800-651: Was battered by the currents and waves of the tsunami for four days while moving south. Outside Corral the crew rescued six nearly unconscious and dehydrated children on board two boats. The boats found were used to navigate in Valdivia River and Corral Bay but had drifted into the high sea. The coastal localities of Mississippi and Mehuín were struck by the tsunami causing the loss of fishing boats. 150 boats, most of them used for fishing are reported to have "disappeared" in Mehuín. Some kilometres north of Mahuín at
13920-628: Was caused by subduction of the Indo-Australian plate under the Euro-Asian Plate, but the tsunami spread over most of the planet and devastated the areas around the Indian Ocean. Small tremors which cause small, nondamaging tsunamis, also occur frequently. A study published in 2016 suggested a new parameter to determine a subduction zone's ability to generate mega-earthquakes. By examining subduction zone geometry and comparing
14040-582: Was once hotter, but not that subduction conditions were hotter. Previously, the lack of pre-Neoproterozoic blueschist was thought to indicate a different type of subduction. Both lines of evidence refute previous conceptions of modern-style subduction having been initiated in the Neoproterozoic Era 1.0 Ga ago. Harry Hammond Hess , who during World War II served in the United States Navy Reserve and became fascinated in
14160-469: Was the most powerful earthquake ever recorded . Most studies have placed it at 9.4–9.6 on the moment magnitude scale , while some studies have placed the magnitude lower than 9.4. It occurred in the afternoon (19:11 GMT , 15:11 local time), and lasted 10 minutes. The resulting tsunamis affected southern Chile , Hawaii , Japan , the Philippines , eastern New Zealand , southeast Australia , and
14280-538: Was the 8.1 M w 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 (7.1 M w ) and 14:55 UTC-4 (7.8 M w ) on 22 May. These earthquakes formed
14400-505: Was wrecked when a tsunami wave engulfed it. All the new infrastructure of the small port of Bahía Mansa was destroyed by the tsunami, which reached heights of up to 10 metres above sea level there. The boat Isabella in Bahía Mansa quickly left the port but lost its anchors. In the Valdivia River and Corral Bay , several vessels were wrecked by the earthquake, among them Argentina , Canelo , Carlos Haverbeck , Melita , and
#44955