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Saturday, September 6, 2014

Europa (moon)

Europa (moon)

From Wikipedia, the free encyclopedia

Europa
Europa-moon.jpg
Europa's trailing hemisphere in approximate natural color. The prominent crater in the lower right is Pwyll and the darker regions are areas where Europa's primarily water ice surface has a higher mineral content. Imaged on 7 September 1996 by Galileo spacecraft.
Discovery
Discovered by Galileo Galilei
Simon Marius
Discovery date 8 January 1610[1]
Designations
Jupiter II
Adjectives Europan
Orbital characteristics[3]
Epoch 8 January 2004
Periapsis 664862 km[a]
Apoapsis 676938 km[b]
Mean orbit radius
670900 km[2]
Eccentricity 0.009[2]
3.551181 d[2]
Average orbital speed
13.740 km/s[2]
Inclination 0.470° (to Jupiter's equator)[2]
Satellite of Jupiter
Physical characteristics
Mean radius
1560.8±0.5 km (0.245 Earths)[4]
3.09×107 km2 (0.061 Earths)[c]
Volume 1.593×1010 km3 (0.015 Earths)[d]
Mass (4.799844±0.000013)×1022 kg (0.008 Earths)[4]
Mean density
3.013±0.005 g/cm3[4]
1.314 m/s2 (0.134 g)[e]
2.025 km/s[f]
Synchronous[5]
0.1°[6]
Albedo 0.67 ± 0.03[4]
Surface temp. min mean max
Surface ≈ 50 K[7] 102 K (-171.15°C) 125 K
5.29 (opposition)[4]
Atmosphere
Surface pressure
0.1 µPa (10−12 bar)[8]
Europa Listeni/jʊˈrpə/[9] (Jupiter II), is the sixth-closest moon of the planet Jupiter, and the smallest of its four Galilean satellites, but still the sixth-largest moon in the Solar System. Europa was discovered in 1610 by Galileo Galilei[1] and possibly independently by Simon Marius around the same time. Progressively better observations of Europa have occurred over the centuries by Earth-bound telescopes, and by space probe flybys starting in the 1970s.

Slightly smaller than the Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of water ice and is one of the smoothest in the Solar System.[10] This surface is striated by cracks and streaks, whereas craters are relatively rare. The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath it, which could conceivably serve as an abode for extraterrestrial life.[11] This hypothesis proposes that heat from tidal flexing causes the ocean to remain liquid and drives geological activity similar to plate tectonics.[12]

In December 2013, NASA reported the detection of "clay-like minerals" (specifically, phyllosilicates), often associated with "organic material" on the icy crust of Europa.[13] In addition, NASA announced, based on studies with the Hubble Space Telescope, that water vapor plumes were detected on Europa and were similar to water vapor plumes detected on Enceladus, moon of Saturn.[14]

The Galileo mission, launched in 1989, provided the bulk of current data on Europa. No spacecraft has yet landed on Europa, but its intriguing characteristics have led to several ambitious exploration proposals. The European Space Agency's Jupiter Icy Moon Explorer (JUICE) is a mission to Europa that is due to launch in 2022.[15] NASA is planning a robotic mission that would be launched in the "mid-2020s".[16]

Discovery and naming

Europa was discovered on 8 January 1610 by Galileo Galilei,[1] and possibly independently by Simon Marius. It is named after a Phoenician noblewoman in Greek mythology, Europa, who was courted by Zeus and became the queen of Crete.[17]

Europa, along with Jupiter's three other largest moons, Io, Ganymede, and Callisto, was discovered by Galileo Galilei in January 1610. The first reported observation of Io was made by Galileo Galilei on 7 January 1610 using a 20x-power, refracting telescope at the University of Padua. However, in that observation, Galileo could not separate Io and Europa due to the low power of his telescope, so the two were recorded as a single point of light. Io and Europa were seen for the first time as separate bodies during Galileo's observations of the Jupiter system the following day, 8 January 1610 (used as the discovery date for Europa by the IAU).[1]

Like all the Galilean satellites, Europa is named after a lover of Zeus, the Greek counterpart of Jupiter, in this case Europa, daughter of the king of Tyre. The naming scheme was suggested by Simon Marius, who apparently discovered the four satellites independently, though Galileo alleged that Marius had plagiarized him. Marius attributed the proposal to Johannes Kepler.[18][19]

The names fell out of favor for a considerable time and were not revived in general use until the mid-20th century.[20] In much of the earlier astronomical literature, Europa is simply referred to by its Roman numeral designation as Jupiter II (a system also introduced by Galileo) or as the "second satellite of Jupiter". In 1892, the discovery of Amalthea, whose orbit lay closer to Jupiter than those of the Galilean moons, pushed Europa to the third position. The Voyager probes discovered three more inner satellites in 1979, so Europa is now considered Jupiter's sixth satellite, though it is still sometimes referred to as Jupiter II.[20]

Orbit and rotation

Animation showing Io's Laplace resonance with Europa and Ganymede

Europa orbits Jupiter in just over three and a half days, with an orbital radius of about 670,900 km. With an eccentricity of only 0.009, the orbit itself is nearly circular, and the orbital inclination relative to the Jovian equatorial plane is small, at 0.470°.[21] Like its fellow Galilean satellites, Europa is tidally locked to Jupiter, with one hemisphere of Europa constantly facing Jupiter. Because of this, there is a sub-Jovian point on Europa's surface, from which Jupiter would appear to hang directly overhead. Europa's prime meridian is the line intersecting this point.[22] Research suggests the tidal locking may not be full, as a non-synchronous rotation has been proposed: Europa spins faster than it orbits, or at least did so in the past. This suggests an asymmetry in internal mass distribution and that a layer of subsurface liquid separates the icy crust from the rocky interior.[5]

The slight eccentricity of Europa's orbit, maintained by the gravitational disturbances from the other Galileans, causes Europa's sub-Jovian point to oscillate about a mean position. As Europa comes slightly nearer to Jupiter, Jupiter's gravitational attraction increases, causing Europa to elongate towards and away from it. As Europa moves slightly away from Jupiter, Jupiter's gravitational force decreases, causing Europa to relax back into a more spherical shape, and creating tides in its ocean. The orbital eccentricity of Europa is continuously pumped by its mean-motion resonance with Io.[23] Thus, the tidal flexing kneads Europa's interior and gives it a source of heat, possibly allowing its ocean to stay liquid while driving subsurface geological processes.[12][23] The ultimate source of this energy is Jupiter's rotation, which is tapped by Io through the tides it raises on Jupiter and is transferred to Europa and Ganymede by the orbital resonance.[23][24]

Scientists analyzing the unique cracks lining the icy face of Europa found evidence showing that this moon of Jupiter likely spun around a tilted axis at some point in time. If this hypothesis is correct, this tilt would be an explanation for many of Europa's features. Europa's immense network of crisscrossing cracks serves as a record of the stresses caused by massive tides in the moon's global ocean. Europa's tilt could influence calculations of how much of the moon's history is recorded in its frozen shell, how much heat is generated by tides in its ocean, and even how long the ocean has been liquid. The moon's ice layer must stretch to accommodate these changes. When there is too much stress, it cracks. A tilt in the moon's axis could suggest that Europa's cracks may be much more recent than previously thought. The reason is that the direction of the spin pole may change by as much as a few degrees per day, completing one precession period over several months. A tilt also could affect the estimates of the age of Europa's ocean. Tidal forces are thought to generate the heat that keeps Europa's ocean liquid, and a tilt in the spin axis might suggest that more heat is generated by tidal forces. This heat might help the ocean to remain liquid longer. Scientists did not specify when the tilt would have occurred and measurements have not been made of the tilt of Europa's axis.[25]

Physical characteristics

Europa (lower left) compared to the Moon (top left) and Earth (right) to scale approximately. (montage)

Europa is slightly smaller than Earth's Moon. At just over 3,100 kilometres (1,900 mi) in diameter, it is the sixth-largest moon and fifteenth largest object in the Solar System. Though by a wide margin the least massive of the Galilean satellites, it is nonetheless more massive than all known moons in the Solar System smaller than itself combined.[26] Its bulk density suggests that it is similar in composition to the terrestrial planets, being primarily composed of silicate rock.[27]

Internal structure

It is believed that Europa has an outer layer of water around 100 km (62 mi) thick; some as frozen-ice upper crust, some as liquid ocean underneath the ice. Recent magnetic field data from the Galileo orbiter showed that Europa has an induced magnetic field through interaction with Jupiter's, which suggests the presence of a subsurface conductive layer.[28] The layer is likely a salty liquid water ocean. Portions of the crust are estimated to have undergone a rotation of nearly 80°, nearly flipping over (see true polar wander), which would be unlikely if the ice were solidly attached to the mantle.[29] Europa probably contains a metallic iron core.[30]

Surface features

Approximate natural color (left) and enhanced color (right) Galileo view of leading hemisphere

Europa is one of the smoothest objects in the Solar System when considering the lack of large scale features such as mountains or craters,[10] however on a smaller scale Europa's equator has been theorised to be covered in 10 metre tall icy spikes called penitentes caused by the effect of direct overhead sunlight on the equator melting vertical cracks.[31] The prominent markings crisscrossing Europa seem to be mainly albedo features, which emphasize low topography. There are few craters on Europa because its surface is tectonically active and young.[32][33] Europa's icy crust gives it an albedo (light reflectivity) of 0.64, one of the highest of all moons.[21][33] This would seem to indicate a young and active surface; based on estimates of the frequency of cometary bombardment that Europa probably endures, the surface is about 20 to 180 million years old.[34] There is currently no full scientific consensus among the sometimes contradictory explanations for the surface features of Europa.[35]

The radiation level at the surface of Europa is equivalent to a dose of about 5400 mSv (540 rem) per day,[36] an amount of radiation that would cause severe illness or death in human beings exposed for a single day.[37]

Lineae

Lineae in an image of Europa in approximately natural color by the Galileo spacecraft
Mosaic of Galileo images showing features indicative of tidal flexing: lineae, lenticulae (domes, pits) and Conamara Chaos.

Europa's most striking surface features are a series of dark streaks crisscrossing the entire globe, called lineae (English: lines). Close examination shows that the edges of Europa's crust on either side of the cracks have moved relative to each other. The larger bands are more than 20 km (12 mi) across, often with dark, diffuse outer edges, regular striations, and a central band of lighter material.[38] The most likely hypothesis states that these lineae may have been produced by a series of eruptions of warm ice as the Europan crust spread open to expose warmer layers beneath.[39] The effect would have been similar to that seen in Earth's oceanic ridges. These various fractures are thought to have been caused in large part by the tidal flexing exerted by Jupiter. Because Europa is tidally locked to Jupiter, and therefore always maintains the same approximate orientation towards Jupiter, the stress patterns should form a distinctive and predictable pattern. However, only the youngest of Europa's fractures conform to the predicted pattern; other fractures appear to occur at increasingly different orientations the older they are. This could be explained if Europa's surface rotates slightly faster than its interior, an effect that is possible due to the subsurface ocean mechanically decoupling Europa's surface from its rocky mantle and the effects of Jupiter's gravity tugging on Europa's outer ice crust.[40] Comparisons of Voyager and Galileo spacecraft photos serve to put an upper limit on this hypothetical slippage. The full revolution of the outer rigid shell relative to the interior of Europa occurs over a minimum of 12,000 years.[41]

Other geological features

Craggy, 250 m high peaks and smooth plates are jumbled together in a close-up of Conamara Chaos.

Other features present on Europa are circular and elliptical lenticulae (Latin for "freckles"). Many are domes, some are pits and some are smooth, dark spots. Others have a jumbled or rough texture. The dome tops look like pieces of the older plains around them, suggesting that the domes formed when the plains were pushed up from below.[42]

One hypothesis states that these lenticulae were formed by diapirs of warm ice rising up through the colder ice of the outer crust, much like magma chambers in Earth's crust.[42] The smooth, dark spots could be formed by meltwater released when the warm ice breaks through the surface. The rough, jumbled lenticulae (called regions of "chaos"; for example, Conamara Chaos) would then be formed from many small fragments of crust embedded in hummocky, dark material, appearing like icebergs in a frozen sea.[43]

An alternative hypothesis suggest that lenticulae are actually small areas of chaos and that the claimed pits, spots and domes are artefacts resulting from over-interpretation of early, low-resolution Galileo images. The implication is that the ice is too thin to support the convective diapir model of feature formation. [44] [45]

In November 2011, a team of researchers from the University of Texas at Austin and elsewhere presented evidence in the journal Nature suggesting that many "chaos terrain" features on Europa sit atop vast lakes of liquid water.[46][47] These lakes would be entirely encased in Europa's icy outer shell and distinct from a liquid ocean thought to exist farther down beneath the ice shell. Full confirmation of the lakes' existence will require a space mission designed to probe the ice shell either physically or indirectly, for example using radar.

Subsurface ocean

Scientists' consensus is that a layer of liquid water exists beneath Europa's surface, and that heat energy from tidal flexing allows the subsurface ocean to remain liquid.[12][48] Europa's surface temperature averages about 110 K (−160 °C; −260 °F) at the equator and only 50 K (−220 °C; −370 °F) at the poles, keeping Europa's icy crust as hard as granite.[7] The first hints of a subsurface ocean came from theoretical considerations of tidal heating (a consequence of Europa's slightly eccentric orbit and orbital resonance with the other Galilean moons). Galileo imaging team members argue for the existence of a subsurface ocean from analysis of Voyager and Galileo images.[48] The most dramatic example is "chaos terrain", a common feature on Europa's surface that some interpret as a region where the subsurface ocean has melted through the icy crust. This interpretation is extremely controversial. Most geologists who have studied Europa favor what is commonly called the "thick ice" model, in which the ocean has rarely, if ever, directly interacted with the present surface.[49] The different models for the estimation of the ice shell thickness give values between a few kilometers and tens of kilometers.[50]
Two possible models of Europa

The best evidence for the thick-ice model is a study of Europa's large craters. The largest impact structures are surrounded by concentric rings and appear to be filled with relatively flat, fresh ice; based on this and on the calculated amount of heat generated by Europan tides, it is predicted that the outer crust of solid ice is approximately 10–30 km (6–19 mi) thick, including a ductile "warm ice" layer, which could mean that the liquid ocean underneath may be about 100 km (60 mi) deep.[34][51] This leads to a volume of Europa's oceans of 3 × 1018 m3, slightly more than two times the volume of Earth's oceans.

The thin-ice model suggests that Europa's ice shell may be only a few kilometers thick. However, most planetary scientists conclude that this model considers only those topmost layers of Europa's crust that behave elastically when affected by Jupiter's tides. One example is flexure analysis, in which Europa's crust is modeled as a plane or sphere weighted and flexed by a heavy load. Models such as this suggest the outer elastic portion of the ice crust could be as thin as 200 metres (660 ft). If the ice shell of Europa is really only a few kilometers thick, this "thin ice" model would mean that regular contact of the liquid interior with the surface could occur through open ridges, causing the formation of areas of chaotic terrain.[50]

In late 2008, it was suggested Jupiter may keep Europa's oceans warm by generating large planetary tidal waves on Europa because of its small but non-zero obliquity. This previously unconsidered kind of tidal force generates so-called Rossby waves that travel quite slowly, at just a few kilometers per day, but can generate significant kinetic energy. For the current axial tilt estimate of 0.1 degree, the resonance from Rossby waves would store 7.3×1017 J of kinetic energy, which is two thousand times larger than that of the flow excited by the dominant tidal forces.[52][53] Dissipation of this energy could be the principal heat source of Europa's ocean.

The Galileo orbiter found that Europa has a weak magnetic moment, which is induced by the varying part of the Jovian magnetic field. The field strength at the magnetic equator (about 120 nT) created by this magnetic moment is about one-sixth the strength of Ganymede's field and six times the value of Callisto's.[54] The existence of the induced moment requires a layer of a highly electrically conductive material in Europa's interior. The most plausible candidate for this role is a large subsurface ocean of liquid saltwater.[30] Spectrographic evidence suggests that the dark, reddish streaks and features on Europa's surface may be rich in salts such as magnesium sulfate, deposited by evaporating water that emerged from within.[55] Sulfuric acid hydrate is another possible explanation for the contaminant observed spectroscopically.[56] In either case, because these materials are colorless or white when pure, some other material must also be present to account for the reddish color, and sulfur compounds are suspected.[57]

Plumes

Water vapor plumes on Jupiter's moon Europa (artist's impression).[58]

Europa may have periodically occurring plumes of water 200 km (120 mi) high, or more than 20 times the height of Mt. Everest.[14][59][60] These plumes appear when Europa is at its farthest point from Jupiter, and are not seen when Europa is at its closest point to Jupiter, in agreement with tidal force modeling predictions.[61] The tidal forces are about 1,000 times stronger than the Moon's effect on Earth. The only other moon in the Solar System exhibiting water vapor plumes is Enceladus.[14] The estimated eruption rate at Europa is about 7000 kg/s[61] compared to about 200 kg/s for the plumes of Enceladus.[62][63]

Atmosphere

Observations with the Goddard High Resolution Spectrograph of the Hubble Space Telescope, first described in 1995, revealed that Europa has a thin atmosphere composed mostly of molecular oxygen (O2).[64][65] The surface pressure of Europa's atmosphere is 0.1 μPa, or 10−12 times that of the Earth.[8] In 1997, the Galileo spacecraft confirmed the presence of a tenuous ionosphere (an upper-atmospheric layer of charged particles) around Europa created by solar radiation and energetic particles from Jupiter's magnetosphere,[66][67] providing evidence of an atmosphere.
Magnetic field around Europa. The red line shows a trajectory of the Galileo spacecraft during a typical flyby (E4 or E14).

Unlike the oxygen in Earth's atmosphere, Europa's is not of biological origin. The surface-bounded atmosphere forms through radiolysis, the dissociation of molecules through radiation.[68] Solar ultraviolet radiation and charged particles (ions and electrons) from the Jovian magnetospheric environment collide with Europa's icy surface, splitting water into oxygen and hydrogen constituents. These chemical components are then adsorbed and "sputtered" into the atmosphere. The same radiation also creates collisional ejections of these products from the surface, and the balance of these two processes forms an atmosphere.[69] Molecular oxygen is the densest component of the atmosphere because it has a long lifetime; after returning to the surface, it does not stick (freeze) like a water or hydrogen peroxide molecule but rather desorbs from the surface and starts another ballistic arc. Molecular hydrogen never reaches the surface, as it is light enough to escape Europa's surface gravity.[70][71]

Observations of the surface have revealed that some of the molecular oxygen produced by radiolysis is not ejected from the surface. Because the surface may interact with the subsurface ocean (considering the geological discussion above), this molecular oxygen may make its way to the ocean, where it could aid in biological processes.[72] One estimate suggests that, given the turnover rate inferred from the apparent ~0.5 Gyr maximum age of Europa's surface ice, subduction of radiolytically generated oxidizing species might well lead to oceanic free oxygen concentrations that are comparable to those in terrestrial deep oceans.[73]

The molecular hydrogen that escapes Europa's gravity, along with atomic and molecular oxygen, forms a torus (ring) of gas in the vicinity of Europa's orbit around Jupiter. This "neutral cloud" has been detected by both the Cassini and Galileo spacecraft, and has a greater content (number of atoms and molecules) than the neutral cloud surrounding Jupiter's inner moon Io. Models predict that almost every atom or molecule in Europa's torus is eventually ionized, thus providing a source to Jupiter's magnetospheric plasma. [74]

Exploration

Europa in 1979 by Voyager 1

Exploration of Europa began in the 1973 with the Jupiter flybys of Pioneer 10 and 11 in 1973 and 1974 respectively. The first closeup photos were of low resolution compared to later missions.

The two Voyager probes traveled through the Jovian system in 1979 providing more detailed images of Europa's icy surface. The images caused many scientists to speculate about the possibility of a liquid ocean underneath.

Starting in 1995, Galileo (probe) began a Jupiter orbiting mission that lasted for eight years, until 2003, and provided the most detailed examination of the Galilean moons to date. It included the Galileo Europa Mission and Galileo Millennium Mission, with numerous close flybys of Europa.[75]

New Horizons imaged Europa in 2007, as it flew by the Jovian system while on its way to Pluto.
Jupiter and Europa as seen in 2007 by the New Horizons spacecraft

Future missions

Conjectures on extraterrestrial life have ensured a high profile for Europa and have led to steady lobbying for future missions.[76][77] The aims of these missions have ranged from examining Europa's chemical composition to searching for extraterrestrial life in its hypothesized subsurface oceans.[78][79] Robotic missions to Europa need to endure the high radiation environment around itself and Jupiter.[77] Europa receives about 540 rem of radiation per day.[80]

In 2011, a Europa mission was recommended by the U.S. Planetary Science Decadal Survey.[81] In response, NASA commissioned Europa lander concept studies in 2011, along with concepts for a Europa flyby (Europa Clipper), and a Europa orbiter.[82][83] The orbiter element option concentrates on the "ocean" science, while the multiple-flyby element (Clipper) concentrates on the chemistry and energy science. On 13 January 2014, the House Appropriations Committee announced a new bipartisan bill that includes $80 million funding to continue the Europa mission concept studies.[84][85]
  • Europa Clipper — In July 2013 an updated concept for a flyby Europa mission called Europa Clipper was presented by the Jet Propulsion Laboratory (JPL) and the Applied Physics Laboratory (APL).[86] The aim of Europa Clipper is to explore Europa in order to investigate its habitability, and to aid selecting sites for a future lander. The Europa Clipper would not orbit Europa, but instead orbit Jupiter and conduct 45 low-altitude flybys of Europa during its envisioned mission. The probe would carry an ice penetrating radar, short wave infra red spectrometer, topographical imager, and an ion and neutral mass spectrometer.
  • Europa Orbiter — Its objective would be to characterize the extent of the ocean and its relation to the deeper interior. Instrument payload could include a radio subsystem, laser altimeter, magnetometer, Langmuir probe, and a mapping camera.[87][88]
  • Europa Lander — It would investigate the moon's habitability and assess its astrobiological potential by confirming the existence and determining the characteristics of water within and below Europa's icy shell.[89]
In 2012, Jupiter Icy Moon Explorer was selected by the European Space Agency (ESA) as a planned mission.[15][90] That mission includes some flybys of Europa, but is more focused on Ganymede.

Old proposals

Europa Lander Mission concept circa 2005 (NASA).

In the early 2000s, Jupiter Europa Orbiter led by NASA and the Jupiter Ganymede Orbiter led by the ESA were proposed together as an Outer Planet Flagship Mission to Jupiter's icy moons, and called Europa Jupiter System Mission with a planned launch in 2020.[91] In 2009 it was given priority over Titan Saturn System Mission.[92] At that time, there was competition from other proposals.[93] Japan proposed Jupiter Magnetospheric Orbiter. Russia expressed interest in sending Europa Lander as part of the international effort.[94] The overall plan collapsed in the early 2010s.[90]

Jovian Europa Orbiter was an ESA Cosmic Vision concept study from 2007. Another concept was Ice Clipper,[95] which would have used an impactor similar to the Deep Impact mission—it would make a controlled crash into the surface of Europa, generating a plume of debris that would then be collected by a small spacecraft flying through the plume.[96][97]
Artist's concept of the cryobot (a thermal drill, seen upper left) and its deployed 'hydrobot' submersible

Jupiter Icy Moons Orbiter (JIMO) was a partially developed fission-powered spacecraft with ion thrusters that was cancelled in 2006.[77][98] It was part of Project Prometheus.[98] The Europa Lander Mission proposed a small nuclear-powered Europa lander for JIMO.[99] It would travel with the orbiter, which would also function as a communication relay to Earth.[99]

The Europa Orbiter received a go-ahead in 1999 but was canceled in 2002. This orbiter featured a special radar that would allow it to scan below the surface.[10]

More ambitious ideas have been put forward including an impactor in combination with a thermal drill to search for biosignatures that might be frozen in the shallow subsurface.[100][101]

Another proposal put forward in 2001 calls for a large nuclear-powered "melt probe" (cryobot) that would melt through the ice until it reached an ocean below.[77][102] Once it reached the water, it would deploy an autonomous underwater vehicle (hydrobot) that would gather information and send it back to Earth.[103] Both the cryobot and the hydrobot would have to undergo some form of extreme sterilization to prevent detection of Earth organisms instead of native life and to prevent contamination of the subsurface ocean.[104] This proposed mission has not yet reached a serious planning stage.[105]

Potential for extraterrestrial life

A black smoker in the Atlantic Ocean. Driven by geothermal energy, this and other types of hydrothermal vents create chemical disequilibria that can provide energy sources for life.

Europa has emerged as one of the top locations in the Solar System in terms of potential habitability and the possibility of hosting extraterrestrial life.[106] Life could exist in its under-ice ocean, perhaps subsisting in an environment similar to Earth's deep-ocean hydrothermal vents. Life in such an ocean could possibly be similar to microbial life on Earth in the deep ocean.[78][107] So far, there is no evidence that life exists on Europa, but the likely presence of liquid water has spurred calls to send a probe there.[108]

Until the 1970s, life, at least as the concept is generally understood, was believed to be entirely dependent on energy from the Sun. Plants on Earth's surface capture energy from sunlight to photosynthesize sugars from carbon dioxide and water, releasing oxygen in the process, and are then consumed by oxygen-respiring animals, passing their energy up the food chain. Even life in the deep ocean, far below the reach of sunlight, was believed to obtain its nourishment either from the organic detritus raining down from the surface, or by eating animals that in turn depend on that stream of nutrients.[109] An environment's ability to support life was thus thought to depend on its access to sunlight.
This giant tube worm colony dwells beside a Pacific Ocean vent. Although the worms require oxygen (hence their blood-red color), methanogens and some other microbes in the vent communities do not.

However, in 1977, during an exploratory dive to the Galapagos Rift in the deep-sea exploration submersible Alvin, scientists discovered colonies of giant tube worms, clams, crustaceans, mussels, and other assorted creatures clustered around undersea volcanic features known as black smokers.[109] These creatures thrive despite having no access to sunlight, and it was soon discovered that they comprise an entirely independent food chain. Instead of plants, the basis for this food chain was a form of bacterium that derived its energy from oxidization of reactive chemicals, such as hydrogen or hydrogen sulfide, that bubbled up from Earth's interior. This chemosynthesis revolutionized the study of biology by revealing that life need not be sun-dependent; it only requires water and an energy gradient in order to exist. It opened up a new avenue in astrobiology by massively expanding the number of possible extraterrestrial habitats.

Although the tube worms and other multicellular eukaryotic organisms around these hydrothermal vents respire oxygen and thus are indirectly dependent on photosynthesis, anaerobic chemosynthetic bacteria and archaea that inhabit these ecosystems provide a possible model for life in Europa's ocean.[73] The energy provided by tidal flexing drives active geological processes within Europa's interior, just as they do to a far more obvious degree on its sister moon Io. Although Europa, like the Earth, may possess an internal energy source from radioactive decay, the energy generated by tidal flexing would be several orders of magnitude greater than any radiological source.[110] However, such an energy source could never support an ecosystem as large and diverse as the photosynthesis-based ecosystem on Earth's surface.[111] Life on Europa could exist clustered around hydrothermal vents on the ocean floor, or below the ocean floor, where endoliths are known to inhabit on Earth. Alternatively, it could exist clinging to the lower surface of Europa's ice layer, much like algae and bacteria in Earth's polar regions, or float freely in Europa's ocean.[112] However, if Europa's ocean were too cold, biological processes similar to those known on Earth could not take place. Similarly, if it were too salty, only extreme halophiles could survive in its environment.[112] In September 2009, planetary scientist Richard Greenberg calculated that cosmic rays impacting on Europa's surface convert some water ice into free oxygen (O2), which could then be absorbed into the ocean below as water wells up to fill cracks. Via this process, Greenberg estimates that Europa's ocean could eventually achieve an oxygen concentration greater than that of Earth's oceans within just a few million years. This would enable Europa to support not merely anaerobic microbial life but potentially larger, aerobic organisms such as fish.[113]
Water vapor plume on Europa (artist concept) (December 12, 2013).[14]
For comparison, the eruption of a natural repeating water geyser on Earth

In 2006, Robert T. Pappalardo, an assistant professor in the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder said,
We've spent quite a bit of time and effort trying to understand if Mars was once a habitable environment. Europa today, probably, is a habitable environment. We need to confirm this ... but Europa, potentially, has all the ingredients for life ... and not just four billion years ago ... but today.[76]
In November 2011, a team of researchers presented evidence in the journal Nature suggesting the existence of vast lakes of liquid water entirely encased in Europa's icy outer shell and distinct from a liquid ocean thought to exist farther down beneath the ice shell.[46][47] If confirmed, the lakes could be yet another potential habitat for life.

A paper published in March 2013 suggests that hydrogen peroxide is abundant across much of the surface of Jupiter's moon Europa.[114] The authors argue that if the peroxide on the surface of Europa mixes into the ocean below, it could be an important energy supply for simple forms of life, if life were to exist there. The scientists think hydrogen peroxide is an important factor for the habitability of the global liquid water ocean under Europa's icy crust because hydrogen peroxide decays to oxygen when mixed into liquid water.

On December 11, 2013, NASA reported the detection of "clay-like minerals" (specifically, phyllosilicates), often associated with organic materials, on the icy crust of Europa.[13] The presence of the minerals may have been the result of a collision with an asteroid or comet according to the scientists.[13]

Life on Earth could have been blasted into space by asteroid collisions and arrived on the moons of Jupiter in a process called lithopanspermia.[115]

Ring of Fire

Ring of Fire

From Wikipedia, the free encyclopedia

The Pacific Ring of Fire
Tectonic plates of the world.

The Ring of Fire is an area where a large number of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a 40,000 km (25,000 mi) horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements. It has 452 volcanoes and is home to over 75% of the world's active and dormant volcanoes.[1] It is sometimes called the circum-Pacific belt or the circum-Pacific seismic belt.

About 90%[2] of the world's earthquakes and 81%[3] of the world's largest earthquakes occur along the Ring of Fire. The next most seismically active region (5–6% of earthquakes and 17% of the world's largest earthquakes) is the Alpide belt, which extends from Java to Sumatra through the Himalayas, the Mediterranean, and out into the Atlantic. The Mid-Atlantic Ridge is the third most prominent earthquake belt.[4][5]

The Ring of Fire is a direct result of plate tectonics and the movement and collisions of lithospheric plates.[6] The eastern section of the ring is the result of the Nazca Plate and the Cocos Plate being subducted beneath the westward moving South American Plate. The Cocos Plate is being subducted beneath the Caribbean Plate, in Central America. A portion of the Pacific Plate along with the small Juan de Fuca Plate are being subducted beneath the North American Plate. Along the northern portion, the northwestward-moving Pacific plate is being subducted beneath the Aleutian Islands arc. Farther west, the Pacific plate is being subducted along the Kamchatka Peninsula arcs on south past Japan. The southern portion is more complex, with a number of smaller tectonic plates in collision with the Pacific plate from the Mariana Islands, the Philippines, Bougainville, Tonga, and New Zealand; this portion excludes Australia, since it lies in the center of its tectonic plate. Indonesia lies between the Ring of Fire along the northeastern islands adjacent to and including New Guinea and the Alpide belt along the south and west from Sumatra, Java, Bali, Flores, and Timor. The famous and very active San Andreas Fault zone of California is a transform fault which offsets a portion of the East Pacific Rise under southwestern United States and Mexico. The motion of the fault generates numerous small earthquakes, at multiple times a day, most of which are too small to be felt.[7][8] The active Queen Charlotte Fault on the west coast of the Haida Gwaii, British Columbia, Canada, has generated three large earthquakes during the 20th century: a magnitude 7 event in 1929; a magnitude 8.1 in 1949 (Canada's largest recorded earthquake); and a magnitude 7.4 in 1970.[9]

Andes

Chile

Earthquake activity in Chile is related to subduction of the Nazca Plate to the east. Chile notably holds the record for the largest earthquake ever recorded, the 1960 Valdivia earthquake. Villarrica, one of Chile's most active volcanoes, rises above Villarrica Lake and the town of Villarrica. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km wide caldera formed during the late Pleistocene, >0.9 million years ago.
Llaima's 2008 eruption

A 2-km-wide postglacial caldera is located at the base of the presently active, dominantly basaltic-to-andesitic cone at the NW margin of the Pleistocene caldera. About 25 scoria cones dot Villarica's flanks. Plinian eruptions and pyroclastic flows have been produced during the Holocene from this dominantly basaltic volcano, but historical eruptions have consisted of largely mild-to-moderate explosive activity with occasional lava effusion. Lahars from the glacier-covered volcanos have damaged towns on its flanks.

Chile has experienced numerous volcanic eruptions from 60 volcanoes, including Llaima Volcano and the Chaitén Volcano. More recently, an 8.8-magnitude earthquake struck central Chile on February 27, 2010, the Puyehue-Cordón Caulle volcano erupted in 2011 and an 8.2-magnitude earthquake struck northern Chile on April 1, 2014. The mainshock was preceded by a number of moderate to large shocks and was followed by a large number of moderate to very large aftershocks, including a M7.6 event on 3 April.[10]

Bolivia

The country of Bolivia hosts numerous active and extinct volcanoes across its territory. The active volcanoes are located in western Bolivia where they make up the Cordillera Occidental, the western limit of the Altiplano plateau. Many of the active volcanoes are international mountains shared with Chile. All Cenozoic volcanoes of Bolivia are part of the Central Volcanic Zone (CVZ) of the Andean Volcanic Belt that results due to processes involved in the subduction of the Nazca Plate under the South American Plate. The Central Volcanic Zone is a major upper Cenozoic volcanic province.[11] Apart from Andean volcanoes, the geology of Bolivia host the remants of ancient volcanoes around the Precambrian Guaporé Shield in the eastern part of the country.

Central America

Costa Rica

A powerful, magnitude-7.6 earthquake shook Costa Rica and a wide swath of Central America at 8:42 a.m. (10:42 a.m. EDT; 1442 GMT) on 09/05/2012.

North American Cordillera

Mexico


Volcanoes of Mexico are related to subduction of the Cocos and Rivera plates to the east, subduction which has produced large explosive eruptions. Most active volcanoes in Mexico occur in the Trans-Mexican Volcanic Belt, which extends 900 kilometres (559 mi) from west to east across central-southern Mexico. A few other active volcanoes in northern Mexico are related to extensional tectonics of the Basin and Range Province, which splits the Baja California peninsula from the mainland.[12] Popocatépetl, lying in the eastern half of the Trans-Mexican Volcanic Belt, is the second highest peak in Mexico after the Pico de Orizaba. It is one of the most active volcanoes in Mexico, having had more than 20 major eruptions since the arrival of the Spanish in 1519. The 1982 eruption of El Chichón, which killed about 2,000 people who lived near the volcano, created a 1 kilometre (1 mi) wide caldera that filled with an acidic crater lake. Prior to 2000, this relatively unknown volcano was heavily forested and of no greater height than adjacent non-volcanic peaks.[12]

United States

Area of the Cascadia subduction zone, including the Cascade Volcanic Arc (red triangles)

In the western United States lies the Cascade Volcanic Arc. It includes nearly 20 major volcanoes, among a total of over 4,000 separate volcanic vents including numerous stratovolcanoes, shield volcanoes, lava domes, and cinder cones, along with a few isolated examples of rarer volcanic forms such as tuyas. Volcanism in the arc began about 37 million years ago, however, most of the present-day Cascade volcanoes are less than 2,000,000 years old, and the highest peaks are less than 100,000 years old. The arc formed by the subduction of the Gorda and Juan de Fuca plates at the Cascadia subduction zone. This is a 680 mi (1,090 km) long fault, running 50 mi (80 km) off the west-coast of the Pacific Northwest from northern California to Vancouver Island, British Columbia. The plates move at a relative rate of over 0.4 inches (10 mm) per year at a somewhat oblique angle to the subduction zone.

Because of the very large fault area, the Cascadia subduction zone can produce very large earthquakes, magnitude 9.0 or greater, if rupture occurred over its whole area. When the "locked" zone stores energy for an earthquake, the "transition" zone, although somewhat plastic, can rupture. Thermal and deformation studies indicate that the locked zone is fully locked for 60 kilometers (about 40 miles) down-dip from the deformation front. Further down-dip, there is a transition from fully locked to aseismic sliding.
American Cascade Range volcano eruptions in the last 4000 years

Unlike most subduction zones worldwide, there is no oceanic trench present along the continental margin in Cascadia. Instead, terranes and the accretionary wedge have been uplifted to form a series of coast ranges and exotic mountains. A high rate of sedimentation from the outflow of the three major rivers (Fraser River, Columbia River, and Klamath River) which cross the Cascade Range contributes to further obscuring the presence of a trench. However, in common with most other subduction zones, the outer margin is slowly being compressed, similar to a giant spring. When the stored energy is suddenly released by slippage across the fault at irregular intervals, the Cascadia subduction zone can create very large earthquakes such as the magnitude 9 Cascadia earthquake of 1700. Geological evidence indicates that great earthquakes may have occurred at least seven times in the last 3,500 years, suggesting a return time of 400 to 600 years. There is also evidence of accompanying tsunamis with every earthquake, as the prime reason they know of these earthquakes is through "scars" the tsunami left on the coast, and through Japanese records (tsunami waves can travel across the Pacific).

The 1980 eruption of Mount St. Helens was the most significant to occur in the contiguous 48 U.S. states in recorded history (VEI = 5, 0.3 cu mi, 1.2 km3 of material erupted), exceeding the destructive power and volume of material released by the 1915 eruption of California's Lassen Peak. The eruption was preceded by a two-month series of earthquakes and steam-venting episodes caused by an injection of magma at shallow depth below the mountain that created a huge bulge and a fracture system on Mount St. Helens' north slope. An earthquake at 8:32 a.m. on May 18, 1980, caused the entire weakened north face to slide away, suddenly exposing the partly molten, gas- and steam-rich rock in the volcano to lower pressure. The rock responded by exploding into a very hot mix of pulverized lava and older rock that sped toward Spirit Lake so fast that it quickly passed the avalanching north face.

Alaska is known for its seismic and volcanic activity, holding the record for the second largest earthquake in the world, the Good Friday Earthquake, and having more than 50 volcanoes which have erupted since about 1760.[13] Volcanoes can be found not only in the mainland but also in the Aleutian Islands.

The most recent activity in the American portion of the Ring of Fire occurred in early 2009 when Mount Redoubt in Alaska became active and finally erupted late in the evening of March 22. The eruption ended in May 2009.

Canada

Map of young volcanoes in Western Canada

British Columbia and Yukon are home to a vast region of volcanoes and volcanic activity in the Pacific Ring of Fire.[14] Several mountains that many British Columbians look at every day are dormant volcanoes. Most of them erupted during the Pleistocene and Holocene. Although none of Canada's volcanoes are currently erupting, several volcanoes, volcanic fields and volcanic centers are considered potentially active.[15] There are hot springs at some volcanoes, while 10 volcanoes in British Columbia appear related to seismic activity since 1975, including: the Silverthrone Caldera, Mount Meager, Wells Gray-Clearwater volcanic field, Mount Garibaldi, Mount Cayley, Castle Rock, The Volcano, Mount Edziza, Hoodoo Mountain, Crow Lagoon and Nazko Cone.[16] The volcanoes are grouped into five volcanic belts with different tectonic settings.

The Northern Cordilleran Volcanic Province (sometimes known as the Stikine Volcanic Belt) is the most active volcanic region in Canada. It formed due to extensional cracking, faulting and rifting of the North American Plate, as the Pacific Plate grinds and slides past the Queen Charlotte Fault, unlike subduction that produces the volcanoes in Japan, Philippines and Indonesia. The region has Canada's largest volcanoes,[14] much larger than the minor stratovolcanoes found in the Canadian portion of the Cascade Volcanic Arc.[14] Several eruptions are known to have occurred within the last 400 years. Mount Edziza is a huge volcanic complex that erupted several times in the past several thousand years and has formed several cinder cones and lava flows. The complex comprises the Mount Edziza Plateau, a large volcanic plateau (65 kilometers long and 20 kilometers wide) made of predominantly basaltic lava flows with four large stratovolcanoes built on top of the plateau. The associated lava domes and satellite cones were constructed over the past 7.5 million years during five magmatic cycles beginning with eruption of alkali basalts and ending with felsic and basaltic eruptions as late as 1,340 years ago. The blocky lava flows still maintain their original forms. Hoodoo Mountain is a tuya in northwestern British Columbia, which has had several periods of subglacial eruptions. The oldest eruptions occurred about 100,000 years ago and the most recent about 7000 years ago. Hoodoo Mountain is also considered active and could erupt in the future. The nearby Tseax Cone and The Volcano produced some of Canada's youngest lava flows, that are about 150 years old.
Mount Edziza, a large shield volcano in northwestern British Columbia

Canada's worst known geophysical disaster came from the Tseax Cone during the 18th century at the southernmost end of the volcanic belt. The eruption produced a 22.5 km long lava flow, destroying the Nisga'a villages and the death of at least 2000 Nisga'a people by volcanic gases and poisonous smoke. The Nass River valley was inundated by the lava flows and contains abundant tree molds and lava tubes. The event happened at the same time with the arrival of the first European explorers to penetrate the uncharted coastal waters of northern British Columbia. Today, the basaltic lava deposits are a draw to tourists and are part of the Nisga'a Memorial Lava Beds Provincial Park.

The Garibaldi Volcanic Belt in southwestern British Columbia is the northern extension of the Cascade Volcanic Arc in the United States (which includes Mount Baker and Mount St. Helens) and contains the most explosive young volcanoes in Canada.[17] It formed as a result of subduction of the Juan de Fuca Plate (a remnant of the much larger Farallon Plate) under the North American Plate along the Cascadia subduction zone.[17] The Garibaldi Volcanic Belt includes the Bridge River Cones, Mount Cayley, Mount Fee, Mount Garibaldi, Mount Price, Mount Meager, the Squamish Volcanic Field and much more smaller volcanoes. The eruption styles in the belt range from effusive to explosive, with compositions from basalt to rhyolite. Morphologically, centers include calderas, cinder cones, stratovolcanoes and small isolated lava masses. Due to repeated continental and alpine glaciations, many of the volcanic deposits in the belt reflect complex interactions between magma composition, topography, and changing ice configurations. The most recent major catastrophic eruption in the Garibaldi Volcanic Belt was the 2350 BP eruption of Mount Meager. It was similar to the 1980 eruption of Mount St. Helens,[17] sending an ash column approximately 20 km high into the stratosphere.[18]
The Mount Meager volcanic complex as seen from the east near Pemberton, BC. Summits left to right are Capricorn Mountain, Mount Meager, and Plinth Peak

The Chilcotin Group is a north-south range of volcanoes in southern British Columbia running parallel to the Garibaldi Volcanic Belt. The majority of the eruptions in this belt happened either 6–10 million years ago (Miocene) or 2–3 million years ago (Pliocene), although there have been some slightly more recent eruptions (in the Pleistocene).[19] It is thought to have formed as a result of back-arc extension behind the Cascadia subduction zone.[19] Volcanoes in this belt include Mount Noel, the Clisbako Caldera Complex, Lightning Peak, Black Dome Mountain and many lava flows.

The Anahim Volcanic Belt is a line of volcanoes stretching from just north of Vancouver Island to near Quesnel, British Columbia, Canada. These volcanoes were formed 8 to 1 million years ago, and the Nazko Cone last erupted only 7,200 years ago.[20] The volcanoes generally get younger as one moves from the coast to the interior. These volcanoes are thought to have formed as a result of the North American Plate sliding westward over a small hotspot, called the Anahim hotspot.[20] The hotspot is considered similar to the one feeding the Hawaiian Islands.[20] The belt is defined by three large shield volcanoes (Rainbow, Ilgachuz and the Itcha Ranges) and 37 Quaternary basalt centers.

Eruptions of basaltic to rhyolitic volcanoes and hypabyssal rocks of the Alert Bay Volcanic Belt in northern Vancouver Island are probably linked with the subducted margin flanked by the Explorer and Juan de Fuca plates at the Cascadia subduction zone. It appears to have been active during the Pliocene and Pleistocene time. However, no Holocene eruptions are known, and volcanic activity in the belt has likely ceased.

Russia

Avachinsky, an active volcano on the Kamchatka Peninsula.

The Kamchatka Peninsula in the Russian Far East is one of the most various and active volcanic areas in the world,[21] with an area of 472,300 km². It lies between the Pacific Ocean to the east and the Okhotsk Sea to the west. Immediately offshore along the Pacific coast of the peninsula runs the 10,500 meter deep Kuril-Kamchatka Trench. This is where rapid subduction of the Pacific Plate fuels the intense volcanism. Almost all types of volcanic activity are present, from stratovolcanoes and shield volcanoes to Hawaiian-style fissure eruptions.[21]

There are over 30 active volcanoes and hundreds of dormant and extinct volcanoes in two major volcanic belts. The most recent activity takes place in the eastern belt,[21] starting in the north at the Shiveluch volcanic complex, which lies at the junction of the Aleutian and Kamchatka volcanic arcs. Just to the south is the famous Klyuchi volcanic group, comprising the twin volcanic cones of Kliuchevskoi and Kamen, the huge volcanic complexes of Tolbachik and Ushkovsky, and a number of other large stratovolcanoes. The only active volcano in the central belt is found west of here, the huge remote Ichinsky. Farther south, the eastern belt continues to the southern slope of Kamchatka, topped by loads of stratovolcanoes.

Japan

Approximately ten percent of the world's active volcanoes are found in Japan, which lies in a zone of extreme crustal instability. They are formed by subduction of the Pacific Plate and the Philippine Sea Plate. As many as 1,500 earthquakes are recorded yearly, and magnitudes of four to six on the Richter scale are not uncommon. Minor tremors occur almost daily in one part of the country or another, causing some slight shaking of buildings. Major earthquakes occur infrequently; the most famous in the twentieth century were: the Great Kantō earthquake of 1923, in which 130,000 people died; and the Great Hanshin earthquake of 17 January 1995, in which 6,434 people died. On March 11, 2011 a magnitude 9.0 Earthquake hit Japan, the country's biggest ever and the fifth largest on record, according to US Geological Survey data.[22] Undersea earthquakes also expose the Japanese coastline to danger from tsunamis.
Mount Fuji at sunrise from Lake Kawaguchi

Mount Bandai, one of Japan's most noted volcanoes, rises above the north shore of Lake Inawashiro. Mount Bandai is formed of several overlapping stratovolcanoes, the largest of which is O-Bandai forming a complex volcano. O-Bandai volcano was constructed within a horseshoe-shaped caldera that formed about 40,000 years when an earlier volcano collapsed, forming the Okinajima debris avalanche, which traveled to the southwest and was accompanied by a plinian eruption. Four major phreatic eruptions have occurred during the past 5,000 years, two of them in historical time, in 806 and 1888. Seen from the south, Bandai presents a conical profile, but much of the north side of the volcano is missing as a result of the collapse of Ko-Bandai volcano during the 1888 eruption, in which a debris avalanche buried several villages and formed several large lakes.

Nearly a century ago, the north flank of Mount Bandai collapsed during an eruption quite similar to the May 18, 1980 eruption of Mount St. Helens. After a week of seismic activity, a large earthquake on July 15, 1888, was followed by a tremendous noise and a large explosion. Eyewitnesses heard about 15 to 20 additional explosions and observed that the last one was projected almost horizontally to the north.

Mount Fuji is Japan's highest and most noted volcano. The modern postglacial stratovolcano is constructed above a group of overlapping volcanoes, remnants of which form irregularities on Fuji's profile. Growth of the younger Mount Fuji began with a period of voluminous lava flows from 11,000 to 8,000 years ago, accounting for four-fifths of the volume of the younger Mount Fuji. Minor explosive eruptions dominated activity from 8,000 to 4,500 years ago, with another period of major lava flows occurring from 4,500 to 3,000 years ago. Subsequently, intermittent major explosive eruptions occurred, with subordinate lava flows and small pyroclastic flows. Summit eruptions dominated from 3,000 to 2,000 years ago, after which flank vents were active. The extensive basaltic lava flows from the summit and some of the more than 100 flank cones and vents blocked drainages against the Tertiary Misaka Mountains on the north side of the volcano, forming the Fuji Five Lakes. The last eruption of this dominantly basaltic volcano in 1707 ejected andesitic pumice and formed a large new crater on the east flank. Scientists are saying that there may be some minor volcanic activity in the next few years.

Philippines

Map showing major volcanoes of the Philippines.

The 1991 eruption of Mount Pinatubo is the world's second largest terrestrial eruption of the 20th century. Successful predictions of the onset of the climactic eruption led to the evacuation of tens of thousands of people from the surrounding areas, saving many lives, but as the surrounding areas were severely damaged by pyroclastic flows, ash deposits, and later, lahars caused by rainwater remobilising earlier volcanic deposits, thousands of houses were destroyed.
Mayon Volcano overlooks a pastoral scene approximately five months before the volcano's violent eruption in September 1984.

Mayon Volcano is the Philippines' most active volcano. The volcano has steep upper slopes that average 35–40 degrees and is capped by a small summit crater. The historical eruptions of this basaltic-andesitic volcano dates back to 1616 and ranges from Strombolian to basaltic Plinian eruptions. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas.

Taal Volcano has had 33 recorded eruptions since 1572. A devastating eruption occurred in 1911, which claimed more than a thousand lives. The deposits of that eruption consist of a yellowish, fairly decomposed (non-juvenile) tephra with a high sulfur content. The most recent period of activity lasted from 1965 to 1977, and was characterized by the interaction of magma with the lake water, which produced violent phreatic and phreatomagmatic eruptions. Although the volcano has been dormant since 1977, it has shown signs of unrest since 1991, with strong seismic activity and ground fracturing events, as well as the formation of small mud geysers on parts of the island.

Kanlaon Volcano is the most active volcano in central Philippines and has erupted 25 times since 1866. Eruptions are typically phreatic explosions of small-to-moderate size that produce minor ashfalls near the volcano. On August 10, 1996, Kanlaon erupted without warning, killing British student Julian Green and Filipinos Noel Tragico and Neil Perez, who were among 24 mountainclimbers who were trapped near the summit.

Indonesia

Mount Merapi in Central Java.
A chart with the heading "Major Volcanoes of Indonesia (with eruptions since 1900 A.D.)". Depicted below the heading is an overhead view of a cluster of islands.
Major volcanoes in Indonesia

The volcanoes in Indonesia are among the most active of the Pacific Ring of Fire. They are formed due to subduction zones of three main active tectonic plates namely the Eurasian Plate, Pacific Plate, and the Indo-Australian Plate.[23] Some of the volcanoes are notable for their eruptions, for instance, Krakatau for its global effects in 1883, Lake Toba for its supervolcanic eruption estimated to have occurred 74,000 BP, which was responsible for six years of volcanic winter, and Mount Tambora for the most violent eruption in recorded history in 1815. The eruption of Mount Tambora in 1815 caused widespread harvest failures in Northern Europe, the Northeastern United States, and eastern Canada in 1816, which was known as the Year Without a Summer.

The most active volcanoes are Kelud and Mount Merapi on Java island, which have been responsible for thousands of deaths in the region. Since AD 1000, Kelud has erupted more than 30 times, of which the largest eruption was at scale 5 on the Volcanic Explosivity Index, while Merapi has erupted more than 80 times. The International Association of Volcanology and Chemistry of the Earth's Interior has named Merapi as a Decade Volcano since 1995 because of its high volcanic activity.

New Zealand

Major volcanoes of New Zealand
View of Mount Taranaki from Stratford.

New Zealand contains the world's strongest concentration of youthful rhyolitic volcanoes, and voluminous sheets blanket much of the North Island. The earliest historically-dated eruption was at Whakaari/White Island in 1826,[24] followed in 1886, by the country's largest historical eruption at Mount Tarawera. Much of the region north of New Zealand's North Island is made up of seamounts and small islands, including 16 submarine volcanoes. In the last 1.6 million years, most of New Zealand's volcanism is from the Taupo Volcanic Zone.

Mount Ruapehu at the southern end of the Taupo Volcanic Zone, is one of the most active volcanoes.[25] It began erupting at least 250,000 years ago. In recorded history, major eruptions have been about 50 years apart,[25] in 1895, 1945 and 1995–1996. Minor eruptions are frequent, with at least 60 since 1945. Some of the minor eruptions in the 1970s generated small ash falls and lahars (mudflows) that damaged skifields.[26] Between major eruptions, a warm acidic crater lake forms, fed by melting snow. Major eruptions may completely expel the lake water. Where a major eruption has deposited a tephra dam across the lake's outlet, the dam may collapse after the lake has refilled and risen above the level of its normal outlet, the outrush of water causing a large lahar. The most notable lahar caused the Tangiwai disaster in December 1953, when 151 people aboard a Wellington to Auckland express train were killed after the lahar destroyed the Tangiwai rail bridge just moments before the train was due. In 2000, the ERLAWS system was installed on the mountain to detect such a collapse and alert the relevant authorities.

The Auckland volcanic field on the North Island of New Zealand, has produced a diverse array of explosive craters, scoria cones, and lava flows. Currently dormant, the field is likely to erupt again with the next "hundreds to thousands of years", a very short timeframe in geologic terms.[27] The field contains at least 40 volcanoes, most recently active about 600 years ago at Rangitoto Island, erupting 2.3 cubic kilometers of lava.

Antarctica


The Pacific Ring of Fire is completed in the south by the continent of Antarctica,[28] which includes many large volcanoes. The makeup and structure of the volcanoes in Antarctica change largely from the other places around the ring. In contrast, the Antarctic Plate is almost completely surrounded by extensional zones, with several mid-ocean ridges which encircle it, and there is only a small subduction zone at the tip of the Antarctic Peninsula, reaching eastward to the remote South Sandwich Islands.[28] The most well known volcano in Antarctica is Mount Erebus, which is also the world's southernmost active volcano.[28] In many respects the geology of the Antarctic Peninsula is an extension of the Andes, hence the name sometimes used by geologists: "Antarctandes". At the opposite side of the continent, the volcanoes of Victoria Land may be seen as the 'other end' of the Antarctandes, thus completing the Pacific Ring of Fire and continuing up through the Balleny Islands to New Zealand.

The volcanoes of the Victoria Land area are the most well known in Antarctica,[28] most likely because they are the most accessible. Much of Victoria Land is mountainous, developing the eastern section of the Transantarctic Mountains, and there are several scattered volcanoes including Mount Overlord and Mount Melbourne in the northern part.[28] Farther south are two more well-known volcanoes, Mount Discovery and Mount Morning, which are on the coast across from Mount Erebus and Mount Terror on Ross Island. The volcanism in this area is caused by rifting along a number of rift zones increasing mainly north-south similar to the coast.[28]

Marie Byrd Land contains the largest volcanic region in Antarctica, covering a length of almost 600 miles (970 km) along the Pacific coast.[28] The volcanism is the result of rifting along the vast West Antarctic Rift, which extends from the base of the Antarctic Peninsula to the surrounding area of Ross Island, and the volcanoes are found along the northern edge of the rift.[28] Protruding up through the ice are a large number of major shield volcanoes, including Mount Sidley, which is the highest volcano in Antarctica.[28] Although a number of the volcanoes are relatively young and are potentially active (Mount Berlin, Mount Takahe, Mount Waesche, and Mount Siple), others such as Mount Andrus and Mount Hampton are over 10 million years old, yet maintain uneroded constructional forms.[28] The desert-like surroundings of the Antarctic interior, along with a very thick and stable ice sheet which encloses and protects the bases of the volcanoes, which decreases the speed of erosion by an issue of perhaps a thousand relative to volcanoes in moist temperate or tropical climates.

Land areas

Discovery learning

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