One of the most violent but beautiful reminders that we live on ageologically restless planet are volcanic ! f/ T1 Q/ M: o
eruptions. Around 550volcanoes have erupted at least once in historic times, and around 50or 60 are
1 l0 X& L7 f" c9 `6 K6 @tvb now,tvbnow,bttvbactive each year. On any given day, as many as 10 volcanoesmay be spewing ash or lava somewhere on Earth.
6 F" I7 r' a+ iSome volcanoes, such as Mount Etna in Italy, erupt almost constantlyfor years on end. Others, like Mount St. Helens, 5.39.217.76* W# J) g! z, @
erupt rarely andsometimes extremely destructively. Like Etna and Mount St. Helens, manyof the most dangerous ) z7 X8 N3 s' Q- l" K/ n
and explosive erupters are stratovolcanoes, whichare made of layers of ash and lava from previous eruptions.
& U; j, U4 B* p- W& L* x( G公仔箱論壇They tendto be steep-sided cone-shaped volcanoes and often rise strikingly abovethe surrounding landscape.7 t' K+ W7 g4 ?5 g4 a
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Many of the stunning images of eruptions captured from space are ofviolent stratovolcanoes, such as the one above
- h, l' j+ j _, K" ?tvb now,tvbnow,bttvbof Kliuchevskoi, themost active volcano on Russia’s Kamchatka peninsula. The image abovewas
% M2 a* o: W V, `6 A& f1 m4 V7 _公仔箱論壇taken by astronauts on the space shuttle Endeavour in 1994, as an eruption was just getting underway. The ash
& u) c5 t% X. q5 _% ^TVBNOW 含有熱門話題,最新最快電視,軟體,遊戲,電影,動漫及日常生活及興趣交流等資訊。plume reached as high as 50,000 feet.tvb now,tvbnow,bttvb0 @% T3 ?. r* C ]4 ]9 q3 F! u
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Augustine Volcano is a 4,100-foot-tall, 7-mile-wide stratovolcano. This eruption was captured by NASA’s Terra
2 A" P; o; ~/ d/ i. |tvb now,tvbnow,bttvbsatellite in 2006. Augustine’s dome collapsed in 1883, during its largest historical eruption. It has been erupting for at least 40,000
$ p2 E4 o2 I) Y5.39.217.76years. The island’s jagged edges were created by massive avalanches.
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Augustine lies in the Cook Inlet at the eastern end of the Aleutian trench which marks the northernmost portion of the Pacific Ring ) s* [7 F) N0 D8 N; [
of Fire. Volcanic activity here is caused by the subduction of the Pacific plate beneath the North American plate. As the wet
5 F* M$ {# r9 B n: ltvb now,tvbnow,bttvbocean crust descends into the molten mantle below, superheated water is squeezed out and rises up to melt the bottom of
! R1 `6 s" n3 N1 v( H: e9 r' D5.39.217.76the continental crust, creating magma that drives the volcanic eruptions
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Astronauts aboard the International Space Station caught a lucky glimpse of the start of this eruption of Sarychev Volcano
. k- M9 n3 I* Iin the Kuril Islands, northeast of Japan, on June 12, 2009. This was the volcano’s first eruption in 30 years.
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The smooth white cloud, known as a pileus cloud, topping the eruption column may be made of water condensation caused by rising
1 y' i9 S7 g' x' B+ p, yand cooling of the air above. In contrast, a dark gray cloud of ash near the ground is probably an avalanche of hot ash and rock known
2 I N/ h q1 t- \3 r: S, ^3 F公仔箱論壇as a pyroclastic flow.
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This photo sparked a debate among scientists about what caused the hole in the clouds above the eruption. Three possible options came up:
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* It could have nothing to do with the eruption and simply be caused by the contrast in temperatures between the ocean and the island.
1 [: I2 J0 Q5 b公仔箱論壇 * A shockwave from the eruption could have blown a hole in the cloud deck.5.39.217.766 ]$ B0 ], z& j. X1 W& y. u
* As the plume rose, air flowed downward along the sides and became warmer and evaporated the clouds.
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Alaska’s Redoubt Volcano erupted five times in one night this year after almost three decades of relative quiet.
! i+ a- }5 F+ g5 tIt continued erupting on and off for weeks afterward. This image was taken by the commercial satellite GeoEye-1 on March 30 whentvb now,tvbnow,bttvb5 B- J# |: |8 @
the ash reached heights of 27,000 feet. The volcano’s alert level is still “advisory,” and the aviation color code is yellow.5.39.217.764 p; y `8 x8 ^& x4 }3 N! W' \
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Redoubt is a 10,200-foot tall stratovolcano 100 miles southwest of Anchorage in the Aleutian Range, west of the Cook Inlet.
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Mount Etna is the second tallest volcano in Europe, at almost 11,000 feet. It is one of the most active volcanoes in
4 o2 j! N4 O, n+ e q! [! @' ? the world and is erupting nearly continuously. It is no surprise that there are many great photos of this volcano erupting, including this one
' F' Z2 y( }$ R6 V$ Ccaptured by astronauts on the International Space Station in 2002. The lighter colored plumes of smoke on the slope of the volcano in 5.39.217.76# }+ p, d# c$ b1 t
this picture are from forest fires ignited by lava.
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Etna is a stratovolcano located on the island of Sicily. It is one of the most studied volcanoes in the world and. at 500,000 years old, it may
G* N4 f# @. y7 w! r! P& S4 x NTVBNOW 含有熱門話題,最新最快電視,軟體,遊戲,電影,動漫及日常生活及興趣交流等資訊。also be the oldest-known active volcano.: ~; f& c5 @$ _8 d* a$ C7 B
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A NASA astronaut spotted this eruption of Cleveland Volcano from the International Space Station in 2006. The volcano is 5,700 feet high
9 ~/ v3 _5 Y1 W( Yand claimed the only known eruption-related death in Alaska’s Aleutian Islands in 1944. Its symmetrical, cone shape is typical of stratovolcanoes./ L. l- x8 t8 o! A. i
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5 x8 S9 n% D, Y+ ]5 wtvb now,tvbnow,bttvbPopoépetcatl, which means “smoking mountain” in the Aztec language, is a very active volcano just 44 miles outside Mexico City. 公仔箱論壇7 o* H' Y' N2 f+ D: {$ ~$ K2 G
The second highest peak in Mexico at 17,800 feet, this glacier-covered stratovolcano has erupted at least 20 times in the last 500 years and has caused # \. u3 ~2 _1 o
multiple evacuations of the city. This eruption in 2001 was caught by astronauts on the International Space Station, near the end of a seven-year period tvb now,tvbnow,bttvb7 ~; |7 w9 T& s' ~
of frequent activity. The plume reached heights of around 30,000 feet.8 a7 L c9 y9 k/ \4 R M
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This eruption of Chaitén caldera in Chile was photographed from the International Space Station in May 2008. Volcanism along the & f% G6 Q& Q6 X; @6 J
west coast of South America is the result of subduction of the oceanic Nazca plate beneath the South American plate.公仔箱論壇3 s t% B) V/ p* a$ u3 ^
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Chaitén was last active more than 9,000 years ago. The violent 2008 eruption inundated the small coastal town of Chaitén with ash, pyroclastic
. H* {# [7 u0 N) q ?5.39.217.76flows and volcanic mudflows called lahars. The caldera is relatively small at less than two miles wide, and sits on the flank of the larger Michinmahuida volcano.
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This image of the Sierra Negra volcano in the Galapagos Islands was taken by NASA’s Terra satellite in 2006. Sierra Negra
V! t6 a' k: Yis a shield volcano, which are made mostly of previous lava flows and tend to be broad and gently sloping. The Galapagos are part of an island chain . F+ ?( j6 ]) W0 x
formed by a hot spot where a plume of hot mantle rises up and melts the base of the ocean crust. As the Pacific plate moves over the relatively tvb now,tvbnow,bttvb# r4 V3 F. m, \# |8 x7 B( b
stationary hot spot, volcanoes are formed. The Hawaiian Islands were formed — and continue forming — the same way.
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7 E% R j& L1 L2 k, ?6 q: C公仔箱論壇NASA’s Terra satellite snapped this image of Shiveluch volcano erupting on Russia’s Kamchatka peninsula at the edge of the Pacific Ring of Fire in 2004. tvb now,tvbnow,bttvb$ f" B+ n g6 j
A lava dome had been growing in the volcano’s crater, followed by intermittent eruptions that lasted weeks. Shiveluch is a 10,400-foot-high stratovolcano
/ g+ Z% P t1 I! `$ k5 z7 MTVBNOW 含有熱門話題,最新最快電視,軟體,遊戲,電影,動漫及日常生活及興趣交流等資訊。that is at least 60,000 years old and has been erupting fairly often for the past 10 years. Its dome has collapsed multiple times, most recently in 1964,
/ T1 r# K4 z3 W2 m& a3 {7 V& e9 O0 R5.39.217.76causing avalanches of debris into the crater. |