One of the most violent but beautiful reminders that we live on ageologically restless planet are volcanic 5.39.217.77:88982 p$ Z; U' E& W: U
eruptions. Around 550volcanoes have erupted at least once in historic times, and around 50or 60 are . l- k5 {1 S* Q z; Y& D
active each year. On any given day, as many as 10 volcanoesmay be spewing ash or lava somewhere on Earth.5.39.217.77:8898( C6 F7 `- o2 K
Some volcanoes, such as Mount Etna in Italy, erupt almost constantlyfor years on end. Others, like Mount St. Helens,
9 @3 j7 E1 T, G/ @* v) I5.39.217.77:8898erupt rarely andsometimes extremely destructively. Like Etna and Mount St. Helens, manyof the most dangerous 5 t+ e- r- p" z) ?0 q
and explosive erupters are stratovolcanoes, whichare made of layers of ash and lava from previous eruptions. 0 h# y' L# r8 d& _
They tendto be steep-sided cone-shaped volcanoes and often rise strikingly abovethe surrounding landscape.# O, k8 M( K6 O) M
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1 g3 u9 Y9 i3 R公仔箱論壇Many of the stunning images of eruptions captured from space are ofviolent stratovolcanoes, such as the one above tvb now,tvbnow,bttvb- r A2 u+ V% L
of Kliuchevskoi, themost active volcano on Russia’s Kamchatka peninsula. The image abovewas
% b* F$ o% {$ J7 v公仔箱論壇taken by astronauts on the space shuttle Endeavour in 1994, as an eruption was just getting underway. The ash 公仔箱論壇7 o6 i) z3 z+ y6 \# u8 r
plume reached as high as 50,000 feet.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。& E" ?( W3 \; g1 h0 u
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* l! ?3 t7 q/ l" z6 Ntvb now,tvbnow,bttvbAugustine Volcano is a 4,100-foot-tall, 7-mile-wide stratovolcano. This eruption was captured by NASA’s Terra
t4 o$ x, r0 wTVBNOW 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。satellite in 2006. Augustine’s dome collapsed in 1883, during its largest historical eruption. It has been erupting for at least 40,000
' M. d! N0 |1 u9 Ayears. The island’s jagged edges were created by massive avalanches.tvb now,tvbnow,bttvb. u# o1 b5 x/ R3 g4 b9 x
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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 ' W( ^+ l- H+ }4 \0 O2 C) Y& K4 d
of Fire. Volcanic activity here is caused by the subduction of the Pacific plate beneath the North American plate. As the wet # E0 k0 `# [) @9 |
ocean crust descends into the molten mantle below, superheated water is squeezed out and rises up to melt the bottom of 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。) k7 [" Z+ ~2 \' i& i- _
the 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
* d. g3 ^ s; O& V8 G, |3 D B公仔箱論壇in the Kuril Islands, northeast of Japan, on June 12, 2009. This was the volcano’s first eruption in 30 years.tvb now,tvbnow,bttvb( C# u' L) i) O! n
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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 tvb now,tvbnow,bttvb- E6 @! `0 {# U; ?2 c1 r
and 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 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。' n% [4 ]+ o2 g1 l# N$ M$ k( A
as a pyroclastic flow./ C6 N3 O! o: x ?
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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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- y! t8 K% E) M6 u/ q( a/ r5 ^ * It could have nothing to do with the eruption and simply be caused by the contrast in temperatures between the ocean and the island.
+ }, S% G. y e- b3 x0 v, Y5.39.217.77:8898 * A shockwave from the eruption could have blown a hole in the cloud deck.5.39.217.77:88983 n; r8 w0 u; Y1 ^% Q* e5 `4 d+ v
* As the plume rose, air flowed downward along the sides and became warmer and evaporated the clouds.tvb now,tvbnow,bttvb. \. t7 c7 b& i' n- S2 y# ~% g
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+ A' ?9 R7 z2 V h) k/ F5.39.217.77:8898Alaska’s Redoubt Volcano erupted five times in one night this year after almost three decades of relative quiet. # B. x5 n! N% d" K4 K, G
It continued erupting on and off for weeks afterward. This image was taken by the commercial satellite GeoEye-1 on March 30 when0 f' n0 Z+ d. _2 b* D h
the ash reached heights of 27,000 feet. The volcano’s alert level is still “advisory,” and the aviation color code is yellow.
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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
% R$ s! K! d- g" J, e: Z公仔箱論壇 the world and is erupting nearly continuously. It is no surprise that there are many great photos of this volcano erupting, including this one
- k/ x( p2 O8 E! y; \0 V9 c. U5.39.217.77:8898captured by astronauts on the International Space Station in 2002. The lighter colored plumes of smoke on the slope of the volcano in
: M, F2 ?6 ]- s. l) S3 \公仔箱論壇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
; W: q9 W" ?( gTVBNOW 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.
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8 Q( M. O; l/ s# X4 w& G# A" u. CA NASA astronaut spotted this eruption of Cleveland Volcano from the International Space Station in 2006. The volcano is 5,700 feet high
1 Y5 H( T$ E, Vand claimed the only known eruption-related death in Alaska’s Aleutian Islands in 1944. Its symmetrical, cone shape is typical of stratovolcanoes.5.39.217.77:8898: @, \* e1 p! S$ }# Q
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Popoépetcatl, which means “smoking mountain” in the Aztec language, is a very active volcano just 44 miles outside Mexico City.
& u& V! }; d s) S1 {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
* x+ o$ q$ w; ?% I0 I" D+ N: f6 _公仔箱論壇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
8 D5 W. ~0 N: j$ [1 J9 o1 [+ x, l- R公仔箱論壇of frequent activity. The plume reached heights of around 30,000 feet.
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. V) [7 J* m" t- V5 ] ?5 a* u N5 g2 B5.39.217.77:8898This eruption of Chaitén caldera in Chile was photographed from the International Space Station in May 2008. Volcanism along the % I' j# }! L' h5 b5 d% I
west coast of South America is the result of subduction of the oceanic Nazca plate beneath the South American plate.
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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
6 d: P* d x# k3 P6 yflows 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.
1 A6 k! @# X J& Z% 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。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。$ }& N3 w( m/ e, E1 m; S

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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 5.39.217.77:8898- {- P& n5 _9 i; x5 o8 \* a
is 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
2 U {6 u' h2 q0 R7 q2 L公仔箱論壇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
) y- c) h9 B2 C+ Estationary hot spot, volcanoes are formed. The Hawaiian Islands were formed — and continue forming — the same way.& S3 V9 R, X1 U9 V/ A
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) O/ u$ K6 A7 S+ `' _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. 公仔箱論壇3 }$ [# v5 L$ T7 N% [+ d
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
: F) \5 X& F& Q) A! u公仔箱論壇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, 公仔箱論壇6 d& }4 v" @+ F7 h3 l( z
causing avalanches of debris into the crater. |