One of the most violent but beautiful reminders that we live on ageologically restless planet are volcanic 公仔箱論壇1 b$ N! S/ o+ B
eruptions. Around 550volcanoes have erupted at least once in historic times, and around 50or 60 are 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。 b' B& [6 Y; w( [; ^* H( g
active each year. On any given day, as many as 10 volcanoesmay be spewing ash or lava somewhere on Earth.
1 Q' Q* g' ]0 B# \公仔箱論壇Some volcanoes, such as Mount Etna in Italy, erupt almost constantlyfor years on end. Others, like Mount St. Helens,
, r. r8 j3 x t l' ^# ]7 ferupt rarely andsometimes extremely destructively. Like Etna and Mount St. Helens, manyof the most dangerous 5.39.217.77:8898# Z5 X I. Z1 ^# j
and explosive erupters are stratovolcanoes, whichare made of layers of ash and lava from previous eruptions. " Z" E$ y& L& W% K! ]8 x
They tendto be steep-sided cone-shaped volcanoes and often rise strikingly abovethe surrounding landscape.公仔箱論壇/ w( ]& E! G I! P) A
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) x8 V7 W' w' t5 N4 vMany of the stunning images of eruptions captured from space are ofviolent stratovolcanoes, such as the one above
* y: j1 h( x( `" a, PTVBNOW 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。of Kliuchevskoi, themost active volcano on Russia’s Kamchatka peninsula. The image abovewas公仔箱論壇: o# e# O, K6 H% Y" Z0 ^' y7 f: q
taken by astronauts on the space shuttle Endeavour in 1994, as an eruption was just getting underway. The ash 公仔箱論壇: p! \% w9 `9 h o# u1 F& \6 q+ N
plume reached as high as 50,000 feet./ E# U2 A3 k1 t& S/ A+ ^- a) P
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Augustine Volcano is a 4,100-foot-tall, 7-mile-wide stratovolcano. This eruption was captured by NASA’s Terra
0 E+ V4 `8 g% h& t' O5 c2 |5.39.217.77:8898satellite in 2006. Augustine’s dome collapsed in 1883, during its largest historical eruption. It has been erupting for at least 40,000 tvb now,tvbnow,bttvb$ h2 y. S9 P3 v. e9 p) V
years. The island’s jagged edges were created by massive avalanches.1 O# U& s3 c* T" P z
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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
$ A5 M" u4 B% J$ E* dof Fire. Volcanic activity here is caused by the subduction of the Pacific plate beneath the North American plate. As the wet 公仔箱論壇/ Z5 o- d; i3 F; `
ocean crust descends into the molten mantle below, superheated water is squeezed out and rises up to melt the bottom of
4 A: f; J* D' `# X& ]1 A) i0 o( L K公仔箱論壇the continental crust, creating magma that drives the volcanic eruptions
/ V1 ?. E4 S0 i) R公仔箱論壇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。: U9 W4 v0 U% w3 p
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Astronauts aboard the International Space Station caught a lucky glimpse of the start of this eruption of Sarychev Volcano
( L2 O# ]5 k( E! l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.5.39.217.77:8898' I0 h7 K6 F9 N' g- p8 O
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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,bttvb9 t( C% }9 k$ x4 [
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 公仔箱論壇' r N4 a4 a$ Y3 x4 K4 Z
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.
7 L% ?; d" H Z2 t7 v# J4 ~# y5.39.217.77:8898 * A shockwave from the eruption could have blown a hole in the cloud deck.
* w' ?9 B. b* D4 P- X# I$ L' rTVBNOW 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。 * 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. * V4 C d$ K0 ]% S- }4 L5 p' c
It continued erupting on and off for weeks afterward. This image was taken by the commercial satellite GeoEye-1 on March 30 when
& P* ?* z7 u& p- F: f$ Atvb now,tvbnow,bttvb 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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: H; x- |; Y( B' T公仔箱論壇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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" Z x1 {5 ?. v1 v& yMount Etna is the second tallest volcano in Europe, at almost 11,000 feet. It is one of the most active volcanoes in公仔箱論壇6 P$ A8 u: D2 N9 k. a
the world and is erupting nearly continuously. It is no surprise that there are many great photos of this volcano erupting, including this one
8 ]5 U: ]5 L3 J5.39.217.77:8898captured by astronauts on the International Space Station in 2002. The lighter colored plumes of smoke on the slope of the volcano in 7 H% H% Y t+ G4 D3 X
this picture are from forest fires ignited by lava.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。0 g/ a {# e( C$ ^) A
3 J$ J: o" V- \1 Z7 [9 ]& A5.39.217.77:8898Etna 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
! [( W1 v5 _7 `# v8 Z7 d6 qalso be the oldest-known active volcano.
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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 - [1 [6 D/ U/ U
and claimed the only known eruption-related death in Alaska’s Aleutian Islands in 1944. Its symmetrical, cone shape is typical of stratovolcanoes." d8 V8 W8 t- L
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。 {7 K/ n# Q: r; u7 Y2 V! ^8 p
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Popoépetcatl, which means “smoking mountain” in the Aztec language, is a very active volcano just 44 miles outside Mexico City. 8 a# T k$ P5 R5 `8 I9 X+ h+ }4 Q: Z
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 tvb now,tvbnow,bttvb G: W; k8 U5 P% {6 L+ s7 W$ n: ?
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 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。, T7 E& H" v1 q5 a
of frequent activity. The plume reached heights of around 30,000 feet.5 G+ {0 I" o8 U* g$ o' G- j& h7 m; J
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+ R* y5 Y- [, E4 xtvb now,tvbnow,bttvbThis eruption of Chaitén caldera in Chile was photographed from the International Space Station in May 2008. Volcanism along the
; v' _ @! }6 x! w' n3 Q5.39.217.77:8898west 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 5.39.217.77:8898" ?; K# C# f: O4 H
flows 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- V" ?; R/ Y1 b4 e+ I公仔箱論壇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 0 \) O. {; m M7 F7 \
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 公仔箱論壇& ~/ e! v5 y2 |* u
stationary hot spot, volcanoes are formed. The Hawaiian Islands were formed — and continue forming — the same way.
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* B0 S0 u5 P+ G8 {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.
! W6 O4 m6 x- k7 [8 H5 G9 l公仔箱論壇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 tvb now,tvbnow,bttvb7 V) G9 ` T) b3 U0 t- D6 w
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, + B$ @+ b, G0 P( K1 \
causing avalanches of debris into the crater. |
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