One of the most violent but beautiful reminders that we live on ageologically restless planet are volcanic . m5 E9 c4 X- X' g6 E
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。4 V: V* r, V/ Z6 X
active each year. On any given day, as many as 10 volcanoesmay be spewing ash or lava somewhere on Earth.) L# Y1 Y; n9 p! X# ^
Some volcanoes, such as Mount Etna in Italy, erupt almost constantlyfor years on end. Others, like Mount St. Helens, 5.39.217.76* x( [: ^. z% _8 h9 X
erupt rarely andsometimes extremely destructively. Like Etna and Mount St. Helens, manyof the most dangerous 5.39.217.76& U, R. _5 h2 M8 j& R) o
and explosive erupters are stratovolcanoes, whichare made of layers of ash and lava from previous eruptions. tvb now,tvbnow,bttvb7 O4 t# {" ? z1 {
They tendto be steep-sided cone-shaped volcanoes and often rise strikingly abovethe surrounding landscape.公仔箱論壇1 t W7 {! H, p# Z6 R! ?9 f
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# j1 k: z( n; j# z6 c2 `% {3 IMany of the stunning images of eruptions captured from space are ofviolent stratovolcanoes, such as the one above
; k R/ }2 `. j) I5 w5 [of Kliuchevskoi, themost active volcano on Russia’s Kamchatka peninsula. The image abovewas: V6 `' B& T ~) r+ v0 B: O0 K
taken by astronauts on the space shuttle Endeavour in 1994, as an eruption was just getting underway. The ash 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。/ i' w% G+ t9 F3 [2 ]
plume reached as high as 50,000 feet. \3 v0 i Z3 G0 L1 o* f( Y N$ 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
6 U5 C0 e* f5 t/ Stvb 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
; ^3 C: f! K, Stvb now,tvbnow,bttvbyears. The island’s jagged edges were created by massive avalanches.
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w; k3 I3 z P; W" Y$ l, l* xAugustine lies in the Cook Inlet at the eastern end of the Aleutian trench which marks the northernmost portion of the Pacific Ring 5.39.217.76* ?. V- Z9 ]6 b; m
of Fire. Volcanic activity here is caused by the subduction of the Pacific plate beneath the North American plate. As the wet 7 G* r8 @6 e6 b9 }+ y0 b3 w
ocean crust descends into the molten mantle below, superheated water is squeezed out and rises up to melt the bottom of
# x0 Y! i2 [0 g' p2 t* ~* ~the continental crust, creating magma that drives the volcanic eruptions( I X6 j5 e0 w% ? M
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Astronauts aboard the International Space Station caught a lucky glimpse of the start of this eruption of Sarychev Volcano
1 b% K8 V; Q% Z5 D) ltvb now,tvbnow,bttvbin the Kuril Islands, northeast of Japan, on June 12, 2009. This was the volcano’s first eruption in 30 years.公仔箱論壇; l0 v* J* ]2 \9 n, }
$ N6 }' j( }- w4 F; L5 U7 L6 u5.39.217.76The smooth white cloud, known as a pileus cloud, topping the eruption column may be made of water condensation caused by rising 公仔箱論壇; E4 N% ~) J1 x, R- p
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 : V3 a. l3 z5 B3 _. w0 n6 @3 _8 e
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:公仔箱論壇5 l4 k# j4 t) q/ M8 T" T
- O- f2 g; V# r) c- {8 D. l公仔箱論壇 * It could have nothing to do with the eruption and simply be caused by the contrast in temperatures between the ocean and the island.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。& l$ R7 H. g& m i
* A shockwave from the eruption could have blown a hole in the cloud deck.5.39.217.76. J+ [2 Y' G9 w2 L0 s+ G5 j
* As the plume rose, air flowed downward along the sides and became warmer and evaporated the clouds.tvb now,tvbnow,bttvb8 V( s6 ?8 o9 L- l. X. ^' a0 P9 m
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Alaska’s Redoubt Volcano erupted five times in one night this year after almost three decades of relative quiet.
% F% N$ r; o0 f2 w8 p# J3 I( GIt continued erupting on and off for weeks afterward. This image was taken by the commercial satellite GeoEye-1 on March 30 when
0 E3 S; d1 G+ b2 e- v4 z. Q$ k5.39.217.76 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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5 c& [ i# i/ N$ e/ btvb now,tvbnow,bttvbRedoubt 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
5 h/ ^! Z( F7 J/ n/ JTVBNOW 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。 the world and is erupting nearly continuously. It is no surprise that there are many great photos of this volcano erupting, including this one / r: h4 l" A" d. M' i3 c2 q- c8 }
captured by astronauts on the International Space Station in 2002. The lighter colored plumes of smoke on the slope of the volcano in
/ l) b( p- D* e- I# p% [& V) R1 Y; gthis picture are from forest fires ignited by lava.tvb now,tvbnow,bttvb+ }' \4 V; o$ K% |, ^4 K, K
# u4 M6 s. ]7 w3 qEtna 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 mayTVBNOW 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。8 b; V' T* F" t! g
also be the oldest-known active volcano.5.39.217.764 \6 L! _, {3 b3 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
+ k3 Q/ I& x/ n0 f: P5.39.217.76and claimed the only known eruption-related death in Alaska’s Aleutian Islands in 1944. Its symmetrical, cone shape is typical of stratovolcanoes.
3 p* Z, s. R4 n( R, U- m7 BTVBNOW 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。
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Popoépetcatl, which means “smoking mountain” in the Aztec language, is a very active volcano just 44 miles outside Mexico City.
( R$ }2 r7 V2 T6 ftvb now,tvbnow,bttvbThe 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
# L3 @6 r8 |7 b4 i2 ?+ t: a5.39.217.76multiple 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
. o, Y* u c1 O' D" L8 KTVBNOW 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 frequent activity. The plume reached heights of around 30,000 feet.
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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。" b8 G9 O& U! d
This eruption of Chaitén caldera in Chile was photographed from the International Space Station in May 2008. Volcanism along the 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。" r& |* e* v2 f* l' h
west coast of South America is the result of subduction of the oceanic Nazca plate beneath the South American plate.0 r0 z) l. \* O, t
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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 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 K7 f l8 M/ o! x" G; A: J
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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: A) S& [2 g0 m6 I" AThis image of the Sierra Negra volcano in the Galapagos Islands was taken by NASA’s Terra satellite in 2006. Sierra Negra
% C7 ? J# o9 {- a1 E# CTVBNOW 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。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
: _4 }+ K3 V Q: ]' 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# l8 K# l! c7 e& G- D4 W% c
stationary hot spot, volcanoes are formed. The Hawaiian Islands were formed — and continue forming — the same way.tvb now,tvbnow,bttvb% H! h0 I; d8 x; B/ y' P4 n7 t
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% i+ v* T! _5 E0 J. t5.39.217.76NASA’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.
# ]& S B4 p0 K" ^4 }% {) n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 # I" L5 z4 M0 {0 e) ~; g
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,
) z0 u$ q- h& `& D6 H( T6 r( d- X公仔箱論壇causing avalanches of debris into the crater. |
發表於 2009-12-22 08:34 AM
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