One of the most violent but beautiful reminders that we live on ageologically restless planet are volcanic : z( y+ X+ o* [+ S7 [. b
eruptions. Around 550volcanoes have erupted at least once in historic times, and around 50or 60 are tvb now,tvbnow,bttvb. x1 I+ x6 n/ M7 i5 E
active each year. On any given day, as many as 10 volcanoesmay be spewing ash or lava somewhere on Earth.2 ~/ y# I. Z$ R
Some volcanoes, such as Mount Etna in Italy, erupt almost constantlyfor years on end. Others, like Mount St. Helens, tvb now,tvbnow,bttvb! n2 J+ K$ _$ V$ U
erupt rarely andsometimes extremely destructively. Like Etna and Mount St. Helens, manyof the most dangerous 7 p) y# `& a3 y5 Y
and explosive erupters are stratovolcanoes, whichare made of layers of ash and lava from previous eruptions. 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。8 z, `- w$ X4 V/ B
They tendto be steep-sided cone-shaped volcanoes and often rise strikingly abovethe surrounding landscape.公仔箱論壇/ p) q+ q' p$ ^* T- L! w$ b
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; Y5 H8 l/ l. D! x$ h7 cMany of the stunning images of eruptions captured from space are ofviolent stratovolcanoes, such as the one above & T% |4 a8 T" ^! Y" S& T/ b; Z1 \
of Kliuchevskoi, themost active volcano on Russia’s Kamchatka peninsula. The image abovewas5.39.217.76# C6 F' P' d( }
taken by astronauts on the space shuttle Endeavour in 1994, as an eruption was just getting underway. The ash
M- w/ k+ Q3 u; wplume 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。) o7 t1 }. N$ _, h/ v5 j0 P4 X
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Augustine Volcano is a 4,100-foot-tall, 7-mile-wide stratovolcano. This eruption was captured by NASA’s Terra
9 w+ N" V) H7 e3 S公仔箱論壇satellite in 2006. Augustine’s dome collapsed in 1883, during its largest historical eruption. It has been erupting for at least 40,000
8 J7 ^( o2 d9 p. V% k L5 S4 a1 D5.39.217.76years. The island’s jagged edges were created by massive avalanches.5.39.217.76. T: Y7 |1 A, {) D5 f' B8 Y
. J: N5 e6 K, V: k; k$ \# a. rAugustine 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 L+ A0 O. n; Q
of Fire. Volcanic activity here is caused by the subduction of the Pacific plate beneath the North American plate. As the wet
. M! r4 a7 H1 Y# Q4 E: U& H/ I* nocean crust descends into the molten mantle below, superheated water is squeezed out and rises up to melt the bottom of ' A. u, c7 a8 f* x; }
the continental crust, creating magma that drives the volcanic eruptions: e, y2 ~) I, b. C# ^0 H; o
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- [% v; ]1 \9 G: s9 `6 WAstronauts aboard the International Space Station caught a lucky glimpse of the start of this eruption of Sarychev Volcano 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。% y- n- Q$ O c
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' U2 | N( W& R, R( O3 O9 a
! y0 G6 M! U. ^* K6 A公仔箱論壇The smooth white cloud, known as a pileus cloud, topping the eruption column may be made of water condensation caused by rising
6 v+ X" R% m6 F: Aand 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
- D1 S3 a% s. G X6 I+ \! Q5.39.217.76as a pyroclastic flow.tvb now,tvbnow,bttvb+ m' m1 |/ m% c; T- _
( t# x6 _: R! S5.39.217.76This 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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0 i( c5 R: q# t) c7 @1 S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." U2 n0 v1 \1 O) R" X7 Q
* A shockwave from the eruption could have blown a hole in the cloud deck.公仔箱論壇6 h3 }. d R* G3 w Y u
* As the plume rose, air flowed downward along the sides and became warmer and evaporated the clouds.5.39.217.766 c6 \& \/ m z5 d( P! T
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Alaska’s Redoubt Volcano erupted five times in one night this year after almost three decades of relative quiet. 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。6 Y1 r& K8 }* m
It continued erupting on and off for weeks afterward. This image was taken by the commercial satellite GeoEye-1 on March 30 when } c3 j3 {. A# f, h8 h
the ash reached heights of 27,000 feet. The volcano’s alert level is still “advisory,” and the aviation color code is yellow.4 z4 O8 u9 m' n
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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& `9 a+ l e0 I. X* n
the world and is erupting nearly continuously. It is no surprise that there are many great photos of this volcano erupting, including this one " u0 n# o/ I% y' b# I1 C" W3 C9 f
captured by astronauts on the International Space Station in 2002. The lighter colored plumes of smoke on the slope of the volcano in : g; y. V/ p+ f: {' s
this picture are from forest fires ignited by lava.3 g& A: K0 c3 z0 v4 M( c+ |8 N
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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 maytvb now,tvbnow,bttvb1 l8 v& ~1 F3 J
also 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
7 R- m3 M' c' x B( F; i% I# Y5.39.217.76and claimed the only known eruption-related death in Alaska’s Aleutian Islands in 1944. Its symmetrical, cone shape is typical of stratovolcanoes.
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Popoépetcatl, which means “smoking mountain” in the Aztec language, is a very active volcano just 44 miles outside Mexico City. 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 m( I& x% S! P8 S
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 ' U+ S0 [4 v: S
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,bttvb. Y" T( \5 h6 B! D M' _/ q- Y
of frequent activity. The plume reached heights of around 30,000 feet.
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, r* L; O/ b6 }$ P( }5.39.217.76This eruption of Chaitén caldera in Chile was photographed from the International Space Station in May 2008. Volcanism along the 0 R- T& V& _5 ^9 S Z# i4 h
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 tvb now,tvbnow,bttvb. O8 n; q/ ^& V( C3 {" O
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.公仔箱論壇# t2 b3 p; \. C1 X
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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
, q: q6 ^8 H7 b7 Z; X5 \7 @5.39.217.76is 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
3 A) D9 M2 \, t: ?$ o" gtvb now,tvbnow,bttvbformed 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
- W6 x5 t5 h# u F5.39.217.76stationary hot spot, volcanoes are formed. The Hawaiian Islands were formed — and continue forming — the same way.
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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.
8 P' ^1 k) @+ X% w9 T) N: h5.39.217.76A 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,bttvb+ Z0 D" i0 W' ?. f! X# W+ T
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,
, E: |+ g1 X6 a3 G) O- F- D9 wtvb now,tvbnow,bttvbcausing avalanches of debris into the crater. |
發表於 2009-12-22 08:34 AM
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