One of the most violent but beautiful reminders that we live on ageologically restless planet are volcanic 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/ ^+ r5 B8 z7 H% ]
eruptions. Around 550volcanoes have erupted at least once in historic times, and around 50or 60 are
O9 a8 d) s x) h! g" p公仔箱論壇active each year. On any given day, as many as 10 volcanoesmay be spewing ash or lava somewhere on Earth.tvb now,tvbnow,bttvb% t3 U- Z) C# g" d, N+ W ^" q+ Y
Some volcanoes, such as Mount Etna in Italy, erupt almost constantlyfor years on end. Others, like Mount St. Helens,
# L- v J2 D5 U$ l5.39.217.76erupt rarely andsometimes extremely destructively. Like Etna and Mount St. Helens, manyof the most dangerous
( y6 |; X! {" B7 {$ R& S' p0 ]2 \and explosive erupters are stratovolcanoes, whichare made of layers of ash and lava from previous eruptions. $ e3 |. `& y, P4 t1 r% e1 Q0 N) N1 I
They tendto be steep-sided cone-shaped volcanoes and often rise strikingly abovethe surrounding landscape.
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Many of the stunning images of eruptions captured from space are ofviolent stratovolcanoes, such as the one above 公仔箱論壇% R& a2 @: H5 l% Y5 r# c
of Kliuchevskoi, themost active volcano on Russia’s Kamchatka peninsula. The image abovewas公仔箱論壇4 x+ n$ g1 c7 R9 S: }6 y/ }
taken by astronauts on the space shuttle Endeavour in 1994, as an eruption was just getting underway. The ash 5.39.217.76. a( L- r# T9 ^$ s
plume reached as high as 50,000 feet.# g H/ }) `! g4 k, D& Q; Y% e
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Augustine Volcano is a 4,100-foot-tall, 7-mile-wide stratovolcano. This eruption was captured by NASA’s Terra tvb now,tvbnow,bttvb' }; [0 o1 u6 ]" r2 H
satellite in 2006. Augustine’s dome collapsed in 1883, during its largest historical eruption. It has been erupting for at least 40,000
9 K8 `2 o8 E1 \: g! j公仔箱論壇years. The island’s jagged edges were created by massive avalanches.公仔箱論壇5 |; r* f" m0 e$ U# t8 l6 r
0 g. @( p/ S1 M( t. R! a- C5.39.217.76Augustine lies in the Cook Inlet at the eastern end of the Aleutian trench which marks the northernmost portion of the Pacific Ring 4 A% n1 C% W& N$ ^3 t8 O- ^
of Fire. Volcanic activity here is caused by the subduction of the Pacific plate beneath the North American plate. As the wet / |1 g8 M. w- P# o5 I
ocean crust descends into the molten mantle below, superheated water is squeezed out and rises up to melt the bottom of
: T0 G6 a$ i7 @+ X" @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
$ j8 D; f( z: F ]! D2 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。in the Kuril Islands, northeast of Japan, on June 12, 2009. This was the volcano’s first eruption in 30 years.5.39.217.76- W1 Y5 N9 p" j) S/ U/ i k; c5 {# r6 f
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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
. F/ C, T* N) R) L4 ~5 qTVBNOW 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。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
( `# M) a& N7 Y! Q: u8 p5.39.217.76as a pyroclastic flow.
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4 \6 |5 R5 p; c* v4 qtvb now,tvbnow,bttvbThis 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. I5 J0 b, W% c) O! n: O
2 C: L `7 F9 W8 M, t$ T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.5.39.217.76# h& Z! P5 j+ F. @1 r# d
* A shockwave from the eruption could have blown a hole in the cloud deck.
1 J# j! J) S. o# Z+ L: v) y1 X7 z! T' t公仔箱論壇 * As the plume rose, air flowed downward along the sides and became warmer and evaporated the clouds.& z ]8 j& D$ B4 N! R
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) l$ O+ O( D. H: v% kAlaska’s Redoubt Volcano erupted five times in one night this year after almost three decades of relative quiet. ' K) p- i/ E( Z1 H; O& w# v. @: }
It continued erupting on and off for weeks afterward. This image was taken by the commercial satellite GeoEye-1 on March 30 when5.39.217.767 H- k. z& Q) K/ b, a) {0 L# G
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.. @, C T8 q( _; J& q/ H, [
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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 in5.39.217.76: J* O H' M `4 m9 b( d. }
the world and is erupting nearly continuously. It is no surprise that there are many great photos of this volcano erupting, including this one 公仔箱論壇# n$ [0 v1 Y8 c: I6 i: r
captured by astronauts on the International Space Station in 2002. The lighter colored plumes of smoke on the slope of the volcano in
* O4 Y! f8 U, K4 j. }+ H: f5 y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
. Z+ Z$ V' M' a% u' v! f; ualso be the oldest-known active volcano.5.39.217.76" ]6 g3 D% v$ x& @
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) n& Q# C, X& V1 K" B/ f公仔箱論壇A NASA astronaut spotted this eruption of Cleveland Volcano from the International Space Station in 2006. The volcano is 5,700 feet high 5.39.217.76/ Y0 Y7 c* F' w5 L2 }( P" h
and 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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, I6 v0 }! f- k$ [( ? g1 Z! c3 FPopoépetcatl, 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。( F# u, E8 z, k" K0 |4 E2 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 tvb now,tvbnow,bttvb6 d* `. P9 A- T5 r
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
) D! J! P5 Z4 {2 ^of frequent activity. The plume reached heights of around 30,000 feet.公仔箱論壇; z' ?9 D+ w0 q) z* q, m) L& t
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This eruption of Chaitén caldera in Chile was photographed from the International Space Station in May 2008. Volcanism along the 5.39.217.76* b& r3 q* q+ H+ L
west coast of South America is the result of subduction of the oceanic Nazca plate beneath the South American plate.. i* K1 k1 |% {
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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: s2 Q0 B9 U0 q8 x: m
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 . N3 Z! G( P! Z1 r# 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 tvb now,tvbnow,bttvb |4 j2 {+ l% X T: F+ V. b, a
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 & y0 B6 e7 J* @1 Z+ [' g# H" f
stationary 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.
/ F9 Q/ Q/ m! d8 ~" u& F) G$ s! V1 E oA 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
. c" `1 I5 ]8 j" X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,
6 y+ |$ T& I8 O7 `# n s( ~5.39.217.76causing avalanches of debris into the crater. |
發表於 2009-12-22 08:34 AM
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