One of the most violent but beautiful reminders that we live on ageologically restless planet are volcanic
( W& ]" r4 |3 m8 n9 T4 W5.39.217.77:8898eruptions. Around 550volcanoes have erupted at least once in historic times, and around 50or 60 are
. o6 b+ B. V+ T# Atvb now,tvbnow,bttvbactive each year. On any given day, as many as 10 volcanoesmay be spewing ash or lava somewhere on Earth.5.39.217.77:88981 m8 y+ Y& B, R% A" p
Some volcanoes, such as Mount Etna in Italy, erupt almost constantlyfor years on end. Others, like Mount St. Helens, tvb now,tvbnow,bttvb1 h* b# N9 L% Z7 \: M$ H* s
erupt rarely andsometimes extremely destructively. Like Etna and Mount St. Helens, manyof the most dangerous # R9 m( U: M3 U" N) P4 Y1 B0 h
and explosive erupters are stratovolcanoes, whichare made of layers of ash and lava from previous eruptions. tvb now,tvbnow,bttvb+ O3 d! F" k$ ~& w% w- m% 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 5.39.217.77:8898+ v! ^9 ~' D! a
of Kliuchevskoi, themost active volcano on Russia’s Kamchatka peninsula. The image abovewas: D, i$ i0 r5 W8 [7 m
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。6 p% F4 X# O4 @( @: I
plume reached as high as 50,000 feet.
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Augustine Volcano is a 4,100-foot-tall, 7-mile-wide stratovolcano. This eruption was captured by NASA’s Terra 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。, p+ ?/ y1 Z, N4 H( O- h
satellite in 2006. Augustine’s dome collapsed in 1883, during its largest historical eruption. It has been erupting for at least 40,000 5.39.217.77:8898) n( s9 z8 t S
years. The island’s jagged edges were created by massive avalanches.tvb now,tvbnow,bttvb6 F, {4 k7 t( ^$ e8 r& L
! J( Y# h, Y' ]& x$ w- Z- t; X6 g/ ZTVBNOW 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。Augustine lies in the Cook Inlet at the eastern end of the Aleutian trench which marks the northernmost portion of the Pacific Ring
, ^+ L% V. K+ R" Z- {of Fire. Volcanic activity here is caused by the subduction of the Pacific plate beneath the North American plate. As the wet " @5 X- C) q) f: M
ocean crust descends into the molten mantle below, superheated water is squeezed out and rises up to melt the bottom of
8 G5 o7 k. d$ K0 v0 M6 D4 s$ M5.39.217.77:8898the continental crust, creating magma that drives the volcanic eruptionstvb now,tvbnow,bttvb* r$ m( T0 U: E. H, J
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Astronauts 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。' \( H9 J3 P' f; E) Y
in 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+ `" x1 _+ F9 w3 x5 T: l. z
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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 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 h( N# y- {5 [. P! r6 |; x& \
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
( t$ j# K- k) x+ Z2 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。as a pyroclastic flow.9 {4 z0 p$ Q. I9 G3 \3 }
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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: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。5 b; V& ` z0 n% v9 c& q3 x+ Q
# y6 q) B# {. w7 s& |! K5.39.217.77:8898 * It could have nothing to do with the eruption and simply be caused by the contrast in temperatures between the ocean and the island.5.39.217.77:8898; K9 r% ~2 j: b+ c
* A shockwave from the eruption could have blown a hole in the cloud deck.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。% ]. M$ W$ f, c: H2 i
* As the plume rose, air flowed downward along the sides and became warmer and evaporated the clouds.
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) M2 o; t* R, q- `9 J& C; w公仔箱論壇Alaska’s Redoubt Volcano erupted five times in one night this year after almost three decades of relative quiet.
X# z. Z6 y4 w7 ?, u4 A+ X5.39.217.77:8898It continued erupting on and off for weeks afterward. This image was taken by the commercial satellite GeoEye-1 on March 30 when
$ b" P7 R6 f5 N! k$ ^7 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。 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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" i, ?) `4 C3 W" v4 M5 v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.tvb now,tvbnow,bttvb* Q# u; m% ^5 \5 W# \# T. q
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" O. g8 c4 b+ e2 U0 G+ LMount Etna is the second tallest volcano in Europe, at almost 11,000 feet. It is one of the most active volcanoes intvb now,tvbnow,bttvb- p* l0 X" A! n) t) D6 f
the world and is erupting nearly continuously. It is no surprise that there are many great photos of this volcano erupting, including this one
7 Y5 c( @8 I- S) d, A1 r8 zcaptured by astronauts on the International Space Station in 2002. The lighter colored plumes of smoke on the slope of the volcano in 9 c4 h/ C: X! R: n+ e) b) T
this picture are from forest fires ignited by lava.
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8 a( v" G4 T! E9 Y4 O6 |- W# u/ F+ pEtna 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
( A+ v8 W |7 u h# b7 c7 Htvb now,tvbnow,bttvbalso be the oldest-known active volcano.
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/ z* Z6 i" {; {A NASA astronaut spotted this eruption of Cleveland Volcano from the International Space Station in 2006. The volcano is 5,700 feet high
+ l6 X4 Z3 n8 b- O4 c" T p' k3 }5.39.217.77:8898and 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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; p1 _1 h& u! r x, u$ D wtvb now,tvbnow,bttvbPopoépetcatl, which means “smoking mountain” in the Aztec language, is a very active volcano just 44 miles outside Mexico City. tvb now,tvbnow,bttvb; ^) [( t5 i5 V/ T% W# {
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 8 P6 Y. K7 @; V
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- V, {8 v1 k y8 L2 G
of frequent activity. The plume reached heights of around 30,000 feet.
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This eruption of Chaitén caldera in Chile was photographed from the International Space Station in May 2008. Volcanism along the 公仔箱論壇4 M9 ^0 g0 S. `, z' q( t7 J' L
west coast of South America is the result of subduction of the oceanic Nazca plate beneath the South American plate.tvb now,tvbnow,bttvb8 h; G: X+ z( i$ d4 i( r5 s( A
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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
% A1 H j: [, K" z9 Eflows 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3 Q0 ?! y* {& r/ 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 # ~6 y& v6 L {; @3 b t0 Q& @
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 5.39.217.77:8898. f) j$ ~" ~: Y
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
2 L% h' a6 X" I1 L s公仔箱論壇stationary hot spot, volcanoes are formed. The Hawaiian Islands were formed — and continue forming — the same way.公仔箱論壇$ H0 I; x) I; k3 j. M4 A- P
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( [3 N; c7 o: S3 W4 G, vNASA’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. 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。5 h7 E; N5 }, _3 V: N
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 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- k8 e8 K) b$ c' W- \# A0 A
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) X) ~" H9 n1 _8 X: ?( G' E* G
causing avalanches of debris into the crater. |