eruptions. Around 550volcanoes have erupted at least once in historic times, and around 50or 60 are 公仔箱論壇0 `; P& Y$ _5 F/ C7 {! r
active each year. On any given day, as many as 10 volcanoesmay be spewing ash or lava somewhere on Earth.
Some volcanoes, such as Mount Etna in Italy, erupt almost constantlyfor years on end. Others, like Mount St. Helens,
erupt rarely andsometimes extremely destructively. Like Etna and Mount St. Helens, manyof the most dangerous 公仔箱論壇2 P. Z* y0 k2 D3 p$ K+ ^
and explosive erupters are stratovolcanoes, whichare made of layers of ash and lava from previous eruptions. 公仔箱論壇& E! r- N5 R5 X/ }* n7 Z
They tendto be steep-sided cone-shaped volcanoes and often rise strikingly abovethe surrounding landscape.
tvb now,tvbnow,bttvb" W: q0 e0 J, B7 h( l! F
7 ]$ b) r7 i, |, hl. Y3 b/ ^, \' D0 L& A+ o
Many of the stunning images of eruptions captured from space are ofviolent stratovolcanoes, such as the one above
of Kliuchevskoi, themost active volcano on Russia’s Kamchatka peninsula. The image abovewastvb now,tvbnow,bttvb& `( u- K' H' B4 E) M7 Z* T
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。& T4 t3 n: \4 b
plume reached as high as 50,000 feet.
Augustine Volcano is a 4,100-foot-tall, 7-mile-wide stratovolcano. This eruption was captured by NASA’s Terra
satellite in 2006. Augustine’s dome collapsed in 1883, during its largest historical eruption. It has been erupting for at least 40,000 Q: f" c2 Y; q1 R' O& t8 Y. J6 y+ I
years. The island’s jagged edges were created by massive avalanches.
公仔箱論壇+ D+ O: P- }0 G: h
Augustine lies in the Cook Inlet at the eastern end of the Aleutian trench which marks the northernmost portion of the Pacific Ring
of Fire. Volcanic activity here is caused by the subduction of the Pacific plate beneath the North American plate. As the wet
ocean crust descends into the molten mantle below, superheated water is squeezed out and rises up to melt the bottom of 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。; V0 x+ A) S& W7 ^, ?
the continental crust, creating magma that drives the volcanic eruptions
公仔箱論壇+ d% J" W9 t7 ]$ |Astronauts aboard the International Space Station caught a lucky glimpse of the start of this eruption of Sarychev Volcano
in the Kuril Islands, northeast of Japan, on June 12, 2009. This was the volcano’s first eruption in 30 years.
$ i, Z! m6 _& F" K+ O, I4 C4 p) M
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,bttvb* t. H7 V. E& j+ C$ G3 z
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 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。9 k6 L& U) N" K. J& ]
as a pyroclastic flow.
This photo sparked a debate among scientists about what caused the hole in the clouds above the eruption. Three possible options came up:tvb now,tvbnow,bttvb E& i/ t1 o' a5 P( X
* It could have nothing to do with the eruption and simply be caused by the contrast in temperatures between the ocean and the island.
* A shockwave from the eruption could have blown a hole in the cloud deck.
* As the plume rose, air flowed downward along the sides and became warmer and evaporated the clouds.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。, @+ v' z% D H' ]* }
tvb now,tvbnow,bttvb* D# x+ ~' @0 M6 t# h* m
公仔箱論壇) k2 f* L8 }1 B1 F# a6 Q& T p# a+ `
Alaska’s Redoubt Volcano erupted five times in one night this year after almost three decades of relative quiet.
It continued erupting on and off for weeks afterward. This image was taken by the commercial satellite GeoEye-1 on March 30 when
the ash reached heights of 27,000 feet. The volcano’s alert level is still “advisory,” and the aviation color code is yellow.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。+ f2 @6 U9 e% C. D, s1 v
Redoubt is a 10,200-foot tall stratovolcano 100 miles southwest of Anchorage in the Aleutian Range, west of the Cook Inlet.% r+ Q3 Z2 m3 e
% ^8 ~: F5 O$ `' U |
Mount Etna is the second tallest volcano in Europe, at almost 11,000 feet. It is one of the most active volcanoes in
the world and is erupting nearly continuously. It is no surprise that there are many great photos of this volcano erupting, including this one $ O1 M& X/ `3 ]/ o! G: M
captured by astronauts on the International Space Station in 2002. The lighter colored plumes of smoke on the slope of the volcano in 2 j! a* T7 G. i- U* `1 w) M8 ~
this picture are from forest fires ignited by lava.tvb now,tvbnow,bttvb; R3 O0 w( x' v- r/ I
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
also be the oldest-known active volcano.www1.tvboxnow.com9 F$ m$ T) F5 j' _
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。# u: Y+ z" q' W) s4 l0 O* [
A NASA astronaut spotted this eruption of Cleveland Volcano from the International Space Station in 2006. The volcano is 5,700 feet high
and claimed the only known eruption-related death in Alaska’s Aleutian Islands in 1944. Its symmetrical, cone shape is typical of stratovolcanoes.公仔箱論壇' Y8 u1 N1 i$ `
Popoépetcatl, which means “smoking mountain” in the Aztec language, is a very active volcano just 44 miles outside Mexico City.
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 公仔箱論壇4 x* H3 y0 O, x# b" E1 c L9 Y: R0 O
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
of frequent activity. The plume reached heights of around 30,000 feet.
This eruption of Chaitén caldera in Chile was photographed from the International Space Station in May 2008. Volcanism along the tvb now,tvbnow,bttvb+ k/ j6 K5 x! J# L2 ]1 _
west coast of South America is the result of subduction of the oceanic Nazca plate beneath the South American plate.
Chaitén was last active more than 9,000 years ago. The violent 2008 eruption inundated the small coastal town of Chaitén with ash, pyroclastic
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.
This image of the Sierra Negra volcano in the Galapagos Islands was taken by NASA’s Terra satellite in 2006. Sierra Negra 公仔箱論壇* G9 l- a; F& D( {
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
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 7 G1 t7 l$ s1 I' S8 \
stationary hot spot, volcanoes are formed. The Hawaiian Islands were formed — and continue forming — the same way.
9 n# M# l, D. v) B4 [) B* DNASA’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. 2 [- c$ h( V( e2 j* y* ^* u3 C( E
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 J% r$ g; s7 b0 E, [
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, 4 H5 P* `' W' c6 I
causing avalanches of debris into the crater.
唔識形容 