Volcanoes — earth-shattering news

火山—驚天動地的新聞

When Mount Pinatubo suddenly erupted on 9 June 1991, the power of volcanoes past and present again hit the headlines.

當(dāng)1991年皮納圖博火山突然爆發(fā)時(shí)，有關(guān)過去和現(xiàn)在火山威力的文章再一次登上了頭。

A?

Volcanoes are the ultimate earth-moving machinery. A violent eruption can blow the top few kilometers off a mountain, scatter fine ash practically all over the globe and hurl rock fragments into the stratosphere to darken the skies a continent away.

火山是終極的“鏟土機(jī)器‘”。一次猛烈的爆發(fā)可以轟掉幾千米高的山頭，細(xì)碎的火山灰灑遍全球，碎石炸入平流層，遮住了整片大陸的天空。

But the classic eruption — cone-shaped mountain, big bang, mushroom cloud and surges of molten lava — is only a tiny part of a global story. Volcanism, the name given to volcanic processes, really has shaped the world. Eruptions have rifted continents, raised mountain chains, constructed islands and shaped the topography of the earth. The entire ocean floor has a basement of volcanic basalt.

然而，典型的火山噴發(fā)——錐形山體，大爆炸，蘑菇云和噴出的熔巖——只是全球火山故事中的一小部分。火山作用，也叫作火山活動，其實(shí)塑造了我們的世界?；鹕絿姲l(fā)撕裂了大陸，抬升了山脈，組建了島嶼，還塑造了地球的地形。五大洋的海底基石就是火山玄武巖。

Volcanoes have not only made the continents, they are also thought to have made the world’s first stable atmosphere and provided all the water for the oceans, rivers and ice-caps. There are now about 600 active volcanoes. Every year they add two or three cubic kilometers of rock to the continents. Imagine a similar number of volcanoes smoking away for the last 3,500 million years. That is enough rock to explain the continental crust.

火山不只組成了大陸，有人認(rèn)為，它們也制造了世界上第一個(gè)穩(wěn)定的大氣層，并且為所有的大洋、河流和冰川提供水資源?，F(xiàn)在，世界上大約有600個(gè)活火山。這些火山每年為大陸增加兩到三立方公里的巖石。試想一下，在過去的35億年中，每年都有大約同等數(shù)量的火山灰。這就足夠解釋我們地殼的來源了。

What comes out of volcanic craters is mostly gas. More than 90% of this gas is water vapor from the deep earth: enough to explain, over 3,500 million years, the water in the oceans. The rest of the gas is nitrogen, carbon dioxide, sulphur dioxide, methane, ammonia and hydrogen. The quantity of these gases, again multiplied over 3,500 million years, is enough to explain the mass of the world’s atmosphere. We are alive because?volcanoes provided the soil, air and water we need.?

火山口中噴出的大部分是氣體。超過90%的氣體是地球深處的水蒸氣：這就能夠解釋，經(jīng)過了35億年，大洋中的水從哪里來。剩下的氣體是氮?dú)?、二氧化碳、二氧化硫、甲烷、氨氣和氫氣。同樣?jīng)過35億年的疊加，這些氣體的數(shù)量就足夠解釋地球大氣層之“大”了。我們之所以活著，就是因?yàn)榛鹕教峁┝宋覀兯枰耐寥?，空氣和水?/p>

B?

Geologists consider the earth as having a molten core, surrounded by a semi-molten mantle and a brittle, outer skin. It helps to think of a soft-boiled egg with a runny yolk, a firm but squishy white and a hard shell. If the shell is even slightly cracked during boiling, the white material bubbles out and sets like a tiny mountain chain over the crack — like an archipelago of volcanic islands such as the Hawaiian Islands. But the earth is so much bigger and the mantle below is so much hotter.

地理學(xué)家認(rèn)為地球有一個(gè)融化的核心，周圍包裹著半融化的地幔和脆脆的外皮。想象一個(gè)半熟的雞蛋能夠幫助我們理解——流淌的蛋黃，堅(jiān)實(shí)又粘稠的淡定和堅(jiān)硬的蛋殼。在沸水中煮雞蛋時(shí)，如果蛋殼有一點(diǎn)點(diǎn)破碎，白色的蛋清就會冒出泡泡來，在裂縫外面形成一條小小的火山鏈——很像夏威夷島嶼一樣的火山群島。但是地球要大得多，里面的地幔也燙的多。

Even though the mantle rocks are kept solid by overlying pressure, they can still slowly ‘flow’ like thick treacle. The flow, thought to be in the form of convection currents, is powerful enough to fracture the ‘eggshell’ of the crust into plates, and keep them bumping and grinding against each other, or even overlapping, at the rate of a few centimeters a year. These fracture zones, where the collisions occur, are where earthquakes happen. And, very often, volcanoes.

即使地幔巖石在上覆地層壓力下保持穩(wěn)定，他們還是可以像濃稠的糖漿一樣緩慢地流淌。人們認(rèn)為這種流淌是以對流形式進(jìn)行的，其力量足以使地殼這個(gè)“蛋殼”破裂成為板塊，并互相碰撞摩擦，，甚至以每年幾厘米的速度互相重疊。這些破碎的地方，就是碰撞發(fā)生的地方，也是地震發(fā)生之處。更是火山經(jīng)常噴發(fā)的地方。

C?

These zones are lines of weakness, or hot spots. Every eruption is different, but put at its simplest, where there are weaknesses, rocks deep in the mantle, heated to 1,350℃，will start to expand and rise. As they do so, the pressure drops, and they expand and become liquid and rise more swiftly.

這些地方是脆弱帶，或熱點(diǎn)。每個(gè)火山噴發(fā)都是不同的，但是簡而言之，在地殼比較脆弱的地方只要地幔深處的巖石加熱到1350℃，就會開始膨脹上升。一旦它們開始這樣做，壓力就會變小，接著它們會膨脹成為液體，然后迅速上漲。

Sometimes it is slow: vast bubbles of magma — molten rock from the mantle — inch towards the surface, cooling slowly, to show through as granite extrusions(as on Skye, or the Great Whin Sill, the lava dyke squeezed out like toothpaste that carries part of Hadrian’s Wall in northern England). Sometimes — as in Northern Ireland, Wales and the Karoo in South Africa — the magma rose faster, and then flowed out horizontally on?to the surface in vast thick sheets. In the Deccan plateau in western India, there are more than two million cubic kilometers of lava, some of it 2,400 meters thick, formed over 500,000 years of slurping eruption.

有時(shí)這個(gè)過程很慢：巖漿（融化的地幔巖石）的巨大泡泡不斷接近地表，慢慢降溫，最后成為顯露出的花崗巖凸起（例如在斯凱島或大玄武巖，熔巖堤壩像牙膏一樣被擠出來，成為英格蘭北部哈德良長城的一部分）。有時(shí)候——例如在北愛爾蘭、威爾士和南非的卡魯——巖漿上升得很快，然后以大厚片的形式垂直涌出地表。在印度西部的德干高原，經(jīng)過50萬年的噴發(fā)，形成了超過200萬立方公里的巖漿，有的有2400米厚。

Sometimes the magma moves very swiftly indeed. It does not have time to cool as it surges upwards. The gases trapped inside the boiling rock expand suddenly, the lava glows with heat, it begins to froth, and it explodes with tremendous force. Then the slightly cooler lava following it begins to flow over the lip of the crater. It happens on Mars, it happened on the moon, it even happens on some of the moons of Jupiter and Uranus. By studying the evidence, volcanologists can read the force of the great blasts of the past. Is the pumice light and full of holes? The explosion was tremendous. Are the rocks heavy, with huge crystalline basalt shapes, like the Giant’s Causeway in Northern Ireland? It was a slow, gentle eruption.

有時(shí)候巖漿移動十分迅速。在噴發(fā)時(shí)沒有時(shí)間冷卻。沸騰的巖石中包裹的氣體突然膨脹，巖漿因?yàn)槭軣岫W閃發(fā)光，它開始泛起泡沫，接著以巨大的威力爆炸。然后，下面稍稍冷卻的巖漿開始冒出火山口。這種事情發(fā)生在火星、月球，甚至是木星和天王星的衛(wèi)星上。通過研究這些證據(jù)，火山學(xué)家就可以理解過去大噴發(fā)的威力。浮巖是不是又輕有充滿小孔？那么這是一次巨大的噴發(fā)。巖石是不是很重，形狀又像北愛爾蘭巨人堤的結(jié)晶玄武巖？那么這是一次緩慢又溫和的噴發(fā)。

The biggest eruptions are deep on the mid-ocean floor, where new lava is forcing the continents apart and widening the Atlantic by perhaps five centimeters a year. Look at maps of volcanoes, earthquakes and island chains like the Philippines and Japan, and you can see the rough outlines of what are called tectonic plates — the plates which make up the earth’s crust and mantel. The most dramatic of these is the Pacific ‘ring of fire’ where there have been the most violent explosions — Mount Pinatubo near Manila, Mount St Helen’s in the Rockies and El Chichón in Mexico about a decade ago, not to mention world-shaking blasts like Krakatoa in the Sunda Straits in 1883.

最為劇烈的噴發(fā)是在大洋中間深深的海底，在那里，新的巖漿正在把大陸撕開，并且以每年五厘米的速度使大西洋不斷變寬?？纯椿鹕?、地震、以及菲律賓和日本這樣的島鏈地圖，你就會大致看出地球所謂的構(gòu)造板塊——這些板塊組成了地殼和地幔。其中最明顯的例子就是太平洋“火環(huán)”，這是最為劇烈的一次噴發(fā)——馬尼拉附近的Mount Pinatubo、落基山脈中的Mount St Helen’以及十年前墨西哥的El Chichón，更不要提撼動世界的大噴發(fā)，例如1883年于蘇丹海峽的Krakatoa。

D?

But volcanoes are not very predictable. That is because geological time is not like human time. During quiet periods, volcanoes cap themselves with their own lava by?forming a powerful cone from the molten rocks slopping over the rim of the crater; later the lava cools slowly into a huge, hard, stable plug which blocks one further eruption until the pressure below becomes irresistible. In the case of Mount Pinatubo, this took 600 years.

但是火山是不能預(yù)測的。這是因?yàn)榈刭|(zhì)時(shí)間與人類時(shí)間不同。在休眠期，火山用溢出火山口的熔巖形成堅(jiān)硬的椎體，將自己掩蓋起來；待熔巖漸漸冷卻成為巨大堅(jiān)硬、穩(wěn)定的塞子，就可以組織進(jìn)一步的噴發(fā)，直到下面的壓力大到不可阻擋位置。例如Mount Pinatubo，這個(gè)過程花了600年。

Then, sometimes, with only a small warning, the mountain blows its top. It did this at Mont Pelée in Martinique at 7.49 a.m. on 8 May, 1902. Of a town of 28,000, only two people survived. In 1815, a sudden blast removed the top 1,280 meters of Mount Tambora in Indonesia. The eruption was so fierce that dust thrown into the stratosphere darkened the skies, cancelling the following summer in Europe and North America. Thousands starved as the harvests failed, after snow in June and frosts in August. Volcanoes are potentially world news, especially the quiet ones.

接著，有時(shí)候，僅僅一個(gè)小的預(yù)警，一座火山就噴發(fā)了。1902年5月8日早晨7點(diǎn)49，在Martinique的Mont Pelée就發(fā)生了這樣的事情。只有兩個(gè)人幸存。在1815年，印度尼西亞的Mount Tambora突然噴發(fā)，炸掉了1280米的山頭。火山噴發(fā)是如此的劇烈，以至于揚(yáng)起的灰塵進(jìn)入平流層，遮住了填空，阻擋了歐洲和北美洲接下來的夏天。經(jīng)過了六月飛雪和八月下霜后，成千上萬人忍受著饑餓，農(nóng)民也沒有收成。火山是潛在的世界新聞，尤其是那些安靜的火山。