Volcanoes — earth-shattering news

火山—惊天动地的新闻

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

当1991年皮纳图博火山突然爆发时，有关过去和现在火山威力的文章再一次登上了头。

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.

火山是终极的“铲土机器‘”。一次猛烈的爆发可以轰掉几千米高的山头，细碎的火山灰洒遍全球，碎石炸入平流层，遮住了整片大陆的天空。

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，典型的火山喷发——锥形山体，大爆炸，蘑菇云和喷出的熔岩——只是全球火山故事中的一小部分。火山作用，也叫作火山活动，其实塑造了我们的世界。火山喷发撕裂了大陆，抬升了山脉，组建了岛屿，还塑造了地球的地形。五大洋的海底基石就是火山玄武岩。

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.

火山不只组成了大陆，有人认为，它们也制造了世界上第一个稳定的大气层，并且为所有的大洋、河流和冰川提供水资源。现在，世界上大约有600个活火山。这些火山每年为大陆增加两到三立方公里的岩石。试想一下，在过去的35亿年中，每年都有大约同等数量的火山灰。这就足够解释我们地壳的来源了。

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. 

火山口中喷出的大部分是气体。超过90%的气体是地球深处的水蒸气：这就能够解释，经过了35亿年，大洋中的水从哪里来。剩下的气体是氮气、二氧化碳、二氧化硫、甲烷、氨气和氢气。同样经过35亿年的叠加，这些气体的数量就足够解释地球大气层之“大”了。我们之所以活着，就是因为火山提供了我们所需要的土壤，空气和水。

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.

地理学家认为地球有一个融化的核心，周围包裹着半融化的地幔和脆脆的外皮。想象一个半熟的鸡蛋能够帮助我们理解——流淌的蛋黄，坚实又粘稠的淡定和坚硬的蛋壳。在沸水中煮鸡蛋时，如果蛋壳有一点点破碎，白色的蛋清就会冒出泡泡来，在裂缝外面形成一条小小的火山链——很像夏威夷岛屿一样的火山群岛。但是地球要大得多，里面的地幔也烫的多。

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.

即使地幔岩石在上覆地层压力下保持稳定，他们还是可以像浓稠的糖浆一样缓慢地流淌。人们认为这种流淌是以对流形式进行的，其力量足以使地壳这个“蛋壳”破裂成为板块，并互相碰撞摩擦，，甚至以每年几厘米的速度互相重叠。这些破碎的地方，就是碰撞发生的地方，也是地震发生之处。更是火山经常喷发的地方。

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.

这些地方是脆弱带，或热点。每个火山喷发都是不同的，但是简而言之，在地壳比较脆弱的地方只要地幔深处的岩石加热到1350℃，就会开始膨胀上升。一旦它们开始这样做，压力就会变小，接着它们会膨胀成为液体，然后迅速上涨。

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.

有时这个过程很慢：岩浆（融化的地幔岩石）的巨大泡泡不断接近地表，慢慢降温，最后成为显露出的花岗岩凸起（例如在斯凯岛或大玄武岩，熔岩堤坝像牙膏一样被挤出来，成为英格兰北部哈德良长城的一部分）。有时候——例如在北爱尔兰、威尔士和南非的卡鲁——岩浆上升得很快，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，经过50万年的喷发，形成了超过200万立方公里的岩浆，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.

有时候岩浆移动十分迅速。在喷发时没有时间冷却。沸腾的岩石中包裹的气体突然膨胀，岩浆因为受热而闪闪发光，它开始泛起泡沫，接着以巨大的威力爆炸。然后，下面稍稍冷却的岩浆开始冒出火山口。这种事情发生在火星、月球，甚至是木星和天王星的卫星上。通过研究这些证据，火山学家就可以理解过去大喷发的威力。浮岩是不是又轻有充满小孔？那么这是一次巨大的喷发。岩石是不是很重，形状又像北爱尔兰巨人堤的结晶玄武岩？那么这是一次缓慢又温和的喷发。

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.

最为剧烈的喷发是在大洋中间深深的海底，在那里，新的岩浆正在把大陆撕开，并且以每年五厘米的速度使大西洋不断变宽。看看火山、地震、以及菲律宾和日本这样的岛链地图，你就会大致看出地球所谓的构造板块——这些板块组成了地壳和地幔。其中最明显的例子就是太平洋“火环”，这是最为剧烈的一次喷发——马尼拉附近的Mount Pinatubo、落基山脉中的Mount St Helen’以及十年前墨西哥的El Chichón，更不要提撼动世界的大喷发，例如1883年于苏丹海峡的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.

但是火山是不能预测的。这是因为地质时间与人类时间不同。在休眠期，火山用溢出火山口的熔岩形成坚硬的椎体，将自己掩盖起来；待熔岩渐渐冷却成为巨大坚硬、稳定的塞子，就可以组织进一步的喷发，直到下面的压力大到不可阻挡位置。例如Mount Pinatubo，这个过程花了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.

接着，有时候，仅仅一个小的预警，一座火山就喷发了。1902年5月8日早晨7点49，在Martinique的Mont Pelée就发生了这样的事情。只有两个人幸存。在1815年，印度尼西亚的Mount Tambora突然喷发，炸掉了1280米的山头。火山喷发是如此的剧烈，以至于扬起的灰尘进入平流层，遮住了填空，阻挡了欧洲和北美洲接下来的夏天。经过了六月飞雪和八月下霜后，成千上万人忍受着饥饿，农民也没有收成。火山是潜在的世界新闻，尤其是那些安静的火山。