Volcanic eruption explained - Steven Anderson

譯者: Lilian Chiu 審譯者: Pui-Ching Siu

In February of 1942, Mexican farmer Dionisio Pulido

1942 年 2 月，

墨西哥農民狄翁尼西歐·普利多

thought he heard thunder coming from his cornfield.

以為他聽到自己的玉米田傳來雷聲。

However, the sound wasn’t coming from the sky.

然而，這聲響並非來自天空。

The source was a large, smoking crack emitting gas and ejecting rocks.

聲源是一條巨大、冒煙的裂縫，

釋放出氣體並彈射出岩石。

This fissure would come to be known as the volcano Paricutin,

這條裂隙就是後來 為人所知的帕里庫廷火山，

and over the next 9 years, its lava and ash would cover over 200 square km.

在接下來的 9 年，

它的熔岩和灰燼覆蓋的範圍 超過 200 平方公里。

But where did this new volcano come from,

但這座新的火山從何而來？

and what triggered its unpredictable eruption?

又是什麼觸發了它無法預測的噴發？

The story of any volcano begins with magma.

任何火山的故事都始於岩漿。

Often, this molten rock forms in areas where ocean water

通常，形成這種熔岩的地方

是海水能夠鑽入地幔的地方，

is able to slip into the Earth’s mantle and lower the layer’s melting point.

因此能將該層的熔點降低。

The resulting magma typically remains under the Earth’s surface

產生出的岩漿通常會 一直留在地球表面底下，

thanks to the delicate balance of three geological factors.

背後的原因則是 三個地質因素的精密平衡。

The first is lithostatic pressure.

第一個因素是靜岩壓力。

This is the weight of the Earth’s crust pushing down on the magma below.

意思是地殼向下推擠岩漿的重量。

Magma pushes back with the second factor, magmastatic pressure.

岩漿反推回來的力量 是第二個因素，靜漿壓力。

The battle between these forces strains the third factor:

這兩股力量之間的對抗 造成了第三個因素：

the rock strength of the Earth’s crust.

地殼的岩石強度。

Usually, the rock is strong enough and heavy enough

通常，岩石夠強、夠重，

to keep the magma in place.

足以讓岩漿留在原處。

But when this equilibrium is thrown off, the consequences can be explosive.

但當這種平衡出現了偏差，

後果可能會非常具有爆發性。

One of the most common causes of an eruption

造成火山噴發最常見的原因之一，

is an increase in magmastatic pressure.

就是靜漿壓力增加。

Magma contains various elements and compounds,

岩漿包含了各種元素和化合物，

many of which are dissolved in the molten rock.

當中有許多在熔岩中溶解。

At high enough concentrations, compounds like water or sulfur no longer dissolve,

濃度夠高時，

像是水或硫這類化合物 就不會再溶解，

and instead form high-pressure gas bubbles.

反而會形成高壓的氣體泡泡。

When these bubbles reach the surface,

當這些泡泡抵達表面時，

they can burst with the force of a gunshot.

它們爆破的力量和開槍一樣。

And when millions of bubbles explode simultaneously,

當數百萬個泡泡同時爆破，

the energy can send plumes of ash into the stratosphere.

產生的能量能夠將灰燼 形成的羽狀煙雲送到平流層。

But before they pop, they act like bubbles of C02 in a shaken soda.

但在爆裂之前，

它們就像將汽水搖動之後 產生的二氧化碳泡泡。

Their presence lowers the magma’s density,

它們出現造成岩漿的密度下降，

and increases the buoyant force pushing upward through the crust.

增加向上推向地殼的浮力。

Many geologists believe this process was behind the Paricutin eruption

許多地質學家相信這是

墨西哥帕里庫廷火山 爆發背後的過程。

in Mexico.

There are two known natural causes for these buoyant bubbles.

這些浮力泡泡的 已知天然成因有兩個。

Sometimes, new magma from deeper underground

有時，在地底更深處的新岩漿

brings additional gassy compounds into the mix.

會把額外的氣體化合物 帶進混合物中。

But bubbles can also form when magma begins to cool.

但在岩漿開始冷卻時， 也有可能形成泡泡。

In its molten state, magma is a mixture of dissolved gases and melted minerals.

在熔融狀態時，岩漿是 溶解氣體與熔解礦物的混合體。

As the molten rock hardens, some of those minerals solidify into crystals.

當熔岩變硬時， 一些礦物就會固化成結晶。

This process doesn’t incorporate many of the dissolved gasses,

這個過程不會用到許多溶解的氣體，

resulting in a higher concentration of the compounds

導致形成爆炸性泡泡的 化合物有更高的濃度。

that form explosive bubbles.

Not all eruptions are due to rising magmastatic pressure—

並非所有的噴發都是 靜漿壓力升高所造成——

sometimes the weight of the rock above can become dangerously low.

有時，上方岩石的重量 會變得危險地低。

Landslides can remove massive quantities of rock from atop a magma chamber,

山崩有可能會帶走大量 在岩漿庫上方的岩石，

dropping the lithostatic pressure and instantly triggering an eruption.

讓靜岩壓力下降， 立刻觸發火山噴發。

This process is known as “unloading”

這個過程叫做「卸載」，

and it’s been responsible for numerous eruptions,

是許多火山噴發的成因，

including the sudden explosion of Mount St. Helens in 1980.

包括 1980 年 聖海倫火山的突然爆發。

But unloading can also happen over longer periods of time

但，就較長的時間來看，

侵蝕或者冰河融化 也有可能造成卸載。

due to erosion or melting glaciers.

In fact, many geologists are worried that glacial melt

事實上，許多地質學家擔心

氣候變遷所造成的冰河融化 有可能會增加火山活動。

caused by climate change could increase volcanic activity.

Finally, eruptions can occur when the rock layer is no longer strong enough

最後，當岩石層的強度 不再足以壓住下方的岩漿時，

to hold back the magma below.

也會發生噴發。

Acidic gases and heat escaping from magma

透過一個叫做熱液蝕變的過程，

can corrode rock through a process called hydrothermal alteration,

從岩漿漏出的酸性氣體 和熱氣就會腐蝕岩石，

gradually turning hard stone into soft clay.

漸漸將堅硬的岩石轉變為軟泥土。

The rock layer could also be weakened by tectonic activity.

岩石層也有可能 因為板塊活動而變弱。

Earthquakes can create fissures allowing magma to escape to the surface,

地震可能會造成裂縫， 讓岩漿能滲出地表，

and the Earth’s crust can be stretched thin

且當板塊彼此遠離時，

as continental plates shift away from each other.

地殼就可能因被拉伸而變薄。

Unfortunately, knowing what causes eruptions

不幸的是，知道噴發的成因

doesn’t make them easy to predict.

並不能協助預測噴發。

While scientists can roughly determine the strength and weight

雖然科學家可以大略判斷出 地殼的強度和重量，

of the Earth’s crust,

the depth and heat of magma chambers makes measuring changes

岩漿庫的深度和熱度

讓測量靜漿壓力變化非常困難。

in magmastatic pressure very difficult.

But volcanologists are constantly exploring new technology

但，火山學家經常在探索新技術

to conquer this rocky terrain.

來克服這多岩的地形。

Advances in thermal imaging have allowed scientists

熱成像的進步讓科學家 可以偵測出地下的熱點。

to detect subterranean hotspots.

Spectrometers can analyze gases escaping magma.

光譜儀可以分析從岩漿漏出的氣體。

And lasers can precisely track the impact of rising magma on a volcano’s shape.

雷射可以精準追蹤 岩漿上升對於火山形狀的影響。

Hopefully, these tools will help us better understand these volatile vents

希望這些工具能協助我們 更了解這些不穩定的噴發口

and their explosive eruptions.

以及它們的爆發性噴發。