How tsunamis work - Alex Gendler

海嘯如何運作—愛麗克絲 • 珍德勒 (Alex Gendler)

譯者: Elly Shih 審譯者: Yao-Jen Chang

In 479 BC, when Persian soldiers besieged

西元前479年，波斯士兵圍攻

the Greek city of Potidaea,

波提狄亞的希臘城邦時，

the tide retreated much farther than usual,

當時的海潮退得比平時更遠，

leaving a convenient invasion route.

剛好方便波斯士兵入侵。

But this wasn't a stroke of luck.

但這並非好運。

Before they had crossed halfway,

就在穿越到一半前，

the water returned in a wave higher than anyone had ever seen,

退去的海水卻更高打回來，

其浪高沒人見識過，

drowning the attackers.

淹死了進攻的波斯士兵。

The Potiidaeans believed they had been saved

波提狄亞人相信是敵軍激怒了海神

by the wrath of Poseidon.

而救了他們。

But what really saved them

但真正救了他們的

was likely the same phenomenon that has destroyed countless others:

其實是摧毀無數生命的自然現象：

a tsunami.

海嘯。

Although tsunamis are commonly known as tidal waves,

雖然海嘯又稱為潮汐波，

they're actually unrelated to the tidal activity caused

但它們與受太陽、月球引力作用

by the gravitational forces of the Sun and Moon.

所形成的潮汐活動並沒有關連。

In many ways, tsunamis are just larger versions of regular waves.

許多方面看來，海嘯其實只不過是

放大版的正常海浪。

They have a trough and a crest,

它們都有波谷及波峰，

and consist not of moving water,

靠的不是流動的海水，

but the movement of energy through water.

而是海水中能量的移動。

The difference is in where this energy comes from.

其不同之處在於能量的來源。

For normal ocean waves, it comes from wind.

一般海浪的形成，

風是其能量來源。

Because this only affects the surface, the waves are limited in size and speed.

由於風的影響僅止於海平面，

海浪的大小和流速因此有限。

But tsunamis are caused by energy originating underwater,

海嘯的形成

則是源於水面下的能量。

from a volcanic eruption,

如火山爆發、

a submarine landslide,

海底崩移、

or most commonly, an earthquake on the ocean floor

或更常見的

海底地震，

caused when the tectonic plates of the Earth's surface slip,

地球表面的地殼板塊滑動時，

releasing a massive amount of energy into the water.

釋放大量能量至水中 而產生海底地震。

This energy travels up to the surface,

這些能量傳達到海面，

displacing water and raising it above the normal sea level,

導致水位變化

高過一般海平面，

but gravity pulls it back down,

然而，地心引力造成的拉力，

which makes the energy ripple outwards horizontally.

使得能量以水平方向波動，

Thus, the tsunami is born,

海嘯因此而生，

moving at over 500 miles per hour.

移動時速超過500英哩。

When it's far from shore, a tsunami can be barely detectable

當海嘯距離岸邊較遠時，

很難被人察覺，

since it moves through the entire depth of the water.

因為它移動的是整個從 海面到海底的水層。

But when it reaches shallow water, something called wave shoaling occurs.

然而，當海嘯到達淺水域時，

便出現波浪淺化效應。

Because there is less water to move through,

因為可移動的海水變少，

this still massive amount of energy is compressed.

不變的巨大能量被壓縮。

The wave's speed slows down,

海浪的流速因此變緩，

while its height rises to as much as 100 feet.

浪高則可高達100英呎。

The word tsunami, Japanese for "harbor wave,"

tsunami（海嘯）一詞

在日文意指「港口的波浪」，

comes from the fact that it only seems to appear near the coast.

是因為它似乎只出現在

靠近海岸的地方。

If the trough of a tsunami reaches shore first,

如果海嘯的波谷先抵達海岸，

the water will withdraw farther than normal

在浪打過來前，海水會退得比平時更遠，

before the wave hits,

這可是有誤導性的危險。

which can be misleadingly dangerous.

A tsunami will not only drown people near the coast,

海嘯不僅會淹沒岸邊的人們，

but level buildings and trees for a mile inland or more,

內陸一英哩或以上的建築物和樹木 也會被摧毀，

especially in low-lying areas.

特別是低窪地區。

As if that weren't enough, the water then retreats,

如果這還不夠糟，

當海水退去時，

dragging with it the newly created debris,

將一併帶走新的殘骸、

以及不幸在它所經之處的

and anything, or anyone, unfortunate enough

to be caught in its path.

任何東西和人。

The 2004 Indian Ocean tsunami

2004年的印度洋海嘯

was one of the deadliest natural disasters in history,

是史上最致命的自然災害之一，

killing over 200,000 people throughout South Asia.

造成整個南亞地區超過20萬人喪生。

So how can we protect ourselves against this destructive force of nature?

所以面對大自然的破壞力，

我們該如何自保？

People in some areas have attempted

有些地區的人們

to stop tsunamis with sea walls, flood gates,

試圖靠海堤、防洪閘門和渠道

and channels to divert the water.

來疏導海水，藉以抵擋海嘯。

But these are not always effective.

但這些方法並非每次都奏效。

In 2011, a tsunami surpassed the flood wall

2011年的一次海嘯 便越過用來保護

protecting Japan's Fukushima Power Plant,

日本福島核電廠的防洪牆，

causing a nuclear disaster

導致核災事故，

in addition to claiming over 18,000 lives.

同時帶走超過1萬8千多條人命。

Many scientists and policy makers are instead focusing on early detection,

許多科學家和決策者

將重點放在早期預警系統，

monitoring underwater pressure and seismic activity,

監測水面下壓力及地震活動，

and establishing global communication networks

並建立全球通訊網絡

for quickly distributing alerts.

以利快速發佈警報。

當大自然的力量 太過強大無法阻擋時，

When nature is too powerful to stop,

the safest course is to get out of its way.

最安全的作法就是別擋它的路。