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  • In 479 BC, when Persian soldiers be seiged

    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

    退去的海水卻更高打回來,

  • than anyone had ever seen,

    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 was likely

    但真正救了他們的

  • 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

    許多方面看來,海嘯其實只不過是

  • of regular waves.

    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,

    一般海浪的形成,

  • it comes from wind.

    風是其能量來源。

  • Because this only affects the surface,

    由於風的影響僅止於海平面,

  • the waves are limited in size and speed.

    海浪的大小和流速因此有限。

  • But tsunamis are caused by energy

    海嘯的形成

  • originating underwater,

    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,

    或更常見的

  • an earthquake on the ocean floor

    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

    導致水位變化

  • the normal sea level,

    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,

    當海嘯距離岸邊較遠時,

  • a tsunami can be barely detectable

    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,

    然而,當海嘯到達淺水域時,

  • something called wave shoaling occurs.

    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,

    tsunami(海嘯)一詞

  • Japanese for "harbor wave,"

    在日文意指「港口的波浪」,

  • comes from the fact that it only seems to appear

    是因為它似乎只出現在

  • near the coast.

    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, which can be misleadingly dangerous.

    這可是有誤導性的危險。

  • 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,

    如果這還不夠糟,

  • the water then retreats,

    當海水退去時,

  • dragging with it the newly created debris,

    將一併帶走新的殘骸、

  • and anything, or anyone, unfortunate enough

    以及不幸在它所經之處的

  • 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

    所以面對大自然的破壞力,

  • against this destructive force of nature?

    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 in addition to claiming

    導致核災事故,

  • 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

    許多科學家和決策者

  • focusing on early detection,

    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。

  • When nature is too powerful to stop,

    當大自然的力量 太過強大無法阻擋時,

  • the safest course is to get out of its way.

    最安全的作法就是別擋它的路。

In 479 BC, when Persian soldiers be seiged

西元前479年,波斯士兵圍攻

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B2 中高級 中文 美國腔 TED-Ed 海嘯 海水 能量 海浪 地震

【TED-Ed】海嘯如何運作 (How tsunamis work - Alex Gendler)

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    Zenn 發佈於 2014 年 06 月 14 日
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