How tsunamis work - Alex Gendler · TED-Ed
了解海啸的成因和破坏力，学习相关词汇和表达，适合练习自然与科技类话题。
In 479 BC, when Persian soldiers besieged the Greek city of Potidaea, the tide retreated much farther than usual,
公元前479年，当波斯军队围攻希腊城市波提代亚时，海潮退去的幅度比平常要大得多。
leaving a convenient invasion route.
这为入侵者提供了一条便捷的路线。
But this wasn't a stroke of luck.
但这绝不是运气使然。
Before they had crossed halfway, the water returned in a wave higher than anyone had ever seen, drowning the attackers.
在他们刚走过一半路程时，海水突然以前所未有的高度涌了上来，将所有攻击者都淹没了。
The Potiidaeans believed they had been saved by the wrath of Poseidon.
波提伊德家族（Potiidae）的人们相信，是他们得到了波塞冬（Poseidon）的庇护才得以幸免于难。
But what really saved them was likely the same phenomenon that has destroyed countless others: a tsunami.
但真正拯救他们的，很可能是那种曾经摧毁过无数其他事物的现象——海啸。
Although tsunamis are commonly known as tidal waves, they're actually unrelated to the tidal activity caused by the gravitational forces of the Sun and Moon.
虽然海啸通常被称为“潮波”，但实际上它们与由太阳和月亮的引力作用引起的潮汐现象并无关联。
In many ways, tsunamis are just larger versions of regular waves.
在很多方面，海啸只不过是普通海浪的“放大版”而已。
They have a trough and a crest, and consist not of moving water, but the movement of energy through water.
它们具有低谷（即能量最低的区域）和高峰（即能量最高的区域），其本质并非由流动的水体构成，而是由能量在水中的传递所形成的现象。
The difference is in where this energy comes from.
这种能量的来源不同，这就是它们之间的区别所在。
For normal ocean waves, it comes from wind.
对于普通的海浪来说，它们的形成原因在于风的作用。
Because this only affects the surface, the waves are limited in size and speed.
由于这种影响仅限于表面，因此海浪的规模和速度都受到限制。
But tsunamis are caused by energy originating underwater, from a volcanic eruption, a submarine landslide, or most commonly,
但海啸是由水下产生的能量引发的——这些能量可能来自火山喷发、海底滑坡，或者最常见的原因。
an earthquake on the ocean floor caused when the tectonic plates of the Earth's surface slip, releasing a massive amount of energy into the water.
海底地震是由于地球表面的构造板块发生滑动而引发的，这种滑动将大量能量释放到海水中。
This energy travels up to the surface, displacing water and raising it above the normal sea level, but gravity pulls it back down,
这种能量会向上传递到海面，将海水挤出海平面并使其高于正常海平面；不过重力的作用又会使海水重新回落至海平面。
which makes the energy ripple outwards horizontally.
这使得能量以水平方向向外扩散（即形成“能量涟漪”）。
Thus, the tsunami is born, moving at over 500 miles per hour.
就这样，海啸形成了，其传播速度超过了每小时500英里。
When it's far from shore, a tsunami can be barely detectable since it moves through the entire depth of the water.
当海啸远离海岸时，由于其波涛会穿过整个海水层，因此几乎无法被察觉。
But when it reaches shallow water, something called wave shoaling occurs.
但是当海水进入浅水区域时，就会发生一种被称为“波浪浅化”的现象。
Because there is less water to move through, this still massive amount of energy is compressed.
由于可供水流通过的水量减少了，因此这仍然巨大的能量被压缩了。
The wave's speed slows down, while its height rises to as much as 100 feet.
海浪的传播速度变慢了，但其高度却上升到了100英尺（约30米）。
The word tsunami, Japanese for "harbor wave," comes from the fact that it only seems to appear near the coast.
海啸”（tsunami）这个词在日语中意为“港湾中的巨浪”；它之所以被称为“海啸”，是因为这种现象似乎只发生在海岸附近。
If the trough of a tsunami reaches shore first, the water will withdraw farther than normal before the wave hits,
如果海啸的最低水位先到达海岸，那么在海浪真正涌来之前，海水会比正常情况下退得更加远。
which can be misleadingly dangerous.
这可能会带来极其危险的后果（甚至具有误导性）。
A tsunami will not only drown people near the coast, but level buildings and trees for a mile inland or more,
海啸不仅会淹没沿海地区的人们，还会将建筑物和树木摧毁，其影响范围可延伸至内陆一英里甚至更远的地方。
especially in low-lying areas.
尤其是在地势低洼的地区。
As if that weren't enough, the water then retreats, dragging with it the newly created debris, and anything,
仿佛这还不够似的，海水随后又会退去，同时将新形成的碎屑以及所有其他物质一并带走。
or anyone, unfortunate enough to be caught in its path.
或者任何不幸被卷入其中的人。
The 2004 Indian Ocean tsunami was one of the deadliest natural disasters in history, killing over 200,000 people throughout South Asia.
2004年印度洋海啸是历史上最致命的自然灾害之一，导致南亚地区超过20万人丧生。
So how can we protect ourselves against this destructive force of nature?
那么，我们该如何保护自己免受这种具有破坏性的自然力量的伤害呢？
People in some areas have attempted to stop tsunamis with sea walls, flood gates, and channels to divert the water.
在一些地区，人们试图通过建造海堤、防洪闸以及设置导流渠道来阻止海啸的侵袭，从而将海水引向其他方向。
But these are not always effective.
但这些方法并不总是有效的。
In 2011, a tsunami surpassed the flood wall protecting Japan's Fukushima Power Plant, causing a nuclear disaster in addition to claiming over 18,000 lives.
2011年，一场海啸冲破了保护日本福岛核电站的防波堤，不仅引发了核灾难，还导致超过1.8万人丧生。
Many scientists and policy makers are instead focusing on early detection, monitoring underwater pressure and seismic activity, and establishing global communication networks for quickly distributing alerts.
许多科学家和政策制定者转而将重点放在早期检测、监测水下压力及地震活动上，并建立全球通信网络，以便迅速发布警报。
When nature is too powerful to stop, the safest course is to get out of its way.
当自然的力量过于强大、无法被阻挡时，最安全的做法就是远离它的影响范围。