This is Siwa.
这是锡瓦
It’s a crowed place with bustling markets
是个拥挤的地方 有着繁忙的集市
and around 33,000 people.
和大约33000人口
Here you can find farms which grow things like dates and olives
在这里 你会发现种植海枣和橄榄等作物的农场
and trees grow as far as the eye can see.
目所能及之处皆为树木
Siwa has been permanently inhabited since the 10th millenium BCE
自公元前10世纪 或是约12000年以来
or for roughly 12 thousand years.
锡瓦一直有人居住
The city contains several archaeological sites
这座城市有数个考古遗址
and is even the site of an oracle temple for the Egyptian deity Amun.
埃及神祇阿蒙的神庙遗址甚至就在此地
What’s all about Siwa is that it’s located here,
外界只知道锡瓦坐落在此
completely isolated in the Egyptian portion of the Sahara desert.
完全隔绝在埃及境内的撒哈拉沙漠中
The nearest big city is 460 kilometres away in Alexandria,
离它最近的大城市是亚历山大市 远在460千米外
and the ocean at its closest is 260 kilometres away.
最近的海洋则在260千米外
This deep in the desert, Siwa receives only 9 inches of rainfall a year,
锡瓦地处沙漠深处 年降雨量不过9英寸
and temperatures in the summer have reached a blistering 118.8°F.
而夏季的气温已经高达118.8°F
Just outside the limits of Siwa,
巨大而壮观的沙丘
tremendous and imposing sand dunes linger,
就徘徊在锡瓦的边界外
constantly threatening to advance.
时刻威胁着前进
So how can a place so deep in the desert
那么 一个如此深入沙漠的地方
be so rich with people, vegetation and history?
怎会居民众多 植被茂盛 历史丰富呢？
Well, as it turns out, Siwa isn’t just a city,
原来锡瓦不止是一座城
but rather an oasis, a fertile patch,
还是一片绿洲 一片沃土
and otherwise endlessly barren land.
在它之外则是无垠的贫瘠之地
But what exactly is an oasis and how do they form?
绿洲究竟是什么？又是如何形成？
In the past, the desert oases have served a crucial role in trade and travel
过去 沙漠中的绿洲是舒适的停靠点
as hospitable stopping points
它们嵌在广阔的沙漠中
wedged between vast expanses of sand and stone.
对旅游和贸易起着至关重要的作用
In places like Siwa, merchants and traders could rest,
在锡瓦这样的地方 来往客商可以停下休息
resupply and most importantly refill the waterskins.
补足物资 最重要的是重新装满水袋
Most oases will have fresh water springs or ponds
大部分绿洲都有位于地表的
above the surface open to the air,
露天淡水泉或淡水池塘
and this is what allows both people and plants to inhabit the area.
这是人和植物能够在此栖息的保障
But a look from above reveals no river
但从空中俯瞰 不见河流
or even stream feeding into these ponds.
甚至不见小溪流入这些池塘
And as I mentioned earlier,
我之前提起过
areas like this received little to no rainfall annually.
这样的地区年降雨量很少 几乎为零
So where does this life-giving water come from then?
那么 这生命之水又如何而来呢？
Let’s keep using Siwa as an example.
依旧以锡瓦为例
Well, this land may receive just a few inches of rainfall a year,
这片土地的年降雨量或许不过几英寸
over a big enough area,
但在一片足够大的区域
a couple inches can add up to a huge amount of water.
几英寸降雨量相加 可得大量的水
And you’ll typically find an oasis at a low point in the desert.
你会发现绿洲通常位于沙漠的低洼处
A look at a elevation map shows the Siwa oasis to be right
地形图显示 锡瓦位于大洼地的正中间
in the middle of a depression, beside the larger Qatar Depression.
在更大的卡塔尔洼地旁
In fact, most of the Siwa oases lies at roughly 19 metres below sea level.
实际上 锡瓦绿洲大部分低于海平面约19米
So, the Siwa and other oases are essentially funnels
因此 锡瓦和其它绿洲实为漏斗
for all water from surrounding areas to flow into.
周边地区所有的水都会流入那里
But again, there aren’t any rivers or streams on the surface
但需要重申 地表没有任何河流或溪流
to bring water to these places,
将水带入这些绿洲
so how does it get there?
那么水是如何流入？
Well, beneath the surface of all land,
在所有土地的表层之下
there is an area where rainwater collects.
有一个收集雨水的区域
We call this an “aquifer”.
我们称之为“地下蓄水层”
If it rains a lot, the average of the aquifer
如果降雨量大 蓄水层的平均水位
called “the water table” will rise.
即“地下水位”会上升
If it rains very little, the water table will drop.
如果降雨量很小 水位会下降
It’s by taking advantage of underground aquifers
正是利用了地下蓄水层
that things like wells and irrigation systems work.
水井和灌溉系统等工程才能运行
Naturally, where the elevation of the earth is higher,
地面海拔越高的地方
so to will the water table be.
地下水位也自然越高
So if you have areas of high elevation
因此 如果是高海拔地区
like towering sand dunes or hills,
比如高耸的沙丘或山丘
directly next to areas of low elevation like a depression,
紧挨着低海拔地区 如洼地
you can get spots like this
便能看到这样的地方
where the water table nears or even exceeds the surface.
那里的地下水位临近地表 甚至超过地表
At these places, water will see from the ground and all into bodies of water.
这些地方的水会露出地面 全部流入水域
Where there is water, there is life.
有水之处即有生命
And while most desert plants are short and dense,
尽管大多数沙漠植物矮小密集
under the right conditions, they too can grow to be tall and lush.
但如果条件合适 它们也能长得高大茂密
And there you have it. An oasis is formed.
就这样 绿洲形成了
It helps to know also that the water table can be further altered
这还帮助我们了解土壤中的不透水层
by impermeable layers in the soil, such as rocks
例如岩石或被称为“硬质地层”的致密层
or dense layers of clay called “hardpans”.
也能进一步改变地下水位
Because water cannot pass through these substances,
由于水无法穿过这些物质
its only choice is to move the water table upwards,
只能抬高地下水位
and this can be another factor in bringing water to the surface,
这样 即使没有洼地 也能将水带到地表
even if there is no depression.
这可能就是另一个原因
And that’s all an oasis is.
以上就是绿洲的形成
Light rains from a large enough area
在大面积区域下的小雨
can flow through an underground aquifer hold by gravity,
由于重力流过地下蓄水层
forming basically an underground river.
大体形成一条地下河
Eventually, plants and animals will find these upwellings water
最终动植物会找到这些上涌的水 在此生长
and grow to create a miniature ecosystem,
形成一个微型生态系统
a microcosm of rich life,
一个生物众多的小世界
and in otherwise to avoid desert.
也能避开沙漠
And if conditions remain quote-unquote favorable,
如果条件保持在所谓的有利状态
oases can exist for thousands of years, virtually unchanged.
绿洲能够存在上千年 几乎不变
In fact, in 2007, in the Siwa oasis,
事实上 2007年 在锡瓦的岩石中
an early hominid footprint was discovered fossilized in the rocks.
发现了一个早期原始人的足迹化石
With estimates for its age ranging as far back as 3 million years,
据估计 它的年代可追溯到300万年前
illustraing just how long an oasis can remain intact
这表明 当绿洲与外界完全隔离时
while completely isolated from the outside world.
能长时间保持完好无损
Thanks for watching. I hope your curiosity is satisfied.
感谢观看 希望我满足了你的求知欲
But if not, I’ve got more videos. You can watch as well.
如果没有 我会上传更多视频 你也可以看看
Like always, if you enjoy, please give this video a like.
一如既往 如果你喜欢 请点赞
And if you wanna keep seeing more videos like this, subscribe.
如果想看更多类似的视频 请订阅
I’ll be back next week with another video, thanks.
下周我会带着另一个视频回来 谢谢