什么是冰川？（速成班地理 26#）--环境科学速成班EP3

What Are Glaciers?

I grew up in Ithic in New York, in the US, where there's a huge variety of landscapes. There are farms and forests and mountains and lakes and massive waterfalls, all within a pretty small region. But swimming in the Finger lakes right in my backyard in the summer, or visiting New York City on field trips, I had no idea that the land I was walking on was actually shaped by glaciers. We'll come back to New York later, But it won't be our only example, because actually, many of the Earth landscapes were shaped by glaciers in some way or another, millions of years ago, and today they're like icy the 1st century canaries in the coal mine, warning us about the massive changes to our world that are coming as climates change and sea levels rise. These bohemouth globs of compressed ice and snow moving across the land, created fertile soils and physical features while also serving as frozen time capsules. They recorded both earth's climatic history over several million years, and contain clues to its climatic future. I'm alice a career, and this is Crash Course geography.

Our journey through physical geography is almost over, and by now, we definitely know the Earth is ever changing, and glaciers have often been a crucial part of that change..Basically, a glacier is a large mass of ice that formed from compressed snow, that moves thanks to its own weight and the pull of gravity. And there are actually two main types. When we find a glacier in a mountain range, it's called an alpine or mountain glacier. And on a larger scale, a continuous mass of unconfined ice bigger than 50000 km² is called a continental glacier, or ice sheet. In 2021, about 10% of the earth's land surface is ice, most of that's found in the Greenland and Antarctic ice sheets. And glaciers have a big influence on our global climate because glaciers covered in snow are so dazzlingly white. They reflect a lot of the solar radiation they get keeping the Earth cool. And we saw in our weather episodes how the enormous temperature difference between the polar regions and the warm equatorial regions drives the system of heat transport around the world. And like we learned in our last episode on groundwater, only 2.8% of the earth's water is fresh water. A tiny bit of that is in lakes and rivers, and almost a 3rd is groundwater. But all the rest is locked in glaciers. So if all the world's glaciers were to melt, sea levels would rise about 70 m changing ocean circulation patterns, which would alter weather and climate in the mid latitudes, not to mention create political, economic and social upheaval, dramatically reshaping coastlines and the lives of over 2.4 billion people who live within 100 km of a coast. Looking to the past, it was glaciers themselves that provided the 1st inkling. There had been big changes in global climates throughout earth's history. Many naturalist and even a poet during the early 19th century, were struck by the fact that the British Isles and the North German Plains, which are areas far from glaciers even today, had deeply eroded. You shaped valleys, massive erratic boulders far from where they formed, and bedrock that was smooth like it had been polished by abrasion. These features were similar to what was seen in the Alps, where there were still glaciers. And they concluded that it was evidence that the British Isles and North German plains also had icy pasts. Today, we know the most recent ice age is one of several ice ages that Earth has experienced in its long history. And it doesn't mean that Earth has to be entirely covered in ice. An ice age alternates between glaciations, or a period when temperatures drop and ice sheets grow and spread outwards over vast areas, and interglaciations, when the climate is milder. And this back and forth between glaciations and interglaciations means an ice age can last for millions of years. Right now, we're actually still in an ice age. We're just in the middle of an interglaciation. Evidence from deep sea sediments actually shows that our ice age started when glacier started growing, about 2.5 to 3 million years ago. Both ice sheets and mountain glaciers were forming at this time, but they have some pretty specific requirements. They form above the snow line, or the lowests elevation, where there's ice and snow all year round, so where the amount of snow that falls each year is more than the annual abolition, or how much is lost by evaporation and melting, then as layers of snow get buried and compacted into ice, the weight of the glacier reshapes and realize the crystals, making them harder and denser. When the ice is about 30 m deep, the millions of ice crystals in the bottom layers change form and become plasticy and in glide over each other, which means that from this depth to its base, the glacier behaves more like silly putty and sort of stretches out, carrying the Britle ice on the surface. So a glacier is not just a hard block of ice that slides down a slope. Glaciers usually flow slowly. Large ice sheets move a few centimeters per day and flow out in all directions, while active mountain glaciers can cover several meters each day as they're pulled downhill by gravity. It's really weird to think about, I know, but glaciers don't flow like rivers. They move much slower, but with tremendous energy, meaning they do a ton of work as they engulf and dramatically reshape the landscape, dragging everything in their wake. When a glacier stays more or less the same size, we say it's in dynamic equilibrium, because the amount of new snow is about equal to how much is melting. But when climates warm, or there's less snow, glaciers retreat and grow smaller. Ultimately, when there are very few or no glaciers on the planet, we consider the ice age over. We're not quite to that point yet, so we're still technically in a nice age. Remember, I said we're in an interglacial period of this ice age, meaning there are a lot fewer and smaller ice sheets and glaciers on Earth compared to their greatest extent about 20000 years ago, known as the last Glacial maximum. At that time, much of North America, europe and southern South America were blanketed in extensive ice sheets and glaciers, which got to be more than 3 km thick in parts of Canada and the US. And when this sheet of frozen water began to melt and retreat quite rapidly some 15000 years ago, it left behind a ridge that was basically a jumbled heap of gravel, sand, silt and clay called a Terminal Moraine. It still stretches more or less continuously across North America, from the Puget Sound in Washington State to its southern limits in mid Western states like Missouri and Nebraska, all the way to Montock Point on New york's Long Island. The ice sheet even shaped New York City as we know it. Original settlers of the area, the indigenous peoples of Algonquin speaking languages, utilized features carved by glaciers, much in the same way we do now, using the waterways for trade and commerce and ridges as easy paths to walk between villages. In fact, if you've ever walked down Broadway, then you've walked down one of these trade paths. In neighborhoods like Brooklyn, queens and Staten Island Terminal Moraine forms the high ground. Initially, as the city grew, these sites were ignored for homes and other buildings because they were stony and inaccessible, and construction was difficult. Instead, this land became parks, cemeteries and golf courses. Even today, these remain the more densely wooded and landscaped sections of these neighborhoods, and are now some of the most attractive locations in these burrows. But back to the ice, like a giant bulldozer. As the glacier moves forward, it drags along everything in its path, picking up tiny pebbles or enormous boulders, often the size of a school bus when it melts, their left, strewn across the landscape as though flung by a giant playing marbles. And central park is full of these stray boulders called erratics because, well, they're erratic. They're far from where they would have originated and have different compositions from the surrounding, often younger rocks. Boulders like these, were what some of the naturalists were noticing over in Europe Marines. And erratics are what we call depositional features, which are features formed from the debris carried by ice as glaciers melts. And they still influence how the land is used today, like we saw here in New York City. So glaciers can be like huge excavators, hauling debris from one place to another, adding features to the landscape as they melted and retreated. But they also changed the land through erosion as they advance. Like the Finger Lakes in Central New York, their distinct, elongated basins were eroded and deepened by ice sheets, and the Great Lakes are actually former river valleys that were greatly enlarged and gouged out by glacial erosion. The bedrock beneath each lake is covered in thick blankets of glacial deposits, which are the bits of rock fragments that the ice picked up as it moved, and as the ice sheet retreated north, meltwater filled in the depressions forming the Great Lakes mountain. Glaciers have also sculpted majestic landscapes and regions like the Himalayas, sierra Nevadas, rockies andes and alps like the matter Horn on the Swiss Italian border is the iconic image of the Alps. Its symmetrical spire with precipitous rock walls. Is a siren call for climbers everywhere. And is the work of glaciers. To start out, we have a mountain glacier slowly advancing down the mountain slope. as it moves. Blocks of rock that have been loosened by weathering get removed or plucked out as part of glacial plucking, partnered with a brace of rock debris sand papering the landscape. This forms an armchair shaped hollow in the side of the mountain called a circ When the ice in two adjacent circs eats away at the ridge between them, it forms a sharp, often serated ridge called an aret. And when three or more circs carve away a mountain mass from different sides, we eventually get a horn, or pyramidal peak, like on the matter Horn. But the work of the Mountain glacier isn't done as the ice grinds over uneven bedrock, and the glacier is stretched as it flows over a convict slope. Deep vertical cracks called crevasses open up on the britle ice on the surface as a response to the stress. Debris that gets left behind. Can form ridges along the side of the glacier, which we call a lateral moraine. And where two glaciers join their lateral moines merged to form a meteor moine, often morines damned the foot of a circ incasing small, shimmering mountain lakes called tarns, which are among the most popular destinations for back country hikers and campers. Further down, a glacier moving through a valley will usually arode the walls and deepen and broaden the valley from A-V shape into a ushaped profile. These glacial landscapes that have been left behind after the last warming, are home to millions of people in Eurasia and North America. They've been plowed to produce crops, dug into for sand and gravel and paved over by concrete and tarmac. Lately, when we hear about glaciers shaping the Earth, it's because they're breaking. Like in 2021, data from uncruded submarines showed that warm water may be weakening critical stability points of the Sways Glacier, which is also part of the West Antarctic Ice Sheet, and known as the Doomsday Glacier. When it breaks, it could raise global sea levels by over half a meter and potentially collapse the entire West Antarctic Ice Sheet, which would flood lowlands and islands across the world. So the story of ice seems to be closely tied to our human story. Ice has advanced and retreated over time, but when the climate stabilized after the ice started melting twelve to 15000 years ago, agriculture flourished, and many nomadic groups shifted to more settled lifestyles, setting the scene for many of our societies today. And as the ice melts further, our lives could shift again. So as we contemplate that future, join us next time for a look at the geography of natural hazards. Many maps and borders represent modern geopolitical divisions that have often been decided without the consultation, permission or recognition of the land's original inhabitant. Many geographical place names also don't reflect the indigenous or aboriginal people's languages. So we at Crash Course want to acknowledge these people's traditional and ongoing relationship with that land and all the physical and human geographical elements. We encourage you to learn more about the history of the place you call home through resources like Native land dot CA, and by engaging with your local indigenous and Aboriginal nations through the websites and resources they provide. Thanks for watching this episode of Crash Course Geography, which is filmed at the Team sand of All Pier Studio, and was made with the help of all these nice people. If you want to help keep crash course free for everyone forever, you can join our community on Patrion. 

译文：

什么是冰川？

我在纽约长大，在美国，那里有一个巨大的各种各样的风景。那里有农场，森林，山脉，湖泊和大片瀑布，都在一个很小的区域内。但是夏天在我家后院的芬格湖游泳，或者去纽约实地考察，我都不知道我脚下的土地实际上是由冰川形成的。我们稍后会回到纽约，但这不会是我们唯一的例子，因为事实上，地球上的许多景观都是由冰川以这样或那样的方式塑造的，数百万年前，今天它们就像1世纪煤矿里的金丝雀，警告我们我们的世界即将发生巨大的变化，随着气候变化和海平面上升。这些波西米亚风格的压缩冰雪球在陆地上移动，创造了肥沃的土壤和物理特征，同时也充当了冰冻的时间胶囊。它们记录了地球数百万年的气候历史，也包含了未来气候的线索。我是爱丽丝，这里是地理速成班。

我们的自然地理之旅几乎结束了，到目前为止，我们肯定知道地球在不断变化，而冰川往往是这种变化的关键部分。基本上，冰川是由压缩的雪形成的大块冰，由于自身的重量和重力的作用而移动。实际上主要有两种类型。当我们在山脉中发现冰川时，它被称为高山冰川或山地冰川。在更大的范围内，超过50000平方公里的连续的无约束冰被称为大陆冰川或冰盖。到2021年，大约10%的地球陆地表面是冰，其中大部分在格陵兰岛和南极冰盖上。冰川对我们的全球气候有很大的影响，因为被雪覆盖的冰川是如此耀眼的白色。它们反射了大量的太阳辐射，使地球保持凉爽。在我们的天气事件中，我们看到了极地和温暖的赤道地区之间巨大的温差是如何驱动全球热传输系统的。就像我们在上一集地下水中学到的那样，地球上只有2。8%的水是淡水。其中一小部分在湖泊和河流中，几乎三分之一是地下水。但其余的都被锁在冰川中。因此，如果世界上所有的冰川都融化，海平面将上升约70米，改变海洋环流模式，这将改变中纬度地区的天气和气候，更不用说造成政治、经济和社会动荡，极大地重塑海岸线，以及生活在距离海岸100公里以内的24亿多人口的生活。回顾过去，冰川本身提供了第一个线索。在整个地球历史上，全球气候发生了巨大的变化。在19世纪早期，许多博物学家，甚至还有一位诗人，都对不列颠群岛和北日耳曼平原受到严重侵蚀的事实感到震惊，即使在今天，这些地区也远离冰川。你塑造了山谷，塑造了远离它们形成地点的巨大的不稳定的巨石，塑造了光滑的基岩，就像被磨擦过一样。这些特征与在阿尔卑斯山看到的相似，那里仍然有冰川。他们得出结论，这是不列颠群岛和北日耳曼平原也有冰封历史的证据。今天，我们知道最近的冰河时代是地球在其漫长的历史中经历的几个冰河时代之一。这并不意味着地球必须完全被冰覆盖。冰河时代交替于冰期和间冰期之间，间冰期是指气温下降、冰盖生长并向外扩散到广大地区的时期，间冰期是指气候较温和的时期。冰期和间冰期的交替意味着冰期可以持续数百万年。现在，我们实际上还处于冰河时期。我们正处在间冰期。来自深海沉积物的证据实际上表明，我们的冰河时代始于大约250万到300万年前冰川开始生长的时候。当时冰盖和高山冰川都在形成，但它们有一些非常特殊的要求。它们形成于雪线之上，或者海拔最低的地方，那里终年都有冰雪，所以每年降雪量大于每年的消失量，或者蒸发和融化损失的量，然后随着雪层被掩埋并压实成冰，冰川的重量重塑并实现晶体，使它们更硬更密。当冰大约30米深时，底部数以百万计的冰晶会改变形状，变得具有可塑性，并在彼此之间滑动，这意味着从这个深度到底部，冰川的行为更像是橡皮泥，它伸展开来，把脆弱的冰带到表面。所以冰川不仅仅是沿着斜坡滑下的坚硬冰块。冰川通常流动缓慢。大冰原每天移动几厘米，向四面八方流动，而活跃的山地冰川每天可以覆盖几米，因为它们被重力拉下山。我知道，想起来很奇怪，但冰川不像河流那样流动。它们的移动速度要慢得多，但却有着巨大的能量，这意味着它们在吞噬并戏剧性地重塑景观的同时做了大量的工作，拖着它们身后的一切。当冰川的大小大致保持不变时，我们说它处于动态平衡状态，因为新雪的数量大约等于融化的数量。但当气候变暖或降雪减少时，冰川就会退缩并变小。最终，当地球上的冰川很少或没有冰川时，我们认为冰河时代结束了。我们还没到那个地步，所以从技术上讲，我们还处在一个不错的时代。记住，我说过我们正处于这个冰河时代的间冰期，这意味着地球上的冰盖和冰川与大约2万年前的最大范围相比要少得多，也要小得多，也就是最后一次极大期。当时，北美、欧洲和南美洲南部的大部分地区都被大片的冰盖和冰川覆盖，在加拿大和美国的部分地区，冰盖和冰川的厚度超过了3公里。大约15000年前，当这片冰冻的水开始融化并迅速退缩时，它留下了一个山脊，基本上是砾石，沙子，淤泥和粘土的杂乱堆，被称为终端冰碛。它仍然或多或少地连续地横跨北美，从华盛顿州的普吉特海湾到密苏里州和内布拉斯加州等中西部州的南部边界，一直延伸到纽约长岛的蒙托克角。冰盖甚至塑造了我们现在所知的纽约市。该地区的原始定居者，讲阿尔冈昆语的土著居民，利用冰川雕刻的地貌，与我们现在的方式大致相同，利用水道进行贸易和商业，利用山脊作为村庄之间的便捷通道。事实上，如果你曾经走过百老汇，那么你就走过了其中一条贸易路线。在布鲁克林、皇后区和斯塔顿岛这样的社区，终碛石形成了高地。最初，随着城市的发展，这些地方被忽略为住宅和其他建筑，因为它们是石头，难以进入，施工困难。相反，这片土地变成了公园、墓地和高尔夫球场。即使在今天，这些仍然是这些社区中树木繁茂、景观优美的部分，现在是这些洞穴中最具吸引力的一些地方。但回到冰面上，就像一台巨大的推土机。当冰川向前移动时，它会拖着沿途的一切，带上小鹅卵石或巨大的巨石，它们融化时通常有校车那么大，它们的左边，散落在地上，就像被一个巨大的弹珠扔出来一样。中央公园到处都是这些被称为“不稳定石”的石头，因为它们是不稳定的。它们离它们的起源很远，并且与周围的岩石成分不同，通常是更年轻的岩石。像这样的巨石，是一些博物学家在欧洲海军陆战队注意到的。不稳定是我们所说的沉积特征，是由冰川融化时冰携带的碎片形成的特征。它们仍然影响着今天土地的使用方式，就像我们在纽约市看到的那样。因此，冰川可以像巨大的挖掘机一样，将碎片从一个地方拖到另一个地方，在它们融化和退缩的过程中为景观增添了特色。但他们在前进的过程中也通过侵蚀改变了土地。就像纽约中部的芬格湖一样，它们独特的细长盆地被冰盖侵蚀和加深，五大湖实际上是以前的河谷，在冰川侵蚀下被大大扩大和凿出。每个湖泊下面的基岩都覆盖着厚厚的冰川沉积物，这些沉积物是冰在移动过程中收集的岩石碎片，随着冰盖向北退缩，融水填满了洼地，形成了五大湖山。冰川还雕刻了雄伟的景观和地区，如喜马拉雅山、内华达山脉、落基山脉、安第斯山脉和阿尔卑斯山，瑞士和意大利边境的matterHorn就是阿尔卑斯山的标志性形象。对称的塔尖和陡峭的岩壁。是对各地登山者的警示。是冰川的杰作。首先，我们有一个山地冰川缓慢地沿着山坡向下移动。随着它的移动。由于风化作用而松动的岩石块被移走或被拔走，这是冰川拔走的一部分，与一堆岩石碎片一起包裹着景观。这就在山的侧面形成了一个扶手椅形状的空洞，叫做“圆”。当两个相邻圆中的冰侵蚀它们之间的山脊时，就形成了一个锋利的、通常呈锯齿状的山脊，叫做“圆”。当三个或更多的环境从不同的侧面雕刻出一个山体时，我们最终得到一个角，或金字塔状的山峰，就像物质角一样。但是山冰川的作用并不是在冰在不平坦的基岩上磨碎时完成的，冰川在蜿蜒的斜坡上流动时被拉伸。作为对压力的反应，表面上脆弱的冰上出现了被称为裂缝的深垂直裂缝。留下的碎片。可以沿着冰川的一侧形成山脊，我们称之为侧冰碛。当两个冰川将它们的横向运动结合在一起形成一个流星运动时，通常会形成一个小的、闪闪发光的山间湖泊的底部，这些湖泊被称为tarns，是最受野外徒步旅行者和露营者欢迎的目的地之一。再往下走，穿过山谷的冰川通常会避开墙壁，使山谷从a-v形状变深变宽，变成一个凹凸不平的轮廓。这些冰川景观是在上一次变暖之后留下的，是欧亚大陆和北美数百万人的家园。它们被用来耕种庄稼，挖出沙子和砾石，铺上混凝土和柏油路。最近，当我们听到冰川塑造地球时，那是因为它们正在破裂。与2021年一样，来自未磨损潜艇的数据显示，温暖的海水可能会削弱斯威斯冰川的关键稳定性点，斯威斯冰川也是南极西部冰盖的一部分，被称为末日冰川。当它破裂时，它可能会使全球海平面上升超过半米，并有可能使整个南极西部冰盖坍塌，这将淹没世界各地的低地和岛屿。因此，冰的故事似乎与我们人类的故事密切相关。随着时间的推移，冰有进有退，但在12至1。5万年前冰开始融化后，气候稳定下来，农业繁荣起来，许多游牧民族转向了更加定居的生活方式，为许多人的生活奠定了基础我们今天的社会。随着冰层进一步融化，我们的生活可能会再次改变。因此，当我们展望未来的时候，下次请和我们一起来看看自然灾害的地理分布。许多地图和边界代表了现代地缘政治的划分，而这些划分往往是在没有征求当地原始居民的意见、允许或承认的情况下决定的。许多地理地名也不反映土著或土著人民的语言。因此，我们在速成班想要承认这些人与这片土地的传统和持续的关系，以及所有的自然和人文地理因素。我们鼓励你通过像NativelanddotCA这样的资源了解更多关于你称之为家的地方的历史，并通过他们提供的网站和资源与当地的土著和土著民族接触。感谢收看本期《地理速成班》，本期《地理速成班》是在所有码头工作室的团队沙地上拍摄的，是在这些好心人的帮助下完成的。如果你想帮助速成班永远免费对所有人开放，你可以加入我们在爱国者上的社区。