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.?

譯文：

什么是冰川？

我在紐約長大，在美國，那里有一個(gè)巨大的各種各樣的風(fēng)景。那里有農(nóng)場，森林，山脈，湖泊和大片瀑布，都在一個(gè)很小的區(qū)域內(nèi)。但是夏天在我家后院的芬格湖游泳，或者去紐約實(shí)地考察，我都不知道我腳下的土地實(shí)際上是由冰川形成的。我們稍后會(huì)回到紐約，但這不會(huì)是我們唯一的例子，因?yàn)槭聦?shí)上，地球上的許多景觀都是由冰川以這樣或那樣的方式塑造的，數(shù)百萬年前，今天它們就像1世紀(jì)煤礦里的金絲雀，警告我們我們的世界即將發(fā)生巨大的變化，隨著氣候變化和海平面上升。這些波西米亞風(fēng)格的壓縮冰雪球在陸地上移動(dòng)，創(chuàng)造了肥沃的土壤和物理特征，同時(shí)也充當(dāng)了冰凍的時(shí)間膠囊。它們記錄了地球數(shù)百萬年的氣候歷史，也包含了未來氣候的線索。我是愛麗絲，這里是地理速成班。

我們的自然地理之旅幾乎結(jié)束了，到目前為止，我們肯定知道地球在不斷變化，而冰川往往是這種變化的關(guān)鍵部分?；旧希ㄊ怯蓧嚎s的雪形成的大塊冰，由于自身的重量和重力的作用而移動(dòng)。實(shí)際上主要有兩種類型。當(dāng)我們在山脈中發(fā)現(xiàn)冰川時(shí)，它被稱為高山冰川或山地冰川。在更大的范圍內(nèi)，超過50000平方公里的連續(xù)的無約束冰被稱為大陸冰川或冰蓋。到2021年，大約10%的地球陸地表面是冰，其中大部分在格陵蘭島和南極冰蓋上。冰川對我們的全球氣候有很大的影響，因?yàn)楸谎└采w的冰川是如此耀眼的白色。它們反射了大量的太陽輻射，使地球保持涼爽。在我們的天氣事件中，我們看到了極地和溫暖的赤道地區(qū)之間巨大的溫差是如何驅(qū)動(dòng)全球熱傳輸系統(tǒng)的。就像我們在上一集地下水中學(xué)到的那樣，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，幾乎三分之一是地下水。但其余的都被鎖在冰川中。因此，如果世界上所有的冰川都融化，海平面將上升約70米，改變海洋環(huán)流模式，這將改變中緯度地區(qū)的天氣和氣候，更不用說造成政治、經(jīng)濟(jì)和社會(huì)動(dòng)蕩，極大地重塑海岸線，以及生活在距離海岸100公里以內(nèi)的24億多人口的生活。回顧過去，冰川本身提供了第一個(gè)線索。在整個(gè)地球歷史上，全球氣候發(fā)生了巨大的變化。在19世紀(jì)早期，許多博物學(xué)家，甚至還有一位詩人，都對不列顛群島和北日耳曼平原受到嚴(yán)重侵蝕的事實(shí)感到震驚，即使在今天，這些地區(qū)也遠(yuǎn)離冰川。你塑造了山谷，塑造了遠(yuǎn)離它們形成地點(diǎn)的巨大的不穩(wěn)定的巨石，塑造了光滑的基巖，就像被磨擦過一樣。這些特征與在阿爾卑斯山看到的相似，那里仍然有冰川。他們得出結(jié)論，這是不列顛群島和北日耳曼平原也有冰封歷史的證據(jù)。今天，我們知道最近的冰河時(shí)代是地球在其漫長的歷史中經(jīng)歷的幾個(gè)冰河時(shí)代之一。這并不意味著地球必須完全被冰覆蓋。冰河時(shí)代交替于冰期和間冰期之間，間冰期是指氣溫下降、冰蓋生長并向外擴(kuò)散到廣大地區(qū)的時(shí)期，間冰期是指氣候較溫和的時(shí)期。冰期和間冰期的交替意味著冰期可以持續(xù)數(shù)百萬年?，F(xiàn)在，我們實(shí)際上還處于冰河時(shí)期。我們正處在間冰期。來自深海沉積物的證據(jù)實(shí)際上表明，我們的冰河時(shí)代始于大約250萬到300萬年前冰川開始生長的時(shí)候。當(dāng)時(shí)冰蓋和高山冰川都在形成，但它們有一些非常特殊的要求。它們形成于雪線之上，或者海拔最低的地方，那里終年都有冰雪，所以每年降雪量大于每年的消失量，或者蒸發(fā)和融化損失的量，然后隨著雪層被掩埋并壓實(shí)成冰，冰川的重量重塑并實(shí)現(xiàn)晶體，使它們更硬更密。當(dāng)冰大約30米深時(shí)，底部數(shù)以百萬計(jì)的冰晶會(huì)改變形狀，變得具有可塑性，并在彼此之間滑動(dòng)，這意味著從這個(gè)深度到底部，冰川的行為更像是橡皮泥，它伸展開來，把脆弱的冰帶到表面。所以冰川不僅僅是沿著斜坡滑下的堅(jiān)硬冰塊。冰川通常流動(dòng)緩慢。大冰原每天移動(dòng)幾厘米，向四面八方流動(dòng)，而活躍的山地冰川每天可以覆蓋幾米，因?yàn)樗鼈儽恢亓律?。我知道，想起來很奇怪，但冰川不像河流那樣流?dòng)。它們的移動(dòng)速度要慢得多，但卻有著巨大的能量，這意味著它們在吞噬并戲劇性地重塑景觀的同時(shí)做了大量的工作，拖著它們身后的一切。當(dāng)冰川的大小大致保持不變時(shí)，我們說它處于動(dòng)態(tài)平衡狀態(tài)，因?yàn)樾卵┑臄?shù)量大約等于融化的數(shù)量。但當(dāng)氣候變暖或降雪減少時(shí)，冰川就會(huì)退縮并變小。最終，當(dāng)?shù)厍蛏系谋ê苌倩驔]有冰川時(shí)，我們認(rèn)為冰河時(shí)代結(jié)束了。我們還沒到那個(gè)地步，所以從技術(shù)上講，我們還處在一個(gè)不錯(cuò)的時(shí)代。記住，我說過我們正處于這個(gè)冰河時(shí)代的間冰期，這意味著地球上的冰蓋和冰川與大約2萬年前的最大范圍相比要少得多，也要小得多，也就是最后一次極大期。當(dāng)時(shí)，北美、歐洲和南美洲南部的大部分地區(qū)都被大片的冰蓋和冰川覆蓋，在加拿大和美國的部分地區(qū)，冰蓋和冰川的厚度超過了3公里。大約15000年前，當(dāng)這片冰凍的水開始融化并迅速退縮時(shí)，它留下了一個(gè)山脊，基本上是礫石，沙子，淤泥和粘土的雜亂堆，被稱為終端冰磧。它仍然或多或少地連續(xù)地橫跨北美，從華盛頓州的普吉特海灣到密蘇里州和內(nèi)布拉斯加州等中西部州的南部邊界，一直延伸到紐約長島的蒙托克角。冰蓋甚至塑造了我們現(xiàn)在所知的紐約市。該地區(qū)的原始定居者，講阿爾岡昆語的土著居民，利用冰川雕刻的地貌，與我們現(xiàn)在的方式大致相同，利用水道進(jìn)行貿(mào)易和商業(yè)，利用山脊作為村莊之間的便捷通道。事實(shí)上，如果你曾經(jīng)走過百老匯，那么你就走過了其中一條貿(mào)易路線。在布魯克林、皇后區(qū)和斯塔頓島這樣的社區(qū)，終磧石形成了高地。最初，隨著城市的發(fā)展，這些地方被忽略為住宅和其他建筑，因?yàn)樗鼈兪鞘^，難以進(jìn)入，施工困難。相反，這片土地變成了公園、墓地和高爾夫球場。即使在今天，這些仍然是這些社區(qū)中樹木繁茂、景觀優(yōu)美的部分，現(xiàn)在是這些洞穴中最具吸引力的一些地方。但回到冰面上，就像一臺(tái)巨大的推土機(jī)。當(dāng)冰川向前移動(dòng)時(shí)，它會(huì)拖著沿途的一切，帶上小鵝卵石或巨大的巨石，它們?nèi)诨瘯r(shí)通常有校車那么大，它們的左邊，散落在地上，就像被一個(gè)巨大的彈珠扔出來一樣。中央公園到處都是這些被稱為“不穩(wěn)定石”的石頭，因?yàn)樗鼈兪遣环€(wěn)定的。它們離它們的起源很遠(yuǎn)，并且與周圍的巖石成分不同，通常是更年輕的巖石。像這樣的巨石，是一些博物學(xué)家在歐洲海軍陸戰(zhàn)隊(duì)注意到的。不穩(wěn)定是我們所說的沉積特征，是由冰川融化時(shí)冰攜帶的碎片形成的特征。它們?nèi)匀挥绊懼裉焱恋氐氖褂梅绞?，就像我們在紐約市看到的那樣。因此，冰川可以像巨大的挖掘機(jī)一樣，將碎片從一個(gè)地方拖到另一個(gè)地方，在它們?nèi)诨屯丝s的過程中為景觀增添了特色。但他們在前進(jìn)的過程中也通過侵蝕改變了土地。就像紐約中部的芬格湖一樣，它們獨(dú)特的細(xì)長盆地被冰蓋侵蝕和加深，五大湖實(shí)際上是以前的河谷，在冰川侵蝕下被大大擴(kuò)大和鑿出。每個(gè)湖泊下面的基巖都覆蓋著厚厚的冰川沉積物，這些沉積物是冰在移動(dòng)過程中收集的巖石碎片，隨著冰蓋向北退縮，融水填滿了洼地，形成了五大湖山。冰川還雕刻了雄偉的景觀和地區(qū)，如喜馬拉雅山、內(nèi)華達(dá)山脈、落基山脈、安第斯山脈和阿爾卑斯山，瑞士和意大利邊境的matterHorn就是阿爾卑斯山的標(biāo)志性形象。對稱的塔尖和陡峭的巖壁。是對各地登山者的警示。是冰川的杰作。首先，我們有一個(gè)山地冰川緩慢地沿著山坡向下移動(dòng)。隨著它的移動(dòng)。由于風(fēng)化作用而松動(dòng)的巖石塊被移走或被拔走，這是冰川拔走的一部分，與一堆巖石碎片一起包裹著景觀。這就在山的側(cè)面形成了一個(gè)扶手椅形狀的空洞，叫做“圓”。當(dāng)兩個(gè)相鄰圓中的冰侵蝕它們之間的山脊時(shí)，就形成了一個(gè)鋒利的、通常呈鋸齒狀的山脊，叫做“圓”。當(dāng)三個(gè)或更多的環(huán)境從不同的側(cè)面雕刻出一個(gè)山體時(shí)，我們最終得到一個(gè)角，或金字塔狀的山峰，就像物質(zhì)角一樣。但是山冰川的作用并不是在冰在不平坦的基巖上磨碎時(shí)完成的，冰川在蜿蜒的斜坡上流動(dòng)時(shí)被拉伸。作為對壓力的反應(yīng)，表面上脆弱的冰上出現(xiàn)了被稱為裂縫的深垂直裂縫。留下的碎片?？梢匝刂ǖ囊粋?cè)形成山脊，我們稱之為側(cè)冰磧。當(dāng)兩個(gè)冰川將它們的橫向運(yùn)動(dòng)結(jié)合在一起形成一個(gè)流星運(yùn)動(dòng)時(shí)，通常會(huì)形成一個(gè)小的、閃閃發(fā)光的山間湖泊的底部，這些湖泊被稱為tarns，是最受野外徒步旅行者和露營者歡迎的目的地之一。再往下走，穿過山谷的冰川通常會(huì)避開墻壁，使山谷從a-v形狀變深變寬，變成一個(gè)凹凸不平的輪廓。這些冰川景觀是在上一次變暖之后留下的，是歐亞大陸和北美數(shù)百萬人的家園。它們被用來耕種莊稼，挖出沙子和礫石，鋪上混凝土和柏油路。最近，當(dāng)我們聽到冰川塑造地球時(shí)，那是因?yàn)樗鼈冋谄屏?。與2021年一樣，來自未磨損潛艇的數(shù)據(jù)顯示，溫暖的海水可能會(huì)削弱斯威斯冰川的關(guān)鍵穩(wěn)定性點(diǎn)，斯威斯冰川也是南極西部冰蓋的一部分，被稱為末日冰川。當(dāng)它破裂時(shí)，它可能會(huì)使全球海平面上升超過半米，并有可能使整個(gè)南極西部冰蓋坍塌，這將淹沒世界各地的低地和島嶼。因此，冰的故事似乎與我們?nèi)祟惖墓适旅芮邢嚓P(guān)。隨著時(shí)間的推移，冰有進(jìn)有退，但在12至1。5萬年前冰開始融化后，氣候穩(wěn)定下來，農(nóng)業(yè)繁榮起來，許多游牧民族轉(zhuǎn)向了更加定居的生活方式，為許多人的生活奠定了基礎(chǔ)我們今天的社會(huì)。隨著冰層進(jìn)一步融化，我們的生活可能會(huì)再次改變。因此，當(dāng)我們展望未來的時(shí)候，下次請和我們一起來看看自然災(zāi)害的地理分布。許多地圖和邊界代表了現(xiàn)代地緣政治的劃分，而這些劃分往往是在沒有征求當(dāng)?shù)卦季用竦囊庖?、允許或承認(rèn)的情況下決定的。許多地理地名也不反映土著或土著人民的語言。因此，我們在速成班想要承認(rèn)這些人與這片土地的傳統(tǒng)和持續(xù)的關(guān)系，以及所有的自然和人文地理因素。我們鼓勵(lì)你通過像NativelanddotCA這樣的資源了解更多關(guān)于你稱之為家的地方的歷史，并通過他們提供的網(wǎng)站和資源與當(dāng)?shù)氐耐林屯林褡褰佑|。感謝收看本期《地理速成班》，本期《地理速成班》是在所有碼頭工作室的團(tuán)隊(duì)沙地上拍攝的，是在這些好心人的幫助下完成的。如果你想幫助速成班永遠(yuǎn)免費(fèi)對所有人開放，你可以加入我們在愛國者上的社區(qū)。