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Time English (United States) Language 2 Action
00:00
Tens of thousands of years ago, gigantic beasts roamed the earth. Ones way bigger than woolly mammoths or dinosaurs.
00:07
They were big enough to dig out this massive lake, cause these giant scratches in the ground, and drop these boulders in the middle of a field.
00:15
And the best part? Some of those big guys are still out here today. I’m talking about... glaciers!
00:24
Hi! I’m Sage, and this is Crash Course Geology.
00:31
Glaciers are enormous masses of ice and snow that flow under their own weight, moving very slowly across the earth.
00:38
Or, at a glacial pace.
00:40
As Miranda Priestly would say, “You know how that thrills me.” And they’re not just boring hunks of ice. Glaciers provide habitats,
00:48
hold over half of the world’s freshwater, and preserve hundreds of thousands of years worth of history within their layers.
00:56
Glaciers are important to the spiritual beliefs of indigenous peoples, from Peru to China to Tanzania. Plus, they’re stunning.
01:03
Like, come on! How is that real? And they’re massive. So, how does all that ice get there?
01:10
Well, it’s a little more complicated than a giant slush pile getting shoved to the edge of a Target parking lot.
01:15
Glaciers form when tons of snow falls in an area that’s so cold, the snow never totally melts.
01:21
It starts to accumulate year after year, building up until the pile is huge— tens of meters deep, and around 4050 square meters in area.
01:29
And when there’s that much snow in one place, it gets so heavy, its frosty base starts to transform.
01:36
First, the snow at the base gets packed so tightly it turns into a state called firn, which is technically still snow.
01:44
But while fresh snow is about 90 percent air, firn is only about 25 percent. That tightly-packed state gets us ready for the next transformation.
01:53
With increasing pressure, the snow recrystallizes, trading its six-armed snowflake shape for dense, rounded crystals of firn that can grow bigger over time.
02:02
The ice is so dense, it absorbs every color of light except for blue, which is what gives glaciers their haunting glow.
02:08
That’s the basic process, but it doesn’t always look exactly the same. Glaciers are super varied in size and shape.
02:14
Like, you’re probably familiar with continental glaciers: thick domes of ice that stretch thousands of square meters across Earth’s surface.
02:22
Sometimes called ice sheets, these vast, frosty expanses exist in only two places today: Greenland and Antarctica.
02:29
But alpine glaciers, or mountain glaciers, are found on every continent except Australia. Although, the Kiwis know there are glaciers in New Zealand. I’m sorry, I don’t know why I thought I could do that.
02:38
True to their name, alpine glaciers form high up on mountains in bowl-shaped formations called cirques— which the glaciers carve themselves!
02:45
If enough ice builds up, these can flow down as valley glaciers. When the ice reaches flat ground, it can spread out into a lobe called a piedmont glacier.
02:53
Like this guy in Greenland, which is called Elephant Foot Glacier, for obvious reasons. And glaciers are always changing. Each one can be broken into a few distinct zones.
03:01
There's the accumulation zone near the top of the glacier, where new snow collects. Then there's the ablation zone where snow and ice blow, fall, or melt away.
03:11
If more snow accumulates than ablates, the glacier grows.
03:15
But if more ice ablates than accumulates, the glacier's front retreats, and the length of the glacier shortens over time.
03:22
Whether a glacier is lengthening or shortening, it’s constantly flowing from place to place.
03:26
As the ice that makes up glaciers deforms and flows, it moves the entire glacier from the inside. That slow, downhill motion is called creep.
03:35
Which is also what Dwayne calls me when I sneak up on him Sometimes, especially in warmer conditions, the glacier’s huge weight causes the bottom to melt, becoming slippery.
03:42
And when a slippery-bottomed glacier meets smooth ground, it moves. Some only move a few millimeters a year, like the Meserve glacier in Antarctica.
03:48
But the fastest glacier ever recorded, the Jakobshavn glacier in Greenland, moves up to 46 meters a day. That thing is booking it.
03:56
Glaciers sliding over the cold, hard ground is like pushing a brick through a sandbox.
04:01
As glaciers flow, bits of sand, gravel, and rock get embedded at the base, grating the ground in a process known as abrasion.
04:09
This can even leave behind huge claw marks, called glacial striations, like these in Ohio. Glaciers can also pluck the bedrock— and I don’t mean yanking out its stray eyebrow hairs.
04:19
As a glacier drags across uneven ground, it can crack off chunks of rock and carry them away. Together, abrasion and plucking shape the landscape in a bunch of ways.
04:28
They can carve out u-shaped valleys and bowl-shaped cirques, like we saw earlier, or even craft flat-faced horns in mountains, like the famous Matterhorn in the Swiss Alps.
04:36
Eventually, all that crushed rock forms mounds called moraines.
04:40
They have different names based on where they form: lateral for the ones along the sides of a glacier, and terminal for the ones at the front end.
04:47
Sometimes, gravel can build up in the channels of melted ice that flow around a glacier, leaving behind winding mounds called eskers, like this one in Minnesota.
04:53
And glaciers can move huge boulders, carrying them far away from their source rock and leaving them lying around as glacial erratics.
05:00
As a certain famous equine would say, “That is a nice boulder.” Glaciers can even create lakes.
05:07
Sometimes small chunks of ice break off of glaciers as they retreat, getting buried in the sediment that washes out from a melting glacier.
05:13
Once those buried ice chunks melt, they can leave behind shallow kettle lakes.
05:17
Other times, massive glaciers carve basins that fill with water as they melt, with moraines around them that keep the water in.
05:23
That process can create lakes so big you might even call them “great.” But glaciers and the features they create aren’t just cool to look at. They can also be a window into the past.
05:31
Let’s learn about one of my geology rock stars…
05:34
In the 1970s, when Kumiko Goto-Azuma was a high school student in Japan, a teacher told her that women couldn’t be professional scientists.
05:42
But she didn’t listen— because she wanted to learn about snow.
05:45
Years later, after earning her doctorate in engineering, she was introduced to ice core research: a method of studying the layers within ice sheets.
05:53
Toward the middle of continental glaciers, the ice flows so slowly that layers form in a pretty orderly fashion, keeping records like the rings inside a tree.
06:03
Glaciologists drill vertical holes in the ice, pulling out tubes of it that they keep frozen for study.
06:08
Scientists like Dr. Goto-Azuma analyze those ice cores to learn how Earth’s climate has changed in the past 800,000 years.
06:16
Like, a layer’s thickness can show how much precipitation the area saw that year. And the amount of greenhouse gases in a layer can reveal the air temperature at that time.
06:25
Ice cores can even hold remnants of past volcanic eruptions!
06:28
Over her forty-year career, Dr. Goto-Azuma has compared ice cores from all over the Arctic and Antarctic, studying the climatic cycles that shape glaciers.
06:37
Today, she’s a professor at the National Institute of Polar Research in Tokyo, where she continues to study ice cores, especially the black carbon— AKA soot— that they contain.
06:45
Black carbon is released by burning fossil fuels, and it can impact how much radiation is reflected by glaciers.
06:52
Dr. Goto-Azuma’s work will be especially useful in combating climate change. Ice cores can tell us a lot about Earth’s past, especially its changing temperature.
07:01
Sometime between 120,000 and 11,000 years ago, the planet was in a cold stretch of time called a glacial period, also called an ice age.
07:09
This was a long chunk of time when glaciers covered vast swaths of the earth. And I mean long.
07:15
That particular ice age took place across more than a hundred thousand years, and others lasted millions.
07:22
At least five ice ages have happened in Earth’s history.
07:25
And even though we associate them with a world full of snow and ice, they can have interglacial periods: warmer times when glaciers retreat, shaping the earth as they go.
07:36
We’re actually in an interglacial period right now! While a lot of our glaciers have retreated since the last ice age, many remain intact… for now.
07:44
Which brings me to the tough part. You’ve probably seen some scary headlines about glaciers melting.
07:51
So let’s get up to speed on why this is happening and what we can do about it.
07:56
Right now, the planet is getting hotter at the rate of about 0.3 degrees Celsius every decade, causing continental glaciers to recede.
08:05
At higher altitudes, where alpine glaciers are, it’s getting hotter even faster. And as we all know, when ice gets warm, it melts.
08:13
Some scientists estimate that more than a third of our remaining glaciers could be gone as early as 2100.
08:19
That might sound far off, but plenty of people born around 2010 or later could live to see that year.
08:25
And that loss would cause some serious problems, including rising sea levels that threaten coastal areas, the disruption of ocean ecosystems,
08:33
and a limited supply of freshwater from glaciers— which many people rely on, especially in southeast Asia.
08:39
This period of warming is different from interglacial periods of the past, mainly because of the super rapid pace of change.
08:46
Before humans, glaciers receded and temperatures warmed over thousands of years, so ecosystems had time to adjust.
08:53
But our spike in temperature has happened over the past hundred years, thanks to the release of carbon dioxide and other greenhouse gases from burning fossil fuels.
09:02
Our interglacial period could very quickly become a glacier-less period. That’s not stressful at all! I’m fine! Are you fine, Dwayne? ‘Cause I’m fine.
09:11
Okay, I’m definitely not fine. But scientists are working to fix this problem.
09:15
Some folks in Switzerland have tried covering melting glaciers with massive insulating blankets called geotextiles.
09:20
Others have tried using artificial snow to slow down glacial melt, shooting it out of cables like a sprinkler.
09:26
And some are looking to drill holes in glaciers so that water at their base can be pumped out and refrozen. These strategies are innovative and impressive, but they’re not practical in a lot of ways.
09:36
They’re often so expensive that they can’t be scaled up to save whole glaciers, especially in lower-income parts of the world. And they can even cause ecological problems of their own.
09:46
So, many scientists say that the most straightforward way to slow the pace of climate change and keep our planet’s glaciers from disappearing is— and say it with me now!— reducing carbon emissions.
09:56
Luckily, you’ve got a whole other Crash Course series about that. Say hey to M for me. So, I’m not gonna sugarcoat it: Earth’s glaciers are in trouble.
10:04
And their loss would have ripple effects on ecosystems, communities, and individual lives— including mine and yours— across the globe.
10:13
But the more we collectively learn about glaciers and commit to cutting carbon emissions, the better chance we have of witnessing these magnificent wonders for generations to come.
10:23
Next time, we’ll learn about asteroid impacts of the past… and the future. See you then.
10:28
Thanks for watching this episode of Crash Course Geology which was filmed at our studio in Indianapolis, Indiana, and was made with the help of all these chill people.
10:35
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