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  • [ intro ]

  • What do you think of

  • when you imagine giant dunes of sand?

  • Maybe punishing heat, little water,

  • and practically no life.

  • Basically, a desert.

  • But the northernmost parts of Alberta and Saskatchewan in Canada

  • are not a desert.

  • It's below freezing for half the year.

  • There's enough precipitation to sustain

  • the world's twentieth largest lake.

  • And yet here, at a latitude of fifty-nine [59] degrees,

  • lies the Athabasca dunes.

  • They're one of the world's northernmost dune fields,

  • and one of planet Earth's most unique habitats.

  • Like much of northern North America,

  • Athabasca sits on the Canadian Shield,

  • a large expanse of nearly exposed bedrock.

  • The Shield formed during past periods of glaciation,

  • when huge sheets of ice covered

  • what is now Canada and parts of the United States.

  • This ice basically scraped everything down to that bedrock.

  • The dunes themselves date to the end of Earth's last glacial period,

  • somewhere around ten thousand years ago.

  • These ice sheets were mind-bogglingly thick --

  • comparable modern ice sheets like Greenland's can be three kilometers deep.

  • And although we think of glaciers as just kind of sitting there,

  • they actually flow in slow motion.

  • The material they scrape off --

  • and by material, I mean stuff like mountains --

  • gets pulverized down into what's called till.

  • As the planet warmed and the glaciers retreated north,

  • much of that till was carried along for the ride.

  • Think about how much water must've been produced

  • by the melting of a kilometer-thick ice sheet the size of Canada.

  • Around eight or nine thousand years ago,

  • that flood dumped a big deposit of till into a massive lake.

  • As that lake receded,

  • it left behind what we now know of as the Athabasca dunes.

  • Then, the wind took over.

  • As the ice sheet pulled back,

  • cold air from the top rushed down

  • and created powerful winds that blew in a southeasterly direction.

  • This cool, dry air was key to slowing the growth of plants

  • that otherwise would have stabilized the sand with their root systems.

  • As the sand blew around, it didn't just pile up into nice, floofy mounds.

  • Instead, it abraded any rock formations

  • that somehow survived being crushed by the ice.

  • This generated even more sand

  • and broke it all down into smaller and smaller bits.

  • Eventually, the climate warmed enough,

  • and the glaciers receded far enough,

  • that the winds shifted to a more northerly angle, where they remain today.

  • But by that point, there was already a lot of sand.

  • Today, individual dunes can rise thirty 30 meters high

  • and stretch for up to a kilometer and a half in length.

  • For a region with such unusual geology,

  • it might not surprise you to know

  • there's a bunch of interesting life, too.

  • The presence of so much water

  • has allowed for the development of an ecosystem

  • that's pretty unlike what you'd find in a desert.

  • There are quite a few rare forms of life found here,

  • and a concentration of specialist species

  • not found anywhere else this far north.

  • In fact, the Athabasca dunes

  • are home to ten endemic species,

  • which means they're not found anywhere else on the planet.

  • None of them are giant worms, unfortunately.

  • All ten of these species are plants,

  • and they've evolved a number of adaptations

  • to the unusual and shifting conditions of the dunes.

  • Their outer protective layer,

  • called the cuticle, is extra tough

  • to withstand the constant abrasion of windborne sand.

  • Many grow especially quickly to help avoid being buried under a shifting dune.

  • And if that doesn't work, some grow rhizomes,

  • which are secondary stems that sprout from the root system.

  • Perhaps the rarest of these species is the Athabasca Thrift.

  • To avoid the dunes entirely,

  • it makes its home on a compacted layer of pebbles

  • and sand called gravel pavement.

  • Another rare species is the Large-headed Woolly Yarrow.

  • It's name sounds kind of ridiculous,

  • the name refers to the tiny hairs that cover its stem

  • and help the yarrow retain precious moisture against the relentless wind.

  • Another species,

  • called Turnor's WIllow,

  • grows up to four meters tall to peek above the shifting sands.

  • If one of its thin, flexible branches does get buried,

  • it can become the start of a root system for a new,

  • cloned copy of the tree.

  • Even its seeds are well adapted --

  • their light weight and fine hairs

  • help the wind carry them to new locations.

  • Unlike a lot of unique environments,

  • the Athabasca dunes are actually pretty well protected.

  • They fall largely within Saskatchewan's Athabasca Sand Dunes Provincial Park,

  • which is accessible only by float plane.

  • Of course,

  • distance from civilization isn't much protection from climate change,

  • but so far the populations of the dunes' most important species seem stable.

  • Let's keep our fingers crossed,

  • because there aren't that many lakeside, snowcapped dunefields out there.

  • In fact, I think there's only one.

  • And now we're going to take you from the freezing dunes of Canada

  • to the more conventional hot ones of the Arabian desert,

  • where there lives another dune-adapted species: the sand cat.

  • They're the world's only desert-dwelling cat,

  • and they have about the cutest cheeks we've ever seen,

  • and you can learn about them in the CuriosityStream documentarySand Cats,”

  • part of the seriesSmall Cats Unknown.”

  • And once you're done learning about cats,

  • CuriosityStream has over 2400 other documentaries and nonfiction titles for you to enjoy,

  • including exclusive originals.

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  • [ outro ]

Thanks to CuriosityStream for supporting this episode!

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カナダ北部の凍結砂丘 (The Freezing Dunes of Northern Canada)

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    林宜悉 に公開 2021 年 01 月 14 日
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