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  • Lots of bodies of water, like rivers and ponds, they change shape and size over time.

  • But lakes? Like, we usually think of lakes as being pretty permanent.

  • Yeah, of course, water levels will rise and drop during years of heavy rain or drought,

  • but lakes themselves, they don't go anywhere, right?

  • Well, except I wouldn't be talking about it if they didn't;

  • some do, and around the world, there are lakes that disappear without warning,

  • and then, even stranger, they come back.

  • This can happen for lots of different reasons,

  • and understanding these mysterious lakes can show us surprising things about Earth's geology,

  • and how water is often connected to hidden processes under the surface.

  • One of these disappearing acts happens every year in the Cascade Mountains,

  • in one of Oregon's so-calledLost Lakes.”

  • If you saw this lake in the winter, you wouldn't notice anything strange.

  • During the wet winter months, it fills up with rainwater and runoff,

  • and covers over 300,000 square meters of land.

  • But when the rainy season ends in the spring, things get weird.

  • Around that time, the lake starts to shrink,

  • and it keeps shrinking until, by summer, the whole thing is a giant meadow.

  • Now, you might be thinking that this lake just evaporated, right?

  • But a few months isn't enough time for a huge lake to just evaporate into thin air.

  • Especially because, let's be real, Oregon isn't that hot and dry in the summer.

  • Instead, something else is happening; something way cooler.

  • The lake is actually leaking constantly through a hole in the lakebed that's around 2 meters wide.

  • It's basically like having a bathtub drain that's constantly open.

  • You just don't notice it in the winter because there's enough precipitation

  • to fill the lake faster than it can drain away.

  • Geologists suspect that this hole, which is not very big,

  • isn't just some random opening in the ground.

  • Instead, they think it leads to a collapsed lava tube.

  • Lava tubes are natural tunnels that form as lava flows down the slopes of a volcano.

  • The lava's outer layer cools into a hard crust,

  • but the inner layers are still molten and they continue to flow downhill.

  • That drains the tube and leaves behind a hollow channel.

  • The lava tube under the Lost Lake formed over 12,000 years ago,

  • and it carries water from the lake into the McKenzie River.

  • From there, it ends up more than 9 kilometers from where it started, in Oregon's Clear Lake.

  • Besides being super cool, this shows us that bodies of water

  • aren't just connected by the usual avenues, like rivers and streams.

  • Ancient volcanic tunnels are still shaping the way water travels today.

  • Next, in the Patagonia region of Chile, another disappearing lake

  • performs its vanishing act on a much less predictable schedule.

  • Lago Cachet Dos is a glacial lake that fills with melting ice from the Colonia Glacier.

  • Normally, this glacier acts as a dam to keep the lake in place.

  • But if the lake gets too full, things reach a breaking point.

  • As the lake fills and water pressure builds, water can start wearing through the ice.

  • And eventually, the water bores through a weak area at the base of the glacier.

  • That creates a channel that extends eight kilometers underground

  • until the water breaks through the other side of the glacier.

  • And then the whole lake comes rushing out that tunnel!

  • An event like this is called a glacial lake outburst flood, or a GLOF.

  • Back in 2012, a GLOF drained a whopping 200 million cubic meters of water in less than a day!

  • That tripled the volume of the river it flowed into.

  • Luckily there aren't too many people in the area around it,

  • but the flooded river did do some damage to roads and farm animals.

  • As the glacier moves, it collapses that underground tunnel,

  • and the lake fills back up, so the same process can happen again and again.

  • Lago Cachet Dos has drained over twenty times in the last decade.

  • And as climate change speeds up melting, the number of GLOFs is likely to increase.

  • GLOFs don't just happen in Chile, though.

  • These glacial lakes appear, and disappear, in other mountain regions,

  • like the Himalayas, the Alps, and even the Rockies.

  • So understanding how they and their outbursts

  • are connected to climate conditions and other waterways

  • can help people stay safe from unexpected floods in the regions around them.

  • Finally, let's bring it back to my home state: Florida.

  • Where there's a third lake in Tallahassee that's famous

  • for yet another type of dramatic disappearance.

  • It's called Lake Jackson, and it's pretty flat and shallow; honestly, it's pretty boring at first glance.

  • But if you look underneath the surface, you'll see something interesting: sinkholes.

  • Lake Jackson has two sinkholes that drop down more than 15 meters towards the Floridan Aquifer.

  • They're often plugged up with sediment, which allows the lake to fill up.

  • But it's a fragile arrangement.

  • Every once in a while, Lake Jackson gets enough water through rain or runoff

  • to break through those plugs and plunge through the sinkholes into the aquifer.

  • When that happens, the lake can empty in as little as a day,

  • draining up to 37,000 liters a minute.

  • Then, over time, sediment naturally plugs the sinkholes again, and the lake fills up.

  • This has happened at least a dozen times since 1840, and, as catastrophic as it sounds,

  • this rush of water is actually a good thing for the local ecosystem.

  • The draining kills off invasive plants and even flushes out native ones,

  • which can start to take up too much space, too.

  • During these dry periods, people can also go in and remove pollutants that drain

  • from urban areas and settle into a thick layer of 'muck' on the bottom of the lake.

  • So this unusual cycle of draining and refilling

  • actually plays a pretty important role in Lake Jackson's ecosystem.

  • Whether these lakes calmly come and go with the seasons

  • or drain suddenly in dramatic and unpredictable events,

  • the fact that they vanish and reappear reveals surprising connections.

  • Our waterways are joined by things as wide-ranging as ancient volcanic activity

  • and recurring sinkholes, which all contribute to how water moves around today.

  • Thanks for watching this episode of SciShow! And thank you to our patrons!

  • It takes a lot of people to make a SciShow video, and we couldn't do it without your support.

  • And if you're interested in supporting us,

  • you can head over to patreon.com/scishow to learn more.

  • [♪ OUTRO]

[♪ INTRO]

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