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"If you live in the northern hemisphere, there's a decent chance you're in a winter wonderland right now. Settle in with a hot drink for this winter compilation and learn about some of the interesting things that make winter wondrous!

Hosted by: Stefan Chin
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Stefan: Well, winter is finally here again.  Two years ago, we made a compilation of winter-y themed episodes, but since putting that together, we've produced a bunch more, so grab your blankets and snuggle up on the couch for our winter compilation, part two.

So when it's cold out and you have to leave your house, you can just throw on a jacket or two to help you stay warm, but insects haven't quite discovered jacket technology yet, so how do they survive out there all winter?  Well, Michael's got the answer in our first episode.

Michael: Unlike us lucky endotherms, insects can’t regulate their own body temperatures. They’re at the mercy of their environment. So when the cold winter arrives, how do they keep from freezing? They basically have three choices: They can leave for warmer places, they can wait it out, or they can kick the bucket.

Just like some birds, there are a few insects, like dragonflies or butterflies, fly south for the winter. The most famous of these has got to be the monarch butterfly. There’s a population that normally lives in the northern U.S. and Canada, but spends the winter in the balmy mountain forests of Mexico. Of course, many insects have shorter lives than birds. So, a special migratory generation of the monarchs flies south thousands of miles to Mexico without reproducing, but it takes four or five generations to make the trip back north.

If an insect can’t leave when winter arrives, option number two is to hunker down and wait for things to warm up again. Insects like ladybugs, emerald ash borers, and mourning cloak butterflies burrow into soil or leaf litter for warmth. There, these adult insects enter a kind of hibernation called diapause, thanks to hormones triggered by the shorter days and cooler temperatures of autumn.

Their metabolic rates drop dramatically, so they don’t need as much food. And some species even pump their tissues full of alcohols that act as a natural antifreeze. Basically, these chemicals lower the freezing point inside their cells, which prevents damaging ice crystals from forming.

Now, plenty of insects, like crickets and grasshoppers, just throw in the towel when the temperature drops. The adults die off after reproducing in the fall, and the next generation spends the winter as dormant eggs or larvae. These babies are usually pretty well-equipped for survival: Eggs and larvae can enter diapause just like adults can, and some get extra help from their doomed parents. Praying mantises, for example, envelop their eggs in a foam-like protective protein case.

These days, climate change is messing with the overwintering strategies of some insects. And it’s even letting some less cold-tolerant species venture farther north. Which... usually isn’t so great. Like, thanks to milder winters, the mountain pine beetle has been expanding its range and killing vast swaths of trees in western North America.

So when it gets cold out, do you put on a coat and keep trucking? Curl up under a blanket with hot chocolate until spring? Or do you make like a monarch and head for the tropics? Whatever your way of dealing, spare a thought for the insects that make it work without central heating – just with some clever adaptations.

Stefan: So I guess some insects just don't survive the winter, poor little guys.  But now we're gonna talk about a place where nothing survives because it's a lava lake in the winter wonderland of Antarctica.  

Hank: Earth is covered in lakes. Mostly these are cool, watery affairs full of life and great for a relaxing vacation. Lava lakes are a little less serene: they’re scorching, seething pools of molten rock. They’re also pretty rare, outside of MineCraft. Permanent lava lakes only exist in a few places around the globe.

One of the strangest lava lakes is atop Mount Erebus, on the frozen continent of Antarctica. Probably the weirdest thing about this lake is that it’s constantly releasing gas, and the composition of that gas changes on a roughly ten-minute cycle.

Erebus was a Greek god, the son of Chaos which is kinda fitting for a place made of ice and fire. Mount Erebus is the tallest peak on Ross Island, which lies close to the Antarctic mainland and is usually connected by ice sheets. It’s an active volcano that’s been bubbling away for decades, occasionally throwing off larger eruptions.

The lava lake is around 20 meters deep, and it sits in a crater which is itself inside Mount Erebus’s main crater. Under the lake is a conduit, a tube that leads down to a chamber full of magma underground lava, in other words. The lake is basically like a bowl with a hole in the bottom sitting on top of a pipe - like a sink, I guess you could say except it goes the other way: it doesn’t go down, it goes up. And all of it’s about a thousand degrees Celsius.

Even in the frigid Antarctic air, the lake’s surface won’t cool into solid rock thanks to convection currents that feed the lake with a steady supply of hot stuff. Hot magma rises to the top of the lake, then spreads outward, cooling off along the way. As it cools it gets denser, so it sinks back down again – and the convection cycle continues.

Lava lakes need that crater, conduit, and magma chamber combo to exist, and not many volcanoes have all those components so well aligned. That’s why molten lava lakes are super-rare there are only about five on Earth that have remained persistently active in recent years.

So the Mount Erebus lava lake is an unusual and remote place, but thanks to some intrepid scientists, it’s an area of active research. Scientists have braved freezing slopes and burning lava bombs, that’s the technical term for flying blobs of lava. And they’ve installed remote sensors to keep tabs on the lake 24/7.

One mystery they’re working on is the lake’s persistent gas emissions. For years, Erebus has been steadily releasing a gas plume, and there’s a weird cycle to it. Over the course of ten minutes or so, there’s a repetitive shift in both the amount of gas produced, and its composition — the overall mix. For example, the carbon dioxide to carbon monoxide ratio changes, as do emission levels of water vapor and sulfur dioxide.

Researchers have been trying to figure out why there’s this repeating cycle, and based on sensor data and computer modeling, they think it has to do with two main sources of gas. One comes from the conduit, and the other comes from diffusion in the lake. The carbon dioxide-rich gas is always rising up from the conduit, and it’s basically constant the amount and composition doesn’t really change. But the conduit also occasionally, like every ten minutes or so, burps out a large blob of magma from deeper in the chamber, like a kind of literal one-way lava lamp.

Once a blob gets near the surface of the lake it releases a fresh set of gases, which adds to the total amount of gas detected and changes the overall composition because it’s rich in water vapor and sulfur dioxide.

In addition to these shorter cycles, the lava lake also has what researchers call explosive degassing. These less frequent but more impressive belches cause small eruptions, hurling lava bombs into the main crater. The two systems seem to work independently. The composition of the gas from the explosive degassing is different from the gas from the shorter cycle, and appears to come from much deeper in the volcano’s magma chamber.

There is still a lot left to learn about Erebus, and lava lakes in general. For example, there are gas cycles with other cycle lengths that aren’t as well studied. Working out if they’re connected, and how, will build up a better model of the inner workings of Mount Erebus.

Mount Erebus also contains a rare type of magma called phonolite. It’s much thicker than the more common basalt variety, which probably affects the fluid dynamics inside the magma chamber and lake. So hopefully the recent studies on Erebus will be useful for scientists working on other lava lakes around the world.

These lakes may be rare, but having good models from the few examples around the world will help geologists understand the similarities and differences between them and the overall rules about how they work.

Stefan: And that's enough about hot gassy things.  Let's talk about something cold and solid: ice.  Specifically, how there are actually a bunch of different kinds of ice.

Olivia: Water is weird. And I mean that in a good way. Its amazing chemical properties can – and have – filled books, and it’s no exaggeration to say the properties of water make life possible. But it really is super weird.

Most chemicals have one solid form, or at most a couple. Depending on who you ask and how you count, water has seventeen or more. And while there’s only the one on Earth, we expect to find these exotic forms of ice in space.

Temperature and pressure have a big influence on whether a chemical will exist in a solid, liquid, or gaseous state at any given moment. They both affect how molecules arrange themselves in a stable way. And there are so many kinds of ice because of the unique chemistry of water molecules.

The oxygen atom in a water molecule has two hydrogens sticking off it, and it also has two lone pairs of electrons. Electrons are tiny, but the negative charges repel each other, so those pairs of electrons actually take up space. Effectively, there are four things sticking off the oxygen. They shuffle around to be as far away from each other as possible, and that takes the form of a tetrahedron with oxygen in the center.

The hydrogen atoms and electron pairs on different water molecules can form hydrogen bonds with one another – one hydrogen with one electron pair. As long as every water molecule is neatly hydrogen bonded with its neighbors in a crystalline form, that’s solid ice. But tetrahedrons can fit together in more than one way. Plus, the electron pairs on nearby molecules repel each other and can push the molecules a bit farther apart. The result is that water molecules are constantly jostling each other around to find a stable configuration. Change the temperature or the pressure just a bit, and the molecules will shift to a different crystalline form.

There are about seventeen of these crystalline forms. Each one gets a Roman numeral, named in order of their discovery, from good ol’ ice one on up. The reason we say "about" 17 is because it’s really hard to achieve the extreme temperatures and pressures needed to make all of them in a lab. Some of the ones that have been observed are meta-stable, or stable-ish.

Another form of ice would theoretically dominate at that temperature and pressure, but the metastable form is the one the molecules have settled into for a moment. There are also forms of ice that have been predicted to exist in computer models and simulations, but we’ve never actually created.

Then, there are forms of ice that exist outside the Roman numeral system, because they’re not crystalline forms. Amorphous ice, for example, doesn’t have a very orderly, repeated crystalline structure, so it doesn’t get a fancy number. But it’s still a solid, like glass, or butter.

And there’s even wilder forms, called super-ionic ices, where the oxygen atoms are locked into a crystal lattice but the hydrogen atoms are free to move around. So how many of these ices have you unknowingly run into, or made snowmen out of? Probably just one.

All of the ice that falls out of the sky and piles up on the ground on home sweet planet Earth is ice one. Specifically, it’s the hexagonal form of ice one. There’s also a cubic form of ice one, which is found in clouds. The crystals grow a little differently, but on a molecular level, they’re indistinguishable. So they both get the same number.

But ice one isn’t the most common form of ice in the universe. That title probably goes to amorphous ice, which space is chock full of. It coats lots of particles of interstellar dust. Amorphous structures, like amorphous ice, form when substances cool too quickly to settle into an orderly crystal structure. And interstellar space can get pretty gosh-darn cold.

Super-ionic ice probably exists on Uranus and Neptune, the ice giant planets. Some scientists think this bizarre ice phase could account for the strange magnetic field properties that have been observed on those planets.

And beyond our solar system, an exoplanet called Gliese 436b is thought to host a whole bunch of super-hot ice ten. Now, that’s not a verbal typo. We don’t normally think of ice as being hot, but the surface temperature of this exoplanet is estimated to be a toasty 439 degrees Celsius.

This is where that temperature-pressure relationship comes into play. The pressure on this exoplanet is huge too – so high that even warm liquid water basically gets squashed solid. There are probably even more weird ices lurking out there in space, ready for us to discover.

Water is something so common and so essential that we don’t tend to think about how peculiar its chemistry really is. But when you take a close look at it, these molecules can surprise you!

Stefan: That's too many kinds of ice, but that's not the only weird thing about ice.  Let's look at another of its strange properties.  Why is it so slippery?  

Olivia: Have you ever been walking on a snowy sidewalk on a freezing day, stepped on a hidden patch of ice, slipped, and fell flat on your butt? Scientists seem to agree that what’s causing the slipperiness is a really thin layer of liquid water on top of the ice, but they’re not entirely sure how it forms.

Most solids don’t have such a layer, but ice isn’t like most solids. So researchers have come up with a couple ideas, involving pressure, friction, and just how the water molecules interact. For decades, people have thought that you can exert pressure on ice to melt the top layer a tiny bit, like when you’re ice skating.

This could happen because of one of water’s weird properties: ice is less dense than liquid water. Thermodynamically, when you put extra pressure on ice – like right under the blade of a skate – the system tries to lower that pressure again by decreasing the volume. Since liquid water takes up less space than ice, its melting point drops a bit, so the solid can melt a little, and you slide across. And once your skate passes, the water refreezes.

So that seems to make sense, but it doesn’t completely check out. Even for a heavier skater, the melting point would only lower by a few degrees at most, which means really cold ice would stay frozen. Plus, a person wearing normal shoes, which put less pressure on the ice than a thin ice skate blade, will still slip.

So another possibility is that the friction from your shoe rubbing against the ice creates enough heat to melt it. And while that’s true, ice is still slippery when you’re standing still. So that explanation doesn’t make the cut either. But there’s a third idea, based on an observation the physicist Michael Faraday made in 1850: He pressed two ice cubes against each other and saw that they froze together. And he figured that the liquid surface layers became solid when they weren’t touching air anymore.

This led modern scientists to look into an idea called surface melting – maybe water molecules on the surface of ice can move around more than the ones inside, since there are no molecules above them to help hold them in place. Because these surface molecules are less stable, they have enough energy to make a liquid-like layer even at below-freezing temperatures. In simpler words: ice is just inherently slippery.

None of these explanations have been completely proven or disproven, so scientists think a combination of them and the weirdness of water are all at play. So the next time a patch of ice takes your feet out from under you, you can remember that ice is a pretty cool solid.

Stefan: Wow!  Ice is so cool, and so is the fluffier version of frozen water: snow.  What would a winter compilation be without at least one episode on snow?  Specifically, there is one kind of snow that you should probably avoid: watermelon snow.  Olivia's got the scoop on this weird stuff.

Olivia:  If it snows where you live, you’ve probably been told not to eat the yellow snow, and for good reason. But what about pink snow that smells vaguely of watermelon, aka watermelon snow?

It’s not pink because it’s contaminated with blood or anything — watermelon snow has algae in it. But you probably still wouldn’t want to eat it.

People have been trying to explain pink snow for a while. Even Aristotle wrote about it, back in the day. But we’ve only known why it’s pink for the past couple of centuries.

In May of 1818, British explorer Captain John Ross was sailing past Greenland, looking for a convenient path between the Atlantic and Pacific oceans. That’s when he spotted patches of pink and red snow on the white cliffs of Cape York.

He took some samples and brought them back home to England, and when the London Times reported on his find, they said that the color came from iron deposits in the underlying soil. But Scottish botanist Robert Brown disagreed. He thought that the pink color might be coming from algae in the snow.

And these days, we know that he was right. It turns out that the color comes from Chlamydomonas nivalis, which is actually a type of green algae. If you look closely enough, the algae’s cells are green — on the inside. But they’re covered in a red outer layer to protect them from solar radiation, which is what turns the snow pink.

And the algae smell kind of sweet, which is why it’s sometimes called watermelon snow. C. nivalis is one of over 60 kinds of snow algae, all of which can withstand cold temperatures, high levels of solar radiation, and low levels of nutrients.

It lives at pretty high altitudes — mostly between 3000 and 3600 meters up. And that means it needs extra protection. At such high elevations, there’s a lot less atmosphere to protect the algae from the sun’s radiation, and the snow reflects lots of light, too.

All that light can lead to photoinhibition, where an organism has a much harder time photosynthesizing. That’s because the light damages a protein that’s critical to photosynthesis, and it can’t repair itself quickly enough. So most plants and algae have pigments called carotenoids that help absorb just enough light for photosynthesis to work properly, but protect them from photoinhibition.

C. nivalis has a carotenoid called astaxanthin, which is red enough to mask the green underneath, and turn the snow pink or red. The algae are dormant during the winter, so you won’t usually see pink snow then. But as the snow melts during the spring, nutrients from things like pollen and plant debris reach the dormant cells underneath the layer of snow.

That’s when the algae wake up from their long winter’s nap and start the germination process, releasing cells that move toward the sunlight. These cells have flagella, small whip-like arms that they use to swim up until they’re close to the snow’s surface. Then, they shed their flagella because they’re just going to stay where they are.

The cells form thick walls with that trademark red pigment, then spend most of their lives feeding off of a combination of photosynthesis and stored nutrient reserves. The reddish color does help protect the algae from some of the sun’s rays, but they still don’t live right on the surface — they’re usually one or two centimeters below, which gives them even more protection.

And as the snow melts throughout the spring and summer, the algae naturally reposition themselves by flowing along with the snow-melt. They help support even more life in the cold, snowy fields, including some single-celled organisms like protozoa and microscopic animals like rotifers.

If you ever come across watermelon snow, you’ll probably notice small divots in the snow where the color is an especially intense red. These indents are called sun cups, and they’re in a kind of positive feedback loop where the darker color absorbs more heat, melting the snow into deeper indentations. That lets the cells move closer together, which intensifies the color even more and leads to more melting.

So, planning your next vacation and on the hunt for some watermelon snow? In the United States, you can find C. nivalis in California’s Sierra Nevada mountain range. But it’s also in other snowy, elevated places all over the world, from Australia to Europe. You probably still don’t want to eat it, though.

Some report that eating too much of the stuff leads to diarrhea, which could derail your whole algae sightseeing adventure. Researchers have actually tested this, because of course they have. They gave seven people half a kilogram each of watermelon snow, and none of them had any digestive issues. But that’s only seven people, so it wasn’t exactly a conclusive study. If you want a natural watermelon snow-cone, eat it at your own risk.

Stefan: Well, there you have it: don't eat the watermelon snow.  Thanks for watching this winter compilation.  You should feel free to continue consuming episodes of SciShow over at  Meanwhile, I'm suddenly craving a watermelon sno-cone.