Under Pressure

Pressure ridge on Lake Winnipeg by Heather Hinam

With the ‘polar vortex’ that held much of North America in its frigid grip last week, it was interesting for this ‘girl of the north’ listen to southerners goggle about phenomena that I’ve been experiencing for most of my life.

I found one event, in particular, rather interesting. Last week, the media and thus a large portion of the population, was introduced to the concept of ‘frost quakes’. Torontonians were rattled out of their beds by thunderous booms that shook parts of the city at random intervals. Soon the headlines were reading that it was so cold in Canada, the ground was cracking.

Lake Winnipeg Cliffs

Large crevasse in the rock, likely split apart by frost action

Having spent a number of winters on the shores of Lake Winnipeg, where  temperatures regularly dip below -30C, I’ve seen first-hand the power of ice and its ability to snap rock in two. Ice expands and contracts with temperature fluctuations. It also becomes less flexible as it becomes colder. Water that finds its way into fissures in the rock or soil can push so hard went it freezes – especially if the temperature drops quickly – that the substrate buckles under the pressure. Here, along the lake, the limestone cliffs are full of cracks forced open by winter’s icy push. Still, these earth-shattering events are extremely rare. You don’t usually see new cracks on a yearly basis.

However, there is another type of frost quake, or ice quake, as I prefer to call them that happens considerably more often. Based on where the events were reported last week along Lake Ontario, I’m willing to bet that it was this type of cryoseism  that residents heard for the most part. While the ground doesn’t crack very often, the ice on the lake does. On large lakes, like Lake Winnipeg or Ontario, a sudden snap of the ice can sound like a cannon shot, nearly knocking you off your feet and rattling windows in their panes. While it’s still not something you experience everyday, such quakes happen on Lake Winnipeg fairly regularly.

That’s because this 23,750 sq km lake freezes completely to a depth of at least a metre every year. That much surface area can’t solidify into one piece. So it freezes into floes that knit together much like the tectonic plates of the earth did when the crust first formed. Like the earth’s crust, the lake’s surface is full of fault lines, or pressure ridges.  These giant cracks can run for kilometres along the lake and usually form in about the same place every year.  Some ridges, known as stamukhi, are grounded along the shoreline, where ice that is held fast to the shore meets the free-flowing ice of deeper waters, while others run along over top of varying depths.

Even frozen, the lake is very much alive and pressure ridges are the sites where this is most noticeable. It’s along these lines that the ice floes move, sliding along, away from and into each other. A particularly violent collision is like a mini mountain building event and along with an ice quake, you will also see a ridge of ice has been pushed sometimes more than 2 meters into the air.  More often, however, the two floes simply press against each other, expanding and contracting like long, drawn-out breaths as the temperatures wax and wane. Eventually, the pressure overtakes the compressive strength of the ice and the ridge snaps in a startling bang that is often followed by the gentle whale-like ‘whoom’ sounds of the pressure waves dissipating through the rest of the ice.

As fascinating as they are, pressure ridges are also dangerous places to be. The ice floes can slide away from each other just as quickly as they can come together and loose plates of ice can trick the unwary into thinking they are still on solid ground. A number of commercial ice fishermen have been lost through shifting ridges over the last century on the lake.

Unless you live along a lake that freezes regularly, Ice quakes are truly something few people get to experience. So, I’m glad that our recent continental cold snap gave more people the chance to learn a bit more about this fascinating phenomena and remember just how powerful nature can be.

Jumpin Jack Flash

White-tailed Deer Flagging by Heather Hinam

If you’ve ever spent any time in North American forests east of The Rockies, you’ve seen it, a sudden flash of white, that snags your attention before disappearing into a tangle of vegetation.

White-tailed deer  (Odocoileus virginianus) are very aptly named.  The bright, snowy fur on the underside of their tail is impossible to miss, especially because they often wave it in the air as they bound away from you.

This behaviour is called ‘flagging’ and it’s an instinct that kicks in only hours after birth.  To a human observer, its purpose is a little hard to understand. Why would an animal that is otherwise very well camouflaged wave a big flag at a predator that essentially shouts “I’m over here!”.  Because it seems so counter-intuitive, flagging has been the focus of a number of studies, but researchers still have yet to come to a consensus in regards to why they do it and who are they doing it for: their fellow deer or whatever is trying to make them dinner.

Some biologists believe that by flagging, their tails at the approach of a predator, deer are signalling each other and maintaining the cohesion of the group while at the same time confusing their stalker by making it hard to pick out an individual in the group.

The problem with that assessment, however, is that deer will flag when they’re by themselves or when others in their group can’t see them. I’ve seen it many times as I’ve approached them. You know you’ve taken a step too far when the tail goes up, even if the deer doesn’t immediately run away.

The consensus now is that this flashy signal is for the predator, not other deer. But, why wave a white flag when you could be better off blending into the background? Deer flag most often when they’re out in the open and when you are still a good ways off. It’s essentially their way of telling the predator (or you) that they’ve spotted the danger and are prepared to outrun it.

The hard part is figuring out how predators respond to such a signal. Humans and domestic dogs don’t understand the language and are poor models of how a coyote or wolf might behave. No one has managed to collect data on how natural predators respond to flagging However, deer aren’t the only animals to use an ‘I see you’ signal when they’ve spotted a predator.

Many ungulates, like Thomson’s gazelles, pronghorn, and springbok will leap from all four feet, straight up into the air, in a behaviour called stotting, when they spot an approaching predator. Like flagging, this jump signals to the predator that its been seen, then takes it one step further by also communicating that they are more than capable of outrunning the threat.  It seems to work. Studies in Africa have found that cheetahs will abandon hunts more frequently when their target stots and if they still choose to initiate a chase, they’re less likely to win.

Like with most animals, these relatively simple signals are just a small part of a whole array of behaviours that make up a complex web of communication between predator and prey. So, take the time to be observant. With patience and intuition, you can learn the language and open your eyes to a whole new level of understanding of the world around you.

Dust From a Distant Sun

Aurora Borealis by Heather HinamAutumn has flown by, marked by brilliant leaves and skies filled with birds winging their way to warmer climes. The bustle of the season swept me up with back to school (I haven’t taught a fall course in over 7 years) and my regular work as a naturalist/guide/illustrator, leaving this blog sitting on the shelf for a while.

However, now, as the nights turn truly cold and the days become darker, I finally have a chance to settle and get back to sharing those things that fascinate me the most. I thank you for sticking with me.

The colder temperatures remind me of the many reasons I love living in the more northerly reaches of the planet. Not the least of those is the chance we get, now and then, to witness one of the most amazing natural phenomena on earth: the auroras. Here, in the northern hemisphere, they are the aurora borealis or northern lights. They’re not actually more common in the colder months; but many tend to associate them with winter, probably because the longer nights give us more opportunity to see them.  The picture above was actually taken in August.

For people who have never seen them, aurora are kind of hard to describe. They appear with no warning, beginning usually with a barely noticeable glow just above the horizon. You stare, transfixed, wondering if you’re seeing things. Suddenly, the silent flames grow, licking out across the sky, a rippling curtain of light that is ceaseless in its movements. The shifting colours hold you in their thrall until, just as quickly as they had appeared, the lights dissolve into the ether, leaving you feeling a little bereft for their loss.

Just what are these silent, shimmering waves of light? Though they are best seen on the darkest of nights, aurora are a product of the sun. Being a giant ball of hot plasma (ionized gas particles), the sun is a tempestuous place to be. Protons and electrons are being flung about the atmosphere, creating ‘solar winds’, which are streams of plasma that escape the star’s gravity and sail across the universe at truly mind-boggling speeds of millions of kilometres per hour. On occasion, fountains of particles will spew out of the sun’s atmosphere in a coronal mass ejection, sending a wave of protons and electrons on a collision course for earth.

When they reach our magnetic field, most are deflected, riding the field lines to the poles, where they start to swirl around, like atomic tornadoes, in the ionosphere (the height at which the International Space Station orbits). Whirling faster and faster, the ions become unstable, colliding with nearby gas atoms, releasing so much energy that they glow. The colour of the light depends on the gas they interact with and how far above the earth they are. The green and yellow we are most familiar with is created by an interaction with oxygen, while blue and violet are caused by nitrogen.

So, what you’re seeing is millions of chemical reactions playing out several hundred kilometres above the earth. The unearthly flame is concentrated in a halo around each pole, an auroral ring that shifts ever so slowly with the movement of our magnetic poles.

For the layperson, the appearance of these ghostly fire dances are impossible to predict. However, scientists in Canada have spent over a hundred years studying the phenomenon and have teased out some trends. Some years are better than others. It turns out that solar activity (solar flares, mass ejections and other radiation) goes through a relatively predictable 11 year cycle that should be hitting its peak sometime over the next few months.  Besides being a treat for aurora watchers, this intensified light show will be invaluable for researchers looking for ways to protect our satellite and communications networks from this increased radiation. While they may be beautiful, the ions spiralling through space can, and have, wreaked havoc on our electrical grids.

This year’s maximum has turned out to be the weakest in over a century, but there are still lights to be seen.  So, look up, look waaay up and hopefully you will have the chance to experience a true natural wonder.

P.S. to find out when and where your best chances for aurora spotting are, visit: www.gi.alaska.edu/AuroraForecast

Writing in the Snow

Qali Growing up, I would hear people quote this statistic: “Eskimos have more than a hundred words for snow.” Actually, I still hear people rattle off this little ‘fact’, especially in winter.  However, there are a lot of problems with this statement, not even including the fact that the indigenous people of North America’s tundra and Arctic regions are known as Inuit, not Eskimo. No, what really grates on me about this blanket statement is the implication that it’s somehow weird to have so many words to describe one thing.

When it’s something that makes up a very large part of your daily life during a significant portion of the year, why wouldn’t you take the time to describe it as accurately as possible? The English language has several words for rain: showers, downpour, drizzle, sheets, so why not snow, especially in light of the fact that it sticks around a lot longer than its warm weather counterpart.  Actually, as a Canadian, I’m surprised that we, as a population, haven’t developed more words beyond flurries, blizzard and slush to describe this white stuff that blankets much of the country for four to six months out of the year.

To do that, we have to turn to other cultures and languages. While the true count is well under one hundred, many Inuit dialects have several useful words to describe the incredible variety of snow that we can encounter throughout the course of the winter.  For those of us who live in forested areas, one handy word to know is qali. It refers to the snow that builds up on the branches of trees, glazing limbs in white and making it look like someone attacked the woods with a decorator’s bag full of royal icing.

I was lucky to have learned several Inuit terms for snow as part of some of my undergraduate university courses and like many people who study winter ecology, they’ve been part of my lexicon ever since. So, it took a bit of digging to figure out where the word qali comes from. According to William Wonders, who wrote the book Canada’s Changing North (2003), the word originates from the Kobuk Valley Inuit of northwestern Alaska, along the edge of the treeline.

Qali can range in thickness from a light dusting that could almost be mistaken for hoar frost to heavy globs of wet snow that drag beleaguered limbs to the ground under its unrelenting weight. All along that spectrum, it has a significant impact on the ecological community.

Many winter residents are affected by qali. Spruce grouse and squirrels that regularly feed on cones often find themselves driven down to the ground by a particularly heavy layer of qali. The snow-covered branches can be hard to navigate, forcing these species to search elsewhere for food. On the other hand, qali can make some food more accessible. With particularly heavy wet snows, the qali that builds up on young birches, willow and aspen pulls the flexible branches down, bringing the young, tender tips within reach of hungry cottontails and snowshoe hare. These contorted trees may also provide shelter for a whole host of wildlife.

You might not have ever realized it, but if you live in an area that experiences snow, qali has likely affected you at some point and I don’t mean that moment when you accidentally brush up against a laden branch and send an unwanted shock of snow pouring down the collar of your coat. I’m talking about more significant impacts. Qali can be very heavy and often trees buckle under the weight taking down whatever else is nearby, which is some cases are power lines. I know I’ve spent the odd cold, snowy night in the dark, waiting for hydro to be restored.  These qali-broken trees also open up the forest floor to new growth, creating pockets of mini forest succession and driving the forest cycle on a smaller scale.

Snow is an amazing thing and qali is only one small facet in a dizzying array of diversity, which thanks to northern cultures, we’re able to describe in accurate and imaginative ways. So, next time you take a winter walk surrounded by white, take a moment and discover that variety for yourself and maybe even create your own words to describe it.

 

Restless Heart

Zugunruhe - migratory restlessnessTo regular readers of this blog, my love of obscure words is not a new thing. Over the last few years, I’ve been creating these ‘definition images’ as my way of bringing life to some of the wonders of nature and the words used to describe them.

Looking back over them all, I realized, much to my surprise, that I’ve crafted more than 70 of them, covering just about every letter of the alphabet. That discovery has led me to challenge myself to visualize words starting with more uncommon letters, like  X, Qand Z. Kind of like an artistic variation on Scrabble.

Autumn has given me the perfect opportunity to address one of my favourite Z words.  It’s another one of those terms that comes up only in the discussion of natural history and animal behaviour and it never fails to raise a few eyebrows if you manage to slip it into regular conversation.

The word is Zugunruhe.

Zugunruhe is a combination of two German words = Zug, meaning to move or migrate and Unruhe, meaning restlessness and it together, the sum is really the combination of the parts: migratory restlessness. For a behavioural ecologist, it’s a word that tends to conjure up thoughts of autumn, or more specifically, late summer.

As the earth lumbers along its orbital path and those of us in the Northern Hemisphere find ourselves canting away from the sun’s warmth, many creatures get antsy. Birds especially are seized by a sudden disquiet and activity levels skyrocket. Sleep patterns change and if the individuals are kept in a cage, they start orienting their activity in the direction they should be migrating in. Most species go through a period of excessive feeding, needing to pack away as much energy as aerodynamics will allow for the journey that inevitably lay ahead. We see it all around us in the clouds of blackbirds roiling through the air or flocks of geese descending on a recently-harvested field. This period of restlessness is referred to as Zugunruhe by biologists who study animal behaviour and it’s a phenomenon observed both in the spring and in the fall, just prior to the mass migrations that move millions of birds along north-south flyways over the continent.

Here, in the boreal forest, it’s a phenomenon that usually starts in August. Our summers are relatively short and as soon as breeding is over, the preparation of the twice-yearly journey gets underway, especially in songbirds, who have to travel thousands of kilometres to Central and South America. With their time here so fleeting and the journey so long and fraught with danger, you can’t help but wonder, why go through all the trouble?

Why not stay in the tropics, where the weather is favourable and save all of the energy and risk associated with long-distance travel? The answer to that question likely varies to a certain degree between species; but evidence suggests that food, or rather the lack of it, was likely the driver behind the evolution of long-distance migration in many birds.

Most of today’s migratory species likely evolved near the equator, enjoying consistently tolerable weather and relatively abundant food. However, as populations started to grow and segment into different species, the pressure on food sources grew to a point where the survival of some depended on searching out new resources. The only place to go was away, into the temperate zones north and south of the tropics. Those that did, discovered abundant resources, millions of insects, and a glut of fruit and vegetation. The problem was it only lasts for a short period of time, forcing those explorers to retreat back to the warm haven to the south during the winter months.

Over millenia, these paths have been extended and entrenched by generations of birds winging their way along now well-established routes.  As those paths have become increasingly ensconced in the collective memories of each species, so has the irrepressible need to travel those routes that spurs everything from hummingbirds to harriers on their way twice a year.

With migration in full swing here in Manitoba, the period of zugunruhe is actually over; but once balance of night and day swings back into the favour of the light, the millions of birds enjoying the warmth of their winter homes will feel the inexorable pull once again, the restlessness building until one day, they’ll have no choice but to take to the air and find their way back to us.

Given to Fly

Alight - Herring Gull LandingI never get tired of watching birds fly. It’s something that’s always entranced me: a warbler flitting between sun-dappled leaves, a gull wheeling lazily against the clear blue of a Manitoba summer sky, or the subtle whisper of an owl’s feathers as it returns to roost.

My fascination with flight started at an early age, much to the consternation of my parents who had to cart me off to the hospital to get my foot x-rayed after an ill-fated attempt to get airborne from the top of a ladder with willow branches strapped to my arms.

I’m pleased to report that there was no permanent damage and I now have a much better grasp on the mechanics of avian flight.

Physicists and biologists alike are still trying to sort out all of the details; but we get the general gist of how it works and much of that knowledge has resulted in the air travel we enjoy today.

A bird in the air has two forces to contend with: gravity (the inexorable force the earth exerts on everything, drawing us back to its core) and drag (the force of the air that pushes back against us whenever we try to move through it). In order to keep itself aloft, the wings of a bird must produce enough lift to counter gravity and reduce drag.

 

Much of that is achieved through the shape the wing. It takes a lot of energy to flap all the time to produce enough thrust to keep you up and moving forward, so having wings that can generate lift and reduce drag as you glide are a beneficial adaptation. Wings aren’t flat, whether they are on a bird or a plane. Diagram explaining how cambered wings create liftFlat wings don’t create lift. Air moving around a symmetrical wing passes over and under its surface at the same speed on both sides. However, if you curve the wing and create a cambered airfoil, then you’re getting somewhere. With a cambered wing, the air passing over the top moves much faster than the air passing below the wing. This creates a pressure differential, with lower pressure above the wing, where air is being swept away and high pressure below where air is piling up, pushing the wing and the bird attached to it, up into the sky. There wasn’t much camber to my willow branches, hence the crash landing.

 

Diagram explaning how the angle of attack of a wing can affect liftAnother way increase that pressure differential is to tilt the leading edge of the wing up, dropping the flight feathers down and building up more air underneath. However, you can go too far with this. Tilt more than about 15o and the airstream separates from the upper surface of the wing, creating turbulence, stalling the bird out. They use this to their advantage when landing, like the gull in the image above. To control the stall, most birds can raise their equivalent of a thumb called the alula. This nub of bone with usually about three feathers on it (you can just see it sticking up behind the top of the gull’s wing in the picture) can split the airstream at the leading edge, forcing it back over the surface of the wing.

 

 

 

Once they’ve vanquished gravity, there’s still the matter of drag threatening to push them back to the ground. Flapping, of course, will keep you moving; but there are several design considerations that birds have made over millenia of evolution.  Birds that do a lot of gliding (e.g. gulls) have long, tapered wings that concentrate any vortices that might form at the wing tips (turbulence caused by the feathers slicing through the air) into two small areas that are as far apart as possible, reducing what is called ‘pressure drag’. Soaring birds, like hawks and Sandhill Cranes, take a different approach, spreading out their primary feathers like fingers, splitting up the wingtip vortices and reducing their impact.

If you found wrapping your head around all that was a bit of a challenge (like I did the first time I had to teach it), understanding what’s going on when a bird is flapping will give you a veritable headache. Things get complicated as the wing starts to move and lift and thrust start happening simultaneously. In a nutshell, however, the lift is generated by the curve in the part of the wing closest to the body, while the tips of the primaries produce the thrust, creating momentum that propels the bird through the air with a grace that always amazes me.

Sometimes taking a phenomenon apart and learning how each component works destroys the magic of the whole thing; but I haven’t found that to be the case with the flight of birds. Understanding the forces that make it possible for them to shed the earth’s shackles only makes it all the more remarkable.

Suspended Animation

My world is getting quieter. As winter descends on the boreal forest, it’s like a veil of silence wraps around us, stilling all motion, save for the whisper of the wind across the newly-formed desert of snow.  One by one, the waterways stop, frozen in time, held captive by the solid grip of truly frigid temperatures.

Around here, the last body of water to succumb to this relentless creep of ice is the great Lake Winnipeg. Staring out over its endless expanse during the summer, it’s hard to believe that this inland ocean, the tenth largest freshwater lake in the world, finally gives in and stills beneath over a metre of ice.

It’s not a quick process and it actually starts a lot earlier than most of us realize. As the days get shorter and the air gets cooler, heat from the lake is slowly released into the atmosphere, often creating lake-effect precipitation, but that’s a story for another day.

As the water cools down, it becomes denser because the molecules’ natural vibrations slow and they cluster together. This denser water sinks deeper into the lake, letting warmer water rise to the surface and release its energy to the skies. This cycle continues until all the water in the lake reaches the same temperature. For freshwater, the magic number is 4 degrees Celsius, not zero, like you may have guessed. The water still freezes at zero degrees, but from 4 degrees on, the water molecules start to form the lattice work that ultimately becomes ice and at this point, this water is less dense than the rest of the layers below it, keeping it at the surface, where it starts to freeze.

At over 23,000 square kilometres, Lake Winnipeg doesn’t go quietly. November is a restless month, with flinty skies and often driving winds. Wild weather churns up this giant, but relatively shallow cauldron, breaking apart the fragile skin that forms on the surface, forcing it to start over.  Still, the cold eventually wins. The ice thickens and sheets knit together, sealing off the water below as it creaks and moans like a giant humpback whale trapped below the surface.

By the end of December, the ice will usually be thick enough to hold the weight of snowmobiles and tank-like Bombardiers used by the commercial fishermen to get to their harvesting grounds. By January, it’s strong enough to hold the weight of fully-loaded semi-trailers charging across the barren ice roads to deliver goods and supplies to towns that in summer can only be reached by air or by boat.

All the while, the lake is still very much alive beneath its frozen shell, reminding us of its presence with rattles and muted groans rising up from the depths. It’s a sound I never tire of hearing because it reminds me that the lake I love is still there, restless and waiting to be released with the warmth of spring.