The Ice Cometh: How much weight can it hold?

When I was a kid, I went with a brother and a couple of friends down to our local river on a cold December Sunday morning. We found the river (actually at that place an estuary, its water level determined by Lake Michigan) frozen clear as glass.

We first thought of skating – but was the ice thick enough? We dropped a couple softball-sized stones from the bridge and, instead of breaking through, each landed with a solid thock! That sent us scrambling down the embankment to the water. One by one, we inched out from shore, the water under the ice less than a foot deep. We kept inching farther, staying well apart, still over shallow water. A few stress cracks showed the ice to be about two inches thick. Mustering our courage, we each tried jumping and landing hard. The ice held firm. Then we moved together into a circle and jumped in unison. Still no sign of weakness.

We ended up skating (with parents’ permission) for hours that day, on ice so clear we could see every detail on the bottom, two to four feet down. But were we really safe? Just how strong is ice? How thick does it have to be to walk on, skate on, drive a car on? I grew up with an old saying, allegedly from someone’s grandfather, that “Two inches of ice will hold a team of horses.” Every authoritative source I’ve read lately contradicts that.

Any discussion of when ice is “safe” must account for the possibility of springs, flowing water underneath (as on a river), snow on top, objects like logs or rocks protruding, recent temperature changes (have there been any freezing/thawing cycles?) and the condition of the ice itself (late-winter ice that is honeycombed is notoriously hazardous). Most experts will tell you there is no such thing as “safe” ice – venturing out is always at your own risk.

Even when we’re talking about clear blue ice – the kind formed from calm, very cold nights – authorities disagree on how much ice is acceptable. Some say to stay off ice three inches or less in thickness. Others say less than two inches will do in some circumstances. I have skated on river ice barely two inches thick. It was creaky, but I didn’t worry too much because I stayed near the bank, over water no more than a foot or two deep. If the ice broke I would at worst end up with cold and very wet feet and lower legs, and the river was right behind my house, so a warming place was nearby.

I won’t be so casual venturing out onto Birch Lake, where the depth just a few dozen yards from our shore drops to eight feet and more. If you’re looking for a little guidance on ice safety, here are a couple of perspectives from knowledgeable sources. The Lincoln (Neb.) Fire and Rescue dive and water rescue team gives this advice:

·        Less than 3 inches: Keep off

·        4-5 inches: Ice fishing and skating (person up to 250 pounds)

·        6-7 inches: Snowmobile or ATV (1,100 pounds)

·        8-11 inches: Light car or truck (3,500 pounds)

·        12-14 inches: Medium truck (8,000 pounds)

The U.S. Army Corps of Engineers breaks it down this way:

·        Less than 1.75 inches: Keep off

·        1.75 inches: One person on skis

·        2 inches: One person on foot or skates

·        3 inches: One snowmobile or a group of people walking single file

·        7 inches: Automobile

·        8 inches: 2.5-ton truck

·        9 inches: 3.5-ton truck

·        10 inches: 7- to 8-ton truck

This guidance applies to clear, blue, sound ice. So the old folk wisdom about the team of horses is not to be trusted. Here is an old saying you can live by:

Thick and blue, tried and true.

Thin and crispy, way too risky.

When in doubt, don't go out. 

The ice cometh: Why is it slippery?

One of my great winter joys has been ice skating – on a lake or river rather than a rink (especially an indoor rink). Nothing beat the first venture with blades onto brand new ice, barely thick enough to be safe, often clear as glass. And I’m not just talking about childhood here. As recently as 10 years ago we lived on a dammed section of river that by Thanksgiving usually had frozen solid. I would skate on it as often as I could, winding upstream through marsh and woods, until snow came and covered the ice. I am hoping one of these years our Birch Lake will freeze and stay clear of snow for at least a few days. It is fascinating to look down into a lake through sheet of ice.

Do you skate on your lake, conditions permitting? Have you ever wondered why you’re able to skate – that is, why ice is slippery? After all, the solid phases of most compounds are not. Perhaps you don’t wonder because you think you know the answer. If you’re like me, you were taught in grade school that we can skate because the pressure of the blades lowers the melting temperature (32 degrees F) at the ice surface, creating a thin film of water on which we glide. But if that’s true, why are we able to slide across ice while wearing flat-soled shoes, which exert much less intense pressure?

It turns out science has pretty well rejected the pressure explanation. In an article in the New York Times (http://www.nytimes.com/2006/02/21/science/21ice.html?pagewanted=all&_r=0) Robert Rosenberg, an emeritus professor of chemistry at Lawrence University in Appleton, Wis., explained why: “The explanation fails, he said, because the pressure-melting effect is small. A 150-pound person standing on ice wearing a pair of ice skates exerts a pressure of only 50 pounds per square inch on the ice. (A typical blade edge, which is not razor sharp, is about one-eighth of an inch wide and about 12 inches long, yielding a surface area of 1.5 square inches each or 3 square inches for two blades.) That amount of pressure lowers the melting temperature only a small amount, from 32 degrees to 31.97 degrees. Yet ice skaters can easily slip and fall at temperatures much colder.”

There are now two other explanations – apparently not mutually exclusive. One is that friction from the skate blade (or shoe) is what heats and melts the ice and creates the slipperiness. The other is that the ice surface is inherently slippery. “This argument holds that water molecules at the ice surface vibrate more, because there are no molecules above them to help hold them in place, and they thus remain an unfrozen liquid even at temperatures far below freezing,” the Times article said.

Among scientists who believe in inherent slipperiness is Dr. Gabor Somorjai at Lawrence Berkeley National Laboratory. His sophisticated tests support the theory and so does a basic observation: A person standing motionless on ice is not creating friction – yet still may easily slip and fall.

One who disputes the importance of the liquid layer is Dr. Miquel Salmeron, also of Lawrence Berkeley. The Times reports that he and colleagues dragged a device similar to a tiny phonograph needle across ice and found the friction to be “very high.” And high friction of course would generate meaningful heat.

“Dr. Salmeron said this finding indicates that while the top layer of ice may be liquid, it is too thin to contribute much to slipperiness except near the melting temperature. In his view, friction is the primary reason ice is slippery,” the Times article said.

Which theory is right? Maybe one or the other, maybe both. Scientists disagree. For all the advances in scientific knowledge, ice remains a mysterious substance. So, let’s not worry too much about the explanation. Let’s get out on the ice and slide around!

The ice cometh. Time to get to know it.

Is there any ice on your lake yet? There’s some on Birch Lake near Harshaw, Wis., where I live. It’s creeping out from the shore in ovoid shapes around the shallow inlet we call Indian Bay. I haven’t seen any ice on the main body of the lake yet, but then we haven’t seen temperatures down into the low 20s and teens, not even the overnight lows. Just give it time I guess.

Ice is a fascinating substance, and I’ll be writing about it in the next few posts. Right now the water in your lake is cooled down close to the freezing point of 32 degrees Fahrenheit (zero degrees Celsius). Or I should say, that’s the temperature at and near your lake’s the lake surface. It’s a little warmer deeper down.

Water is a peculiar compound in that it doesn’t continue getting denser as it cools. It reaches its greatest density at about 4 degrees Celsius (39 degrees Fahrenheit). And of course denser water sinks. So the water at the bottom of your lake is at around 4 degrees C, and the water at the surface is about ready to freeze. A very cold night or two will get the job done, forming a skin of ice over the surface that will thicken with more cold weather.

Here’s an interesting thought: What would happen if water and ice behaved the way most compounds do with falling temperature? That is, what if the coldest water were the densest and ice were denser still? Well, if you were to take a jar full of melted wax, and drop in a chunk of wax, that solid piece would drop to the bottom.

If water behaved that same way, ice forming at your lake’s surface from exposure to very cold air would sink. As more and more ice formed, it would continue dropping to the bottom, until after a long winter the lake most likely would be frozen solid from top to bottom. Nothing would survive the winter. In fact, deeper lakes probably would not thaw completely even through the summer.

As it is, ice floats. And the ice sheet that forms on your lake provides insulation that allows most of the water below to remain in a liquid state. So the fish, clams, turtles, frogs, snails and all sorts of macro- and microscopic life get through the winter just fine.

This anomalous density pattern is just one of many interesting properties of ice. In the next post we’ll explore why ice is slippery. You probably think you know the answer – I thought I did – but the latest scientific consensus says that answer is wrong.

The ice cometh: The hard work of freezing

In freshman high school science class my teacher led us through a simple but enlightening experiment to show the difference between water and ice. It’s worth describing as we wait for our lakes to freeze over, likely in a month or so from now.

The teacher had us half-fill two glasses with water. Into one we dropped an ice cube, and into the other an equal volume of ice water. We then recorded the temperature of the water in both glasses for half an hour.

In the glass that received the ice water, the temperature dropped instantly, but then began rising and kept doing so. In the glass that received the ice cube, the temperature dropped more slowly, but then bottomed out and stayed down as the ice melted. The teacher then asked: Which would be the better way to cool a drink on a summer day?

The answer was obvious. What the experiment illustrated was a property of water called the heat of fusion, which will soon come into play on your lake and mine. Heat of fusion for water is the amount of heat energy that has to be removed to turn it from liquid to ice.

The definition of a calorie is the heat required to raise the temperature of one gram of water by one degree Celsius. It turns out that it takes a great deal more energy to turn water into ice than simply to change its temperature. In fact, 80 calories must be removed from that one gram of water in order to freeze it – and during the process the water’s temperature doesn’t change.

This works in reverse, too: It takes 80 calories to melt a gram of ice. In other words, it takes 80 times as much energy to melt ice as to warm water by one degree; or the same energy to melt ice as to warm water from zero degrees all the way to 80 degrees Celsius.

Now, let’s think about our lakes. As the days and nights get colder, the water temperature is dropping, rather quickly. Overnight low temperatures are now routinely below the freezing point of water, which is zero degrees Celsius (32 degrees Fahrenheit). So, why don’t our lakes freeze sooner? It’s because of that heat of fusion.

The water temperature will get down near the freezing point fairly quickly, but once it does, the water must give up a very large amount of heat energy before becoming ice. Finally, as the days and nights keep getting colder, we’ll see ice crystals forming along the shore, then a skin over the shallows, and finally, after a very cold, still night, a sheet of ice over most or all of the lake.

I saw the ice go off our lake last May. This year will be my first chance to watch day to day as a lake freezes. I am looking forward to it.

Wind, leaves, needles, walleyes

If you went down to your lake yesterday, you no doubt saw its near-shore surface decorated. About noon a strong wind arose, breaking the now-tenuous bond between leaves and their twigs.

As I walked the 57 (yes, I’ve counted) steps down to Birch Lake, near Harshaw, Wis., oak leaves drifted by, sliding through the air like paper airplanes. Maple leaves spiraled down. Brown clusters of discarded white-pine needles littered the stairway. Around the pier, those same items dotted the water and lay on the bottom.

I had never fished this late in the season before – have you? It’s a beautiful way to watch the season wind down. The sun, amid gray clouds, slowly settled toward the woods. The trees to the east (mostly the oaks) still bore their colors, though less brilliantly, and more sparsely. As I anchored over my favorite reef, the wind, less energetic than earlier in the day, put what anglers call a “walleye chop” on the surface. Between my boat and shore, a musky angler drifted by, tossing a slender crankbait.

It soon became clear I had some things to learn about this late-fall fishing. The walleyes still haunted the reef, which rises to five feet below the surface, from 17 feet on the deep side and 10 or 12 toward shore. It took just a few minutes for the first walleye to grab a minnow and pull my chartreuse-topped slip bobber down. I waited to a count of 10, then yanked back on the rod and...nothing. I reeled in the minnow, still lively.

I cast out again. The bobber soon disappeared. I counted to 15...nothing. Next cast, count of 20 and...nothing. In summer a five-count was enough. These fish were behaving differently. I pictured the walleyes swimming slowly, mouthing the minnow, as if savoring before swallowing.

I learned to wait until a count of 30, or 40. I ended up with two keepers in the livewell, both lip-hooked even after the long delays. Given that much time in summer, the fish would have gulped the minnow down, the hook embedded deep in the throat, a situation to be avoided.

The lights went down on the evening, until I could barely see the bobber on the wavelets. It slid under the surface, and I waited. My basketball coach used to say always to end a practice on a made shot. I wanted to end my season with a caught fish (because, in all likelihood, this was my last outing of 2013).

I counted: 20...30...40... 45. Set! The season’s last fish – a 9-inch walleye. Lip-hooked. Released unharmed. I motored at low thottle through the semi-dark to the pier. On the way up the stairs I could half-see, half-feel, oak leaves still gliding down. The two walleyes? They'll be frozen and saved for a winter fish fry -- in memoriam.

What color are your lake’s loons now? Are they still around?

Long years ago a friend and I took our first autumn fishing trip, to a Northwoods lake we usually visited in June. As we set up on our fishing spot on a chilly mid-October morning, a bird popped up near our rowboat. It had a shape like a loon – the graceful neck, the long, pointed bill – but its colors were different, the sleek black of the head replaced by brownish gray, the spots now sparser and on a gray background.

Something told me even than that is was a loon, in its winter plumage. I’m not sure how I knew; perhaps because no other bird (in these parts anyway) has that distinctive shape, and I knew loons haunted the lake where we were fishing.

Have your lake’s loons changed their plumage? In all likelihood they have. I saw a loon in winter dress as far back as September 6, on a small wilderness lake in Wisconsin’s Northern Highland-American Legion Forest. There was a loon on our Birch Lake (near Harshaw, Wisconsin) as late as last Saturday, Oct. 5. I never got close enough in the fishing boat to see its markings; it was more skittish than loons on our lake usually are (and anyway, as ethics require, I didn’t pursue, only hoped our paths would cross close enough to allow a good look).

I’ve wondered: How exactly do loons change their plumage? It seems to happen pretty quickly. I’d seen September loons on our lake in summer attire, then that specimen on the backwoods lake decked out for winter. Well, it turns out the color changes through molting: Summer feathers fall out to reveal winter ones grown or growing in. At the same time, the loons' eyes lose their bright red and fade to brown. They also pretty much quit calling.

Neighbors here on Birch Lake have expressed concern for the remaining loon, which they say should have left by now. I suspect there is still plenty of time; there is no risk yet of the bird getting iced in, and won’t be so long as enough water remains open for a long runway. As it keeps getting colder, this loon and others will head south toward the ocean for open water and a ready food supply. Loons gather in groups during migration – as many as a hundred, or even more. That would be a sight worth seeing.

Keep an eye out for your lake’s loons – if not gone already, they soon will be. They won’t start their journey back until February or March, and they’ll time their arrival here for just after ice-out. They’ll be dressed for summer – wedding attire.

Closing time

This season for me begins the fulfillment of a dream: To spend an entire year on a Northwoods lake. Of course, this is now our one and only home, so with luck that year will turn into many. For now we enjoy the magic of peak fall color reflected in water.

Do you live at your lake? Stay for the summer? Visit for the occasional week or weekend? Until this year I had never been here in the north to experience the slow turn toward winter. Right now we’re on the brink. Have you seen your lake this way? We’re torn between carving out a few more fishing days and giving up, pulling in the pier and buttoning the boat up for storage.

Recent evenings it has been mesmerizing to watch a slip bobber float on a gently undulating palette of reflected oranges, yellows and reds. Such evenings now are numbered. Yesterday I took the last dozen minnows, anchored the boat on a favorite reef, and tried once more for the walleyes and smallmouth bass that haunt the rocks. The sky threatened. Wind poked through my fleece jacket. Waves tossed my bobber around. Nothing bit. This could be the time when the fish retreat to the depths and become harder to find. Or a few more warm days could intervene and change the pattern.

Back at the pier, the boat tied off, I sat on our bench and scanned the shore. The trees lining the lake had taken longer to turn than those at the top of our hillside, but now they blazed, especially when for a few interludes the sun pierced the gray sky. Years ago my father, returning from two weeks in Norway, said that so much beauty, seen everywhere, brought a kind of fatigue. I feel that way now, not just viewing fall’s majesty but surrounded by it, immersed in it, splashes of brilliance outside our every window, around every bend in the road, arcing over our narrow private road and the town roads I travel on bicycle. It is fleeting, I know. We are just a few days, or a frigid night, or a strong wind, from lights out, the trees suddenly bare, the ground a colored kaleidoscope for a few days, then brown.

So if you are visiting your lake now, even if you have been through all this before, get out and see it. Autumn is closing down. Winter closing in.