Fish in winter

What happens to fish when the lake or river freezes up?

An ice sheet forms on the water body, leaving below it a slightly warmer world, though with an icy ceiling.

When water freezes to form ice, only the uppermost layer freezes. Ice is lighter than water, and floats on it, like a toy floating in a tub of water. Ice is also an excellent “insulator” – it prevents heat from escaping out. So under the ice sheet, is a warmer world, at around 1 to 4 degrees Celsius. This is why Eskimos from Iceland and Greenland build igloos to live in. Even though it is built of ice, the inside of an igloo is warmer than outside.

An Inuit village in Baffin village, Canada. © photographed from a book by C.F.Hall.

An Inuit village in Baffin village, Canada.
© photographed from a book by C.F.Hall.

Under the icy ceiling, fish can live quite happily, because they are ‘cold blooded’ – they can adjust their body temperature to the temperature of the surrounding water. We are warm blooded – we have to maintain our body temperatures in all situations. where life carries on as usual, even in peak winter. They also do the ‘usual tricks’ of storing fat in their bodies, like squirrels and birds.

Still, they do have to eat once in a while! Big fish eat smaller fish, so they don’t have much of a problem. Smaller fish eat insect larvae and small insects found in the muck at the bottom of ponds and rivers, and can get by until warm weather.

Gritting roads

It does not allow water to freeze, and makes ice melt faster.

First of all, what is gritting?

A gritting truck at work (Stephen Craven)

A gritting truck at work (Stephen Craven)

Those of you in cold countries where there is snow and ice must have seen it. Huge ‘gritting trucks’ go out in large numbers at night, to add something on the road. You will probably see the ‘grit’ on the roads the next day.

Although it is called gritting, there is actually no grit involved. Grit is small pieces of stone, pebbles and sand. But, gritting roads uses rock salt. Rock salt is similar to cooking salt, but it’s too rough and has too many other things in it, so we don’t use it for cooking.

How does it work?

For water to freeze, enough of its ‘molecules’ have to meet together and hold hands. (A molecule is too small for you to see, but it’s there is everything – it is the building block of things, same as bricks are used to make a building.)

When rock salt is added, water molecules keep meeting up with salt molecules instead of other water molecules. They cannot hold hands anymore, so water is unable to freeze and form ice.

Rock salt also interferes with ice. Ice is just water molecules, packed tightly together. Rock salt manages to get inbetween the molecules in ice, and breaks them apart, making ice melt.

So rock salt does two things: it prevents water from forming ice, and makes ice melt and form water again. Now you can walk safely on the roads, and people with cars can drive without skidding off the roads.

Why do we slip on ice?

Because the uppermost layer of ice has a thin layer of water on it. 

An icy road

An icy road (Erin McKittrick)

Ice is like an extremely thick stack of newspaper. The top most layer of the ice we move on is ‘loose’ compared to the lower layers. Lower layers have each other to stick to. The upper layer is in contact with the air above. It is warmer than the lower layers, and so tries to melt and become water.

When we move on ice, we are actually helping it become water. I’ll tell you how. Our shoes (and skates) rub on ice, causing friction. Friction warms the ice further, making it more water than ice. This makes ice slippery.

So it’s actually the water on the ice that makes us fall – not the ice itself.

How does gritting help? Go here to find out.