- In some places it is too cold for all the snow to melt - This snow begins to pile up - The weight of all the snow piling up causes the crystals to reform into something that looks like sugar - With more pressure these crystals begin to form together and the air spaces between them get smaller until there is a thick ice layer - The glacier is now formed and will now begin to “grow” - Due to the forces of gravity and the presence of water under the glacier or silt the glacier will start to move down and out!

Fresh Snow Old Snow Granular Snow Glacial Ice PRESSUREPRESSURE Water from glacier melting then refreezing Reduced air space

So what’s an ice cap then? No it’s not a delicious caffeinated drink from Tim Hortons! It’s a glacier that forms on a large area of relatively flat land and flows outward from its center. Ok, well then what’s an icefield? It is an upland area of ice that feeds two or more glaciers.

Valley Glaciers – form in a mountain range as the temperature rarely allows the snow to melt during the summer. Ex) Athabasca Glacier Continental Glaciers – huge mass of ice and snow that usually occurs near the North and South poles. They are so thick that they cover most of the mountain ranges below them Ex) Antarctica and Greenland

An icefall occurs when a glacier flows over a cliff. It does not simply break off because glaciers are not entirely liquid or solid!

As the glaciers are moving and stretching they may stretch too much causing a crack or crevasse. How is it different than crevice?

-Glaciers will either be advancing or retreating. -Advancing – the front edge of the glacier is moving further down the hill. -Retreating – the front edge of the glacier appears to be moving up the hill. -Despite this, the glacier is ALWAYS moving downhill. -This happens when the rate of melting of the edge of the glacier is greater that the rate the glacier is advancing. -THIS means the glacier is retreating, the glacier is not actually moving back up the hill it’s just melting rapidly!

-Pack ice – sheet of ice rarely more than 5 m thick that forms on the ocean that easily breaks off. - With that said icebergs DO NOT come from pack ice! - Icebergs – large chunks of ice that originate from continental glaciers. - Chunks of ice calve, break off, from the glaciers as they move into the ocean - Did you know that glaciers are huge under the water compared to what you see? Why do you think this is??

Even after glaciers are gone there is much evidence that they were once present! Glacial Erosion -Glaciers are amazing eroders! They bulldoze, break up, and scrape the underlying rock sediment. Evidence Left Behind -Striations – marks left by the rocks in the bottom of the glacier in the underlying rock - Cirques – bowl-shaped basins caused by erosion - Arête – caused by two cirques on either side causing a ridge. - Horn - - caused by three or more cirques causing a sharp peak. -U-Shaped Valley – caused by glaciers because they grab rocks from the side and the bottom as opposed to rivers.

- Moraine – a large ridge sediment left as a result of the glaciers bulldozing action. - Till – the mixture of different sized sediments dropped from the glaciers base as it has melted - Outwash – material deposited by the water of a melting glacier. - Erratics – huge rock fragments picked up from one location and dropped at another by advancing and retreating glaciers. - Esker – a ridge of sand and gravel left by a river of melt water within the glacier.

- Water from the glacier melting flows down the glacier. - It can be seen as rivers or streams on top of the glacier but usually eventually plunge deep into the glacier via millwells. - A millwell is carved by the streams as they move down through the glacier. They can be 30 stories deep! - These millwells lead to a network of streams below the glacier which eventually emerge from the toe of the glacier. - Glaciers act as incredible stores of freshwater. They slow down the water cycle and hold the water for when it is needed most, the summer - They also provide a vast amount of information about the Earth’s past climates because of the way they accumulate ice.

-Despite what you may think there have been at least 7 major ice ages in the past several million years! - The last one covered almost ALL of Canada! - How do we know this?? (Think about what we were JUST talking about) - There are many hypothesis as to how an ice age starts: reductions in the Sun’s radiation, increase in volcanic activity, mountain formation, tectonic plate movement changing currents, or changes in Earth’s tilt.

Review: 1)What is the difference between an ice cap and an icefield? 2)List as many evidence for glacial activity as you can. 3)Why are glaciers crucial for life on Earth?