Glaciers I have known

Glaciers I have known.

OK, so I have learned some stuff about glaciers that I didn't know before and that I find interesting. So here goes.  About 10% of the earth's surface is covered in glacer ice and about 75% of the earth's fresh water is contained in them.  At the height of the last ice age, about 35% of the earth's surface was covered with glaciers.  When the ice looks white, it still contains tiny bubbles of air.  After the  ice has been compressed by its weight, the air is forced out and it looks blue.

Here you can see the blue in the ice
 of the exit glacier near Seward 

 They are not just big blocks of ice that slide down hills or make lakes in Denali. Beginning with the obvious, if enough snow falls that it can't all melt in the summer, the snow builds up. The weight of the snow changes it to ice. The pressure of the huge layer of ice causes the it to melt at the base of the glacier so that the whole thing is sitting on a layer of water that lubricates its movement over the bedrock. There is always water flowing out of the base of a glacier unless they are at really cold places like the South Pole. Note that this business of water liquifying under pressure instead of staying ice is one of the really unique properties of water. Most things solidify under pressure but water does not. Ice is also less dense than water, so it floats. That is also unique. All right, enough physics.

Now, we have this huge slab of ice on a rollercoaster ride down the mountain. It can speed up or slow down; it can bend downward or bend upward. The top and bottom can move at different speeds. All of this causes the ice to crack open or push up in ridges. Scientists who have drilled holes in the ice see that the holes never stay straight. The hole bends as the ice travels its different speeds.




The lower end of a network of water conduits

The water coming from a glacier not only comes from underneath it, but also from the top surface of the glacier in the summer. As the sun melts the ice, rivers form on the top and flow downward. The ice in the glacier is very hard and not easily penetrated. However, the top water can flow into cracks and begin to melt its way through the glacier. These openings become the beginning of a network of "pipes" through the glacier where the water is staying liquid even though the temperature is below freezing. I remember seeing a Nova show on some French scuba divers who dove into these openings with movie camera. They were in water that was several degrees below freezing but still liquid. The pictures were amazing and they were some brave people.

this gives you some idea
of how big the opening is

So now look again at the picture of me standing in front of the "cave" in the face of the Worthington Glacier near Valdez and realize that it is the opening of one of these pipes. In this picture you can see a little way up inside the glacier.

The top of the glacier is a field of ice with the only thing showing above the ice are the tops of mountains which appear as rocky hills above the ice. Individual glaciers then come from the ice field down different mountain valleys, so several glaciers can share the same ice field. You can see this in the picture of the Portage Glacier with the Spencer glacier to its right. The Northeastern side of the Kenai peninsula is very mountainous and the Harding ice field that is 40 by 60 miles starting at the area south of Seward. Many of the glaciers go down to the ocean and form icebergs. This area is known as the Kenai Fjords National Park. Just at the north edge of Seward is a place where you can walk up to the Exit Glacier which is coming from the northern edge of the ice field. Again you can see the water coming out from under it.

As the glacier ice moves down to the foot of the glacier, it collects rock and earth that can be pushed onto the front and top faces of the ice.  In several of the glaciers I visited, they looked dirty, but when you picked up some of this material it was rocky and gritty with no organic matter such as you find in most soil.  An extreme example of this is the foot of one of the northeast glacier forks coming off of Mt. McKinley.  The central bench in this picture is actually the edge of the ice that has come some 16 miles down from the mountain and collected enough stuff on it to grow grass.  It looks like a canyon wall, but is ice.

More information about glaciers