The great ice mass that began the Ice Age in North America has been called a continental glacier, it may have been about 15.000 feet thick in its center. This great glacier probably formed and then melted away at least four times during the Ice Age.
The Ice Age or glacial period that took place in other parts of the world still has not had a chance to melt away! For instance, the big island of Greenland is still covered with a continental glacier, except for a narrow fringe around its edge.
In the interior, this glacier often reaches heights of more than 10.000 feet. Antarctica is also covered by a vast continental glacier which is 10.000 to 12.000 feet high in places!
So the reason we still have glaciers in certain parts of the world is that they have not had a chance to melt away since the Ice Age. But most of the glaciers that exist today have been formed in recent times. These glaciers are usually the valley type of glacier.
It starts in a broad, steep-walled valley shaped like a great amphitheater. Snow is blown into this area or slides in from avalanches from the slopes above. This snow doesn’t melt during the summer but gets deeper year by year.
Eventually, the increasing pressure from above, together with some melting and refreezing, forces the air out of the lower part of the mass and changes it into solid ice.
Further pressure from the weight of ice and snow above eventually squeezes this mass of ice until it begins to creep slowly down the valley. This moving tongue of ice is the valley glacier.
There are more than 1.200 such glaciers in the Alps of Europe! Glaciers are also found in the Pyrenees, Carpathian, and Caucasus Mountains of Europe, and in southern Asia. In southern Alaska, there are tens of thousands of such glaciers, some from 25 to 50 miles long!