A moraine is an embankment or delta of boulders and crushed rock deposited by a glacier or ice river. Though commonly at the end, it may be both along the side and at the end of a glacier, or of the channels which the glacier once filled. All the mountainous National Parks have important glacial records or ruins that almost entirely cover them. These are moraines, soil-deposits, glaciated cañons, and lake-basins.
Vast is the quantity of material picked up and transported by glaciers. Mountains are moved piecemeal, and are ground to boulders, pebbles, and rock-flour in the moving. Besides the material the glacier gathers up and excavates, it carries the wreckage thrown down upon it by landslides, and also the eroded matter poured upon it by streams from the heights. Most of the material that falls upon the top of the upper end of the glacier gradually works its way to the bottom. At last, with the other gathered material, it is pressed against the bottom and sides and used as a cutting, rasping, or grinding tool till worn to pebbles or powder.
A part of the rocky material gathered is carried to the end of the glacier, where the melting of the ice unloads and releases it. This accumulation at the end is called the terminal moraine, and corresponds to the delta of a river. For years the bulk of the ice may melt away at about the same place; thus at this point accumulates an enormous amount of débris. An advance of the ice may plow through this and repile it, or the retreat of the ice, or a changed direction of its flow, may pile débris elsewhere. Many of these terminal moraines are an array of broken embankments with small basin-like holes and smooth, level spaces.
Many of the lakes have been filled with sediment, and in them and on them forests now flourish. The glacier lakes were slowly created. Most of them are being slowly filled. Those most favorably situated may still live on for thousands of years, but an avalanche may extinguish one in a single day. Eventually all must be filled and lost. They come into existence as a part of the work of the glacier. For a period they lie beautiful in the sunlight; then they are gone forever.
The extensive glacial records that show the past triumphs of the Ice King sometimes make the mind restless, and it wants to know: "Will the Ice King come again? Will mountains of white and silent snow again pile upon a lifeless world?"