Life on Glaciers
All sorts of things are blown onto the glaciers by wind: small plants, seeds, pollen, tiny insects, sometimes even birds! Most of these things freeze and eventually die, but some things manage to survive on the snow and some even spend their entire lives on the glaciers. Glaciers in Denali are covered with algal cells, minute plants so small that they can’t be seen with the naked eye. These algal cells, or algae, provide food for other organisms. Food chains on the glacier are very simple when compared to food chains in other habitats, but they provide an elegant example of how energy flows through a system. The sun shines on the snow and the algae. The algae use the sun to produce food for themselves and are eaten by insects, such as springtails. The springtails may die, decompose and return their nutrients to the glacier, or they may become food for larger animals, such as beetles.
One thing all organisms living on the glaciers share in common is size. They are all tiny! This is because resources, such as nutrients, are in short supply. Larger animals could not survive on such meager rations. Temperatures on the ice and snow are always at or below freezing. This means that there is usually very little free water. All organisms need water to survive. But if ice forms inside an animal’s body it can cause tissue damage or death. Glacier organisms have many adaptations that help them to cope with freezing temperatures. When the temperature drops, some types of invertebrates can isolate water in their bodies and cause it to form ice crystals in non-critical areas of their system. This prevents their tissues from being damaged. They may also produce a type of glycerol that acts as an antifreeze in the cells, keeping them from freezing completely.
But that’s not all! When the sun shines on the glacier, the ultraviolet rays bounce on the ice crystals and subject organisms to heavy doses of radiation. To help prevent damage from the radiation, glacial organisms have developed different types of "sunscreen". For example, one type of algae is colored red (causing "watermelon snow"). The red pigmentation is a type of kerotene, a substance that acts as a sunscreen for the algae.
The Glaciers of Denali
Glaciers cover one million acres, or one-sixth of Denali National Park. Like the many arms of an octopus, glaciers flow away from the mountains transporting hundreds of thousand of tons of ice each year. This ice eventually melts in the lower reaches of the glaciers and rapidly fills rivers with turbulent muddy water that flows into the oceans. The iconic image of a glacier calving ice chunks into the ocean cannot be seen here - these glaciers are more distant and rougher, eking out an existence high in the Alaska Range.
The most massive glaciers in the park drain snow and ice from the flanks of Denali. Hundreds of unnamed glaciers and at least 40 named glaciers flow from heights as high as 19,000 feet and descend to elevations as low as 800 feet above sea level. The Peters Glacier flows from the north and northwest portion of the mountain, whereas the Kahiltna Glacier is situated on the southwestern side of Denali and shares the southern slopes with an arm of the Ruth Glacier. The Ruth Glacier primarily occupies the southeast side Denali.
From the very top of Denali, Harper Glacier dumps snow and ice into the upper reaches of Muldrow Glacier, which carries snow and ice off Denali's northeast slopes. Of these glacial systems, the Ruth, Kahiltna and Muldrow Glaciers are the longest glaciers in the park; each is more than 30 miles long. The Kahiltna Glacier, which is not only the longest glacier in the park but also in the entire Alaska Range, is 44 miles in length.