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Geologic History of Denali
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During the long history of Denali National Park several different kinds of rocks have formed. The earliest known rocks are blue limestone and calcereous slate from the Ordovician Period. Next are argillates, cherts, and greenwacks from the Devonian or Silurian period. Then from the early Devonian is gneiss and rhyolite and from the late Devonian is blue limestone with interbedded slates. The large amount of limestone suggests that a large body of water once covered the area and when animals would die their remains would collect on the bottom, compact, cement, and form the limestone.
During the Carboniferous Period more sedimentary rocks like conglomerates and red sandstones showed up. Volcanic activity also started increasing. Early in the Jurassic Period the ammount of igneous rocks greatly increased [mostly basalt] and the few sedimentary rocks that remained were slate and limestone.
In the middle Jurassic volcanic activity decreased and more sedimentary rocks like conglomerates, sandstones, slate, and limestone took over. During the upper Jurassic shale, sandstone, conglomerates, tuff, and arkose dominated the landscape. These were formed by the breakdown of the newly formed mountains. In the late Jurassic volcanic activity increased again and granitic rocks began rebuilding the mountains. Throughout the Ceataceous Period volcanic activity dwindled and black slates, conglomerates, and limestone flourished.
Through the Tertiary Period sedimentary rocks continued to dominate. Conglomerates, limestones, sandstones, and shales were abundant. In the post-Eocene volcanic activity rose and the rocks were mostly gabbro and basalt.
In the Quarternary period volcanic activity once again decreased and large amounts of sediments began to be deposited. Silts, sands, gravels, and glacial depositsdominate the landscape today
The force that caused all these changes is the Denali Fault. It stretches 1,300 miles from the Aleutian pennisula to the Yukon border. It's constant activity keeps Mt.McKinley's height rising. Enventually, Mt.McKinley will overtake Mt. Everest and become the tallest in the world.
As you can see Denali's six million acres contains a wide variety of rocks and has gone through many changes over the years.
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Climate of Denali
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Denali is in Alaska, so naturally it is a cold park. It has a sub-arctic climate with much of its precipitaion coming in the form of snow. Annually the park has an average of 15 inches of rain and 83 inches of snowfall. The average high is 37 degrees F. The average low is 16 degrees F., although in the winter the average can drop to negative 8 degrees F. Most of the weather is caused by cold northerly winds descending from the arctic. This wind brings the cold temperature and weather fronts, frequently causing blizzards. Frost can be found throughout the year, even in the warmest parts of summer. The frequent blizzards and constant cold conditions has caused glaciers to form at the peaks of the mountains.
The country rock in Denali National Park is weathered mostly by rivers, wind abrasion, and glaciation. Glaciers came down from the northwest in a long passed era and helped build the mountains that we see in the park.
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