Uplift, Erosion, Uplift, Erosion: A Compressed History Of Appalachia

images/voice_uploads/smallshendoah.gif">
Most Appalachian residents will tell you their mountains are unique, but most probably don’t understand just how special they really are. It isn’t the highest mountain range in the world, by any means, but it once was.

What is most remarkable about the chain is its incredible age, about 300 million years. It’s possibly the world’s oldest mountain chain, or at least among the oldest.

When the last dinosaurs died, the Alps and the Himalayas didn’t exist. The Rocky Mountains were just being created. The Appalachians, by that time, were already visibly worn, the formerly majestic, craggy peaks worn down to stumps.

The Appalachians, like nearly all other chains, were created when continents crashed into one another. The earth is mostly comprised of liquid rock, magma, upon which the rigid blocks of solid rock, called plates, float. The continents drift along with the magma’s currents and sometimes slowly crash into one another. Earthquakes, volcanoes, and mountain-building is a caused by this process, called plate tectonics.

When a large plate collides with a small one, the lesser will normally slide under the larger plate, sometimes creating earthquakes as they slide back and forth. The entire earth’s surface, or lithosphere, is comprised of about a dozen large plates and several small ones.

Sometimes, however, large plates crash into one another with such violence that their edges crumble, thrusting rock upwards. When this happens, mountains are born.

The Appalachians began about 380 million years ago, when North America collided with Europe. The earth began to buckle, starting in New Hampshire and running along the meeting point of the two plates. This collision began the Caledonian mountain system, which ran from what is now northern Alabama to Scotland.

Roughly 100 million years later, the southern Appalachians were formed as North America collided with Africa. This two-pronged creation is why the highest mountains in the Appalachians are so far apart — Mount Washington in New Hampshire and Mount Mitchell in North Carolina — and why the mountains’ height tapers slightly in the middle of the chain, i.e. Pennsylvania and West Virginia.

It also accounts for the different character of the northern and southern parts of the chain, from the disorderly, random configuration of mountains in New England to the long, multi-state north-south spines in the southern United States.

Over the next 200 millions years, while the dinosaurs came and went, the rugged Appalachian peaks eroded to stumps. Likewise, deep sediment, eroded from the peaks, covered the bases of the mountains before the Himalayas, Rockies, or Alps were even created.

All mountain chains begin as rugged, rocky peaks, but over millions of years, erosion wears them down. Young mountains like the Himalayas (10 million years old) are tall and craggy while older chains, like the Appalachians (300 millions years old) are lower, their summits more rounded.

Three hundred million years from now, the mighty Himalayas will look much as the Appalachians do today, and Mt. Everest, the highest peak on earth, will look more like North Carolina’s Mount Mitchell or New Hampshire’s Mount Washington, themselves once among the world‘s highest peaks. Newly created ranges will take the Himalayas place as the world’s highest chain.

The collision which created the Appalachians also formed the supercontinent Pangaea, where all the earth’s major land masses became one in a random configuration of the lithosphere at a random moment in earth’s history. With no natural barriers, plant and animal life were free to expand their ranges from continent to continent.

But some animals that thrive in Appalachia today didn’t arrive until much later. The brook trout, for instance, is an ice age immigrant that has only lived in southern and central Appalachia for the past few thousand years.

There were several successive ice ages. During each of them glaciers flowed across the northern Appalachians. During an ice age about 10,000 years ago, the weight of the massive glaciers caused the northern half of the North American plate to sink into the molten magma below, while the southern half of the continent was thrust upwards. East and westerly flowing rivers were replaced by new ones flowing northward.

Brook trout, moving away from the advancing glaciers, swam up these temporary ice age rivers, fleeing from advancing glaciers nearly two miles thick. They swam up scores of Appalachian rivers, establishing reproducing populations to the headwaters.

As the earth warmed, however, the glaciers melted and water in most southern Appalachian rivers became intolerably warm for brook trout, hindering reproduction. Eventually, they died out, except for those in the northern part of the chain and along a narrow north-south corridor along the Appalachian’s highest ridges, extending down through Pennsylvania and into northern Georgia.

During the ice ages, the southern Appalachians served as refuges for more than just brook trout. Because glaciers never made it further south than northern Pennsylvania, the southern Appalachians never were scoured by icebergs or covered with permafrost. Nonetheless, conditions here got cold enough from the presence of glaciers to the north to allow many northern species to colonize our highest peaks.

Pollen data show that spruce and jack pine were the dominant trees in the southern Appalachians at the height of the last ice age. When the earth finally warmed and the glaciers retreated northward, many plant and animal communities were marooned in the highest elevations of the southern Appalachians, where conditions were still cool enough to provide suitable habitat. Examples include our spruce-fir forests and species such as paper birch.

This site uses Akismet to reduce spam. Learn how your comment data is processed.