Geology and Ecology of National Parks

Great Smoky Mountains National Park

Great Smoky Mountains National Park is situated on over 800 square miles of the Southern Appalachians between Tennessee and North Carolina. The Great Smoky Mountains, and the entire Southern Appalachians Mountains of which they are a part, are rich in geologic history, biodiversity, and beauty.

Great Smoky Mountains National Park is situated on over 800 square miles of the Southern Appalachians between Tennessee and North Carolina. The Great Smoky Mountains, and the entire Southern Appalachians Mountains of which they are a part, are rich in geologic history, biodiversity, and beauty. The origins of the landscape stretch back a billion years, and the park is the most biologically diverse in the entire National Park system. The Great Smoky Mountains are one of the oldest mountain ranges in the world, and the rocks there reveal a fascinating history. The effects of this history are what allows for the vast array of plant and animal species found in the Smokies, which are supported by its present rainy, temperate climate.

 

Geology

Map of the physiographic provinces of Great Smoky Mountains National Park showing the boundaries of the park

Map of the physiographic provinces of Great Smoky Mountains National Park showing the boundaries of the park, Tennessee and North Carolina’s shared border and the location of various faults, peaks, and valleys.

(Public domain.)

Bedrock Geology

The oldest rocks that can be found in the Great Smokies, and throughout the Southern Appalachians, are over a billion years old. This bedrock traces its origins to the formation of an ancient supercontinent called Rodinia (There is actually evidence of several supercontinents that have formed and broken over the course of Earth’s history!). Much of the core of North America is composed of remnants of the Rodinia supercontinent (Figure 1).

Around 750 million years ago, the supercontinent began to pull and break apart. As low areas were created, new oceans formed over time (Figure 2). One of the oceans was the Ocoee Basin, which formed near present-day western Carolinas, eastern Tennessee, and northern Georgia, where the Great Smokies sit today. Rivers and streams carried massive amounts of sediment into this basin over millions of years. These layers of sediment were eventually cemented into layers of rocks over nine miles thick.

Younger sedimentary rocks in the Great Smokies were formed 450 to 540 million years ago. These rocks were formed when what is now the Appalachian region was a shallow marine continental margin. Sediments deposited here formed limestone rocks and fossils can be found among them. Fossils here include worm burrows and shells of tiny crustaceans.

 

Deformation and Mountain Building

About 470 million years ago, the continents that had pulled apart started moving towards each other again. The movement of continental plates is slow, occurring at a rate of a few inches per year over many millions of years. But eventually, what we now know as Africa collided with the eastern edge of ancestral North America around 270 million years ago, part of the formation of the supercontinent Pangea (Figure 3). As ancestral North America and Africa collided, the entire Appalachian region was uplifted, creating mountains whose elevations were likely higher than the Rockies today. Continental collisions generate huge amounts of pressure and heat, which has a number of interesting effects.

One of those effects is the creation of plutons. As the continental blocks rode over each other, the tremendous pressure and heat melts some rocks. If the molten rock makes it to the surface it forms volcanoes or lava flows. If it stays underground, however, it cools and hardens forming igneous blocks of rock called plutons. The heat and pressure also metamorphosized the sedimentary rocks that had previously existed in the area. The process of metamorphosis turned sedimentary rocks like sandstone and shale into quartzite and slate, respectively.

Yet another process associated with the continental collision was folding and faulting. Faults are fractures that occur between blocks of rock where movement occurs (the link provides information from USGS on different types of faults and examples throughout the world including animations). Earthquakes are the result of sudden movement of the blocks of rock at a fault. During this time, earthquakes would have been commonplace in the Southern Appalachians. In fact, we can see evidence of faulting in the Great Smoky Mountains National Park today. Typically, younger rocks lie on top of older rocks, but in Cades Cove in the Great Smoky Mountains the limestone of the valley is younger than the surrounding mountains. This is a result of the older rocks being pushed over top of the younger rocks when faulting occurred. Over time, the older rocks were weathered away giving as “window” to see the younger rocks underneath. Learn more about the geology of the park in the a USGS publication Birth of the Mountains: The Geologic Story of the Southern Appalachians.

 

Erosion

Around 240 million years ago, the continents began pulling apart again in the breakup of Pangea. This continental breakup is what formed the Atlantic Ocean as we know it. In fact, the Atlantic Ocean is still getting wider today. The previously uplifted Appalachian Mountains were subject to intense erosion. The Appalachian Mountains that we see today are just the remnant cores of the mountains that stood some 100 million years ago. The sediment was carried away towards the Gulf of Mexico and Atlantic Ocean. As sandstone and quartzite from the mountains is weathered, eroded, and transported away from the mountains it is broken into smaller and smaller pieces ultimately forming sand. Some of that sand eventually finds its way to the beaches of the Gulf and Atlantic.

Rates of erosion were not constant across the Appalachian Mountains. Different types of rocks erode at different speeds. Rocks made from hard pebbles and sand are more resistant to weathering and erosion and form the peaks of the mountains we see today. Softer rocks made from fine-grained sediments, like silt and clay, are more easily weathered and are found in lower areas. The difference in weatherability between rock layers is what allows for the waterfalls that can be found in the Smokies today (for more information on waterfall formation). Water has amazing erosional power, particularly in times of flood and high-water flow.

Cosby Creek

Cosby Creek

(Public domain.)

Glacial History

Starting about three million years ago, Earth experienced a series of ice ages, during which huge sheets of ice extended up or down from the poles. During the last period of glaciation, around 1.1 million to 11 thousand years ago, glaciers dominated the landscape just some 200 miles north of Great Smoky Mountain National Park. The effects of glaciation can be seen in both the geologic record and in the wildlife and plants present in the park today. One piece of evidence of the glaciers and freezing temperature is the presence of boulders in Great Smoky Mountains National Park. Water permeates through the rock layers and then expands when frozen, pushing the rocks apart. As this happened over and over again boulders were formed as rock was broken apart into giant chunks. Cold temperatures also pushed animals and plants native to more northern climates southward and into the Southern Appalachians. Many of those animals can still be found in the park today.

For more detailed information on the geologic history of the Great Smokies including a cross-section of the region check out the Geologic Map of the Great Smoky Mountains National Park Region, Tennessee and North Carolina and the accompanying explanation prepared by U.S.G.S scientists in cooperation with the National Park Service. The USGS Scientific Investigations Map 2830Geology Of The Southern Appalachian Mountains can be downloaded for more information, pictures, and graphics.

 

Ecology of Great Smoky Mountains National Park

Aerial image from the NASA/USGS Landsat program depicting Great Smoky Mountains National Park in summer.

Aerial image from the NASA/USGS Landsat program depicting Great Smoky Mountains National Park in summer. The trees are at their most vibrant green.

(Public domain.)

Great Smoky Mountains National Park is known to be the most biologically diverse in the entire National Park system. This biodiversity is in part a result of its past as a refuge for animals and plants migrating south away from glaciers. It can also be attributed to its mild, rainy climate. Scientists have identified 19,000 different species of plants and animals in the park and think that as many as 100,000 other species may have yet to be identified.

The vast majority of Great Smoky Mountains National Park is covered with forest—almost 95%. A quarter of that forest is considered old growth, which is a mature, mostly undisturbed forest with trees that are hundreds of years old. There are four different types of forest with the park: Spruce-fir forests, Northern Hardwood forests, Hemlock forests, and Pine-and-Oak forests. Spruce-fir forests are found at the highest elevations in the park some 4,500 feet above sea level and are a boreal forest. These forests are similar to those that can be found in Maine and Canada. Northern Hardwood forests are indicated by American beech, birch, and maple trees and grow mostly in the middle to upper elevations of the park. This is the forest type that creates the beautiful fall colors for which the Appalachians are famous. You can see the changing colors of the forests in seasonal images from the USGS/NASA Landsat program.

Hemlock forests grow in shady places often in almost pure stands. They are an ecologically important species, but unfortunately their existence is threatened by the hemlock woolly adelgid, a tiny non-native insect. Pine and oak forests grow best in the drier parts of the park where steep slopes allow the soil to drain quickly. Forest fires are an important of the natural system in this forest type.

Image of a 2016 forest fire in Great Smoky Mountains National Park near the Chimney’s landmark.

Image of a 2016 forest fire in Great Smoky Mountains National Park near the Chimney’s landmark. The forest fire became known as the Chimney Tops 2 Fire.

(Credit: Warren Bielenburg, USGS. Public domain.)

Other ecosystems that can found within Great Smoky Mountains National Park include grassy and heath balds and wetlands. Balds are large meadows found in the middle and upper elevations of the park which support unique plant and animal types. Heath balds are composed of shrubby plants, and grassy balds are made up of grass and other shade-intolerant plants. Wetlands make up only a tiny part of the land area of Great Smoky Mountains National Park, but over 20% of the plant species found in the park are associated with these unique ecosystems. These wetlands support key ecological services including flood control, groundwater recharge, and prevention of stream erosion, among others.  

Gum Swamp, a karst-depression wetland in Great Smoky Mountain National Park, Tennessee.

Gum Swamp, a karst-depression wetland in Great Smoky Mountain National Park, Tennessee.

(Credit: Alan Cressler, USGS. Public domain.)

Great Smoky Mountains National Park is home to more than 200 bird species, 67 native fish species, 65 different mammal species, and over 80 species of reptile and amphibians. Probably most notable among those mammal species, and the symbol of the park, is the black bear. There are about 1,500 black bears living in the park. These bears mostly eat berries and nuts with insects and animal carrion constituting a much smaller part of their diet. In the summer male black bears weigh on average about 250 pounds and female bears around 100, but in the fall, when bears are preparing for hibernation, bears over 600 pounds have been documented. Other mammal species of particular interest include elk and North river otters. Both species were recently reintroduced to the park after being wiped out. Before being reintroduced, elk had last been seen in the Southern Appalachians in the early 1800s.

A group of USGS scientists outside a cave in Great Smoky Mountains National Park.

A group of USGS scientists outside a cave in Great Smoky Mountains National Park. Their research studies the effects of a certain fungus on salamander populations. Photo by Alan Cressler/USGS

(Public domain.)

Great Smoky Mountains National Park is a particularly important site for salamanders. In fact, the Great Smoky Mountains are known as the  "Salamander Capital of the World.” Salamanders are lungless and “breathe” through tiny blood vessels in their skin. They are moist and slimy to the touch and most likely to be found along streams under rocks and leaves. One type of salamander found in the park, the Hellbender, can grow to 29 inches in length. Research done by USGS scientists plays an important role in the protecting and understanding these species.

Image of a 16-inch Hellbender salamander. Hellbenders can grow as long as 29-inches and are just one of many types of salamander

Image of a 16-inch Hellbender salamander. Hellbenders can grow as long as 29-inches and are just one of many types of salamanders that live in Great Smoky Mountains National Park.

(Public domain.)

The same streams that provide habitat for the park’s salamanders are also home to a number of fish species including lampreys, darters, shiners, minnows, suckers, bass, and trout. Fish and other aquatic animals are particularly vulnerable to environmental changes and degradation. There are already four federally-protected fish species in the park: the spotfin chub (threatened), duskytail darter (endangered), smoky madtom (endangered), and yellowfin madtom (threatened). USGS scientists in collaboration with National Park Service staff are currently working on a project to better understand the effect of high levels of acid deposition resulting from atmospheric emissions of nitrogen and sulfur oxides on vulnerable aquatic species.

Great Smoky Mountains National Park also supports over 240 species of birds, with new species being documented as recently as 2017. The variety of forest types and ecosystems within the park provide refuge for a diversity of bird types including a number of migratory species. More than a 100 bird species use the park as a breeding ground including species migrating from the neotropics and northern climes. The Smokies are the southernmost nesting limit for a number of northern birds, and the northernmost nesting limit for many southern birds. A study by USGS researchers in 2005 examined the differences in bird populations between the park’s old growth and secondary forests. 

Close-up of a mason bee, Osmia sandersoneae, from Great Smoky Mountains National Park.

Close-up of a mason bee, Osmia sandersoneae, from Great Smoky Mountains National Park. This image is from the USGS Native Bee Inventory and Monitoring Program, which designs surveys of native bee species and develops identification tools, including creating accurate and detailed pictures of native bees and the plants and insects they interact with. For more  up-close images of insects, visit the Native Bee Inventory and Monitoring Lab page.

(Public domain.)

The diversity of plant life and rich ecosystems in Great Smoky Mountains National Park would not be possible without its pollinators. These include bees, beetles, ants, flies, wasps, butterflies, and moths. The USGS Native Bee Inventory and Monitoring Lab surveys and identifies native bees like those found in Great Smoky Mountains National Park. More than 4,000 Ultra Hi-Res public domain images of these amazing insects are available!