How are mountains formed? The 4 main types of mountains

a scenic view of blue ridge parkway at sunset, blue ridge mountain range

Geologists say that the Smokies were likely once taller than they are today (photo by Ruth Peterkin/shutterstock.com)

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I don’t remember why we picked geology. 

It was our freshman year at the University of Tennessee. My friend Hobby and I needed a science course.

I imagine the class time – not too early, not too late – factored heavily into our decision-making. 

But it was one of the best decisions I made during my time at UT. It was a great class. I found the study of geology fascinating. 

And while I don’t have a reason to use geology much in my everyday life, I’ve found it’s great for little dad facts which I’m sure the kids love. 

As we drive along I-40 through the mountains of North Carolina, I talk to the kids about angles of repose and how rockslides happen. In addition, I point out the places where rockslides have occurred and what they’ve done to fix them. 

When we’re out along the mountain creeks, they might hear about the different types of rocks. These include metamorphic rock, igneous rocks and sedimentary rocks, in case you’d forgotten from your middle school science books. 

Road trips can include discussion of tectonic forces or the highest peak in the Smokies versus the highest point in the contiguous United States – which is Mount Rainier in the Western United States if you’re keeping score at home. 

Now, to be clear, two semesters of freshman-level geology 30 years ago doesn’t make me an expert. I just retained enough geological formations trivia to really boost my dad points. 

Whenever you can talk about volcanic activity while driving through the Smokies, it’s a bonus. 

Yellow rays of the setting sun, Morton Overlook
Morton’s Overlook is a great place to see a mountain view, located below Newfound Gap on the border of Tennessee and North Carolina (photo by Natural Stock/shutterstock.com)

Wait. Are the Smoky Mountains volcanic? 

No. They’re not.

But talking about volcanic mountains gives me a chance to work in my Dr. Evil pronunciation of “magma” and a dad has to work his material in where he can. 

Also, this was basically a rumor that started as an April Fool’s Day prank on the internet.

Read Also: Are there volcanoes in Tennessee? Your burning questions answered

Fog over the Great Smoky Mountains
The Smokies are folded mountains, and they were once much taller than they are now (photo by Robert Gubbins/shutterstock.com)

If the Smokies aren’t volcanic, how were they formed?

We are not going to rely on my 30-year-old freshman geology class for this one. 

The Smokies are what’s known as folded mountains

According to our friends at the National Park Service, the Smokies began somewhere between 310 and 245 million years ago.

The planet’s movement of tectonic plates, which create mountainous forms, brought the eastern edge of the North American Plate against the African tectonic plate, creating part of the supercontinent known as Pangaea. 

Basically, continental plate collisions take place at the rate of a few inches per year and continue over many millions of years.

There is evidence of earlier plate tectonic geologic events in rocks of the Great Smoky Mountains.

Hiker Walking With Rocky Mountains in View
The Rocky Mountains, pictured above, are a younger mountain range than the Smokies (photo by Alaina O’Neal/TheSmokies.com)

Did you know the Smokies used to be taller?

The NPS says the Appalachians were once likely much higher than they are today. In fact, the elevations were likely similar to our younger cousins to the West, the Rocky Mountains.

During a “last great episode of mountain building”, older, buried rocks were pushed up and over younger rocks and left a flat-lying thrust fault, known as the Great Smoky Fault, according to the NPS. 

After this, Pangaea broke apart. Then, the major tectonic plates moved into the positions they are today. 

Grotto Falls
Most of the beautiful waterfalls in the park were formed where downcutting streams encountered ledges of resistant metasandstone, according to the NPS (photo by Andrew S/shutterstock.com)

The ancient ancestors of the Smokies

The NPS says that the new rugged highlands, following Pangaea being broken apart, were subjected to intense erosion from ice, wind and water.

Eroded sediment was transported toward the Atlantic Ocean and Gulf of Mexico via rivers and streams.

The rock layers which were most resistant to erosion formed the highest peaks in the Smokies, such as the hard metasandstone on top of Clingmans Dome.

Today, geologists estimate that the mountains are being eroded about two inches every thousand years.

This process has turned what we know as the Smokies, in fact, all of the Appalachian Mountains, into the relatively small mountains that they are today.

What are the types of mountains?

A mountain is generally considered to be at least 1,000 feet above sea level. The main types include:

  1. Volcanic mountains
  2. Folded mountains 
  3. Fault block mountains 
  4. Upwarped mountains

The different types of mountains are essentially created by the same process underneath the Earth’s crust. Specifically, plate movements and volcanic eruptions. 

Mountain ranges are typically classified by the processes that created them. However, they are all the result of plate tectonics in one way or another. 

Traveler viewing Padar Island on a Volcanic Mountain
Padar Island is home to a volcanic mountain in Indonesia (photo by B_Beum/shutterstock.com)

1. Volcanic mountains

Volcanic mountains are probably the easiest to understand. The moving plates create volcanoes. This rupture in the crust of the Earth allows lava and other “nasty stuff” to escape from the magma chamber below the Earth.

The Pacific Ring of Fire is the most well-known group of volcanoes running along West North America, South America and Eastern Asia.

Essentially, it’s the rim of the Pacific Ocean. Volcanoes are mostly found on the ocean floor along the mid-ocean ridges of the tectonic plates. 

Examples include Mount St. Helens in North America and Mount Kea and Mount Loa in Hawaii.

View from Cades Cove
The Smokies, as viewed in Cades Cove, are an example of folded mountains (photo by Morgan Overholt/TheSmokies.com)

2. Folded mountains

When plates collide, one plate can slide under the other – an action called subduction.

When this happens, the plates will buckle and fold, forming mountains. Most major continental ranges, including our Smokies, are folded mountains created by subduction zones. 

Mount Everest and the Alps in Europe are fold mountains. In fact, fold mountains are the most common type of mountain on earth, according to World Atlas.

tetons in wyoming in front of lake
The Tetons in Wyoming are an example of fault block mountains (photo by Pat Tr/shutterstock.com)

3. Fault block mountains

And now we really start to get into the reason why I didn’t take sophomore-level geology. It’s just one definition after another as the actual concept gets further and further from my understanding. 

But essentially, fault block mountains are the result of a rift – a linear zone where the lithosphere is being pulled apart. What is the lithosphere?

It’s the rigid outermost rocky shell of a terrestrial planet. Basically, it’s the top part of the Earth’s surface.

As that is being pulled apart, the magma and volcanic stuff can break through. Fault block mountains can be volcanic, but they don’t have to be. 

The Tetons in Wyoming are an example of fault block mountains.

Black Elk Peak Custer State Park SD
Black Elk Peak at Custer State Park in South Dakota Black Hills Area is an example of an unwarped mountain (photo by Exploring and Living/shutterstock.com)

4. Upwarped mountains

Upwarped mountains are kind of like the end of a chain reaction car crash. They form far away from the collision site where the pressures are not as severe.

This creates mountains with dome-like structures or dome mountains. The Black Hills of South Dakota is a good example of upwarped mountains.

Which mountains have you visited? Let us know in the comments below. 

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