Geology of the National Parks

Welcome to Unit 4


Introducing Mountain Building, Obduction & Tsunamis

Introducing Obduction

Great Smoky Mountain National Park. Farm land in the front & 3 mountain ridges behind.
The folded Appalachian Mountains of southern Pennsylvania and adjacent Maryland. A collision between the “Old World” (Europe and Africa) and North America squeezed the rocks in a process called obduction, making folds in the rocks that are something like rumples in a carpet, and pushing the rocks up to form the Appalachians.
Credit: R.B. Alley
"No matter how sophisticated you may be, a large granite mountain cannot be denied—it speaks in silence to the very core of your being."
—Ansel Adams, The Spirit of the Mountains

Old, cold sea floor goes down subduction zones beneath warmer sea floor or continent, but what happens when a high-floating continent or island arc tries to go down a trench under another continent or island arc?

The answer is obduction, a BIG collision. The Great Smokies, Mt. Nittany near Penn State's University Park campus, and all of the Appalachians were formed by just such a collision when Africa and Europe hit the Americas, causing a long, thin slab of crust to become a short, thick one by folding and thrust-faulting. Higher mountains have deeper roots (for the same reason that toy boats can float in less water than aircraft carriers, and the iceberg that sank the Titanic stuck farther down in the water than did the ice cubes in the drinks on deck). When erosion lowers a mountain range, the root floats up, bringing metamorphic rocks to the surface that have been "cooked" by heat and pressure deep within the Earth.

Before we go any further, take a look at the following short video introduction by Dr. Anandakrishnan...

Duck Mountains Under Construction
Click Here for Transcript of Duck Mountain Video


Oh, hi. Welcome to the GEOSC 10 Tectonics III Section, Mountain Building. We're going to be talking about how the Appalachians were built, why they're still as high as they are now. And we're gonna talk a little bit about icebergs. Now, what does all that have to do with rubber duckies, and why am I in the bathtub surrounded by rubber duckies? Well, let's find out.

So why are we in a tub with rubber duckies? Imagine that these ducks represent the mountains that surround us right here in Happy Valley. This is Mount Nittany. Here's the Great Smoky Mountains. And these are all the ridges and valleys that spread up and down the east coast of North America, known as the Appalachian Mountains.

About 300 million years ago, North America and what's now Europe and Africa all collided to form a super-continent known as Pangaea. And when these continents collided, because they're both about the same density, neither one subducted beneath the other. In fact, as they crashed together, they formed larger and larger mountains that wrinkled up. And that's what we had 300 million years ago with the Appalachians. This big duck represents the mountains at the end of that mountain building phase.

So after that collision, we have the proto-Appalachians. They were big. They were tall. They were high.

But for the last 300 million years, they've been eroded, and eroded, and eroded. But still, we have mountains around here that are a couple thousand feet high. If you go further down towards Tennessee and Kentucky, there are mountains that are 4,000 or 5,000 feet high. Why are they still high? Well, it has to do with buoyancy.


Credit: Dr. Anandakrishnan

And....a Word About Tsunamis

Pull-apart, slide-past, push-together obduction and push-together subduction plate boundaries plus hot-spots make earthquakes, volcanoes, and steep slopes that can landslide. If any of these happen underwater, great waves called tsunamis can be generated, with catastrophic consequences. Fortunately, warning systems can be devised to reduce the loss of life, and building with a little foresight can reduce property damage. We'll be looking into these as we wrap up our multi-week exploration of Plate Tectonics and Mountain Building.

Learning Objectives

  • Differentiate between the three basic tectonic styles: pull-apart, push-together, and slide past
  • Identify which plate tectonics created various mountain ridges
  • Understand how various types of obduction zones work to create geologic formations
  • Visually identify various types of rocks

What to do for Unit 4?

You will have one week to complete Unit 4. See the course calendar for specific due dates.

As you work your way through the online materials for Unit 4, you will encounter a video lecture, several vTrips, some animated diagrams (called GeoMations and GeoClips), additional reading assignments, a practice quiz, a "RockOn" quiz, and a "StudentsSpeak" Survey. The chart below provides an overview of the requirements for this unit.

Overview of Unit 4 Requirements
Read/view all of the Instructional Materials for Unit 4: No, but you will be tested on the material found in the textbook.
Take the Unit 4 "RockOn" quiz Yes, this is the fourth of 12 end-of-unit RockOn quizzes and is worth 4.5% of your total grade.
Continue working on Exercise #2: Geology is All Around You Yes, this is the second of 6 Exercises and is worth 5% of your total grade.
Complete the "StudentsSpeak #5" survey Yes, this is the fifth of 12 weekly surveys and is worth 1% of your total grade.


If you have any questions, please feel free to email "All Teachers" and "All Teaching Assistants" through Canvas conversations.

Keep Reading!

On the following pages, you will find all of the information you need to successfully complete Unit 4, including the online textbook, a video lecture, several vTrips and animations, and two overview presentations.

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Students who register for this Penn State course gain access to assignment and instructor feedback, and earn academic credit. Information about registering for this course is available from the Office of the University Registrar.