Mountain BuildingMountain Building

MountainsMountains

• Most of Earth’s crust is below the surface of the world’s oceans (about 70%)

• The remaining portion is what we call “land”

• If an area sticks above the surrounding land, we call it a mountain

The Largest MountainsThe Largest Mountains

• The tallest mountain on the surface is Mt. Everest. It is 29,029 feet above sea level, and is part of Himalayas

• Despite being the tallest on the surface, Everest is NOT the tallest mountain on Earth. The big island of Hawaii is actually the tallest mountain on Earth (when measured from the floor of the Pacific Ocean, it is 33,476 feet tall).

Still BiggerStill Bigger

• Still taller… the giant volcano Olympus Mons on Mars towers over 88,600 feet above the surface (almost 3 times taller than Mt Everest).

A Few “Terms”A Few “Terms”

• Remember that the crust (the continents and the ocean floors) “float” on the mantle like a boat.

• This buoyancy is called ISOSTASY

• As the continents weather and erode away, they tend to float a little higher in the mantle (we call this ISOSTATIC REBOUND)

The term we use to describe any mountain-building event is OROGENY

Creating MountainsCreating Mountains• Mountains are formed

when forces change Earth’s crust

• Most often these forces are a result of Tectonic Plate movement– Plate Boundaries– Along Faults

• The three types of stress include…– Compression– Tension– Shear

• Mountains like the Cascades in Oregon, Washington and Northern California are the result of plate movement at the boundaries

• Mountains like those in Nevada are the result of fault movement

Mountains formed by Oceanic-Oceanic Mountains formed by Oceanic-Oceanic Convergence (Plate Boundaries)Convergence (Plate Boundaries)

• When two oceanic plates converge, subduction occurs

• A chain of volcanic islands can grow from the ocean floor

• The Aleutian Islands in Alaska are an example

Mountains formed by Oceanic –Mountains formed by Oceanic –Continental Convergence (Plate Continental Convergence (Plate

Boundaries)Boundaries)• When an oceanic

plate converges with a continental plate, subduction occurs

• A chain of volcanic mountains can grow from beneath the continent

• The Cascade Mountains are an example

Mountains formed by Continental –Mountains formed by Continental –Continental Convergence (Plate Continental Convergence (Plate

Boundaries)Boundaries)

• When two continental plates collide, subduction does NOT occur

• Neither plate gives way, and they both rise up• The Himalayas are the best, and youngest, example

Mountains can form at Divergent Mountains can form at Divergent BoundariesBoundaries

• The Mid-Atlantic Ridge is a chain of mountains

• It formed when two plates pulled apart from one another

• It is actually the longest mountain range in the world

Uplifted MountainsUplifted Mountains

• Mountains can also form where the crust is stretched-out and then lifted

• We call these Uplifted Mountains

• The Adirondacks in New York State are a good example

Fault-Block MountainsFault-Block Mountains

• Fault-Block Mountains form when pieces of Earth’s crust move, shift, rise or fall along faults.

• Some Fault-Block Mountains can be large, while others can be small.

Volcanic MountainsVolcanic Mountains

• The Hawaiian Islands are actually mountains, but they are not associated with convergent boundaries.

• The “Hot Spots” that creates these volcanoes rise off the floor of the Pacific Ocean can be more than 30,000 feet tall, and have HUGE bases!