Mountain Building

Unit 3: Lesson 3Objectives:

Mountain DistributionConvergent Boundary MtnsOther Mountain Types

Crust–Mantle Relationships When you look at a map of the

Earth, you immediately notice the oceans and continents.

Changes in elevation are best seen by using a topographic map.

Differences in elevation are not caused by a difference in density.

The Himalayans

Isostasy The displacement of the Earth’s mantle by

the continental and oceanic crust is a condition of equilibrium known as isostasy.

The crust and the mantle are in equilibrium when the force of gravity of the crust is balanced with the upward buoyancy of the mantle.

Similar to people getting into and out of a boat. As people get in, the boat goes down; as people get out, the boat rises.

Continental Buoyancy Continents are said to float on the

mantle, because the continents are less dense than the underlying mantle.

Mountain Building Video Let us discuss the different forces of

gravity and buoyancy in the next slide.

Isostasy Example

Isostasy and Erosion Since erosion works against mountains,

tearing them down, why do some mountains still exists today?

As the mountain erodes, the mountain root will disappear. This allows the crust to rise, due to the buoyancy force, equals the mountain’s force.

This slow process of the earth’s crust rising as a result of the removal of the overlying material, mountain, is called isostatic rebound.

Convergent-Boundary Mountains

When one oceanic plate converges with another oceanic plate, one plate descends into the mantle and creates a subduction zone.

As the material in the subduction zone melts, some material is forced up to the surface as magma and results in a volcano.

The volcano grows until a volcanic mountain is formed.

What would the soil or rock be like on this mountain?

Oceanic-Continental Convergence

This type of boundary also creates a subduction zone.

Can produce major mountain ranges due to the uplift of the continental plate Andes, South America Ring of Fire, Pacific Ocean

Continental-Continental Convergence

The Earth’s tallest mountains are formed by the convergence of two continental plates.

The Himalayans are the world’s tallest mountains, above sea level.

Instead of melting like at a subduction zone, the material is folded and the magma hardens underground adding to the uplift.

Other Mountain Types Divergent Boundary Mountains

Generally found along and comprising the Mid-Atlantic Ridge. As sea-floor spreading occurs, magma rises to fill the gap and is built up over eons.

Uplifted Mountains Formed by the slow uplift of

continental material. The magma has hardened below the surface and is then forced up by the upward force of the mantle. Adirondacks, New York

Volcanic Peaks As the volcano mountain moves

away from the hot spot, the volcano becomes dormant and eventually extinct.

Shield volcanoes make up much of the Hawaiian Islands, are formed in this manner.

Greatest Mountains on Earth Video Compilation