Four Types of Mountain Formation

Constructive vs. Destructive Constructive Earth processes are changes that add to the surface of the Earth by building up land forms. Destructive forces break down land. 

Volcanic mountains The first type of mountain-building comes from volcanoes. Most volcanoes happen near plate edges, but some happen over hot spots.

Shield Volcanoes Shield volcanoes have basalt lava that flows easily, meaning they are rarely explosive. Active shield volcanoes erupt for many years at a time. This creates their shape: wide at the bottom with gently sloped sides. They can be 20 times as wide as they are tall.

Basalt lava flow The lava that flows from shield volcanoes is basalt and it creates wide, thin layers that can flow for miles In Hawaii the lava can flow clear to the sea, increasing the size of the island.

Shield Volcanoes The largest volcano on Earth is Mauna Loa, Hawaii. Its summit is only 4,170 m above sea level, but it is a staggering 17,000 m above its base. It is so heavy that it bends the oceanic crust it sits on down by 8,000 m.

Shield volcanoes are not that common Since shield volcanoes are rarely found at subduction zone, they are not the most common type There are others besides Hawaii – several in Africa and several in the Galapagos Islands (both are on hot spots that are part of spreading centers)

Volcanoes at divergent boundaries Did you know that the mid-ocean ridges can be considered ONE volcano even though it is 40,000 miles long? They create a vast system of mountains and canyons.

Composite Volcanoes Composite volcanoes are the most dangerous. Their layers alternate between basalt and ash, and when they erupt they often blow themselves apart because their lava is viscous (it does not flow easily) They are found in subduction zones and include the most dramatic eruptions ever!

Subduction Zone in the USA? Once upon a time, there was an oceanic plate called Farallon. When North America started moving west, it was subducted. All that’s left is a few scraps; one is called Juan de Fuca.

Mount St. Helens Composite volcanoes often destroy themselves when they erupt!

Mountain building in the slow lane: Folding and faulting As the convection currents in the Earth’s mantle push and pull on the tectonic plates of the Earth’s crust, the rocks of the crust are broken and bent.

Folded mountains When rocks bend instead of breaking it is called folding. A fold can be a syncline – U-shape with young rock in the center A fold can be an anticline – Arch- shaped with young rock on the outside

Many mountains are folded and faulted When rock undergoes folding, where the pressure is too great or too sudden, faults will form. Where you find folding, you will also find faulting.

Tension and uplift When the surface is being pulled apart and there is uplift, block-fault mountains form. Notice that all of the peaks in a block fault range are not squared off.

Uplift and erosion When land forms are uplifted because of forces in the mantle, mountains can grow higher, and large, flat areas become higher. A broad, flat area that has been uplifted is a plateau.

A Dramatic Landscape Uplifting also causes relatively flat areas to be eroded more dramatically. The Grand Canyon was created when the uplifted Colorado Plateau was eroded by the Colorado River.

What’s the difference between a plain and a plateau? Elevation! Plains tend to be closer to sea level and plateaus are much higher.