Mountain Building

MountainA large landform that stretches above the surrounding land in a limited area.Mountains are formed through tectonic forces or volcanism. Height from the surface of the earth by over 1000 feet (300 m).

The term refers to the geological processes that underlie the formation of mountains.

And the process is also known as orogenesis ,mountain building.

Orogeny It refers to forces and events leading to a large structural deformation of the Earth's lithosphere (crust and

uppermost mantle) due to the engagement of tectonic plates.

Mountain Formation

Tectonic geomorpholgy & Neotectonics

The branch of science to understand landscape features in terms of underlying tectonic process is called Tectonic Geomorphology .

The field of study dealing with geological young or ongoing process is called Neotectonics.

Continental shield

Old mountains which are completely worn away and exist in form of flat regions .

Isostacy

Isostasy is the concept that Earth’s crust is floating in gravitational balance upon the material of the mantle.

Because of isostasy, deformed and thickened crust will undergo regional uplift both during mountain building and for a long period afterward.

Isostatic adjustment is the process of establishing a new level of gravitational equilibrium.

Isostatic Adjustment

Isostatic Adjustment in Mountains

Removal of material from the top will induce uplift at the surface. Removal of material from the bottom will produce subsidence. Thus, in the case of tectonic extension, isostasy will produce an effect that is opposite to thermal uplift.

TYPES OF MOUNTAIN

Volcanic mountainsFault block mountainsFold mountainsUplifted/upward mountains, Dome

MountainsNon boundary mountainsResidual Mountains

Volcanic mountains

Sheild volcanoComposite /strato volcano

Movements of tectonic plates create volcanoes along the plate boundaries which erupt and form mountains. A volcanic arc system is a series of volcanoes that form near a subduction zone where the crust of a sinking oceanic plate melts.

Ocean-Ocean Convergence

Shield volcanoes can span across hundreds of miles .Shield volcanoes have a slow slope and consist of frozen lava after it is hardened. Shield volcanoes almost always have large craters at their summit. gently sloping cone due to low viscosity of emitted material .(4-6 degree)

Shield volcano

Composite volcanoes have another name called “Strato Volcanoes.” Composite volcanoes consist of lava that is mixed with sand or gravel which in turn creates cinders or volcanic ash. steep rising cone due to high viscosity.(33 – 40 degree)

Composite volcano

Most volcanoes form along plate boundaries

• Less common: forming over a hotspot (far from a plate boundary)

• More than 400 volcanoes – 80% of all active volcanoes above sea level – are along subduction zones in the Pacific Ocean– Active = erupting or has

erupted in recorded history– “Ring of Fire”

Ocean-Continental Convergence

Fold Mountains

Fold Mountains

• Fold mountains are mountains that are made when two of the earth’s plates collide.

• When two plates collide the pressure compresses the rocks, forcing them to buckle and fold. Think of what happens to the bonnet of a car during a crash.

Fold Mountains

Convergence

Young Fold Mountains• As we know from previous sections, the earth’s

plates are constantly colliding in different parts of the world. These collisions are still increasing the height of some fold mountains today.

• The world’s young fold mountains are already about 30-35 million years old.

• These mountains are called Alpine Fold Mountains. They are very high because they have not been worn down by weathering and erosion.

Alpine Fold Mountains

• There are 4 major mountain ranges formed during the Alpine Folding period. These are,

• 1. The Rockies in North America.• 2. The Andes in South America.• 3. The Alps in Europe.• 4. The Himalayas in Asia.

Thrust faults main cause Of folded mountains

Large-scale normal faults are associated with structures called fault-block mountains.

• Fault-block mountains are formed as large blocks of crust are uplifted and tilted along normal faults.

• Grabens are formed by the downward displacement of fault-bounded blocks.

• Horsts are elongated, uplifted blocks of crust bounded by faults.

Fault block mountains

Fault-Block Mountains

Alternating normal faults lead to a characteristic pattern called aHorst and Graben system. An area under tension will often haveMultiple mountain ranges as a result.

Overthrust Faults

• If the plate that suffers the fault has already undergone folding, & its folded layers are then push up & thrust over layers on the fault’s other side, an Overthrust Fault occurs.

Dome /uplifted Mountains • Dome mountains are the result of a great amount of melted

rock (magma) pushing its way up under the earth crust. • Without actually erupting onto the surface, the magma

pushes up overlaying rock layers. At some point, the magma cools and forms hardened rock. The uplifted area created by rising magma is called a dome because of looking like the top half of a sphere (ball). The rock layers over the hardened magma are warped upward to form the dome. But the rock layers of the surrounding area remain flat.

• As the dome is higher than its surroundings, erosion by wind and rain occurs from the top. This results in a circular mountain range.

• Domes that have been worn away in places form manyseparate peaks called Dome Mountains.

Dome Mountains

Domed Mountains

Non-Boundary Mountains

Non-Boundary Mountains

Not all mountains are formed by plate boundaries. Some are formed by hot spots or regional extension or stretching.

Continental Accretion

Mountain Formation

Terranes• Terranes are any crustal fragments that have a geologic history

distinct from that of the adjoining fragments.

Accretion is a process that occurs when crustal fragments collide with and stay connected to a continental plate.

• Terranes occur along the Pacific Coast.

Mountain Building by Continental Accretion

Residual Mountains

These are mountains that are really plateaus that have worn down from erosion.