Download File - Geological Engineering

Mountain Building
Mountain
A 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).
Mountain Formation
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.
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 mountains
Fault block mountains
Fold mountains
Uplifted/upward mountains, Dome
Mountains
Non boundary mountains
Residual Mountains
Volcanic mountains
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.
Sheild volcano
Composite /strato volcano
Ocean-Ocean Convergence
Shield volcano
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)
Composite 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)
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
Fault block 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 faultbounded blocks.
• Horsts are elongated, uplifted blocks of crust bounded by faults.
Fault-Block Mountains
Alternating normal faults lead to a characteristic pattern called a
Horst and Graben system. An area under tension will often have
Multiple 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 many
separate 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.
Mountain Formation
Continental Accretion
 Accretion is a process that occurs when
crustal fragments collide with and stay
connected to a continental plate.
 Terranes
• Terranes are any crustal fragments that have a geologic history
distinct from that of the adjoining fragments.
• 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.