Transcript Tectonic Features Contents

Tectonic Features
Contents
Folding and Fold Mountains
Faulting and its associated Landforms
Volcanism and the Earth’s Crust
Ocean Ridges, Ocean Trenches and
Island Arcs
Earthquakes
Folding and Fold Mountains
All major mountain chains are ‘foldbelts’ or called ‘orogenic belts’
Features and Characteristics of
Fold Mountain Areas
There are parallel belts of fold mountains separated by
intermountain plateau where sedimentary strata are much
less intensely folded.
They are mainly composed of thickness of sedimentary rock
strata. But when the core of fold mts. has been exposed,
igneous and metamorphic rocks are also found.
Young fold mts. Zones represent lines of weakness of the
earth’s crust and most of the world’s recently active
volacnoes lie and where the greater majority of earthqaukes
originate.
The rock strata have been compressed into various kinds of
folded structure.
Geometrical Varieties of Folds
Three geometrical varieties of folds can be
distinguished, anticlines, synclines and monoclines.
Elements of Fold
Types of folding
The profile of a fold is its form as seen in a plane
perpendicular to the axis.
Simple / Symmetrical Fold
• Two limbs dip symmetrically as similar angles
Asymmetrical Fold
• One limb dips more steeply than the other.
Over Fold / Overturned Fold
Recumbent Fold
• The axial plane is roughly horizontal
Overthrust Fold
• The sheet of rocks that has moved forward along the thrust plane.
Anticlinorium & Synclinorium
• A complex of folds of different orders
Types of folding
Formation of Fold Mountains
According to the plate tectonic theory, fold
mt originates where two plates of crust
converge.
The full development of an orogenic belt
requires collision between plates.
Formation of Fold Mountains
The surface is being actively eroded supplying a large
amount of sediments.
An accumulation of great depths of sediments in a
geosyncline (large depression) under an ocean.
Two plates move toward each other producing a great
compressional force.
The sedimentary rocks are folded up
Fold mountains are formed
Magma of the mantle may also flow out to the earth’s
surface forming volcanoes in this process.
Faulting is very common.
Eg. Himalayas (boundary between Eurasian plate and
the Australian Plate)
Faulting and its associated
landforms
Fault is a fracture of dislocation in the
earth’s crust along which there has
been displacement of the rocks strata.
The movement of the rocks on a fault
may have been in any direction, vertical,
or horizontal or some combination of
these.
Elements of fault
Fault types
Faults may be divided into several categories in relation to
the movements that have taken place on them.
Normal Fault
It is caused by tension
The hanging wall is displaced downwards relative to those
against the footwall along the fault plane.
‘Downthrow’ and ‘upthrow’ for the two sides are purely
relative.
Feature: Horsts (block mountain) and Graben
Reverse Fault / Thrust Fault
It is caused by comression
The hanging wall is upthrow the footwall along the
fault plane.
Feature: Horsts and Graben
Tear Fault / Wrench Fault
It is called transcurrent or strike-slip faults.
It is formed where the movement was dominantly
horizontal.
Block Mountain and Rift Valley
Regions which have been
divided by faulting into
relatively elevated or
depressed blocks are said
to be block faulted.
The upstanding fault
blocks may be small
plateaux or long ridgelike block mountains or
horsts.
A long fault trough is
known as rift valley.
Example: East African Rift
Valley.
Cross-section of East African Rift
Valley.
Volcanism and the Earth’s Crust
Vulcanicity is the process by which matter is transferred from
the earth’s interior and erupted on to its surface.
Volcanoes eruption are undoubtedly one of the greatest
natural hazards to life on this planet.
Below the crust, despite the high temperatures at depth, the
material is usually solid because of the great pressure exerted
by the superior masses of rock.
At times, a local increase of heat or/and reduction in pressure,
the Basal layers of the crustal SIMA to become magma.
Magma may be able to rise to the surface of the earth
through conveniently placed fissures and pipes or vents.
All such activities are known as vulcanicity.
There are two types of vulcanicity: Intrusive and Extrusive
vulcanicity
Intrusive Forms of Vulcanicity
The results of the forcing into the earth’s crust of
magma depend on
Degree of fluidity
The character of the planes of weakness, such as joints
and faults….
Intrusive Forms of Vulcanicity
Dykes:
These are formed when magma has risen through near-vertical
fissures and solidifying to form ‘walls’ of rock cutting across the
bedding planes of parent rock.
Sills:
Horizontal sheets of rock solidify from magma which has been
ejected between bedding planes.
Laccoliths:
These features are produced where tongue-like lateral intrusions of
viscous magma have forced the overlying strata into a dome.
Batholiths:
Large masses of rock occur in the heart of mountain range.
Large scale intrusion in the great depth and magma cooled slowly
to form large-crystalled rocks such as granite.
Intrusive rocks can be classified into Hypabyssal (dykes,
sills and laccoliths) and Plutonic (Batholiths).
Extrusive Forms of Vulcanicity
A volcano consists of vent or opening at
the surface of the crust through which
material is forced in eruption.
This may accumulate around the vent
to form a hill, or it may flow widely over
the country rock as an extensive level
sheet.
Three types of extrusive materials
Extrusive materials
Gases:
Include gaseous compounds of sulphur and hydrogen with
carbon dioxide.
Stream is the most important factor affecting the eruption.
Solid:
Pyroclastic Debris / Pyroclasts / Tephra
Include:
• Country rocks
• Finer materials: (lapilli, dust, ash)
• Volcanic bombs: lava are thrown into the air solidify
before reaching ground.
Extrusive materials
Liquid:
Lava
• The form of a volcanic cone and the nature of eruption depend
on a large extent upon the nature of lava.
Acid lava:
• High silica (SiO2) content, high melting-point, viscous, solidify
rapidly and flowing very slow.
• It builds high, steep-sided cones.
• They may solidify in the vent and cause recurrent explosive
eruption.
Basic lava
• Relatively poor SiO2 content, low melting point and flows faster,
and produces much flatter cone / shield cone.
• Its eruption is quiet.
Structure of Volcanoes
Three Types of Volcano
They are classified by eruption type
Explosive eruption
• Cinder cones and composite cones
Quiet eruption / Fissures eruption
• Shield Cones and lava plateaux
Cinder Cones
They are the smallest volcanoes
They are formed by Pyroclastic Debris, tephra and volcanic
ashes
Cinder cones rarely grow to more than 150 to 300m in height.
Basic Lava Cones / Shield Cones
They are built by basic lava.
Characteristics of basic lava (Basalt)
Dark Colour with Low content of SiO2
Low viscosity, Low melting-point and fast flowing.
Volcanoes with gentle slope (4o to 5o)
Eg. Hawaiian Islands
Acid Lava Cones
Light colour and viscous acid lava flows very
slow for high content of SiO2.
It produces a steep dome.
Volcanic Plug
When the vent of lava cone was solidified by acid
lava.
When the country rocks were removed, the
solidified vent is called volcanic plug.
Volcanic Plug
Composite Volcanoes
Most of the world’s great volcanoes are composite
cones.
They are built pf layers of cinder and ash
alternating with layers of lava.
Many composite volcanoes lie in a great belt, the
circum-Pacific ring (ring of fire) and Mediterranean
group of volcanoes.
The eruption of large composite volcanoes is
accompanied by explosive issue of steam, cinders,
bombs, ash and by lava flows.
The crater may change form rapidly.
Example: Fujiyama in Japan.
Composite cones
Calderas
Volcanic explosive so violent as to destroy the entire
central portion of the volcano.
There are remain only a great depression, a caldera.
Example:
Krakatoa (in Indonesia), exploded in 1883, leaving a
great caldera.
75cubic km of rock disappeared during the explosion.
Great tsunamis appeared and kills thousands of people of
Java and Sumatra.
Calderas
Calderas
Active, Dormant and Extinct Volcanoes
Active Volcanoes:
Eruption periodically in historic times.
Dormant Volcanoes:
Renewal of eruption activity is possible.
Eg. Vesuvius had been dormant so long before
its eruption of AD 79 that it was thought to be
extinct.
Extinct Volcanoes:
They were formed in long-past geological
times and with no sign of any volcanic activity.
Distribution of volcanoes
Pacific Ring of Fire
Distribution of Volcanoes
There are many known active volcanoes all
over the world. 80 active and ten calderas
locates here.
Pacific Ring of Fire
2/3 world’s volcanoes occur here.
The chain of volcanoes near 3200 km
America:
St. Helens is very active in recent years.
Highest peaks in S. America
Aconcagua (7021m), Guayatiri (6060m)
Distribution of Volcanoes
Africa:
They are found along the East Africa Rift Valley.
Mount Kenya (5195m), Kilimanjaro (5889m)
Asia and Europe:
Alpine-Himalayan belt which forms the most
tectonic features (folding, faulting, volcanoes…..)
Others:
Volcanic activity is widespread in Iceland.Several
Atlantic islands, which have many eruption .
Ocean Ridges, Ocean Trenches
and Island Arcs.
Ocean Ridges
They connect through all the oceans to
form a worldwide feature nearly 60000
km long.
They are all composed of basaltic lava.
They are formed by fissure eruptions with
a fairly uniform rate of lava emission.
Iceland is built astride the Mid-Atlantic
Ridge system.
Ocean Trenches
Ocean Trenches
The deepest parts of the oceans are
elongated troughs descending to depths
of over 10000 metres.
Sediments accumulating on the trench
floors.
Nearly all the trenches occur around the
margins of the Pacific Ocean and arc of
volcanic islands is commonly present on
the continental side of the trenches.
Island Arcs
Island arcs are mostly found around western
margin of the Pacific Ocean and in the northeast
of the Indian Ocean.
They formed on the subduction zone.
Island Arc - Japan
Island Arc - Japan
Japan is the largest area of land formed by island
arc.
MT. Fuji reaches nearly 4000m, and several other
peaks on Honshu top 3000m.
Honshu is largely a pile of basalt and andesite lying
between the Japan Trench and the Sea of Japan.
It seems that the subducted ocean-floor becomes
mobilized as magma when it reaches 120km depth.
When the descending plate reaches over 100km in
depth partial melting takes place, magma rises to
form a pile of volcanic rocks and the island arc
begins to rise / form.
Earthquake
Earthquakes
Contents
Introduction
Seismic Waves
Distribution
Earthquake and Plate Tectonic
Effects of Earthquake
http://www.nstm.gov.tw/earthquake/A_2.htm
Introduction
Earthquakes - natural vibrations within
the earth’s crust.
Some of these are violent and are
responsible for large scale death and
destruction.
Most earthquakes are twoo small to be
felt by man and only be detected by
seismographs.
Seismic Waves
The investigation of earthquakes and the transmission
of earthquake waves is known as seismology.
Earthquake generates elastic vibrations or ‘waves’
Four kinds of seismic waves
Primary Waves (P waves)
Secondary Waves (S waves)
Love waves (L waves)
Rayleigh waves
P and S waves
P waves
It is also called compressional waves which consists of
longitudinal vibrations.
These waves propagate very rapidly through both solids
and liquids and are usually the first indication that an
earthquake has occurred.
The speed of P-waves
• Crust: 5.5 km/s; Upper mantle: 8 km/s; Lower mantle: 13.5 km/s
S-waves
It is also called Shear waves which are transverse
vibrations with an movement at right angles to their path.
The speed of S-waves is 60% of P-waves.
It cannot propagate through the liquid (core)
The P-waves and S-waves are body waves.
P-waves and S-waves
L-waves and R-waves
L-waves:
It is also called Love waves which travel around the
periphery the earth.
R-waves:
It is also Rayleigh waves which travel similar to winddriven ocean waves.
L-waves and R-waves are surface waves.
P-waves is the fastest and L-waves are the slowest,
but L-waves have the greatest amplitude and are
those that do the most damage.
Distribution
It is very similar with the distribution of volcanoes.
Distribution
80% originate in the ‘Circum-Pacific Ring
of Fire’.
15% in the Mediterranean and TransAsiatic zone.
5% in other parts of the world.
Formation
Refers to the theory of plate tectonic.
http://www.nstm.gov.tw/earthquake/A_2.htm
Effects of Earthquake
Shattered buildings
Displaced roads and railways
Collapsed bridges
Great cracks in ground
Changes in sea level
Tsunamis
Fire and flood
Famines and disease
Loss of life