Tectonic Features

1
Tectonic Features
2
Contents

• Folding and Fold Mountains
• Faulting and its associated Landforms
• Volcanism and the Earths Crust
• Ocean Ridges, Ocean Trenches and Island Arcs
• Earthquakes

3
Folding and Fold Mountains

• All major mountain chains are fold-belts or
  called orogenic belts

4
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 earths crust and most of the worlds
  recently active volacnoes lie and where the
  greater majority of earthqaukes originate.
• The rock strata have been compressed into various
  kinds of folded structure.

5
Geometrical Varieties of Folds

• Three geometrical varieties of folds can be
  distinguished, anticlines, synclines and
  monoclines.

6
Elements of Fold
7
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

8
Types of folding
9
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.

10
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
  earths surface forming volcanoes in this
  process.
• Faulting is very common.
• Eg. Himalayas (boundary between Eurasian plate
  and the Australian Plate)

11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
Faulting and its associated landforms

• Fault is a fracture of dislocation in the earths
  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.

18
Elements of fault
19
Fault types

• Faults may be divided into several categories in
  relation to the movements that have taken place
  on them.

20
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

21
Reverse Fault / Thrust Fault

• It is caused by comression
• The hanging wall is upthrow the footwall along
  the fault plane.
• Feature Horsts and Graben

22
Tear Fault / Wrench Fault

• It is called transcurrent or strike-slip faults.
• It is formed where the movement was dominantly
  horizontal.

23
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 ridge-like block mountains or horsts.
• A long fault trough is known as rift valley.
• Example East African Rift Valley.

24
Cross-section of East African Rift Valley.
25
Volcanism and the Earths Crust

• Vulcanicity is the process by which matter is
  transferred from the earths 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

26
Intrusive Forms of Vulcanicity

• The results of the forcing into the earths crust
  of magma depend on
• Degree of fluidity
• The character of the planes of weakness, such as
  joints and faults.

27
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).

28
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

29
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.

30
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.

31
Structure of Volcanoes
32
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

33
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.

34
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

35
Acid Lava Cones

• Light colour and viscous acid lava flows very
  slow for high content of SiO2.
• It produces a steep dome.

36
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.

37
Volcanic Plug
38
Composite Volcanoes

• Most of the worlds 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.

39
Composite cones
40
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.

41
Calderas
42
Calderas
43
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.

44
Distribution of volcanoes

• Pacific Ring of Fire

45
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 worlds 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)

46
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 .

47
Ocean Ridges, Ocean Trenches and Island Arcs.
48
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.

49
Ocean Trenches
50
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.

51
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.

52
Island Arc - Japan
53
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.

54
Earthquake
55
Earthquakes
56
Contents

• Introduction
• Seismic Waves
• Distribution
• Earthquake and Plate Tectonic
• Effects of Earthquake
• http//www.nstm.gov.tw/earthquake/A_2.htm

57
Introduction

• Earthquakes - natural vibrations within the
  earths 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.

58
Seismic Waves

• The investigation of earthquakes and the
  transmission of earthquake waves is known as
  seismology.
• Earthquake generates elastic vibrations or waves

59
Four kinds of seismic waves

• Primary Waves (P waves)
• Secondary Waves (S waves)
• Love waves (L waves)
• Rayleigh waves

60
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.

61
P-waves and S-waves
62
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
  wind-driven 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.

63
Distribution

• It is very similar with the distribution of
  volcanoes.

64
Distribution

• 80 originate in the Circum-Pacific Ring of
  Fire.
• 15 in the Mediterranean and Trans-Asiatic zone.
• 5 in other parts of the world.

65
Formation

• Refers to the theory of plate tectonic.

• http//www.nstm.gov.tw/earthquake/A_2.htm

66
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