Crustal Deformation Processes Volcanoes, Folding and Faulting

1
Crustal Deformation Processes Volcanoes,
Folding and Faulting

• Results of Plate Movements

2

• Volcano - conical or dome-shaped landform built
  by the emission of lava, gases and solid
  fragments from a narrow vent in the surface.
• Volcanic materials include lava, gases and
  solid particles - tephra particles of all
  sizes, ash, volcanic bombs .

3
Landforms of Extrusive Volcano

• The nature of eruption and the resulting
  volcanic landforms depend on the nature of lava
• FELSIC LAVA - high degree of viscosity, resists
  flow gt violent, often explosive eruptions
  causing steep composite cones.
• Eruptions of felsic lava typically create strato
  volcanoes, also known as composite volcanoes
• Features of a strato volcano
• steep slopes, - lots of tephra, - violent
  explosions, - explosive discharge of gases.
• Examples of composite volcanoes are Mt. Etna
  (Italy), Kilimanjaro (Africa), Fujiyama (Japan)
  Cotopaxi (Equador) Penatubo (Phillipines)

4
Landforms of Extrusive Volcano --2

• MAFIC LAVA - highly fluid gt relatively quiet
  eruptions causing lava flows
• Mafic lava (basaltic) produces effusive eruptions
  that create shield volcanoes with gentle long
  slopes (e.g. Hawaii)
• lava often flows from fissures - cracks - on the
  sides of the volcanic dome to form extensive
  deposits of plateau basalts, or flood basalts

5
A Volcanic Cone
6
Volcanic Mountains Islands

• Submarine volcanoes sometimes form Islands
  (Hawaii, Philippines, Japan, Sicily).
• Some of the highest mountains in the world were
  formed by volcanoes
• a) Mt. Fujiyama in Japan,
• b) Mt. Cotopaxi in Ecuador, South America
• c) Mt. Kilimanjaro in Tanzania, Africa,
• d) Mount Shasta in California and Mt.
• Rainier in Washington state, USA.

7
Eruption of Mt. Pinatubo, Philippines, June 1991
8
Magma

• Magma is a molten or partially molten rock
  beneath the Earth's surface. When magma erupts
  onto the surface, it is called Lava.
• Magma typically consists of a liquid portion.
  Magma collects inside a volcano's magma chamber
  before it erupts (see diagram).

9
Lava Flow

• Lava is the word for magma when it erupts onto
  the Earth's surface.
• Geologists also use the term to describe the
  solidified deposits of lava flows and fragments
  hurled into the air by explosive eruptions (e.g.,
  lava bombs or blocks).
• Lava is derived from the Italian word for stream,
  which is derived from the verb lavare -- to wash.
• Left A fast-moving lava flow from Mt. Etna in
  Sicily.

10
Volcanic Vent

• Vents are openings in the Earth's crust from
  which magma and volcanic gases escape onto the
  ground or into the atmosphere.
• Vents may consist of a single, circular-shaped
  structure, a large elongated fissure and
  fracture, or a tiny ground crack.
• Steam rises from a vent on Mount Asahidake, a
  volcano on Hokkaido, Japan (see picture on left).

11
Caldera

• A caldera is a large, usually circular depression
  at the summit of a volcano formed when magma is
  withdrawn or erupted from a shallow underground
  magma reservoir.
• Calderas are different from craters, which are
  smaller, circular depressions created primarily
  by explosive excavation of rock during eruptions.
• Left Mount Aso vents a large cloud of steam at
  Japan's Aso National Park. The mountain's caldera
  is one of the world's largest.

12
Tephra

• Tephra is a general term for fragments of
  volcanic rock and lava that are blasted into the
  air by explosions or carried upward by hot gases
  in eruption columns or lava fountains.
• Tephra includes large, dense blocks and bombs and
  small, light rock debris such as scoria, pumice
  and ash
• Picture A fountain of hot lava and tephra erupts
  from a crater in Hawaii's Kilauea East Rift in
  1983

13
Intrusive Extrusive Volcanic Features
14
Intrusive volcanoes

• Dyke thin vertical veins of igneous rock that
  form in the fractures found within the crust.
  Because these intrusive features cool quickly
  their rocks are dominated with fine mineral
  grains.
• Sill horizontal planes of solidified magma that
  run parallel to the grain of the original rock
  deposit
• Batholith large plutonic masses of intrusive
  rock with more than 100 square kilometers of
  surface area.
• Volcanic Pipe if a dyke reaches the surface of
  the Earth it is then called a volcanic pipe.

15
Distribution of Volcanoes
16
Folding and faulting

• Compressional forces squeeze sedimentary deposits
  that lie between the converging continental
  plates and folds them into synclines and
  anticlines
• Extreme stress and pressure can cause rocks to
  shear along a plane of weakness creating a fault.
  Lateral forces pull continental plates apart to
  form rift valleys

17
Folding

• Stress and strain causes rock to buckle and
  fracture or crumple into folds.
• Folding of initially flat layers (typically
  of sedimentary rocks) creates fold belts
  consisting of
• anticlines - arclike upfolds, and . . .
• synclines - troughlike downfolds

18
Folding

• A fold is a bend in rock that is the response to
  compressional forces.
• Folds are most visible in rocks that contain
  layers (strata)

19

• Synclinal folds in bedrock, near
  Saint-Godard-de-Lejeune, Canada. (Source Natural
  Resources Canada - Terrain Sciences Division -
  Canadian Landscapes
• More complex fold types can develop in situations
  where lateral pressures become greater. The
  greater pressure results in anticlines and
  synclines that are inclined and asymmetrical

20

• Normal fault Normal faults occur when tensional
  forces act in opposite directions and cause one
  slab of the rock to be displaced up and the other
  slab down.
• Tranform or strike-slip faults are produced where
  the stresses are exerted parallel to each other.
  A well-known example of this type of fault is the
  San Andreas fault in California.

21
A graben and a horst

• A graben is produced when tensional stresses
  result in the subsidence of a block of rock. On a
  large scale these features are known as Rift
  Valleys
• A horst is the development of two reverse
  faults causing a block of rock to be pushed up
  over the other blocks.

22

• The 6000 miles East African Rift Valley
• Formed the Red Sea, and several rift valley lakes
  in East Africa (Tangayika, Nyansa, Turkana etc.)
• Several block mountains (horsts) rise within the
  rift valley (Mt. Ruwenzori)

23

• Transcurrent fault zones on and off the West
  coast of North America.
• (Source U.S. Geological Survey)