Mountains and Volcanoes

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Mountains and Volcanoes
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Mountains

• Mountains are over 300 m in height and have
  sloping sides.
• Orogeny is the process of mountain building
• Takes tens of millions of years usually produces
  long linear structures, known as orogenic belts

Two main processes that form mountains 1)
Deformation continental collisions resulting in
folding and
faulting. 2) Volcanic Activity opening in crust
which allows magma to escape from below
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Types of Mountains

• Types are based according to their origin
• Fault-block tension, normal faulting
• Folded compression, reverse faulting
• Dome magma pushing up on Earths crust
• Volcanic Shield and stratovolcano
• Complex mixture of most of the above

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Fault-Block Mountains

• Form at faults (plates slipping by).
• Edges of plates catch and push, which generates
  pressure.
• Pressure can cause earthquakes, or push parts of
  plate upward to form mountains.

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Tilted fault-block range Sierra Nevada from
east, Steep side of block fault Ansel Adams photo
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Horst and Graben

• 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.

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Folded Mountains

• Form at convergent boundaries (continental-contine
  ntal).
• One plate plunges into the mantle, while the
  other folds under pressure.
• ex) Rocky Mountains
• and Himalayas.

http//www.geography.info/images/coco.gif
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Rocky Mountains, BC. North American plate
collides with Juan de Fuca plate
The Himalayas, Asia. Eurasian plate collides
With Indian-Australian plate
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Dome Mountains

• Form when magma from mantle rises and interacts
  with parts of the crust that wont crack.
• Magma pushes section of crust up to form a dome.
• ex) Mount Royal, Quebec

http//www.montrealbb.ca/img/mont_royal.jpg
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Volcanic Mountains

• Three types
• a) Shield volcanoes
• b) Stratovolcanoes
• c) Cinder cones

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Shield Volcanoes

• Found anywhere in a plate, not just edges.
• Form above hot spots in the mantle.
• Magma collects in large pools and eventually
  melts the rock above it and pours out through a
  hole in the crust.

Mauna Loa, Hawaii
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Shield Volcanoes

• Magma that flows out is called lava.
• Lava is runny and flows like rivers.
• Hardens to form basalt rock.
• Hardens more quickly if occurs in ocean and forms
  cones.
• Shield volcanoes do not explode.

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Mauna Loa in Background Kilaeua is Behind
Mauna Loa
Mauna Kea
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Stratovolcanoes

• Volcanoes that explode and blow ash and rock
  everywhere!
• Forms where two plates collide, one plate slides
  under the other (subduction).
• The descending plate heats up and melts, magma
  rises and escapes through a hole in the top
  plate.

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Stratovolcanoes

• Magma is thick and sticky.
• Water from descending plate heats up and forms
  steam.
• Steam increases pressure in volcano, which causes
  it to explode.
• ex) Mount St. Helens, Washington

Mount St Helens, 1980
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Cinder Cones

• Built from lava fragments called cinders. 
• The lava fragments are ejected from a single vent
  and accumulate around the vent when they fall
  back to earth.

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Status of Volcanoes

• Active currently erupting or has erupted within
  the last 200 years
• Dormant has not erupted recently (within the
  past few thousand years) but is considered likely
  to do so in the future
• Extinct has not erupted for a very long time
  (tens of thousands of years) and is considered
  unlikely to do. Truly extinct volcanoes are no
  longer fueled by a magma source.

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Complex Mountains

• Continental-continental collision
• Tend to have a little of everything volcanoes,
  folds, and faults

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Orogenic Belt

• Long tracts of highly deformed rock
• Parallel strips of rock exhibiting similar
  characteristics along the length of the belt

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ANATOMY OF AN OROGENIC BELT
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Anatomy of an Orgogenic Belt

• Oceanic Plate plate containing the ocean floor
• Accretionary Prism sediment collected at a
  subduction zone
• Igneous Arc collection of igenous rock where
  lava is cooling
• Foreland land that develops next to a
  mountain/volcano
• Craton stable part of a tectonic plate found
  near the middle of the plate