Transcript Mountains and Volcanoes

Mountains and Volcanoes
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
Types of Mountains
• Types are based according to their origin
•
•
•
•
•
Fault-block: tension, normal faulting
Folded: compression, reverse faulting
Dome: magma pushing up on Earth’s crust
Volcanic: Shield and stratovolcano
Complex: mixture of most of the above
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.
Tilted fault-block range: Sierra Nevada from east,
Steep side of block fault; Ansel Adams photo
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.
Folded Mountains
• Form at convergent boundaries
(continental-continental).
• One plate plunges into the mantle, while
the other folds under pressure.
• ex) Rocky Mountains
and Himalayas.
http://www.geography.info/images/coco.gif
Rocky Mountains, BC.
North American plate collides
with Juan de Fuca plate
The Himalayas, Asia.
Eurasian plate collides
With Indian-Australian plate
Dome Mountains
• Form when magma from mantle rises and
interacts with parts of the crust that won’t crack.
• Magma pushes section of crust up to form a
dome.
• ex) Mount Royal, Quebec
http://www.montrealbb.ca/img/mont_royal.jpg
Volcanic Mountains
Three types:
a) Shield volcanoes
b) Stratovolcanoes
c) Cinder cones
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
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.
Mauna Loa in
Background
Kilaeua is
Behind Mauna
Loa
Mauna Kea
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.
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
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.
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.
Complex Mountains
•Continental-continental
collision
•Tend to have a little of
everything: volcanoes, folds,
and faults
Orogenic Belt
• Long tracts of highly deformed rock
• Parallel strips of rock exhibiting similar
characteristics along the length of the belt
ANATOMY OF AN OROGENIC BELT
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