Transcript Earth Dynamics Chapter 8 Earth Science Ch.8 L.1 Bellwork ● Isostasy: is the equilibrium between continental crust and the denser mantle below it ● Subsidence:

Earth Dynamics
Chapter 8
Earth Science
Ch.8 L.1 Bellwork
● Isostasy: is the equilibrium between continental
crust and the denser mantle below it
● Subsidence: downward vertical motion of Earth’s
surface
● Uplift: upward vertical motion of Earth’s surface
● Compression: squeezing stress
● Tension: stress that pulls something apart
● Shear: parallel forces acting in opposite directions
● Strain: a change in the shape of rock caused by
stress
Balance in the mantle
● Continents rise above seafloor
o
o
Crust is less dense than mantle
 floats on mantle like ice floats in water
 mass of the continent is equal to the mass of
the mantle it displaced
Mountains taller than continental crust below it
● Isostasy= equilibrium between
continental crust and the denser mantle
below it
ONE STEP UP
● What happens if the mass of the crust
increases?
● What happens if the mass of the crust
decreases?
Piggybacking glaciers
● 20,000 years ago there was a thick 1km
layer of ice covering North America
o
What do you think this did to the crust?
● What do you think happened as the ice
melted?
Types of stress
● Compression:
squeezing stress
● Tension: stress that
pulls something apart
● Shear: parallel forces
acting in opposite
directions
o
All three happen as plates
move horizontally
Types of strain
● Strain: a change in the shape of a rock
caused by stress
o
o
Elastic strain: NOT permanent
 small strain or very large rock
 rock goes back to original shape when strain
removed
Plastic strain: permanent
 small rock or large strain
 rock doesn’t go back to original shape
Deformations
● Upper mantle/lower crust:

o
o
Rocks deform plastically like putty
Compression
 Thickens and folds layers of rocks
Tension
 Stretches and thins layers
● Failure (upper colder part of crust):
o
when strain breaks rocks instead of changing
shape
 Forms fracture/faults
Rock cycle
● Plate tectonics= horizontal motion
● Isostasy= vertical motion
● Uplifting= brings igneous and metamorphic rock to
the surface
o On surface erosion turns rocks into sediment
● Buried sediment becomes sedimentary rock
● Sedimentary rock becomes metamorphic rock
● Subduction takes all the rocks deep into the earth to
melt and start over
Homework Ch8 L.1
● p.258 #1-10
● Study for quiz
Lab
● One play-dough per student
● Take a piece and make it into a rectangular
shape
● Practice modeling the three types of stress
● Answer questions (what shape forms?)
o
o
o
o
What happens during shearing?
What happens during tension?
What happens during compression?
Is this plastic or elastic deformation?
● TURN THIS IN
Bellwork Ch 8 L.2
● Ocean trench: deep, underwater troughs created by
one plate subducting under another plate at a
convergent plate boundary
● Volcanic arc: curved line of volcanoes that forms
parallel to a plate boundary
● Transform fault: formed where plates slide horizontally
past each other
● Fault zone: an area of many fractured pieces of crust
along a large fault
Landforms created by plate motion
● Plates move 1-9
cm/year
● Compression,
tension and
shearing happen at
the boundaries
o
tall mountains=
compression stresses
Compression creations
● Mountain ranges
o
o
o
on land
two continental plates
slow mountain formation
● Ocean trenches
o
o
deep, underwater troughs
created by one plate subducting
under another plate at a
convergent plate boundary
deepest places in Earth’s oceans
Compression creations cont’d
● Volcanic arcs
o
o
volcanic mountains form
in ocean where plates
converge and one
subducts under another
curved line of volcanoes
that forms parallel to a
plate boundary=
volcanic arc (aka island
arc)
Tension creations
● Mid-ocean ridges: crust spreads apart and
lava rises so it pushes the seafloor up which
creates mountain ranges
● Continental rifts: splits in Earth’s crust that
occur within a continent. Upper part of crust
splits (forms a fault) and blocks of crust
move downward forming valleys.
Shear creations
● Transform faults: where
tectonic plates slide
horizontally past each
other they form
● Fault zones: area of
many fractured pieces
of crust along a large
fault
Homework Ch8 L.2
● p.266 1-10
● Study for quiz
Bellwork Ch8 L.3
● Folded mountain: made of layers of rock
that are folded
● Fault-block mountain: parallel ridges that
form where blocks of crust move up or down
along faults.
● Uplifted mountain: form where large
regions rise vertically with very little
deformation.
Converging plates
● At converging plates, combination of folds,
faults and uplifting creates mountains.
● Forces that created the mountains can
eventually become inactive
o
o
mountains stop increasing in size
Can create one new continent if movement brings
together two continents
Collisions and Rifting
● Plates generally diverge
very close to the location
where they first collided
o
Rift forms, gets larger, fills with
water, and becomes an ocean
● Newer mountains can form
on top of older ones if
collisions happen again
Weathering
● Mountain ranges
are weathered so
older mountains are
more rounded at the
tops than newer
ranges
Erosion and Uplift
● With erosion, how do
mountains that are millions
of years still exist?
o
Isostasy!
 As a mountain weathers,
the crust rises and rocks
under continents rise
slowly.
Folded mountains
● Rocks deeper in the crust are
warmer than rocks on the
surface
o
o
they form folds instead of faults when
under high pressure
form when plates collide, exposed
when erosion weathers away upper
part of crust
● fold is perpendicular to the
direction of pushing
Fault-block mountains
● Tension pulls crust apart to
form faults, blocks of crust
can both fall and rise.
o
tension is perpendicular to
direction of mountains
 if mountains are north to
south then the tension is
east to west
Uplifted mountains
● Large regions rise
vertically with very
little deformation
Volcanic Mountains
● Special type of
mountain
o
some of largest
mountains made by
volcanic eruptions
Homework Ch8 L.3
● p.274 1-8
● NO QUIZ
Ch8 L4: Continent building
● What are two ways continents grow?
● What are the differences between interior
plains, basins and plateaus?
Bellwork Ch8 L.4
● Plains: extensive area of level or rolling land
● Basin: areas of subsidence and regions with
low elevation
o
subsidence: the gradual caving in or sinking of an
area of land
● Plateau: flat regions with high elevation
Structure of continents
● Most high elevations
are located at the
edge of continents
● Interiors of continents
are mostly flat
o
Billions of years of
erosions have leveled
them out
How continents grow
● Addition of igneous
rock via volcanic
eruptions
● Tectonic plates carry
island arcs, whole
continents or fragments
of continents
o
Can add pieces to a
fragment
Continental Interiors
● Rocks in continental
interiors are stable,
flat, old and strong.
o
o
Usually more than 500
million years old
Oldest rocks more
than 4.2 billion years
old (Canada)
Formation of Interior Plains
● Plain: extensive area of level
or rolling land
● Most of central region of
North America
● Were covered by shallow
seas at different times in
history
● Flattened out by million years
of weathering and erosion
Formation of basins
● Basins: area of subsidence and regions with
low elevation
● Sediment eroded from mountains
accumulate in basins
o
o
Over millions of years heat and pressure convert the
plant and animal remains in basins into oil, natural
gas and coal
Most of energy resources extracted from
sedimentary basins
Formation of Plateaus
● Plateau: flat regions with
high elevation
o
o
Some form from uplifting
(Colorado plateau)
 Grand Canyon in this
plateau was created by a
river that cut through and
eroded the plateau
Some form from eruption of
lava
Homework Ch12 L.4
● p.281 1-10
● Study for test
● Extra credit outline