Transcript metamorphic rocks

th
8
Grade Science
Unit 8: Changes Over Time
Lesson 2: Changes in the Rocks
Vocabulary of Instruction
1. Landform
• Landforms are natural
features of the
landscape.
• They are natural physical
features of the earth's
surface.
• Examples of Landforms
are: valleys, plateaus,
mountains, plains, hills,
loess, and glaciers.
1-A. Landform - Valley
• A valley is a hollow
or surface
depression of the
earth surrounded by
hills or mountains.
• It is a natural trough in
the earth's surface,
that slopes down to a
stream, lake, or the
ocean, formed by
water and/or ice
erosion.
1-B. Landform - Plateau
• A plateau is a large
highland area of fairly
level land separated
from surrounding land
by steep slopes.
• Some plateaus, like the
plateau of Tibet, lie
between mountain
ranges. Others are higher
than surrounding land.
• Plateaus are widespread,
and together with
enclosed basins they
cover about 45 percent
of the Earth's land
surface.
1-C. Landform - Mountains
• Mountains are formed
by volcanism, erosion,
and disturbances or
uplift in the earth's
crust.
• Most geologists believe
that the majority of
mountains are formed by
geological forces such
as heat and pressure
producing changes and
movements under the
earth's crust.
1-D. Landform - Plains
• Plains are broad, nearly
level stretches of land that
have no great changes in
elevation.
• Plains are generally lower
than the land around them;
they may be found along a
coast or inland.
• Coastal plains generally
rise from sea level until they
meet higher landforms such
as mountains or plateaus.
• Inland plains may be found
at high altitudes.
1-E. Landform - Hills
• Hills are elevations of the
earth's surface that have
distinct summits, but are
lower in elevation than
mountains.
• Hills may be formed by a
buildup of rock debris or
sand deposited by glaciers
and wind.
• Hills may be created by
faults. Faults are a slight
crack in the earth which
can cause earthquakes.
• Hills are formed when
these faults go slightly
upward.
1-F. Landform - Loess
• Loess is a geologically recent
deposit of silt or material
which is usually yellowish or
brown in color and consisting
of tiny mineral particles
brought by wind to the places
where they now lie.
• It is a product of past glacial
activity in an area.
• It is a sedimentary deposit of
mineral particles which are
finer than sand but coarser
than dust or clay, deposited
by the wind.
• Loess is a type of silt which
forms fertile topsoil in some
parts of the world.
• Loess deposits are usually a
few meters thick.
1-G. Landform - Glacier
• A glacier is a huge mass
of ice that flows slowly
over land.
• They form in the cold polar
regions and in high
mountains.
• The low temperatures in
these places enable large
amounts of snow to build
up and turn into ice.
• Most glaciers range in
thickness from about 91
to 3,000 meters.
• Glaciers are formed when
more snow falls during the
winter than melts and
evaporates in summer.
2. Contour Line (Isoline)
• A contour line is a line
on a map that connects
points or places of
equal elevation.
• The bottom part of the
diagram shows some
contour lines with a
straight line running
through the location of
the maximum value.
• The curve at the top
represents the values
along that straight line.
3. Topographic Map (Contour Map)
• Is a map that shows the
change in elevation of
the Earth’s surface
using contour lines.
• It shows shapes and
features of the Earth
surface such as roads,
lakes, and cities.
• Traditional definitions
require a topographic
map to show both natural
and man-made features.
4. Rock Cycle
• The Rock cycle describes
the dynamic transitions
through geologic time
among the three main
rock types: sedimentary,
metamorphic, and
igneous.
• As the diagram to the right
illustrates, each type of
rock is altered, changed,
or destroyed when it is
subject to factors such as
heat, pressure, cooling,
and erosion.
4-A. Rock Cycle - Diagram
• The rock cycle starts at is the
magma chamber. The magma
comes out of the volcano and
cools into igneous rocks.
• Next, the igneous rocks erode
and turn into sediments.
• The sediments go through years
of pressure and cementation
which turns the sediments into
sedimentary rock layers.
• Once again the sedimentary
rocks go through heat and
pressure and turn into
metamorphic rocks.
• Then the new metamorphic
rocks go through heat and
turn into magma.
4-B. Rock Cycle – Diagram … Cont…
• Also, igneous rocks
can go through heat
and pressure and
become
metamorphic rocks.
• Metamorphic and
sedimentary rocks
can become
sediments.
• That is how the rock
cycle works.
4-C. Rock Cycle – Diagram
Cont…
• Another
representation of
the rock cycle
processes is
shown on the
picture to the left.
4-D. Rock Cycle
Three Types of Rocks
1. Igneous Rock
• Lava flowing from
a volcano in
Hawaii forms
igneous rocks.
4-D. Rock Cycle
Three Types of Rocks
2. Metamorphic
rock
• In Arizona
metamorphic
rocks show
formerly flat
sedimentary
layers squeezed
into new shapes.
4-D. Rock Cycle
Three Types of Rocks
3. Sedimentary Rock.
• Metamorphic Rocks
in Hawaii have been
broken into
sediments and have
accumulated on this
beach, where they
might form a
sedimentary rock
through pressure and
cementation.
4-D. Rock Cycle
Three Types of Rocks
• Sedimentary and
metamorphic
rocks in Arizona
were broken into
sediments and
carried away,
leaving the Grand
Canyon behind, one
of the wonders of
the world.