Transcript AUSTRALIA – TO THE HORIZON AND

AUSTRALIA – TO THE HORIZON
AND BEYOND - Part 2
Yr 7 Science
Topic 4
(Chapter 10)
Introduction
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The land surface is always changing through
weathering and erosion
Australia has 36, 000 Kms of coastline
constantly be washed by the great southern
oceans
The centre of Australia is dominated by vast
deserts. Many plants and animals have learnt
to survive in this arid environment
Weathering & Erosion DP21
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Weathering is the breaking down of the Earth’s
crust. There are two types of weathering
physical & chemical. Many environmental
forces (or agents) lead to weathering.
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Erosion is the wearing down and carrying away
of the weathered material
Physical Weathering DP22
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Physical weathering involves the breakdown
(breaking apart) of rocks into smaller and
smaller pieces without any change to the
mineral composition of the rock
Physical Weathering DP22 cont
Types of physical weathering (p333)
Temperature changes – cracks in rocks caused
by repeated heating and cooling
Ice cracking – water in crevices freezes
(expands) and creates cracks
Root action – roots in crevices grow and create
cracks
Chemical Weathering DP23
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Chemical weathering involves a permanent
change in the mineral composition of the rock.
This change in chemical composition causes
the rock to crumble
Chemical Weathering DP23 contTypes of chemical weathering
Oxidation – air attacks rock minerals making them into
softer, weaker substances that crumble e.g. iron
minerals turn rusty brown and become weakened
Water (hydration) – rocks containing clay swell / expand
with water then dry out and contract causing cracks
etc
Acids – acids produced by plants and pollution attack
rocks. Carbon dioxide in the air dissolves in water to
produce carbonic acid which breaks down rocks such
as limestone
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Erosion DP 26, 30 & 31
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Erosion is the wearing down of the Earth’s crust and
the carrying away of weathered material.
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The more weathered (degraded) the rock or surface
the more susceptible it is to erosion
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Particles of weathered and eroded rock is known as
sediment. Sediment is graded from gravel to sand, to
silt, to clay in accordance to particle size.
Erosion DP 26 contAgents of erosion are:
Moving water – rain, rivers and waves
Gravity – downward force on weakened surfaces
Wind – picks up and transport sediment
Moving ice – glaciers carve out valleys and
transports rocks, pebbles down the valleys
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(see diagrams p335, slumping etc)
Practical activity
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Like the natural environment the built
environment also is at the mercy of weathering
and erosion
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Take a walk around the school yard and find
examples of weathering and erosion. Note
these in your prac-book under a suitable
heading
Jenolan Caves
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Jenolan Caves in the Blue Mountains of NSW and
are thought to be the oldest known open caves in
the world.
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Caves form in limestone and occasionally in
dolomite. The carbon dioxide comes from decaying
organic matter in soil, and also directly from the
atmosphere. This slightly acidic water dissolves
the rock, forming cavities which can enlarge and
join up to make larger cave systems.
Stalagmites and stalactites
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Limestone is a rock made up largely of calcium
carbonate and is readily dissolved by rainwater.
Water seeping through the rock picks up the calcium
carbonate and the evaporation of the laden drops of
water leaves a deposit that, over a great period of time,
creates stalagmites and stalactites.
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"When the mites go up the Tights come down"
Landforms caused by erosion
DP 27
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Mesas (Spanish for "table") is an elevated area of land
with a flat top and sides that are usually steep cliffs. It
takes its name from its characteristic table-top shape.
Landforms caused by erosion
DP 27 Cont
Inselberg is an isolated hill, knob, ridge, or small
mountain that rises abruptly from a gently sloping or
virtually level surrounding plain. It is formed as all other
weaker material is eroded from around it. Example:
Uluru (Ayers Rock)
Landforms caused by erosion
DP 27 Cont
The terms U-shaped and V-shaped are descriptive
terms of Geography to characterize the form of valleys
(I.e. a cross section view)
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U–shaped valleys are formed by moving glaciers
whereas V-shaped valleys are formed by moving
water. Which type of valleys do we have in our region?
Landforms caused by the
deposition of sediment DP 28
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An alluvial fan is a fan-shaped deposit formed where a
fast flowing stream flattens, slows, and spreads
typically at the exit of a canyon onto a flatter plain. Due
to the slowing of flow any solid material carried by the
water is dropped (Monaro High Plains)
Landforms caused by the
deposition of sediment DP 28 cont
Deltas form wherever rivers encounter standing bodies
of water such as lakes or oceans. The sudden
decrease in energy causes the river to drop its
sediment load. Deltaic deposits therefore become finer
grained the farther out into the lake or ocean
(gradation of particle sizes) . This is a type of flood
plain sediment. (E.g. Murray River flood plains)
Landforms caused by the
deposition of sediment DP 28 cont
Glacial Moraines are landforms created at the
margins of glaciers by the melt-out of debris from the
glacier and by the bulldozing action of the ice.
Moraines are classified according to their position
relative to the former glacier. (E.g. Monaro High Plains)
Landforms caused by the
deposition of sediment DP 28 cont
Sand Dunes are mounds or ridges of drifted sand I.e
as found along our coast lines and in our deserts. Sand
dunes can form where ever there is sufficient sand and
wind. However, the shape (morphology) of coastal
dunes and inland dunes differ considerably even
though the process of formation is very similar.
Billabong formation DP 29
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A billabong is an isolated pond left behind after
a river changes course.
Sediment deposit & erosion
What size particles (or weight) are dropped first?
Rocks Types
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What are the 3 basic types of rocks?
Igneous
– ‘formed by fire’
Sedimentary – ‘composed of sediment’
Metamorphic – ‘changed form’
Igneous Rock DP 34 & 36
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Igneous rocks are formed directly from cooling magma.
This is an exothermic process (it loses heat) and
involves a change from liquid to the solid state. The
earth is made of igneous rock - at least at the surface
where our planet is exposed to the coldness of space.
Igneous rocks are given names based upon two things:
composition (what they are made of) and texture (how
big the crystals are). Examples of igneous rock are:
basalt
and granite
Sedimentary DP 34 & 36
Sedimentary rocks are layers of loose material (weathered &
eroded rock) compacted and cemented together. The majority of
the Earth’s crust is covered by a thin layer of loose sediment.
Common sedimentary rocks are:
Limestone
sandstone
coal
Conglomerate rock is sedimentary rock with
large components (pebbles and stones held
together by dissolves minerals)
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Metamorphic Rock DP 34 & 36
The metamorphic rocks get their name from
"meta" (change) and "morph" (form). Almost
any rock can become a metamorphic rock
through a rise in temperature and pressure.
Common metamorphic rocks include:
slate
schist
marble
quartz (green)
Rock Types DP 35
Rock Cycle
Rock Cycle cont-