1. Year 9 Science Seaview High School
Rocks Under Pressure
Year 9 Science
Seaview High School
Tightly folded rock in the walls of Hamersley Gorge National Park, WA
Adapted from:
Lofts, G.L. & Evergreen, M.J. (2012), Science Quest 9 (Australian Curriculum Edition),
John Wiley and Sons, Milton, Queensland.

2. Moving Rocks
As the tectonic plates of the Earth move, rock in the crust is constantly being pushed, pulled, bent and twisted.
This takes some very large forces. So large in fact, that they fold the crust into rolling hills and valleys, put cracks in it and move them up and down or sideways.
Examples of folded rocks can be found well away from the plate boundaries. For example, inland Australia.
Rock folding in inland Australia

3. Bend and not Break
If I take a piece of paper and place one hand at each end, then move my hands towards each other, the paper bends upwards or downwards.
The movement of the tectonic plates has a similar affect on the Earth’s crust.
This process is known as folding.
Write this in your book now:
Folding is the process by which the Earth’s
crust is forced to bend and crumple, without
breaking. This is a result of tectonic plate
movement.
As the Indian land mass pushes northwards to collide with the
Eurasian plate, the folding of the Himalayas continues.

4. Folding
Folding is responsible for most of the major mountain ranges around the Earth.
The Himalayas continue to rise in height as land masses collide.
Write this in your book now:
Folds that bend upwards are called anticlines
Folds that bend downwards are called synclines.
Anticline
Force
(Blue arrows)
Syncline

5. Anticlines and Synclines
Usually form well below the surface of the Earth.
Only visible when exposed by erosion or manmade cutting of rocks, for example:
When roads are cut into hills and mountainsides
Cliffs formed by fast flowing rivers (erosion).
Sideling Hill syncline, Maryland, US. Formed about 350 million years ago, the syncline
was only exposed when workers cut into the rock to build the highway.

6. The Great Dividing Range
If you’ve driven from here to the east coast of Australia, you have likely crossed the Great Dividing Range.
It stretches from northern Queensland to Tasmania.
It is a result of folding
Consists of several different mountain ranges joined together
Carnarvon Range, Queensland
Blue Mountains, NSW
Australian Alps, Vic
Dandenong Ranges, Vic
Central Highlands, Tas

7. Faults
Sometimes the forces on the rocks cause them to crack rather than fold.
Write this in your books now:
When movement occurs along a crack in the earth, it is called a fault.
Spencer Gulf and Gulf St Vincent (where we live) has been formed by a series of faults causing two blocks of the crust to drop down.
These sunken blocks are called rift valleys
In between these two sunken blocks is a block that has been pushed upwards to form the Yorke Peninsula.
This is called a horst.
The movement along these faults is responsible for the occasional earthquake in and around Adelaide.

8. The South Australian Gulfs
A – represents the Eyre Peninsula
B – represents the Fleurieu Peninsula
Faults caused the region between these
points to drop. In the middle, the land
pushed up to create the Yorke Peninsula.
Spencer Gulf and Gulf St Vincent
Represent the rift valleys.
The York Peninsula is an example of a
horst.

9. Reverse and Normal Faults
A reverse fault occurs when one side of the fault moves up relative to the other.
A normal fault occurs when one side of the fault moves down relative to the other.

10. Slip faults
A slip fault is the result of plates slipping horizontally past each other (sideways movement).
A famous example of a slip fault is the San Andreas Fault in California, US.
It is about 1200 km long. Movement often causes large earthquakes.
With time, pressure builds up along this fault line.
This pressure is then released as an earthquake.
The last major quake in this region was 1989.
Scientists believe it won’t be too long before another major slip occurs.

11. San Andreas Fault q Above: San Andreas Fault line
Left: A map showing the path of the fault line
Right: A once straight fence and path
Below: Damage caused by the 1989 San Francisco
quake.

12. ABC Splash Video
Copy these questions into your book now. Leave room for answers!
New Zealand is used as an example of a place that is tectonically active. What does this mean?
What evidence is there of past tectonism in Australia?
Watch the demonstrations of bending and folding. What conditions make it more likely for rock to bend and fold than to fault?