Rocks are Dynamic
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Transcript of Rocks are Dynamic
RocksDynamic!
Hi my name isRocky
are
•Sedimentary
•Igneous
There are 2 main types
Sedimentary Rocks• Sedimentary rock is made from other
rocks that have eroded into sand.
• The sand is carried away by water and deposited as sediment when it slows down.
• The layers of sediment sink down & are compressed over millions of years into rock.
I am being squashed
Sedimentary Rocks include
• Shale made from mud.
• Limestone made from shells of sea animals.
• Fossils made from dead living things
• Table Mountain Sandstone made from sand
I have lots of photos of sandstone
‘Stadsaal’. A wind weathered sandstone cave in the Cederberg where bushmen had meetings
These bushman paintings were drawn on sandstone in the Cederberg mountains
Sandstone is easy to climb because it has many rough hand holds to use
The orange red colour shows that iron is present in the rock
Pillars of Sandstone
A large rectangularslab of sandstone
Mushroom RockIn the Cederberg
We conquered a sandstone pillar!
The Sandfontein Arch in the Cederberg
The Sandfontein Arch – muchlarger than it looked!
This stunning formation in the Cederberg is called the
‘Maltese Cross’
Sneeuberg
Can you see the tiny people?
This spectacular sandstone formation was called ‘The finger of God’. I took this photo in 1975. Further wind erosion has made it fall.
What a pity!
Spectacular!
‘Space ship’ formation in the Cederberg
The
Martians
have landed!
Fossils• Fossils are formed
when the skeleton of an animal or plant has been buried whole in wet sand or mud and special conditions stop it from decaying into dust as usual.
•The bone gradually absorbs minerals and changes into a perfect copy made of solid rock.
Igneous Rocks• Igneous rock is
made when magma (hot molten rock) from deep inside the Earth bubbles up and cools down near the surface.
I’mboiling
Igneous Rocks:
• Granite is a very hard rock it contains
• white quartz crystals, black mica crystals and pink feldspar crystals.
• Granite rock formed below the sandstone of Table mountain and now outcrops in various places around our Penninsula.
• It erodes into large round boulders.
An enormous granite outcrop in the desert!Can you see the people?
4 finger rock in Namibiais a piece of hard granitesitting on top of other softer rock
This is the opposite of Table Mountain
where the sandstone is on top of the granite.
More igneous rocks
• Magma that pushes up through cracks to the Earth’s surface cools quickly and so does not contain crystals.
• It often forms a dark black rock called basalt or dolerite or iron stone.
• Magma that is frothy and cools quickly at the Earth’s surface can be very light and is then called pumice.
Black igneous rock has
pushed up through a
crack. This called a dyke.
Volcanic rock ‘squirted to the surface through softer rock and then hardened into a ‘pipe’.Since then it has eroded less than the rock around it.
There are 2 other categories of rock which come from sedimentary or igneous rocks
Crystalline Rocks• Cracks and caves open up underground
• Rain water seeps into cracks and may contain dissolved minerals.
• As the water dries out, the minerals form into crystals
There are many types of crystalline rocks
• They are nearly all smooth and shiny and form into crystals with sharp edges and flat faces.
Examples:
• Quartz Rose Quartz
• Amethyst Tigers Eye
• Agates
• Desert rose
An outcrop of quartz
Enormous rocks ofsemi-preciousRose quartz
Fluospar glows a blue colour when thrown on hot coals
Metamorphic Rock• Metamorphic rock is made from igneous
and sedimentary rock.• They are changed by heat and pressure
inside the Earth’s crust.
•Like batter being baked into a cake!
Metamorphic Rocks
• sandstone into quartz.
• shale into slate.
• limestone into marble.
• trees into coal.
• Coal into diamonds
Great heat and pressure turns
Weathering• As soon as rocks are exposed at the
surface, they begin to erode (are worn down).
• The wind blows sand at them.• Rushing water wears them down.• Plant roots crack them and release
chemicals to dissolve them.• Daily heating causes expansion so many
times they crack.
Let’s take a trip to see some water erosion
The sea constantly pounds and erodes our coastline
A dry river bed.Flash floods erode the soft sandy rock.
A donga erodedBy storm water
The sand ends upIn the sea below
The Disa River in Hout BayErodes its banks
This is the Liesbeek River full to the brim of its canal in 1983
The Fish River has carved a deep canyon intosedimentary rock.Notice the different layers of hard and soft rock.
Original surface
Hard terraces
Renewed carvingto a new level
Later surface
Sandstone Cliffs in the Fish River Canyon
Over thousands of years, a river has worn a deep crack into the sandstone
Rapids and waterfalls format places where the water does not wear hard granite rock down as easily as other rocks.
The Augrabies waterfall on the Orange river is eroding the sandstone
This river pool is called‘Maelgat’ (whirlpool hole)
Can you see where the boys are
going to dive in?
Maelgat
Polished round river bouldersin the Fish River Canyon
A pot hole is made when river water pushes a rock round and round in a depression
Daily heating and cooling changes the shape of
rocks
Daily expansion and contraction have causedthis rock to exfoliate (a surface layer loosensand falls off)
There are strong pressure forces below ground which
cause shakes, cracks, slipping and folding.
A fault has caused a hard slab of rock to slide down from above. It has formed a natural shelf for
a waterfall.
Look how earth movement has twisted this rock!
Sedimentary rock is normally horizontal. Here it has been bent into a vertical position by heat and fault movement .
A fantasticfolded rockformationat a deep sea poolon theOtter trail
Soon after we dived in, this boy noticed
some enormous sharks swimming at
the bottom of the pool.
We got out fast but later dared each
other to swim across above them!
diver
Red hot liquid rock - lava
Thousands of tons per second of super heated sticky rockand ash blast upwards
Powdery ash fallsPeople die from suffocation(can’t breathe)or they are buried 20 metres deep!
Lapilli – a deadly ‘rain’ of rocks falling at 140 km/h
As material falls, it starts a pyroclastic surge. A boiling avalanche of debris shooting out sideways
A towering wall of destruction: Gas, ash & rock racing nearerat 320 km/h
Scattered like straw, mature trees were flattenedby the hot wind up to 14 km away
A violent micro-climate of lightning storm and rain
Mudflows move houses hundreds of metres
Mudflows kill more victims than the eruption!
Cooked to Death!
Idylliclandscapeturnedinto a‘nightmarethat makesthe moonseemlike agolf course’PresidentCarter