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