Unit 1: Topic 1 - Rocks And Landscapes Flashcards
What is a Geological Timescale?
- Where is CLAY found?
- Where is CHALK found?
- Where is LIMESTONE found?
- Where is GRANITE found?
A geological timescale consists of eras. An era consists of many periods which can be studied to find types of rocks. For example, limestone can be found within the carboniferous period.
CENOZOIC ERA (65M years ago)
- Quotenary
- > Ice Age
- Neogene (23M years ago)
- Palaeogene (Tertiary) -> CLAY
- > Formation of Alps caused by folding of rocks in UK.
*Quotenary period is divided into the PLEISTOCENE (ICE AGE) and the most recent period (from 10,000 years ago until the present day) called the HOLOCENE.
MESOZOIC ERA (251M years ago)
- Cretaceous (145M years ago)
- > CHALK, CLAY
- > Much of UK covered by sea.
- Jurassic (199M years ago)
- > CLAY
- > Limestone deposited that now forms Cotswold hills.
- Triassic (251M years ago)
- > Much of the UK would have been desert.
PALEOZOIC ERA (LATE, 416M years ago)
- Permian (299M years ago)
- > GRANITE
- Carboniferous (359M years ago)
- > LIMESTONE
- > Tropical conditions affect UK. Coal forms.
- Devonian (416M years ago)
PALAEZOIC (EARLY, 542M years ago)
- Silurian (443M years ago)
- Ordavician (488M years ago)
- > Volcanoes active in wales
- > Great Glen Fault formed in Scotland
- Cambrian (542M years ago)
- Pre-Cambrian (after 542M years ago)
Types of Rocks
- What are Igneous Rocks?
- What are Sedimentary Rocks?
- What are Metamorphic Rocks?
IGNEOUS ROCKS
- Formed by cooling of magma
- > Fast cooling = Small Crystals
- > Slow cooling = Large Crystals
- e.g. Granite, Dolerite, Obsidian
SEDIMENTARY ROCKS
- Formed by rocks compacting and naturally cemented together.
- Sediments include coal and precipitates such as limestone.
- Forms layers and so these rocks are often called Strata rocks.
- Examples include: Sandstone, Limestone.
METAMORPHIC ROCKS
- Formed by altering pre-existing igneous, metamorphic and sedimentary rocks by intense heat and pressure.
- Crystalline and irregular layers.
- Examples include: Gneiss, slate.
Define ‘Weathering’
Define ‘Erosion’
Weathering
- Breakdown or rotting of rocks in situ.
Erosion
- Rocks being WORN DOWN or scraped by a moving agent such as, wind, rivers and glaciers.
Physical/Mechanical Weathering
- What is ‘Freeze-Thaw’?
- What is ‘Exfoliation’?
FREEZE THAW
Water expands when it freezes by 10%. This can move rocks when trap in gaps of rocks. This is a continuous process (day and night) until the rock is completely displaced.
EXFOLIATION
Likewise, Exfoliation is also a continuous, day and night process.
As rocks are bad conductors, only the outer layer gets heated and expands. When it cools it contracts. Repeated cycles of expansions and contractions will cause the rocks outer layer to peel. This will feature rounded domes.
The presence of water will make the rock more vuneravle to flake.
Chemical Weathering
- What is ‘Carbonation’?
Carbonation particularly affects limestone and chalk (CaCO3)
1: Rain naturally becomes acidic.
H2O + CO2 -> H2CO3 (Carbonic Acid)
2: Rain reacts with Calcium Carbonate in Limestone.
H2CO3 + CaCO3 -> Ca(HCO3)2 (Calcium Bicarbonate)
Biological Weathering
What is biological weathering?
This is caused by living organisms such as roots and animals.
For example, roots growing in bricks will expand and break the bricks.
Or when animals burrow into the ground; this can weaken the foundation.
Phytomining of copper is another method of Biological weathering.
Limestone - Introduction
What is the its colour?
Is it hard?
Is it permeable?
What type of weathering affects limestone the most?
Shape?
Other features?
- Very hard and Strong
- Permeable (Lots of cracks)
- Easily weather by carbonation. Not so much by Freeze-Thaw as there is too many cracks.
- Light grey in colour.
Horizontal Cracks = BEDS
Vertical Cracks = JOINTS
Limestone - Underground Features
4 features. What are they and how are they formed?
Calcite is essentially the liquid form of CaCO3. It is deposited in caverns to produce stalactites and stalagmites.
Stalactites - Top (thin, long)
Stalagmites - Bottom (thick, stubby)
Curtains is another feature which is produced by depositing calcite over a wide surface.
Pillars are created when a stalactite meets a stalagmite.
Limestone - Surface Features
4 features. What are they and how are they formed?
What is the general term to describe the limestone structure?
Limestone is useful as it is permeable. Water can run through the stone until it runs along an impermeable surface such as shale. When the water emerges, it can be a useful water source for settlements. This is known as a RESURGENCE.
A SWALLOW HOLE is an enlargened joint from which the water falls into.
Another surface feature would a limestone GORGE. This is formed when a cavern’s roof collapses. This gives the features of a steep-sided valley.
Whereas with the DRY VALLEYS, it is suggested that when the water table was much higher, this hydraulic action eroded surface to form a valley. The water table is at present lower and so the valley is dry. On the other hand, it is hypothesised that the valley water table was frozen during the ice age, creating an impermeable surface. When snow melt runs along the surface, the limestone is eroded away.
THE LIMESTONE PAVEMENT
There is no soil because 15,000 years ago, glaciers scraped the limestone a removed the soil. Aditionally, when the limestone has chemically weathered down, the soil is moved through grikes (weathered joint) of the clint (weathered limestone block)
FLUTES are the small holes or dents of a limestone block when it is chemically weathered down.
Granite - Introduction
Where?
What feature(s) is there in the granite landscape?
What type of weathering is this feature susceptible to?
What are the characteristics of this feature(s)?
Granite is found scattered across the Scottish midlands.
It is also found in Cornwall, Plymouth and South Devon.
As well as Ireland in Carlow, Wicklow and West of Donegal.
The main feature of granite is the ‘Tor’. The tors are large granite rocks found ln steep whaleback hills.
It is weathered down by CHEMICAL WEATHERING giving the rocks rounded edges.
Similarly to limestone is has many joints and beds but is also susceptible to FREEZE-THAW. In contrast, tors often have many ‘tiers’ and the rocks appear to be stacked.
Due to freeze-thaw, the granite often collapses, leaving a trail of granite pieces on the ground.
How are Tors formed?
Rocks are metamorphed when lava bakes and pushes up from ground. The lava then cools, which causes it to shrink forming joints and beds of the landscape.
Tors are formed by weathering (physical and chemical) of cover rocks (rocks that have close joints). Tors are also susceptible to freeze-thaw which is why there is often broken rocks near the tor.
But tors have unusually widely-spaced joints so it is less susceptible to weathering. The removal of the cover rocks leaves the tor to be still standing. The closer the joints, the faster the weathering process.
Granite Landscape
Reliefs - Slopes of land
Steep-sided, flat topped hills with tors on top.
Granite is impermeable and has plenty of peat so that means there is poor drainage. This also means there are lots of rivers.
Marshy plains and stagnant ponds. Featureless blanket bogs with no trees.
Uses (Dartmoor)
Dartmoor is located in the South-West of England.
AGRICULTURE
- Rough grazing for sheeps and horses
- Pony trekking
BUILDING MATERIAL
- Bi-product of granite is china clay which can be used for toothpaste, tablets and paint. This is mined using very powerful water jets. But it is also an eyesore.
- Crushed rock (aggregate) for road building.
- Granite used to make Dartmoor Prison.
OTHER USES
- Military training ground
- Tourism (geography)
- Water Power
Chalk - Introduction
- Permeable, so few surface streams
- White colour
- Quite strong but relatively soft. Strong enough to form cliffs.
- Sedimentary
- May contain fossils
- Alkaline rock
- Breaks - sharp edges
Clay - Introduction
- Impermeable (pottery)
- Quite hard when dry. If soft, it is relatively soft.
- Weak (Gentle slopes)
- Grey colour
- May contain fossils
- Jurassic, Cretaceous, Palaeogene
- Can flake off if dry
