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Catastrophe Damburst 3 Survey

Geology notes

SS1

MineralsRocks consist of one or more minerals. A mineral is an element or compound that exists naturally.

Rock TypesThere are 3 types of rock.

SedimentaryExamples: chalk, sandstone, limestone.

Characteristics: made up of grains, often easy to break, sometimes porous.

IgneousExamples: granite, basalt.

Characteristics: made up of crystals, usually hard and resistant to chemicals, usually non-porous.

MetamorphicExamples: marble, slate.

Characteristics: made up of crystals, can be in layers, usually hard, always non-porous.

Porous rocks have spaces inside so can soak up water and let it pass through.

Some materials are non-porous, like concrete.

WeatheringExposed rock surfaces are constantly being changed. Weathering breaks up rock into smaller pieces, called sediments.

Chemical weatheringSome water is acidic. Acidic water reacts with some rock minerals, such as calcium carbonate in chalk and limestone. The minerals are broken down in chemical reactions.

Some minerals are soluble. They dissolve in water.

Physical weathering…can be caused by water or wind moving over rocks, by ice forming in cracks and by rocks getting hot and then cold.

Biological weatheringPlant roots and burrowing animals can break up rocks.

ErosionMoving water, ice and wind can carry rock sediments away from weathered rock surfaces. This is erosion.

Over millions of years, weathering and erosion can level mountain ranges.

SedimentThe size of sediments varies from huge boulders to tiny pieces of clay. Very fine sediment is called silt.

The biggest pieces of sediment can only be carried by fast-flowing water. They are deposited as the water slows down. Silt can be carried huge distances – even by slow-flowing rivers – before it is deposited.

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Catastrophe Damburst 3 Survey

Evidence

SS2

Source: Geological Society websiteLandslides may be triggered by earthquakes, volcanic eruptions, heavy rain and flooding.

Source: Indostani newspaper of 1981The Sefin Dam was completed today 20 months ahead of schedule and well under budget. The speed at which it was built has led to worries about the quality of its construction.

Source: Visual safety check of Sefin Dam (1 year ago)Suggest monitoring a small bulge in the dam wall on the lower right corner of the upstream side.

Source: Dam safety check manualWithout a solid foundation the dam will collapse. If there are signs that water is flowing under a dam the gap must be filled with concrete immediately.

Source: Visual safety check of Sefin Dam (1 year ago)The spillway tunnel had to be cleared of sediment to prevent a blockage building up.Source: Nayson Bhatt (geologist)Heavy rainfall erodes rocks. This increases the amount of sediment being carried into the reservoir.

Source: Paul Hine (civil engineer)Overtopping (water flowing over the top of a dam) for several months could wear away the rocks of the dam walls.

Source: Ian Cezair (construction worker)Concrete is a wonderful building material. It is strong, waterproof and does not break up easily.

Source: Local weather monitoring stationRainfall in the Sefin dam area in the week before the dam burst was 40 cm – more than double normal levels for this season.

Source: Local resident Anil AgarwalI walk past the dam every day. The day before the dam burst I saw water falling over the top of it. I have never seen this before.

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Catastrophe Damburst 3 Survey

Possible causes – evidence for and against

SS3

Possible Cause Evidence for this being the cause Evidence against this being the cause

1 There was a build up of sediment in the reservoir.

2 There was a landslide into the reservoir.

3 The dam was built on unsuitable foundations.

4 The dam was built out of unsuitable material.

5 The waterproof core cracked.

6 The spillway got blocked.

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Weathering can be:

Physical Very low temperatures all year round can lead to freeze–thaw weathering where water freezes and expands in cracks in rocks.Extreme differences between day and night temperatures leads to onion skin weathering.

ChemicalAcid in water reacts with chemicals like carbonates in rocks. Rain is naturally quite acidic but in polluted areas it can be more acidic. Water that contains decayed plant material will also be acidic.

BiologicalRoots of plants and animals walking over rocks can cause them to break up.

Catastrophe Damburst 3 Survey

Weathering in the world

SS4

Area 1: African rainforest. The Congo river runs through this lush tropical forest home to thousands of species of plants and animals. There is high rainfall throughout the year.Area 2: Beijing. The capital city of China. A high population and growing industry means that this city is known for its pollution. Seasonal dust storms plague the city.Task1 Rocks in the areas on the map are frequently weathered. For each area explain the most likely type(s) of weathering to take place with reasons.

2 The pieces of rock formed by weathering (called sediment) are moved away or eroded by moving water, ice or wind. For each area explain the most likely type of erosion to take place with reasons.

Area 3: The Himalayas. This mountain range is home to around15,000 glaciers (moving ice). The highest areas are covered in snow all year roundArea 4: Sahara desert. This massive desert has days reaching 50°C and nights where the temperature is below freezing.