GEO - engineering geology topic 4

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RIVER PROCESSES Why are river processes important regarding geology?
- erode and transport
- erode and deposit
- transport and deposit
Sediment is transported by three processes, these are determined by the size and weight of the particles
- suspension
- suspended
- saltation
- traction/creep
What happens in suspension?
- very fine particles are carried by the water flow
- particles bounce along the river bed
- particles to coarse for the aforementioned processes are rolled along the bed
what happens in traction or creep?
- very fine particles are carried by the water flow
- particles bounce along the river bed
- particles to coarse for the aforementioned processes are rolled along the bed
what happens in saltation
- very fine particles are carried by the water flow
- particles bounce along the river bed
- particles to coarse for the aforementioned processes are rolled along the bed
What determines the size of particles carried?
- discharge and depth of water
- volume and speed of flow
- the state of the river bed
The upper catchment, engineering, which is untrue?
- ground is steep and rivers are fast flowing
- erosion and transport are high, while deposition is low
- steep sided river valleys are unstable
- large quantities of vedgetation make excavation diffcult
- difficult to build on, limited flat space and slope failure possible as valley sids are undercut
- sudden high precipitation can lead to flash floods
Lower catchement, engineering, which is untrue?
- ground is less steep
- erosion still apparent, but depostion occurs
- rivers path will change due to meanders over time
- suitable for building
- flooding common
- can flood during peak discharges
Flood plain sediments, which is not a type?
- Scroll sands: river deposits on the inside bend of the river
- terrace sediments: when the river cuts down into the previous valley floor
- grey sands: deposits made where the river flow suddenly drops, such as where it meets the sea or a slower river
- levee silts and bedded alluvium: durring flooding flow decreases and deposits are made, these will make bedded layers of sediments and mounds called levees
- old channel lenses: a dried up oxbow lakes deposits
- Peat: organic sediments forms in wet land areas
Building on flat ground at a valley bottom... tempting but which is not one of the problems?
- alluvial soils weak, requires special foundations
- sediments may be very wet, saturated. This further reduces strength
- Subject to flooding, affects housing and can undermines foundations
- land usually not fertile
Which is not a problems regarding built flood defenses?
- embankments may be breached or overtopped at some time
- interfers with the natural behaviour of the river
- decreases water flow, and encourages groundwater flow
- usually means there will be flooding elsewhere
River erosion of land and structures... Which is untrue?
- Meandering rivers tend to move, so care must be taken when placing bridges and roads
- River flow rates are unpredictable
- rivers will erode banks and structures
- bank protection will never be permanent, a river will always do what it wants to
Which is untrue about an aluvial fan?
- formed when a small valley joins a large one and dumps sediment
- scale varies from metres to 100s of kms
- heavy materials deposited first
- may have multiple river channels
- building is safe on alluvial fans
- rivers can change course over night, unpredicatbaly
COASTAL PROCESSES What is the main source of erosion in coastal regions?
- wave action
- rivers entering the sea
- wind
Wave action is also what?
- responsible for transportation
- responsible for deposits
- responsible for both
What is the ultimate 'goal' of wave action?
- to make the coastline flat
- to erode and transport sediment across the ocean
- to cover land
what is the relationship between bays and headlands?
- material eroded from the headlands is transported away until the headland becomes the same level as the bay
- eroded material from the headland eventually fills the bay as it is deposited
- the headlands channel the wave energy, making the bay deeper and deeper
the eroded material from the headlines does what?
- fills the bay and makes beaches
- makes islands in the bay
- is transported out to sea
CLIFF EROSION which correctly describes the process?
- waves cause mechanical erosion, a notch is cut and part of the cliff collapses, the eroded material is then further eroded until it disappears
- the waves cause mechanical erosion, undercutting the cliff and causing it to collapse and recede inland, the water then carries away and deposits the debris
- the waves cause lateral erosion breaking loose bits of the cliff away, these fragments strike the cliff causing it to erode
The rate of cliff erosion largely depends on what?
- the force of the waves
- the type of material composing the cliff
- the particles already in the water
What transports sediments in deep water?
- gravity and fish
- currents
- neither it isn't
describe longshore drift, the process allowing sediments to move along a coastline how does it occur?
- occurs when waves approach obliquely to the shore line, depositing sediments as they arrive
- cycling currents behind the wave transfer the sediments from one wave group to another
- the wind blowing and causing the waves is not perpendicular to the shore
which describes the process in more detail?
- the waves, blown by the wind, come up land at a different direction of a approach. Using this momentum, the backwash picks up previously deposited sediments and carries it away at the same angle of approach in the other direction
- the waves, blown by the wind, come up land at a different direction of a approach. Using this momentum, the backwash picks up previously deposited sediments and carries it away in a perpendicular direction to the shore
- the waves approach and backwash in a circular but progressive shape, forced forward by the wind and waves behind
This process tends to deposit where?
- when it mets an obstacle (man made or natural) or a corner of a coast
- when it mets an obstacle or a river entering the sea
- the sea mets a river, an obstacle is met where wind/wave energy decreases
coastal engineering, defense which is untrue about coastal engineering defenses
- accounts for the majority of engineering projects on the coast
- best systems dissipate wave energy
- relatively cheap
- only a temporary solution
- very expensive
- structures should be porous, made from rock or concrete
The best coastal defence is a beach, which is an untrue statement about beach however?
- can be created or maintain with obstacles
- prevents erosion
- can cause increased erosion elsewhere
- encourages extreme depostion, which can cause land to be created
GLACIATION Which is untrue about glaciation?
- glaciers stop when they reach the sea
- Glaciers form when snow melts on mountains and doesn't melt away in summer, the snow becomes ice due to recrystalisation, caused by temperature and pressure
- when mass is great enough the ice flows down hill very slowly, causing huge erosion
- currently glaciation is occuring in the higher and lower latitudes and the biggest mountain ranges
- glacial deposits are ususally fertile
- glaciation cover 2/3 of britain, and has therefore had a large influence
Glacial erosion Which is not a feature of glaial erosion
- U shaped valleys: glacier carves a u shaped valley due to its weight and erosion rate
- corrie: bowl shaped hollow near the top of a mountain where the snow orginally collected
- sinkholes: glacier plukes large rocks from the ground and water enters the ground, if there is limestone a sink hole will occur
- rock basins: basins gouged out by the glacier as it travels down the valley
- tarns and lakes: tarns are small lakes that collect in corries
- glacial lakes: lakes collected in rock basins and/or behind moraine dams
draw a typical cross section of a u shaped valley!
- DONE IT, not sure if its right though
- NAH I know it
- Did it and its right
If we don't know we're in a U shaped valley we can look at some characteristic features. Which is not one?
- Striae: ice and trapped material are dragged across the local bedrock, scratching the bedrock
- roche moutonee (sheep rock): ice pucking debris from the down flow side of a rock body
- crag and tail: formed when a hill of hard rock is left less eroded and a tail of softer rock is left behind it
- Erratic pit: Formed when very large rock is plucked from the ground
Glacial deposition Which of the following is true?
- Glaciers erode most upland where velocity and mass are greatest, deposition occurs mainly where the glacier melts
- glaciers collect and transport down the valley, not much debris is lost or deposited in the upper reaches
- glaciers continuosly erode until they melt completely, when everything is then dropped
There a several names of the glacial deposits. Which is not one?
- Moraine, (lateral, median, terminal)
- Glacial till/boulder clay
- drumlins
- erractric
- kames
- contromakes
As before, which is not one?
- Eskers
- perigrinal rocks
- lacustrine deposits
- peat
which correctly describes moraine?
- mounds of debris dropped from the glacier where it collected once the ice melts/recedes. Typically collects at the sides,middle and the end
- rock debris deposited along the valley floor when the glacier melts
- the debris left at the end of glacier
Which best describes glacial till?
- higly varied sizes of materials deposited by the glacier
- material deposited under the glacier or ice sheet, highly varied in sizes and types of material
- large range of materials at different sizes, usually found under a glacier
which best describes a drumlin?
- low, elongated hills of glacial till, forming behind a harder rock
- elongated hills of glacial till formed as an ice sheet passes over flat ground
- glacier depositing rocks infront of a large boulder
which best describes an erractic?
- huge boulder pluked from the ground and left stranded in an unusual place when the ice melts
- large hole left by a huge rock being plucked from the ground
- a conglomeration of rocks and materials found in an unusually place, usually the only sign of very old glacial paths
What is a Kame?
- Hill of gravel and sand formed where it collects behind a large rock
- Hill of gravel and sand formed where it collects inside a hollow
- Hill of gravel and sand formed where it collects infront of a large rock
What is an esker?
- long ridges of alluvial sand and gravel formed and deposited by streams flowing under the glacier
- streams running through the glacier form bands of rocks, this happens during summer and is encouraged by animals living in the ice as they clear paths
- where groundwater reaches the surface and makes a spring under the glacier, the glacier deposits rocks into the spring, causing deep holes of morraine
Which best describes a lacustrine deposit?
- deposits filling a body of water, includes large rocks and fine grains
- an ultra fertile deposit where a forrest very quickly grows
- lakes formed by moraine or rock basins are filled by fine grained alluvial material.
Which best describes peat?
- An saturated area of land where the water cannot escape, unsuitable for building
- forms around glacial ponds and tarns that have filled with moss
- saturated land that organic material thrives on due to the high mineral content of the soil
Tundras and periglcial environments which is not a correct description?
- affected by by cold, but indirectly by glaciation. Snow falls in winter and melts in the summer
- outwash from the glaciers forms alluvial sediments in low lying areas. Large areas also covered in wind blown sediments from glacial region.
- deep subsurface is frozen all year round, with the top few metres freezing and thawing annually. this layer prone to extreme weathering
- biological activity is rare due to the harsh environment
- in summer the active layer is very wet. Water cannot drain due to frost below, lots of peat and on slopes landslide are common
- in winter active layer freezes and is subject to frost heaves. Can cause hills to rise up out of the terrain.
What are the engineering implications in tundra environments
- construction is difficult in these regions, permaforst is very hard
- active layer is saturated and prone to subsidence when thawed. Difficult to support heavy structures
- usually flat and exposed to the wind, rain rare
- cannot afford to heat the permafrost in winter as this will damage foundations. Piling to the permafrost or heating a building on insulated foundations are
KARST LANDSCAPE What is a karst landscape?
- the typical landscape formed by long term erosion of limestone by carbonic acid
- a landscape made of limestone eroded or not
- an area or limestone that is exposed to the elements, heavily eroded by many different actions
What are common in karst landscapes? Which is not one?
- voids and caverns, can causes sinkholes when they collapes
- lowered water table due to downward erosion of surface streams
- clints and grykes are formed and appear on the surface (clint block appearance, gryke dividing gaps)
- As grykes and open up the rock head begins to take on a pinacled shape
- groundwater rivers, leaving an intact surface
- Cave openings in rivers, where ground water has eroded through
What potential problems are there in a karst landscape for engineers? One of these is not one.
- Sinkholes, may unwittingly build on one and it may collapes. even filled sink holes could cause subsidence. Generally unpredictable.
- Cave collapse: Cavern roofs falling, can be caused by over loading.
- drainage and water table: can change, and when it does can transport underground deposits and leave voids. Can also erode natural supports. Excavation and building can greatly affect this.
- effective stress: limestone subject to compression, large constructions can sink into the ground over time
- foundations: difficult to place on pinnacled rock heads and buried sink holes
Knowing about karst landscapes is important, why?
- so that we can design safe structures and build correclty
- so that we no not to build on them
- It is important to allow engineers to alter the landscape to allow for design

GEO - engineering geology topic 4

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