rocks and weathering Flashcards
how long ago was the earth estimated to form
4.6 billion years ago
who was the notion of plate tectonics first investigated by
Alfred Wegener
what did Wegener deduce in terms of plate tectonics
that the earth was once one land mass- a super continent called Pangea but it later split into Gondwanaland and Laurasia before breaking into more land masses
how does geology evidence plate tectonics
many rocks of a similar age, structure and composition have been found on land masses now thousands of miles apart
what are the 5 forms of evidence for plate tectonics
geology, fossils, climatic evidence, sea floor spreading and paleomagnetism
describe the lithosphere
the outermost layer composed of the crust and the rigid upper mantle
give 2 characteristics of continental plates
average of 125km thick, reach their greatest thickness at large mountain ranges, composed of older lighter granitic rock that is rich in minerals such as silica and may range from 50-70km thick
give 2 characteristics of oceanic plates
are thinner and reach 50-100km thick of which the upper 5-10km may be crust, composed of younger and denser rock of basaltic origin
has the earths core retained much of its radioactive heat from early transformation
yes
describe the slab-pull mechanism
the oldest edge of a plate furthest from the molten magma become cooler and more solid, the denser material descends at a subduction zone
what are hotspots
vertical plumes of magma that can be found at both plate and within the middle of a plate
what are the three main types of movement of plates
convergent (together), divergent (apart) and transform (side by side)
explain a constructive plate boundary
occurs when tectonic plates move apart creating an upwelling of magma from beneath. As the plates rarely move rapidly and with little contact together, seismic activity is less, volcanic activity may be present
explain a conservative plate boundary
by two plates moving side by side and often will move at different rates or directions which will increase the stress between both so when friction increases there will be a potential for earthquakes
explain a destructive plate boundary
results from a convergence of oceanic and continental plates, as they are forced together the denser oceanic plate subduct under the thicker and less dense continental plate, the subducting plate becomes increasingly magmatic due to intense heat and pressure as its destroyed. volcanic activity may result along with seismic activity
explain a collisional plate boundary
occurs when two plates of equal thickness and densities collide, though this may be at a relatively slow rate, the extreme pressure is great enough to develop huge mountain chains, continental crust is thickest here and as a result magmatic intrusions are rare
explain ocean plate-ocean plate boundary
one of the plates is pushed, or subducted, under the other. Often it is the older and colder plate that is denser and subducts beneath the younger and warmer plate. It results in submarine volcanoes that may eventually breach the surface to form islands, several chains may be formed called island arcs, oceanic- oceanic sub ducting zones result in seismic and volcanic activity
explain sea floor spreading
a mechanism of continental drift, where divergent plate boundaries act as a constant conveyor belt motion creating enough new ocean floor to widen the Atlantic Ocean by 2cm a year
describe oceanic trenches
or deep sided trenches are long narrow depressions in the surface of the seafloor (deepest past of the oceans) along a plate boundary formed as a result of the descending oceanic plate
describe a Benioff zone
an area in the subduction zone in a destructive plate boundary. the area is normally the oceanic crusts path downwards, normally between 30 to 60 degrees in angle. It is responsible for earthquakes
describe fold mountains
are formed by the compression of marine sediments trapped between the converging lithospheric plates at a convergent boundary. these marine sediments are distorted under extreme pressure and thrust upward creating a chain of mountains and volcanoes
define mountain building
areas of the earths surface that experience upthrusting as a result of convergent plate boundaries, all major mountain chains are the result of this process of mountain building ororogenesis
give 3 conditions where weathering is greatest
there are extreme weather conditions, there are poorly resistant rock types, the rock has been exposed for a long time
describe free thaw weathering
where ice crystals are formed from water in the cracks and joints of rocks and as it freezes it will occupy 9% more space so cause pressure on the rock and pieces will shatter away
describe salt crystallization ( salt weathering)
results from the expansion of salt particles that have entered pore spaces within the rock
define slope
the hill slopes where gravitational influence exceeds the force of resistance
how do slopes develop
Slope development occurs over time and results largely from the interactions of the climate and rock type as well as the vegetation, soil and human activity occurring there.
define rock structure
the rock structure refers to the rock and lithology to its physical characteristics
how can rock structure influence the shape of a slope
degree of resistance, angle of orientation and dip, type of extent of faults and folds
how does the structure and texture of soil influence a slope
will influence how much water it can hold and the ability for vegetation to grow
warm moist areas are most susceptible to weathering- true or false
true
define slope processes
are exogenetic processes operating on an inclined surface of the Earth.
what does the nature of the slope influence
the hydrology of a drainage basin, its forms and features.
how is the soil profile of a slope detrmined
The soil profile is largely determined by the parent material underlying the slope but is in part formed by the breakdown of organic material on the surface.
Slopes with high root density are less likely to undergo slope failure. true or false
true
why are slopes with high root density less likely to undergo slope failure
This is because a high root length density and soil water level could be used as indicators of slope stability and possibly could be used to predict future slope failure.
how does heavy rainfall lead to a higher chance of mass movement
When heavy rain is present the land may become heavily saturated and the resultant increase in weight can lead to slumping and mass movement.
what is weathering
The natural process of decompositions and disintegration of rock in situ.
how is weathering different to erosion
Weathering is brought by changes in atmospheric conditions such as temperature, moisture and wind acting on a stationarity object.
what affects the rate of weathering
There are extreme weather conditions, there are poorly resistant rock types, the rock has been exposed for a long period of time
where does mechanical weathering take place
Altitude areas, artic areas and deserts
what is freeze thaw weathering
Process where ice crystals are formed from water in the cracks and joints at 0 degrees
describe salt crystallisation
Results from the expansion of salt particles that have entered pore spaces within the rock.
explain thermal expansion
is the tendency for minerals to expand and contract based on temperature. Rapid temperature fluctuations, such as day-night cycles, cause rocks to expand and contract. This causes stress within the rocks and small cracks form.
what is oxidation
Occurs when rocks become exposed to air.
what is hydrolysis
Significant in the decomposition of rocks to form clays. The process by which chemical bonds are broken and the components partner up to form different elements.
what is acidification
Process by which liquids become acidic and is common way in which rocks and minerals are dissolves
what is carbonation
The process where carbon dioxide often from rain water produces carbonic acid such as chalk and limestone and as a result the interaction rock will dissolve away rock
what is acid rain
Caused by greater concentrations of carbon dioxide, sulfur dioxide and nitrogen oxide as a result of human activity. These gases then form acids as they combine with water vapor and fall as rain.
what is hydration
Related to absorption of water by rocks. Certain rocks are particularly capable of absorbing water into pores and cracks in the structure. The rocks then swell sometimes repeatedly in alternating dry and wet conditions and can even change state.
what is biological weathering
Combined process of mechanical and chemical weathering
describe vegetation root action
Plants and plant roots also tend to pull rock apart (a form of mechanical weathering). Roots follow nooks and crannies along in the subsurface and, as they get older, expand. … When the plant falls over, the roots, still clinging to the rocks, literally “throw” up and move around soil and surface material.
what are the 3 basic mechanisms of mass movement that can be identified
slide, flow, heave
what is a slide
the movement of a cohesive unit with minimal internal dislocation and deformation
what is flow
distorts and shapes to the land over which is travel like a viscous liquid, the rate of flow, just like a river, is influenced by its gravitational potential
what is a heave and give 2 variants
when soil or clay expands causing an upward movement, ground heave is when the ground sinks due to the expansion, frost heave occurs at high altitudes when water freezes and expands causing the ground to move upwards
define soil creep
a slow mobbing phenomenon that usually occurs on vegetated slopes in temperate regions at a rate of less than 1cm a year
explain the 2 main reasons for a soil creep
- alternating wet and dry periods which cause the soil to expand then contract, in wet periods the soil absorbs more water and becomes heavier and then moves downhill under the influence of gravity. in periods with little or no rainfall the soil dries out and contacts
- an alternative cause is from freeze thaw, during freezing ice crystals expand forcing regolith closer to the surface of the slope, when the ground later thaws the displaced material falls back but under the influence of gravity will end up further down the slope
define regolith
the layer of unconsolidated solid material covering the bedrock of a planet.
mudflows require higher saturation level than earth flows- true or false
true
what is the difference between slides and flows
The fundamental difference between slides and flows is that flows suffer internal deformation whilst slides move together and are not affected by internal derangement.
describe planar landslides
Are caused when weathered rock becomes detached from the parent rock usually along a plane or joint. As a result the break is often clean and straight. Gravity pulls the material as one down the angle of slide until it reaches the bottom or a point of friction where resistance is greater than gravity. The exposed upper cliff is known as a scarp.
explain the formation of rotational slides
Are sometimes referred to as slumping and are formed on a curved failure surface, as water infiltrates permeable surface rocks it will add weight, this added weight will make the cliff face heavier and other weathering such as freeze thaw will weaken the cliff more, the cliff will collapse in a rotational movement and expose a scarp at the top
explain rock falls
Are sudden debris movements. When rock or earth falls, bounces, or rolls from a cliff or down a very steep slope. They occur on exposed slopes exceeding 40 degrees with rocks that can become fragmented as a result of their structure.
explain debris avalanche
Is a sudden catastrophic and fast collapse of unconsolidated material from an unstable slope, most frequently on volcanoes. They can either be hot- forming as the result of an expanding magma chamber within the cone or cold- as a result of seismic instability.
when did the Nevado Del Ruiz eruption occur
13th November 1985
a lahar killed many during Nevado del Ruiz, what is a lahar?
A lahar is a large mud and debris flow as a result of volcanic activity.
how did the lahar occur during Nevado del Ruiz
Due to a high mountainous area having a high altitude it will be colder and therefore may have ice. This means when volcanic activity occurs even if it is small, the ice will melt causing a boiling hot mud flow.
how many people died in Nevado del Ruiz
2000
where is Nevado del Ruiz located
Northern Columbia
beforehand why was Nevado Del Ruiz named the sleeping lion
hadn’t erupted in 150 years but murmurs were heard months before the eruption
how fast did debris and mud flow down the mountain Nevado del Ruiz
50km/h
what are 3 human causes that alter slope processes
land overuse and clearance (deforestation), urbanization and slope stability, mining and extraction
what is pinning to modify slopes
involves bolting unstable rock faces to increase cohesion and stability and prevent slippage, using metallic bolts, tie-rods, steel soil nails driven horizontally into the cliff. It reduces mass movements and thus reduces net erosion rates.
define land grading to alter slopes
Grading refers to the movement of soil, sand, rock gravel or other sediment on a site in a manor that alters the natural contour of the land
where and when did the mudflow of Aberfan happen
South Wales, October 21st 1966
how many deaths occurs in the mudflow of aberfan
147 deaths- 116 were children, 5 were teachers
what process was the mudflow of aberfan an example of
slope overload
explain excavation
Refers to the cutting and removal or displacement of rocks and soil. It must be done before any modern construction as it keeps the building strong and secure. This allows for the foundation of a building to be bound to the ground almost and strengthens and weaknesses.
explain water on land
Water leakage has often been linked to landslides. The water gets absorbed in the land and makes it heavier causing gravity to have more influence and the excess moisture will act as a lubricant, reducing fiction and increasing the risk of sliding.
explain peat bogs and how erosion of them will impact
These are carbon sinks and through acid rain these are eroding. They can act as flood protection so with constant erosion a natural defense is removed. Erosion of peat bogs also can cause water supply issues as the water becomes contaminated and companies have to spend money on water cleaning.
what are the 4 solutions to slope movement
slope stability analysis, landslide hazard analysis, structural engineering, afforesting areas
explain slope stability analysis
This is designed to assess human made or natural slopes using mathematical models to ensure the angles of the slopes and the weight of the soil, rock and debris and whether the forces of gravity and friction are in balance. Stable slopes are balanced or heavily weighted to a rigid and stable structure. The main objective of this solution is to assess a risk of movement and analyze a potential hazard.
explain landslide hazard analysis
Indicates the possibility of landslides occurring throughout a given area. An ideal landslide hazard map shows not only the chances that a landslide might form at a particular place, but also the chance that it might travel downslope a given distance. It assists in the development of guidelines for sustainable land use planning.
explain structural engineering and give 2 examples
Refers to the design and implantation of stabilizing strategies and equipment. There are soft and hard approaches that can be used depending on the structure. Soft engineering strategies use more natural approaches and the use of the local environment. This can include plant vegetation to bind the soil and intercept rainfall. Hard engineering approaches rely on construction of physical features that will hold or support. Along many alpine roads wire nets and gabions are used to prevent rockfall.
