stint
i walked out of my house without knowing that i wasn't wearing the right pair of spectacles. besides, someone thinks that the black one looks better. syo ended early today. then there was this crazy guy at the mrt who kept saying 'hi' to yuze and me.
just came back from dinner. there was salmon sashimi, chicken curry rice, californian maki, gyoza and tofu. now that's a hearty farty meal! tiong bahru plaza was bustling with people. omg too many people around, it was so noisy!
i'll revise lithology 2 now!
lithology 2
weathering is the in situ breakdown of rocks. there are five geometries of rock breakup. they are block disintegration, granular disintegration, shattering, exfoliation and spheroidal. rocks break up in these ways due to three main types of weathering: physical, chemical and biological.
four processes of physical weathering:
1. pressure release
2. freeze-thaw action
3. insolation weathering
4. salt weathering
five processes of chemical weathering:
1. solution
2. hydration
3. hydrolysis
4. oxidation
5. carbonation
biological weathering involves both physical and chemical processes, but are termed 'biological' because they are caused by living organisms. these processes include root prising and chelation.
the humid tropics are characterised by dominant chemical weathering. this is because of the high temperatures near the equator, and the high annual rainfall. dense vegetation also contributes to biochemical weathering. the result is a thick layer of regolith over rock layers. this then contributes to the lack of physical weathering processes, since physical weathering processes are superficial. the masking effect of the thick regolith prevents fresh rock from being exposed to physical weathering processes.
the seasonally humid tropics are characterised by dominant chemical weathering. however, unlike the humid tropics, there is less buildup of regolith. the vegetation is less dense, and hence surface wash is greater. fresh rock exposed after surface wash is then ready for chemical weathering processes to take place again, and repeated cycles result in the characteristic inselbergs.
hot deserts are dominated by physical weathering. the large diurnal temperature ranges favour insolation weathering. the process is superficial, and thus weathering is very slow. studies by blackwelder and griggs have shown that water, even in minute amounts, play a role in such insolation weathering processes.
temperate regions have very strong freeze-thaw action during winter months. compared to glacial regions, the freeze-thaw processes may be more active at temperate regions. this is because glacial regions are consistently cold, while temperatures at temperate regions fluctuate above and below freezing point. there is high chemical weathering potential at glacial regions, but cold temperatures inhibit the processes.
mass movement is defined by the downward movement of weathered rock materials in response to gravity.
two things govern the rate of mass movement: shear stress and shear strength.
shear stress involves factors which cause movement. these include, gravity, slope angle, and water. shear strength involves factors which resist movement. these include friction, cohesion of particles, solidification and crystallization, structure, and water. water plays a role in shear stress and strength. in small amounts, it can act as an adhesive, via surface tension, to bind particles together. as such, a dry slope may be more prone to movement compared to a moist slope. however, saturation of water would add weight to the materials, and lubrication would cause movements to start.
triggering mechanisms can be due to natural processes like earthquakes and undercutting by rivers, and human processes like uncontrolled hillside developments.
seven types of mass movement processes:
1. soil creep - gravity creep and soil heave
2. solifluction
3. rockfall
4. land/rock-slide
5. earth/mud-flow
6. slump
7. avalanche
humans and nature play a role in causing mass movements. use these case studies as examples: holbeck hall hotel in scarborough (slump - 1993), favelados in rio de janeiro (landslide - 1966-7), himalayan roads in india (rockslide - 1995). tiltmeters and extensometers can be used to gather information about ground tilting. computer modelling can be used to map hazard areas, and governmental policies can restrict development at these areas. vegetation should be kept, as plant roots have binding properties. human structures like ripraps, rock gabions, retaining walls, nails and sandbags can be used to prevent slope failures. debris catches and dams can be built to protect property, while drainage systems can be enhanced to prevent saturation of soils.
limestone is a sedimentary rock formed under the sea millions of years ago. it contains calcerous remains of organisms, as well as fossils. it contains the mineral calcium carbonate, which is very susceptible to carbonation processes. limestone is a rock of low primary permeability and high secondary permeability. large proportions of limestone are carried away after weathering, and this leaves behind only the insoluble fossils.
at temperate regions, dolines and uvalas dominate karst landscapes. dolines form over limestone rocks which are highly fractured. once a sinkhole develops, throughflow guides water towards the centre of the sinkhole, which causes weathering to speed up, forming dolines. if dolines grew and merged over time, with new dolines developing in the old ones, uvalas are formed.
collapsed dolines can occur in the humid tropics. they usually develop over water-filled caves, aided by upwards erosion by the water. however, the dominant karst lanscapes in the tropics are cockpit karsts. formation still begins with selective weathering at concentrated joints. however, the nature of rainfall in the tropics dictate that water will flow over the surface of the limestone rock for brief periods of time. surface gullying takes place to intensify weathering along the joints, which cause elongated depressions. as these depressions join together, they form interconnected cockpits, isolating conical residual hills. tower karsts develop after sufficiently long periods of time have passed. as downward weathering is prohibited, lateral weathering takes place and leads to formation of steep towers.
karren features refer to micro-solutional features of limestone rock. these include limestone pavements (clints and grikes) and spitzkarren (pinnacles).
drainage features of karst landscapes include karst gorges, which exist only in early limestone development. swallow holes, dry valleys and blind valleys come together. this happens when a river flows over limestone, selectively erodes a swallow hole, and disappears underground. downstream of the swallow hole is the dry valley, and upstream is the blind valley. a series of swallow holes, dry valleys and blind valleys can develop towards the river source, until the river reaches the boundary between limestone and non-limestone rock.
caves form in temperate zones. groundwater moving through joints and bedding planes will develop fissures into large cavities. localized solution of the rock forms cave conduits. stalactites and stalagmites will form due to deposition of calcite.
granite is an instrusive igneous rock formed from rhyolitic magma. solidification underground is slow, and thus leads to growth of large crystal minerals for granite. it usually forms batholiths, which are exposed after denudation. exposure of granite to pressure and temperatures at the surface of the earth often leads to development of cracks, as pressure release occurs. as such, granite is high in secondary permeability. interlocking crystals of granite result in low primary permeability. the main mineral in granite is feldspar, which is susceptible to hydrolysis and forms kaolinite clay. the result of weathering granite is thick regolith.
in the humid tropics, only a thick layer of regolith can be created. ruxton and berry proposed the model of a deep weathered layer. there are four zones:
zone 4: partially weathered rock
zone 3: corestones with residual debris
zone 2: residual debris with corestones
zone 1: residual debris
in the seasonally humid tropics, regolith is now allowed to build up as much, since surface wash, aided by lack of vegetation, ensures that weathered materials are removed. this forms inselbergs. inselbergs develop over geological time, through pluvial and interpluvial periods. during pluvial periods, precipitation results in a build up of weathered material, which are deeper at areas that are highly fractured. during the interpluvial periods, the weathered materials are removed to expose the basal surface of weathering. over time, the basal surface of weathering becomes more and more undulating. ruwares forms first, followed by bornhardts.
just came back from dinner. there was salmon sashimi, chicken curry rice, californian maki, gyoza and tofu. now that's a hearty farty meal! tiong bahru plaza was bustling with people. omg too many people around, it was so noisy!
i'll revise lithology 2 now!
lithology 2
weathering is the in situ breakdown of rocks. there are five geometries of rock breakup. they are block disintegration, granular disintegration, shattering, exfoliation and spheroidal. rocks break up in these ways due to three main types of weathering: physical, chemical and biological.
four processes of physical weathering:
1. pressure release
2. freeze-thaw action
3. insolation weathering
4. salt weathering
five processes of chemical weathering:
1. solution
2. hydration
3. hydrolysis
4. oxidation
5. carbonation
biological weathering involves both physical and chemical processes, but are termed 'biological' because they are caused by living organisms. these processes include root prising and chelation.
the humid tropics are characterised by dominant chemical weathering. this is because of the high temperatures near the equator, and the high annual rainfall. dense vegetation also contributes to biochemical weathering. the result is a thick layer of regolith over rock layers. this then contributes to the lack of physical weathering processes, since physical weathering processes are superficial. the masking effect of the thick regolith prevents fresh rock from being exposed to physical weathering processes.
the seasonally humid tropics are characterised by dominant chemical weathering. however, unlike the humid tropics, there is less buildup of regolith. the vegetation is less dense, and hence surface wash is greater. fresh rock exposed after surface wash is then ready for chemical weathering processes to take place again, and repeated cycles result in the characteristic inselbergs.
hot deserts are dominated by physical weathering. the large diurnal temperature ranges favour insolation weathering. the process is superficial, and thus weathering is very slow. studies by blackwelder and griggs have shown that water, even in minute amounts, play a role in such insolation weathering processes.
temperate regions have very strong freeze-thaw action during winter months. compared to glacial regions, the freeze-thaw processes may be more active at temperate regions. this is because glacial regions are consistently cold, while temperatures at temperate regions fluctuate above and below freezing point. there is high chemical weathering potential at glacial regions, but cold temperatures inhibit the processes.
mass movement is defined by the downward movement of weathered rock materials in response to gravity.
two things govern the rate of mass movement: shear stress and shear strength.
shear stress involves factors which cause movement. these include, gravity, slope angle, and water. shear strength involves factors which resist movement. these include friction, cohesion of particles, solidification and crystallization, structure, and water. water plays a role in shear stress and strength. in small amounts, it can act as an adhesive, via surface tension, to bind particles together. as such, a dry slope may be more prone to movement compared to a moist slope. however, saturation of water would add weight to the materials, and lubrication would cause movements to start.
triggering mechanisms can be due to natural processes like earthquakes and undercutting by rivers, and human processes like uncontrolled hillside developments.
seven types of mass movement processes:
1. soil creep - gravity creep and soil heave
2. solifluction
3. rockfall
4. land/rock-slide
5. earth/mud-flow
6. slump
7. avalanche
humans and nature play a role in causing mass movements. use these case studies as examples: holbeck hall hotel in scarborough (slump - 1993), favelados in rio de janeiro (landslide - 1966-7), himalayan roads in india (rockslide - 1995). tiltmeters and extensometers can be used to gather information about ground tilting. computer modelling can be used to map hazard areas, and governmental policies can restrict development at these areas. vegetation should be kept, as plant roots have binding properties. human structures like ripraps, rock gabions, retaining walls, nails and sandbags can be used to prevent slope failures. debris catches and dams can be built to protect property, while drainage systems can be enhanced to prevent saturation of soils.
limestone is a sedimentary rock formed under the sea millions of years ago. it contains calcerous remains of organisms, as well as fossils. it contains the mineral calcium carbonate, which is very susceptible to carbonation processes. limestone is a rock of low primary permeability and high secondary permeability. large proportions of limestone are carried away after weathering, and this leaves behind only the insoluble fossils.
at temperate regions, dolines and uvalas dominate karst landscapes. dolines form over limestone rocks which are highly fractured. once a sinkhole develops, throughflow guides water towards the centre of the sinkhole, which causes weathering to speed up, forming dolines. if dolines grew and merged over time, with new dolines developing in the old ones, uvalas are formed.
collapsed dolines can occur in the humid tropics. they usually develop over water-filled caves, aided by upwards erosion by the water. however, the dominant karst lanscapes in the tropics are cockpit karsts. formation still begins with selective weathering at concentrated joints. however, the nature of rainfall in the tropics dictate that water will flow over the surface of the limestone rock for brief periods of time. surface gullying takes place to intensify weathering along the joints, which cause elongated depressions. as these depressions join together, they form interconnected cockpits, isolating conical residual hills. tower karsts develop after sufficiently long periods of time have passed. as downward weathering is prohibited, lateral weathering takes place and leads to formation of steep towers.
karren features refer to micro-solutional features of limestone rock. these include limestone pavements (clints and grikes) and spitzkarren (pinnacles).
drainage features of karst landscapes include karst gorges, which exist only in early limestone development. swallow holes, dry valleys and blind valleys come together. this happens when a river flows over limestone, selectively erodes a swallow hole, and disappears underground. downstream of the swallow hole is the dry valley, and upstream is the blind valley. a series of swallow holes, dry valleys and blind valleys can develop towards the river source, until the river reaches the boundary between limestone and non-limestone rock.
caves form in temperate zones. groundwater moving through joints and bedding planes will develop fissures into large cavities. localized solution of the rock forms cave conduits. stalactites and stalagmites will form due to deposition of calcite.
granite is an instrusive igneous rock formed from rhyolitic magma. solidification underground is slow, and thus leads to growth of large crystal minerals for granite. it usually forms batholiths, which are exposed after denudation. exposure of granite to pressure and temperatures at the surface of the earth often leads to development of cracks, as pressure release occurs. as such, granite is high in secondary permeability. interlocking crystals of granite result in low primary permeability. the main mineral in granite is feldspar, which is susceptible to hydrolysis and forms kaolinite clay. the result of weathering granite is thick regolith.
in the humid tropics, only a thick layer of regolith can be created. ruxton and berry proposed the model of a deep weathered layer. there are four zones:
zone 4: partially weathered rock
zone 3: corestones with residual debris
zone 2: residual debris with corestones
zone 1: residual debris
in the seasonally humid tropics, regolith is now allowed to build up as much, since surface wash, aided by lack of vegetation, ensures that weathered materials are removed. this forms inselbergs. inselbergs develop over geological time, through pluvial and interpluvial periods. during pluvial periods, precipitation results in a build up of weathered material, which are deeper at areas that are highly fractured. during the interpluvial periods, the weathered materials are removed to expose the basal surface of weathering. over time, the basal surface of weathering becomes more and more undulating. ruwares forms first, followed by bornhardts.
-fin
posted by ivan at 9:21 PM
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