Lithospheric Processes, Hazards and ManagementStructure of the
Earth1. The Core Inner and outer core, outer liquid about 3500km
radius, inner solid about 1255km The core is heavy and dense, and
nickel-iron alloy called Nife2. The Gutenberg Discontinuity
Separates core from mantle, zone of discontinuity Slowing of
seismic waves in region3. The Mantle3.1 Lithosphere, Asthenosphere
and Mesosphere Deepest solid layer is mesosphere, the semi-molten
layer is the asthenosphere, the solid layer above, including crust,
is lithosphere The rigid lithosphere is broken into plates which
can move over the molten asthenosphere4. The Mohorovicic
Discontinuity Between crust and lithosphere5. The Crust Outermost
layer of Earth. Continental crusts thicker than oceanic crusts, and
often older because of the impermanence and subduction of oceanic
crust5.1 Oceanic Crust (Sima) Made of basalt, or sima (silica and
magnesium), so it is dense at 3gm/cm35.2 Continental Crust (Sial)
Granitic, or sial (silica and aluminium), less dense at
2.7g/cm3Theory of Continental Drift1. Essence of Theory All
continents were joined 225 million years ago as Pangaea, which
split into Laurasia and Gondwanaland, and further drifting resulted
in their present locations today2. Supporting Evidence2.1
Continental Refits Observation that the shorelines and continental
shelves of several continents fit each other, such as S America and
Africa2.2 Structural and Lithological Evidence2.2.1 Structural
Evidence Belts of structures such as fold mountains and shields
should be traceable from one edge of a continent to a previously
joined one Caledonian Mountains in Scotland and Scandinavia can be
linked to the Appalachians in the United States2.2.2 Lithological
Evidence Sequence of rock types, or stratigraphy, there is a high
correlation of rock types during the time when continents were
supposedly joined2.3 Palaeomagnetic Evidence2.3.1 Magnetic Field
and Rock Magnetism A rock gains its magnetism when it is iron rich
and cools beyond Curie temperature (400-600C), aligning with the
prevailing magnetic field If age of rock is known, rock magnetism
can determine the position of magnetic poles at time of formation
of rock2.3.2 Polar Wandering Curve Collection of rock samples of
varying ages, can determine location of poles at different times.
If positions for North pole are plotted through time for a
continent, a polar wandering curve is derived These show that the
poles appear to have moved greatly over time, but it is known to be
rather improbable. Furthermore, each continent has its own curve
Either each continent has its own poles, or the continents have
moved relative to each other On a refit map, the poles all fall
within the range of the actual poles2.4 Palaeoclimatic
Evidence2.4.1 Glaciation of the Southern Continents Tillites and
striae are present on Southern continents, which are now close to
the equator, thus the climate would not be suitable for the
formation of such features Also, glaciers moved inland from the
ocean in Africa, S America and Australia, which is impossible since
glaciers move towards the ocean, unless there was land there
previously2.4.2 Glaciation in Africa and South America Extensive
glacier erosion in Africa and tillite deposition in South America
can be explained if they were connected previously2.5
Palaeontological Evidence Fossil evidence fossils of certain
ancient animals and plants are widespread and found on many
continents, which would indicate that they used to be joined3.
Limitation of Theory The mechanism for movement was unknown, but is
now proposed to be the theory of Plate TectonicsTheory of Plate
Tectonics1. Seafloor Spreading1.1 The Sea-floor Spreading
Hypothesis Discovery of mid-ocean ridges and rift valleys and
splitting due to tension. Also, ocean basins were found to be
relatively young Mid-ocean ridges were the locations for generation
of new crust due to cooling magma forming new crust where it
diverged1.2 Supporting Evidence1.2.1 Rock Magnetism The earths
magnetic field frequently reverses its polarity, so Vine and
Matthews suggested that fossil magnetism at such rift valleys will
have alternating bands of normal and reversed polarity symmetrical
on both sides of the rift Confirmed by magnetic survey of Reykjanes
Ridge and other mid-ocean ridges1.2.2 Geothermal Heat Flow
Generated by Earths interior, measured by thermistor probe Over
mid-ocean ridges, temperature may be several times higher than
normal, which may be from mantle injection1.2.3 Seismic Activity
Distribution Mid-ocean ridges are centres of activity, key areas of
volcanoes and earthquakes1.2.4 Dating of Volcanic Activity In
Iceland, most recent volcanic activity occurs in a band down the
centre, with older volcanoes moving east and west North Atlantic,
farther from ridge are older islands, which can be explained by
sea-floor spreading1.2.5 Pattern of Sedimentation Moving away from
ridge, one should find older sediment on older crust Deep Sea
Drilling project produced evidence regarding sedimentation
pattern2. Subduction2.1 The Subduction Hypothesis If sea-floor
spreading is accepted, subduction accounts for the Earths volume
staying constant, since crust has to be remelted somewhere 2.2
Supporting Evidence2.2.1 Seismic Activity Distribution Most intense
seismic activities coincide with ocean trenches2.2.2 Distribution
Pattern of Earthquake Foci Benioffs examination of the Kurile
Trench shows that earthquake foci get deeper further from the
trench and towards the cordillera of island arcs Termed the Benioff
Zone, about 45 degree inclination. Line of disturbance caused by
passage of oceanic plate as it was subducted2.2.3 Geothermal Heat
Flow Geothermal heat is cooler over ocean trenches, indicating cold
crust descending and cooling the mantle3. Mantle Convection
Currents The earths plates move around the surface of the earth via
convection. New crust generated by upwelling magma at mid-ocean
ridges, plates move away, carrying continents, and at ocean
trenches they are re-absorbed into the mantle Decoupling of the
lithosphere and asthenosphere Source of tectonic movement is the
heat generated by residual cooling off of planet, and the decay of
radioactive materials in the core, releasing heat Rocks nearer to
source are heated and become less dense and more buoyant than
surrounding rock, rising to base of lithosphere, moving laterally
and releasing heat, and then sinking to remix. This cycle maintains
the convective motion4. Limitations of the Theory Paradoxes: the
possibility of an expanding EarthGlobal Structural Landforms1.
Divergent/Constructive Plate Boundaries Zones of tension where
plates split and are pulled apart, and new crust is formed Either 2
convective flows are dragging plates apart, or mantle plumes or hot
spots cause tensional stress, where doming and three-armed rifting
occurs1.1 Rift Valleys Hot rising plume causes crustal stretching
and formation of tensional cracks. Plates move away from upwelling,
broken slabs are displaced down, creating downfaulted valleys
called rifts or rift valleys1.1.1 Features of Rift Valleys Large
tracts of land may be broken up, and vertical displacement can
produce horsts and graben Horsts are slabs of crust left
upstanding, and graben are crust downthrown by rifting1.1.2 The
East African Rift Valley Extends from Jordan to Mozambique, 5500km.
In central part, divides into two branches, Albertine and Gregory
rifts The Kenyan rift valley exemplifies main features of rift
faulting Simplest faulting results when two parallel faults allow
valley floor to sink between inward-facing scarps, producing bold
and high fault scarps at 600m or more More commonly, a number a
faults result in step faulting, and smaller faults result in grid
faulting Volcanoes also occur in rift valley due to crustal
weaknesses, such as Longonot, Kilimanjaro Lakes also occur where
rifting goes below the water table, such as Naivasha and Malawi.
Soda lakes as a result of sodium carbonate from magma and volcanoes
also occur, like Magadi and Natron1.1.3 Merits of the Concept of
Three Armed Rifting Tension caused by mantle plume explains plan of
rift, which is three armed, like the Rhine Rift Valley and the Red
Sea Rift system, who both have failed arms in the Hess arm and the
Abyssinian Rift. Also, the uplift and tilt of horsts and graben is
explained by mantle plumes but not simple tension1.2 Mid Ocean
Ridges1.2.1 Features of Mid-ocean Ridges Further spreading will
cause rift valleys to lengthen and deepen into ocean Thousands of
km long, hundreds of km wide, about 0.6-3km above seafloor Hot
mantle decreases density due to thermal expansion, causing rocks
near ridge to elevate. As they move away, the cool and subside due
to density Central rift runs down middle of most ridges like in Red
Sea, where temperature is higher and pillow like appearance of lava
due to rapid cooling underwater Great transform faults, resulting
is staggered path1.2.2 The Mid-Atlantic Ridge Great submarine
mountain chain1.2.3 Volcanic Islands Atlantic islands located close
to mid ocean ridges where is reaches surface of the sea, like the
Azores, Ascension Island and St Helena Majorly, Iceland, a
tholeiitic basalt plateau. A rift valley, the Central Icelandic
Depression, lies down centre of island, coinciding with recent
volcanic activity Iceland grows outward from centre, so rocks get
older further from fissure2. Convergent/ Destructive Plate
Boundaries Main stresses which occur are compressional. Depends on
the type of crust involved Oceanic-oceanic results in the denser
plate being subducted Continental-oceanic results in the oceanic
plate being subducted Continental-continental results in folding
since neither is dense enough to subduct much2.1 Ocean Trenches
Long narrow troughs in the ocean bed marking zones of subduction,
Mariana Trench is deepest at 11022m deep Found where trench fringes
a continent due to continental-oceanic collision, or in the ocean
floor as a result of oceanic-oceanic collision. The former has high
incidence of active volcanoes, and the latter has volcanic island
arcs2.2 Continental Volcanic Arcs Orogenesis occurs when sediments
along coasts are compressed by folding and faulting to form
mountain chains such as Andes, Alps and Himalayas
Continental-oceanic, continental volcanic arcs may be formed
Oceanic crust is bent and subducted, leading to partial melting of
the water-rich oceanic crust, magma formed less dense and slowly
rises, which is usually andesitic or granitic in nature, cooling
and crystallizing greatly underground to give batholiths Magma may
migrate to surface, causing volcanic eruptions. When volcanoes have
been eroded, the batholiths are exposed and observable Faults occur
in shallow zone of mountain, and deeper underground intense
metamorphism of rocks occur2.3 Island Arcs May be produced by an
oceanic-oceanic collision Formed by partial melting of plate and
lithosphere along the Benioff Zone Lava ascends to form arc of
volcanic islands, such as Japanese islands and Aleutians Lavas are
dominantly andesitic, which have 15% more silica and 3 times
potassium oxide by weight than ordinary basalt Composition of
andesites vary in proportion to depth of Benioff Zone, with more
andesite the deeper it is Heat produced for melting is caused by
friction between the two plates2.4 Fold Mountains
Continental-continental collision causes crust to be fused together
because neither is dense enough to sink and subduct They are pushed
up to form mountain ranges such as the Alps and Appalachians
Intense folding, faulting and buckling up of material. Deeper
buried rocks maybe more plastic due to higher temperatures, and
thus only fold, not fracture3. Transform Plate Boundaries Zones of
shearing where plates slide past each other at transform or
strike-slip faults Limited construction and destruction Zones of
intensely shattered rock, forming narrow valleys on land and ridges
on the sea floor3.1 The San Andreas Fault Major branches include
Hayward and Calaveras faults Great length and complexity, thus
named a fault system Offset stream channels and elongated ponds
mark the fault and its movement Responsible for earthquakes along
the fault, as segments either slip regularly or store energy for
years where rocks are more elastic, generating earthquakes of
varying intensities4. Hot Spots Intraplate activity and large scale
landforms are explained by mantle plumes instead of plate tectonics
Regions where flow of geothermal heat is higher than average,
commonly sites of volcanism and the lava is rich in alkali (Group
I) metals They remain relatively stationary4.1 The Hawaiian Chain
of Islands A stationary hot spot and a moving seafloor, a volcano
can only remain in contact with the hot spot for about a million
years, after that the volcano will become inactive The Hawaiian
islands provide evidence volcanoes increase with age away from
Hawaii4.2 Other Hot Spot Activities Possibly in other areas like
the Mid-Atlantic Ridge or Yellowstone National Park Exact role in
plate tectonics is unclearSeismic Activities1. Causes and
Characteristics of Earthquakes 95% of earthquakes are interplate at
plate boundaries. Intraplate earthquakes are less common1.1
Deformation and Fracture of Rocks At the outermost layer of crust,
rocks are strong but brittle. When plates move, compression,
tension or shear of rocks build up pressure, resulting in
concentrated releases of energy, forming faults. May come in a
single shock or series of shocks Friction at plate boundaries build
stresses and strain, bending and deforming rocks. When limits of
deformation are exceeded, the rocks rebound, releasing energy,
producing earthquakes1.2 Earthquakes and Faulting Fracture in a
rock along which movement occurs is a fault. Movement along a fault
can be vertical or horizontal Rocks above a fault is the hanging
wall, rocks below is the foot wall Dip-slip faults in a normal
fault, hanging wall moves down. In a reverse fault, the hanging
wall moves up. The break in slope is a fault scarp. Normal is often
divergent, reverse often convergent Strike-slip faults left-slip
and right-slip, depending on direction. Most fault systems appear
as a combination of fault movements1.3 Focus and Epicentre Focus is
the point where an earthquake releases the elastic strain by
fracturing Can be shallow (70km), intermediate (70-300km) or deep
(300-700km) At divergent and transform, normally shallow focus, but
at convergent normally at the Benioff Zone Epicentre is the point
on crust directly above focus1.4 Seismic Waves Seismic waves spread
out from focus in all directions Body waves radiate in all
directions, surface waves are vibrations trapped near the surface
of the earth Primary pressure waves are longitudinal body waves
travelling by compression and expansion, while secondary shear
waves cause ground to vibrate perpendicular up and down. Primary
waves are faster and thus felt first, but secondary waves are more
destructive because buildings can withstand little horizontal
stress. Love waves are surface waves that cause horizontal
shearing, and Rayleigh waves, or ground roll, travel like ripples.
Love waves are generally faster, but Rayleigh more destructive
Surface waves are slower but more destructive than body waves
because they induce resonance in buildings1.5 Global Patterns of
Earths Seismicity1.5.1 Divergent Boundaries Narrow belts of
shallow-focus earthquakes coinciding with crests of oceanic ridges
at divergent boundaries less than 70km deep, small magnitude Crests
of oceanic ridges normal faulting, basaltic magma intrusions. Also,
vertical faulting, associated with ridge topography Shallow focus
at transform faults no volcanic activity1.5.2 Convergent Boundaries
Widespread and intense subduction zones, inclined at moderate to
steep angles, focuses as deep as 700km can be brittle at that
depth1.5.3 Intraplate Seismicity Not associated with known faults
or historical activity result from crustal stresses e.g. uplifting
of mountains like Himalayas Built up stress by plate moving
vertically while moving over asthenosphere2. Earthquake Magnitude
and Intensity2.1 Intensity and the Mercalli Scale Intensity is the
strength of shaking by an earthquake at a location, determined by
effects on people, structures and the environment The Modified
Mercalli Scale measures damage and human perception of an
earthquake by using descriptors It is not a measure of an
earthquakes size or energy, but rather its perceptible effects and
damages, thus useful for comparing effects Dependent on variations
in population density, building materials and methods and distance
from epicenter Useful in ranking earthquakes before technology was
available to measure them, as well as creating isoseismal graphs2.2
Magnitude and the Richter Scale Magnitude refers to the absolute
size of and amount of energy released by the earthquake, using
amplitudes of the seismic waves The Richter Scale is used to
measure magnitude3. Effects of Earthquakes3.1 Ground Motion Passage
of seismic wave through surface rock layers and regolith damage and
destroy buildings3.2 Tsunamis Series of large waves created by
abrupt displacement of water. Long period, crests are very high and
troughs very low. Troughs arrive at shore first, causing sea level
to fall and exposing the seabed Generated when sea floor abruptly
deforms and displaces the overlying water, especially submarine
earthquakes at subduction boundaries Boxing Day Indian Ocean
Tsunami in 2004 230000 in 14 countries died3.3 Landslides and
Liquefaction At convergent plate boundaries, steep slopes are prone
to landslides when shaken. Also, soil layers may liquefy, causing
mudflows. Liquefaction is particularly dangerous as soil in a
suspended state cannot bear any load, causing structures built on
it to collapse Landslides in Gansu Province, December 16, 1920,
killed 180000 1964 Niigata, El Salvadors land is tephra,
consolidated pyroclasts3.4 Fires Fires caused due to fracturing of
gas pipes, ruins of wooden and other flammable materials.
Exacerbated due to blocked streets and damage water supplies Tokyo
1923, lunchtime. Wooden fuel, typhoon created fire storms, water
main were broken San Francisco, 1906 700 deaths and $400 million in
property damage due to fires3.5 Factors Affecting Damage Natural
phenomena only become natural hazards when humans are affected
Several factors: population density, prediction abilities, geology
and topography, magnitude, preparation, governance and economic
ability, building design, time of earthquake4. Managing
Earthquakes4.1 Earthquake Forecasting and Prediction4.1.1
Earthquake Forecasting Identifies areas prone to earthquakes and
man-made structures vulnerable to damage from earthquake shaking.
Can be used to develop building codes and response plans Less
precise, long term, based on seismic gaps4.1.2 Earthquake
Prediction Calculating likelihood of an earthquake of a certain
magnitude in a given timeframe. Scientists monitor earthquake
precursors. Animal behaviour: Suspicious animal behaviour before
onset of earthquakes 1975 EQ in Haicheng. Animals 7.5 times more
likely to go missing a week before an earthquake 75% accuracy
Tiltmeters: earthquakes are accompanied by tiny tilts of the earths
surface, so these are used to measure variations and changes in
slope Seismic monitoring: use of seismographs e.g. Global Seismic
Network. Singapores Meteorological Services Division has 7 seismic
stations Recurrence Intervals: Average times between ruptures are
recurrence intervals, used to calculate probability. Seismic gaps
are areas which are likely to break badly in future e.g. 1975
research in Los Angeles eight major earthquakes since 565, spaced
at intervals of 55 and 275 years Foreshocks: many large earthquakes
are preceded by foreshocks. Past data allows calculations whether
small foreshocks will result in a large mainshock later, such as
the San Andreas fault4.1.3 Problems Associated with Earthquake
Prediction There is currently no foolproof method Animal behaviour
failed to predict the 1976 Tangshan earthquake, no foreshocks nor
precursors Recurrence intervals and foreshocks are only averages,
not precise e.g. Parkfield California, predicted in 1993 but only
struck in 20044.2 Mitigating Earthquake Hazards4.2.1 Building
Design Isolated-base technology flexible support placed between
structure and foundation, counteracting movement of seismic waves
and preventing resonance Work well in new buildings, but most
structures in earthquake prone zones were built before such
techniques were developed4.2.2 Hazard Mapping Show hazards from
earthquakes that experts agree could occur Useful in identifying
areas prone to liquefaction, landslides and ground shaking, in
order to set insurance, develop safety codes and identify safe
locations4.2.3 Controlled Earthquakes Pumping water into ground
under high pressure to release pressure and act as lubricant old
oil wells in Colorado and South Africa However, the magnitude might
not be able to be controlled, and can result in more damage4.2.4
Evacuation Measures Earthquake drills educate population, properly
designed warning system, so evacuation is possible. Haicheng 1975,
buildings evacuated several hours before earthquake. Successful
because a variety of signals were monitored4.3 Earthquake Response
Response efforts occur in stages: search and rescue, immediate
relief such as medical attention, shelter and food, reconstruction,
recovery and long term development Immediate relief: food and
water, hygiene and disease, shelter, medical care, communication,
crime (looting) and psychological supportExtrusive Volcanism1.
Components of Volcanic Eruptions1.1 Lava Flows Magma is molten rock
beneath earths surface. Magma is less dense than surrounding rock,
moving towards surface, upon reaching is called lava1.1.1 Types of
Magma Three distinct types, depending on their silica content:
basaltic (50%), andesitic (60%) and rhyolitic (70%) Finer grained
rocks have lesser time available to crystallize because they cool
at the surface (basalt, andesite and rhyolite) Coarser grained
rocks cool underground and thus produce larger crystals (gabbro,
diorite and granite) Basalt, being fluid, limited time for
crystallization. Rhyolitic magma is more viscous, flows less
readily and has more time to crystallize. Thus basalt and granite
are more common than gabbro or rhyolite1.1.2 Types of Lava Less
fluid magma usually solidifies underground, intrusive volcanism
Fluid magma more likely to make way to surface to form lava flows,
such as basaltic magma forming pahoehoe and aa flows Underwater,
most are pillow lavas1.1.3 Pasty Lava High Viscosity Restricted to
continental edges and strings of islands Carribean, Japan Piles up
around vent as lava dome, made of rhyolite1.2 Pyroclasts Pulverised
rock and lava, deposit of pyroclasts is tephra1.2.1 Types of
Pyroclasts Ash (64mm) Ash falls occur when ash ejected into
atmosphere settles over wide area. Ash flow are clouds of ash and
gas flowing along land surface Bombs are twisted, globular shapes
which cooled while being ejected, blocks are angular pieces of rock
ripped from volcano during eruption Sorting of material heavier
material falls closer to volcano1.2.2 The Generation of
Lahars/Mudflows Large composite volcanoes can form mudflows or
lahars When ash and debris become saturated with water, such as
snow or ice melt due to eruption (Mount St. Helens in May 1980,
30km/h), lahars can form destroying homes and infrastructure up to
100km/h1.3 Gases1.3.1 Composition of Volcanic Gases Largely water
vapour, then carbon dioxide, sulphur and nitrogen1.3.2 The
Generation of Nuee Ardente/Pyroclastic Flows Formed when hot,
incandescent gases combine with rocks and ash Due to the hot gases,
they travel extremely fast due to being almost frictionless, up to
200km/h, found 100km from source2. Types of Volcanic Eruptions Can
be mild or violent, depending on the nature of the magma2.1 Magma
and Viscosity Viscosity depends on silica content of magma.
Rhyolitic magma is thus viscous and forms short, thick flows but
basalt is more fluid and travels longer up to 150km Higher
temperature = lower viscosity and longer flows The greater the gas
content, the more fluid magma is2.2 Magma and Nature of Eruption
Depends on viscosity and gas content of magma At higher pressure,
more gas can be dissolved in magma. As magma rises up, pressure is
largely reduced, allowing gases to be released These gases form
bubbles. Fluid magma allows gas to escape readily, but viscous
magma impedes the escape of gas. Thus, fluid magma eruptions are
less violent, but viscous magma collect gases as bubbles which
increase in pressure, resulting in more explosive ejections
Furthermore, viscous magma is likely to clog up vents, such as in
lava domes, building up even more pressure2.3 Types of Eruption
Basaltic lava tends to form shield volcanoes and runny lava.
Eruptions such as Icelandic (basalt plateau), Hawaiian (shield,
runny flows) and Strombolian (explosive, frequent gas explosions of
runny lava) are attributed to basaltic lava. Rhyolitic magma tends
to form composite volcanoes with viscous lava. Eruptions include
Vulcanian (violent, viscous lava with many pyroclasts), Vesuvian
(more violent, powerful blasts of gas) and Plinian (most explosive,
greating great clouds of gas and debris and pyroclastic flows).3.
Features of Extrusive Volcanism3.1 Shield Volcanoes Basaltic lava
form broad, domed structures called shield volcanoes Average
surface slope of a few degrees, normally less than 10, but wide
base over 100km in diameter Small percentage of pyroclastic
material, largely successive layers of basaltic lava, which form
thin sheets over large distances, such as Mauna Loa and Mauna Kea
Convex slope, since it flows readily at summit but as it cools,
becomes more viscous and so slope angle increases near the base3.2
Composite Volcanoes Stratovolcanoes are formed by relatively
viscous andesitic or rhyolitic magmas Large and symmetrical,
concave slope formed by alternate layers of lava and tephra Sorting
of pyroclastic material with more bombs and blocks near summit,
gradually sorting to ashes Steep summits and flatter bases due to
this sorting, concave profile May form lava domes, plugging the
central vent Mount Mayon and Fujiyama, Vesuvius, Pompeii3.3 Cinder
Cones Volcanic peaks consisting of pyroclastic cinders Pyroclasts
accumulate around vents after being ejected by eruptions Form
small, steep-sided cones of about 33 degrees depending on angle of
repose of materials Parasitic cones on or near larger volcanoes,
often in groups. Many form within calderas of larger volcanoes,
final stage of activity Wizard Island in Crater Lake, Oregon,
formed after Mount Mazamas summit collapse to form caldera3.4
Basalt Plateau Largest amount of volcanic material is exuded from
fissures in the earth Very fluid basaltic lava, successive flows
building lava plains (Deccan Plateau). Can flow up to 150km from
source Basalts are resistant to erosion while surrounding rock may
not, and thus can form plateau basalts3.5 Calderas Circular
depressions in volcano summit, normally composite Formed when
summit collapses into empty magma chamber below after an eruption
(Crater Lake, Oregon)4. Volcanic Hazards Lava flows are a hazard to
property, confined to the slopes only. At frequently active
volcanoes, lava flows are generally well understood by residents
Ash fall, extending 1000km away, can bringing total darkness,
suffocating animals, smothering plant life and preventing machinery
use Pyroclastic flows and mudflows, greatest hazard, developing
rapidly, up to 200km/h5. Volcanic Hazard Management5.1 Prediction
of Volcanic Eruptions First outburst of activity can be predicted,
mostly fluid eruptions impossible to predict subsequent direction
or intensity Kilauea, Hawaii, Nov 1959 forecasted Viscous magma
still cannot be predicted Nevado del Ruiz, Columbia, Nov 1985,
killed 20000 in heated mudflows5.1.1 Land Deformation Measurement
Ground deformations around volcanoes due to underground movements
of magma. Mt St Helens tiltmeters 0,5-1.5m a day preceding eruption
Tiltmeters successfully predicted Kilauea5.1.2 Seismic Activity
Monitoring Magmas can apply stress to rocks, fracturing them. Such
earthquakes occur at depths of less than 10km, low magnitude
Volcanic tremors long period vibrations indicating resonance
(predicted Mt Redoubt in Alaska on 2 Jan 1990), and regular
vibrations indicating origin and nature of magma Not all activity
associated with volcanism can indicate cessation of activity5.1.3
Geomagnetic and Geoelectric Effects Volcanoes contain ferromagnetic
materials, changing local magnetic field. Magnetism reduces with
temp, decreasing field may indicate rising magma. Field may
increase due to piezomagnetism as pressure and stress exerted
Resistivity of subsurface layers of volcano. Telluric currents may
indicate natural conduits for magma movement5.1.4 Gases Analysis
Analysing gaseous constituents restricted by need to analyse
instantly5.2 Volcanic Hazard Mitigation Look at measurement of
slopes to indicate buildup of magma, seismometers and seismographs
(long period event, resonance, compression, Bernard Chouet),
analysis of gas activity and content (Williams, fumaroles, but may
not be accurate due to clogging of vents) Hazard Management:
Evacuation (Mount Pinatubo), planning beforehand, diversion of lava
flows and mudflows (Sakurajimas drainage channels to divert lahars
but cost a lot of money, Icelands cooling of lava flow to solidify,
requires a lot of water)5.3 Response to Volcanic Eruptions Lava
flows are likely to follow existing valleys, can be diverted or
cooled Eruptions cannot be contained or directed evacuation
considered. Need adequate morgue facilities, local emergency
facilities for burns or lungs damaged by hot ash, apparatus for
emergency workers and civilians like face masks Local guidelines
for heavy ash fall following Mount St Helens in 1980. Sweep ash
from roofs, authorities equipped to measure levels of toxic gases,
analyse particle size. Alternative sources of drinking water
located. Transport may not work due to ash fall can also interfere
with radio and TV transmissions.Classification of Rock TypesRock
cycle movement of material through space and time as it is
transferred and transformed from one type of rock in one location
to other rock types and places.1. Igneous Rocks Solidification of
molten magma or lava. Most common rock type. Crystal of minerals,
often silicates. Crystallisation of these materials causing rock to
solidify Nature of rock dependent on mineral content and rate of
crystallisation1.1 Intrusive vs. Extrusive Igneous Rocks Intrusive
rocks were formed under the surface, and mostly have large crystals
(phaneritic) due to slow cooling and crystallization underground
(thousands to millions of years). Granite. Coarse texture.
Extrusive were formed above surface from cooled lava. Microscopic
crystals (aphanitic) due to quick cooling. Basalt. Fine texture.2.
Sedimentary Rocks Distinguished by strata present in rocks,
separated by bedding planes.2.1 Types of Sedimentary Rocks2.1.1
Sedimentary Rocks of Mechanical Origin Rocks where the constituent
material has been derived from elsewhere and transported as solid
particles to the ultimate site of deposition Detrital/clastic rocks
Loose clasts or organic material undergo diagenesis, causing clasts
to bind together, and in the process of lithification turn into
rocks Diagenetic processes occur by compaction (buried under great
pressure) and cementation (minerals crystallizing in pore spaces,
cementing clasts together) Transporting agents of wind and water
tend to sort particles by size, so size is a subdivision for
clastic rocks Small (2mm, conglomerates, breccias)2.1.2 Sedimentary
Rocks of Chemical Origin Precipitation from a solution of dissolved
salts, of chemical origin Formed close to site of deposition and
mixed with detrital sediments E.g. evaporates formed by evaporation
of salts in shallow seas (anhydrite, gypsum, halite) and
lithified2.1.3 Sedimentary Rocks of Organic Origin Formed by
accumulation of organic matter remains, such as fossils Limestone
from remains of sea creatures subjected to diagenetic processes,
calcium carbonate and calcareous rocks3. Metamorphic Rocks Changing
mineralogical composition or physical structure of rock via high
pressure and temperature Uses tectonic forces, such as plate
movement, to compress and heat rocks. Happens in the solid state3.1
Contact vs. Regional Metamorphism Contact metamorphism only
involves extreme heat, not pressure. Grade of metamorphism depends
on distance from heat source. Chemical content does not change, but
can be altered, such as water composition or recrystallisation e.g.
limestone to marble Regional metamorphism involves both temperature
and pressure, and often occur at convergent plate boundaries
Gradual increases in heat and pressure can lead to metamorphic
gradation Recrystallisation perpendicular to compressional force
can lead to layered appearance, or foliated textureWeatheringThe in
situ breakdown of rock by natural agents. Response by rocks at
surface to low temperatures, pressures, and the presence of air and
water. Denudation of the landscape.1. Geometry of Rock Breakup1.1
Block Disintegration Breaking down of rocks into large blocks,
common in rocks with well developed bedding planes or joints
intersecting at right angles Concentrated weathering at secondary
joints leads to large, angular boulders, such as limestone Commonly
the first stage, followed by other modes of weathering1.2 Granular
Disintegration Rock is broken down into numerous smaller fragments
into grains, common in crystalline rocks like granite and
sedimentary rocks like sandstone Grains separated along the
original crystal or grain boundaries1.3 Exfoliation Detachment of
concentric slabs from the rock mass, leaving behind smaller
spheroidal bodies. Also known as spalling. Thickness depends on
process insolation weathering leads to smaller layers, pressure
release leads to thicker layers1.4 Frost Shattering Disintegration
of rock along new surfaces of breakage to produce highly angular
fragments with sharp edges. Irregular because they do not break
along defined planes of weaknesses1.5 Spheroidal Weathering Rock
rounded from an initial block shape, as a result of uneven
weathering on the rock surface, with edges and corners being eroded
more rapidly2. The Processes of Weathering2.1 Physical Weathering
Uses mechanical force to break up the rock, often depending on
temperature fluctuations to produce stresses, thus superficial and
occurs only near surface2.1.1 Pressure Release / Dilatation Breaks
down rock through exerting physical stress. Can lead to sheet
joints or exfoliation Regolith above rock removed by erosion,
resulting in lesser pressure and expansion of rock, potentially
fracturing it Can result in sheet joints, aiding the weathering
process In extreme situations, exfoliation occurs forming
exfoliation domes, followed by block disintegration into smaller
rocks Rocks formed at great depths are particularly susceptible Can
occur on a micro scale granular disintegration2.1.2 Freeze-Thaw
Weathering / Frost Shattering Water from precipitation enters
joints and beddings in rocks. Upon freezing, expands about 9%,
exerting pressure Closed system generates pressure which can easily
exceed rock tensile strength Repeated stress with each cycle of
thawing and freezing can lead to cryofracturing over time Can occur
on a smaller, granular scale when water penetrates pore spaces and
freezes into ice crystals, such as in chalk Requires oscillation
about freezing point, such as a wide diurnal temperature range in
Alpine environments Moisture content of rock is important if not
saturated, freeze-thaw has lesser effect since the pores can absorb
water2.1.3 Insolation Weathering Disintegration of rocks due to
expansion and contraction through heating and cooling, effective in
large diurnal temperature range (deserts) Rock is poor conductor of
heat, so heating is confined to surface. Sharp thermal gradient
develops, with surface expanding more than within, causing stresses
to develop If stresses exceed strength, sheet joints form leading
to exfoliation of thin layers (since limited to surface) Can result
in granular levels if grains are made of different colours, darker
colours expand more, such as darker mica than sandstone within
granite Efficacy may not be very significant since exfoliation is
on a very small scale. Also, Blackwelder and Griggs experiment
showed that water is more significant (no change even with 100C of
changes for 244 years) However, laboratory results do not reflect
real conditions, such as stress from rocks surrounding, or not
really 244 years of weathering experienced2.1.4 Salt Weathering
Physical weathering, although chemical reaction is involved When
water within rock is saturated with salt, salt will crystallize and
exert pressure on rock This process, repeated over time with salt
crystals growing, can split rocks Often cause honeycombing patterns
Important in arid environments, as groundwater is brought to
surface by capillary action, evaporating and leaving salt behind
Salt inflicts thermal expansion or by wetting and crystallizing
Coastal deserts are susceptible due to availability of salt water
and high temperatures2.2 Chemical Weathering Breakdown of rocks by
altering chemical composition of minerals by water, oxygen, acids.
Can occur at great depths due to infiltration and percolation of
water Thus dependent on availability of water. Produces fine
grained regolith2.2.1 Solution By soil moisture and groundwater.
Quartz can dissolve in water to give silica in solution2.2.2
Carbonation Weakened by carbon dioxide dissolved in rainwater.
Calcite (limestone) reacts with carbonic acid to form calcium and
calcium bicarbonate, which can dissolve in solution with water2.2.3
Hydration Affects rocks which can take up water, absorbing water
into minerals. Can cause expansion of a mineral. Iron oxide is
hydrated by water to give hydrated iron oxide2.2.4 Hydrolysis
Reaction with pure water. Feldspar reacts with water to give
kaolinite as an eventual end product2.2.5 Oxidation Reaction with
oxygen from soil or atmosphere. Rusting of iron with oxygen to give
iron oxide2.3 Biological Weathering Any weathering carried out by
living organisms or their by-products Biomechanical weathering:
carried out by plant roots prising and breaking rocks apart, common
in urban areas. Opens passageways to allow for water and other
forms of weathering Biochemical weathering: by plants, organic
matter creating organic acids to carry out chemical weathering and
chelation2.4 Classification of Weathering Most rock disintegration
is affected by complex interplay of all three processes, difficult
to truly distinguish them Operate in conjunction to assist each
other3. Climate and Weathering Determinants of the rate and type of
weathering: rock characteristics, climate, geological structure,
vegetation and soil cover, level of water table, topography of
local areas, mans activities. Climate is one of the most
important.3.1 Weathering in Different Climatic Zones Much
weathering depends on water and temperature Differences in
precipitation and temperature thus has effects on weathering in the
different morphoclimatic regions3.1.1 Weathering in the Humid
Tropical Regions High temperature results in faster chemical
weathering (vant Hoff: speed of reaction increases 2.5 times with
rise of 10C) High precipitation also results in more chemical
weathering (solution, hydration, hydrolysis etc.) Dense vegetation
and organic matter helps chemical weathering, almost 4 times as
rapid in humid tropics than temperate regions Physical weathering
limited due to masking effect of thick regolith covering surface
Uniformly high temperature does not support it either Results in
thick layer of regolith due to deep chemical reaction. Regolith
removal is slow due to vegetation, so there is a build-up of
regolith3.1.2 Weathering in the Seasonally Humid Tropical Regions
Due to heavy seasonal rainfall, chemical weathering is also rapid,
but not as much as the tropics Less dense vegetation also means
easier removal of regolith and thus thinner layer, which can expose
the basal surface of weathering3.1.3 Weathering in the Hot Arid
Environment Physical weathering dominant due to high range of
diurnal temperature, especially insolation and salt weathering Only
some chemical weathering, due to sources of moisture such as
infrequent rains, dew and fog In general, low rates of weathering
and largely superficial, so regolith is very shallow. Furthermore,
no cover or organic material means it is removed without time to
accumulate3.1.4 Weathering in the Temperate Regions Chemical
weathering is only moderately active due to moderate temperatures
and rainfall Physical weathering can play an important role through
freeze-thaw weathering in winter, but it rarely goes to any great
depth3.1.5 Weathering in the Glacial Regions Abundant snowfall and
low temperatures oscillating around 0C means freeze-thaw weathering
is dominant in glacial regions In summer, rain falling can dissolve
carbon dioxide and oxygen to form weak acids3.2 Peltiers Diagrams
Shows relationship between climate and both types of weathering3.3
Strakhovs Diagram Precipitation and average temperatures
correlation with basal surface of weathering (divides weathered
from unweathered rock)4. Rock Characteristics and Weathering While
on macro scale, climate differences affect weathering, on a local
scale, weathering is more influenced by rock type4.1 Rock Strength
and Hardness Harder rocks are more resistant to physical
weathering, depending on minerals making up the rock and strength
of cementation between minerals Older rocks are normally harder
since they undergo more cementation and compression4.2 Chemical
Composition Affects resistance to chemical weathering, determines
if minerals are susceptible or not Limestone prone to carbonation
due to being mainly calcium carbonate Sedimentary rocks may have
resistant clasts, but not resistant cement May affect physical
weathering, such as different coloured minerals affecting expansion
and contraction, leading to granular disintegration 4.3 Rock
Texture Coarse or fine grained. Coarse grained rocks allow for
chemical weathering to reduce coherence, and large pore spaces
allow for high primary permeability, trapping water for chemical
and frost weathering Numerous boundaries between fine grains
increases surface area for chemical agents, speeding up chemical
process4.4 Rock Structure Joints and Beddings Selective weathering
along lines of weaknesses in rocks, high secondary permeability
allowing water to easily penetrate, increasing surface area for
both chemical and physical weathering5. Other Factors Affecting
Weathering Topography affects weathering, as steep slopes aid to
remove regolith Altitude affects weathering above the tree line,
temperature is suitable for freeze-thaw, but too high is not
because of lack of oscillation around 0 Aspect affects weathering,
like whether it is on north-facing or south-facing sides6.
Landforms Associated with Weathering6.1 Scree/Talus Slopes and
Block Fields Commonly associated with freeze thaw weathering.
Screes or talus are made of angular fragments of rock accumulated
at the bottom of steep slopes Can form blockfields on gentler
slopes6.2 Exfoliation Domes Formed by exfoliation of massive rock,
like granite, due to pressure release and unloading, sheeting6.3
Limestone Pavements Formation by chemical weathering along joints.
Limestone surface exposed to reveal joints, which are enlarged via
carbonation, forming clints and grykesMass Movement1. Initiation of
Mass Movements Mass movement is downslope movement of weathered
materials in response to gravity Dependent on shear strength and
shear stress of slope1.1 Shear Strength vs. Shear Stress Depends on
instability on hill slope when equilibrium has been disturbed
Safety factor is measured by ratio of resistance against movement
to force trying to enact movement (shear strength against shear
stress) Speed of movement depends on how much stress exceeds
strength1.2 Factors Affecting Mass Movement1.2.1 Gravity, Slope
Angle and Shear Stress Gravity induces movement downslope,
depending on angle of slope and weight of regolith Angle of repose
is when stress = strength, when friction balances gravity Regolith
is pulled down faster on steeper slopes1.2.2 Nature of Slope and
Shear Strength Sand and gravel slopes generate friction between
particles Silt and clay slopes depend on cohesion and water Rock
slopes depend on internal strength of solidification and
crystallization Bedding planes or joints of weakness might focus
failure on these areas1.2.3 Role of Water Water increases stress
while decreasing strength Rainfall can saturate soil, reducing
cohesion due to pore pressure between pore spaces. It also
lubricates, reducing friction. Also increases weight A bit of water
is still necessary for maintaining cohesion in clays1.2.4 Role of
Triggering Mechanisms Earthquakes can trigger mass movements by
vibrating and shaking regolith materials loose, reducing friction
Undercutting of slopes can also trigger2. Classification and Types
of Mass Movement2.1 Carson and Kirbys Classification of Mass
Movement Plots mass movements along a continuum, flexible
classification according to speed and moisture content2.2 Mass
Movement Processes2.2.1 Soil Creep Slow but widespread and highly
effective. More material is moved by creep than any other means.
Creep is faster in dryer, colder areas (10mm/year) Gravity creep
and soil heave. Gravity creep occurs when soil particles are
disturbed by flora and fauna, which then move downslope because of
gravity. Chain movement of particles continues until initial
movement is absorbed Soil heave happens because of expansion and
contraction, due to heating and cooling, wetting and drying or
frost action. Expansion heaves at right angles to surface, but
contraction is affected by gravity to give a net downslope
migration2.2.2 Solifluction Common in periglacial areas.
Waterlogged soil slides slowly over the impermeable permafrost,
resulting in solifluction lobe2.2.3 Fall Occur on steep slopes
where angle of friction is greatly exceeded. Slope made of hard
rocks which are able to maintain high angles Weathering allows
detaching of rock to fall due to gravity. Falls until it reaches
its angle of repose2.2.4 Slide Sudden and rapid, occur at high
relief and unstable slopes. Triggering action is usually needed
Mass slides down a shear plane until it shatters at the bottom.
Slide planes can be lubricated or selectively weathered Landslides
occur in sands or clays, due to buildup of groundwater, increasing
stress while decreasing friction strength Common when weak layers
support heavier ones above2.2.5 Slump Occur in weaker rocks than
slides, have a rotational movement along a curved slip plane,
resulting in terraces and a flow at the bottom Occur where moisture
is concentrated at base of water soaked clay rich soil When the
lower toe becomes mobile due to water, after heavy rain, it flows
away, resulting in material slumping away from the top2.2.6 Flow
Soil moisture content is high, rapid form of movement. Flow is
greatest at surface and decreases to zero at the bottom Internal
deformation under its own weight, dependent on saturation of water,
like clay, so fine particles are prone to flows Earthflows are
linear movements of moist clay rich regolith. Slower than
landslides, a few feet/hour, day, or even month Mudflows are more
rapid and less viscous, occur in areas with sparse vegetation, and
is thus quickly saturated2.2.7 Others Debris and snow avalanches
are also possible3. Human Activities and Mass Movement3.1 Human
Induced Mass Movements3.1.1 Undercutting and Mass Movement
Undercutting a previously stable slope, such as building roadways
on mountainous terrain As a result, landslides are more common, and
slopes are more saturated 12 September 1995, Kulu, Himachal
Pradesh, India, landslide killed 65 people due to undercutting of
slope3.1.2 Construction and Mass Movement Clifftop buildings
increases the stress on slopes, increasing instability Holbeck Hall
Hotel in Scarborough, 5 June 1993, rainfall plus hotel caused the
ground to slump3.1.3 Deforestation Due to Population Pressure
Cities like Hong Kong and Rio de Janeiro expanding onto marginal
land to accommodate population pressure. New roads and buildings
built on deforested steep slopes, which reduces stability4.
Managing Hazards Associated with Slope Failure Worldwide,
landslides have caused average of 7500 deaths/year and US$20billion
per year from 1980-2000. Landslides increase as more people settle
in less suitable areas most deaths occur in LDCs. 4.1
Predicting/Preventing Slope Failures 4.1.1 Landslide Hazard Maps
Avoid building in places prone to landslides GIS can used to make
debris flow and landslide hazard maps, prescribing restrictions in
land use like road building, timber harvesting, housing
subdivisions4.1.2 Controlled Development Pre-construction
assessment: Study of area before construction, geologic feasibility
report. Modify landscape as little as possible Controlled
development: Controls on hillside development through zoning laws
(affluent countries: hillside properties for scenery, congested
cities: slums on hillside like favelas) Should not be any
construction steeper than 27 degrees4.1.3 Slope Monitoring
Monitoring: extensometers and tiltmeters to detect micromovement on
slopes Modelling: Computer modeling to simulate scenario of mass
movement, useful in land use planning, hazard planning and
evacuation plans4.2 Mitigating Slope Failures4.2.1 Improving
Drainage Drainage: Proper drainage required to prevent saturation
of soil and reduce water pressure, such as outlets and
culverts4.2.2 Improving Vegetation Cover Vegetation: Should be left
in natural state to enhance drainage and increase stability by
removing water through evapotranspiration. Can also stabilize
slopes.4.2.3 Construction of Retaining Structures Retaining
structure: Holds back earth and stabilizes soil and rock from
downslope movement, such as gabions and walls Debris catch or dam:
Structures used to catch falling material and trap flow debris,
such as wire netting, dams and barriers4.2.4 The Use of Weights For
slopes overloaded at the top, add load to the lower part of the
slide to resist movement pile heavy boulders on toe to increase
stability. Angle can be changed by removing slope top, adding
weight to base, remaking entire slope with lower angle.4.3
Responding to Slope Failures Search and rescue, provision of
medical care, food, shelter, water, long term recovery. Like
earthquakes and volcanoes.Limestone and the Karst Landscape1.
Limestone1.1 Formation of Limestone Calcite deposition in deep-sea
conditions, calcareous remains of plant and animals Skeletons
filled with mud and precipitates, diagenetic processes form
limestone1.2 Types of Limestone Importantly, carboniferous
limestone forms landforms, but not oolite1.3 Characteristics of
Limestone Carboniferous limestone and dolomite1.3.1 Chemical
Composition Limestone at least half the rock contains more than 50%
carbonate minerals, with calcite as most common, pure limestone is
at least 90% calcite Physically resistant to weathering, but
chemically unstable, carbonation Landform associated with limestone
is probably solutional and found in humid or temperate regions1.3.2
Structural Control Low primary permeability and high secondary
permeability Selective weathering at joints, not uniform
weathering, will occur. Carboniferous limestones secondary
permeability is much higher than oolite, explaining landform
formation in carboniferous and not oolite Older the rock, lower
primary and higher secondary, due to increased lithification with
age1.3.3 Weathered End Product Leaves behind little impurities
after weathering because most is removed in solution, but still
leaves behind insoluble calcite which will blanket the surface,
preventing further erosion Leaves behind little regolith, in
contrast with granite2. Karst Landforms2.1 Enclosed Depressions
Common in karst areas, enclosed basins where precipitation is
drained internally by subterranean conduits. Extent of depression
depends on rainfall, thus determining types of landforms in
temperate and humid2.1.1 Dolines Medium sized closed depressions
Percolating rainwater causes selective weathering at fissures and
bedding planes, especially where groups of fissures are Rate of
solution becomes greater due to increased surface area, void
created and subsides, producing depression Throughflow directed
towards base of hollow, enhancing solution and continuing
cycle2.1.2 Uvalas A combination of dolines into areas with
sub-basins and uneven floors, increasing size but decreasing number
of depressions2.1.3 Cenotes / Collapse Dolines Depressions with
circular, smooth-walled vertical shaft, develop where water filled
cave just below ground Fractured rock weakened by percolating
rainwater and upward solution of cave water, collapsing and
producing a shaft2.1.4 Cockpit Karsts Same as dolines, but
torrential nature of rainfall in humid tropics causes surface flow
and weathering via surface gullying along joints, causing elongated
depressions along joints which eventually interconnect, forming
deep irregular cockpits separated by cones2.1.5 Tower Karsts
Further weathering of cockpits until base level of erosion is
reached, clogging up the floor with impermeable calcite. Weathering
then forms the cones into tower karsts2.2 Karren Features
Microsolutional features which form on exposed limestone surfaces
Clints and grykes, limestone pavements, exposed plain of limestone
caused by glacial erosion. Blocks and grooves created by joints are
accentuated by chemical weathering Karren forms, such as
spitzkarren in tropical and Mediterranean areas where processes
have operated for a long time in high rainfall Grykes bounding
clints are widened and deepened by erosion2.3 Drainage
Features2.3.1 Karst Gorges Karst landscapes may contain major
rivers, due to being in early stages of karstification when
fissures are not yet developed enough to absorb rivers Valleys
eroded by streams are gorges, with vertical cliffs and scree slopes
Well-jointed limestone maintains verticality by falling when
weakened, no other mass movement results in no gentle sloping2.3.2
Swallow Holes, Dry Valleys and Blind Valleys Rivers flowing on
limestone will eventually create openings in rock bed due to
selective weathering, creating a swallow hole which leads into
subterranean drainage Downcutting of valley will stop downstream,
forming a dry valley and may create a cliff due to reversal of
gradient Upstream, vertical erosion continues, downcutting the
blind valley Successive sinks cause headward migration of stream
and developing new blind valleys Streams may eventually reemerge as
resurgent streams2.4 Caves Limestone caves are subterranean stream
networks, carved out by the water it channeled Groundwater
dissolves rock along joints and bedding planes, forming large
cavities Cave conduits are formed due to low primary and high
secondary Migration of water table can cause caves to form at
different levels Speleotherms depositions of calcite. Water
supersaturated with carbon dioxide will cause crystallization of
calcite, forming stalactite on ceilings, and water dripping onto
ground forms stalagmites, eventually joining to form columnsGranite
and Associated Landforms1. The Formation and Characteristics of
Granite1.1 Formation of Granite Intrusive igneous rock formed from
solidification of rhyolitic magma underground Solidifies to form
batholiths, plutonic features Exposed after denudation of landscape
Especially prone to pressure release as a result1.2 Characteristics
and Weathering of Granite1.2.1 Chemical Composition Quartz,
feldspar and other minor minerals Prone to chemical weathering of
hydrolysis: Feldspar -> kaolinite clay Forms gruss, residual
debris, within which are embedded corestones due to block and
spheroidal weathering1.2.2 Rock Texture Phaneritic, large
crystals1.2.3 Rock Structure High secondary permeability due to
shrinkage joints and sheet joints as a result of cooling and
pressure release Selective weathering along joints, block
disintegration and spheroidal2. Granite Landforms2.1 Landform
Development in the Humid Tropics High temperatures and rainfall
cause rapid chemical weathering, resulting in deep regolith of
saprolite2.1.1 Model of Deep Weathered Layer Ruxton and Berrys time
dependent model of weathering Mature stage: Zone 1 is residual
debris, Zone 2 is residual debris with corestones, Zone 3 is
corestones with residual debris, Zone 4 is partially weathered
rock2.2 Landform Development in the Seasonally Humid Tropics
Thinner regolith than humid trops, due to lesser chemical
weathering during drought period, as well as lesser vegetation to
prevent surface runoff from removing the regolith layer, may expose
basal surface of weathering2.2.1 Tors Small hills or heaps of
boulders rising abruptly from surface Exposed by stripping to basal
weathering surface e.g. Zimbabwe, Dartmoor2.2.2 Inselbergs Steep
sided isolated hills Ruwares are incipient inselbergs, with smooth
convex surfaces. In etchplains (land surfaces with more than one
phases of deep weathering followed by removal of regolith), pluvial
periods cause dominant selectvie weathering where joints are
numerous. Interpluvial periods cause surface wash to strip regolith
due to degenerating vegetation. Undulating basal surface of
weathering exposed the ruware. With repeated cycles of pluvial
periods, ruware becomes higher Bornhardts are the next stage, where
heights can exceed 300m with a convex summit with rock slabs due to
sheet joints because of pressure release, but the rock dome is
otherwise very durable Blocky inselbergs resemble tors, where
rectangular jointing is prominent, with selective weathering giving
is similar appearance to tors Castle koppies are degraded, old
inselbergs subjected to weathering. Low, irregular hills 2.3
Landform Development in the Temperate Regions2.3.1 Temperate Tors
Dartmoor. Probably due to previous climates, when warmer, more
tropical climates were experienced by current temperate areas21