Geology Flashcards
How old is earth
4.5 billion years old
Earths radius
6371km
What two elements are most abundant in the earths crust
Oxygen 45.2% Silicon 27.2%
What causes changes in the geological time scale
mass extinctions and change in climate
What is stratigraphy
study of rock layers
What are stenos three laws
law of original horizontally
law of superposition(oldest at bottom)
law of original continuity(erosion)
what does brittle deformation cause
(snaps) faulting
what does ductile deformation cause
(stretch) folds
What are the three types of faults
normal
reverse/thrust
strike slip
What are the two components of a fold
the hinge(peak) and the limb(side)
What are the four types of a fold
upright(equal forces)
inclines(one stronger)
overturned(limbs over each other)
recumbment
What is the antcline and syncline of a fold
anticline is oldest rock in middle
syncline is youngest at bottom
what are the 3 fundamental rock groups
igneous
sedimentary
metamorphic
what is volcanism
the transfer of heat and matter betweeen earths interior and its surface
what are volcanoes
openings or vents where lava, tephra and gasses escape onto earths surface
what are igneous rocks
rocks that are a product of volcanoes and volcanism
how are igneous rocks formedd
minerals crystallising from a melt known as magma ie cooling of magma and/ or lava (magma on earths surface)
what are the two types of igneous rocks
intrusive/plutonic- magma cools and solidifies deep underground
extrusive/volcanic- magma cools and solidifies at the surface as lava
how can crystal size be used to classify igneous rocks
intrusive- cooled slowly deep so are more course grained or phanertic(>1mm)
extrusive- cooled quickly at surface so no tike to grow, fine grained or aphanitic (<1mm)
How can chemical composition be used to identify igneous rocks
the amount of chemical compounds in particular SiO2, can affect colour
what is a dike
magma extrudes vertically through existing fractures in rocks
what is a sill
horizontal intrusions occur when magma exploits weaknesses in horizontal layers
what are the characteristics of an effusive eruption
basic, low viscosity, thin and runny lava, hottest, produces wide land forms with low slopes, found at constructive margins and hot spots, frequent but gentle erosion’s
what are the characteristics of explosive eruptions
acidic, high viscosity, thick and sticky lava, produces steep sides cones, found and destructive margins to produce subduction zones, infrequent violent eruptions
what types of volcano does low magma viscosity produce
shield volcano- wide gentle cones
how are sedimentary rocks formed
the accumulation of material derived from the physical disintegration and chemical decomposition of older rocks
what are thr four processes involved in sedimentary rocks production
weathering- breaking up of pre-existing rocks
erosion- transportation of the particles either as solid particles or in a solution
deposition- and accumulation of the particles(or chemical precipitation)
lithification- cementation of a sediment so that it becomes a rock
how to classify sedimentary rocks
clastic- subdivides by grain size
chemical- subdivided by type of chemical precipitation
organic- subdivided by origin of organic material
what is layering (sedimentary)
a general term for any
type of layering in a sedimentary
rock
what is bedding (sedimentary)
large distinct layers of
sedimentary rock that form over
time due to changes in
depositional conditions (>1cm)
what is lamination (sedimentary)
very thin layers
within a bed (mm thick), formed by
minor variations in deposition
what are asymmetric ripple marks (sedimwntary)
ripples indicate flow direction, with the steep
slope on the down-current direction.what
what are symmetric ripple marks (sedimentary)
ripples form as a result of constant wave
energy oscillating back and forth
what is cross bedding (sedimentary)
beds inclined relative to one another in the direction if wind or water, boundaries between represent an erosion surface, common in beach deposits
what is graded bedding (sedimantary)
As current velocity decreases, first the larger or more dense particles
are deposited followed by smaller particles.
Multiple graded-bed sequences called turbidites
what are the two types of metomorphism
contact and regional
what is contact metamorphism
when rocks encounter a heat sources eg magma without significant pressure
how does the extent of metamorphism vary
with distance from igneous rock
what is regional metamorphism
formed during mountain-building (orogeny), at
collision of lithospheric plates (destructive plate margins), combined effect of increased temperature and pressure
what is diagenesis (metamorphism)
all physical, chemical and biological
changes that occur in sediments after they are
deposited but before they become metamorphic rocks
chemical characteristics of continental crust
10-70 km thick
granitic so mostly made of oxygen and silicon
chemical characteristics of oceanic crust
2-10 km thick
basaltic so more magnesium, less silicon than continental crust
chemical characteristics of mantle
3488 km thick
made of peridotite
solid but deforms so can convect
chemical characteristics of the core
2882 km radius
made of iron and small amounts of nickel
physical properties of the litosphere
100 km thick
physical properties of the asthenosphere
250-350 km thick
viscous, soft and flow easily
physical properties of the mesophere
2500 km thick
capable of flowing
physical properties of the inner core
1230 km radius
iron and nickel, solid
physical properties of the outer coer
2250 km thick
iron and nickel, liquid
ways to know the chemical and physical composition of earth
seismology
drill holes
exposures
mineralogy
What are the two types of seismic waves
body (p and s) waves
travel through earths inner layers
surface (love and raleigh) waves
can only move along earths surface
P Wave
primary, fastest wave
moves through solid and fluids
particles move in the same direction as wave propagation
S Wave
secondary wave, slower than P
only moves through solid rock
particles move up and down or side to side ie perpandicular to wave propagtion
Surface waves
only travel through earths crust, lower frequency
arrive after body waves
Love waves
fastest surface waves
move side to side
Rayleigh waves
Roll along ground, moving up and down and side to side
what is a seismograph
Detects and records vibrations
produced by seismic waves
generated from earthquakes,
volcanic eruptions or human
activity
Seismogram
shows amplitude
and frequency of
seismic waves
what are the two ways to measure seismic activity
richter scale, max amplitude of seismic wave
modified mercalli, amount of intensity, shaking and damage
how do seismic waves provide evidence for the earths structure and composition
waves travel
quicker though denser materials, so faster with depth
slower through hot areas
slower through a liquid than a solid
P waves slower through molten areas
what are seismic discontinuities
Sudden change in
seismic velocities across a geological
boundary
Results in reflections, refraction (bending),
and the production of new wave phases (e.g.,
an S wave produced from a P wave)
what are the 5 major seismic discontinuities in the earths interior
moho
LVZ
670 km
gutenburg
lehmn
what is the moho(rovicic) disconitnuinty
seismic waves from
shallow-focus earthquakes were
recorded twice on seismograms: 2 sets
of P-waves and 2 sets of S-waves [first
set is direct path, second is
refracted/reflected when hitting
boundary]
One set must have travelled more slowly
(i.e. through the upper part of the crust)
and one through a faster medium
what is the LVZ (low velocity zone)
Represents zone of weakness in the
upper mantle called the
asthenosphere
what is the 670 km seismic discontinuity
Results from a phase change in mantle minerals
is a major boundary separating less dense upper
mantle from a more dense lower mantl
what is the gutenberg discontinuity
found at Core-Mantle Boundary
molten core beginning at ~2900
km depth. S (Shear) waves
could not penetrate this molten
layer and P waves would be
severely slowed and refracted –
thus the outer core must be
liquid.
Evidence for internal Earth structure and composition
what is the lehman discontinuity
found in the inner core
a sudden increase
in P wave velocities at a depth of
5150 km.
This velocity increase is
consistent with a change from a
molten outer core to a solid inner
core
what was the evidence that proved the existence of pangea
wegners evidence of fossils and similar rock types indicating a large ice sheet
holmes idea of an ‘internal mechanism’ causing continental drift
marie tharps mapping of the ocean floor backing up the continental drift theory
hess’ idea of convection currents spreading plates
magnetism
how was magnetism used to prove the theory of plate tectonics
the metal core creates a magnetic field
at mid ocean ridges minerals in magma align in direction of magnetic field forming a symmetric pattern on each side
what is the slab pull mechanism(come back to)
convection currents stretch and weaken crust, magma is initially less dense than surrounding crust, as it cools it increases density causing it to move away from the ridge, denser oceanic plate is forced under continental plate
what are the characteristics of continental plate
thicker, less dense, heterogeneous, oldw
what are the characteristics of oceanic plate
thine, more dense, homogeneous, younge
what are the three types of plate boundaries
converging- two tectonic plates move towards each other
diverging- two tectonic plates move apart from each other
transform- two tectonic places horizontally slide past each other
what is a glacier
A large, perennial accumulation of crystalline ice, snow, rock, sediment, and often
liquid water that originates on land and moves down slope under the influence of
its own weight and gravity
how much of the worlds freshwater is held in glaciers
70%
why are glaciers important
source for water, agriculture and hydropower
indicate climate change
sea levels rising
how is glacier ice formed
by firnification as snow accumulates and is compacted to fern then the expulsion of air, recrystalisation and compaction results in glacier ice
what is the glacier mass balance
the annual balance between the accumulation of snow and the ablation of ice
what is a positive glacier mass balance
accumulation > ablation = glacier advance
what is a negative glacier mass balance
ablation > accumulation = glacier retreat
what is the equilibrium line of a glacier
boundary between the accumulation and ablation zones
For a glacier in equilibrium mass balance, the accumulation
area ratio (AAR) = ~0.6
what is the thermal regime of a glacier
refers to whether the ice at the base of a glacier is above or below melting
point, can be affected by pressure
what is a warm based glacier
Ice is melting across the
glacier bed
Glacier moves by basal
sliding and/or soft-sediment
deformation
Glacier plucks and abrades
what is a cold based glacier
Ice is frozen to its bed
Glacier moves by internal
deformation only
Erosion is insignificant: the
glacier protects the land
beneath
glacier movement- internal deformation (creep)
Movement of ice within a glacier due to deformation of ice crystals under the stress of
glaciers weight
Cold based glaciers = frozen to bedrock, movement primarily in upper layers
Warm based = deformation is faster, partial melting at the base accommodating basal sliding
glacier movement- basal sliding
The glacier slides over its bed because
of a lubricating film of meltwater
Pressure melting must be present
across wide areas of the glacier sole
glacier movement- soft-sediment deformation
The glacier rides on a layer of
pressurised, water-saturated sediment.
Must be warm-based ice and presence
of multiple sediment layers
how do glaciers erode landscape
with tools such as sediments, which are incorporated by plucking and quarrying
warm based are effective at eroding
what are the three ways sediment is transported in a glacier
suparglacial- ncorporation at
glacier surface
englacial- Incorporation within
the body of a
glacie
basal- along the bed of a
glacier (plucking
and abrasion)
what are glacial deposts
till or moraine
what is a slopw failure
the irreversible loss of strength of
slope-forming materials
what is a mass movement
the downslope movement of slope
material under the influence of the
gravitational force of the material itself
and without the assistance of moving
water, ice or air
what is the equation for stability
resisting forces (Cohesion and
frictional strength of
the material) over driving forces (Gravity or other external
stresses trying to pull
material down a slope)
what is normal stress
force holding the material to a slope and is determined by weight force and slope angle
what does frictional strength depend on
frictional properties if the material, smooth on smooth = low frictional potential and rough on rough = high frictional potential
how is strength providedd
by cohesion
eg by electrostaic and molecular forces
cement
roots
what is the influence of water on a slope
add extra weight and changes cohesion as well as reduces the frictional strength through buoyancy
what is the effect of having saturated soil
water pushes particles in apart changing where weight is concentrated
what is the effect of earthquakes on slope stability
shaking induced temporary, cyclic increases in driving stress and reduction in resisting stresses
what is the factor of safety used to measure
how close a slope is to failure and describes the balance of forces acting on a slope
what is the simple equation for the factor of safety
F= shear resistance/shear force
what are all the elements involved in factor of safety
cohesion of rocks/soil
weight of a slope
angle of a slope
pore water pressure
angle of internal friction
where does the shear plane develop
when the two lines on a graph for shear strength and shear stress cross
how is a slopes stability defined if the factor of stress is greater than 1.3
stable- major events and long term environmental changes needed to cause hazard
how is a slopes stability defined if the factor of stress is between 1.0-1.3
conditionally stable- minor triggering event needed
how is a slopes stability defined if the factor of stress is less than 1.0
actively unstable- imminent failure
what are the four mass movement processes
falls
topples
slides rotational and transnational
flows
what is a fall
collapse of material from a cliff of steep slope
what is a topple
forward rotational movement of rock
what is a rotational slide
failure of material at depth then movement by sliding along surface
what is a transnational slide
the down-slope movement occurs along a weakness
what is a flow
the movement of material in the form of a fluid
what are the three fundamental processes of material motion
pure flow- thin layers sliding over each other
pure slide- slip of a rigid block moving at the same velocity
pure heave- up and down movement of individual particles
what is laminar water flow
layers of water of molecular thickness slide over each other, curved velocity profile shows surface water travels fastest
what is turbulent water flow
chaotic eddies produce irregular paths and variable velocities
what is lift force (bernoulli effect)
convex surface of grain acts like aeroplane wing so flow has to accelerate
=low pressure above particle
=lift force
once lifted particles are entrained into turbulent eddies and carried downstream
After being entrained, how are particles transported
1.Rolling along the
bed (bedload)
2. Sliding along the
bed (bedload)
3. Bouncing along
bed i.e. saltation
(bedload)
4. Suspended in
water column
(suspended load)
5. Dissolved mineral
and organic matter
(solute load)
what are the factors that effect a channel form
valley slope- steep or gentle
sediment supply- high or low
sediment supply- coarse or fine
water discharge variation- high or low
what is a characteristic of meandering rivers
deposition on inner beds (slow moving water), erosion on outer beds (at thalweg)
what are braided rivers
network of river channels separated by sediment bars
mid channel bars
flood channels
chutes
what is lanes balance
Erosion and deposition based on the balance between aggradation and discharge rate
what happens if the < Sediment load and/or > discharge
=degradation (erosion)
what happens if > Sediment load and/or < discharge
=aggradation (deposition)
what is aggradation caused by
decrease in discharge
increase in sediment load
increase in grain size
decrease in slope
characteristics of a wave
wave particles move in circular (orbital) motions
crest is the highest part
trough is the lowest
distance between in wavelength
what slows a wave and shortening its wavelength
frictional between orbital motions and seabed
what happens when wave energy is compressed
increase in height
water becomes too shallow to sustain wave height at H/L= 1/7, thus breaking waves
what is the difference between summer and winter waves
summer waves deposit as a bern and winter waves erode that and deposit it as a longshore bar
what is the swash
forward movement of
water as wave breaks
what is the backwash
movement of water
towards ocean
what is shore normal
water flows
directly towards beach: sediment
transported up and down the
beach rather than along it building
features like berms
what is longshore drift
approaches
shore at oblique angle, transport
sediment along shore creating
spits and sandbars
constructive waves
swash>backwash = sediment moves up beach
destructive waves
swash<backwash = sediment moves down beach
