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removal of rocky material from its "original location", erosion results in the "wearing down" of the land’s surface
loose, solid particles of minerals/rocks that originate from weathering and erosion of preexisting rocks (detrital sediments) or from precipitation from solution in water (chemical sediments)
form through sharing of outer (valence) electrons between atoms
FeldsparsPyroxenes, Amphiboles, Quartz, Micas, Olivine
CalciteDolomite, Gypsum, oxides and sulfides
basic building block of the silicates -- 4 oxygen ions bonded to 1 silicon ion (hybrid bond) SiO with a net -4 charge
streams that gain water from the saturated zone, rainy regions
felsic minerals melt at lower temps and thus will melt first, so if a rock undergoespartial melting, it will tend to produce a magma enriched in silica, Al, Na, & K.
mixing of magmas with different compositions can produce a magma of intermediate composition
b. Hardness-Moh’s hardness scale 1 talc – 10 diamond
c. Streak d. Luster e. External form f. Cleavage vs. fractureg. Density/Specific gravity h. Chemical tests i. Special Properties
Faster cooling near surface-extrusive
Slower cooling at depth-Intrusive(plutonic)
Mid-Ocean Ridge Basalts
divergent plate boundariesthrough decompression melting of a small weight percent of the ultramafic mantle
at convergent plate boundaries due to addition of water to mantle above subducting slab
shieldcomposite, cinder cone, dome
physically breaking down rocks into smaller fragments
the rounding of rock due to more rapid weathering of corners and edges
cracks called sheet joints develop in igneous rocks that formed at depth under high pressure conditions when they are exposed at the Earth’s surface.
plant roots break up bedrock
some minerals such ascalcite (found in limestone) dissolve in weakly acidic ground waters
acidic rain water and ground water react with feldspar minerals to produce clay minerals
higher temperatures generally lead to more rapid chemical weathering
humid climates generally lead to more rapid chemical weathering
due to overburden: sediment grains are packed closer together as the weight of sediments increases with deeper burial.
minerals precipitate from water moving through the pore space between sediments andcement the grains together producing a solid rock. Most commonly, these cements are composed of calcite or silica.
form from fragments of preexisting rocks
form from minerals that have precipitated from water (mostly seawater).
composed of organic carbon compounds
streams that form from meltwater at the snouts of glaciers tend to have heavy sediment loads and thus produce large numbers of gravel bars & large numbers of channels
the percentage of rock or sediment that consists of voids or open spaces. measurement of a rocks ability to hold water.
(Vadose) – some water in pore space, but pore spaces are not filled. highger moisture content at unsaturated.
transition zone between unsaturated & saturated zones. zone base just above the water table
all pore spaces filled with water
Perched water tables
saturated zone separated from main water table beneath it. usually formed by ground water collecting on top of less permeable rock (shale) within a more permeable rock within a more permeable rock (sandstone)
has water table, is only partly filled with water. rapid water movement can be recharged, water level rises and falls
completely filled with water has aquitard at top, which separates it from surface, recharges slowly through surrounding shale beds, slow water movement. has no response to wet/dry seasons
streams that lose water to the saturated zone. in dry climates or disconnected area from the saturated zones
Pleistocene Glacial Maximum
(maximum extent of glaciers) at ~18,000 years ago, entered interglacial at ~10,000 years ago (beginning of the Holocene)
Zone of Ablation
region in lower part of glacier where more snow/ice melts than accumulates resulting in loss of glacial ice or because of the calving of icebergs and direct evaporation (only in the coldest parts of the world)
the line between the zone of accumulation & zone of ablation at the end of the warm season – can usually be seen as the line separating white snow on the surface of the upper part of the glacier from darker snow/free ice in the lower part of the glacier.
meltwater often forms near the base of glaciers & can act as a lubricant to facilitate the glacier as a whole sliding over underlying rock as a single body
(abrasion): formation of rock flour – rock fragments trapped in ice at the base of the glacier grind away at the bedrock beneath, fine white particles turn meltwater milky greenish white
striated surfaces VS polished
direction of flow indicators – striations in bedrock can indicate the direction of previous glacial flow from large sharp edged particles , versus polished surfaces from fine particles
glaciers tend to cut U-shaped valleys, with very steep walls & flat valley floors
streams tend to cut V-shaped valleys
truncated spurs form where larger glacial valleys erode away the ends of arêtes.
glacially deposited sediments that tend to be angular & very poorly sorted (glacial ice can carry everything from fine dust to house-sized boulders
deposits of till at the terminus of the glacier
deposits of reworked till that form in tunnels carved under glaciers by meltwater
Permeability and pore connectedness
capacity of a rock to transmit a fluid through pores & fractures. measures easr of water flow. The dregree to which openings in a rock interconnect. Slow: small poorly connected pores. Fast: large and well connected pores
cones of depression – results when water is pumped faster than recharge can refill the region near the well
the addition of new water to the saturated zone
form in some confined aquifer systems. when water is under pressure and rises in a well to a level above the water table
caves, speleothems (stalactites & stalagmites), sinkholes, springs
Global changes in climate
cyclic climatic changes related to orbital forcing
Global changes in sea level
as water is tied up in glacial ice sea level drops, as glaciers melt sea level rises
(alpine) glaciers – occupy valleys in mountainous regions
continental size, can be kilometers thick +50000km
Glacier ice formation
snow loses its points, turns into granular snow becomes compacted into firn then eventually recrystallizes into glacial ice
if the equilibrium line advances down the valley it indicates a net gain in glacial ice and the glacier is advancing; Advance of the glacier can be seen over longer time spans through (+) movement of the terminus
If the equilibrium line moves up the valley, it indicates a net loss in glacial ice & the glacier is said to be retreating. Retreat of the glacier can be seen over longer time spans through (-) movement of the terminus
Flow of Rigid zone
the top part of glaciers (to a depth of ~40m) deforms in a brittle fashion & is called the rigid zone. This part of the glacier mostly just goes along for the ride on top of the lower part of the glacier. because this part is zone is so rigid it does not effect to changes in topography
Zone of plastic flow
lower part of the glacier which due to the pressure of the overlying ice deforms in a plastic fashion (it flows).
Velocity profile with depth
the edges & base of the glacier move more slowly due to frictional drag on the bedrock
Formation and evolution of crevasses
crevasses form in the rigid zone, where the ice is under tension such as on the outside of curves in the valley or where the glacier goes over convex topography.
Plastic flow dominates
glacial ice in continental ice sheets tends to be very thick, so plastic flow in the lower part of the ice sheet dominates; Basal sliding may also contribute
Hanging valleys and stream
hanging valleys form where smaller glacial tributary valleys are not eroded to the same extent as the major glacial valleys, often producing spectacular waterfalls
till deposited on the valley floor beneath the glacier
mound-shaped deposits of till
fine-grained wind blown deposits; rock flour
formed from wetter conditions in glacial ages
Lowering of Sea Level
water locked up in ice
drowned glacial valleys that formed as glaciers retreated and sea level rose
flooded glacial valleys that formed as sea level rose
evidence of temperature & greenhouse gases fluctuations preserved in ice cores from Antarctica & Greenland
lithified till deposits provide evidence of very old periods of glaciation
a. Deserts are dry areas, defined by Annual rainfall < 25 cm (~10 inches) or Aridity Index of 4 or greater
b. Vegetation type and abundance – not devoid of life
related to thermal forcing at the equator – warm moist air rises at the equator and cools -- dry air descends at 30°N and 30°S latitudes, where most deserts are found
Coriolis Force plus convection leads to prevailing wind patterns
air loses moisture as it rises over mountains producing rain shadows on the downwind side
many desert regions have internal drainage into low lying basins, forming shallow playa lakes
rare rain events can produce local intense floods
Dry Washes – dry stream beds through most of the year can become full rapidly during flash flooding events. have vertical wall and flat gravel covered floors
produces strong rain shadow effects
Basin and Range
fault-block bounded mountain ranges with valleys in between
region of flat lying sedimentary rocks at high elevation
horsts are uplifted fault blocks that form mountain ranges
downdropped fault blocks forming valleys in between
cone shaped deposits of sediments at the mouths of mountain canyons
shallow evaporate lakes that form in flat “playas” on the valley floors
form where alluvial fans coalesce.
Erosion and Transportation
wind picks up loose fine-grained material & moves sand via saltation
bouncing or skipping along the surface
strong winds that pick up large quantities of dust
features & mechanism of formation – rocks abraded by wind blown sand
Deflation and Blowouts
removal of fine-grained material by the wind – may contribute to development of desert pavement.
Distribution of loess
loose fine-grained material from desert regions and/or glacial deposits of rock flour is picked up by the wind & deposited. Large loess deposits in the Mississippi River Valley area & in China
form from accumulation of sand transported by the wind through saltation & deposition on the slipface (the steep downwind side of the dune) -- can be preserved in the rock record as cross-bedded sandstones.
vertical distance from trough (low part) to crest (high part)
horizontal distance from crest to crest or trough to trough
time for one wavelength to pass by a given point
Orbital particle motion
individual water particles move in near circular orbits as a wave passes by.
relationship to wavelength – particle motion diminishes with depth until it is gone at a depth of about ½ the wavelength
Changes in wave characteristics
as waves approach shore, they slow down, wavelength decreases & wave height is increased
Relationship to wave base
once the water depth is less than the wave base, the wave starts to “feel” the sea floor. The interaction of the sea floor & the wave results in drag on the orbiting water particles & slows the bottom of the wave
Formation of breakers
the top of the wave continues to move more rapidly than the lower part & results in the wave toppling over or “breaking”
waves coming in at an angle to the shoreline feel the drag effects of the sea floor at one “end” of the wave first, causing part of the wave to slow down, while the part of the wave that is still in deeper water continues to move more rapidly – this causes the wave to bend or “refract” until it becomes closer to parallel to the shoreline.
waves still coming in a small angle to the shore result in development of a current parallel to the shoreline known as a longshore current.
a prevailing wind direction produces a longshore current with a prevailing direction.
sediment moves up the beach in the swash at an angle, while sediment moves back seaward in the backswash directly down the beach face, resulting in a net motion in the direction of the longshore current
result from water piling up along shore due to longshore currents. Move seaward as narrow near surface currents in places of lower wave heights for incoming waves
gently sloping landward part of beach
steeply sloping part of beach in swash zone
Seasonal effects on sediment distribution
winter storms can remove beach sediments depositing them in offshore bars, while calmer wave activity in summers can move sediment from offshore bars back to beaches.
form as spits extend all the way across the mouths of bays
sand deposits that form when longshore currents that move sand along
the shoreline encounter deeper water in a bay & drop their sediment loads
sand deposits that build up behind sea stacks (isolated islands near the coast)
Jetties, Groins, and Breakwaters – man-made structures designed to keep channels open, interrupt longshore currents and stabilize beach sediments, and maintain quiet waters
Implications for sand movement and distribution in Anthropomorphic intervention
these man-made structures can have undesired effects, contributing to erosion or deposition of beach sediments.
River deposition and redistribution
most beach sands sourced from rivers and reworked by longshore currents and wave action
Wave focusing on erosional coasts
most wave energy absorbed by headlands
Coastal straightening on erosional coasts
erosion of headlands and deposition in bays results in straightening of coastline
Wave cut platforms
flat platforms cut by wave activity
erosional remnants of headlands
sea caves through eroded headlands that form arches
Barrier islands – islands that parallel coastlines with lagoons behing them
flooded river valleys that formed as sea level rose
melting of glaciers led to rise in sea level
old flat terraces that were below sea level that are exposed due to uplift
Coasts shaped by Organisms
Mangrove swamps and reef systems
plate tectonic motions result in large horizontal forces
force per unit area at a particular point
squeezing together, force from opposite directions shortening and flattening rocks, usually found at convergent plate boundaries (pushing or shoving rocks)
pulling apart from opposite directions stretching and extending rocks, usually found at divergent plate boundaries
(sliding past) force from opposite directions on a parallel plane, usually along active faults
deformation that results from stress
non-permanent deformation; if a material recovers its original shape after stress is reduced/removed. Rocks can only deform elastically up to their elastic limit (degree to which a rock can be stressed/strained and still return to its original shape). Past this limit, deformation will be permanent.
breaking of the rock; fracture at forces > than the elastic limit Ex faults or joints at/near the surface with low pressure
Rock deforms plastically; folds/bends under stress but no returning to original form if stress is removed. Does not require much stress increase to continue strain.
From slow pressure increase OR considerable confining pressure (buried) with high temp
rapid strain rate tends to result in brittle deformation, slower strain rates can result in ductile deformation
Effect of temperature on strain and stress
warmer temperatures lead to more ductile deformation
maps showing geological formations & structural elements with strike & dip symbols to indicate the orientation of layers, faults, & folds "map view"
representations of vertical slices through the earth
a theoretical line that if moved parallel to itself will form the shape of the fold, hinge line. Usually folds dip away from their hinge line. In the book picture is horizontal
a planar surface containing the fold axis or hinge lines for each layer of the fold. divides a fold into its two limbs. In the book picture is vertical.
a fold with a horizontal fold axis & a vertical axial plane. if the axis or axial are tipped the fold is assymetrical
a fold with a plunging (non-horizontal) fold axis. On the surface looks like a V or horseshoe shape
a fold with broad, open limbs
a fold with nearly parallel limbs
a fold with an overturned (upside down) limbs. Cannot use superposition to determine layer age
a fold “lying on its side” (with a horizontal fold axis & horizontal axial plane)
arch with oldest layer in the center.
plunging anticlines - surface V or horseshoe points in the SAME direction as the plunge
trough with youngest layer in the center.
plunging anticlines - surface V or horseshoe points in the OPPOSITE direction of the plunge
circular upwarped structure. dips AWAY from a central point with the oldest rocks in the center
Dome has Oldest in the center (DO)
downwarped structures. dips TOWARD a central point with the youngest rocks in the center
Basin has Youngest rocks in the center (BY)
joints are fractures across which there has been little displacement. They form perpendicular to tensional stress directions at shallow depths from brittle deformation with slight divergence from bending or shifting
fractures across which there has been displacement (slip).
slip is in the direction of dip. up or down movement of the hanging wall relative to the footwall
Hanging wall vs. Footwall
Hanging wall refers to the block above the fault, while footwall refers to the block below the fault plane
faults where the hanging wall moves down relative to the footwall. Caused by tension.
faults where the hanging wall moves up relative to the footwall. Caused by compression
low angle (shallow dipping) reverse faults. caused by compression
slip is in the direction of strike (faults are near vertical); slip is mostly horizontal
Right-lateral vs. left-lateral
relative motion between blocks moves fault block on the opposite side of the fault either to the right or the left
components of both dip-slip & strike-slip motion. Up or down COMBINED with horizontal movement
Causes of earthquakes
sudden release of energy (strain) accumulated in deformed rock
i. Tectonic stress – stresses along plate boundaries from plate motion
ii. Strain accumulation – rock deforms elastically in response to stress
iii. Rupture during earthquake – slip along fault releases energy from strain accumulation
hypocenter – point within the earth where rupture occurs – seismic waves originate from the focus
point on the Earth’s surface directly above the focus
travel through the Earth’s interior
(primary, compressional) –fastest, arrive first at seismic stations, travel through solids & fluids
(secondary, shear) – slower, arrive second at seismic stations, only travel through solids
travel along the Earth’s surface away from the epicenter
instruments that detect seismic waves
paper or digital records of seismic waves
P vs. S arrival
P waves arrive first; Late arrival of surface waves – surface waves arrive later
Relative amplitude of wave types
surface waves have higher amplitudes & result in more damage
Location of earthquakes
distance from seismic station to earthquake epicenter can be estimated by time difference in P and S waves. We know the velocities of these waves traveling through the earth, to generate travel time curves for P and S waves and the P-S interval.
Triangulation based on range derived from travel-times
using records from three or more seismic stations, we can determine the location of the epicenter by the intersection of circles with radii equal to the distance of the seismic station from the epicenter.
scales used to estimate the amount of energy released in an earthquake
older open-ended scale, found by measuring the amplitude of different types of seismic waves
Measures the amount of energy released from earthquake (magnitude)
on a scale of 1-10, usually fall within 2 to 8. not really used for earthquakes >7
newer method of determining amount of energy released in an earthquake based on the amount of slip along a fault, the rupture area on the fault, & the rock strength
a measure of an earthquake’s effect on people & buildings. The most commonly used is the Modified Mercalli scale. This scale is used when instrumental records are not available (mostly for historic earthquakes).
Global Distribution of earthquakes and the Relationship of size and type to plate tectonic setting
largest earthquakes occur along subduction zones – smaller earthquakes occur on transform fault boundaries (can still produce large earthquakes ~M8), & along divergent plate boundaries
determined by looking at past seismicity along with possible impact on people (population density)
smaller earthquakes that happen after an earthquake
when water saturated soils or sediments lose their strength & flow due to the shaking
can be triggered by earthquakes
Travel at 100’s of km/hr, but ocean is large, so early warning systems may be effective.
time between earthquakes of a given magnitude for a particular region – often employ paleoseismology to determine. Can be used to forecast probability of events of a given magnitude occurring for a given time interval
caused by offset in sea floor due to earthquake (or by submarine landslides)