if rock layers bend rather than break, they are folded- anticlines(old in middle), synclines, adn recumberent folds. If the hinge line of a fold is not horizontal-plunging.
fracutres are either joints or faults: joint is where movement has not occured
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the compass direction of a line formed by the intersection of an inclined plane with a hor plane is
strike
folds in rocks hsow that the rock behaved in a
ductile way
anticlines are
a fold shaped like an arch with the oldest rocks exposed in the center.
syncline is
trough spaced fold with the youngest rocks exposed in the center
bed dips away from middle/oldest rock exposed in the center
structural dome
fracuture in bedrock along which movement has taken place aer called
faults
normal fault, the hanging wall block has moved downward relative to the footwall
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normal faults occur where there is horizontal extensions
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faults that typcially move older rock on top of younger ones aer thrust faults.
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Chpter 16: elastic rebound theory- involved the sudden release of progressively storied strain in rocks, causing movememtn along a fault
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the point within earth where seismic waves orginate is called
focus
p waves are compressional; fastest
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ritcher scale measures magnitude
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beniof zones- oceanic trenches
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earthquakes at divergent plate boudnaries are shallow focus
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a zone of shalloe earthquakes alone normal fault-div
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seismic gap is an active fault where earthquakes havent occurred for a long time
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Chapter 19: southern superr-Gon
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sliding of the sear floor benearth a continent or island ar is
subduction
plates are oart of a ridig outer shell of the earth called the
lithosphere
san Andreas- transform fault
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ocean ocean converegence
island arc
ocean cont
madmatic arc
con con
suture zone
passive continental margine aer created by div
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haw islands-mantle plume
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metalic ores- via hydro thermal process.
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Summary: foliation in metamorphic rock due to differental stress(compressive stress or shearing) slate, phylite,schist,and genesis are folaited rock that indiacte increasing grade of regional metamorphism
Contact met-produced during metamorphic usually without significant differential stress but with high temp
reg met-involves heat, confining pressure, and different stressed, has created mot of the metamorphic crust
hydrothermal veins- hot water precipates crystallizes into minerls.
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Which is not regarded as a low grade metamorphic rock?
greenschist, phylitte, slate,gnesis
g
shearing is a type of
differential stress
metamorphic rocks witha planar texture
foliated
metamorphic rocks are classifed prmarily on
texture
which is not a foliated metamorphic rock?
gneiss
schist
quartzie
slate
quar
limestone recrystallizes during metamorphism into
marble
quartz sandstone is changed during metamorphism into
quartizle
sequence of rocks that are fomed when shale undergoes prograde metamorphism
slate,phylite, schist,gnesis
m
metamorphism/metasoatism
metso- ions
ore bodies at divergent plate boundaries can be created via
hydrothermal process
a schist that developed in a high pressure low tem enviormned is likely formed
in the lower part of the con crust
a met rock has undergone partical melting to produce a mixed igneous metamorphic rock is
migmaitite
sediment- loose particles
sand-sandstome
'clay is the finest sediment
deposition-transported mineral comes to rest/accumluation of sediment
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lithification-process that converts loose sedment into sedimentary rock
-compaction and cementation
Sed breccia is a sed rock fromed by the cemenation of frags of rubble
conglomerae-formed by the cementation of rounded gravel.
sandstone- by the cemenation of sand grains.
fine grained rocks of silt and clay are shale, siltstone, claystone,a dn mudstone. shale-split layers. `
silt-silt
claystone-claysized particles but no fissility
mudstone-silt/clay
limestone is a carboante rock of calcite. \(tufa.travertice-alter dolomite
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sed rocks form by lithe of sediment, crust from soltuions, consolidation of remains or organisms.
Conglomerate-rounded sediments. sandstone from sand deposits, shale from river. Limestone-calciee
dolomite-limestone by mag rich solutions
chert-silica
evopr
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corss beds and ripple mark developing moving sediment
ugh
graded bed-decreasing water flow velocity in a turbidity current
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Explosive eruptions(merapi/st helens/kilaueu) solid volcanic fragements
-effects on climate-mt pinatubo put fine partices in the air/offset the temperature for years.
1815 eruption of tamnbora-largest in millennium. that year was the year without summer
flank-vent
Pahoehoe:ropy or billowy sureface-formed by rapid cooling
Aa is a flow that has jagged/rubbery surface
flood basalts are outpouring mafic lava form fissures(columanr jointing)
Pillow structure-pillow shapeed mass-produced by paehoe lava flows i
Viscosity-resistance to flow
-Felsic rocks are silica rich-rhylotie
mafic rocks are silica deficient-basalt
intermediate-between-andesite
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Pyroclastic Materials- dust/ash. small-cinder,lapilli(peach), blocks no rounded edges or corners.
mt unzen, st peirre,
Shield volcanoes- broad/gently sloping/basalt
cinder cones-pyro vent
composite-alternating layers/andesite
ring of fire-mt helens,crater lake,lassen peak
med belt-mt vesuvis
lava domes are masses of volcanic rock from viscous lava
caldera is a volcan depression
5 major types of volcanoes- shield-built up by eruptions of mafic lave
cinder cone-loose pyrcalsts
composite cone-alternating layerslava dome, and caldera.
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rocks-igneous(form when magma solidifies), metamorphic, and sedimentary.
if the unconsolidated sediment becomes lithified(cemented into rock) becomes sedimentary.
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Igenous rocks- basalt(form magma), magma is a molten rock rich in silica, granite(feldspar and quartz), xenoliths-frag of rock that are distinct from the body of igneous rocks.
Rock textures
Crystaline textures-interlocking crystals(feld/quar); glassy-few/if any; fragmented rocks-frag). Pegmatite.
glassy texture-obsidean, scoria(vesicular basalt), pumice
Fragmented texture-pyroclasts(ash debirs)
igneous rocks are commonly composed of quartz, plagioclase feld, potassium feld, amphibole, pyroxene, biotite, olivine.
Mafic rocks-silica poor-gabbro, basalt.
Felsic rocks(al)-Rhyolitw, Grainte,obsidian,
intermediate rock(ferll)-amphiolea and pyro, andes
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Igneous rocks form form solidification of mama-either extrusive/intrusive. volcano necks soldificed within vocanoes. sill(concordant//) dike-discondordant.
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Felsic are rich in silica.
igneous rocks-granites,diorites,gabbro, rhy,andes,basalt.
granite and andesite are associated with subduciton.
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Major difference between intrusive rock and extrusive igneous rocks is what
where they solidify
Which isnt an igneous rock
gabbro, diorite,granite,andesite
andesite
by definition, stocks differ from batholits in size
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geothermal gradient is
30
coninuous branch of bowens reaction theories contians the mineral
plagioclase
discontinuous-
pyroxene,amphiobole,biotite
Most commong igneous rock
quartz
granitic magma
convergent boundaries and magmatic underplatting
rocks are defined as naturally formed aggregates of mineral or mineral like substances
minerals-naturally occuring-mag, iron, calcium, graphite
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silica is the element used to make computer chips. Silica is a term for oxygen combined with silicon. Silicon is the second most abundant element is the crust, most minerals contain siica,
THe common mineral quartz is pure silica that has crystallized.
Qu
Feldspar is a framework silicate, so is quartz.
Non silicate minerals- no silica: like calcite(one of the most abundant minerals at the earths surface and occurs mainly in limestone)
In dolomite, also a carbonate, a magnesium replaces some calcium
Common silicate mineral- olivine-with mag olivine
Minearls that show solid solution- plagioclase feldspar and augite-centers crystals dominated by one type of cation. THe grains of plagioclase in certain igneous rocks typical have calcium rich centers
Polymorphism- have the same chemical composition. Examples are calcite and aragonite, graphite, diamond
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Ferromagnesium minerals-iron, mag bearing- such as augite, hornblende, olivine and biotite are green or black
mineral quartz, gypsum, calcite and PF can be white.
streak is the color of the powder formed when a mineral is crushed.
Luster is the quality and intensity of light that is reflected from the surface-its either metallic/nonmetallic(glassy: feldspar, quartz,micas, pyroene.
hardness0 "scratchability: quartz can always scratch calcite or feldspar-harder than both minerals
cleavage is the ability of a mineral to break, when struck or split, along preferred planar direction--important in identifying minerals.
There most common mineral groups- feldspars, amphiboles, and the pyroxenes.
Feldspar-90 degree/good quality
amph-56/good
pyro-90/fair
fracture is teh way a substance breaks where not controlled by cleavage-no cleavage=irregular fracture.
some minerals break along curved fracture-quartz/garnet
plagioclase feldspar-straitions
magentite-magnet
Most common minerals are silicates which included quartz, olivine's, and the feldspars(play and pot feld)
some minerals crystallize from volcanoes-sublimation
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Two mostabundant elements in earths crust are oxygen and silicon. cleavage-most important in identifying elemnet. crystal form, fracture, hardness,luster,color and streak and gravity.
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A substance that cant be broken down into an substance by chemically methods is an
element
the subatomic particle that contributes mass and as ingle positive electron
proton
Atoms of an element containing different number of neutrons but the same number of protons are
isotopes
atoms with either positve or negative charge are called
ions
Bonding between CL and Na in halite
Ionic
Which is not a type of silicon structure
isolated double chain
single chain
sheet
framework
pentagonal
pentagonal
Which is not a silicate
quartz
pyroxnene
biotite
calcite
feldpsar
calcite
window glass has a hardnes of about
5-6
the ability of a mineral to break along preferred directions is
clevage
striations are associated with
pot feld
crystalline substances are always
minerals
Geology is the scientific study of Earth
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Earthquakes, hurricanes, volcanic eruption, landslides, floods, tsunamis are the most common geologic hazards.
Jan 12- magnitude 7 earthquake-portauprine,capital of haiti
Feb 10- 8.8 mag hit off the coast of central chile-6th largest ever recorded.
Geologist understand that the outer part of the earth is broken into slabs called tectonic plates.
largest earthquake ever recorded-1960-chile.
jan 11, 2012- mag 9 earthquake-japan(largest earthquake to ever hit japan)
Mt pinatubo-1991-second largest volcanic eruptin of the 20th centur.
Nevado del ruiz in columbia in 1985-mudflow overwhelmed Armero.
The earth system is a small part of the larger solar system:
It is consist of atmosphere(the gases that envelop the Earth), hydrosphere(water on or near earths surface), biosphere(is all of the living or once living material on earth.
-The geosphere or sold earth system is the rock and other inorganic material that
All 4 of earths systems interact with one another to produce soil, such s we find in farms, gardens, and forest. The solid dirt is a mix of decomposed and disintegrated rock and organic matter. the organic matter is from decayed plants(biosphere)
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Earths internal heat engine is driven by heat moving from the hot interior of the earth toward the cooler exterior. Moving plates and earthquakes are products of this heat engine.
Earths external heat engine is driven by solar power. Heart from the sun pr
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The mantle si the most voluminous of earths three major concentric zones- solid rock.
Other 2 zones are the crust and the core. the crust of the earth is analogous to an apple. We have direct access to only the crust.
Two major types of crust are oceanic and continental. Crust under the ocean is much thinner.
The crust and the uppermost part of the mantle are rigid and make up the lithosphere.
The uppermost mantle underlying the lithosphere is the astenosphere-soft and flows more readily than the underling mantle.
Forces generated inside the earth are tectonic plates.
Plate tectonics regards the lithosphere as broke into plates that are in motion
Divergent Boundaries involve two plates that are moving apart from each other.
submarine ocean ranges- mid oceanic ridges.
-initially initiate withint a contineent.
-rock that forms when magma soldies is igneaous rocks. the igneaous rock that soldiifes on the sea floor and in the issuers necomes oceanic crust.
Convergent boundaries are where plates move toward each other.
-ex: andes, cascade mtn ranges. Convergent boundaries are the sites of teh largest earthquakes in the world.
Characer of the plates that are involved: ocean continent, ocean ocean, and continent continent.
Ocean continent: plate capped y oceanic crust and the other by continent cost, the less dense will override the denser oceanic plate. The oceanic plate bends beneath the continent plate and sinks along what is known as the subduction zone- where an oceans
where the top of the subduction zone slides-melting takes place. Magma is created along the subduction zone works its way upward and either erupts at volcanoes on the earths surface to solidify extrusive igneous rock or solidifies within the crust to beco
Ocean ocean convergence is when both converging plates are oceanic, the denser plate will subduct beneath the less dense plates.
Rising magma forms volcanoes that grow from an ocean floor rather than on a continent-resutls in a volcanic arc
ex: aleutian islands, and the islands that make up japan.
Continent - contient convergence is when both converging plates are continent, and a quite different geologic deformation process takes place at the plate boundary-neither plates subducts because the much less dense than the mantle below
Ex; Himalayan- tallest- continue to grow in height.
Continent continent convergence is preceded by oceanic continental convergence- an ocean basin between two continent closes because oceans lithosphere is sub ducted beneath one of two continents.When con
Transform boundaries occur where two plates slide horizontally past each other rather than toward or away from one another.
San andreas and alpnie fault.
Most transform faults are found along mid oceanic ridges, occasionally one cuts through a continental plate
Portions of the crust also can rise because of isostatic adjustment, vertical movement of sections of earths crust to acheive balance.
Continental rock is less dense than oceanic crust will tend to float higher over the mantle than oceanic crust(this is w
Where moving water ice and wind loose and removes material- erosion takes place.
The new material, stable under condition at earths surfaces are said to be in equilibrium- adjusted to the physical and chemical conditions of their environment so they dont alter with time.
The product of breakdown rock is sediment,
With the cementation of the loose particles, the sediment becomes lithified(cemented or otherwise consolidated into sedimentary rock. Sedimentary rock that becomes deeply buried in the earth may later be transfor
Geologist is the scientific study of earth. we benefit from geologist because we need geology to find and maintain a supply of minable commodities and sources of energy; geology helps protect the environment; applying knowledge about geologic hazards save
earths systems are the atmosphere, the hydrosphere, the biosphere, the geosphere.
geologic investigation indicates that earth is changing because of internal and surficial processes. internal processes are driven mostly by temperature differences within earths mantle. external-solar energy. internal forces may cause the crust to move.
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Plate tectonic theory visualizes the lithosphere(crust and the uppermost mantle) as broken into plates that move relative to one another over the asthenosphere. The plates are moving away from divergent boundaries usually located at the crests of mid ocea
Ocean continent convergence- lithosphere with oceanic curst is sub ducted under lithosphere with continental crust.
Ocean ocean convergence involves subduction in which both plates have oceanic crust and the creation of a volcanic island arc.
continent co
erosion takes place at earths surface where rocks are exposed to air and water. rocks that formed under high pressure and temp inside earth are out of equil at the surface and tend to alter to substances that are stable at the surface. sediment is transpo
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Plate tectonics is a result of earths internal heat engines, powered by
heat flowing from earths interior outward
a typical rate of plate motion is
1-10 cm
volcanic islands arc are associated with
divergent boundaries
the division of geology concern with earth material, changes in the surface and interior of the earth, and the dynamic forces that cause those changes is
physical geology
largest zone of earths interior is the
mantle
ocean and continental crust differ in
composition, density, thickness
plate tectonis is a
theory
name plate boundaries
...
lithosphere is
the curst and the uppermost mantle
Tectonic forces at work: Tectonic forces deform parts of the lithosphere, particularly along plate margins.
Deformation may cause a change in orientation, location, and shape of a rock body.
When studying deformed rocks, structural geologists typically refer to stress(a force per unit).
Where stress can be measured, its expressed as the force per unit area at a particular point. It is difficult to measure stress in rocks that are buried.
We can observe the effects of past stress(caused by tectonic forces confining pressure from burial) when rock bodies are exposed after uplight and erosion.
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We can observe in exposed rocks the effects of forces on a rock that was stressed. Strain is the change in shape or size(volume), or both, in response to stress.
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The relationship between stress and strain can be illustrated by deforming a piece of silly putty.
If the silly putty is pushed together or squeezed from opposite directions, the stress is compressive. Compressive stress results in rocks being shortened or flattened.
An elongate piece of silly putty may shorten be bending, or folding, wheres a ball of
A tensional stress is caused by forces pulling away from one another in opposite directions. Tensional stress results in a stretching or extension of material.
If we apply a tensional stress on a ball of silly putty, it will elongate or stretch parallel to the applied stress. If the tensional stress is applied rapidly, the silly putty will first stretch and then break apart. At divergent plate boundaries, the li
When stresses act parallel to a plane, shear stress is produced.
Its much like putting a deck of cards in your hands and shearing the deck by moving your hands in opposite directions.
A shear stress results in a shear strain parallel to the direction of the stressed. Shear stresses occur along actively moving faults.
How do rocks behave when stressed?
Rocks behave as elastic, ductile, or brittle materials, depending on the amount and rate of stress applied, the type of rock, and the temperature and pressure under which the rock is strained.
If a deformed material recovers its shape after the stress is reduced or removed, the behavior is elastic.
Example: If a tensional stress is applied to a rubber band, it will stretch as long as the stress is applied, but once the stress is removed, the rubber band returns(recovers) to its original shape and its behavior is elastic.
However, once the stress app
A rock that behaves in a ductile or plastic manner will bend while under stress and does not return to its original shape after the stress is removed.
Silly Putty behaves as a ductile material unless he rate of strain is rapid.
Rocks exposed to elevated pressure and temperature during regional metamorphism also behave in a ductile manner and develop a planar texture,foliation, due to the alignment of mi
A rock exhibiting brittle behavior will fracture at stresses higher than its elastic limit, or once the stresses are greater than the strength of the rock.
Rocks typically exhibit brittle at or near Earths surface, where temperatures and pressure are low. Under these conditions, rocks favor breaking rather than bending. Faults and joints are examples of structures that form by brittle behavior of the crust.
Example: A sedimentary rock exposed at Earth's surface is brittle; it will fracture if you hit it with a hammer. Sedimentary rocks become bent or deformed in a ductile way because either stress is increased very slowly or the rock was deformed under consi
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How do we record and measure geologic structures?
The study of geologic structures is of more than academic interest.
Petroleum and mining industries employ geologist.
Understanding and mapping geologic structures is also important for evaluating problems related to engineering decisions and seismic risk
Geologic Maps and Field Methods.
-Geologist ordinarily use observations from a number of individual outcrops (exposure of bedrock at the surface) in determining the pattern of geologic structures.
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A geologic map, which uses standardized symbols and patterns to represent rock types and geologic structures, is typically produced from the field map for a given area.
On such a map are plotted the type and distribution of rock units, the occurrence of structural features(folds, faults, joints), ore deposits,.
Strike and Dip.
According the the principle of original horizontality, sedimentary rocks and some lava flows and ashfalls are deposited as horizontal beds or strata. Where these originally horizontal rocks are found tilted, it indicates that tilting must
Someone studying a geologic map would want to know the extent and direction of the tilting. By convention, this is determined by plotting the relationship between a surface of an inclined bed and an imaginary horizontal plant.
Strike, direction of dip, and angle of dip. The line of strike is found where an inclined bed intersects a horizontal plan. The dip direction is always perpendicular to the strike and in the direction the bed slopes. The dip angle is the vertical angle of
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Strike is the compass direct of a line formed by the intersection of an inclined plane with a horizontal plane. (example N50*E)
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Angle of dip is measured downward from the horizontal plane to the bedding plane (an inclined plane).
Note that the angle of dip is measure within a vertical plane that is perpendicular to both the bedding and the horizontal planes.
-The dip angle is always measured at a right angle to the strike, that is perpendicular to the strike line.
The direction of dip is the compass direction in which the angle of dip is measured.
If you could roll a ball down a bedding surface, the compass direction in which the ball rolled would be the direction of the dip.
A specifically designed instrument called a Brunton pocket transit is used by geologists for measuring the strike and dip.
-the device contains a compass, a level, a device for measuring angles of inclination.
Geologic Cross Sections- represents a vertical slice through a portion of Earth. It is much lie a road cut or the wall of a quarry in that it shows the orientation of rock units and structures in the vertical dimensions. Geologic cross sections are constr
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Folds are bends or wavelike features in layered rock. Folded rock can be compared to several layers of rugs or blankets that have been pushed into a series of arches and troughs. Folds in rocks often can be seen in roads cut or other exposures.
The fact that the rock is folded or bend shows that it behaved as a ductile material. The rock exposed in outcrops is generally brittle and shatters when struck with a hemmer.
The rock is not metamorphosed(most metamorphic rock is intensely folded because
Geometry of folds.
Determining the geometry or shape of folds may have important economic implications(because of the many oil and gas deposits and some metallic mineral deposits are localized in folded rock).
Also important in unraveling how a rock was strained and how it might be related to the movement of tectonic plates. Folds are usually associated with shortening of rock layers along convergent plate boundaries but are also commonly formed where rock has
Because folds are wavelike forms, two basic fold geometries are common- anticlines and synclines.
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An anticline is a fold shaped like an arch the oldest rocks in the center of the fold.
Usually the rock layers dip away from the hinge line(axis) of the fold.
The counterpart of an anticline is a syncline, a fold shaped like a trough with the youngest rocks in the center of the fold.
The layered rock usually dips toward the synclines hinge line.
Each anticline and adjacent syncline share a limb.
Each plane is an axial plane, an imaginary plane containing all of the hinge lines of a fold.
The axial plane divided the fold into its two limbs.
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Its important to remember the anticlines are not necessarily related to ridges nor synclines to valleys because valleys and ridges are nearly always erosional features.
In an area that has been eroded to a plain, the presence of underling anticlines and synclines is determined by the direction of the dipping beds in exposed bedrock.
The oldest exposed rocks are along the hinge ling of the anticline. THis is because lower
Plunging Fold
So far, the folds shown have contained horizontal hinge lines.
In nature, anticlines apt synclines are apt to be plunging folds- folds in which the hinge lines are not horizontal.
On a surface leveled by erosion, the patterns of exposed strata(bees) resemble Vs or horseshoes. Plunging anticlines and synclines are distinguished form one another in the same way as are nonplunging folds- direction of dip or by relative ages of bed.
plunging synclines- contains the youngest rocks in its center or core, and the V or horseshoe pints in the direction opposite of the plunge.
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Plunging anticline contains the oldest rocks in its core and the V points in the same direction as the plunge of the fold.
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Structural Domes and Structural Basins:
A structural dome
a structure in which the beds dip away from a central point, and the oldest rocks are found in the center or core of the structure. In cross section, a dome resembles an anticline and is sometimes called a doubly plunging anticline.
A structural basin
the beds dip toward a central point, and the youngest rocks are exposed in the center of the structure. In cross sections, it is comparable to a syncline (doubly plunging syncline).
Domes and basins tend to be features on a grand scale( some are more than a hundred kilometers across) formed by uplift somewhat greater(domes) and less(basins) than that of the rest of the region.
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Interpreting folds.
folds occur in many varieties and sizes.
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Open folds have limbs that dip gently, and the angle between the limb is large. All other factors being equal, the more open the fold, the less it has been strained by shortening.
-Right fold- the angle between the limbs of the fold is small.
-isoclinal f
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A fold that has a vertical axial plane is referred to as an upright fold. (where the axial plane of a fold is not vertical but is inclined or tipped over, the fold may be classified as asymmetric).
-If the axial plane is incline to such a degree that the
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Looking at an outcrop where only the overturned limb of a fold is exposed, you would probably conclude that the youngest bed is at the top. THe principles of superposition cannot be applied to determine top and bottom for overturned beds. You must see eit
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Recumbent folds are overtuned to such as extent that the limbs are essentially horizontal. Recumbent folds are found in the cores of mountain ranges such as canadian rockies, alps, himalayas, and record extreme shortening and shearing of the crust typical
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Fractures in rocks.
-if a rock is brittle, it will fracture. Commonly, there is some movement or displacement. If essentially no shear displacement occurs, a fracture of crack n bedrock is called a joint.
-If the rock on either side of a fracture moves pa
Most rocks at or near the surface is brittle, so nearly all exposed bedrock is jointed to some extent.
Joints
-Columnar jointing, in which hexagonal columns form as the result of the contraction of a cooling, solidifying lava flow
-Sheet jointing, a type of jointing due to expansions is caused by the pressure release due to removal of overlying rocks and h
Columnar and sheet joints are examples of fracture that form from non tectonic stresses and are therefore referred to as primary joints.
Joints are among the most commonly observed structures in rocks. A joint is a fracture or crack in a rock body along which essentially no displacement has occurred. Joints form at shallow depth in the crust where rocks break in a brittle way and is pulled
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Faults are fractures in bedrock along which sliding has ten place. The displacement may be only several cm or may involved greater distances. Most faults are no longer active.
the nature of past movement ordinarily can be determined where a fault is exposed in an outcrop. geologist look for dislocated beds or other features of the rock that might show how much displacement has occurred and the relative direction of movement.
-Geologist describe fault movment in terms of direction of slippage: dip-slip fault(movement is parallel, strike-slip fault(indicates horizontal motion parallel to the strike of the fault surface, and oblique-slip fault(has both strike slip and dip slip c
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Dip Slip Faults- the movement is up or down parallel to the dip of the inclined fault surface. The side of the fault above the inclined fault surface is called the hanging wall, whereas the side below the fault is called the footwall.
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Normal and reverse faults(most common type of dip slip faults) are distinguished from each other on the basis of the relative moment of the footwall black and the hanging wall block.
In a normal fault, the hanging wall block has moved down relative to the footwall block.
In reverse faults, the hanging wall block has moved up relative to the footwall block. Horizontal compressive stresses cause reverse faults. reverse faults tend to sh
Strike Slip Falls is a fault where the movement is predominately horizontal and therefore parallel to the strike of the fault. The displacement along a strike slip fault is either left lateral or right lateral and can be determined by looking across the f
If a person looks across the fault and sees the stream displaces to the right(RL).
Large Strike Slip Faults- san andreas fault in cali
Summary:
tectonic forces result in deformation of the earths crust. Stress is a measure of the tectonic force and confining pressure acting on bedrock. Stress can be compressive, tensional, or shearing. Strained(changed in size or shape) rock records past
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A geologic map shows the structural characteristics of a region. Strike and dip symbols on geologic maps indicate the orientation of inclined surfaces such as bedding planes. The strike and dip of a bedding surface indicate the relationship between the in
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If rock layers bend(ductile behavior) rather than break,they become folded. Rock layers are folded into anticlines and synclines and recumbent folds. If the hinge line of a fold is not horizontal, the fold is plunging. Older beds exposed in the core of a
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Fractures in rocks are either joints or faults. A joint indicates that movement has not occured on either side of the fracture; displaced rock along a fracture indicates a fault. Dip slip faults are either normal or reverse, depending on the motion of the
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In a strike slip fault, which can be either left lateral or right lateral, horizontal movement parallel to the strike has occured.
Strike slip faults accommodate shearing strain in the brittle, uppermost lithosphere, and may alos represent transform plate
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True or False.
When forces are applied to an object, the object is under stress.
Strain is the change in shape or size, volume, or both while an object is undergoing stress.
stresses can be compressive, tensional, or shear.
true
The compass direction of aline formed by the intersection of an inclined plane with a horizontal plane is called
strike
folds in a rock show that the rock behaved in what way
ductile
an anticline is what
a fold shaped like an arch with the oldest rocks exposed in the center of the fold.
a syncline is what
a trough shaped fold with the youngest rocks exposed in the center of the fold
a structure in which the beds dip away from a central point and the oldest are exposed in the center is a what?
structural dome
Which is not a type of fold
open, isoclinal, overturned,recumbent, thrust
thrust
fractures in bedrock along which movements has taken place are called
faults
in a normal fault, the hanging wall block has moved ____ relative to the footwall block
downward
normal faults occur where
there is horizontal extensions
faults that typically move older rock on top of younger rock are
thrust faults.
Approximately 0.6 of the earths water is ground water, and 97% is ocean.
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Ground water is the water that lies beneath the ground surfaces, filling the pore space between grains in bodies of sediment and clastic sedimentary rock and filling cracks and crevices.
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Ground water is a major economic resource
Ground water is commonly less contaminated and more useful than surface water.
How much water soaks into the ground is influenced by
climate, slope of the land, and soil and rock type and vegetation. 15% of total precipitation ends up as groundwater in general.
Porosity
Porosity, the percentage of rock or sediment that consists of voids or openings, is a measurement of a rocks ability to hold water. Sandstone, conglomerate, and many limestones have high porosity and can hold a considerate amount of water. Sand-30% to 50%
Permeability
refers to the capacity of a rock to transmit a fluid through pores and fractures; allow water to pass through them. This measure the relative ease of water flow and indicates the degree to which opening sin a rock interconnect.
A rock that holds much water s called porous; a rock that allows water to flow easily through it is permeable.
Most sandstones and conglomerates are both porous and permeable. An impermeable rock is the one that does not allow water to flow through easily- like unfractured granite and schist are impermeable. Shale is porous but low permeability(pores too small for
The Water Table
The rate of groundwater flow tends to decrease with depth because sedimentary rock pores tend to be closed by increasing amounts of cements and the weight of the overlying rock. Sed rock overlies igneous and metamorphic crystalline basement rock(low poros
The subsurface zone in which all rock openings are filled with water is called the saturated zone.
If a well were drilled downward into this zone, groundwater would fill the lower part of the well. THe water level inside the well marks the upper surface of the saturated zone; this surface is the water table.
The water level at the surface of most lakes and rivers coincides with the water table
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Above the water table is a zone where not all the sediment or rock openings are filled with water. THis is the unsaturated zone.
Within this zone, surface tension causes water to be held above the water table. The capillary fringe is a transition zone with higher moisture content at the base of the unsaturated zone just about the water table.
Sediments
gravel
25 to 40 percent porosity
permeability is excellent
Sediment - sand
porosity- 30 to 50
permeability- good to excellent
sediment- silt
por- 35 to 50
per- moderate
sediment- clay
por- 35 to 80
per- poor
sediment- glacial till
por- 10 to 20
per poor/moderatel
Rock conglomerate
por is 10 to 30
per- moderate to excellent
sandstone
wellsorted, little cements
average
poorly sorted, well cemented
per 20 to 30
10 to 20
0 to 10
per is good to very good
moderate to good
poor to moderate
shale
0 to 30
very poor to poor
limestone, dolomite,
cavernous limeston
0 to 20, up to 50
poor to good; excellent
crystalline rock
unfractured, frac
0 to 5, 5 to 10
poor
volcanic rock
0 to 50, poor to excellent
A perched water table is the top of a body of ground water separated from the main water table beneath it by a zone that is not saturated.
groundwater collects above a lens of less permeable shale within a more permeable rock(like sandstone). If the perched water table intersects the land surface, a line of springs can form along the upper contact of the shale lens. The water perched above a
Most groundwater moves relatively slow through rock underground. Groundwater moves in response to differences in water pressure and elevation, causing water within the upper part of the saturated zone to move downward with the slope.
Ground water may move hundred of meters vertically downward due to combined effects of gravity and the slope of the water table
The slope of the water table strongly influences ground water velocity. Steeper the slope, the faster the groundwater moves. Water table slope is controlled largely by topography- the water table roughly parallels the land surface.
How fast groundwater flows depends on the permeability of rock and other materials through which it passes. Permeable materials, such as unconsolidated gravel or cavernous limestone.
An aquifer is a body of saturated rock or sediment through which water can move easily.
Highly permeable and saturated with water. Good: sandstone, conglomerate, well jointed limestone, bodies of sand and gravel, volcanic rock such as columnar basalt. Shall usually impermeable. Wet mud has porosity of 80 to 90. Crystalline rocks(not very por
Unconfined aquifer- has a water table because it only partly filled with water and a confined aquifer is completely filled with water under pressure and is usually separated from the surface by impermeable confining bed or aquitated such as shale.
Unconfined awuifer is recharged by precipitation. Confined aquifer is recharged slowly through shale beds; may have no response to wet or dry seasons.
Well is a deep hole, that is dug or drilled into the ground to penetrate an aquifer within the saturated zone.
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The addition of new water to a saturated zone is called a recharge. WHen water is pumped from a well, the water table is drawn down around the well into a depression shaped like an inverted cone known as a cone of depression, and tends to chance the direc
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In unconfined aquifers, water rises in shallow wells t the level of the water table. In confined aquifers, the water is under pressure and rises in wells to a level about the top of the aquifer.
Such as a well is called an artesian well, and confined aquifers are also called artesian aquifers. In some artisan wells, the water rises about the land surface, producing a flowing del that spouts continuously into the air unless its capped.
Spring is a place where water flows naturally from rock onto the land surface.
Climate determines the relationship between stream flow and the water table. In rain regions, most streams are gaining streams; they receive water from the saturated zone. in dry climates, rivers tend to be losing streams and they are losing water to the
Contamination of groundwater
Because its a widely used source of drinking water, the contamination of groundwater can be very serious problem
Pesticides and herbicides(diazinon, atrazine, DEA, 2-4D)- applied to crops and find their way into groundwater when water leaches the contaminants downward into the soil. Fertilizers like nitrate- harmful
Rain can leach pollutants from city landfills into groundwater supplies. Heavy metals(mercury, lead, chromuim, copper, cadmium) can poison groundwater supplies. Great concern to old landfills because new landfills are engineers with impermeable layers of
Soil and rock filter contaminates out of groundwater. Filtering capability depends on the permeability and mineral composition of rock and soil. Sewage is cleaned by the absorption of clay minerals and humus(decomp by soil organism in the biosphere)
Contaminated groundwater is extremely difficult to clean up. Heavily pumped wells near coast can be contaminated by saltwater intrusion- becoming a serious problem as the demand for drinking water increases in coastal communities.
Balancing Withdrawal and recharge- a local supply of groundwater will last indef if its withdrawn for use at a rate equal to or less than the rate of recharge. Groundwater is withdrawn faster than being recharged; so it will one day be gone.
As water is withdrawn the ground surface may settle because the water is no linger supporting the rock and sediment. Subsidence- can crack buildings, roads, pipelines. Overpuming of groundwater causes compaction and porosity loss in rock and soil, and can
Effects of groundwater
caves, sinkholes, karst topography
Caves are naturally formed underground chambers. Develop when slightly acidic groundwater dissolves limestones along joints and bedding planes, opening up cavern systems as calcite is carried away in solution. Natural groundwater is commonly slightly acid
Most caves are formed by groundwater circulating below the water table. Geologist disagree where caves are formed.
Deposits of calcite built up in caves by dripping water are called dripstones, or speleothems.
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Stalactites are iceclelike pendants of dripstones hanging from the cave ceilings.
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Stalagmite are cone shaped masses or dripstones formed on cave floors, usually directly below stalactites. Usually thicker that stalactites. They may grow to eventually form a column.
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In some caves, water flows in a think dilm over the cave surfaces instead of dripping from the ceiling. Sheetlike or ribbonlike flowstone deposits develop from calcite that is precipitated by by flowing water on cave floors and walls.
Floors of most caves are covered with sediment- residual clay- fine grained particles left behind as insoluble reside when a limestone containing clay dissolves.
Sinkholes are closed depressions found on land surfaces underlain by limestone.
They form either by the collapse of a cave roof or by solution as descending water enlarges a crack in limestones. Sinkholes - limestones; underlain by gypsum or rock salt - soluble in water.
Karst Topography- an area with many sinkholes and cave systems beneath the land surface. these areas are characterized by a lack of surface streams.
Streams sometimes disappear down sinkholes to flow through caves beneath the surface - A true underground stream exist. Rare.
Other effects- petrified wood, develops when porous buried wood is either filled in or replaced by inorganic silica carried in by groundwater.
Result is a hard permanent rock commonly preserving the growth rings and other details of the wood. Calcite or silica cared by groundwater can also replace the original material in marine shells and animal bones.
Sedimentary rock cement(silica or calcite) is carried into place by groundwater. When a considerable amount of cementing material precipitates locally in a rock, a hard rounded mass called a concretion develops, typically around an organic nucleus such as
Ge
Geodes are partly hollow, globe shaped bodies found in some limestones and locally in other rocks. Outer shell is amorphous silica, well formed crystals of quartz, calcite, and other mineral.
Origin of geodes is complex byt clearly related to groundwater. Crystals in geodes may have filled original cavities or have replaced fossils or other crystals.
In arid or semiarid climates, alkali soil may develop because of the precip of great quantitie
Hot water underground- Hot springs are spring in which the water is warmer than human body temperature. Gains heat by 1)groundwater may circulate near a magma chamber or a body of cool igneous rock. 2) unusually deep in the earth(sulphur springs,
Geyser is a hot spring that periodically erupts hot water and steam.
Hot groundwater comes to the surface and cools, it may precipitate some of its dissolved ions as minerals. Travertine is a deposit of calcite and often forms around hot springs, while dissolved silica precipitates as sinter(geyserite when deposited by a g
Sinter high temp than travertine. Mudpot is a special type of hot spring that contains thick, boiling mud. Usually marked by small amounts of water and strongly sulfurous gases
Geothermal Energy- harnesed naturally occuring stream and hot water in areas that are hot underground.
Geothermal areas- tap stream, piped to powerstream, turns a turbine that spins a generator.
Problems- workers need protection from toxic hydrogen sulfide gas. ions such as mercury and lead.
15% of water that falls to earth goes underground to become ground water
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Porous rock=rocks can hold water
Permeable rock= rocks that permit water to pass through them
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The water table is the top surface of the saturated zone and is overlain by the unsaturated zone.
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Groundwater velocity depends on rock permeability and the slope of the water table.
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An aquifer is porous and permeable, and can supply water to wells. A confined aquifer holds water under pressure, which can create an artesian well.
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Gaining streams, springs, and lakes form where the water table intersect the land surface. Losing streams contribute to the groundwater in dry regions.
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Groundwater can be contaminated by city landfills, agriculture, industry, sewage disposal.
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A pumped well causes a cone of depression.
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Artificial recharge can held create a balance between withdrawal and recharging.
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Solutions of limestone by groundwater forms caves, sinkholes, and karst topography. Calcite precipitating out of groundwater forms speleothems such as stalactites and stalagmites in caves.
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Precipitation of material out of solution by groundwater helps form petrified wood, other fossils, sedimentary rock cement, concretions, geodes, and alkali soils.
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Geysers and hot springs occur in regions of hot groundwater. Geothermal energy can be tapped to generate electricity.
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Porosity
The percentage of a rocks volume that is openings
Permeability
the capacity of rock to transmit a fluid
The subsurface zone i which all rock openings are filled with water is called the
saturated zone
An aquifer is
a body of saturated rock or sediment trhough which water can move easily.
What rock would make the best aquifer? shale, mudstone, or sandstone
sandstone
Which of the following determines how quickly groundwater flows
elevation, water pressure, and permeability.
Groundwater flows
from areas of high hydraulic head to low hydraulic head
The drop in the water table around a pumped wll is the
drawdown.
Mass Wasting
The movement in which bedrock, rock debris, or soil moves downslope in bulk, or as a mass, because of the pull of gravity.
Mass Wasting includes movement so slow that its called creep, as well as landslides(term for slow very rapid descent of rock or soil).
Mass Wasting effect people in many ways. Anything from devastating effects to a fence being pulled apart by a soil creep. More people died from landslides in 3 months of 1985 than in the past 20 years from other geologic hazards.
Type of flow - creep(soil), earthflow, debris flow, mudflow, debris avalanche, rock avalanche(bedrock)
Slide- debris slid or earth slide/rockslide
fall- landslides, and rockfall(bedrock).
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Classification of mass wasting- based on the rate of movement, type of material, and nature of the movement.
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Rate of movement- movement of soil at a rate of less than a cm a year is slow movement.
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type of material - mass wasting processare are usually distinguished on the basis of whether the descending mass started as bedrock.
Any unconsolidated or weakly consolidated material at which the earths surface- soil. (can be debris, earth, or mud).
Debris implies that coarse grained fragements predominate in the soil.
Fine grained (sand, silt, clay) is called earth
Mud- high content
type of movement
Flow implies that the descending mass is moving downslope as a viscous fluid.
Slide means the descending mass remains relatively intact, moving along one or more well defined surfaces.
A fall occurs when material free falls or bounces down a cliff.
In a t
Controlling Factors in mass wasting- summarizes the factors that influence the likelihood and the rate of movement of mass wasting.
1. slope were exceptionally steep. 2the relief(the vertical distance between valley floor and men summit). thickness of soil over bedrock, orientation of planes of weakness in bedrock. Climatic factors- ice in gruond, water in soil, waer in soil or debris
Gravity- the driving force for mass wasting is gravity.
normal force is perpendicular to the slope and is the component of gravity that tends to hold the block in place.
Shear force- is parallel to the slope and indicates the blocks ability to move.
Shear resistance is the force tht would be needed to move the
Water is a critical factor in mass wasting. When soil is saturated with water, it becomes less viscous and more likely to fowl downslope. Added gravitation shear force from increased weight is usually less important than the reduction in shear strength. T
Loose grains adhere to one another because of the surface tension created by the film of water(added there when water doesn't completely fill the pore spaces between the grains of soil), is what allows you to build a sand castle. IF sand is too wet, it me
Triggers- a sudden event may trigger mass wasting of a hillside that is unstable. Movement would occur without the trigger if conditions slowly becomes more unstable
Earthquakes-commonly trigger landslides. Landslides often are triggered by heavy rainfall.
Common types of mass wasting
Creep(or soil creep) is a very slow downslope movement of soil. Shear forces over time, are only slightly greater than shear strengths. usually less of cm per year. Two factors that contribute to creep are water in the soil and daily cycles of freezing an
Flow occurs when motions is taking place within a moving mass of unconsolidated or weakly consolidated material. Grains move relative to adjacent grains or motion takes place along closely spaces, discrete fracutrs. Varieties of flow- earth flow, debris f
E
Earthflow, earth moves downslide as a viscous fluid the process can be slow or rapid. Usually occur on hillsides.
Flowing mass remains covered by a blanket of vegetation, with a scarp(steep cut) developing where the moving debris has pulled away from the upper slope.
Rotational sliding(slumping) takes place about the earth flow(soil particles moving past one another
One variety of earth flow is usually associated with colder climates. Solifluction is the flow of water saturated soil over impermeable material. Because the impermeable material beneath the soil prevents water from draining freely, the soil between the v
The impermeable material beneath the saturated soil can be either impenetrable bedrock- permafrost, ground that remains frozen for many years. Permafrost is a zone that if the soil is saturated is frozen during the winter and indistinguishable from the un
Solifluction is not the only hazard associated with permafrost. Areas become swampy in summer due to permafrost like in the arctic and subartic regions.
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Debris and Mudflow.
A debris flow is a flow involving soil in which coarse material \(gravel, boulders) is predominant. A debris flow can be like an earth flow and travel relatively short distances to the base of a slope.
Mudflow is a flowing mixture of soil and water, usual
Debris Avalanche
The fastest variety of debris flow is this; its rapidly moving, turbulent mass of debris, air, water.
Rockfalls and Rockslides.
When a block of bedrock breaks off and falls freely or bounces down a cliff- rockfall. bedrock-crakcs(joints) and other planes of weakness such as foliations(met rock), or sedimentary bedding planes. Commonly oan apron of fallen rock fragments called talu
A rock slides is the rapid sliding of a mass of bedrock along an inclined surface of weakness, such as a bedding plane, a major fracture int eh rock or a foliation plane.
A rock avalanche is a very rapidly moving turbulent mass of broken up bedrock. Flowage on a grand scale. Only difference between a rock avalanche and a debris avalanche is that a rock avalanche begins its journey as bedrock. Rockslide or rock As come to r
Underwater landslides- the steeper parts of the ocean floors sometimes have landslides.
Underwater debris avalanche- turbidity current.
Preventing landslides- mass movement of soil usually can be prevented.
Construction generally makes a slope more susceptible to mass wasting of soil in several ways.
-the base of the slope in undercut, removing the natural suppose for the upper part of the slope
-vegetation is removed during construction
-buildings construct
Preventing Rockfalls and Rockslides on Highways
planes of weakness are inclined into the hill, there is no chance of a rockslide. rockslide may occur where the planes of weakness are approx parallel to the slope of the hillside.
Various techniques are used to prevent rockslides- detailed geological stu
Mass Wasting is the movement of a mass of soil or bedrock toward the base of a slope.
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Soil is unconsolidated or weakly consolidated material regardless of particle size.
Soil=predominantly fine material; its earth.
Predominately coarse; its debris
Movement can take place as a flow, slide, or fall. Gravity is the driving force.
Components of gravitational force that propels mass wasting is the shear force, which occurs parallel to a slope. The resistance to that force is the shear strength of a rock or soil. If shear force exceeds shear strength, mass wasting takes place. water
Number of other factors determine whether movement will occur and what type.
Creep- occurs relatively gentle slopes, usually aided by water by soil. Colder climates- repeated thawing and freezing of water within the soil contributes to creep.
Landslides- more rapid mass wasting of rock, soil, or both,.
Flows- earthflows, debris flow, mudflows, and debris avalanche.
Earth flows- finer grained material is predominant.
debirs avalanche(more rapid)- turbulant masses of debris, water, and air.
Solifluction- special variety of earth flow, takes place in arctic, where ground is permanently frozen(permafrost)
Debris Flow involves coarse material that is present in earthflow.
Mudflow-slurry of mostly clay, silt and water.
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rockfall- the fall of broken rock down a vertical or ner vertical slope.
rockslide- slab of rock sliding down a less than vertical surface.
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What is the slowest type of mass wasting process?
debris flow, rockslide, creep, rockfall, avalanche
creep
the largest landslide has taken place
on the sea floor
a descending mass moving downslope as a viscous fluid is referred to as
flow
the driving force behind all mass wasting processes
gravity
the resistance to movement or deformation of soil is its
shear strength
Flow of water saturated soil over impermeable material is called
solifluction
A flowing mix of soil and water, usually moving down a channel
mudflow
an apron of fallen rock fragments that accumulates at the base of a cliff is
talus
How does construction destabilize a slope
addes weight to the top of the slope
How can landslides be prevented during construction
retaining walls, vegetations, install water drainage pipes.
When rocks that formed deep in Earth become exposed at the Earth's surface, they are altered by what?
mechanical and chemical weathering
The processes that affect rock are
weathering, erosion, and transportation
Weathering
refers to the processes that change the physical and chemical character of rock at or near the surface.
Weathering breaks down rocks that are either stationary or moving.
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Erosion
The picking up or physical removal of rock particles by an agent such as running water or glaciers. Weathering helps break down a solid rock into loose particles that are easily eroded.
After a rock fragment is eroded, it is then transported.
Transportation is the movement of eroded particles by agents such as rivers, waves, glaciers, or wind.
Weathering and Earth Systems -
Atmosphere, Hydrosphere, and Biosphere.
Atmosphere.
Oxygen and Carbon dioxide are important for chemical weathering. Water (evaporated from the hydrosphere and distributed as moisture, rain and snow) is critical to both chemical weathering and mechanical weathering.
Weathering has a dramatic impact on the composition of Earth's atmosphere. Chemical weathering removes carbon dioxide from the atmosphere, allowing it to be transformed into limestone and stored in the crust. Without chemical weathing, the elevated levels
Hydrosphere - Water is necessary for chemical weathering to occur. Oxygen dissolved in water oxidizes iron in rocks.
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Carbon dioxide mixed with water makes a weak acid that causes most minerals to decompose this acid is the primary cause of chemical weathering.
Running water contributes to weathering and erosion by loosening and removing particles and by abrading rocks during transportation in streams. Freezing and thawing of water in cracks in rock is very effective at mechanical breaking them up.
Biosphere. Plants can physically break apart rocks when they grow in cracks. When plants and animals decompose , they become mostly carbon dioxide. While carbon dioxide dissolved in rain makes the water slightly acidic, soil water is much more acidic due
Soil is formed by weathering and includes organic matter from decayed plants. Organic carbon compounds and minerals released by weathering provide the nutrients required for plant growth.
Mechanical Weathering (physical disintegration)
This includes several process that break rock into smaller pieces. The change is rock is physical; there is little or no chemical change. Example: Water freezing and expanding in cracks cause rocks to disintegrate physically.
Chemical Weathering
The decomposition of rock from exposure to water and atmospheric gases (principally carbon dioxide, oxygen, and water vapor). As rock is decomposed by these agents, new chemical compounds form.
Mechanical Weathering breaks up rock but does not change the composition.
A large mass of granite may be broken into smaller pieces by frost action, but its original crystals of quartz, feldspar, and ferromagnetism minerals are unchanged.
If granite is chemically weathered, some of the original minerals are chemically changed into different minerals.
Feldspar will change into a clay mineral (with a crystal structure similar to mica).
The effects of chemical and mechanical weathering are interrelated because they both usually occur at together.
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Weathering is a long and slow process.
Typically cracks in rocks are caused by frost acton or plant growth, and as a result more surfaces are exposed to attack by chemical agents.
Chemical weathering initially works along contacts between mineral grains. Tightly bound crystals are loosened as weathering products form at their contacts.
Solid minerals are not the only products of chemical weathering. Calcite dissolves when chemically weathered.
Look along the edge or corners of old stones structures for evidence. Like if the inscriptions on statues or gravestones may no longer be sharp
Building blocks of limestone or marble exposed to rain and atmospheric gases may show solution effects of chemical weathering. Granite and slate gravestones and building materials are much more resistant to weathering due to the strong silicon-oxygen bond
After centuries, the grains in granite may be loosened, cracks enlarged, and the surface discolored and dulled by the products of weathering.
Surface discoloration is also common on rocks outcrops, where rock is exposed to view with no plant or soil to cover. (Geologists carry rock hammers to break rocks to examine unweathered surface).
As rock is destroyed through weathering, valuable products are produced.
Soil is produced by rock weathering, so most plants depend on weathering for the soil they need in order to grow. In a sense, all agriculture depends on weathering.
Weathering products transported to the sea by rivers as dissolved solids make seawater salty and serve as nutrients for many marine organisms.
Some metallic ores, such as those of copper and aluminum, are concentrated into economic deposits by chemical weathering.
Spheroidal Weathering occurs where rock has been rounded by weathering from an initial blocky shape.
Its rounded because chemical weathering acts more rapidly or intensely on the corners and edges of a rock than on the smooth rock faces.
Differential weathering describes the tendency for different types of rock to weather at different rates.
Shale (composed of soft clay minerals) tends to weather and erode much faster than sandstone (composed of hard quartz mineral). [Layers of resistant rock tend to weather to form steep cliffs while soft layers form shallow slopes of eroded rock debris].
The reduction of pressure on a body of roc can cause it to crack as it expands; pressure release is a significant type of mechanical weathering.
A large mass of rock(batholith) originally forms under great pressure from the weight of several kilometers of rock above it. This batholith is gradually exposed by tectonic uplift of the region followed by erosion of the overlying rock.
The removal of the great weight of rock about the batholith, usually unloading, allows the granite to expand upward.
Cracks called Sheet Joints develop parallel to the outer surface of the rock as the outer part of the rock expands more than the inner part.
Frost Action
the mechanical effect of freezing water on rocks- commonly occurs at frost wedging or frost heaving.
Frost Wedging
The expansion of freezing water pries rock apart. Most rock contains a system of cracks called joints, caused by the slow flexing of brittle rock by deep seated Earth forces. Water that has trickled into a joint in a rock can freeze and expand when the te
The expanding ice wedges the rock apart, extending the joint or even breaking the rock into pieces.
Frost wedging is most effective in areas with many days of freezing and thawing (mountain tops). Partial thawing during the day adds new water to the ice in the crack; refreezing at night adds new ice to the old ice.
Frost Heaving
Lifts rocks and soil vertically. Solid rock conducts heat faster than soil, son on a cold winter day, the bottom of a partially buried rock will be much colder than soil at the same depth.
As the ground freezes in winter, ice forms first under large rock fragments in the soil. The expanding ice layers push boulders out of the ground.
Frost heaving bulges the ground surface upward in winter, which can often break roads and leave lawns spongy and misshaped after the spring thaw.
Other processes- several other processes mechanically weather rock (but are usually less effective than frost action and frost heaving).
Plant growth-roots growing in cracks can break up rocks, as can burrowing animals. Such activities help to speed up chemical weathering by enlarging passageways for water and air. Extreme temperature change(like in a forest fire or the desert) can cause a
Types of Mechanical Weathering
pressure release, frost action, and frost heaving are the most effective. Others include, plant growth, burrowing animals, extreme changes in temperature, and the pressure of salt crystals.
Chemical Weathering (rock decomposition) transform rocks and minerals exposed to water and air into new chemical compounds.
The new minerals are weathering products. They have adjusted to physical and chemical conditions at or near Earth's surface. Minerals change gradually at the surface until they come into equilibrium(balance) with the surrounding conditions.
Role of Oxygen: Oxygen is abundant in the atmosphere and quite active chemically, so it often combines with minerals or with elements within mineral that are exposed at Earth's surface.
An example of chemical weathering - the rusting of an iron nail exposed to air. Oxygen from the atmosphere combines with the iron to form iron oxide. Iron oxide formed in this way is a weathering product of numerous mineral containing iron, such as the fe
hematite is the mineral that is formed from the iron oxide (brick red color when powdered). If water is present, hematite combines with water to form limonite (mostly amorphous, hydrated iron oxides, which also includes the mineral goethite; yellow/brown
The brown, yellow, or red color of soil and many kinds of sedimentary rock is commonly the result of small amounts of hematite and limonite released by the weathering of iron containing minerals.
Role of Acids: The most effective agent of chemical weathering is acid.
Acids are chemical compounds that give off hydrogen ions when they dissociate, or break down, in water. Strong acids produce a great number of hydrogen ions; weak acids produce relatively few ions.
The hydrogen ions given off by natural acids disrupt the orderly arrangement of atoms within most minerals.
These ions have a positive electrical charge, and can substitute for other positive ions. The substitution changes the chemical composition of the mineral and disrupts its atomic structure. The mineral decomposes, often into a different mineral, when its
Some strong acids occur naturally on Earths surface, but they are relatively rare.
Sulfuric acid is a strong acid emitted during many volcanic eruptions. It can kill trees and cause intense chemical weathering of rocks near volcanic vents. Strong acids also drain from some mines as sulfur containing minerals such as pyrite oxidize and f
The most important natural source of acid for rock weathering at Earths surface is dissolved Carbon dioxide in water.
Water and carbon dioxide form carbonic acid, a weak acid that dissociates into the hydrogen ion and the bicarbonate ion. Even though carbonic acid is a weak acid, it is so abundant at Earths surface, that it is the single most effective agent of chemical
Earths atmosphere(mostly nitrogen and oxygen) contains .03 carbon dioxide. Some of this carbon dioxide dissolves in rain as it falls, so most rain is slightly acidic when it hits the ground.
Large amounts of carbon dioxide dissolve in water that percolates through soil. The openings in soil are filled a gas mixture that differs from air. Soil has a much more higher content of carbon dioxide(10%) than does air, because carbon dioxide is produc
Solution weathering: Some minerals are completely dissolved by chemical weathering. Calcite foes into solution when exposed to carbon dioxide and water.
The carbon dioxide and water combine to form carbonic acid, which dissociates into the hydrogen ion and the bicarbonate ion. Rain can discolor and dissolve statues and tombstones carved from the metamorphic rock marble, which is mostly calcite.
Chemical Weathering of Feldspar- the weathering of feldspar is an example of the alteration of an original mineral to an entirely different type of mineral as the weathered product.
When feldspar is attacked by the hydrogen ion of carbonic acid (from carbon dioxide and water), it forms clay minerals.
Clay Mineral is a hydrous aluminum silicate with a sheet-silicate structure like that of mica. The entire silicate structure of the feldspar crystals is altered by weathering.
Feldspar is a framework silicate, but the clay mineral product is a sheet silicate, differing both chemically and physically from feldspar.
K-feldspar forms potassium ions. Na-feldspar and Ca-feldspar (plagioclase) form sodium ions and calcium ions.
The ions that result from the weathering of Ca feldspar are calcium ions and bicarbonate ions, both of which are very common in rivers and underground water.
Chemical weathering of other minerals. The weathering of ferromagnesian or dark minerals is much the same as that of feldspar. Two additional products are found on the right side of the equations - magnesium and iron oxides (hematite, limonite, and geothi
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The susceptibility of the rock forming minerals to chemical weathering is dependent on the strength of the minerals chemical bonding within the crystal framework.
Because of the strength of the silicon oxygen bond, quartz is quite resistant to chemical weathering. Quartz is the rock forming mineral least susceptible to chemical attack at Earths surface.
Ferromagnesian minerals such as olivine, pyroxene, and amphibole include other postiviely charged ions such as Al, Fe, Mg, and Ca. The presence fo these positively chargend ions int eh crystal framework makes these minerals vulnerable to chemical attack d
Olivine weathers rapidly because its isolated silicon oxygen tetrahedra are held together by relatively weak ionic bonds between oxygen and iron and magnesium.
Weathering and Diamond Concentration. Diamond is the hardest mineral known and is also extremely resistant to weathering because of the very strong covalent bonding of carbon.
Diamonds are concentrated by weathering. Diamonds are brought to Earths surface in kimberlite pipes, columns of brecciated or broken ultramafic rock that have risen from the upper mantle. Diamonds are widely scattered in diamond pipes where they form.
Weathering Products.
Look at powerpoint. Notes: Calcite and silica are the most common materials precipitated as cement, which binds loose particles of sand silt, and clay into solid sedimentary rock.
Factors affecting weathering. The intensity of both mechanical and chemical weathering is affected by a variety of factors.
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Chemical weathering is largely a function of the availability of liquid water. Rock chemically weathers much faster in humid climates in arid climates.
Limestone- (extremely susceptible to dissolution) weathers quickly and tends to form valleys in wet regions. In arid west, limestone is a resistant rock that forms rebids and cliffs. Temperature is also a factor in chemical weathering. The most intense ch
Mechanical Weathering intensity is also related to climate (temperature and humidity) as well as to slope.
Temperature climates where abundant water repeatedly freezes and thaws, promote extensive frost weathering. Steep slopes cause rock to fall and break up under the influence of gravity. Most intense mechanical weathering occurs in high mountain peeks (comb
Soil. Soil forms an essential interface between the solid Earth (geosphere), biosphere, hydrosphere, and atmosphere.
Regolith-loose, unconsolidated material that covers most of Earths surface. Soil is a layer of weathered, unconsolidated material that contains organic matter and is capable of supporting plant growth. A mature and fertile soil is the product of centuries
An average soil is composed of 45% rock and mineral fragments(clay), 5% decomposed organic matter(humus) and 50% pore space.
The rock and mineral fragment proved an anchoring place for the roots of plants. Clay minerals attract water molecules and plant nutrients ions. The humus releases weak acids that contribute to chemical weathering of soil; also produces plant nutrients an
(the size and number of pore space-meaning the ability of a soil to transmit air and water- are largely a function of the texture of soil.
Soil texture refers to the proportion of different sized particles, generally referred to as sand, silt and clay. Quartz generally weathers into sand grains that help keep soil loose and aerated, allowing good water drainage. Partially weathered crystals
Silt particles are between clay and sand in size. A soil with approximately equal parts sand,silt,and clay is called a loam.
Loamy soils are well drained, may contain organic matter, and are usually very fertile and productive.
Soil Horizons: O, A, E, B, C.
Soil Horizons are soil layers.
Topsoils are O and A. Then E. Subsoils are B. Then there is C. and after that, unweathered parent material.
The O horizon.
The uppermost layer that consist entirely of organic material. Ground vegetation, recently fallen leaves and needles, and decomposed plant material(humus) make up this horizon. The humus mixes with weathered mineral matter just below to form the A horizon
The A horizon.
A dark colored soil layer that is rich in organic matter and high in biological activity, both plant and animal. The two uppermost horizons are called Topsoils.
Organic acids and carbon dioxide produced by decaying plants in the topsoil percolate down into the E horizon, Zone of leaching, and help dissolve minerals such as iron and calcium.
The downward movement of water in the E horizon carries dissolved minerals, and fine grained clay minerals into the soil layer below. This leaching(eluviaton) of clay and soluble mineral can make the E horizon pale and sandy.
The material leached downward from the E horizon accumulates in the B horizon, zone of accumulation.
This layer is quite clayey and stained red or brown by hematite and limonite. Sometimes calcite. Subsoil. With this horizon, a hard layer of earth material called hardpan may form in wet climates where clay minerals, silica, and iron compounds have accumu
The C horizon.
incompletely weathered parent material that lies below the B horizon. The parent material is commonly subjected to mechanical and chemical weathering from frost acton, plant acids, roots and other agents. This horizon is transitional between the unweather
Factors Affecting Soil Formation: Most soil takes a long time to form. The rate of soil formation is controlled by rainfall, temperature,slope, and the type of rock that weathers to form soil.
-Parent Rock. Additional factors include slope, living organisms, climate, time.
Parent Rock
Is the source of the weathered mineral matter that makes up most of a soil.
Granite will be sandy and as sand sized particles of quartz and feldspar are released from the granite.
Feldspar grains weather completely, fine grained clay minerals are formed.
The fine grained feldspars in the basalt will weather directly to fine grained minerals. Since the parent rock had no coarse grained minerals and no quartz to begin with, the resulting soil may lack sand. Such soil may not drain well, although it can be q
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Residual and Transported Soil.
Residual Soils develop from weathering of the bedrock beneath them. Transported soils do not develop from locally formed rock but from regolith brought in from some other region(That its not the soil itself that is transported but the parent material from
Slope
The slope of the land surface provides an important control on the formation of soil. Soils tend to be thin or nonexistent on steep slopes, where gravity keeps water and soil particles moving downhills. Vegetation is sparse on steep slopes(there aren't ma
Living organism
The biosphere plays an important role in soil development. The chief function of living organisms is to provide organic material to the soils. Decomposing plants form humus, which supplies nutrients to the soil and aids in water retention. Decaying plant
Climate- the most influential fact affecting sol thickness and character.
Temp and precipitation-determine whether chemical or mechanical weathering processes will dominate and strongly influence the rate and depth of weathering. Also determines amount and type of vegetation and animal life.
Soils in most climates tend to be thick and are generally characterized by downward movement of water through earths materials.
These soils tend to be fertile and have a high content of aluminum an iron oxides and well developed horizons. Marked by downward leaching due to high rainfall and to the acids produced by decay of humus.
Arid climate's soils are thin and are characterized by little leaching, scant humus, and the upward movement of soil water beneath land surface.
Salts are precipitated within the soil. Sand buildup within in the soil can be found in the desert alkali soils, heavily toxic sodium salts that prevent plant growth.
Tropical rain forests- the high temperature and rainfall combine to form extremely thick red soils called oxisols, or laterites.
That are highly leached and infertile.
Time- the character of soil changes with time.
Soil that has been weathering for a short time, the characteristics are largely determined by the parent material. Young soils can retain the structure of the parent material. In the long term, the only characteristic of the parent rock to have significan
Soil Erosion- Soil accounts for an almost insignificant fraction of ll earth materials, its one of the most significant resources in terms of its effects on life.
Soil provides nourishment and physically supports human existence. Soil is abused and the earth has lost 10% of its productive value.
How soil erodes- Soil particles are small and easily eroded by water and wind.
Splash erosion- raindrops strike unprotected soil and dislodge the soil particles. As rain continues, thin sheet of running water forms over the landscape, carrying the dislodged particles away(sheet erosion). Currents hat form in the sheet of water cut t
Rate of erosion. Influenced by soil characteristics, climate, slope, and vegetation and type of rainfall.Coarse grained soils with organic content tend to have larger pore spaces and can absorb more water.
fast moving water does not infiltrate and has a greater ability to dislodge and transport soils particles down from the slope. Plant roots form networks. Thick vegetation reduces wind velocity.
Consequences of erosion.
A lot of the areas effected by erosion can not support life as they once would. This essential resource is what the base of all life rests.
Soil Classification- different types of soil could form on the same underlying rock.
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Alfisols
Gray to brown surface horizon. Clay accumulation. med to high in plant nutrient ions. Humid forests. CF- climate and organisms
Andisols
Formed in volcanic ash. CF are parent material.
Aridisols
Dry climates, low in organic matter. Having horizons of carbonate, gypsum and salt. CF are climate
Entisol
no horizon due to young age of parent material or constant erosion. CF are time and topography.
Gelisols
weakly weathered soils with permafrost within 2 meters of the surface. CF is climate
Histosols
wet, organic soils with little mineral material. swamps or marshes. CF is topography.
Inceptisols
young soils that have weakly developed horizons and little/no subsoil clay accumulation. CF time and climate
Mollisols
black surface horizon rich in organic matter and plant nutrient ions. subhumid to semiariad midlat grasslands. CF are climate and organisms.
Oxisols
heavily weathered soils low in plant nutrient ions, rich in aluminum and iron oxides, humid tropical climates- also called late rites. CF time and climate
Spodosols
acid soils low in plant nutrients ions. accumulation of humus (aluminum and iron). cool humid pine forests - sandy parent material . CF parent material, organism, and climate
ultisols
strongly weathered soils low in plant nutrients ions with clay accumulation. humid temp and tropical acid forest environments. CF are climate time and organisms
vertisols
clayey soils that swell when wet and shrink when ry. deep cracks. CF parent material
Physical disintegration of rock into smaller pieces is called
mechanical weathering
The decomposition of rock from exposure to water and atmospheric gases is called
cw
which is not a type of mechanical weathering: frost wedging, pressure release, frost heaving or oxidation
oxidation
most effective agent of chemical weathering at earths surface is
carbonic acid, h2co3
most common end product of the chemical weathering of feldspar
clay minerals
most common end product of the chemical weathering of quartz is
quartz dos not usually weather chemically.
Soils with approx equal amounts of sand, silt, and clay along with a generous amount of organic matter is
loam
The soil horizon containing only organic materail is
O
Hardspan forms in the
b