Download UNIT 2 INTERNAL ENERGY AND LANSFORMS The movement of

UNIT 2 INTERNAL ENERGY AND LANSFORMS
The movement of plates generates forces that deform and change rocks.
1. Compressional stress is caused by convergent forces and squeezes an object.
2. Tensional/extensional stress is caused by divergent forces and stretches an object.
3. Shear stress is caused by parallel forces (convergent and divergent) and tears an object.
FAULTS are fractures in the rocks on the earth’s surface that have
displaced, and are caused when tectonic forces are greater than
rocks’ resistance.
Parts of the fault:
 Fault plane
 Throw: distance between the top of a footwall block and
the top of a hanging wall block.
 Striae: scratches or grooves on a rock.
 Footwall block
 Hanging wall block.
Types of faults:
1. Dip-slip faults: vertical movement.
 Normal faults: the hanging wall block moves down relative to
the footwall block due to divergent forces.
 Reverse faults: the hanging wall block moves up relative to the
footwall block due to convergent forces.
 Vertical fault: (not in the pictures) the fault plane is vertical.
2. Strike-slip faults: horizontal movement.
 Left lateral/ sinistral tear fault: the far side moves to the left.
 Right lateral/dextral tear fault: the far side moves to the right.
FOLDS are created when rocks deform due to compressional forces,
but instead of breaking, they bend.
Parts of a fold:
 Hinge is the place where the fold angle is bigger.
 Axial plane is the imaginary line that shows us the angle of a
fold.
Folds according to:
1. Curvature:
 Anticline
 Syncline
 Neutral
2. The angle of the axial plane.
 Symmetrical
 Inclined
 Overturned
 Recumbent.
THE ROCK CYCLE: rocks are made up of pre-existing rocks that had undergone processes that
had changed them. This processes can be external (form exogenous rocks such as sedimentary
rocks) or internal (form endogenous rocks like igneous or metamorphic rocks)according to the
energy source that generates them.
Weathering: rocks break up due to
temperature and external agents.
Erosion: loosen pieces of rock move.
Transportation: sediments are
transported to rivers and finally to
seas.
Sedimentation: deposition of
materials transported by air, water
and ice.
Diagenesis: the process of
compactation and formation of
sedimentary rocks.
Metamorphism: the change of
minerals composition, geological
texture due to great heat and
pressure.
Igneous rocks can be extrusive (if they are crystallized in the exterior of the Earth) or intrusive
(if they have crystallized in the interior of the Earth).
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FORMATION OF MAGMA/ MAGMATISM: from the internal heat and pressure inside the
Earth. Magma can be formed because of :
A rise in temperature produced by friction, contact with a heat surface or presence of
radioactive substances.
A drop in pressure (the melting point is caused when pressure of rocks is equal to the
atmospheric pressure). An example is the one in mid-ocean ridges, where the presence of
fractures and the thinning of the lithosphere reduce the pressure on the rocks. Other example
is in hot spots, where less dense material rises towards the surface where pressure drops.
The presence of water: for example, the friction in a subduction zone, where water in the
sediments makes the melting point of rocks lower and friction rises the temperature, melting
the rocks.
METAMORPHISM: a process where the type or distribution of minerals in rock changes
because of high pressure and temperature. The chemical composition of the rock doesn’t
change, and that is why it is name isochemical process.
Types of metamorphism:
 Contact or thermal metamorphism is produced by
a rise in temperature at low pressure.
 Regional or dynamothermal metamorphism is
produced by an increase in pressure and
temperature.
 High pressure or dynamic metamorphism is
produced by an increase in pressure.
Metamorphism can sometimes occur in faults and areas
of meteorite impacts, but they are normally found where
plate boundaries collide or in subduction zones (convergent).
OROGENESIS OR FORMATION OF MOUNTAIN RANGES: Orogens are found in orogenic belts,
and were formed during orogenies, geological periods in the past when the crust was
deformed, folded and formed cordilleras. They usually coincide with episodes of continental
collision.
Subduction orogens: oceanic lithosphere is destroyed and continental lithosphere reconstructs
with the sediments of the accretionary prism (marine sediments accumulated between n
oceanic lithosphere and a continental lithosphere) and magma from the volcanic arcs. It takes
hundreds of millions of years and produces an orogen on the boundary of the continent. The
convergent boundaries stop subducting when a great continental mass reaches the trench and
joins the oceanic plates. An example is the Andes.
Continental collision or obduction orogens: They are formed due to the
collision of two continents. The Alps, the Himalayas and the Pyrenees are
examples of this type of formation, and are called Alpine-type orogens. The
differences between continental collision orogens and subduction orogens is
that they are formed in a much faster process in a geological scale and in
the continental collision orogens, volcanoes are hardly created, seismic
activity covers a wide area and deformation and metamorphism of rocks is
greater.
1) The continents begin to collide
2) The orogen begins to form and
subduction stops.
3) The orogen takes on a definite
structure and, with erosion, it
gradually wears down.
Accretion orogens: collision of terranes* is produced when small ridges in
the oceanic plate (island arcs or small pieces of continental lithosphere) reach a trench,
colliding with the continent but continuing subducting. Fragments are added to the
continental lithosphere. An example is the Rocky Mountains. *Terrane: fragment of the Earth’s
crust surrounded by faults.
1) A number of
terranes approach
the trench.
2) The terranes are
encrusted on the
edge of the
continent and
deform it.
ISOSTASY is an ideal theoretical balance of the lithosphere and where it lies, on the
asthenosphere, composed by a plastic and ductile rock. “Isostasy controls the regional
elevations of continents and ocean floors in accordance with the densities of their underlying
rocks” (Encyclopaedia Britannica). This means that isostasy is the state of equilibrium and, if
the density of the lithosphere increases, it sinks into the mantle while if it decreases, it rises.
Due to the high rigidity and thickness of the lithosphere, changes have to be great so as it
moves. Movements are very slow.
Isostasy associated with glaciations: the creation of an ice cap makes the lithosphere sink and
its melting rise, recovering its initial equilibrium.
Isostasy associated with deposition and erosion:
Deposition of a thick layer of sediments in a sedimentary basin makes the bottom of the basin
sink (subside process) and the erosion of a mountain range makes the lithosphere lose weight
and causes an isostatic rise.
LANDFORMS
Glacial landforms: dynamic geographical features where glaciers are the main shaping agent.
They are created where temperature is below 0C, usually in polar climates and sometimes in
alpine climates (forming polar and alpine glaciers). There is little vegetation.Glaciers are
accumulated snow that have transformed into ice due to compactation, and move slowly
downwards, transporting sediments and forming U shape valleys. The accumulation of
sediments left after a glacier is called a moraine (classified into lateral, central and subglacial
moraines). This are the parts of a glacier:
Periglacial landforms: the shaping agent is ice, which freezes and melts, causing frost
weathering, a process where rocks are broken into smaller fragments. They are found near
glacial landforms, in areas sometimes above 0 where lichens and mosses can grow. Fragments
are found in scree slopes, talus piles and flat areas, accumulation of sediments in slopes, on
the base of a steep slope and in flat areas forming polygonal shapes.
Desert landforms: it is characterized because there is not rain and intense evaporation, that
causes that there is little vegetation (cactus don’t need much water to survive and resist to
high temperatures) and little water in the ground. It leads to extreme temperature changes in
the ground (very low temperatures during the night and high temperatures during the day).
The exposure of the ground produces thermal stress weathering (mechanical weathering).
Wind transports the sediments forming sandy deserts and dunes. There are different desert
landforms: rocky highland zone (hamada), stony plateau (reg) where we can find mushroomshaped rocks, transverse dunes and barchane dunes.
Fluvial landforms: rain and rivers are the basic agents. Water and vegetation cause chemical
weathering of the rocks. Erosion and transportation take place in the upper course, a steep
slope in a mountain. Sediments are transported and sedimented in the middle-lower course. In
the mouth of the river, where water slows down and no current transport sediments,
sedimentation occurs.
Coastal landforms: dynamic regions were land is sculpted by water, tides and currents and
doesn’t depend on weather. The predominating process is erosion though we can find
transportation and deposition too. Its parts are:
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Wave cut platform: a flat area that have been formed by the effect of waves.
Cliff: a vertical rock exposure formed by erosion and weathering.
Tombolo: an islet attached to the coast by a narrow piece of land.
Marsh: a type of wet land located between aquatic and terrestrial ecosystems.
Beach: a landform along the shoreline.
Lagoon: a small body of water separated by a barrier from a larger body of water.
Split: a deposition landform found off coasts .
Karts landforms: They are rock formations that result from the excavating effects of
underground water on limestone. They don’t depend on the climate. What makes these rocks
dissolve isn’t water, but the combination of water and carbon dioxide, which forms H2CO3
(carbonic acid). When it gets in contact with limestone, Ca CO3, they transform into Ca (HCO3)2
(calcium bicarbonate) which is soluble in water and creates the following formations, that can
be Surface formations:
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Limestone pavements: a flat surface with graves that seems like artificial pavement
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Sinkholes: a natural depression on the Earth’s surface, formed by water or sand.
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Polje: a large flat-floored depression that can be several tens of kilometers long.
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Canyons: is a big crack in the ground, or a very deep valley that has been formed because
of an earthquake or a river during a long period of time
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Springs: underground water that arises into the surface.
 Underground formations
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Ponors: natural surface openings (holes) at the bottom of sink holes or poljes
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Pit caves: underground cave formed as a result of long-term erosion by water.
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Stalactites, stalagmites and columns: Deposits of calcium carbonate (cal) by dripping
water. Stalactites develop on cave ceilings and stalagmites on cave floors. In stalactites
and stalagmites, the calcium bicarbonate gets in contact with the air in the cave and is
transformed back into calcium carbonate, and limestone starts to form around the crack.
Columns are formed when they join together.
Landforms associated with faults:
 That cover large areas normal faults are often connected and form horsts or ridges
(faults have raised upwards) and grabens or trenches (depression where rocks have gone
downwards) sediments can be deposited there.
 Associated to compression the plane fault is almost horizontal. If the angle of inclination
(dip) is small, a thrust plane is formed (a minor displacement) and if the dip is major
nappes (larger sheets of folded rocks) can be produced. The parts of fault landforms are:
window (hole eroded in a nappe), klippe (rock that remains from the erosion of a nappe)
and thrust plane.
Landforms associated with folds: areas where rocks have undergone compression (e.g
mountain ranges). If the surface of the folds is hard, it can’t be eroded and forms combes
(depressions in the hinges of anticlines) and water gaps. Synclines coincide with valleys and
depressions. It is the normal relief, but we can found inverted relief if the surface is soft and
erodes, revealing the synclines (highest areas) and anticlines, which are now the lower areas.
Check these links, some of them are really good:
http://web.arc.losrios.edu/~borougt/GeologicStructuresDiagrams.htm
http://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Earthquakes-andFaults/Different-types-of-Faults
http://en.wikipedia.org/wiki/Fold_%28geology%29
http://legacy.belmont.sd62.bc.ca/teacher/geology12/photos/structural/
http://www.geolsoc.org.uk/ks3/webdav/site/GSL/shared/images/education_and_careers/Roc
kCycle/Rock%20Cycle%20all%20labels.jpg
http://geowords.com/h_/a17/a17
http://www.ikonet.com/en/visualdictionary/static/us/mountains
http://www.geocraft.com/WVFossils/Articles1.html
http://gomyclass.com/geology10/files/lecture13/html/web_data/file48.htm
http://global.britannica.com/EBchecked/topic/296537/isostasy
Thank you for the information of the panels of experts.