Download what causes earthquakes what is a fault? (traduzione del

WHAT CAUSES EARTHQUAKES?
AT THE PLATE BOUNDARIES, PRESSURE BUILDS AS THE FRICTION BETWEEN THE PLATES STOP
THEIR MOVEMENT. FINALLY, THE PLATES SLIP, AND THE PRESSURE IS RELEASED IN A SERIES OF
WAVES. THIS MOVEMENT SHAKES THE EARTH, CAUSING AN EARTHQUAKE.
WHAT IS A FAULT?
A FAULT IS A FRACTURE ALONG WHICH THE BLOCKS OF CRUST ON EITHER SIDE HAVE MOVED
RELATIVE TO ONE ANOTHER PARALLEL TO THE FRACTURE.
(TRADUZIONE DEL BRANO A GRUPPI CON DIZIONARIO INGLESE-ITALIANO)
THIS NETWORK OF PLATES COVERS THE EARTH’S CRUST. MOVEMENTS OF
THE EARTH’S CRUST ARE CONCENTRATED IN NARROW BELTS ALONG
RIDGES, DEEP-SEA TRENCHES AND MAJOR STRIKE-SLIP FAULTS. THESE
LONG LINEAR FEATURES ARE NOT ISOLATED, BUT ARE INTERCONNECTED IN
A GLOBAL NETWORK AND REPRESENT THE BOUNDARIES FOR ~ 12 PLATES.
PLATE TECTONICS 1
HTTP://MATHINSCIENCE.INFO
WHAT ARE THE THREE TYPES
TYPES OF PLATE BOUNDARIES
BOUNDARIES?
DIVERGENT PLATE BOUNDARY
CONVERGENT PLATE BOUNDARY
TRANSFORM PLATE BOUNDARY
VOLCANOES
AT A DIVERGENT PLATE BOUNDARY, LITHOSPHERIC PLATES MOVE AWAY FROM EACH OTHER. THE
MID-ATLANTIC RIDGE, A TOPOGRAPHICALLY HIGH AREA NEAR THE MIDDLE OF THE ATLANTIC
OCEAN, IS AN EXAMPLE OF A DIVERGENT PLATE BOUNDARY.
AT A CONVERGENT PLATE BOUNDARY, LITHOSPHERIC PLATES MOVE TOWARD EACH OTHER. THE
WEST MARGIN OF THE SOUTH AMERICAN CONTINENT, WHERE THE OCEANIC NAZCA PLATE IS
PUSHING TOWARD AND BENEATH THE CONTINENTAL PORTION OF THE SOUTH AMERICAN PLATE, IS
AN EXAMPLE OF A CONVERGENT PLATE BOUNDARY.
AT THE TRANSFORM PLATE BOUNDARY, PLATES SLIDE PAST EACH OTHER. THE SAN ANDREAS
FAULT IN CALIFORNIA IS AN EXAMPLE OF A TRANSFORM PLATE BOUNDARY, WHERE THE PACIFIC
PLATE SLIDES PAST THE NORTH AMERICAN PLATE.
ONE OF THE MOST DRAMATIC EFFECTS OF PLATE MOVEMENT IS THE FORMATION OF VOLCANOES.
MOST VOLCANIC ACTIVITY OCCURS NEAR THE BOUNDARY OF CRUSTAL PLATES. WHEN PLATES
COLLIDE, CRUSTAL MATERIAL IS SUBDUCTED, OR MOVES, INTO THE ASTHENOSPHERE. THERE AN
INCREASE IN PRESSURE RAISES THE TEMPERATURE OF THE ROCKS. EVENTUALLY THE ROCKS MELT,
FORMING MAGMA. WHERE PLATES DIVERGE, PRESSURE IS RELEASED, ROCKS MELT, AND MAGMA
RISES THROUGH RIFTS, AS IN ICELAND.
THE ROCK CYCLE
Background: Plate Tectonics: From the Inside Out!
COURTESY OF USGS
TECTONICS IS A TERM THAT DESCRIBES MOVEMENT OF THE EARTH’S
CRUST.
PLATE TECTONICS IS THE THEORY THAT THE EARTH IS MADE UP OF LARGE
LITHOSPHERIC PLATES THAT MOVE ABOUT ON ITS SURFACE BY SPLITTING,
COLLIDING OR SLIDING PAST EACH OTHER. INTENSE GEOLOGIC ACTIVITY
OCCURS AT PLATE BOUNDARIES.
PLATES CONSIST OF THE LITHOSPHERE THAT IS OCEANIC OR CONTINENTAL
CRUST AND THE UPPERMOST MANTLE.
Rocks analysi
analysis
a. Are the colors all the same?
•
B.
ARE THEY ALL AS HARD AS EACH OTHER?
c. Do they look as they have the same texture? (feel)
D.
DO THEY SHINE? (LUSTER)
e. What do you think is the cause for all these differences?
ROCK
THE SOLID PART OF EARTH.
MINERAL
A NON-LIVING SUBSTANCE THAT ROCKS ARE
MADE OF.
PROPERTY
ARE THOSE CHARACTERISTICS OF MATTER THAT
CAN BE USED TO DESCRIBE IT.
CLEAVAGE
HOW A ROCK BREAKS APART.
STREAK
THE COLOR THE MINERAL MAKES WHEN
SCRATCHED ACROSS A SURFACE.
HARDNESS
HOW HARD THE ROCK IS IN COMPARISON TO
OTHER ROCKS.
TEXTURE
HOW THE ROCK FEELS.
COLOR
THE COLOR THE MINERALS HAVE.
LUSTER
THE SHININESS OF A ROCK.
GEOLOGY
THE STUDY OF THE EARTH.
broken continent in opposite directions carried by the convection
currents. This idea received very little attention at the time.
Not until the 1960's did Holmes' idea receive any attention. Greater
understanding of the ocean floor and the discoveries of features like
mid-oceanic ridges, geomagnetic anomalies parallel to the midoceanic ridges, and the association of island arcs and oceanic
trenches occurring together and near the continental margins,
suggested convection might indeed be at work. These discoveries
and more led Harry Hess (1962) and R. Deitz (1961) to publish
similar hypotheses based on mantle convection currents, now
known as "sea floor spreading". This idea was basically the same
as that proposed by Holmes over 30 years earlier, but now there
was much more evidence to further develop and support the idea.
PLATES TECTONICS: THE MECHANISM
The main features of plate tectonics are:
The Earth's surface is covered by a series of crustal plates.
The ocean floors are continually moving, spreading from the center,
sinking at the edges, and being regenerated.
Convection currents beneath the plates move the crustal plates in
different directions.
The source of heat driving the convection currents is radioactivity
deep in the Earths mantle.
drifted northward into the Asian continent thus forming the
Himalayas.
Wegener eventually proposed a mechanism for continental drift that
focused on his assertion that the rotation of the earth created a
centrifugal force towards the equator. He believed that Pangaea
originated near the south pole and that the centrifugal force of the
planet caused the protocontinent to break apart and the resultant
continents to drift towards the equator. He called this the "polefleeing force". This idea was quickly rejected by the scientific
community primarily because the actual forces generated by the
rotation of the earth were calculated to be insufficient to move
continents. Wegener also tried to explain the westward drift of the
Americas by invoking the gravitational forces of the sun and the
moon, this idea was also quickly rejected. Wegener's inability to
provide an adequate explanation of the forces responsible for
continental drift and the prevailing belief that the earth was solid
and immovable resulted in the scientific dismissal of his theories.
In 1929, about the time Wegener's ideas began to be dismissed,
Arthur Holmes elaborated on one of Wegener's many hypotheses;
the idea that the mantle undergoes thermal convection. This idea is
based on the fact that as a substance is heated its density
decreases and rises to the surface until it is cooled and sinks again.
This repeated heating and cooling results in a current which may be
enough to cause continents to move. Arthur Holmes suggested that
this thermal convection was like a conveyor belt and that the
upwelling pressure could break apart a continent and then force the
and Africa. The same was true for fossils found in Europe and
North America, and Madagascar and India. Many of these
organisms could not have travelled across the vast oceans that
currently exist. Wegener's drift theory seemed more plausible than
land bridges connecting all of the continents. But that in itself was
not enough to support his idea. Another observation favouring
continental drift was the presence of evidence for continental
glaciation in the Pennsylvanian period. Striae left by the scraping of
glaciers over the land surface indicated that Africa and South
America had been close together at the time of this ancient ice age.
The same scraping patterns can be found along the coasts of South
America and South Africa.
Wegener's drift hypothesis also provided an alternate explanation
for the formation of mountains (orogenesis). The theory being
discussed during his time was the "Contraction theory" which
suggested that the planet was once a molten ball and in the
process of cooling the surface cracked and folded up on itself. The
big problem with this idea was that all mountain ranges should be
approximately the same age, and this was known not to be true.
Wegener's explanation was that as the continents moved, the
leading edge of the continent would encounter resistance and thus
compress and fold upwards forming mountains near the leading
edges of the drifting continents. The Sierra Nevada mountains on
the Pacific coast of North America and the Andes on the coast of
South America were cited. Wegener also suggested that India
Wegener's theory and tectonics plates
Close examination of a globe often results in the observation that
most of the continents seem to fit together like a puzzle: the west
African coastline seems to snuggle nicely into the east coast of
South America and the Caribbean sea; and a similar fit appears
across the Pacific. The fit is even more striking when the
submerged continental shelves are compared rather than the
coastlines.
In 1912 Alfred Wegener (1880-1930) noticed the same thing and
proposed that the continents were once compressed into a single
protocontinent which he called Pangaea (meaning "all lands"), and
over time they have drifted apart into their current distribution. He
believed that Pangaea was intact until the late
Carboniferous
period,
about 300 million years ago, when it began to break up and drift
apart. However, Wegener's hypothesis lacked a geological
mechanism to explain how the continents could drift across the
earths surface as he proposed.
Searching for evidence to further develop his theory of continental
drift, Wegener came across a paleontological paper suggesting that
a land bridge had once connected Africa with Brazil. This proposed
land bridge was an attempt to explain the well known
paleontological observation that the same fossilized plants and
animals from the same time period were found in South America
slide past each other horizontally. This is called a transform plate boundary.
Volcanoes and earthquakes help define the boundaries between the plates.
Volcanoes form mostly at converging and diverging plate boundaries, where
much magma is generated. Earthquakes occur at all three types of
boundaries. Because the plates are rigid, they tend to stick together, even
though they are constantly moving. When the strength of the rocks at the
plate boundary is exceeded, they move rapidly, "catching up" with the rest of
the plates. We feel this release of energy as an earthquake.
(brano letto e tradotto in classe in presenza del lettore di madrelingua)
The surface of the Earth seems to be divided into water and land.
Islands look disconnected, and many children even think that they are
floating on the water. Many books describe plate tectonics as if
the plates are the continents. This is not true. The continents are
embedded in the plates. Many continents occur in the middles of plates,
not at their boundaries or edges. Plates also underlie the Earth’s
oceans. A single plate often includes both continental and oceanic
regions. It is important that students begin to visualize or understand
that the plates are a solid rock shell which includes both dry land and
the "land" underneath the oceans.
Plates are composed of the Earth’ s crust and upper mantle, which are
collectively called the lithosphere. This layer is like an eggshell compared to
the total thickness of the Earth. Plates do not extend all the way to the center
or the Earth.
All of the plates are moving. They are slow, moving at speeds of centimeters
to tens of centimeters per year. They slide along on top of an
underlying mantle layer called the asthenosphere, which contains a
little magma (molten rock).
The plates are layers of rigid, solid rock. However, as they move, plates
interact at their edges or boundaries. There are three basic directions or
types of boundary interactions. In some places, two plates move apart from
each other; this is called a diverging plate boundary. Elsewhere two plate
move together; this is a converging plate boundary. Finally plates can also
ITC ROSA LUXEMBURG - BOLOGNA
PLATE TECTONICS
•
planisfero suddiviso in placche
animazioni (su movimenti relativi tra placche) estratte dal sito
“ www. geology.com. (Convergent movements, divergent movements and transform
fails; )
•
•
“ Wegener's hypotheses and actually plate tectonics theory” da cui vengono
letti e tradotti i brani salienti
ATTIVITÀ PRATICA :
-
ricostruzione della Pangea (a gruppi di 2 vengono ritagliate le sagome dei
continenti, assemblate secondo le indicazioni e poi lentamente spostati e fatti
ruotare nella posizione attuale)
-
Studio dell'interno della Terra
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Schema del ciclo delle rocce
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Laboratorio di Scienze: Campioni di rocce di tipo continentale ed oceanico.
Descrizione di una roccia con l'aiuto di questionario e glossario
-
prova di Verifica