Download Most earthquakes are the result of huge pieces of rock in the earth

Colliding Sliding, and Separating Plates
The crust of the earth, along with the rigid uppermost part of the mantle, is called the
lithosphere. The lithosphere is 18-120 kilometers thick. It covers the earth’s interior and is
broken into pieces called plates. The rocks that make up these plates grind, collide, move past
one another, and separate as they float on a flowing, taffy-like, solid upper mantle called the
asthenosphere. The place where plates meet is called a plate boundary. At some plate
boundaries, the plates collide, and mountains and trenches form. AT other plate boundaries, the
plates try to slide past one another. When this happens, energy builds up in the rock as it
compresses or twists. When the force between the plates gets too great, the rock breaks or
ruptures, and an earthquake may occur.
Lithospheric plates can be either continental or oceanic. Continental plates contain the
earth’s continents. They are thick but less dense than oceanic plates are. Oceanic plates, which
occur under the world’s oceans, are thin and dense because of their composition.
When two continental plates collide, their boundaries crumple and uplift to form
mountains. This is what happened when the Indian-Australian Plate collided with theEuroasian
Plate millions of years ago. Their collision formed (and is still forming) the Himalayas.
When a continental plate collides with an oceanic plate, it’s a different story. The dense
oceanic plate sinks and slides under the continental plate. An older, colder oceanic plate can also
slide under a younger, warmer oceanic plate, and the old plate moves deep into the earth. (This is
because cold things are often denser than warm things.) When an oceanic plate moves under
another plate, the bending of the sinking plate creates a trench, or deep valley, in the ocean flow.
AS the oceanic plate sinks deeper into the earth’s hot interior at the trench, it is subjected to heat
and pressure. AS the temperature rises, part of the rock may melt. This molten, or melted, rock
rises to earth’s surface and is the source of volcanoes.
Sometimes a new boundary can form under a continent. Hot rock flowing under a plate
can cause the continent to split in two. The surface of the plate thins and fractures. The place
where the plate splits is called a spreading plate boundary. If the fracture is deep, melted rock
may flow to the surface. Like hot air that rises above cold air, melted rock inside the earth rises
because it is less dense than the cooler, solid rock around it. The rising, melted rock heats the
crust and causes it to expand and bulge upward to form a ridge, or mountain-like landform. If
water from an ocean enters the place where the plate split, a mid-ocean ridge, is formed.
Sometimes two plates slide past one another. No new land forms there. This is discussed
later.
Earthquakes and Faults
Most earthquakes are the result of huge pieces of rock in the earth that rub or press
against one another as a result of changes inside the earth. As forces are applied to the rock, the
rock slightly deforms. Energy builds up within and between pieces of rock. Suddenly, they slip
past one another. Energy is released and the ground ruptures and shakes. The longer the force is
applied to the rock, the greater the amount of energy that will be stored in the rock and the more
severe the earthquake.
Plate boundaries occur along fractures or breaks in the earth’s outer layer. A fault is a
fracture along which blocks of rock on opposite sides of the fracture move. The San Andreas
Fault in California is an example of a fault that is also a plate boundary. Plates on either side of
the fault (the North American Plate and the Pacific Plate) move vertically. No new land is
created along this boundary. But the rocks along the fault have jagged surfaces that “hook” onto
each other. One of the variables that affect how a fault behaves is the amount of friction between
fault surfaces. Young faults have rough surfaces. When a fault ruptures repeatedly, its rough
surfaces, or protrusions, wear down and become smooth.
The powerful forces from the moving plates push on the rock along the fault. If the
forces are very strong, the fault will break, causing the rock to bend and fracture. When this
happens shallow earthquakes occur. Fences, rivers, and other structures on the land along the
fault can change shape as a result of the forces created by the moving plates.
Colliding Sliding, and Separating Plates
The crust of the earth, along with the rigid uppermost part of the mantle, is called
the______________________________. The lithosphere is 18-120 kilometers thick. It covers
the earth’s interior and is broken into pieces called plates. The rocks that make up these plates
grind, collide, move past one another, and separate as they float on a flowing, taffy-like, solid
upper mantle called the_______________________________________. The place where plates
meet is called a ___________________________________
__________________________.. At some plate boundaries, the plates collide, and mountains and
trenches form. At other plate boundaries, the plates try to slide past one another. When this
happens, energy builds up in the rock as it compresses or twists. When the force between the
plates gets too great, the rock breaks or ruptures, and an _____________________________ may
occur.
Lithospheric plates can be either continental or oceanic. Continental plates contain the
earth’s continents. They are thick but less dense than oceanic plates are. Oceanic plates, which
occur under the world’s oceans, are thin and dense because of their composition.
When two continental plates collide, their boundaries crumple and uplift to form
mountains. This is what happened when the Indian-Australian Plate collided with theEuroasian
Plate millions of years ago. Their collision formed (and is still forming)
the__________________________.
When a continental plate collides with an oceanic plate, it’s a different story. The dense
oceanic plate sinks and slides under the continental plate. An older, colder oceanic plate can also
slide under a younger, warmer oceanic plate, and the old plate moves deep into the earth. (This is
because cold things are often denser than warm things.) When an oceanic plate moves under
another plate, the bending of the sinking plate creates a trench, or deep valley, in the ocean flow.
AS the oceanic plate sinks deeper into the earth’s hot interior at the trench, it is subjected to heat
and pressure. AS the temperature rises, part of the rock may melt. This molten, or melted, rock
rises to earth’s surface and is the source of volcanoes.
Sometimes a new boundary can form under a continent. Hot rock flowing under a plate
can cause the continent to split in two. The surface of the plate thins and fractures. The place
where the plate splits is called a____________________________________
___________________________
___________________________. If the fracture is deep,
melted rock may flow to the surface. Like hot air that rises above cold air, melted rock inside the
earth rises because it is less dense than the cooler, solid rock around it. The rising, melted rock
heats the crust and causes it to expand and bulge upward to form a ridge, or mountain-like
landform. If water from an ocean enters the place where the plate split, a mid-ocean ridge, is
formed.
Sometimes two plates slide past one another. No new land forms there. This is discussed
later.
WORD BANK
Himalayas
earthquake
lithosphere
asthenosphere
spreading plate
boundary
plate boundary
Earthquakes and Faults
Most earthquakes are the result of huge pieces of rock in the earth that rub or press
against one another as a result of changes inside the earth. As forces are applied to the rock, the
rock slightly deforms. Energy builds up within and between pieces of rock. Suddenly, they slip
past one another. Energy is released and the ground ruptures and shakes. The longer the force is
applied to the rock, the greater the amount of energy that will be stored in the rock and the more
severe the earthquake.
Plate boundaries occur along fractures or breaks in the earth’s outer layer. A
__________________________ is a fracture along which blocks of rock on opposite sides of the
fracture move. The ________________________________________ in California is an example
of a fault that is also a plate boundary. Plates on either side of the fault (the North American
Plate and the Pacific Plate) move vertically. No new land is created along this boundary. But the
rocks along the fault have jagged surfaces that “hook” onto each other. One of the variables that
affect how a fault behaves is the amount of _______________________________ between fault
surfaces. Young faults have rough surfaces. When a fault ruptures repeatedly, its rough surfaces,
or protrusions, wear down and become smooth.
The powerful forces from the moving plates push on the rock along the fault. If the
forces are very strong, the fault will break, causing the rock to bend and fracture. When this
happens shallow earthquakes occur. Fences, rivers, and other structures on the land along the
fault can change shape as a result of the forces created by the moving plates.
WORD BANK
fault
friction
San Andreas Fault