Download ESVolcanoes - Cole Camp R-1

EARTH SCIENCE -- CH. 13
Volcanoes
7.1 Volcanoes and Plate Tectonics
Scientists have no direct way to measure temperatures deep within the earth.
 Despite the high temperature in the asthenosphere, most of this zone remains solid
because of the great pressure of the surrounding rock.
 Sometimes areas of the solid rock will melt, forming _________________________.
 Geologists think that magma forms in areas where the surrounding rock exerts less
pressure than normal.
▪The lower pressure allows the rock particles to move more quickly; thus,
the rock becomes liquid.
 Any activity that includes the movement of magma toward or onto the surface of the
earth is called ____________________________________.
▸Pockets of magma grow due to melting of some of the surrounding rock.
▸As more rock melts, the magma pockets expand.
▸The magma slowly pushes upward into the crust because it is less dense than
solid crustal rock.
▸The magma slowly rises, forcing its way into cracks in the overlying rock.
 Most magma forms at plate boundaries, where one lithospheric plate, usually of
oceanic crust, is ____________________________ beneath another plate, often of
continental crust.
▸ The subducting plate moves deep into the hot asthenosphere, where parts of it melt to
become magma.
▪Magma that erupts onto the earth's surface is called __________________.
 The opening through which the molten rock flows onto the surface is called a
______________________________.
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▸The vent and the volcanic material that builds up on the earth's surface
around the vent is called a ________________________.
Major Volcanic Zones
 Most of these active volcanoes are found in zones near both ____________________
and ____________________ boundaries of the lithospheric plates.
Subduction Zones (Review Material)
 Many volcanoes are located along subduction zones, where one plate moves under
another plate.
▸When a plate with oceanic crust meets a plate with continental crust, the oceanic
crust, which is more dense, moves beneath the continental crust.
▸A _________________________________ forms on the ocean floor along the
edge of the continent where the plate is being subducted.
▸The plate with the continental crust buckles and folds, forming a line of
________________________ along the edge of the continent.
 A major zone of active volcanoes is caused by subducting plates encircling the
Pacific Ocean.
▸ This zone, called the ___________________________, results from plates
subducting along the Pacific coasts of North America, South America, Asia, and the
islands of the western Pacific Ocean.
▪The Pacific Ring of Fire is also one of earth's three major earthquake
zones.
▸As a plate descends into the mantle, it melts.
▸Some of the resulting magma breaks through to the surface along the trench.
▪
In time, a string of volcanic islands, called an _____________________________,
forms along the trench.
 The early stages of this type of subduction produce an arc of small
____________________________________.
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▸ Example: _____________________________________, which stretch across the
North Pacific Ocean between Alaska and Siberia.
 As more magma surfaces, more islands appear, become larger, and join, such as the
group of volcanic islands that make up __________________________.
 The greatest amount of magma comes to the surface where plates are moving apart
along ____________________________________.
▸ A major zone of volcanoes is the interconnected mid- ocean ridges that circle the
earth.
▸ Magma rises through the fractures and comes to the surface along long, narrow cracks
called __________________________________.
 Most volcanic eruptions along the mid-ocean ridges go unnoticed.
(Exception: _________________________________)
 Iceland is a part of the Mid-Atlantic Ridge that _____________________________.
▸
▸
▪The middle of Iceland is cut by large fissures, cracks through which lava
flows.
 Areas of volcanism within plates are called ______________________________.
▸ Example:
▪
7.2 Volcanic Eruptions
 The lava that erupts from volcanoes provides an opportunity for scientists to study
first hand the materials that form deep within the earth's mantle.
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 By analyzing the types of minerals found in hardened lava, geologists have
concluded that there are two general types of lava:
 1)
▪
 2)
▸
▪Felsic lava is usually from melted ________________________.
 Other lavas have a range of compositions that fall between the mafic and the felsic
varieties.
▸ Thin, mafic lava usually hardens with a wrinkled surface.
▪This lava is known as _________________________________, (meaning
"____________________" in Hawaiian)
 Rapid cooling on the surface of the lava forms a crust that breaks into jagged chunks
as the liquid below continues to flow.
▸The lava deposit that remains is described by its Hawaiian name _________,
which refers to the sharp, blocky shapes into which the hardened lava
breaks.
 Sometimes the outer part of a mafic lava flow cools so rapidly that it forms a
hardened shell around a liquid interior that flows out, leaving tunnels in the hardened
lava shell. When lava flows out of fissures on the ocean floor, it cools rapidly, often
in rounded shapes.
▸ This is called _______________________________________.
▪
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
▸____________________________________________, both those that erupt on the
ocean floor and those that erupt on oceanic islands, usually are produced
_______________________________________.
▪
Mafic lava is very ___________________________________________________.
Because gases can easily escape from mafic lava, eruptions from oceanic volcanoes
like those in Hawaii are usually quiet.
◦___________________________________ flows are produced
 The ___________________________________________________________, such
as ______________________________________, tend to be cooler and thicker.
▸
▸When a vent or fissure opens up, the dissolved gases within the lava boil out
explosively, sending molten and solid particles shooting into the air.
 Unlike mafic lava, which tends to flow quietly, _____________________________,
throwing _________________________ into the air.
▸____________________________, sometimes called _________________________,
is rock fragments ejected from a volcano.
▪
◦
Tephra particles less than
Particles
▸Some of the smallest dust particles may travel completely around the
earth.
 Larger tephra particles, less than __________________in diameter, are called
___________________________ (Latin word meaning "_____________________")
▸Lapilli generally fall ______________________________.
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 Large clots of lava are thrown out of an erupting volcano while they are red-hot. As
the clots spin through the air, they cool and develop a round or spindle shape.
▸ These tephra particles are called _________________________________.
 The largest tephra, formed from solid rock blasted from the fissure, is known as
___________________________________________.
 Volcanic cones that are broad at the base and have gently sloping sides are called
__________________________________________.
▸A shield cone covers a wide area and generally results from quiet lava eruptions.
▸Layers of hot __________________________________ out around the vent,
harden, and slowly build up to form the cone.
▸EXAMPLE:
The _______________________________ are a chain of shield
cones.
 Some explosive eruptions form __________________________________.
▸ A cinder cone is made of solid fragments ejected from the volcano. Most cinder cones
have very steep slopes, often close to ________, and are rarely more than a few
hundred meters high.
▪During a quiet eruption, the cone is __________________________________.
Then an explosive eruption occurs, depositing large amounts of tephra
around the vent. The explosive eruption is followed again by quiet lava
flows. The resulting cone is formed of alternating layers of hardened lava
flows and tephra.
 Composite cones, also known as ______________________________________,
often develop into high volcanic mountains.
▸ EXAMPLES:
▪
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 The funnel-shaped pit at the top of a volcanic vent is known as the
____________________________.
▸The crater is formed when material is blown out of the volcano by explosions.
▸A crater usually becomes wider as magma melts and breaks down the walls of
the crater, allowing loose materials to collapse back into the vent.
▸When the magma chamber below a volcano is emptied,
________________________________________________.
 Explosions may also completely destroy the upper part of the cone, leaving a large,
basin-shaped depression called a _________________________________
▸ EXAMPLE:
▪___________________________________, a volcanic island in
Indonesia
7.3 Extraterrestrial Volcanism
 Indications are that many of the planets and moons in the solar system, including the
earth's moon, were volcanically active in the past.
▸
 The earth's moon is covered with _____________________________________.
▸This is evidence that sometime in the past, active volcanoes dotted the surface
of the moon.
▸Most of the craters on the lunar surface result from
___________________________________________.
▸Some of them have smooth, lava flow interiors and gently sloping, channeled
exteriors. These features suggest that the craters were once active
volcanoes.
 Spacecraft have orbited Mars and have sent back photographs that show numerous
volcanoes and volcanic features on the Martian surface.
▸ The largest of these is the shield volcano ________________________________.
▪It rises nearly
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▪Its base measures
▪Its caldera,
 Olympus Mons is the __________________________________________________
▸It is thought that the volcano has grown to such a tremendous size because,
unlike the earth's crust, ________________________________________.
 __________, one of Jupiter’s _______moons, is the first planetary body on which
active volcanoes have been sighted.
▸ Io,
▸ Scientists calculate that volcanoes on Io eject several thousand metric tons of material
each second.
▪
 Volcanoes on lo appear to be much more powerful than those on earth.
▸ Io moves inward and outward in its orbit around Jupiter because of the gravitational
pull of the other moons of Jupiter.
▪As
▪Heat from the friction caused by this surface movement probably results in
the melting of the interior of Io and leads to volcanism.
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