Chapter 5 Study
Guide
Volcanoes
Where
do volcanic belts form?
Answer: Volcanic belts form along the boundaries of
Earth’s plates.
What
is the difference between magma and lava?
Answer: Magma is a molten mixture of rock-forming
substances, gases, and water from the mantle.
When magma reaches the SURFACE of the Earth, it is called lava.
True
or False---
After
magma and lava cool, they form solid rock.
TRUE!!!!
What
is the Ring of Fire?
Answer: It is one major belt of volcanoes that
includes the many volcanoes that rim the Pacific Ocean including those along
the coasts of North and South America and those in Japan and the Phillipines.
What
is a string of islands created by volcanoes formed from converging boundaries?
Answer: an island arc
What
is another way that volcanoes can form other than along plate boundaries?
Answer: A volcano forms above a HOT SPOT (an area
where material from deep within Earth’s mantle rises through the crust and
melts to form magma).
List
and explain the parts of a volcano (a system of passageways through which magma
moves).
1.
Magma chamber-All volcanoes
have a pocket of magma beneath the surface.
Beneath a volcano, magma collects in a magma chamber. During an
eruption, the magma forces its way through one or more cracks in Earth’s crust.
2.
Pipe-Magma moves
through a pipe, a long tube that
extends from Earth’s crust up through the top of the volcano, connecting the
magma chamber to Earth’s surface.
3.
Vent-Molten rock and
gas leave the volcano through an opening called a vent. Some volcanoes have a
single central vent at the top. But
volcanoes often have vents on the sides also.
4.
Lava flow-a lava flow is
the spread of lava as it pours out of a vent.
5.
Crater-a crater is a
bowl-shaped area that may form at the top of a volcano around the central vent.
True
or False---
When
a volcano erupts, the force of the expanding gases pushes magma from the magma
chamber through the pipe until it flows or explodes out of the vent. TRUE!!!!
What
is silica?
Answer: Silica is a material found in magma that
forms from the elements oxygen and silicon.
Name
two types of volcanic eruptions:
1.
Quiet eruptions-a volcano
erupts quietly if its magma is hot or low in silica. Hot, low silica is thin and runny and flows
easily. The gases in the magma bubble
out gently. Low-silica lava oozes
quietly from the vent and can flow for many kilometers.
Quiet eruptions can produce different
types of lava:
Pahoehoe (pah HOH ee hoh
ee) forms from fast-moving, hot lava that is thin and runny. The surface of pahoehoe looks like a solid
mass of ropelike coils.
Aa (AH ah) forms from lava that is
cooler and thicker. The lava that aa
forms from is also slower-moving. It has
a rough surface consisting of jagged lava chunks.
Example
of a quiet eruption: the Hawaiian Islands
2.
Explosive
eruptions-a
volcano erupts explosively if its magma is high in silica. High-silica magma is thick and sticky. It can build up in the volcano’s pipe, plugging
it like a cork in a bottle. Dissolved
gases cannot escape from the thick magma.
The trapped gases build up pressure until they explode. Lava is powerfully thrown into the air where
it breaks into fragments of different sizes.
The smallest pieces are volcanic ash, and the larger pieces, called
bombs, may range from the size of a golf ball to the size of a car.
Example
of an explosive eruption: Mount St.
Helens in Washington State (1980)
What
is a pyroclastic flow?
Answer: It is a mixture of hot gases, ash, cinders,
and bombs that flow down the sides of a volcano when it erupts
explosively. Landslides of mud, melted
snow, and rock can also form from an explosive eruption.
What
are the stages of volcanic activity?
Answer:
1-
Dormant—a sleeping volcano
that scientists expect to awaken in the future and become active.
2-
Extinct---a dead
volcano that is unlikely to ever erupt again.
3-
Active---a live
volcano is one that is erupting, or has shown signs that it may erupt, in the
near future.
What
is a caldera?
Answer: A caldera is a huge hole left by the collapse
of volcanoes.
What
landforms do VOLCANIC ERUPTIONS
create?
Answer:
1-
Calderas—large holes at
the top of volcanoes formed when the roof of a volcano’s magma chamber
collapses.
2-
Shield Volcanoes---wide, gently
sloping mountains made of layers of lava and formed by quiet eruptions.
Example
of a shield volcano: Mauna Loa in Hawaii
3-
Cinder Cone
Volcanoes---steep,
cone-shaped hills or small mountains made of volcanic ash, cinders, and bombs
piled up around a volcano’s opening.
Example
of a cinder cone volcano: ParicutÃn in
Mexico
4.
Composite
Volcanoes---tall,
cone-shaped mountains in which layers of lava alternate with layers of ash and
other volcanic materials.
Example
of a composite volcano: Mount Fuji in
Japan & Mount St. Helens in Washington State
5.
Lava Plateaus---thin, runny
lava flows out of several long cracks in an area and travels before cooling and
solidifying. After millions of years,
repeated floods of lava can form high, level plateaus. These are called lava plateaus.
Example
of a lava plateau: Columbia
Plateau—covers parts of Washington State, Oregon, and Idaho
What
landforms does MAGMA create?
*Sometimes magma
cools and hardens into rock before reaching the surface. Over time, forces such as flowing water, ice,
or wind may strip away the layers above the hardened magma and expose it.
1.
Volcanic Necks---form when
magma hardens in a volcano’s pipe and the surrounding rock later wears away.
2.
Dikes---form when
magma forces itself across rock layers and hardens.
3.
Sills---form when
magma squeezes between horizontal rock layers and harden.
4.
Dome Mountains---form when
uplift pushes a large body of hardened magma toward the surface. The hardened
magma forces the layers of rock to bend upward into a dome shape.
5.
Batholiths---masses of
rock formed when a large body of magma cools inside the crust.
