VOLCANOES!
WHAT IS A VOLCANO?
A VOLCANO IS A MOUNTAIN MADE OF LAVA
AND/OR TEPHRA.
WHAT IS A MOUNTAIN?
A MOUNTAIN IS AN AREA SIGNIFIGANTLY
HIGHER THAN ITS SURROUNDINGS.
WHERE DO VOLCANOES
OCCUR?
PLATE BOUNDARIES
AS THE PLATES MOVE, PULLING APART OR
COMING TOGETHER ALONG THEIR BORDERS,
TREMENDOUS ENERGIES ARE UNLEASHED
RESULTING IN TREMORS THAT TRANSFORMS
THE EARTH’S SURFACE. NO SINGLE PLATE CAN
MOVE WITHOUT AFFECTING OTHERS, AND THE
ACTIVITY OF ONE CAN INFLUENCE ANOTHER
THOUSANDS OF MILES AWAY.
PLATE BOUNDARIES
PLATE BOUNDARIES
PACIFIC
NORTHWEST
VOLCANOES
Where do Volcanoes occur?


Divergent Plate boundaries
– These boundaries are constructive plate
boundaries. This is where seafloor spreading
occurs.
Convergent Plate boundaries
– The location where the crust is destroyed and
recycled back into the interior of the earth
– Known as subduction zones where mountains and
volcanoes are located
CONVERGENT BOUNDARIES
HOT SPOTS
AREAS IN THE MANTLE HOT ENOUGH TO
MELT THROUGH THE CRUST.
WHAT IS LAVA?
LAVA IS LIQUID ROCK ON THE EARTHS SURFACE.
HOW IS LAVA DIFFERENT FROM
MAGMA?
MAGMA IS LIQUID ROCK BELOW EARTHS
SURFACE. THE ONLY DIFFERENCE IS WHERE IT
IS.
TEPHRA
TEPHRA IS LIQUID ROCK THAT COOLS AND HARDENS
IN THE AIR AND FALLS TO THE GROUND AS A SOLID.
TYPES OF TEPHRA ARE CLASSIFIED BY
THIER SIZE
1.
2.
3.
ASH
CINDER
VOLCANIC BOMBS
ASH
1. ASH IS THE SMALLEST FORM OF TEPHRA.
2. ASH RANGES FROM THE SIZE OF FINE
POWDER TO THE SIZE OF COURSE SAND.
3. ASH TRAVELS THE FARTHEST FROM THE
VOLCANO.
4. ASH OFTEN WILL COMPLETELY CIRCLE
THE EARTH.
5. ASH CAUSES PROBLEMS BY EFFECTING
BREATHING, COVERING CROPS, KILLING
FISH, AND DESTROYING MECHANICAL
DEVICES.
CINDERS
1. CINDERS ARE MEDIUM SIZED TEPHRA.
2. CINDERS RANGE FROM THE SIZE OF A PEA TO
THE SIZE OF A SOFTBALL.
3. CINDERS DO NOT TRAVEL AS FAR AS ASH.
CINDERS ARE USUALLY FOUND WITHIN A FEW
MILES OF THE VOLCANO. CINDERS ARE
OFTEN USED AS DECORATIVE ROCK OR IN
BARBEQUE GRILLS.
VOLCANIC BOMBS
1. VOLCANIC BOMBS ARE THE LARGEST FORM
OF TEPHRA.
2. VOLCANIC BOMBS CAN BE FROM VOLLYBALL
SIZED TO THE SIZE OF A CAR.
3. THEY ARE CALLED BOMBS BECAUSE THEY
OFTEN EXPLODE WHEN THEY HIT THE
GROUND. AS THEY FLY THROUGH THE AIR, THE
OUTER PART COOLS AND HARDENS BUT THE
INSIDE STAYS LIQUID. WHEN THEY HIT THE
GROUND, THEY BREAK AND THE LIQUID INSIDE
IS THROWN OUT
TEPHRA DIAGRAM
WHAT CAUSES A VOLCANO TO
ERUPT?
FACTORS DETERMINING THE TYPE OF AN
ERUPTION

THE AMOUNT OF SILICA, DETERMINES THE
THICKNESS, OF THE MAGMA.
 THE TYPE OF MAGMA IS DETERMINED, IN
PART, BY THE SILICA CONTENT.
 SILICA IS A LIGHT COLORED MINERAL THAT
THICKENS MAGMA

THICKNESS IS OFTEN TERMED AS VISCOSITY
 HIGH SILICA CONTENT MAGMAS HAVE
HIGHER VISCOSITY
 LOW AMOUNTS OF SILICA HAVE LOWER
VISCOSITY

THE AMOUNT OF TRAPPED GASSES AND
WATER VAPOR TRAPPED IN THE MAGMA

HOW WELL SEALED THE OPENING OF
THE VOLCANO IS.
TYPES OF MAGMA
THREE TYPES OF MAGMA:
1.
BASALTIC
2.
GRANITIC
3.
ANDESITIC
BASALTIC MAGMA





LOW IN SILICA,
BALSALTIC ROCKS ARE DARK IN COLOR
DUE TO THE LOW AMOUNT OF SILICA
LOW VISCOSITY
ERUPTIONS ARE LOW IN VOLATILITY
FLOWS LIKE WATER IN MANY CASES
GRANITIC MAGMA
 HIGH IN SILICA
 GRANITIC ROCKS ARE LIGHT IN
COLOR BECAUSE OF THE HIGH
AMOUNTS OF SILICA
 HIGH VISCOSITY (THICK AND PASTY)
 ERUPTIONS ARE VERY EXPLOSIVE
AND IMPRESSIVE DUE TO HIGH GAS
VOLATILITY
ANDESITIC MAGMA
• SILICA CONTENT IS IN BETWEEN
•
•
•
BASALTICS AND GRANITICS.
COLOR OF ANDESITIC ROCKS IS IN
BETWEEN BASALTIC AND GRANITIC
BECAUSE THE AMOUNT OF SILICA IS IN
BETWEEN
ANDESITIC MAGMA IS THICKER THAN
BASALTIC BUT THINNER THAN GRANITIC
ERUPTIONS ARE RELATIVELY
EXPLOSIVE, VERY IMPRESSIVE
PARTS OF A VOLCANO
PARTS OF A VOLCANO

MAGMA CHAMBER: AREA UNDER THE
VOLCANO THAT CONTAINS MAGMA.
 CONDUIT: TUBE LEADING FROM THE
MAGMA CHAMBER TO THE VENT.
 VENT: OPENING AT THE END OF THE
CONDUIT.
 CRATER: OPENING AT THE TOP OF THE
VOLCANO.
PARTS OF A VOLCANO

SILL: layer of magma between horizontal
layers of sedimentary rock
 DIKE: magma that fills a vertical crack that
cuts across other rocks
 FLANK: the side of a volcano
 SIDE VENT: a smaller secondary volcano
on the side of a large volcano
TYPES OF VOLCANOES
SHIELD VOLCANOES
LOW, VERY WIDE VOLCANOS MADE FROM
LAYERS OF LAVA FLOWS ONLY.
MAINLY MADE OF BASALTIC LAVA FLOWS
BECAUSE OF THE LOW VISCOSITY
CINDER CONE
•
A TALL, NARROW VOLCANO MAINLY MADE OF
TEPHRA ONLY
• LITTLE OR NO LAVA
• ERUPTIONS ARE SHORT LIVED AND VERY
THICK AND PASTY
• VERY VIOLENT, EXPLOSIVE, EXCITING
ERUPTIONS
COMPOSITE VOLCANO
• A TALL, WIDE VOLCANO MADE OF
ALTERNATING LAYERS OF LAVA AND TEPHRA
• EXPLOSIVE ERUPTIONS DUE TO A
COMBINATION OF HIGH SILICA AND HIGH
VISCOSITY
PYROCLASTIC FLOW
FLOWS OF SUPERHEATED GASSES AND ASH MOVING
AT HIGH SPEED DOWN A VOLCANO.
LAHAR
FLOWS OF MUD, WATER,
ASH AND DEBRIS
FLOWING DOWN THE
VOLCANO.
VOLCANIC LANDFORMS
FEATURES CREATED BY VOLCANIC ACTION
THAT ARE NOT ACTUALLY VOLCANOES.
CALDERA
WHEN THE TOP OF A VOLCANO COLLAPSES INTO
THE MAGMA CHAMBER
BATHOLITH

LARGE INTRUSIVE ROCK FORMED
ACROSS ROCK LAYERS
BATHOLITH
LACCOLITH
• LARGE INTRUSIVE ROCK FORMED
BETWEEN ROCK LAYERS
• PUSHES ROCKS UP INTO A DOME SHAPE
DIKE
• MAGMA FILLING A VERTICAL CRACK
AND HARDENING.
SILL
MAGMA FILLING HORIZONTAL CRACK AND
HARDENING
VOLCANIC NECK

FORMED WHEN A VOLCANO ERODES
LEAVING THE SOLID INNER CORE
DIVERGENT BOUNDARIES

Divergent boundaries are constructive plate
boundaries. This is where seafloor spreading occurs.

If new land is formed at these boundaries, it is the
release of magma from the Earth’s mantle which
builds the new crust.

Divergent boundaries are located mainly along
oceanic ridges where seafloor spreading occurs, but
can also occur on land where they are called “rift
valleys”.
CONVERGENT BOUNDARIES
THE LOCATION WHERE THE CRUST IS
DESTROYED AND RECYCLED BACK INTO THE
INTERIOR OF THE EARTH.
THESE AREAS ARE KNOW AS SUBDUCTION
ZONES IS THE AREA WHERE MOUNTAINS AND
VOLCANOES ARE LOCATED.