Download Volcanoes - Plain Local Schools

VOLCANOES
volcanism - any
activity which
includes
movement of
magma toward
or onto the
earth’s surface
magma –
molten rock
below the
surface
lava – molten
rock at or
above the
surface
vent - the
opening in the
crust through
which magma
flows onto the
surface
volcano - the structure formed
around the vent by layers of
volcanic materials
Volcanoes occur mostly in areas
near convergent and divergent
plate boundaries.
Convergent Plate Boundaries
oceanic crust and continental crust
 oceanic plate subducts
beneath a continental plate
 seawater combines with the
melting rock and mantle
 violently explosive volcanoes
 along the edges of the
continents
 examples: Andes, Cascades
Convergent Plate Boundaries
oceanic crust and oceanic crust
Oceanic plates
subduct below other
oceanic plates
Chain of volcanoes
produced behind the
trench called island
arcs
Example: Aleutian
Islands, Alaska
Divergent Plate Boundaries
oceanic crust and oceanic crust
Called mid-ocean
ridges or rifts
Oceanic crust spreads
apart
Creates new seafloor
Lots of magma comes
to the surface here  Undersea volcanoes can also be
present
 Most go unnoticed, as they occur
deep on the ocean floor
Mid-Ocean Ridge Example
Iceland
Divergent Plate Boundaries
continental crust and continental crust
Diverging plates pull apart
continents
Rift valleys are formed
have characteristic
fissures (cracks in the
crust that lava flows
through
Example: Great Rift
Valley, Africa
East African Rift Valley
continental crust and continental crust
Volcano formed from rift valley
Mt.Kilamanjaro,Tanzania,Africa
HOT SPOTS
Stationary (non-moving)
areas of volcanism
within the interiors of
lithospheric plates
Plate above the hot spot
continues to drift slowly
Plate carries the volcano
on the surface away A new volcano begins to form over
from the hot spot
the hot spot
Activity in the 1st volcano slows,
then ceases.
Hot Spot Volcano Example
Hawaiian Islands
TYPES OF LAVA
Two general
types
Depends on the
chemical
composition of
the rocks and
minerals
TYPE 1. FELSIC/ANDESITIC LAVA
less dense
more viscous or
thick/sticky (moves
slowly)
lighter in color because it
contains more silica
(quartz is made of silica)
makes up most of the
continental crust
denser
more fluidic
dark-colored
rich in Mg and
Fe
forms the
oceanic crust
TYPES OF MAFIC/BASALTIC LAVA
aa (pronounced ahh-ahh)
 sharp, jagged surfaces
TYPES OF MAFIC/BASALTIC LAVA
pahoehoe (pronounced puh-hoy-hoy)
 wrinkled, rope-like surface
VIOLENCE OF ERUPTIONS
Basaltic/mafic lava
Very hot
Thin and fluidic
Gasses escape easily
“Quiet” eruptions
VIOLENCE OF ERUPTIONS
Andesitic/felsic lava
Cooler flows
Thick (viscous) and
“sticky”
H2O & CO2 gasses
get trapped inside
Explosive and
violent eruptions
LAVA TUBE - A LARGE PIPE FORMED FROM
SUCH RAPIDLY COOLING BASALTIC LAVA
THAT A HARDENED SHELL FORMS AROUND
THE STILL-MOVING
MOLTEN ROCK
INTERIOR
DANGERS OF LAVA TUBES
Looks like
normal ground
on top, but can
collapse when
tourists walk
over them
Poisonous gases
can escape
when lava tubes
collapse
SHIELD VOLCANOES- HUGE VOLCANOES
MADE OF BASALTIC/MAFIC LAVA, WITH
BROAD BASES AND GENTLY SLOPING
SIDES - THE HAWAIIAN ISLANDS
CINDER CONES - SMALL, STEEP-SIDED
VOLCANOES MADE OF CINDERS AND
OTHER PYROCLASTIC
MATERIALS; THERE IS LITTLE LAVA FLOW,
AND THEY OFTEN OCCUR IN GROUPS
Pu`u ka Pele
Paracutin
VIOLENT ERUPTIONS
VOLCANIC MATERIALS ARE BLOWN OUT OF
THE TOP OF THE VENT
CALDERA - LARGE, BOWL-SHAPED
DEPRESSION WHICH MAY FORM AT THE
SITE OF A VOLCANO AFTER THE MAGMA
CHAMBER BELOW EMPTIES OF MAGMA
CRATER LAKE IS A CALDERA WHICH
FILLED WITH WATER AFTER THE
ERUPTION AND SUBSEQUENT
COLLAPSE OF MT. MAZAMA.
PYROCLASTIC MATERIALS
When viscous magma reaches
the vent it will expand and
release the gasses trapped
inside. At this time a violent
eruption occurs and lava is
broken into pieces of all sizes.
TEPHRA (GREEK, FOR ASH) IS A
GENERIC TERM FOR ANY AIRBORNE
PYROCLASTIC ACCUMULATION.
Volcanic Dust –
pyroclastic
material smaller
than 0.25mm in
diameter
VOLCANIC ASH - PYROCLASTIC MATERIAL
SMALLER THAN 2 MM IN DIAMETER
LAPILLI (“LITTLE STONES”) - PYROCLASTIC
MATERIAL LESS THAN 64 MM IN DIAMETER
VOLCANIC BOMBS - LARGE BLOBS OF LAVA
THROWN OUT OF THE VENT WHICH COOL
INTO A SPHERICAL OR OVAL SHAPE
SOLID ROCK BLASTED
FROM THE VENT
FISSURES - CRACKS IN THE CRUST
THROUGH WHICH LAVA FLOWS
BASALTS
OCCUR WHEN ASH AND DEBRIS BECOME
SATURATED WITH WATER AND FLOW DOWN
THE VOLCANO’S SLOPES, USUALLY
FOLLOWING STREAM VALLEYS.
OTHERS ARE TRIGGERED WHEN HEAT
FROM THE VOLCANO MELTS SNOW AND ICE.
VOLCANISM
INCLUDING OUR MOON, HAVE BEEN
VOLCANICALLY ACTIVE IN THE PAST.
THESE ARE CALLED MARIA, AND SUGGEST
THAT VOLCANISM WAS ONCE PRESENT ON
THE MOON.
LUNAR VOLCANISM, AS THERE IS NO
EVIDENCE OF PLATE TECTONICS OR
CONVECTION CURRENTS TO SUPPLY THE
HEAT REQUIRED FOR SUCH ACTIVITY.
METEORITE BOMBARDMENT.
VOLCANIC FEATURES ON MARS.
SIZE OF ARIZONA.
PLANET MAY ALSO BE ACTIVE
SEISMICALLY.
VOLCANICALLY ACTIVE BODY IN OUR
SOLAR SYSTEM.
PRIMARILY SULFUR AND SULFUR
OXIDES.
COVERS IO’S SURFACE.
Olympus Mons:
A Shield Volcano
on Mars
Earth’s Largest Volcano: Mauna Loa
9 km high
120 km across
x 3=
Olympus Mons:
24 km high
550 km across
Mars ≈ 1/2 of Earth’s diameter
Olympus Mons ≈ 3 times the size of Earth’s largest Volcano
Huge size disparity due to Mars’ stationary crust, hence
enormous hot-spots that build-up in stationary positions
BUILDING UP HEAT FROM FRICTION.
THIS SURFACE MOVEMENT MAY
RESULT IN THE MELTING OF THE
INTERIOR AND VOLCANISM.