INTRODUCTION: HOW DO VOLCANOES ERUPT?

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INTRODUCTION HOW DO VOLCANOES ERUPT? 1.) Heated
material from deep (asthenosphere/mantle) rises
as solid 2.) magma is created by
decompression (lessening of pressure) 3.)
increasing water content lowers melting point
further 4.) gasses come out of solution-expands
BANG-Soda analogy ND pg. 158 fig. 6.8 Then ND
pg. 157 fig. 6.6
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TWO TYPES OF ACTIVITY 1.) Violent and Explosive
a.) Occur at subduction zones. WHY? b.) Mt St.
Helens
BECAUSE (ND pg. 153 /fig. 6.3) 1.) more heat
with depth 2.) subducting plate has water 3.)
asthenosphere mafic material mixes with
over riding felsic material 4.) mafic turns
crystallizes sooner leaving felsic material in
liquid. state
Courtesy of USGS
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TWO TYPES OF ACTIVITY 2.) Passive/Easy Going
Flow a.) hot spots and oceanic ridges WHY? b.)
Hawaii c.) (ND pg. 153 /fig. 6.3)
Courtesy of USGS
BECAUSE 1.) they sit above hot asthenosphere
zones 2.) small amount of silica in mafic
material 3.) ridges/spreading centers
produce low pressure pulling up material.
Courtesy of USGS
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WHY THE DIFFERENCE ERUPTION TYPES? A.
Viscosity of magma 1.) Resistance to flow (runny
versus sticky/clunky) 2.) Water versus honey?
Which is more viscous? 3.) Plugs up the
outlet. B. Gas content of magma 1.) More
gas more explosivity 2.) Dry ice in a bottle
example
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VISCOSITY The mobility of magma/lava 1.)
TEMPERATURE of magma/lava 1.) Consider cold
honey and warm honey. 2.) COMPOSITION of
magma/lava 1.) Felsic Lots of silica more
viscous does not flow easily 2.) Mafic Less
silica and is less viscous flows easily. 3.)What
is so special about silica? Lets talk. (N.D. pg.
154/Fig. 6.4) 4.) Basalt-mafic
Andesite-intermediate Rhyolite-felsic (ND pg.
156/Table 6.5)
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VISCOSITY The mobility of magma/lava 3.)
MINERAL CONTENT (this needs to be added
to published notes) 1.) The more solid chunks
the slower the flow. 2.) How related to
content? Which will flow easier? Honey or
oatmeal. Assumptions?
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PASSIVE ERUPTIONS gas content? Silica
content? Plate location?
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VIOLENT ERUPTIONS gas content? Silica
content? Plate Location?
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VOLCANIC EXPLOSIVITY INDEX Determined by 1.)
volume of material ejected 2.) altitude the
eruption 3.) duration of the major blast 4.)
Ranges 0-8 5.) Largest ever VEI7 Tambora
(Indonesia) 1815 ND pg. 167/Table 6.8
Courtesy of USGS
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WHAT COMES OUT OF VOLCANOS? VOLCANO
VOMIT 1.)Characteristic Gases a.) most abundant
is water vapor (50-80) b.) carbon dioxide
(CO2) (15) c.) small amounts of nitrogen,
sulfur, chlorine, carbon monoxide, and
hydrogen d.) these can be detected in various
amounts and help with understanding volcanos
(more later)
Courtesy of USGS
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WHAT COMES OUT OF VOLCANOS? VOLCANO
VOMIT Pyroclastics-chunks of rock particles.
Bombs/blocks- BIG bigger than 64mm6.4cmabout
3in.
Courtesy of USGS
Courtesy of USGS
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WHAT COMES OUT OF VOLCANOS? VOLCANO
VOMIT Pyroclastics-chunks of rock particles.
Lapilli Rock fragments between 2 and 64
mm (0.08-2.5 in) in diameter that were ejected
from a volcano during an explosive eruption
Courtesy of USGS
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WHAT COMES OUT OF VOLCANOS? VOLCANO
VOMIT Pyroclastics-chunks of rock particles.
Peles Tears Small bits of molten lava in
fountains can cool quickly and solidify into
glass particles shaped like spheres or tear
drops called Pele's tears, named after Pele,
the Hawaiian goddess of volcanoes.
Courtesy of USGS
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WHAT COMES OUT OF VOLCANOS? VOLCANO
VOMIT Pyroclastics-chunks of rock particles.
Volcanic ash consists of rock, mineral, and
volcanic glass fragments smaller than 2 mm (0.1
inch) in diameter, which is slightly larger
than the size of a pinhead.
Not like other ash
Courtesy of USGS
Courtesy of USGS
Courtesy of USGS
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WHAT COMES OUT OF VOLCANOS? VOLCANO
VOMIT Pyroclastics-chunks of rock particles.
Pyrocalstic Flow 1.) Chunks of ash, blocks,
etc. 2.) Races down slope 3.) Can be super
hot Nuee ardente (glowing cloud)
Courtesy of USGS
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WHAT COMES OUT OF VOLCANOS? VOLCANO
VOMIT Pyroclastics-chunks of rock particles.
Lahars Lahar is an Indonesian word for a rapidly
flowing mixture of rock debris and water
that originates on the slopes of a volcano
Courtesy of USGS
Courtesy of USGS
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WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT
Lava Lava is from the Italian word for
stream, which is derived from the verb lavare--to
wash.
Lava Delta Lava entering the sea often builds a
wide fan-shaped area of new land called a lava
delta.
Courtesy of USGS
Courtesy of USGS
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WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT
Aa (pronounced "ah-ah") is a Hawaiian term for
lava flows that have a rough rubbly surface
composed of broken lava blocks called clinkers.
Courtesy of USGS
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Volcanoes erupt as magma is created (melting)
by begins with higher heat at depth-rises as
solid how can we melt solid rock a.)
lowering pressure- decompression
melting b.) raising the temp. c.)
increasing water content
Courtesy of USGS
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THREE BASIC TYPES OF VOLCANOS
1.) SHIELD VOLCANO (low viscosity, low
volatiles, large volume) A.) Broad gently
sloping flanks, large size B.) Composed of mafic
laba layers C.) Passive eruption-low viscosity
lava D.) Effusive eruption (next slide) E.)
Example Hawaiian Islands
Courtesy of USGS
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EFFUSIVE ERUPTION A.) dominated outpouring
lava B.) not violent C.) lava may beaa or
pahohoe
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THREE BASIC TYPES OF VOLCANOS
2.) SCORIA or CINDER CONES(medium viscosity,med.
volatiles, small volume) A.) Steep sides and
small B.) Composed of pyroclastic chunks
and ourpouring of baslatic lava from base C.)
Common on sides of bigger volcanos and in
groups D.) Strombolian-type eruptions (hold on,
next slide) E.) Example- Sunset Crater AZ
Sunset Crater Courtesy of NPS
Courtesy of USGS
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STROMBOLIAN ERUPTIONS 1.) Intermittent explosion
or fountaining of basaltic lava 2.) single vent
or crater 3.) Each episode is caused by the
release of volcanic gases 4.) typically occur
every few minutes 5.) rhythmically or
irregularly 6.) partially molten volcanic bombs
Courtesy of USGS
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THREE BASIC TYPES OF VOLCANOS
3.) COMPOSITE or STRATOVOLCANO (High
viscosity, high volatiles, large volume) A.)
Steep flanks and large in size B.) Different
layers of felsic to intermediate lava and
pyroclastics (andesitic to rhyolite) C.) Both
passive and violent eruption types D.)
pyroclastic flows common (nuee ardente) E.)
Example-Mt. St. Helens 1980 and Krakatau 1883
Courtesy of USGS
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Pg. 27 ADD Lets look at patterns of ERUPTION
STYLES VEI COMPOSITION VOLCANO
(??viscosity??) TYPE ICELANDIC
0-1 Basalt/mafic Small shield/plateau HAWAIIAN
0-1 Basalt/mafic Large shield
STROMBOLIAN1-3 Basalt-andesite Scoria
cone VULCANIAN 2-5 Basalt-rhyolite Scoria-strat
ovolcano PLINIAN 3-8 Andesite-rhyolite Stratovol
canoes CALDERA 3-8 Andesite-rhyolite Caldera N.
S. 164/ Fig. 164
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2 TYPES OF FISSURE ERUPTIONS No volcano cone-like
feature HUGE AMOUNTS OF VOLCANIC MATERIAL
1.) FLOOD BASALTS a.) effusive type of
eruption b.) large sheets of lava c.) form
plateaus/huge flat areas examples Columbia
Plateau Snake River Siberia India
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2 TYPES OF FISSURE ERUPTIONS No volcano cone-like
feature HUGE AMOUNTS OF VOLCANIC MATERIAL
2.) PYROCLASTIC/CALDERA a.) high explosivity b.)
no central vent/caldera OR collapsed
stratovolcano. c.) High viscosity, high
volatiles, SUPER large volume d.) similar to
composite/strato may involve Stratovolcano) but
VERY HIGH VOLUME Examples Yellowstone Plateau ND.
Pg. 177/Fig. 6.35 Snake River Plain Hot Spot
trail WHAT!?!?!?!?I thought hot spot Katmai
National Monument
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USGS link
Pg 27 add VOLCANO MONITORING 1.) Earthquake
Swarms Seismic activity Tiltmeters 2.) Ground
deformation 3.) Changes in gas content
(ratios) 4.) Groundwater changes (level and temp)
Courtesy of USGS
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Pg 27 add WARNING SYSTEMS 1.) Like EQ/faults
each has its own pattern pre-eruption 2.) Quick
explosions to slow lava flows. 3.) Lahar warning
system Lahar warning system problems?
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