Download Rock and Lava: Felsic vs. Mafic

Rock and Lava:
Felsic vs. Mafic
• FELSIC ROCK
• MAFIC ROCK
Types of Volcanoes:
•SHIELD
• Cinder Cone
•Composite
(stratovolcano)
•Dome
• Caldera
Types of Volcanoes
Stratovolcanoes vs. Shield Volcanoes
• Shield volcanoes are significantly more voluminous
than stratovolcanoes
– Especially true when considering the size of the volcano at its
base
• Note the differing profiles (concave up vs. concave
down) for the two types of volcanoes
Mt. Etna, Sicily
Nyiragongo and Nyamuragira Volcanoes
CINDER CONES
Types of Volcanoes
• Steep conical hills of Cinder
volcanic fragments that
accumulate around and
downwind of the vent
– Sides straight with slopes
of ~30° (angle of repose)
Cones
Red Cones, Long Valley
Caldera, California
• Pyroclastic material
(a.k.a. tephra): ejected
material of all sizes (a.k.a.
ash, bombs, blocks, etc.)
– Solid by the time it hits
ground
• Most numerous type of
volcano
• Small: 10’s to 100’s of
meters tall
• Rarely reactivated (i.e.,
rarely erupt a 2nd time)
Downwind Side
Kilauea Iki, Hawaii
Types of
Volcanoes
Cinder Cones
Stromboli, Italy
Downwind
Side
• Low/Medium Viscosity
• Medium/High Volatiles
• Small Volume
Sunset crater, AZ
Mauna Loa, Hawaii
SHIELD VOLCANO
Types of Volcanoes
Shield Volcanoes
• Broad, gentle slopes which are convex upward (like a warrior’s
shield laid on the ground)
• Layered - built by the repeated eruption of fluid, low viscosity lavas
• Enormous volcanic edifices with huge footprint because
– Lava flows across the ground easily
– Lava can form tubes that enable lava to flow tens of kilometers from an
erupting vent with very little cooling
• Largest volcanoes on Earth
Mauna Loa,
Hawaii
STRATOVOLCANOES, or Composite Volcanoes
Mt. Fujiyama,
Japan
Types of Volcanoes
Stratovolcanoes (a.k.a. composite
Steep, conical volcanoes volcanoes)
•
• Slopes have a concave
upward profile
• Produce both highly
explosive and effusive
eruptions
• Composed of alternating
layers of pyroclastic
material and viscous
lava (i.e., they are
stratified)
• May have secondary
vents with cinder cones
and lava domes on
flanks
• Typically occur on the
landward side of
subduction zones
Mount Mageik, Alaska
Mt. Etna viewed
from space
Mt. St. Helens “Flyby”
Rainier
Saint Helens
Mt. St. Helens
Mt. St. Helens Eruption Sequence
• The following slide
displays the series of
events involved in the
Mount Saint Helens
eruption of 1980.
Mount Saint Helens
• The 1980 eruption of
Mt. St. Helens was
equivalent to
detonating one
“Hiroshima-sized”
atomic bomb every
second for seven
hours.
• There are three main areas where
volcanoes will occur (2 of which are plate
boundaries)
Lithospheric Plate Boundaries.
They are marked by earthquake epicenters (yellow dots) and volcanic
activity (red triangles).
The “Circum-Pacific Belt” (Ring of
Fire) is the outer boundary of the
Pacific Plate.
• A subduction zone
creating a volcanic
mountan chain, like
the Cascade
Mountains in
northwest United
States.
• A subduction zone
creating an Island
Arc volcano chain.
The islands of Japan
are an example of
this.
Divervent
Volcanism:
A result of
Seafloor
Spreading or
continental
rifting.
Types of
Volcanic
Eruptions
• Magma formed at
subduction zones when
subducting plate
reaches 100 km
Explosive
• As magma moves
upward it melts part of
the overlying crust to
produce magma highly
variable composition
• In general, magma temperature decreases
while SiO2, volatile content and viscosity
increase.
– This makes the volcano more
explosive.
• Vents often blocked with congealed
magma, allowing gas pressures to
increase to catastrophic levels
– This makes the volcano more explosive
Mt. Pinatubo,
Philippines, 1991
Mt. St. Helens,
Washington,1980
Types of Volcanic
Eruptions
Explosive
• Sudden, violent eruptions of
magma, rock, and debris
• Erupted material
– Large chunks of material can
be thrown 100’s m
– Finer material can be ejected
high into the stratosphere
(~40 km) and travel 1000’s of
km
• Eruptions often short-lived
(hours, days)
• Vents often blocked with
congealed magma, allowing
gas pressures to increase to
catastrophic levels
Mount Spurr, Alaska
Pyroclastics
Ash and Pumice
(a.k.a. Tephra)
Explosive
• Pyroclastic material: fragments of
volcanic rock and lava (regardless of size)
blasted into air by explosions or carried
upward by hot gases in eruption columns
or lava fountains
• Larger fragments usually fall near volcano
• Smaller fragments may be transported far
from the source
Bombs
Blocks
Volcanic
Explosivity
Index (VEI)
Historic
Eruptions
In the last 10,000 yrs
–
–
–
–
–
–
4 VEI 7 eruptions
39 VEI 6 eruptions
84 VEI 5 eruptions
278 VEI 4 eruptions
868 VEI 3 eruptions
3477 VEI 2 eruptions
Volcanic Eruptions
Plinian Eruptions
• Large, explosive eruptions
• Form enormous dark
columns of tephra and gas
that extend high into the
stratosphere (>11 km)
• Driven upward by
buoyancy of hot gasses
• Associated hazards
– Pyroclastic flows and surges
as eruptive column collapses
– Extensive ash falls
– Ash Clouds
• High viscosity
• High volatiles
• Large volume
Mt. St. Helens,
Washington
Volcanic Eruptions
Phreatic Eruptions
• Produced when
groundwater
comes in contact
with hot rock or
magma and
flashes to steam
• No new magma is
expelled
• Only preexisting
rock is erupted
Mt. St. Helens, Washington,
April 4, 1980
Types of Volcanic Eruptions
Effusive (non-explosive)
Oceanic (divergent boundaries and
oceanic hot-spots)
• Form pillow lava as
molten rock flows into
the ocean and rapidly
cools
Types of Volcanic Eruptions
Effusive (non-explosive)
• May initiate with shortlived episode of lava
fountaining (10-500
meters high)
• Dominated by gentle
outpourings of lava onto
the ground, usually from
a central vent or conduit
• Eruptions often longlived (days, weeks,
years)
Lava lake at Pu`u ` O `o
Cinder Cone, Kilauea
Volcano, Hawaii
Types of Lava
Pahoehoe (Effusive)
Ropy
Pahoehoe
• Smooth, hummocky, or ropy texture
• Typically advances as a series of
small lobes and toes that continually
break out from cooled crust
• Very fluid (i.e., not very viscous)
Pahoehoe toe
Kilauea Volcano, Hawaii
Types of Lava
Aa (Effusive)
• Rough, rubbly surface composed of broken lava blocks called
clinkers
• Aa flows composed of
– Spiny, irregular surface
– Massive, dense inner core
• Viscous
• Difficult and slow to traverse once solidified
Kilauea
Volcano,
Hawaii
Kilauea Volcano,
Hawaii
A Typical Rift Eruption
• Eventually, the rift
eruption coalesces
to a central vent
• A stage of lava
fountaining ensues
• Low Viscosity
• Low Volatiles
• Large Volume
Pu`u ` O `o Eruption
1983 to Present
Hot-Spot
volcanism: A result
of superheated
mantle “plumes”
extending up
through the
asthenosphere.
Lithospheric pates
move across these
stationary hot
areas, forming a
new volcano as an
old one fades away
from the spot. The
Hawaiian Islands
and the Emperor
Seamount (which
includes Midway
Island) are
exampes.
Volcanic Hazards
Lava Flows
• Molten rock that
pours, oozes, or
fountains from
erupting vent
(effusive or explosive)
• Flow speed depends
on
Channel
Flow
– Viscosity
– Topography
– Type of flow
• Broad sheet
• Confined channel
• Lava Tube
Broad
Sheet
Kilauea,
Hawaii
Lava Flows
• Royal Gardens
Subdivision,
Kalapana, Hawaii
– Subdivision located on
South Flank of Kilauea
Volcano
– What wasn’t destroyed
was totally cut off by
impassable lava flows
– Tube-fed pahoehoe
flow
• World-wide, as
populations increase,
a greater number of
populations/structures
are in the way of
potential lava flows
Mount Saint Helens,
Washington
May 18,1980 Eruption – Ash Cloud
Advancing ash cloud
Clark Air Force Base
Mt. Pinatubo,
Philippines
1991
Damaged Jet
Turbine Blades
Eruption
Cloud
Melted Ash
Coating
Volcanic Hazards
Ash Falls
1997 Soufrière Hill, Montserrat, West Indies
1991 Mt. Pinatubo, Philippines
1997 Soufrière Hill, Montserrat, West Indies
1994 Rabaul, Papau New Guinea
• Ash: smallest tephra fragments
– <2mm in diameter
– Can be carried by wind
– Can travel 1000’s of km
• Affects far more people than
other, more lethal volcanic
hazards
• Covers everything, infiltrates
most openings, and is highly
abrasive
• Buries objects close to source
• Potential Effects
– Daylight turns to darkness
– Roofs collapse from weight
– Machinery and vehicles
abraded
– Farmland covered
– Streets become
slippery/blocked
– Power plants forced to shut
down
– Sewer systems clog
Volcanic Hazards
Ash Falls
Mount Saint Helens, Washington
May 18,1980 Eruption – Ash Fall
• Ash fall accumulations
http://wrgis.wr.usgs.gov/fact-sheet/fs027-0
Mt. Pinatubo, Philippines
Clark Air Force Base, 1991
Volcanic
Hazards
Ash Falls
• Certain
prehistoric
eruptions dwarf
many modern,
familiar
eruptions
• Ash falls from
largest
prehistoric
events affected
areas of
continental
scale
Volcanic Hazards
Pyroclastic Flows
Ground-hugging, high-density
mixtures of hot, dry rock
fragments and hot gases
• Travel at >80 km/hr
• Temperature of 200-700°C
• Pyroclastic flows
– Destroy by direct impact
– Bury sites with hot rock debris
– Melt snow and ice to form
lahars
– Burn forests, crops, buildings,
& all other combustible
material
• On margins of flow, serious
injury may result from burns
and inhalation of hot ash and
gasses
1980 Mt. St. Helens, Washington
Volcanic Hazards
Pyroclastic Flows
988 Colima Volcano, Mexico
Collapsing lava dome
1984 Mayon Volcano, Philippines
Eruption
Volcanic
Hazards
1991 Mt. Pinatubo,
Philippines
Pyroclastic Flows
Charred stream
channel 5-6 km from
lava dome
1982 El Chichón,
Mexico
1997 Soufrière Hill,
Montserrat, West Indies
Remnants of a building with
bent steel reinforcing rods
Mount Saint Helens, Washington
May 18,1980 Eruption – Pyroclastic Flows
• Leaves a “Pumice Plain” its
wake
Pyroclastic Flows
Unzen Volcano, Japan
• 1991-1995: Growth of lava
dome with frequent
pyroclastic flows
– Traveled up to 5 km
• One such flow killed 43
people including 3
volcanologists
• Areas damaged by ash
cloud surge extend beyond
pyroclastic flow deposits
Ash Cloud
Surge Effects
Pyroclastic Flows
Soufrière Hills Volcano,
Montserrat
• 1995-Present: Episode of
lava dome formation
• Collapse of the lava dome
generated a series of
pyroclastic flows and
surges
Volcanic Hazards
Lahars
• Rapidly flowing mixture of
rock debris and water
• Can travel 10’s of km’s,
typically down river valleys
• Hot or cold
• Especially common at
stratovolcanoes
• Generated
– Without eruptions
• Landslides mixed with water
– During eruptions
• Melting of snow and ice by
pyroclastic flows, lava flows
– After eruptions
• Heavy rainfall erodes
deposited ash, etc.
• Sudden release of water
from crater lakes
Mt. St. Helens,
Washington
(1 year later)
• By eroding rock debris and
incorporating additional
water, lahars can grow to
>10 times their initial size
– As slows, looses sediment
load and becomes smaller
again
Volcanic Hazards
Lahars
Nevado del Ruiz
Volcano, Columbia
• Effects
– Destroy by direct impact;
Often contain larger
boulders and trunks
– Bury buildings,
communities, and valuable
land in cement-like layers
of rock debris
– May trap people
– Increase sedimentation
rates in local streams and
rivers; Leads to flooding
and secondary lahars
– Block tributary streams
creating lakes that may
suddenly flood
A lahar destroyed the
town of Armero,
November 13, 1985
Volcanic
Hazards
Lahars
1992-93 Unzen volcano,
Japan
1985 Nevado del Ruiz
eruption, Armero, Columbia
Lake formed behind lahar deposits
from the 1991 Mt. Pinatubo,
Philippines eruption
Mount Saint Helens, Washington
May 18,1980 Eruption – Lahars (a.k.a. mudflows)
Poisonous Gas
• 30,000 Britons
killed by 1783
Icelandic
eruption.
• Some scientists
believe poisonous
gas from volcanic
eruptions helped
wipe out the
dinosaurs
2004 Boxing Day Epicenter
Mount Merapi
Extraterrestrial Volcanism
The Moon
•
•
•
•
•
Lunar maria
Latin for “seas”
Large, plains of basaltic rock
Cover about 17% of the lunar surface
Lava erupted from broken crust associated
with impact craters
• Lunar equivalent to flood basalts
• 4.3 to 3.1 billion years old
”Houston, tranquility base HERE. The eagle has landed.”
• Mare Tranquillitatis
• “Sea of Tranquility”
• Landing site for
Apollo 11
Mars
•
•
•
•
Shield volcanoes similar to those in Hawaii
3.7 billion to 500 million years ago
Possibly still ongoing. Possibly is a long state of dormancy.
Includes extensive lava flows and the largest known volcanoes in
the Solar System
Tharsis Montes
• Ascraeus Mons
• Pavonis Mons
• Arsia Mons
Olympus Mons
• 624 km in diameter
• 25 km high
• The largest known
mountain in the Solar
System
Venera
Soviet probe successfully
landed on venus.
Venus
• More volcanoes than any
other planet in the Solar
System
• Surface is 90% basalt
• Young surface due to this
outpouring of flood basalt
Maat Mons
• Coronae
• Volcanic features
unique to Venus
• Believed to be hot
spot related
Io
• Moon of Jupiter
• Io has more than 150 active
volcanoes
• Lava flows
• Praterae (similar to caldera)
• Plumes of S and SO2
• Patera
Enceladus
• Moon of Saturn
• Few craters show that
it is geologically
active.
• Cryovolcanism
Triton
• Moon of Neptune
• Cryovolcanism Volcanoes and rift
valleys
• Triton geysers may erupt
for up to a year
• Note: very few craters
Geyser-like
eruptions of liquid
nitrogen leave
traces on the
surface.
What is the source of heat for
this volcanism?
Observed Active
Volcanism
Observed Evidence of past
Volcanism
Earth
The Moon
Io
Mars
Enceladus
Venus
Triton