IGNEOUS ROCKS &
VOLCANISM
a rock is an aggregate of mineral(s) or mineral matter which occurs in
massive deposits
bedrock is a massive unbroken solid rock directly overlain by soil in
many locations
an outcrop is a massive unbroken solid rock exposed at the Earth’s
surface
IGNEOUS ROCK FAMILY
• Definition of igneous rock
• Origin of magma
• convergent plate boundaries
(subduction zones)
• divergent plate boundaries (ridges or
rifts)
• isolated magma plumes (hot spots)
IGNEOUS ROCK FAMILY
• Assimilation
• melting of other rock material
incorporated into a magma causing
original composition magma to change
• an example is the mixing of magma
originating in mantle with a different
composition of continental crust as
magma rises
IGNEOUS ROCK FAMILY
• Intrusive and extrusive as applied to
magmas and igneous rocks
• intrusive refers to any igneous activity
below Earth’s surface
• extrusive refers to any igneous activity at
the Earth’s surface
IGNEOUS ROCK FAMILY
• Texture, mineral composition , and igneous
rock names
• texture
• grain size of mineral fragments in rock
and depends on the cooling rate of
magma
• smaller in rock if magma cools fast
• larger in rock if magma cools slower
IGNEOUS ROCK FAMILY
• kinds of textures
• phaneritic (coarse grained)--intrusive
• aphanitic (fine grained)--extrusive
• glassy--extrusive
• vesicular (comprised of many holes
called vesicles --extrusive
• porphyritic--more than 1 size
mineral fragment present-phenocrysts and matrix
IGNEOUS ROCK FAMILY
• pegmatitic--intrusive
• pyroclastic--extrusive
Igneous Rock Textures
Phaneritic
Aphanitic
Igneous Rock Textures
Glassy
Vesicular
Porphyritic
Pegmatitic
IGNEOUS ROCK FAMILY
• mineral composition
• igneous rocks are comprised of a
combination of silicate minerals
• Bowen’s mineral series
• describes an orderly sequence of
mineral formation from a cooling
magma and explains specific mineral
combinations in the rock
• discontinuous and continuous series
• hydrothermal solutions
IGNEOUS ROCK FAMILY
• magma composition
• can change (1) as cooling progresses
and minerals separate; (2) magma
assimilation
• igneous rock names
• essential minerals
• minerals in rock used to classify
rock by name
• accessory minerals
• minerals not used to classify rock
IGNEOUS ROCK FAMILY
• felsic
• rocks light in color and contain a lot
of feldspar and quartz
• mafic
• rocks dark in color because they
contain a lot of biotite, hornblende,
or other dark minerals
• ultramafic
• rocks that contain augite and olivine
• igneous rock chart
Igneous Rock Classification Table
Phaneritic Textured Igneous Rocks
Granites
Diorite
Gabbro
Dunite
Aphanitic Textured Igneous Rocks
Rhyolite
Basalt
Porphyritic Textured Igneous Rocks
Granite Porphyry
Rhyolite Porphyry
Andesite Porphyry
Glassy and Vesicular Textured Igneous Rocks
Obsidian
Pumice (2)
Scoria
IGNEOUS ROCK FAMILY
• Igneous rock bodies
• intrusive (plutons)
• discordant-- bodies which cut across
sedimentary rock contacts or
boundaries
• batholith--largest pluton body and
irregular in shape--ore deposits like
gold, silver, copper etc. are often
associated with these
Batholiths in Western USA
IGNEOUS ROCK FAMILY
• stock--smaller irregular shaped body
with possible associated ore bodies
• dike--very small tabular shaped body
• concordant--do not cut across
sedimentary rock boundaries
• laccolith--large lens shaped body
• sill-- a small tabular shaped body
Igneous Rock Bodies (Plutons)
IGNEOUS ROCK FAMILY
• Important uses of igneous rocks
• used as building materials and
tombstones--this use is the same for all 3
families of rocks
• pumice is used an an abrasive material
VOLCANISM
VOLCANISM
• Some common terms
• volcanism
• the processes by which magma and/or
gases or volatiles are transferred to the
Earth’s surface
• volcano
• an elevated area or mountain formed
from accumulations of lava and/or
pyroclastic materials
VOLCANISM
• active, dormant, and extinct volcanoes
and volcanic areas
• active--eruption can occur in the near
future--Mt. St. Helens and other
Cascade mountains are examples
• dormant--presently inactive but
believed capable of future eruptions
• extinct--expected not to erupt again
• Origin and global distribution of volcanism
• origin of volcanic materials
VOLCANISM
• global distribution
• “Ring of Fire” or circum-Pacific region
is the greatest concentration of volcanic
activity on Earth
• Mediterranean Region---2nd largest
region of volcanoes on Earth
Concentration of Volcanic areas on Earth
VOLCANISM
• Volcanic rocks, volatiles (gases and
vapors), and manner of eruption
• volcanic rocks
• include all extrusive textured rocks and
include basalt, andesite, rhyolite,
pumice, scoria, tuff, obsidian and
volcanic breccia
• volatile emissions
• steam (water vapor)--most abundant
VOLCANISM
• carbon dioxide is next abundant while
sulfur dioxide, nitrogen, and sulfur
trioxide are others
• carbon dioxide additions into the
atmosphere can add to the “Greenhouse
Effect” and the others can contribute to
acid rain formation
• burning or decomposition of fossil
fuels are synthetic contributions to
the“Greenhouse Effect and acid rain
VOLCANISM
• manner of eruption (passive or explosive)
• depends largely on viscosity of magma
• viscosity depends on composition
and temperature of the magma
associated with the eruption--the
higher the silica content or the cooler
the magma, the more explosive the
eruption, and vice versa
• most ocean basin eruptions are
passive while most continental are
explosive--why???
Volcanic Eruptions on Continents
VOLCANISM
• Major categories of volcanic deposits
(Classification of volcanoes)
• deposits are comprised of lava flows
and/or pyroclastics
• shield type---broad with gentle slopes
• thick deposit of basaltic lava flows
with little or no pyroclastic materials
• associated with ocean basin eruptions
• Hawaiian shield is about 28,000 feet
thick with pimple-like islands
Shield Type of Volcanic Deposit
Shield Type of Volcanic Deposit-Kilauea–
Hawaiian Islands
Earth’s most
active and
Mauna Loa—
Earth’s largest
volcano
Shield Type of Volcanic Deposit--Hawaiian
Islands
VOLCANISM
• cinder cone or scoria cone
• small deposit of pyroclastic or ejected
materials
• steep slopes and less than 1000 feet tall
• represents last stage (cooler) of basaltic
or less commonly andesite eruptions
• example is Paricutin, Mexico which
erupted in 1943 and grew 120 feet tall
the first day
Cinder Cone Type of Volcanic Deposit
Cinder Cones in Arizona
VOLCANISM
• composite or stratovolcano
• very tall deposit of alternating lava
flow and pyroclastic deposits
• comprised of andesite or rhyolite,
occur on the continents and are
explosive
• examples include: Mt. Vesuvius, Mt.
Fujiyama, Mt. Kilamanjaro and
mountains in the Cascades including
Mt. St. Helens
Stratovolcano Type of Volcanic Deposit
VOLCANISM
Famous Composite Volcanoes
Mt. Fuji
Mt. Shasta
Mt. Kilimanjaro
volcanic dome
solidified lava, hundreds of meters high
volcanic ash mixed with rock fragments
viscous felsic or intermediate magma piled
up around a vent found in composite volcanoes
VOLCANISM
• Eruptions with special volatile emissions
• strombolian type
• incandescent cloud is stable over vent
and reflects light from magma
• Mt.Stromboli is best example and
called “Lighthouse of the
Mediterranean”
VOLCANISM
Mount Stromboli
VOLCANISM
• Nuee Ardentes (fiery or glowing cloud)
type---pyroclastic flow
• a very hot cloud of volatiles and ash
• Mt. Pelee on Martinique emitted a 700
degree (C) cloud and killed 30,000
people in a few minutes in St. Pierre
VOLCANISM
pyroclastic flow
VOLCANISM
St. Pierre after Mount Pelee’s eruption
Art 06.08a1
VOLCANISM
Artist’s conception of
Vesuvius’ eruption in A.D. 79
over Pompeii and Herculaneum
VOLCANISM
Lake Nios type
volcanic carbon dioxide trapped in the
subsurface was emitted and killed 1746
villagers in Cameroon, Africa in 1986
Special features and benefits associated
with volcanism
special features
continental flows
Continental Lava Flows in Western USA
VOLCANISM
• ocean basin flows--associated with the
shield type deposit
• pahoehoe--ropy surface lava
• aa--blocky surface lava
• lava tubes or tunnels
• volcanic neck and radiating dikes
Volcanic neck and Radiating Dikes
at Shiprock, New Mexico
VOLCANISM
• caldera
• a crater caused by the collapse of a
volcanic cone
• Crater Lake, Oregon is the best
terrestrial example
• Crater Lake is 5 miles in diameter
Formation of a Caldera
Crater Lake, Oregon
Could the Yellowstone Caldera Cause a Future Disaster?
Yellowstone is one of the world’s largest active volcanic areas.
Abundant geysers, hot springs, and other hydrothermal activity are
leftovers from its recent volcanic past. It erupted about 600,000 years ago
and is about time again.
Olympus Mons, Mars---Shield Type with
Caldera
formally known as Nix Olympica, it
rises about 13 miles high, or 3 times
higher than Mtn. Everest and covers
an area equal to Arizona. It is the
largest volcano in the solar system—
it has 6 calderas—
VOLCANISM
• Benefits related to volcanism and igneous
activity
• fertile soils formed from weathering of
igneous rocks
• magma in contact with or in the vicinity
of groundwater produces steam which is
a source of geothermal energy
VOLCANISM
Geothermal Energy From Hydrothermal
Ocean Vents
CLICK HERE
subsurface volcanic water mined on
extra-terrestrial bodies may affect
colonization of those bodies
VOLCANISM
• Mass wasting associated with volcanism
• severe damage can result from mudflows
on the sides of volcanoes---these flows are
called lahars which can form when highly
unstable layers of volcanic ash and debris
are saturated with water
VOLCANISM
A house moved by a lahar
VOLCANISM
Lahar mudflow
VOLCANISM
• Prediction of volcanic eruptions
• the increase in the number and magnitude
of earthquakes associated with volcanic
activity favors volcanic activity sooner
• the magnitude of bulging of Earth’s
surface can be used an eruption predictor
• tilt meters and laser mirrors can be
used to measure the magnitude of
bulge
VOLCANISM
• Volcanism in the solar system
• on the moon
• presence of light colored and basaltic
lava flows
• Mars
• Olympus Mons and other caldera, and
is 13 miles high and its base covers an
area the size of Arizona—good extraterrestrial example of a shield volcano
VOLCANISM
• Io, a moon of Jupiter
• only other place where volcanic
activity was actually observed
happening