Download F08 5 Emplacement

ERTH 1010 & 1100
Emplacement of Igneous Liquids
Volcanoes and Plutons
Ooh…born of “Fire”
Hot matter will emit light. For a perfect emitter (a
blackbody), temperatures above 390ºC produce visible
brightness. 500ºC will look dull red in a lighted room.
Fire emits light, but hot rocks are not on fire.
Under the surface
Volcanoes are where
magma reaches the
surface.
But magma may
originate deep within
the earth.
Erosion may reveal the
movement of magma
within the crust.
Dikes
Magma moving
in fractures that
cut geologic
strata forms
dikes.
The substructure
Dikes and necks at
Ship Rock, NM
Sills
Magma that exploits a
stratgraphic bed is
called a sill.
The sill exploits the
preexisting weakness
in the Earth crusts.
Plutons
Pluton exposure is
somewhat tricky - we
only get to see a small
portion.
Mt. Monadnock (NH)
and Stone Mountain
(GA) are domed
exposures shaped by
weathering (exfolation).
The true shapes of
plutons are often
hidden.
Ongoing crystallization
Making room
Intrusions have to
make room for
themselves. The
mechanism isn’t
always apparent.
More room
Sheet plutons
Eastern Wichita Mountains
Qtr
Cambrian
Perm
Schematic Section
Granite intrusion required low
viscosity
Structural Trapping
Geospatial information
Looking below
Looking below
The geophysical
data reveals the
shape of the
igneous
intrusions at
depth
Same but…
Mount Scott
Granite
Rush Lake
Granite
Medicine Park
Granite
Subtle contacts
Small differences in rock type does not
result in major changes in the Earth’s
surface
Mount Scott Granite
An intergrowth
of quartz and
feldspar
Likely result of too
few nucleation sites
Undercooling
Viscosity contrasts
Rapid diffusion
Volcanoes
Where partial melts of the Earth’s Interior
reach the surface.
•Partial melts – magmas (mostly liquid with
some solid)
•These are hotter than surroundings – lose
heat and solidify
•These originate at depth – depressurize as
they ascend
Q: What determines the nature of a volcanic
eruption? How do these factors influence the
morphology of a volcanic structure?
Hey…it’s a rough world out there!
Earth’s surface is dynamic
Advantages: transfer of abundant energy
Rivers (from mountains) to Hydrothermal
Life utilizes the energy in these systems - not
just in an electrical generation sense!
Disadvantages: transfer of abundant energy
Volcanoes, earthquakes, and floods
Produce enough energy to displace matter and
wreck habitats
79 AD Vesuvius
An eruption that
resonates
throughout western
civilization
Pyroclastic Flow
Imagine superheated air, steam, ash, and rocks
traveling faster than any river.
Magma is shape
The shape given to volcanic edifices is due to its
eruptive style. It’s eruptive style is due to magma:
Composition – including dissolved gasses
Low Si – more fluid
High volatiles – more explosive
Supply rate – material from the Earth’s interior
Fast – frequent eruptions from same vent
Slow – vents solidify, more explosive
The nature of an eruption is a function of the
pressure of the magma.
Surface volcanoes and their location
Note that
there are
marine
volcanoes
all along
the midoceanic
ridges
Iceland
In addition to being
the home of the
world’s most difficult
language, Iceland is
where the midAtlantic ridge is
above water.
Surtsey surfaces in 1963
Kilauea, Hawaii
March, 1996
Q: What are some common volatile
components in a magma?
Cooling joints
Contraction during
cooling can form
polygonal columns
Mato Tipila | Devils Tower
Northeastern Wyoming
Another volcanic neck,
this time with prominent
cooling joints.
40.5 million years ago,
magmas intruded the
older sedimentary rocks
of this area. These have
eroded away
Volcanic structures
In general, the
#1 control on
viscosity is
silica content
Felsic
eruptions are
more viscous
than mafic
ones.
shield volcano
Hawaii: Hot asthenospheric mantle, below
provides hot material that intrudes
lithosphere and melts below oceanic crust.
Generally low Si
Low volatile
High rate
Mauna Kea, Hawaii
Cinder Cones
Shield
Q: What tectonic feature produces
volcanism in Hawaii?
Pu’u Hulu
Mauna Loa, Hawaii
Pahoehoe
Q: What are the names given to
these two types of lava?
Kalapana Gardens
Kilauea, Hawaii
Lava flows overruns
everything. In this
Kilauea eruption, a
palm forest left lava
encrusted casts.
Fissure
Heating, inflation, and
intrusion can deform the
surface, cause long
breaks that become lava
conduits
Cinder Cone
Low Si
High volatile
high rate
Mauna Kea, HI
Mauna Loa
Summit Cone, Mauna Kea
Pu’u O’o cone
Q: What does this lava
lake signify in terms of
volatiles?
Large scale eruptions
Periodic eruptions of large
amounts of lava
Close association with
extinctions
Composite volcano
Mixed but generally
Composite volcanoes build up
over time from localized vents.
Higher Si
High volatile
Low rate
Mount Saint Helens: pre 1980
Mount Saint Helens is an example of
a composite stratocone - the locus of
volcanism for hundreds of thousands
of years
Q: What tectonic feature produces
volcanism in the Cascades?
In 1980, the mountain began
to erupt small plumes of ash
from an area near the
summit.
The first eruption in the
conterminous US since that
of Mount Lassen (northern
California) in 1914.
Mount Saint Helens:
March, 1980
Mount Saint Helens
The climatic eruption
would be weeks
away. Observations
revealed a bulge in
the north flank,
attributed to magma
intrusion and inflation.
The north side of the
mountain swelled during
April and early May. It
failed and slid away on May
18 releasing the gasses and
magma in a cataclysmic
explosion.
Mount Saint Helens:
May 18, 1980 0832
Silicosis - long-term exposure to crystalline silica. Phage
resistant, small particles remain intact after phagiocytosis.
Pneumonoultramicroscopicsilicovolcanoconiosis* is
silicosis specifically brought on by long-term exposure to
volcanic ash.
Boys** in Yakama, WA
wear dust masks in the
days after the May 18,
1980 eruption of Mt. Saint
Helens. Yakama, in
central Washington, was
darkened by ash on May
18.
Dust in the environment
is difficult to remediate
*Longest word in OED and Websters, also mentioned on The Simpsons 2F07
**Prof owned same sporty orange vest in 1980, however his bike was 30% less
cool (darn fenders!).
North slope failure
Destruction
The release of heat melted
the glaciers. Gas propelled
ash into the upper
troposphere.
Mount Saint Helens:
May 18, 1980
Wyerhouser Logging Trucks
Mount Saint Helens
Meltwater, fallen trees, and
ash choked the streams,
destroying adjacent lands.
The eruption removed the top
1,800 feet of the mountain.
View from the north
Several smaller eruptions
continued through 1980.
This included two that sent
ash southward over the city
of Portland, OR.
Portland, OR
View from South Rim, June 1991
Q: What is a
volcanic dome?
Lessons
Eruption from one of
the stratocones is
more than just
igneous materials.
The heat melts the
snow and ice,
resulting in a deluge
of mudflows and
lahars.
This has been
applied to other
volcanic hazards
Dome on Soufriere Hills Volcano
Montserrat
Soufriere Hills Volcano
Montserrat
Soufriere Hills Volcano
Montserrat
Q: How might volcanoes contribute
to continental growth?
Caldera
Moderate – high Si
High volatile
Low rate
Eruptive volume
Movement of felsic
magma, like that at
Yellowstone, can
lead to voluminous
and violent
eruptions. In all
cases, much of the
eruptive material is
discharged into the
atmosphere.
Climate change
ensues.
Caldera
Crater Lake, Oregon
Caldera forming
40,000 years ago
The pinnacles
Llao rock
Krakatau 1883
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Energy