Download Igneous Rocks Intrusions and Volcanoes

Igneous Rocks Intrusions and Volcanoes
Igneous rocks are associated with molten material. This material can be from the mantel or
melted crust material. Texture, iron content and silica content determine the type of igneous rock. The
texture determines the cooling temperature. Rapid cooling gives small to no crystal formation. This
means that the rock formed on the surface. The main minerals for igneous rocks are quartz, feldspar,
mica pyroxene amphibole and olivine. Mantel rock will have mainly olivine, and pyroxene. Melted
crustal rock has large amounts of quartz in it. Texture is a clue to the environment, internal (intrusive) or
external (extrusive). This was known for 200 years and later confirmed with the developing of polarizing
microscope and the careful grinding of a rock thin section (ground rock so thin light can pass through it).
Texture is created by cooling temperatures. Ions in hot magma have too much energy to bond together
and form a crystal. As cooling proceeds the ions lose energy and can then form crystals. Pressure will
also help in this since it forces ions together regardless of the heat energy. If the cooling proceeds slowly
as in intrusive material you have large crystals, if ejected into the surface you get small crystals or no
crystals.
Intrusive rocks are coarse textured (phanorytic.) These rocks
have slow cooling regimes cooling over thousands and thousands of
years in the crust of our planet. The heat is held in by the overlaying
rock. Elephant rocks in Missouri are a perfect example of such a rock.
This is an igneous intrusive body injected into the crust over a billion of
years ago.
Extrusive rocks have different types of appearances, one composed of
fine grained aphenitic another by glassy (no crystals) rocks. These categories
are dependent on how they erupted from the volcanoes. Lavas have a range
of appearances dependent on their chemical make-up and temperature.
Pyroclastic formation is characterized by violent
eruption with lava thrown into high into the air. If
the material is ejected rapidly and cools rapidly it forms volcanic glass- mineral
free since amorphous. Pumice is a form of igneous rock that forms from
volcanic glass with air pockets or vesicles. These vesicles are formed by the
degassing of the molten material (CO2, H2O, etc.). Volcanic ash is composed of
fragmented rocks, lavas and/or volcanic glass. It is thrown high in the air and
smaller fragments will travel around the globe. Bombs have a range of shapes and made up of solidified
lava. They are tossed into the air and fall along the sides of the volcanic cone. The last two are scoria and
pumice. These are gas filed lava. Pumice (to the left) is so light that it floats.
There is one more texture, a mixed texture indicating two different cooling regimes. This is
called porphyritic texture or porphyry. Here a slow cooling regime starts and
large visible crystals form. These are then there is a volcanic eruption before
more large crystals can grow and this gives us the two different crystal types.
Igneous material is also classified by chemical content. We break the material into four types according
to the proportion of silicate minerals. Specific minerals form at specific temperatures. Minerals with a
high proportion of iron and magnesium and calcium compared to silica form this group and are called
mafic from magnesium. The mafic and felsic mineral suites are on page 112 in your book. The feldspar
group is divided into potassium rich (orthoclase), sodium rich plagioclase and calcium rich plagioclase.
The last two the sodium and the calcium are end the
members of a solid solution where the plagioclase
Labradorite- tectosilicate
formula is NaAlSi3O8;CaAl2Si2O8. The more calcium in
the plagioclase the more mafic the forming rock and
- Ca(50-70%) Na(50-30%) (Al, Si)AlSi2 O8
the higher the melting temperature to the right is an
example of these mixture. The more sodium, the more
felsic the magma melt and the lighter the igneous
rock( look at the chart on page 113).
Mafic Rocks a have large amounts of olivine
and pyroxenes giving the rocks their characteristic dark
colors. There may be a small to moderate amount of
calcium plagioclase. The lava form of this is called basalt. There are several areas of sheets of basalt such
the Columbian Plateau along the Columbia River in Washington. India as an even larger area, the Deccan
Traps, where kilometers thick layers of basalt contributed to the Cretaceous extinction event and
another in Siberia with an area as large if not larger also associated with an extinction event (Permian).
There is another mafic rock form. This form is called ultra-mafic. The mineral suite is primarily
made up of olivine with a small amount of pyroxene. This is the material that makes up the upper
mantel. The basalt upwelling at the spreading centers formed the ocean crust.
Felsic Rocks are poor in iron and magnesium. They are also poor in calcium. These rocks tend to
be light in color and one of the most abundant intrusive igneous rocks. They contain approximately 70%
silica and are abundant in quartz and orthoclase feldspar with some
sodium feldspar (albeit minerals). The intrusive form of this igneous
rock is Granite, the extrusive form is Rhyolite. These rocks can appear
as light brown, salt and pepper, pink, or orange or in some cases
almost purple (Missouri rhyolite). The Picture on the left is an image
of this rhyolite. Notice that it is porphyritic.
Between
the end members
of these two rock
types are the rocks
that are called the
intermediate.
These rocks have
less silica then the
felsic and more than the mafic. They have some quartz, micas and may have some pyroxene. They may
also have amphiboles. The intermediate is divided into granodiorite and diorite. Granodiortite is
very difficult to differentiate from granite. This is done by looking at difference in the percentages of
quartz, orthoclase and sodium plagioclase. We will then only talk about diorite and its extrusive form
andesite. This material has a mineral suite with pyroxene like mafic and calcium plagioclase but it also
has amphiboles, micas, a mix of the sodium/calcium plagioclase minerals and some quartz. The variation
in the amount of silica gives its melt a variety of properties that can swing from one extreme to another.
The last is the composition factor impacting the melting is the chemical formula. The more mafic the
melt, the higher the melting temperature for mineral formation and mafic melts are characterized by
less silica in the melt and more iron and magnesium. Conversely the more felsic the melt represented by
more silica, the lower the melting temperature.
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We know from seismic waves that the Earth is solid until we reach the liquid outer core. Where
does the magma come from? While we are
still working on this question we do know
some factors that impact the temperature at
which this solid will melt. One of the big ones
is pressure. Most of these solids are at such a
high temperature that they should have
melted. The pressure prevents this by
preventing atoms from moving apart thereby
keeping it a solid. The only way to overcome
this is an even greater temperature. Water
content also impacts this. Water enters the
system at convergent plate boundaries and by
water circulating naturally close to a magma
body (think Yellowstone geysers).
The last is the composition factor
impacting the melting is the chemical formula. The more mafic the melt, the higher the melting
temperature for mineral formation and mafic melts are characterized by less silica in the melt and more
iron and magnesium. Conversely the more felsic the melt represented by more silica, the lower the
melting temperature.
Looking more closely at temperature it was found that a magma chamber only undergoes partial
melting. This partial melt is determined by the temperature of the chamber and the mineral
composition of the magma. Only certain minerals will melt at a given temperature. It is like the new
"lava cake" desert. The cake turned solid at one temperature but the temperature wasn't low enough
for the chocolate center to turn solid. As water enters the melt this temperature will lower for many of
the minerals and there will be a more complete melt. We geologist use this information to determine
how different kinds of magma form in different regions of the Earth's interior. Since magma is formed
from rock in which only the minerals with the lowest temperature melts.
As you go deeper into the Earth the pressure increases. This increase in pressure (as mentioned
earlier) increases the melting temperature. Because of the convection currents mantel material will
move to an area of lesser pressure in the region of the spreading centers. This allows for the
decompression melting of the mantel creating the basalt of our seafloor.
Water impacts the behavior on the melting temperatures. The impact of large amounts of water
on melting temperatures can be seen with the mineral albite which melts at 1000oC. When water is
added to the melt drops to 800oC. Water is present as a gas and dissolves into the molten albite. There is
a rule to explain this. This states that if you dissolve one material into another lowers the melting
temperature of the solution. It also impacts the melting temperature of mixture of other sedimentary
and other rocks .These rocks are often water rich and will melt.
Magma chambers are formed by the change in density as material is heated. The magmatic
material will rise through and upward. Being fluid the partial melt moves up through the pores and
boundaries of surrounding rock. As the drops of molten material rises they can coalesce into larger
bodies. It also cam melt the host rock forming magma chambers or cavities in the lithosphere.
Magmatic differentiation can partially account for the different types of igneous rock found on
this planet. In the chamber as it cools high temperature mineral will form. This will remove more iron,
magnesium and calcium/silica tetrahedrons creating the ultramafic and mafic material. This leaves
behind more silicate tetrahedrons per cation so more high temperature minerals that are silica rich and
felsic form. These only form, though, as the melt cools. The process is called fractional crystallization
and gives different minerals in the same chamber. By studying the Bowin's Reaction Series (bottom of
last page)you can predict a magma temperature by the minerals present.
The diagram to the left demonstrates magmatic differentiation and fractional crystallization. The initial
minerals that come out of the melt are more rich in iron and magnesium. As they crystalize out then
remove these cations leaving behind a progressively more silica rich melt. By the time there is later
crystallization the magma body has cooled and the excess silica gives you the minerals found on the
lower portion of the Bowin’ s reaction series.
While magmatic differentiation and fractional crystallization explains how there are different
minerals in a magmatic intrusion it doesn't answer the questions of where did all of the granite come
from. Granite is one of the most common igneous continental rocks. The idea rose of a complicated
process that had both partial melting giving basaltic magma at the spreading centers followed by the
formation of intermediate andisitic magma with the mixing of basaltic magma and sedimentary rocks at
ocean-ocean convergent plate boundaries while the melting of igneous, metamorphic and continental
crust at ocean-continental convergent plate boundaries might melt to produce granite if magmas.
formation of rifts and is presently happening in the
magma can then intrude into these fractures.
Igneous intrusions take
place as the rising magma intrudes
into the country rock. They wedge
open the overlying rock as the
magma lifts up the overlying rock in
extension. This lifting up and
fracturing cam be seen with the
Basin and Range of our own west. The
As the body rises by breaking off the overlying rocks which may or may not melt into the
chamber. If the rock pieces melt they will change the composition of the melt in that region. If they
don't melt they remain as xenoliths in the magma that can be seen when the material cools and is
exposed by weathering.
The structures
that form by these process
are called Plutons and can
be from one cubic
kilometer to hundreds of
kilometers in size. The
largest of these plutons is
called a Batholith. These
large structures make up
not a single mountains but entire chains of mountains such as the Sierra Nevada Mountains. Smaller
plutons are called stocks and laccoliths are often the size of a single mountain.
Material that squeezes through the cracks from these bodies can cut across the country rock
making dikes. These magma bodies can also create their own cracks from the pressure they exert as
they rise. These are not a linear structure as they appear in a road cut but are actually a three
dimensional structure or can invade the country rock and spread along it in a horizontal structure called
a sill. You can view a dike here in Missouri at the Silver Mines State Park and on State Highway 72 on the
way to Arcadia.
The last features associated with igneous bodies are hydrothermal
veins. This can also be seen in sedimentary and metamorphic rocks. These can
be as small as millimeters or as large as a km in size. These veins can be in the
form of hydrothermal solutions often with quartz and valuable minerals
dissolved in it. These originate as water that permeates the country rock
(ground water) and forms into hydrothermal If they cool quickly they form
small crystals forming a sheet like tabular structure. These veins are an
important source of metallic ores.
Magmas form at two types of plate boundaries, the mid-oceanic ridges, where there is
divergence. The other plate boundary where magma is common is at the convergent plate boundaries.
There is another major source of magma, the mantle plumes. This are not associated with plate
boundaries and are the result of partial melting and form near the core-mantle boundary.
At the mid-oceanic ridge there is a decompression melt which then seeps up the fissures at the
divergent plate boundaries. The magma forms pillow lava of basalt. These columns of basalt are cut by
dykes cutting into the basalt country rock. Below this is the magma chamber. In the magma chamber
magmatic differentiation takes place with the olivine and pyroxenes precipitate out to form a peridotite
layer. Adjacent to the magma chamber is a layer of gabbro. The gabbro layer is adjacent to the hotter
magma layer becoming metamorphosed. Above the basalt layer is layers of sediment and sedimentary
rocks.
These form the Ophiolite Suites on land. This appears when to plates move so fast that the
ocean
plate is
forced
on and
over the
lighter
continental crust. As the plates move further from the magma more gabbro forms. The areas of
subduction are another area in which magma makes its way to the surface. The composition of the
magmas are dependent on what is being subducted. With this form of magma there is fluid induced
melting. The water in the subducting oceanic crust decreases the melting temperature of the overlaying
mantel material (peridotite rich) and the basaltic crust. There is also a portion of sediment that is left on
this subducting oceanic crust. This material has a very low melting temperature and melts readily.
The composition of these magmas should be basaltic considering they are formed from the
basaltic oceanic crust and the peridotite layer but there is a lot of variation. This variation comes from
the amount of accumulated sediment and sedimentary rock that is incorporated. As the magma rises up
and through the overlaying lithosphere there is also the effect of fractional crystallization giving an
increasingly more silica rich melt. When the oceanic crust is subducted beneath a continental crust felsic
rock melts and contribute to this melt. The different compositions of these melts and the amount of
gases present have a major impact in the eruption style of the volcanoes that are formed in this area.
The last type of "magma factories" is the mantle plume. They originate in the mantle itself and is
thought as a mechanism for cooling the core. It forms a
column of nucleated rock that rises up through the rest of the
mantel in the shape of a diapere. When it reaches the
lithosphere this flattens out and undergoes a decompression
melt forming the magma and the models predict large scale of
eruptions that can last millions of years such as the Deccan Traps
in India and the Siberian Traps in Russia. While the models
predict millions of years eruptions this is often not the case.
This plume is often postulated to be fixed with the
overlaying plate moving over it giving a string of volcanoes from the same magma chamber but of
different ages. While this is often true there are other plumes that are geographically stable such as the
one in Iceland and the Azores off of the coast of Africa.
While plumes can either form flood basalts or strings of volcanoes the volcanic composition can
very. The plume material itself is basalt with high temperature minerals containing a high iron and
magnesium content and low silica content when they appear below a continent other process can take
place. The underlying basalt magma can melt the continental rock; both the granite and the sedimentary
rocks creating a more felsic melt with high silica content.
Volcanic Eruptions
Basaltic lavas are mafic in composition (high iron,
magnesium and calcium) with the lowest of all magma
compositions. The eruption temperatures from these lavas are high,
anywhere from 1000 to 1200oC (1832-2192oF). This lava has the
fastest downhill speed (62 mph) on a steep slope due to this high
temperature and low silica content.
This gives three different basaltic lava appearances. The
high temperature fast moving is called
pahoehoe a Hawaiian word. This gives
pahoehoe
aa
a ropey appearance to the lava field. As
the lava cools a skin forms over the
flow with hot lava continues to flow
beneath. As the lava cools and slows
the "aa" forms. This forms a thick
skin that breaks as it flows giving an angular blocky appearance. The last form that basaltic lava forms is
pillow lava. This lava captures air as the lava flows over itself moving forward. This form develops as the
magma erupts under water. This forms a bulbous form that resembles "pillows".
Andesitic
lavas from the andesitic magmas have a higher silica content than the basaltic lava this
Pillow Lava
means that the minerals formed at this lava is made up of lower temperature minerals, no olivine. This
decreases the speed and distance of the flows. Their flows are stick forming blocky with few or no air
vesicles. They seldom get beyond the intermediate area of the volcano itself.
Rhyolite lavas are the highest in silica content (over 68%). The minerals are low temperature in
nature and the silicate minerals are high in sodium and potassium. The temperature of this lava is
600-800oC (1,112-1,472oF). This lava seldom leaves the crater and moves 10 times slower than basaltic
flows.
Volcanic eruptions are not always in the form of lavas. If water comes into contact with hot, gas
charged magma you can have a phreatic or steam explosion. One of the largest in history involved the
island Krakatau. This eruption started from an andesite chamber. The volcanic islands magma chamber
had emptied and collapsed (caldera formation) and sea water poured in triggering a violent phreatic
explosion that sent a major tsunami into much Indonesia as well as sending ash and debris travelled
over water onto the adjacent island of
Sumatra.
Pyroclastic flows and debris form
when water and gases come out of the
magma.
Pressure in
the magma
chamber
will keep
these
volatiles
from escaping. When the pressure drops
during an eruption the gases come out of solution. This can form an explosive eruption. This will shatter
the overlaying rock and also form gas charged fragments in the air.
Pyroclastics or tephra have different sizes and these different sizes have different names: 1. ash,
2. lapelli, 3. agglutinates, 4. bombs and 5. blocks The smallest is the volcanic ash and are less than 2 mm
in size and are usually glass in nature. If you have larger blobs different things are formed. Blocks can are
greater than 64 mm in size and are formed from angular
solid rocks from the plugs in the volcano itself. Bombs are
greater than 64 mm but are formed from molten magma
and can have different shapes. Agglutinates form either
cinders (scoria) or pumice depending on are 2-64 mm in
Pumice
size and are formed from smaller vesicular blobs. Pumice
is formed from volcanic glass and the air filling the vesicles.
Pumice is characterized by being able to float on water.
The caldera eruption takes place when the magma
chamber partially empties itself and triggers a collapse of
the unsupported material (roof of the chamber). This
then triggers a cataclysmic eruption with the pieces forcing
upward and out with much of the remaining magma in the
camber. The volcano doesn't present a cone at this stage
but a large valley ringed by the edges of the former magma
chamber. Calder eruptions can take place with any volcano
but are common with volcanoes such as Yellowstone and
stratovolcanoes.
Volcanic
processes- The
anatomy of a volcano can vary depending on the volcano
type. The common features for all volcanoes include a magma
chamber and a transport mechanism. The magma chamber
which lies in the crust portion of the lithosphere. The
chamber is filled by rising magma from the asthenosphere or
by the melting of the overlying rock by the rising magma.
Next is the transport mechanism. This can be in the form of a
central vent and side vents or from a fracture or fissure
through the overlaying rocks and into the magma chamber.
If there is
magmatic
eruption from a vent system you then get these volcanic
features. The most common is the volcanic cone. The overall
shape of this structure is dependent on the eruption type
and the magma type. Craters are a bowel shaped pit at the
summit of the volcanic cone. This is over type
volcanic central vent. Another structure is the
volcanic dome. This structure is associated with a
more felsic magma and can act as a plug to the
central vent trapping magma and gas beneath
them. Here the pressure will increase until there is
an explosion.
The last feature is the caldera. Here the magma has
escaped at such a rapid rate that the chamber can
no longer support the overlaying rock. This rock
then collapses into the chamber. This often leads to
an even more violent eruption as the remaining
melted material is expelled from the chamber. The picture on the left is the famous Crater Lake in
Oregon. It is a 6 mile wide caldera that formed after the volcano Mt. Mazamo erupted over 7,000 years
ago. The volcano in the center (Wizard Island) formed much later.
Volcano Types
Fissure volcanos are characterized by large lava fields that latter form plateaus. They are
basaltic in nature and have little to no gas. If gases are present then you will see other volcanic forms
associated with them. Massive flood basalts
from fissure volcanoes have been linked to at
least one extinction event, the Permian and
possible another, the Cretaceous. There have
been many smaller flood basalts from fissures,
one of these is the Columbia Plateau in
Washington and Oregon. Other examples of
fissure volcanism are the massive spreading
centers at the divergent plate boundaries.
Shield volcanoes have a melt with
gases as well as basalt magma. There is a central vent as well as side vents. The temperature and speed
of flow gives the shape of this
volcano. The initial lava is pahoehoe.
This gives the gentle angle of the
shield near the central vent. As the
lava cools it forms aa and has a
steeper angle along the sides of the
volcano giving it the characteristic
shield shape. These volcanoes are
common in areas of divergence as well as oceanic hot
spots such as Hawaii and the Galapagos islands. There are
often fissures and side vents opening up on the sides of the
shields.
Stratovolcanoes form from two different types of
eruptions. You have an alternation of pyroclastics and lava.
This is due to the characteristics of the intermediate melt.
When there is a high gas content combined with a silica
rich melt (more felsic minerals such as sodium plagioclase,
micas and quartz) you have an explosive eruption
and the cone that forms is of rock fragments and
assumes a steep angle. This material can be
covered in a subsequent by lava when the melt is
more basaltic in nature having less silica in it. This
melt would have more high temperature
minerals, plagioclases with more calcium and less
sodium, pyroxenes and little mica. This coats the
rock fragments and maintains the steep angle of
the cone. These volcanoes are seen along
convergent plate boundaries such as the Andes,
the Cascades, Japan and the Aleutians.
The last volcanic cone is the cinder-cone. This is made up by solid fragments builds up into a
cone, this allows for a steep angled cone. These have a small central vent and the magma is gas charged.
These can form on the flanks of shield volcanoes and stratovolcanoes. Once the gases have been
expelled from the magma a side vent often
opens and lava flows out. These volcanoes
erupt only once then their vent seals with cold
magma.
There are multiple hazards with a
volcanic eruption but while we have heard of
many of these hazards such as lava and
massive explosions. VOG or volcanic “smog” is seldom
looked at. Volcanic gases vary in composition. Two of
the most common gases are CO2 and H2O. The amount
of CO2 is 0.25 gigatons a year. Large eruptions can have
profound effects on global warming. Other gases
include H2O. Other toxic gases include: HCL
(hydrochloric acid), HF (hydrofluoric acid), CO (carbon
monoxide) SO2 (sulfur dioxide) and H2S (hydrogen
sulfide). The sulfur compounds will interact
with water to form sulfuric acid. The
picture to the right shows the gases exiting
Kilauea’s central vent. These acidic gases
cause widespread devastation to plant and
animal life on both land and in the sea. This
gas is reportedly equivalent to over a pack
of cigarettes a day. To complicate things if
the sulfur compounds enter the upper
atmosphere the droplets from the acid
they form reflects sunlight and causes
widespread cooling. The eruption of
Tambora caused a year without summer in 1815 and widespread starvation. The eruption of Toba
approximately seventy thousand years ago is credited with a ten year volcanic winter and 1,000 years
of cooling. We are overdue for such an eruption from Yellowstone and Long Valley volcanoes in the
United States.
Ash is a pyroclastic product. It is small enough in size that it and can travel miles away (smaller
particles go worldwide) from the source. Ash clogs the stomata of plants
preventing the exchange of gases and suffocating the plants. Ash is rock and
volcanic glass shards. When animals breathe in ash it enters the lungs and
damaging the alveoli. Exposure can and often does prematurely age these lungs.
This material can also turn into a concrete like material and suffocate people
and animals. Both ash and pumice adds weight to structures roofs. This weight
can collapse buildings. One more problem with the ash is the impact
on engines. These can get clogged by the ash and stop working. Jet
engines are very susceptible to the ash and are the reason that jets are
routed around or cancelled when there are ash clouds. The picture on
the right shows layers of ash from Mt. St. Helens. This is a record of
not just the 1980’s eruption of many past eruptions.
Another hazard is the lahar. This is a mud flow is a mixture
of volcanic debris and water. The water can be from melting
glaciers as in Mt. St. Helens, or rain fall as in Mt. Pinatubo’s
eruption. This mud flow can cover landscapes to hundreds of feet
deep, destroys bridges and homes. With speeds up to
10-60miles/hour a lahar can be linked to thousands of deaths. They
travel along existing water ways onto floodplains.
The deadliest hazard of them all is the pyroclastic flows and surges. Both of these are a mixture
of ash and toxic gases with temperatures as high as 1,000 °C (1,830 °F). Their speed is controlled by the
slope of the volcano (steeper slope more speed) 700 km/h (450 mph). These are normally caused by
the eruption column collapse. There are two layers,
the basal layer will hug close to the ground and
contains larger courser material. The upper layer is
the extremely hot ash plume mixed with the toxic
gases. There is mixing of the cold atmosphere and
the hot gases due to the turbulence causing
expansion and convection.
The pyroclastic surge has less material and
more gas making it act differently than the flow.
Lacking the courser material makes the surge more turbulent and it can rise over ridges and hill crest
while flows are more constrained.
The first thing that I will talk about in predicting volcanic eruptions is what constitutes an active
volcano. If there has been an eruption in the last 10,000 years the volcano or volcanic field it is active.
After saying this there are exception to this rule. These are volcanoes that haven’t had an eruption in
over 10,000 years. They are called active if they have indication of an active magma chamber beneath
them such as thermal features (hot springs, geysers and mud pots), magmatic gases (sulfur gases, and
CO2) and seismic activity. Two examples of ancient volcanoes that haven’t erupted in thousands of
years are Long Valley and Yellowstone.
To predict the eruption you monitor the region for the
things that indicate activity. The first can be seismicity. There is
a type of earthquake called the harmonic tremor that indicates
magma entering a chamber. The seismogram to the right shows
Mt. St. Helens harmonic tremors prior to eruption. Below is a
seismogram supposedly shows Yellowstone with harmonic
tremors during 2008.
You also look for an
increase in the release of magmatic
gases such as CO2 and H2S and SO2.
Both Long Valley and Yellowstone shows such an increase.
Another indication of an impending eruption is ground deformation. This is normally measured
by a tilt meter and indicated magma moving upward towards the vent. Below is a false color map
showing not one bulge in Yellowstone but two.
With magma moving upward closer to the
surface you will also find an increase in surface
temperatures. In 2002 the Norris Geyser Basin (arrow
on the left) ground temperature rose to the
temperature to the temperature of boiling water.
I have been using both Long Valley and
Yellowstone as examples of earthquake prediction for
several reasons. The most obvious is that they both
have all of the eruption indicators but haven’t
erupted. The second reason is what such an eruption
from these volcanoes would mean to mankind.
The image to the right shows the extent
of Yellowstone’s last eruption. The area
stripped of vegetation is the area where
large amounts of ash would be deposited.
This ash deposit impacts the continental
United States as far east as Louisiana and
as far south as far as Mexico. This region
is the bread basket of the world as well as
the United States. So famine would
fallow. It would propel sulfuric acid and
ash into the stratosphere leading to a
global winter for 10 years. The last time there was an eruption close to this magnitude (Toba ~74,000
years ago) there where many extinctions and close extinctions. The current theory is that the population
of the Earth was reduced to 1,000 humans.