Welcome back earth scientists this time we will be talking a little bit about volcanoes
volcanoes are quite interesting because
I think especially living in California
most of us are most concerned with the
fact that we have earthquakes because of
the San Andreas Fault but the reality is
we actually have an incredible history
looking back with in our volcanics going
back into when we had the subduction of
the Farallon plate between the Pacific
and the North American plate which
therefore created the Sierra Nevada
mountain range also introduced the
Cascades farther to the north but we
also do have a supervolcano in
California Mono Lake so we have a lot of
volcanics, which is quite interesting
because again most people are just
concerned about the earthquake portion
but we we live in a dynamic place it's
pretty awesome so let's first introduce
some of the the factors that really help
us understand some of these eruptions so
again remember when referencing the
differences between magma and lava
magma is deep underneath the surface and lava is what we see on top. So moving into
that some of the factors that affect
eruptions there's three physical
characteristics of magma that we look at
the first being is composition next
being temperature and the last being the
dissolved gases that are within that
material now moving into composition we
have three primary families we have a
fourth one which is considered  ultra,
ultramafic but that's not as important
for this course here but the three that
will be really focusing on will be
felsic, intermediate or mafic so we'll
introduce what that means. The next step
is looking at its temperature we have
once we consider extremely hot and then
what we consider as being cooler again
the cool is still quite hot but there is
a variation within those temperature
within those plumes and material.
Last is the dissolved gases we find is
that when you have more dissolved gases
in the material as that material moves
closer towards the surface in that
convective current because of decreased
pressure it can actually cause more of
an explosion or at least those gases
become released
well let's also talk about viscosity
viscosity can be kind of challenging but
I  think that the best way to kind of
compare
is one like looking at the differences
between honey and water you know they're
both a liquid but they also move very
differently they move very fluidly but
one's much more slow one is a lot
quicker and so we'll kind of talk about
that they're so viscosity is the measure
of a materials resistance to flow or to
measure of its mobility so let's look at
something that may have high silica and
ions that have high silica will also
have high viscosity much like honey
we'll see that the temperature ranges
between 650 and 900 degrees Celsius
these would be fake felsic lavas
such as perhaps a rhyolite looking more
at an intermediate zone the medium
silica material having intermediate
viscosity will between 800 degrees and
1050 degrees Celsius these type of
materials we also identify as being an
andesite and then lastly low silica
material will have low viscosity things
such as well not such as water water
does have low viscosity but in that
sense of how it flows those will be
between temperatures of one thousand to
twelve hundred and fifty degrees Celsius
those would be more mafic in material
such as assault
so again when looking at viscosity we
can see that there's definitely
correlation with what's what is viscous
or not based on its silica and it's the
temperature range that it has now
another way to kind of visualize this
would be looking at this diagram here so
again we have felsic intermediate and
then mafic we can see them there they
give us different types of rock types so
the pink area there is outlining felsic
or granite rhyolite the intermediate is
diorite and andesite and the last one
there's mafic inches gabbro and basalt I
know there's ultra ultramafic on the far
right but that's a little bit beyond our
level here so the reason I like this
diagram is on the bottom again it's
another way to represent material that's
more towards the left we'll have
increased silica items that are more to
the right will have less also looking at
temperatures items that are more to the
right or warmer and then the ones on the
after a little bit cooler but again when
I say cool it is significantly cooler
you know by what 500 degrees Celcius,  but it's still incredibly hot to us as
humans but nonetheless I guess think
this is a different way to examine it
you know what I think is also helpful
with this as if you reference the the
activity that we did earlier in the
semester by looking at that diagram and
once you filled in the different types
of rocks so you can see that there is a
difference between things such as a
granite and a basalt
because we also find that those
materials cool at different rates which
therefore can create different
crystalline size moving forward this is
again kind of moving back into what we
did earlier in the term here we have
examples of that so here we have a
granitic nava at missouri magma and
acidic magma and then basaltic magma
again these are some of the properties
that are within there the image on the
bottom left more granitic magma that is
gonna be a rhyolite the one in the
middle is an andesite and the one on the
far right is actually just basalt again
this is just to kind of put in
perspective that when we look at
volcanic s-- there's a lot of different
material involved you know we can see
that we have multiple different types of
materials so therefore as we'll see
further in this presentation that we
have different types of volcanoes that
will produce this and that really does
make a difference on how they operate
and also the people that live around
them so again this is kind of kind of
put that whole perspective into a bigger
picture now some of the nature of
volcanic such as lava flows are very
unique and different so basaltic lavas
make up about 90% of all lava on the
surface that's flowing fluid in its
nature and they flow in sheets or stream
like ribbons now rhyolitic lava is make
up only about 10% they move very slow
and do not travel very far we find in
most rhyolitic makeups that is usually
very thick layers that have just slowly
merged out and created these larger
lines deposits pahoehoe is a very very
runny material resembles like a twisted
ropey texture Aa is a term that we use
for very rough jagged or blocky lava on
the surface so looking at the images
below
do you identify based on just that
definition which wouldn't be a pahoehoe
or an Aa and I'm assuming you answered
out loud and I'm hoping that you're
correct because they're in the same
order it's the question that I asked so
these are some different examples moving
forward lava tubes actually what's
interesting about lava tubes is we have
them here in Mohave National Park this
is part of the the lava tubes that we
have often these flows will develop into
cave like tunnels called lava tubes
these lava tubes form and in the
interior of the lava flow where it
remains very hot very long after the
exposed surface cools so what's
interesting about these is you can
actually walk down them and you can walk
through the tunnel you can see how that
material slowly moved within it but as
it moved through you can see the the
tunnel it kind of got straw so I imagine
that as that material is moving through
and then once it's all passed through
all you're left with is the straw itself
so this is a really interesting thing to
be able to to experience especially in
this area this area also is known for
their lava bombs which I'll talk about
later which are pretty cool pillow lavas
are also a very different type of
feature that we can identify on the
surface so most of the Earth's volcanic
occur along ocean ridges or had been an
ocean ridge so we actually do find
looking into the historic geology of
these features you can find these pillow
lavas somewhere else like in the middle
of a different state which then would
help us kind of assume the fact that
when they were deposited that they must
have been near a margin of some sort
with water so what I'm happening is as a
material flows out it quickly solidifies
because it's getting being cool because
the water is cold and it forms this
volcanic glass it results in these
numerous tube-like structures called
pillow lavas it kind of looks like a
bunch of boba that's merged together and
they the obviously cool
and turns into a harder material so we
actually have examples of this in
several parts of California but this is
a photo of one from San Francisco so
again this is another another nature of
these volcanic sand how we can identify
them and
landscape so what type of material do we
also see well the the main one is what
we consider pyroclastic material so what
does that mean well pyroclastic material
is a name given to particles produced in
volcanic eruptions now the size range
can be from everything from a powder to
items larger than a car so as an example
these are some of the you know the key
words are the names there's traditional
ash cinder there's lapilli and there's
also blocks and bombs so I actually have
these in somewhat of an order after
being the smallest cinder being I know
they're usually pea sized lapilli
is more like the size of like a quarter
and then walnuts we don't walnut size
and then the blocks and bombs will
really become significantly larger so
these are all examples of that material
that can be thrown so when you have
maybe you've seen or learned to Pompeii
it wasn't the lava that killed those
people it was the pyroclastic material
because this material is also made out
of you know the composition of that
molten magma it's usually broken up into
different parts of silica so it's
essentially like extremely extremely hot
find a coarse grain pieces of glass that
is being thrown at incredible speeds and
some of which is still liquid as it's
being projectiled
and then cools in midair such as the you
know the blocks and bombs themselves the
ones that becomes they're very large so
to kind of give you some examples so
here we have some of those perhaps you
can pick which one is which from the
previous slide the one I want to talk
about is that one on the bottom right
looks kind of like an old nerf football
that there's a lot of bombs so that
would have cooled while it was a mid
flight from an explosion and then can
you imagine that it's being thrown
several thousand yards that size and
hitting things it'd be quite devastating
so we actually have a volcanic field an
old one obviously in the Mojave range
they're known for their lava bombs
they're all over the place and you can
actually pick them up they're quite
quite large so let's talk about some of
the anatomy of a volcano so the big
three we have weird identify as being
either composite cinder or a shield
volcano really it's based on its
appearance and then based off of
identifying off of that and we
understand how it operates
so the volcano itself is a mountain
formed of lava and or a pyroclastic
debris the crater is the depression at
the summit of the volcano caused by the
releasing gas so an example of a crater
just hear me out it'd be just like maybe
you have a black head under nose and you
sit you squeeze it out so you all that
material leaves the pore and then
essentially that you're left with you
know a cavity in that sense a hole in
your nose where that blackhead was but
then you create a depression at the
summit of that pimple so that's
essentially what a crater is is you're
taking the material out and you're left
behind with this very large cavity which
just then brings into the calderas
formed when a very large eruption of
magma or lava leaves a gigantic empty
chamber underground which it will
collapse and what we find is that even
most caldera systems you know they're
great developers of large lakes
I'm sorry craters as well because we've
created National Park the calderas it
can be as well and then last is the
conduit the conduit is the pipe that
actually carries that material to the
surface so to kind of see these vocab
words and play here's a little diagram
showing the conduit we can have a crater
the fan at the lava we can see
additional pyroclastic material that is
built up on the side now you don't know
anything about the different names but
again I mentioned the three names or the
big three of that we have so you know if
you were to think of off those names
which one what do you think this be
would this be and I'll go back real
quick so you can see it would this be
composite cinder or shield now again you
don't know a whole lot about those words
but do you think you can kind of deduct
it well
you're right this one it would be a
composite volcano and we'll talk about
that in a moment but as you can see
there's multiple layers that had been
layered on it so here we are composite
composite volcanoes are composed of both
lava and pyroclastic material and they
end up being actually the most violent
so a great example of a composite
volcano would be Mount st. Helens Mount
st. Helens was a very unique eruption in
which it didn't necessary blow out the
top and more blew out the side and in
doing so became very devastating for up
to 17 miles within its.. pretty much
all the material than 17 miles of the
volcano itself it was the material was
so hot and so abrasive then it actually
caused the bark to fall off trees the
ones that were standing at 17 miles away
so 17 miles away from Santa Clarita
you're looking at Oh probably just shy of
Burbank so it would be quite quite a
distance so again we can see the lava
the lava flows themselves we can see
these different branches within so it's
not a traditional volcano that just
blows at the top he builds off of its
size as well so they're also known as
stratovolcanoes due to the large sorry
structure of alternating layers of
cinders and ash that is with embedded in
itself the most destructive of all now
the next type we'll talk about or cinder
cones we actually have a ton of these
along the eastern sierra perhaps you
have driven on 395 heading up towards
Mammoth you might look out the side and
see this nice little pointy red cones
there on your right-hand side and
thought gosh I wonder if those are
volcanoes well you'd be right those are
cinder cones or small and built of these
again pyroclastic events or groups an
example be Mount lassen they're very
steep site at having slopes between 30
to 40 degrees resulting also the top
with these deep craters they're also
very destructive they can throw
materials very very far in which it will
also
cool within mid-flight but again they're
not again these are more the type that
blow their tops versus their side that
we saw before but we have a lot of these
I mean again when we say you know
they're big I mean you could easily walk
to the top of one but they're still
quite large especially in the landscape
so again like I said driving to 395
right hand side you look up this side oh
my gosh all these little red little
mountains he's already cones while
they're actually read cinder cones for
California though our last major
eruption was about well 700 years ago
along the Eastern Sierra so we haven't
seen anything quite sometime over there
but we have seen more activity in the
more north and northwest corner looking
up at Mount lassen that was right before
1920 is like 1917 so around there there
was an eruption up there but it wasn't
too devastating wasn't as devastating as
Mount st. Helens which happened in the
80s anyway nonetheless we move forward
look at shield volcanoes but I think
it's shield volcanoes I think of Captain
America because it looks like a shield
it's very--it's it can be tall but the
it's very broad so when's up happening
here is has gentler slopes because as
the volcano runs at this top it's not
very explosive so the material slides
down on either side and creates these
very gentle slopes and it should say
usually have steep calderas at the
summit that will then collapse and
create these massive massive holes with
in the middle but again shield volcanoes
produced by the accumulation of fluid
basaltic lavas and look like Captain
America shield an example that would be
mono lava so again
make sure these eruptions that we are
left with these very large words that
cover the landscapes and topography that
we identify again he's called dara'a or
large depressions we've got lava
plateaus where basaltic material will
extrude from the crust and fracture
these what we call fissure eruptions
fissure eruptions are what happened when
material will say as an example two
pieces of content la crust diverge and
tear apart and it's a huge wall of magma
that then turns into lava that shoots
into the air and we can have plutons
futons are considered an intrusive
igneous structure that results in the
cooling and hardening of magma very very
large again we have massive plutons that
squeezed in within the Sierra Nevada
when that was slowly drying and cooling
is one big rock we have laccoliths which
are lens-shaped masses that arch
overlying strata upward in the last that
we have here a batholith which are very
large masses of igneous rocks formed
when magma intrudes and became a rock so
batholiths are very very very very large
so again these are just some nature of
those eruptions lightheartedly
nonetheless now what i want to ask you
to do is when we're done here I'm gonna
have you just go ahead and go back
throughout your modules and having you
check out the supervolcano ted-ed video
that kind of puts it in perspective as
we learn then a little bit more about a
supervolcano here in the United States
the you know the biggest one that we've
got it would be Yellowstone National
Park we also have a supervolcano in
California that would be Mono Lake and
the mo no craters which is to again
northeast of us but the big statement
here is the Yellowstone supervolcano
again we're looking at a rupture that
happened over a hundred and one hundred
and seventy four thousand years ago so
quite some time ago but we still see
geologic activity we still see
geothermal hot springs we still see
these different attributes that tell us
that perhaps the volcano itself is
extinct but we but there's still
something else nearby that's happening
and so it helps us understand a little
bit more about that bigger picture again
thank you for for participating here and
we'll talk soon
