Welcome back earth scientists we've got
a new discussion we'll be talking about
today which is really the introduction
of geomorphology so this set of the
module really talks us through how our
landscape has been changed by different
processes and so what we'll do is we'll
introduce this idea of geomorphology as
a whole and then narrow down into the
specific areas in which this module will
cover so nonetheless let's move on to
the first slide which is well what is
geomorphology well when you break
down that word geo meaning earth morph
is the change and ology is to study so
what we're doing is we're learning how
to study in which the ways the earth has
changed so there's different attributes
so I found this little diagram I threw
on there you know earth wind water ice
to fire and we've already discussed a
little bit about earth and how earth
continues to change due to plate
tectonics we've discussed in the
previous module about volcanics and
looking at fire so really were to take
an opportunity within this presentation
to discuss wind water and ice so how do
those things change our landscape well
let's start with wind so there's a fancy
word for this which is called Aeolian so
wind Aeolian geomorphology or studying
how the earth changes by way of wind now
when has energy or the capacity to do
work so that being said wind is able to
erode transport and then deposit
materials so when can erode surfaces and
features it can then take that material
and debris and relocate it and move it
along its way and then lastly it will
deposit that material somewhere else but
this brings us back into just, where
does one come from again and
simplistically went is caused by the
uneven heating of our earth's surface
and because of wind we're able to then
identify very unique and distinct
landscapes so not just extreme weather
that can then change the landscape but
looking more at erosion and
transportation elements so these
pictures that provided are all things
that environments that deal with wind I
mean are there other agents involved
absolutely but we can also contribute on
most of what we see done by wind so
let's bring in one of the most iconic
things that we identify when looking at
wind which are sand dunes so sand dunes
are the most abundant and easily
identified features found within areas
that are affected by Aeolian processes
so although there's many different types
we're just gonna focus on these six that
we see here in the diagram but
nonetheless we're going to learn them
pretty much all the same so what I'd
like to start with first is the diagram
on the bottom this guy right down here
so what we have here is a traditional
profile or side view of a traditional
sand dune development there are two
sides there is the stoss side notice it's
the longer word stoss and the longer
side and then we have the lee side the
shorter word the shorter side the stoss
side is the side that is hit by the flow
of wind so it the wind hits this side
moves the material up up up up up until
it finally falls down on this side the
lee side is sheltered so you're not
receiving any wind right here the
material brings up here to the brink of
this crest and then it drops down to its
side what's interesting about this is
that if you have a consistent
not variable amount of sand very much
like a conveyor belt, the sand will take
from here move up to here and Transplant
here and actually cause the dune itself
to migrate now if you are in an area
that has lots of sand and you continue
to gain volumes this little angle right
here I know you guys are all scared of
math but if this angle increases so
will the dune but nonetheless, this is a
traditional profile sad being said all
dunes have two dominant sized stoss and
leeward side now what really regulates
the difference is between the six sand
dunes that you see in the top left-hand
corner
are two variables one being the wind
direction and wind variability and the
second be the supply of sand how much
sand we have
so we'll start up here this is the first
and we'll discuss at first dune the top
left is called a barchan dune a barchan
dune is your classic crescent-shaped
dune we can identify this little angle
right here being your estas the
sheltered side being the leeward side
but they're very distinct Crescent
shapes these are your classic little
horns that can develop here the horns
actually point in the direction the wind
is flowing and that's important for
people who study these features because
maybe you're studying them in an
environment that there isn't wind but
you're gonna be able to identify the
direction which the wind was flowing
when these were deposited size-wise
these can be very small maybe just a
couple feet otherwise they can be very
large over a mile you know in distance
across from horn to horn along these
crests so this is dominantly known as a
dune that will be available when you
have a justifiable or large sand supply
and you have one dominant wind direction
now moving over to the right we see that
this one here has two merging flows of
wind and look at how elongated these
dunes have become so be like putting
play-doh in your hands and rolling your
hands together and making a long snake
so because of these converging winds we
create these long or linear broken bark
and dunes we call these linear dunes or
longitudinal moving again clockwise to
the middle right these are very unique
dunes first thing you notice there's
water involved and there's vegetation to
the you know behind them these are
called parabolic dunes these are the
only times that the horns were actually
facing in the same direction the wind is
flowing creates converging motions lots
of reasons why simplistically you've got
vegetation and water involved the sand
gets wet so it doesn't operate the same
way as it would in a drier environment
but really if you see there's water and
plants that we know that it has to be a
parabolic do like a parabola again these
are one direction of flow moving down
here this is a star dune,  this isn't a very good example we
have velocities in California especially
in the the Mojave Desert region area you
have multiple directions of wind flowing
merging all to one place and you create
this very unique sea star or star dune
shapes again you have a very large
supply sand and you'll have it may be
wind blowing this way wind blowing this
way that way that way which leaves these
two on the left so one of them this one
here is called a transverse dune and
then the bottom left is a barchanoid ridge
so what ends up happening is in
this story you have barchan dunes
develop then let's say that you
introduce a new supply of sand so what
ends up happening is that this fills out
and turns into a barchanoid Ridge so
these are again all your little bargains
but see they're all coalescing they're
all touching so it's filled into itself
it looks very pointy right see point
point point then maybe you get enough
sand that it completely fills in the
area where you get these nice very clean
waves this is called a transverse tune
so you lose the point so you have
transverse, barchanoid Ridge and then a
barchan dune,  so these actually can
transition back and forth between each
other depending on the supply of sand
you have now to put this in a
perspective of a location would be
familiar with what about Death Valley
National Park not necessarily gonna be
on the exam but just to kind of put
things in perspective
so what's interesting about Death Valley
National Park is it's within the Greater
Mojave Desert it was first protected as
a state park in 1933 by President
Herbert Hoover but it wasn't made into a
formal national park until October 31st
of 1994 it is unbelievably massive over
5,300 square miles and is also home to
the lowest elevation at negative 282
feet below sea level
that means it's negative 282 feet below
or the ocean is on the beach you might
think well then why does an ocean water
fill it well it's because the way that
the mountain ranges are built around it
has no access to the ocean it's also
home to the devil
racetrack which is the place where rocks
can move by themselves if you've never
heard of it you definitely have to
google it it's quite impressive
and it's also ranked the hottest and
driest National Park and arguably can be
the hottest place measured on earth the
photo I picked there is a National Park
poster of Ubehebe crater really
interesting crater it's a steam volcano
that essentially blew up which allows us
to be able to still see the underlying
stratigraphy without destroying it like
with traditional molten material so is
mostly steam that built up another fun
fact Death Valley although is one of the
hottest and driest places in the world
it used to be a massive freshwater lake
known as Lake manly it just evaporated
very rapidly moving into our next
process we'll talk about water or
fluvial geomorphology so we understand
by this point that the earth hydrologic
cycle is much more than evaporation rain
and snow we understand the importance of
understanding this process especially
since we're experiencing drought in
certain areas of the world
the fluvial geomorphology introduces
the hydrologic cycle and that if it
as a science is devoted to the
understanding of rivers but both in a
natural and human-induced environment so
we look more than just your traditional
it evaporates and turns into rain and
comes back down we want to look at the
process and how these rivers are formed
looking at the depositional material and
and also looking at the erosional
landscape so this next slide kind of
takes us to a very brief story so we can
see that this larger image here is
broken up into three parts zone 1 zone 2
zone 3 so ideally this is all one
progressive River from start to
finish but we I can identify each region
as its own element so zone 1 is really
considered young and the next one
is going to be mature transition into
old age and then zone 3 will be just
your old age so we're seeing this
transition of time just like with people
and what's interesting with that
comparison going from young mature and
old age is that even as humans we don't
associate it with time we associated
associated with the development or
maturity of it in the
and that's the same thing here because
all rocks operate differently the erode
differently they build up differently so
we can't say that oh just because this
environment looks a certain way it must
be X number of years old
it really takes into consideration its
development and the big thing that we
see that's different amongst all three
of these it's going to be its slope so
starting with zone 1 you have your
mountain ranges it's very steep we find
that there's active incision where the
river is actually cutting down and
creating very steep channels once that
those higher landscapes have been eroded
away we end up with a zone to where
lower elevation streams merge into a
flow that into a more of a gentle slope
the valleys begin to broaden which means
you've dug down deep enough that the
sides have collapsed and created a very
small floodplain at some point you
continue to dig down to the deepest
element which everything becomes very
very very wide and not very very
aggressively sloped with a gradient so
at the lowest elevations a river will
meander me and get it zigzags back and
forth within the floodplain and I'm at a
river's mouth which is where the river
ends it may divide into separate
channels known as the Delta system
things to kind of point out within these
features yeah we just to kind of put
them out here and these are really
unique these are abandoned channels at
one point the channel did you know was
part of this but it has since been
abandoned because of the widening of
this stream when a stream comes into the
main channel we call that a tributary
because tributaries contribute to the
main channel we can also look at
watersheds I mean this dendritic style
of systems, of river systems that you
know that are merging or contributing to
we can identify all of this as being
part of a watershed something that this
diagram the bottom left-hand corner
shows that I think is really important
is you see the dark blue line that runs
within the river that's called the towel
leg line that is the deepest and fast as
part of a stream like often compared to
driving in the freeway it's usually
associated in the middle of the free
in the middle lane that's the fastest
lane why because you have less friction
from cars coming on and off the freeway
and things of that sort but what happens
when the freeway makes a very sharp turn
while imagine about your car you just
went to the grocery store you have all
your food in the backseat and you make a
sharp right hand turn the energy forces
all of the things in your car to be
thrown to the left in doing so you will
create what we call a cut bank so
looking at this diagram in the bottom
left hand corner looking at the sinuous
which means that it has curves following
that line see the river is making a
sharp right-hand turn but that energy
gets forced to the left then it get
moves again to the left-hand turn but
that energy is forced to the right and
if you create these pools these pools
are essentially erosion it what it does
is it takes the material here widening
this river channel and then bringing
that material and depositing it over
here so this is what we call a point bar
this is also a point bar in here point
bars are those iconic you're watching a
movie grandpa's with his grandson
they're fly-fishing on a little sandy
beach along a river because this is
where the energy is very low and a river
because to see the end of the fastest
line the towel wedge is way out here so
official you know Wade and kind of hate
you hang around here if they want to
leave they move into the towel way which
is like a current and forces them away
so again just to put some things into
perspective looking again at I could
bigger putting it together type image
and this is the Chaco Canyon diagram
what was interesting about this is you
can see all these different vocab words
so I'll point those out very quickly
moving at the top where the river is a
source
those are your headwaters so in this
diagram the water is flowing towards us
we can see the tail wag is that deepest
fastest part and oh actually sorry now
that I'm looking at this the water is
flowing away from us and notice these
little arrows down here and then the last the
waters flowing this way so this would be
the headwaters this would be the mouth
where the rivers ending we can see that
the river has now created this flood
channel itself these levees and natural
levees are caused when you
of extensive flow and water overflows
like in a flood system and moves and
material onto the side here we have the
water moving down the channel here this
would be your cut Bank these are your
point bars what ends up happening is
these curves become so large at some
point the water may shoot through and
cut through it and when the water cuts
through this large rich meander this
becomes an abandoned channel which can
then become an oxbow, oxbows are a  word for a channel that will become abandoned and
will be you know essentially a scar on
the landscape of showing where the water
used to be here we have a Terrace
terraces developed when a river system
velocity increases so when the river
system increases it actually causes
incision or the river to cut down
abruptly leaving a terrace so a great
example of terraces would be like a
Disneyland where they have the River
Terrace Cafe so you have the restaurant
and there's a step down where the people
walk back and forth and there's one more
step down where you then go into the
rivers of America so you have these
multiple steps or terraces that have
been developed this diagram here just
kind of gives some additional features
this you know as outlining this whole
region this being a watershed
here's your source or your headwaters
there's the mouth where a river would
end and here's all your contributing
tributaries another question I get asked
often is well what's the difference
between a creek and a stream and a river
and a chute and all these different real
words that we use to identify and really
it's it's this vernacular that we use to
describe in size but rivers are the main
channel and then everything else has
kind of works its way to a smaller
attribute so you have your main River or
channel then you can have your
tributaries which depending on their
size can be very very small
itty bitty creeks of drainage or they
can also be smaller river systems within
themselves so again I guess saw this
diagram was pretty interesting I found
online and I thought I'll sure because
this kind of puts some of the images
together so again to put this flooville
aspect into perspective perhaps you've
been to the Grand Canyon so fun facts
again the Grand Canyon National Park is
our 15th National Park 1919 by President
Woodrow Wilson
it's nearly 18 miles at its widest
almost too
miles deep Oh fix that guy over there
almost two miles deep within its
exposure so what we're dealing with then
is all of that geologic history that had
been underlaying
and not seen from know at this point
over 1.8 billion years is now exposed we
can see all of this material so that
being said the formation of the Grand
Canyon is really only about six million
years old but show's over 1.8 billion
years of geologic history everything
from inland seas to volcanic events to
metamorphism you know one of the oldest
rocks dated in the Grand Canyon it's
called the Vishnu schist
it's a metamorphic rock that has these
very large rich granite garnets excuse
me that it would thin them and they used
the garnets to be able to do the carbon
dating to see how old that exposed rock
was and how old was it when it was
developed and that's where we got the
dates of 1.8 billion years old so again
really impressive in that sense the last
thing we'll talk about her glaciers
glacier Jim morphology so I use this cuz
it's in our backyard Mount Whitney which
is our Everest at 14,508 feet Mount
Whitney is this taller peak here that's
Mount Whitney these are additional Peaks
that have names there's a whole mountain
and within the Sierra Nevada
there's Lone Pine peak there's Mormon
point, all these different peaks are
within that range but nonetheless I
wanted to point that out because again
all of that is that exposed granite was
plucked and carved by ice so glaciers
are large bodies of frozen water that
developed where the seasonal
accumulation of snow exceeds the melting
rate now with nearly three-quarters of
all of our total freshwater locked up in
glaciers and snow caps we don't only
have a lot of fresh water available to
us in reservoirs that being said our
last major ice age was about 2.5 million
years ago during the Late Pleistocene
and then our last interglacial period or
sugar cold snap ended 10,000 at the Late
Pleistocene at the end of it so what's
interesting about that 10,000 year mark
is that seems to be the time in which a
lot of our historic mammals - had then
deceased we had in California we had man
we had pygmy mammoths we had camels we had giant sloths we had smilodon
which were the saber-tooth cats so that
it seemed to be really the end of that
era of creatures but nonetheless we can
move into some of these features this is
one of my favorite photos this is
convict Lake Inn along the Eastern
Sierra this is really a great example of
two features one is that this Lake this
is a glacially formed lake called a Tarn
and that Tarn is within what we call a
Cirque C i r q u e
a Cirque is a amphitheater shape a
bowl-shaped feature that's been carved
by I so think of it kind of like if you
had ice cream and you had your big ice
cream scoop and you put that scoop in
there and carved out your nice big round
piece of ice cream that carving in that
rock would represent the cirque search
the first place to freeze and then the
last place to melt and the reason it's
this round shape is because as water
freezes it expands and in its process of
freezing expanding it freezes into the
rock material and plucks and carves and
removes it all the way so we get this
very neat rounded shape we also can
identify the features here we can see
the highest points appear would be
considered horns we can also see blade
like ridges that are kind of off to the
sides or hard to see in this perspective
we'll identify those as Aretes
we'll talk more about some of these
features here's a great example of
cartoon on the left hand side then the
drawing on the right that kind of puts
some of these words into perspective
again glaciers are absolutely massive
and I think is very interesting to think
that within California's history if you
take it way back we've had obviously
glaciation we've had volcanic we have
earthquakes we have just about
everything within our geologic history
which is really impressive so again this
image on the left is showing during
glaciation the one of the right is after
glaciation here we can see this nice
rich cirques that have formed a nice big
amphitheater shape and as the material
freezes and accumulates at higher
altitude because of its own weight and
gravity pushes the ice down down down
down towards what we call the foot or
the terminus of that glacier
these dark language might ask what those
are those are called moraines so the
material is being scooped out of here
and as it gets dragged down it gets
pushed to the sides the same thing here
so these would be a medial moraine
because it's pushing the material this
way and that way they're meeting
somewhere in the middle we can see these
high points these high points are called
horns or pyramidal Peaks often around
there we see this really nice blade has
blade like ridge there's one here
there's one along here there's some up
in here those are called aretes, it
means blade-like ridge it doesn't cause
because it's the cirque and the ice itself
is being develop is pulling that
material away you're left with those
really sharp ridges so a great example
here I'm gonna move over to this diagram
to the right where we can see what ends
up happening after glaciation well
what's interesting is traditionally
rivers form v-shaped valleys in this
case glaciers because as the ice expands
creates these really deep u-shaped
troughs in doing so we have where things
can be truncated or completely chopped
off that's what that means
so spur means a location truncation
means this whole thing has been cut off
so this is part of an erect system but
the whole end of that arete here would
have been cut off here we have a again a
Tarn which is a lake within a Cirque
that water's draining and as it drains
you see because this has been truncated
it now creates a waterfall
so this valley is hanging above the main
trough which we identify as a hanging
valley this phrase Paternoster Lakes it
makes reference into Catholicism
actually meaning rosary beads we do
dealing with the Father so we find a
bunch of lakes that are joined like a
bracelet of beads that's what that
stands for the bees are a chain of
Paternoster Lakes yes individually
they're cirques but since they're all
being joined together we call them
Paternoster Lakes so interesting fact we
know looking at this so now saying how
big this u-shaped valley is think about
Yosemite Valley and the fact that we
have an iconic feature they're called
Half Dome now you begin to question that
well wait a minute
would have Half Dome been a whole dome
but had that half been knocked off by
ice and I think that you'd be surprised
to find that that's the case much of the
Yosemite Valley itself it shows the very
clear carving or
moving of that material there's some
great documentaries on the formation of
the Yosemite Valley in particular is
because it is a very distinct u-shape
that is borderline box shape and that's
because of a thing like this these are
called they're called terminal or end
moraines because that's where the
glacier had ended that being said where
the glacier ends it creates a lake
behind it see this big lake that's
developing here so as that material in
the fine grain material gets moved by
that ice it begins to deposit those
salts and can create a box shape that's
what ends up happening Yosemite this is
kind of one of those fun facts there so
that being seven looking at glaciers
glaciers carve in a road and pluck and
move all this material at a very very
fast pace but what's interesting about
it is it breaks things down to its
finest course material being your silts
in your clays so it's really impressive
granted most glaciers don't know that we
observe today many of them don't move
very fast but they actually still do
some can move several meters a day which
means you essentially could watch them
move on their own which is I think
terrifying you're especially looking at
how climate has been changing and seeing
how particular glaciers that are still
observed on the landscape especially in
the more northern latitudes how we're
seeing that they're moving you know 50
to 40 50 to 45 meters per day in retreat
not really an advancement meaning that
they're melting back and breaking away
so we talked about a glacier retreating
essentially isn't happening is that
because it becomes too warm down here
the ice will actually crack and when it
cracks this falls off leaving a new line
there so then it's not really pulling
back you know like we would think when
you say the word retreat it's more the
fact that it's breaking and melting off
another interesting argument some people
say that well we are seeing that the
surface of some glaciers is expanding
we're seeing expansion within surfaces
of glaciers and the answer is yeah you
in some areas we do but it's density is
not the same so it'd be kind of like the
example I use is like play-doh so if I
open a container of play-doh when I
stick it on the table I go we'll look it
doesn't cover a lot of area but it's
about five to six inches of depth well
could I if I had the patients or maybe if
perhaps a child can do it because
they're good at that could you spread
that play-doh over an entire desk and
the answer is yes you could you could
cover an entire desk with that play-doh
you know does that mean you have more
because it's covering a greater area and
the answer's no it's not it's still the
same amount it's just thinner so some
things to think about
within that another fun place to kind of
talk about more of these features is
then after the glacier is gone what's
left behind so these are a lot of words
I'm not asking you to memorize all of
these but to do be familiar with some of
them again something can be interesting
to talk about
drumlins drumlins are asymmetrical hills
made of glacial till
so it's causes them as the ice itself is
retreating and melting back leaving
these unconsolidated hills of material
or glacial till T I l l another feature we
can look at is or would be kettles
kettles are caused by when the glacier
is moving and plucks out big pieces of
rock or leaves behind big pieces of ice
and it turns into a lake down here on
the valley floor we can see there's
additional Marines meaning that as the
glacier advanced or retreats at least
behind these big piles of debris when I
think of moraines I think of going to the
beach and sticking your feet in the sand
and as you push all of that sand away
you create a big hill without be a
marine you displaced all of that
material so we can see that moraines can
happen at the farthest extent being a
terminal can happen when the glacier
retreats but advances during winter as a
recessional or like a recessional
hairline or it can even be found at the
whole bottom gets a nice little layer of
it called a ground moraine here's a
traditional adult environment because
you end up having water that drains
underneath the glacier depositing
additional material everything beyond
the terminal moraine is called the
outwash plain eschars are the remnants
of rivers that were flowing underneath
the glacier and up top the soil surface
itself again when we talk about glaciers
I think it's hard for us to imagine how
large they are again to put in
perspective like I said with a kettle
kettles are caused by either rocks being
dislodged or large pieces of ice being
deposited and hitting in the ground and
making indentation
if you ever have the opportunity you're
privileged to go to New York
they have Central Park in Central Park
has these massive massive rocks that
have been deposited in that Park
well those rocks are not from there
they're orogeny is many many miles away
there's in fact these rocks have these
very large carvings on them or
striations showing the direction which
they were moved so we end up finding
that these rocks that have been
transported and we can measure the
direction in which they were moving
based on the scratches found upon them
and we can date you know when they were
moved when they're placed and where
they're orogeny or where they developed
from so again a lot of information I
absolutely understand that but it's a
great way to kind of oversee all of
these different environments so we've
discussed desert regions very quickly
with don''t looking at how wind changes
the landscape we also looked at how
rivers can change landscapes and lightly
how glaciers can change the landscape as
well be sure to check out all the
supplementary material within the module
itself and I'm excited we'll talk soon
