Why is the mississippi river delta important
Historic Mississippi River Deltas--Phenomenon Explained
hey guys mr. Klein here and I'm standing
on the edge of a bluff this is really
weird because I'm in south Louisiana
between Lafayette and st. martinville
we're not supposed to have cliffs and
Bluffs like this it's all supposed to be
flat like what you see behind me this
right here is a really important bluff
line for what we will be discussing
today this is actually the Western
Valley wall of the Mississippi River
Valley down there is as far west as the
Mississippi River has traveled in the
past tens of thousands of years and it
shows us that all the land this way was
formed far more recently in the geologic
past than what's right here and we can
confirm this through soil testing and
also whenever we look at the rock layers
below we can get far enough down and we
can see where they matched up through
relative age dating now today we're
going to be looking at the
characteristics of the historic river
deltas that made up this deltaic plain
of the Mississippi River as well as what
was left over from these geologic act
essentially this region makes up
everything between Baton Rouge and
Lafayette from east to west and from
about Baton Rouge southward to the Gulf
you can see these borders actually just
by looking at the satellite imagery
based on the changes in vegetation the
borders of the Mississippi River Valley
are relatively high Bluffs like here in
Baton Rouge at the old State Capitol is
actually built on the bluff and across
this from across the street this Bluff
is actually pretty impressive when
looking at the deltaic plain you can see
the natural levee spread over a
relatively large area so what you see
here is actually this phenomenon natural
levees are formed during major floods
were rivers deposit sediment over time
the sediments deposits form a barrier
that limits the spread of future floods
you can see how high the river has
flooded over geologic time by looking
for the furthest levy from the river
flood waters never get past that point
so there's no natural levee formation if
you ever see a flat flat plain near a
river stand near the bank and look away
from the river what you'll see is that
these levees will grow gradually and
this phenomenon is actually what we call
Ridge and swell topography Southeast
Louisiana was
formed in the past seventy five hundred
years is earth warm from the last major
Ice Age now over time the Mississippi
River moved laterally like a snaking
firehose spreading sediment throughout
the region and building land in the
process geologists have identified five
Delta regions based on sediment samples
and looking at the ridge and swell
topography alongside bayous that are way
larger than a lazy by you could create
by itself and a lot of places like
Wikipedia and even my Louisiana
geography textbook back in 2004 you
might see a listing of seven Delta's if
you look at Roger T Sasuke's
encyclopedic work on the lower
Mississippi River Valley he even has the
section where he explains the
misconception that led to this incorrect
levee count I'll link the document back
down in the show notes below in order
from oldest to youngest the deltas are
Tamara Gua the Tesh the st. bernard
elephant and Elsa then we're going to
take a tour of these regions and look at
some of their unique features so let's
go ahead and take a drive and let's go
look the oldest Delta complex is the
mera Grande Delta which isn't exposed on
the surface but it's evident just below
the surface behind me in Vermillion Bay
in the Gulf of Mexico studying
subsurface sediments showed definitive
evidence for a delta these locations are
shown in nautical charts such as ship
shoal Tiger shoal and Trinity shoal and
from my research the sea level at the
time was up to 25 feet lower than it is
now so the sea level rise is responsible
for burying this Delta complex the next
belt of the form was the Tesh Delta this
is the oldest Delta you can actually see
on the surface it's the westernmost
Delta complex and you can see a former
channel in the form of Bayou Teche right
here Bayou Teche served as an important
connection for shipping in the 1800s and
actually until the 1900s until the
Atchafalaya Basin levees were built and
the advent of trucking at the time the
Mississippi Delta was being created the
opposite side of the valley wall formed
a very shallow estuary with depths like
vermilion Bay which by the way is less
than three meters or ten feet deep the
next Delta region on our tour is the st.
Bernard Delta now the timing of this
Delta's initial formation Berry's
pending on the model of sea-level rise
however by 1000 BCE geologists agreed
that sea levels had stabilized and the
Mississippi River shifted from the
western edge of the valley wall toward
Lafayette and moved to the eastern edge
more toward Baton Rouge barrier islands
are actually already present around New
Orleans where I'm standing but the land
being built grew out from there
one major consequence of this Delta was
the creation of this lake pontchartrain
now before it was formed the North Shore
which you actually can't see because
it's over the horizon take that flat
earthers was on the Gulf of Mexico but
the building of sediment over time
created this southern shoreline enclosed
in the lake the land New Orleans sits on
was created and its delta reaches for
others the Chandeleur Islands east of
Louisiana time to time the portion of
the Mississippi River would turn to the
south this way instead of heading
eastward into the st. Bernard Delta
about 2,000 years ago the main channel
and turned actually to the south on this
spot right here to begin developing the
Lafourche Delta this spot where I'm
standing until 1904 whenever Bayou
Lafourche was cut off would have
actually received water from the
Mississippi River during high waters now
in this Delta the Mississippi River
managed to fill in the gap that was in
between the Tesh and st. Bernard deltas
the result of this is Louisiana now has
its characteristic shoreline this also
includes the barrier islands such as
Grand Isle which is the only settled one
left in the state finally the modern
Delta region began forming in the past
1,000 years when the main flow of the
Mississippi began to switch from Bayou
Lafourche to the distributaries in the
st. Bernard Delta region and by 1400 C
or less than one hundred years before
Europeans began exploring and colonized
in the Western Hemisphere in force the
Mississippi changed its modern path to
the Gulf unlike the other Delta
formations the modern Delta reaches the
continental shelf where the depth of the
ocean increases dramatically instead of
spreading out like the other Delta
complexes the sediment simply pours deep
into the Gulf of Mexico
leaving the Delta much smaller and also
way more vulnerable to erosion and it
would otherwise be and with that comes
the end of our tour of the Mississippi
river deltas as
this series on the geography and geology
of the Mississippi River in southern
Louisiana operation German team even
looked at the Morganza spillway easy
Anna as well as the rest of the United
States and we've ended it here looking
at how these processes keep on occurring
over geologic time now this series was
actually born out of a curiosity of mine
about the topic and based on the
feedback I've received and views from
the videos on YouTube it's apparently
I'm not the only one who's interested so
if you're interested in the Bonney carré
spillway well don't worry the spillway
is closed at the moment and one of these
days once the spillway is closed I'm
gonna return and do another video on the
structure itself it's something that
because of the flood waters I wasn't
able to do at Morganza so if you enjoyed
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always thanks for watching
