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

this video and want to see more content

like this please consider liking the

video also we want to see more contents

like this click on the subscribe button

as well and if you want to be informed

of any time I release a new video click

on the bell icon you have any questions

put in the comments below and if as

always thanks for watching