Mississippi Delta

Question 1

Length of Mississippi River

Answer 1

2,350 miles (although it fluctuates due to varying rates of erosion and deposition at the coast)

Question 2

Catchment area of Mississippi River

Answer 2

1,200,000 miles^2 (31 states + 2 Canadian provinces)

Question 3

Mean average rainfall of Mississippi River

Answer 3

508mm

Question 4

Average discharge of Mississippi River

Answer 4

16,790m^3/s

Question 5

Upper Mississippi

Answer 5

From the source to the confluence with the Missouri River

Question 6

Middle Mississippi

Answer 6

From the Missouri River to the confluence with the Ohio River

Question 7

Lower Mississippi

Answer 7

From the confluence with the Ohio River out to the Gulf of Mexico

Question 8

Coastal landforms of deltas

Answer 8

Wetlands, barrier islands, beaches

Question 9

Sediment of the Mississippi Delta

Answer 9

30% clay, 40% silt, 30% fine sand

Question 10

Previous lobes of the Mississippi Delta

Answer 10

• The Salé-Cypremort delta formed 7,500 to 5,500 years ago when relative sea level rapidly rose.
• The Teche delta formed 5,500 to 3,500 years ago after relative sea level rise dropped.
• The St. Bernard delta formed 4,000 to 2,000 years ago caused by the river breaking away and relocating to the east of present day New Orleans.
• The Lafource delta formed 2,500 to 500 years ago from a second break in the river causing it to relocate to the west of present day New Orleans.
• Modern day development 1,500 years to present formed the Plaquemines delta (Bird’s foot delta).
• Movement of the river towards the Atchafalaya river began 500 years ago with the Balize delta emerging in the 20th century.

Question 11

Width of Mississippi River

Answer 11

6m to 1.77km

Question 12

The Mississippi River is the ??? longest river system in the world

Answer 12

Third

Question 13

Average surface speed of the Mississippi River

Answer 13

1.2mph (varies)

Question 14

How was the Mississippi Delta formed?

Answer 14

• The Mississippi delta was formed over the last 7,000 years in a dynamic process known as the delta cycle.
• Each delta cycle results in a new delta lobe, each lobe is created between 1,000-2,000 years.
• This occurs because of the sediment that the river has transported from the upper/middle course is now deposited near the mouth of the river.
• When enough sediment is built up plants and vegetation start to grow and this process continues and eventually transforms into a thriving plant communities that is well anchored on the coast.
• As the delta lobe continues to build up the river’s path to the gulf becomes longer and more difficult (river’s like the easiest/shortest route) therefore the river changes course and abandons the older lobe and cuts a shorter route – which starts the process again.

Question 15

Coastal wetlands on the Mississippi Delta

Answer 15

• 40% of the coastal wetlands in the lower 48 states are found in the Mississippi River Delta.
• These millions of acres of wetlands were built over thousands of years by Mississippi River floodwaters that deposited huge amounts of sediment at the river delta.
• These wetlands range from a forest area to a flatter grassland area, there is also many interconnected habitats including freshwater, brackish and salt marshes.
• The wetlands are massively under threat from humans due to the construction of river levees, channels, canals, dams – all to either regulate the flow or to make it easier for trade.
• In addition humans have drained areas of wetlands for urban development. Finally global warming has a key part in the loss of wetlands due to the rising sea levels that will put these low lying coastal deltaic environments at huge risk.

Question 16

Barrier islands on the Mississippi Delta

Answer 16

• The Chandeleur Islands are a chain of uninhabited barrier islands 50 miles long located in the Gulf of Mexico. The islands were formed over 2,000 years ago as the rim of the St.Bernard Lobe of the Mississippi delta.
• On the barrier islands is the Breton national wildlife refuge which was established in 1904, as it is an important migration point for many birds on their way south.
• Due to hurricane destruction between 1915-2005 the barrier has been shrinking and migrating landward.
• Barrier islands take the brunt of impact from an incoming storm, thereby protecting the habitats and structures behind them, but they receive damage as well.

Question 17

Beaches on the Mississippi Delta

Answer 17

• Beaches that form on deltas are no different to those actually on the coast. Beaches are formed via deposition and transportation of sediment – in this case it is mainly sand.
• The material is deposited along the coast of the delta and then is smoothed out and redistributed via longshore drift.
• Longshore drift is more complex in a delta system but it acts in the same way by moving the material along the coast, however the changes in direction along the coast are much more frequent, therefore there are less generic features e.g. tombolos etc.
• The beaches here are made up of very fine and easily eroded or moved material, making them quite vulnerable in stormy conditions.

Question 18

How are the features of the Mississippi Delta interlinked?

Answer 18

• All of the features and the delta itself are all linked.
• If one feature is eroding/building up so will all the other features, the history of the Mississippi is very important to understanding the formation of this unique landscape.
• The delta environment is formed through the deposition of material because of the low energy in the lower course of the river causing the sediment to be dropped.
• However more recently sea level rise and the damage from hurricanes has led to an increase in erosion of the delta.