Louisiana can be divided into three geographic land areas. The East Gulf Coastal Plain lies to the east of the Mississippi River and north of Lake Pontchartrain. The land is quite low and is marshland near the river. The land rises slightly in the north to rolling hills. The Mississippi Alluvial Plain stretches along the Mississippi River from Arkansas in the north to the Gulf of Mexico in the south. This area has many ridges and hollows. Fields near the river are called the “frontlands”. The land slopes away from the frontlands to the “backlands”, which are made up of clay and silt. This region includes the Mississippi Delta, at the mouth of the Mississippi River, which covers about 13,000 square miles (about 1/4 of Louisiana) and includes silt deposited by the river, making this area excellent for growing crops.
The West Gulf Coastal Plain is to the west of the Mississippi Alluvial Plain. Along the gulf, this region contains barrier beaches. Behind the barrier beaches are marshes that extend about 20 miles inland. To the north of the marshlands are the Louisiana Prairies, with a gently rolling landscape. The highest elevation in the state is Driskill Mountain at 535 ft (163 m), in Bienville Parish; the lowest, 8 ft (2 m) below sea level, in New Orleans.
Louisiana has the most wetlands of all the states, about 11,000 sq mi (28,000 sq km) of floodplains and 7,800 sq mi (20,200 sq km) of coastal swamps, marshes, and estuarine waters. The largest lake, which is actually a coastal lagoon, is Lake Pontchartrain, with an area of more than 620 sq mi (1,600 sq km). The most important rivers in the state are the Mississippi, Red, Pearl, Atchafalaya, and Sabine. The Mississippi River meet the Gulf of Mexico in Louisiana, and the Mississippi Delta extends far into the Gulf. The changing course of this great North American river has created the huge Atchafalaya River basin and has dumped tons of sediment along the coast. This sediment is what makes the Delta a fertile growing area.
Most drainage takes place through swamps between the bayous, which serve as outlets for overflowing rivers and streams. Louisiana has nearly 2,500 coastal islands covering some 2,000 sq mi (5,000 sq km).
The beachless areas of the coast are eroding at a rate of about 24 square miles (62 square km) per year. This loss has been caused in part by the system of levees (or embankments) constructed to keep the Mississippi in a central channel, which left side channels open to erosion. In 2005 Hurricane Katrina eroded an additional 73 square miles (189 square km) of the Louisiana coastland.
Louisiana has a subtropical or semi-tropical climate, with hot, humid summers, frequent afternoon thunder showers, and mild winters. Average annual temperatures range from 64 °F (18 °C) in the far north of the state to 71 °F (21 °C) at the mouth of the Mississippi River. Summers are very humid, and the average rainfall ranges from around 45 inches (1,140 mm) at Shreveport to more than 55 inches (1,420 mm) at New Orleans. The all-time high temperature is 114°F (46°C), recorded at Plain Dealing on 10 August 1936; the all-time low is –16°F (–27°C), at Minden on 13 February 1899.
