Louisiana’s Physical and Cultural Geography Unit 1 Louisiana’s Physical and Cultural Geography

Louisiana’s Geologic History Geology is the study of how the earth was formed. Geologists look at rocks, fossils and land formations to determine how each region of the earth was formed. Pangaea (Greek for all land) is the name of the supercontinent that geologists believe connected all of the world’s landmass about 250 million years ago.

Louisiana’s Geologic History At the end of the Paleozoic Era, Pangaea began to break apart in a process known as continental drift. An ancient Gulf of Mexico formed between North and South America, covering the area that is now Louisiana. During this time the mouth of the Mississippi River was located in modern day Arkansas.

Gulf Coastal Plain Over millions of years, the Mississippi River deposited sediment into the Gulf of Mexico and began to slowly fill part of it up. When the river current slowed, sediments settled to the bottom and created a coastal plain, a relatively low, flat region built up river sediment. Louisiana is the only state made up entirely by the Gulf Coastal Plain.

Louisiana and the Ice Age Most of the gulf coastal plain was made up during a time when Earth’s climate when through long periods of warming and cooling. During Ice Ages, much of the world’s water was trapped in glaciers, and sea levels were about 400 feet lower than they are today. Louisiana’s coastline extended all the way out to the continental shelf (the edge of landmass where the Gulf’s floor drops into very deep water.)

Time Zones The world is divided into 24 time zones, and the U.S. is divided into 6. A time zone is a region on Earth that has a uniform standard time for legal, commercial and social purposes. In most places, the sun is directly overhead at 12:00 noon.

Mississippi River Floodplain The Power of Rivers Floodplains Mississippi River Floodplain When rainfall brings more water than a river can handle, excess water spills over the riverbank and covers the flat valley floor. This area is a floodplain and serves as a reservoir until the river can move the water into the Gulf.

The Power of Rivers Meandering Streams Because water always seeks the path of least resistance, Louisiana’s rivers meander or wind in loops and curves. When water flow encounters an obstacle the current will bounce to the opposite riverbank and begin to erode it. This forms a curve that allows water flow to return to the other bank.

Point Bars and Oxbow Lakes The Power of Rivers Point Bars Point Bars and Oxbow Lakes When the current slows along the inside of a meander, the sediment falls to the bottom of the river creating a point bar. The meander gets larger until it creates nearly a full circle. Because water seeks the path of least resistance, the river eventually straightens itself out by cutting across the point bar. The ends of the old meander close up to form an oxbow lake.

The Power of Rivers Natural Levees are created when a river overflows its banks and spills onto the floodplain. Most of the sediment settles along the riverbank, and as the bank builds up higher and higher, it angles away from the river toward the floodplain. This process raises the riverbed, and it eventually become higher than the floodplain around it.

The Power of Rivers Terraces Over time, the floodplains surrounding the Mississippi River eroded leaving old river beds as elevated ridges known as terraces. Most terraces are 50-100 ft. higher than the surrounding floodplain. Macon Ridge and Highland Road are examples of terraces.

The Power of Rivers Deltas Bars Deltas occur when a river flows into an ocean. Sediment settles on the ocean floor in a fan-shaped pattern. When water is shallow, new land is built up. A bar is a barrier of mud (also made of river sediment) that interferes with a river’s current. Following the path of least resistance, the river splits to flow around the bar.

The Power of Rivers Coastal Marshes Mud Lumps Coastal marshes are wet grasslands formed by river sediment deposited along the coast. Depending on their nearness to the ocean, coastal marshes can be freshwater, saltwater, or brackish. Mud lumps are strange formations caused by pressure. As heavy sediment piles up on the river bottom, lighter sediment is squeezed to the surface in an almost geyser-like way. Mud lumps can be up to 12 ft. high and cover 20 acres.

The Power of Rivers Barrier Islands Barrier Islands are extremely important : They help absorb the impact of storms They protect the mainland from erosion They block saltwater from entering the marsh during storms They serve as habitat for birds, turtles, fish and shellfish Barrier islands are created when a river abandons its delta. Without fresh sediment, the delta begins to erode and marsh is washed away leaving a lagoon between the mainland and the bar. Grand Isle is moving at a rate of 16 feet per year due to erosion on the western end and sediment build-up on the eastern end.

Rivers and Bayous Mississippi River “Mississippi” is an Algonquian Indian word meaning large river. The Mississippi is the largest river in the United States and the 4th largest in the world. It starts in Minnesota and flows over 2000 miles to the Gulf of Mexico. It drains 32 states and 2 Canadian provinces. 375 billion gallons of water flow through Louisiana each day

Rivers and Bayous Red River The only major river in Louisiana that has white water rapids. The Red River is the 2nd largest river in Louisiana. Begins in New Mexico and enters the Mississippi River near Simmesport. Named for the reddish sediment it carries. Has high salt content due to the fact that it flows over an underground salt dome near the Texas-Oklahoma border.

Rivers and Bayous Atchafalaya River The Atchafalaya Basin is the largest swamp wilderness in the United States. Half of all the nations migratory birds winter here Home to 200 bird species Largest refuge of the Louisiana Black Bear Supplies the world with 23 million lbs. of crawfish each year. The largest distributary of the Mississippi River. Distributary is a branch of a river that flows away from the main stream. Flows 125 miles from the Mississippi at Simmesport to the Gulf of Mexico at Morgan City.

Rivers and Bayous Ouachita River Ouachita begins in Arkansas mountains and runs through northeast Louisiana. Merges with Tensas and Little River to form Black River Tamed by a series of locks that allow commercial barge traffic to travel to Arkansas.

Sabine, Pearl and Calcasieu Rivers Rivers and Bayous Sabine, Pearl and Calcasieu Rivers Calcasieu lies entirely within the state beginning in west-central La. and flowing past Lake Charles to the Gulf. Sabine River begins in north- central Texas and makes up the Louisiana-Texas border. Toledo Bend reservoir built in 1960s. The Pearl River begins in central Mississippi and forms our boundary with Ms. At the toe of the Louisiana boot. Named because mouth of the river was a popular place for the French to look for pearls.

Rivers and Bayous Bayou Teche Bayou Lafourche Begins near Opelousas and joins the Atchafalaya near the Gulf of Mexico. Settled by Acadians (Cajuns) Important tourist region Now a distributary, used to be a channel of the Mississippi River Exits the river at Donaldsonville Settled by many French, Spanish, African and Native Americans. HWY 1 runs the length of the bayou and is known as the “longest street in America because of the many communities along it.

Intracoastal Waterway Rivers and Bayous Intracoastal Waterway Gulf of Mexico 3000 mile waterway allows ships to go from Texas to Florida Provides ships a safe inland route along the Gulf Coast 5th largest sea in the world Covers almost 600,000 square miles and has and average depth of 5300 ft. Louisiana has over 1000 miles of coastline along the Gulf (6th longest coastline of any state) Gulf affects climate and economy

Lakes Oxbow Lakes Depression Lakes Formed when two ends of a meander fill in with sediment Very common in Louisiana False River and Lake Bruin created by Mississippi River Created when land sinks along a fault Examples: Catahoula Lake, Calcasieu Lake, Lake Maurepas, and Lake Pontchartrain

Lakes Raft Lakes Coastal Lakes Only found along the Red River Created when bayous flooded as a result of the Great River Raft (log jam) Examples: Lake Bistineau, Black Lake, Saline Lake, and Iatt Lake Lakes dried up when jam was cleared in the 1830s Man-made dams have allowed lakes to fill up again Formed when cheniers (ridges of high ground in the coastal marsh) slowed the flow of water into the Gulf

Lakes Toledo Bend Reservoir Reservoirs Man-made lakes found mainly in North Louisiana. Used to control floods, supply water to cities and provide a place for recreation. Toledo Bend Reservoir is the 3rd largest man-made lake in the U.S. 1200 mile shoreline Covers 186,000 acres Home to hydroelectric dam that provides electricity to the region.

Coastal Erosion