WWC - Water's Effect on Coastlines Lesson

 

Water's Effect on Coastlines

Water has several effects on coastlines. Some of these effects are created by wave and current action and will be explored in a later module. The other effect has to do with defining the coastlines of land regions.

Over Earth's history, the sea level has risen and fallen as climates have changed. Cooler average temperatures produced more frozen precipitation worldwide, and as this snow and ice accumulated on land, sea levels dropped. As global temperatures rose, much of this land ice melted and flowed back into the oceans, causing sea levels to rise.

As sea levels rise and fall, coastlines and the shapes of the continents are defined. During the height of the last ice age (about 20,000 years ago), the oceans were about 120 meters (400 ft) shallower than they are today. The lower sea levels meant that much of the continental shelf that is underwater today was exposed land. The best-known example of this effect is the Beringia land bridge, which connected North America to Asia, and is thought to be a major passageway of the first humans to move into North America.

 

Long before then, though, sea levels were much higher. Draw a line on a map of Georgia connecting the cities of Columbus, Macon, Milledgeville, and Augusta, and you will have defined the ancient shoreline 65 million years ago. Florida was completely submerged, as was the lower half of Georgia. The line that you drew is known as the fall line and defines two very different regions of Georgia - the Coastal Plain and the Piedmont. The Coastal Plain is comprised of loose, sandy soil, while the Piedmont is harder and mainly clay. Rivers that flow south and east from the northern part of Georgia turn into waterfalls at the fall line, which means that early trading vessels coming from the oceans had to stop moving upriver at these points. As a result, the four cities mentioned above originated due to trading outposts that were established on the Chattahoochee, Ocmulgee, Oconee, and Savannah Rivers at the very locations of these falls.

What would the Earth look like if all of the ice on it melted? Think back to 65 million years ago, when Florida and half of Georgia were submerged...

 

 

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