Sea Level Changes: Shorelines, Types & Impact

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

If you've ever enjoyed a trip to the beach, this lesson might be for you. Here, we'll discuss different types of shorelines as well as how changes in plate tectonics and climate change contribute to changing shores.

What Are Shorelines?

Have you ever been to the beach? The beach is a popular place for many of us to enjoy the summer, with warm sand heating our feet and a cool breeze flowing through the air. This boundary between the land and the ocean is known as the shoreline. If you've been going to the same beach for a few years, you might feel like the shoreline is pretty consistent. However, on a long-term scale of evolutionary history, shorelines are anything but stable. Even from year to year the shoreline erodes as ocean currents carry away sediment from the land. Today, we're going to learn about different types of shorelines and the geological processes that occur and cause them to go through changes.

Emergent vs. Submergent Shorelines

Shorelines can be classified into two categories, emergent and submergent shorelines. Imagine how great it would be if your favorite, ever-crowded beach could get a little bigger. This is what happens with emergent shorelines.

Emergent shorelines occur where there is a reduction in sea level or a rise in the land beneath the ocean due to tectonic activity. This makes the sea level decrease and the land portion of the shoreline increase. Emergent shorelines often have rocky coasts where tectonic activity has lifted the land up. The West Coast of North America is an example of an emergent shoreline. These shorelines feature rocky cliffs created from the tectonic activity of the North American Plate and the Pacific Plate.

The western coast of North America is an example of an emergent shoreline
California coast

Submergent shorelines occur when there is a rise in sea level either due to increased water levels or submergent activity of tectonic plates. As sea levels rise, or land sinks, the water levels rise and the shoreline becomes submergent. The Chesapeake Bay of the Eastern United States is an example of a submergent shoreline. During the last ice age, the Chesapeake River extended to the ocean in a river valley. However, as the glaciers melted, this area was flooded into a submergent shoreline, forming the Chesapeake Bay.

Chesapeake Bay is an example of a submergent shoreline
Chesapeake Bay

Sea Level Change

So, now we know that sea level changes can cause changes to the shoreline. But, how do these changes occur? Scientists classify sea level changes in two categories, eustatic and isostatic changes.

Eustatic changes are changes to the sea level that occur on a global scale. Eustatic changes to sea level occur due to changes in the amount of water stored in glaciers. For example, our current sea level is about 130 meters higher than it was during the last ice age. This is because the glaciers melted, releasing more water into the ocean and causing an increase in sea level.

Isostatic changes to sea level are localized, rather than global. Isostatic changes occur due to tectonic plate movement in a localized area. For example, during times of glacial deposits, the glaciers push down on the Earth's crust, depressing it. As the glaciers melt, the land is free of the pressure and is able to rebound, thus decreasing the local sea level.

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