Overview

One of the major driving forces for large-scale change in coastal environments over geologic time is sea level change. When coastal change occurs as growth of coastlines outward toward the ocean, the coastline is said to be prograding. This generally produces more land area above sea level as a result of sea level fall. In contrast, when coastal change occurs as the retreat of shorelines back from the ocean, the coastline is said to be retreating - often as a result of sea level rise. Thus, substantial land areas often succumb to erosional processes as sediments are reworked and moved back into the sea where much more space is created for it. In the photo below, taken in May of 2012 after some severe winter storms hit Wallops Island, Virginia, you can see one of the characteristic features that develops when severe high water level events, including storm surge, work to destabilize and undercut vegetated dunes. With such erosion, once the main flood event is over, the fresh water table drops and much of the vegetation dies as the root systems are disconnected from their water supply. Without a strong, vital root system working to hold the dune sediments in place, the very next storm will do even more damage and will result in rapid bluff recession. In just a few storms, significant portions of the shoreline can be eroded back. This process is exacerbated by high water events whether short-term over a few hours to days or long-term over 10s of years or more.

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Figure 4.1: Photo taken along the northeastern shoreline of Wallops Island, Virginia near the Chincoteague Inlet. Hurricanes Irene and Sandy produced substantial erosion of the primary and secondary historical dunes at this location. In this image, maritime forest and dune scrub vegetation growing on the dunes is being eroded and is collapsing as the wave action undermines the dunes.
Credit: Sean Cornell

In this module, we will take time to explore the mechanisms that produce sea level change and the time periods over which sea level change takes place. Before we can truly conceptualize how sea level change impacts human societies, we need to answer a few questions. Thus, in the module ahead, we will explore how scientists define and measure sea level in the first place. We will explore how sea level changes from one day to the next, one season to the next, one year to the next, and beyond. We will explore mechanisms that produce sea level change on various time scales and think about how human activities are contributing to climate change and associated sea level rise historically and into the future. You will gain first-hand knowledge of sea level trends as you are asked to access, download, graph, and analyze trends in tidal data from a range of sites around the globe.