Sudden Sea Level Change

Typically, sudden changes in sea level (i.e., storm surge, tsunami events, earthquakes and sudden subsidence/uplift, etc.) are related to major storms or other "out of the norm" factors – more on these later, in Module 5.

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Figure 4.7: Extreme coastal flooding from storm surge during a hurricane. This home, built a few feet off the ground is severely flooded. Historically, homes like these were built with a flood door in the floor so that flood waters, when they occurred, could easily come in and out without lifting the home off its foundation.
Credit: Image courtesy of the National Oceanographic and Atmospheric Administration (NOAA).

Suffice it to say that relative sea level changes outside of the normal periodic, monthly, and seasonal tidal ranges are prone to produce significant impacts on coastal landscapes, both natural and human, because they are not typically responsible for producing coastal landscapes, and are often a surprise to people living in these areas.

• Case Example: This was especially true in the Indian Ocean region as a result of the Boxing Day Earthquake in 2004, and several subsequent earthquakes in 2005. The earthquake swarm produced a number of pronounced changes in local sea levels that were related to tectonic activity (uplift and subsidence).
• NASA and associated scientists have photographic examples of uplift and subsidence from the region. In the website (http://earthobservatory.nasa.gov/Features/Aceh/aceh3.php), they show:
  • a group of palm trees on Nias Island completely inundated by sea water as a result of ground subsidence/slumping. When this occurs along a coastline and coastal features become submerged geoscientists refer to this as a submergent coast. In contrast:
  • entire coral reefs were left high and dry after the earthquakes as a result of uplift of areas once under water. In the case example, corals along the shore of Babi Island died as a result of exposure. When coastal features are uplifted relative to water level, geoscientists refer to this as an emergent coast.