What is a Cuspate Foreland?
Cuspate forelands are geographical features found on coastlines and lakeshores that are created primarily by accretion of sand and shingle. The landform extends outwards from the shoreline in a rather triangular shape. Many geologists believe that cuspate forelands are created when two ridges of sediment move along a shoreline in opposite directions. The merging of these ridges forms the cuspate foreland. Cuspate forelands are characterized into two groups. Some may be stabilized (by vegetation), while others migrate down the shoreline, (due to currents and river mouths). Because of the influx of water and sediment into the bays, lagoons, and estuaries from rivers, cuspate forelands begin to move away from the direction of the river mouth. Cuspate forelands are composed of three parts: the central apex, and two marginal wings. The photo below shows the parts of Keansburg’s cuspate foreland:
Offshore Bar Formation:
An offshore bar is an area of sediment that sits just off the beach. It can be composed of sand, gravel, or other types of sediment. This sediment bar is located just off the beach because when the waves approach a gently sloping coast, like Keansburg, friction between the waves and the sea bed causes the waves to break at some distance from the coast. These waves bring up sediment and debris, leading to a build-up of material. Offshore bars are extremely beneficial to cuspate forelands in several ways. These formations help refract waves, preventing the foreland from being eroded away by tidal action. In addition, sediment bars are a source of sand and other types of sediment that help enlarge a cuspate foreland. When sand erodes from the offshore bar, it can get carried onto shore, increasing the foreland’s area.
Logging Tasks:
- You may need to wade in the water to complete this logging task. Enter at your own risk. Is there an offshore bar of sediment present at this beach? How does the presence or absence of the bar impact the formation of a cuspate foreland at the GZ?
- What part of the cuspate foreland are you standing on at the GZ?
- Based on your observations at the GZ and what you’ve learned in the description, what direction do you think the cuspate foreland will move in the future?
- Observe the direction the waves are crashing onto the beach. Are they crashing directly onto the shoreline or at an angle?
- Besides the offshore bars, what is a local source of sediment for the cuspate foreland to continue to grow?
- As of June 2019, earthcaches now contain required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. Please post this in your log.
Sources:
http://worldlandforms.com/landforms/sandbar/
https://golearngeo.wordpress.com/2010/08/24/formation-of-offshore-bar/
https://en.wikipedia.org/wiki/Cuspate_foreland#Formation_in_narrow_straits_or_on_open_coastlines
Enjoyed finding this EarthCache? Consider awarding it a favorite point!
| We have earned the Geological Society of America's highest level: |
 |
