Montauk Point EarthCache
Hidden : 9/4/2012
Difficulty:
1.5 out of 5
Terrain:
2 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

Erosion: Erosion is the process by which soil and rock are removed from the Earth's surface by natural processes such as wind or water flow, and then transported and deposited in other locations.

While erosion is a natural process, human activities have dramatically increased (by 10-40 times) the rate at which erosion is occurring globally.

Excessive erosion causes problems such as desertification, decreases in agricultural productivity due to land degradation, sedimentation of waterways, and ecological collapse due to loss of the nutrient rich upper soil layers. Water and wind erosion are now the two primary causes of land degradation; combined, they are responsible for 84% of degraded acreage, making excessive erosion one of the most significant global environmental problems we face today. Industrial agriculture, deforestation, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regards to their effect on stimulating erosion. However, there are many available alternative land use practices that can curtail or limit erosion—such as terrace-building, no-till agriculture, and revegetation of denuded soils.

The planners of the Montauk Point Lighthouse were well aware of erosion. The governments agents noted that "Montauk Point is washed by the sea in storms" and "wastes very fast". They erected the lighthouse at the extreme west end of the Turtle Hill plateau, at a distance of approximately 300 feet from the bluff. Over the past 200 years approximately 200' feet of montauk point was washed into the Atlantic Ocean. Today the lighthouse stands less than 100 feet from the edge of the bluff.
EROSION: Problem
cross section diagram of unprotected bluff

CAUSES OF EROSION
STORM WAVES 
Storm waves at the toe of the bluff causing soil to fall.		 GROUNDWATER FLOW 
Ground water sinks through the layer of sand and flows laterally on the hard layer of clay. A concentrated stream pours from the bluffs face, rapidly carrying soil with it. The top of the bluff is undermined and carried to the beach below.
RAIN 
Erosion of the bluff by rain is a slow but steady process.		 GROUNDWATER SEEPAGE 
Halted by a further layer of clay groundwater seeps from the permeable layer of glacial till (sand, gravel and boulders). Surface particles are gradually carried away.

 

EROSION: Solution
cross section of protected bluff

METHODS OF EROSION CONTROL
PROTECTING THE TOE  
TOE WALL 
Beyond the sea wall a TOE WALL buttresses the base of the bluff. A filter cloth lining behind and benaeth the toe wall prevents storm waves from removing soil and undermining boulders.

SEA WALL 
The largest boulders form a SEA WALL to break the force of storm waves.
STABILIZING THE SLOPE  
FILTER BOX TERRACING 
The slope above the toe wall is reshaped to a more stable angle which is maintained by terracing and vegetation. The terraces constructed of lumber and secured by steel stakes provide a stable surface for vegetation. A filter cloth lining prevents the filter bed from washing away. Beach grass and rosa rugosa planted on the terraces do the most work to hold the bluff face. Their roots hold the soil in place and draw groundwater from the bluff. Their foliage softens the impact of rain and slows water runoff.
   
DRAINAGE SYSTEM 
A drainage system is critical to the stability of the bluff. Here a Water Collection Box is set in the bluff face to capture the stream of groundwater flowing on top of the layer of clay. The water is collected in a concrete trough and funneled into a discharge pipe to run out harmlessly onto the boulders of the toe wall. The top of the water collection box is planted in the same fashion as the filter box terraces.

Please email me at mmacgown@aol.com your answer to the following question: From your observations here, provide me with a list of the types of materials that are used to prevent the bluff from further erosion. Are these materials real or artificial? Pictures of the lighthouse are welcome, providing they do not give away any of the answers.

Enjoy your visit!

References: To Save a Lighthouse by Giorgina Reid and Against All Odds by Greg Donohue from the Montauk Lighthouse website. Wikipedia

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