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Weathering and erosion
1. WEATHERING
You start with hard, solid rock. Slowly, this rock
breaks down into smaller pieces (weathering). Most
of the time, this breakdown occurs when other small
pieces of rock driven by water, gravity, or wind
crash into the rock (mechanical weathering).
Another way to break rocks down occurs when
chemical reactions actually remove individual
elements from the rock (chemical weathering).
Usually chemical weathering causes the remaining
rock to weaken so that mechanical weathering
works even faster.
http://education.usgs.gov/schoolyard/RockWeathering.html
The following slides from http://www.nicholas.duke.edu/eos/geo41/wea.htm
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14. Website with weathering photos
• http://academic.brooklyn.cuny.edu/geology/leveson/• http://academic.brooklyn.cuny.edu/geology/leveson/
15. EROSION
As soon as a rock particle (loosened by one of the
two weathering processes) moves, we call it
erosion or mass wasting. Mass wasting is
simply movement down slope due to gravity.
Rock falls, slumps, and debris flows are all
examples of mass wasting. We call it erosion if
the rock particle is moved by some flowing agent
such as air, water or ice.
http://education.usgs.gov/schoolyard/RockWeathering.html
30. How it is hurting…
• The houses are destroyed
• Beaches are covered in water
• Debris is brought back into the ocean
• Animals eat the debris or get caught in it
• Animals cannot breed on the beaches (turtles)
• Sand is washing away with waves and leaving
nothing but sediment
• People try to bring in sand, but it costs over 1
million dollars per mile!
31. • Removing sand from beaches and dunes for
construction purposes causes erosion and the loss of
beaches and coastal lands, destroying the natural
heritage of the coast and reducing the vibrancy of the
tourism industry.
• Building too close to the beach interferes with the natural
sand movement and may impede beach recovery after a
serious storm or hurricane.
• Badly planned sea defenses may cause the loss of the
beach, and of neighboring beaches.
• Pollution from human activities on the land may damage
coral reefs and sea grass beds; these biological systems
protect, and provide sand to the beaches.
• Removing vegetation from the dunes destabilizes these
protective sand barriers; and clearing sites inland results
in increased soil and dirt particles being washed offshore
and smothering coral reef systems.
32. What can we do?
• Planning new development so that it is a ‘safe’ distance behind the
beach will reduce the need for expensive sea defense measures in
the future.
• Re-vegetating dunes with native vegetation e.g. grasses and vines,
and planting beach areas beyond the reach of storm waves with
salt-resistant, deep-rooting trees, such as sea-grape. (Additional
development controls are required in the fragile offshore cays.)
• Resorting to ‘hard’ engineering structures such as seawalls,
revetments and bulkheads, only when there is a need to protect
beachfront property from wave action. Such structures, even with
careful design, result in the loss or narrowing of the beach over time.
• Considering all other beach enhancement measures such as
offshore breakwaters, groins and beach nourishment (placing sand
from the offshore zone or from an inland source on the beach) at a
particular site. All such measures require careful design and
environmental impact assessments, so always first consult the
Department of Physical Planning.
33. DEPOSITION
• The sediments stop moving (deposition or
sedimentation) when they reach their
destination.
http://education.usgs.gov/schoolyard/RockWeathering.html
