Weathering and erosion

WEATHERINGYou 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

Website with weathering photos

• http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/weathering/picture_gallery/w_pics_menu.html

• http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/weathering/picture_gallery/w_pics_menu2.html

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

http://www.fotosearch.com/bigcomp.asp?path=BMS/BMS132/083177.jpg

Beach erosion…

• Pictures…

• How it is hurting…

• What can we do?...

RAY’S BEACH HOUSE

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!

• 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.

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.

DEPOSITION

• The sediments stop moving (deposition or sedimentation) when they reach their destination.

http://education.usgs.gov/schoolyard/RockWeathering.html

• http://www.fotosearch.com/bigcomp.asp?path=UNY/UNY002/u11911439.jpg

http://www.fotosearch.com/bigcomp.asp?path=UNT/UNT234/u15315045.jpg

http://www.fotosearch.com/bigcomp.asp?path=UNT/UNT234/u11540667.jpg

What causes them?

Weathering = Breakdown

• Wind• Ice• Water• Plants• Temperature

Erosion = Transport• Wind• Running water• Ice• Gravity• Waves

PhysicalGeography.net (definitions)

• http://images.google.com/imgres?imgurl=http://www.nhj.k12.in.us/teachers/klesko/erosion_deposition.jpg&imgrefurl=http://www.nhj.k12.in.us/teachers/klesko/erosion.htm&h=297&w=547&sz=117&tbnid=yKqU2oZ_38cGyM:&tbnh=72&tbnw=133&prev=/images%3Fq%3Ddeposition%2Bphotos%26um%3D1&start=1&sa=X&oi=images&ct=image&cd=1