Weathering, Erosion, and Deposition - September 25

Weathering, Erosion and Deposition
September 25

Note:  Our test on Minerals will also include weathering, erosion, deposition and some quick review facts about rocks.  You have already taking a 10-questions test on rock so I will be selecting 3-4 of those and adding question about these new topics for a 20-questions multiple choice test on Tuesday or Wednesday (October 3- 4).


  1.  Weathering is the chemical and physical breakdown of rocks into sediment.
  2. Chemical weathering is when a chemical change occurs within the atomic bonds holding the rocks together break down creating smaller pieces of rock.
    1. Oxidation – oxygen combines with metals in rocks…example iron-based rocks mix with oxygen creating rust
    2. Hydrolysis – think water. Water will seep into rocks and soften/cut away softer minerals found in the rock….This was how the Grand Canyon was formed
    3. Carbonation – think about the bubbles in sodas.  Those bubbles are releasing carbon dioxide in the rock wearing away minerals to create areas like caverns!
  3.  Physical (mechanical weathering) is the process that breaks rocks apart without any change to the chemical composition of a rock.  Have you ever seen the old cartoons where the person in jail is using a large mallet to break a large rock down into smaller rocks – same idea as physical weathering
    1.  Glaciers and ice will break down rocks by the following processes:
      1. Abrasion – by the movement of rock scraping along other rocks via water movement, glacial movement or wind picking up sand and scraping established rocks.
      2. Ice Wedging – Potholes!  When water seeps into a crack in the road or rock, it may possible turn into ice which expands the crack.  When the temperature rises, the crack may contract a bit causing the rock to become weaker.  After several sessions of ice expansion and heat contraction, a hole will develop often causing rocks to fall along mountain roadways.
      3. Plant roots can get a hold in a small crack of a rock and begin to grow.  Have you ever notice sidewalks in the city where trees are planted along the sidewalk?  The broken sidewalk acts like rock where roots have gotten into those cracks.
      4. Some animals will burrow under rocks or around rocks.  Their burrowing may cause a softer rock to chip down into a finer sediment.
      5. Gravity – the downward pull of gravity may eventually cause a mountainside rock to fall breaking off pieces of itself and other rocks that it may meet along the way.
  4. Erosion is the process that moves rocks or soil from one place to another by:  gravity, water, wind or ice
  5. Deposition is the process in which sediments, soil and rocks added to a landform such as: deltas, flood plains, sandbars, dunes.
  6. Running water is the primary agent of erosion.  The velocity (or speed) is based and the amount of water running through an area and the slope of the area.  The greater the slope and faster the water, the greater size of particles can be carried by the water.
  7. Rivers are changed by the sediments that they carry.  Young rivers are most like to be fast-flowing in a V-shaped valley with waterfalls and rapids.  Mature rivers have less energy and move more slowly creating meandering (curvy) rivers with sandbars (like the Neuse River along our southern county border).  An old river will be very slow and shallow as a result of the large amounts of sediment left within the riverbed.  Where our North Carolinas meet the Atlantic Ocean, you will find broad, shallow rivers creating small islands, deltas (a fan-shaped area formed by the release of sediment at the mouth of a river).
  8. Wind can pick up sand and small particles and blow across rocks.  This creates unexpected rock sculptures like found in Arizona or sand dunes in deserts. 
  9. Gravity may create fast rock falls like landslides or slower rock falls called slump or creep.  Mud flows down the side of a hill or mountain are also the result of gravity moving sediments.
  10. Glaciers moved as far south as the end of our Appalachian Mountains.  These glaciers have melted and crept back up to colder norther climates.  This movement created U-shaped valleys.  A moraine is an area of rock and sediment that accumulated as the glaciers lost energy and dropped their loads.  Kettle lakes are scattered across some of northern states and Canada because parts of the glaciers lost energy and melted into the holes that they created during their movements.
  11. Wave erosion and deposition is the results of waves moving along our shorelines.  On the western side of our country, the Pacific is hitting rocky coastlines creating erosive events.  Here is North Carolina, along the Atlantic, our sandy beaches are the results of older rivers depositing their loads near or along our shoreline.


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