• Monday, April 13- Tuesday April 21st

    Weathering Rates on Earth

    You should now be familiar with how Earth's climate and atmosphere work to break down rock, physically and chemically. This section of the unit will help you understand the rate at which this weathering takes place. That is how fast it happens. Now, in nearly all cases it takes a very long time, generally hundreds to thousands of years (but not necessarily millions) to weather a rock into smaller components. However, one interesting thing to note, is that bedrock 50 feet down that is not exposed to rain, ice, tree roots, etc, may not weather at all until it is finally exposed at the surface. Remember, only rocks at or near the surface, with the exception of caverns, weather. So it may take many tens to hundreds of millions of years to weather away an entire mountain in the Alps or Himalayas or Andes or Rockies or Appalachians. However, the speed the rock weathers is not the same in all places. I mentioned that a little in the last lesson. The rate is also not the same on all rock and mineral types, and that is the basis of our next lesson.

     

    Simply put, physical weathering primarily happens from frost action, so it will happen fastest in places that are often above and below freezing (like Western New New York for half the year or more) and hardly at all in places that never freeze like Florida.

     

    The infograph on P. 5 in the noteset is an important graphic to summarize weathering rates. You need to know how to "read" it so that you will be able to answer questions based on it. This graphic will be the basis of your graded assignment, "Weathering Rates". Though the image below is not identical to the one in your notes or the graded assignment, the concept is the same. This one has temp. and precip on different axis, but otherwise the idea is the same. Try the examples below to begin to learn how to "read" the graph.

    Example 1 : What type of weathering would occur in a city with a yearly average temperature of +10 degrees Celsius and precipitation of about 100cm per year? 

     

    Example 2: What type of weathering would occur in a location with an average temperature of -15 degrees Celsius and precipitation of about 75cm per year?

     

    Example 3: What type of weathering would occue in a location with an average temperature of 15 degrees Celsius and precipitation of about 200cm per year.

    See the source image

     

     

    Example 1 Answer: Moderate Chemical Weathering

    Example 2 Answer: Moderate Physical Weathering

    Example 3 Answer: Strong Chemical Weathering

     

    Let this graph make sense, connect it to prior learning. Why is there strong chemical weathering in warm climates with high rainfall? Because chemical reactions to dissolve rock need water (rain) and chemical reactions happen faster in warmer temperatures. Why is there only slight weathering in areas with very little precipitation both warm and cold? Most weathering requires water. Frost Action (Physical Weathering) requires water to seep into cracks and then freeze and expand to bust the rock apart. Chemical weathering requires water to dissolve rock, so if it does not rain, very little weathering takes place. Got it? Good!!

    Now take a look at your notset on P. 5 and try the questions that are below the weathering rates graphic. Once you feel comfortable with that graph, move on to the assignment in MS Teams called "Weathering Rates" It is due by Tue. April 21st. You must submit it in MS Teams this time. Please email or text me in Remind if you are having trouble submitting it in Teams.