Weathering and Soils Chapter 4 in review-book

Weathering and Erosion  Weathering is the break down of rocks that have been exposed to the atmosphere.  Once the rocks are broken down, the pieces are transported from one place to another. This process is called erosion. Erosion is caused by wind, moving water (streams, waves, ocean currents), ice (glaciers), and by gravity.  Most erosion that takes place on Earth is caused by moving water.

Types of Weathering  Mechanical weathering – is when the rocks are broken down into smaller pieces without changing their composition (what they’re made of).  Chemical weathering – is when the rocks break down as their minerals change in composition (they become different substances).

Types of Mechanical Weathering  Ice wedging/frost action – water enters small cracks in the rock. When it freezes, it expands and forces the crack to open more. The process repeats over again until the rock breaks apart.  Wetting and drying – breaks up rocks that are made from clay. When they are wet they expand, and they shrink as they dry. As this repeats over and over, the clay becomes weak and cracks (think of all the projects you have made out of clay…they all crack and fall apart)!

Types of Mechanical Weathering  Abrasion – Collisions between individual rocks which wear the rocks down (rounded and smooth)  Exfoliation – soil and rock is removed (glaciers or uplifting), exposing rock found deep underground. This releases the pressure causing the surface of the rock to expand and eventually crack.

Types of Chemical Weathering  Hydrolysis – water (hydro) reacts with minerals such as feldspar and form clay.  Oxidation – oxygen reacts with some minerals, especially those containing iron (magnetite) to form rust (called iron oxide). This occurs faster with water!  Carbonic acid – carbon dioxide (CO²) dissolves in water to form this acid. It can cause minerals to dissolve, especially those containing calcite!

Weathering Rates – Many factors affect the rate of weathering. They are: The rock’s resistance to weathering (hardness). The amount of surface area. Climate:  Chemical weathering occurs faster in warm, wet climates.  Mechanical weathering occurs faster in cold or dry climates.

How do soils form?  Soil is a mixture of weathered rock and organic remains.  The characteristics of soil depend on the parent rock type and climate.  The layers of soil are broken into different “horizons”.  New York soil is almost all “transported”.

How are weathered materials transported?  Downhill movement of sediments or rock debris by gravity alone (not water etc.) is called mass movement or wasting.  Includes, slow creep, slumping, and landslides.

Erosion by Water  Running water is the main agent of erosion in moist areas.  Sediment in solution is so small that it cannot be filtered out. (Colloids are microscopic).  Sediment that is “suspended” may drop to the bottom if the velocity of the stream is reduced.

Velocity of streams  Steeper the gradient the faster the flow or discharge.  Faster the discharge the larger the pieces of sediment that can be carried (ESRT pg.6).  Broad flat valleys often form meanders which eventually get cut off and form an “ox-bow” lake.

Erosion by ICE  GLACIERS  U-SHAPED VALLEYS  PARALLEL GROOVES  STRAITIONS  UNSORTED SEDIMENTS