Everyday Science Academy

Weathering, Erosion and Deposition

 

 

 

Essential Question:

How do changes in the Earth’s surface occur over time?

Standard:

Explain the effects of physical processes (plate tectonics, weathering, erosion, deposition, volcanic eruption, gravity) on geological features including oceans (composition, currents and tides).

Weathering

  • Weathering is the process that breaks down rock and other substances at Earth’s surface.
  • Weathering wears mountains down to hills and can produce strange rock formations.

There are two types of weathering:

  • Mechanical (Physical) Weathering
  • Chemical Weathering

Mechanical Weathering

  • Rocks are broken apart by physical processes (heat, water, ice, pressure, temperature, etc.)
  • The overall chemical makeup of the rock stays the same
  • Each piece has characteristics similar to the original rock

Example of Mechanical Weathering:

  • Frost
  • Wedging

Example of Mechanical Weathering:

  • Rock expands when the pressure of overlying rock is removed causing it to break into flat sheets [Exfoliation].

       Example of  Mechanical Weathering:

       Exfoliation

  • The expansion and contraction of rock, caused by temperature changes

[Thermal Expansion]

  • Expand
  • Contract
  • Thermal shattering of rock due to a forest fire
  • For example, heating of rocks by sunlight or fires can cause expansion of their minerals. This stress  eventually cause the rock to crack apart.
  • The heated exterior will expand faster than the cool interior, causing the exterior to break.
Example of Mechanical Weathering:
  • Biological Weathering

       Water and nutrients collect in the cracks of rocks that can result in the growth of plants. As the roots grow, they enlarge the cracks.

       Burrowing animals also cause mechanical weathering. They loosen sediment and push it to the surface as they burrow (dig).

  • Weathering can also occur by the rubbing of one object or surface against another [Abrasion].  
  • Sand rubbing against the rock
  • Rocks and other sediment rubbing against one another

Chemical Weathering

  • Chemical reactions dissolve or change the minerals in rocks or change them into different minerals [changes the chemical composition]

Example of Chemical Weathering:

Rocks and minerals can dissolve in acidic waters [Dissolution].

  • Dissolution
  • Caves form when slightly acidic groundwater dissolves limestone.
  • Cave formed by acid dissolved limestone
  • Some plants give off acids that also dissolve minerals in rock. The rock is weakened and eventually breaks into smaller pieces.

Example of Chemical Weathering:

  • The chemical compounds (mixes) in rock can breakdown due to a reaction with water [Hydrolysis]. An example is Feldspar changing to Clay.
  • Chemical Weathering Feldspar into Clay [28 sec]
  • When minerals containing iron are exposed to water and oxygen in the air, the iron reacts to form a new material that looks like rust [Oxidation].
  • Due to oxidation, iron-containing minerals like magnetite can weather to form a rust-like material called limonite.
  • Magnetite
  • Limonite

 

Erosion

  • Erosion transports weathered rock material.

What are some ways that weathered material can be transported?

  • Erosion by Gravity
  • Rocks and other materials, especially on steep slopes, are pulled toward the center of Earth by gravity.

Here, the weathering occurs by frost wedging

The erosion occurs by gravity

Erosion by Gravity

  • Slump
  • Rock Slide
  • Mud Slide

Erosion by Wind

  • When air moves, it picks  up loose material and transports it to other places.
  • Strong Winds
  • Dust Storm
  • Sandstorm

Erosion by Water

  • When water moves, it picks  up loose material and transports it to other places.
  • Rivers or Streams
  • Rain
  • Flooding
  • Runoff
  • Waves eroding the shoreline
  • Images of Wave Erosion

Erosion by Ice

  • When a glacier moves, it picks up loose material and transports it to other places.
  • Images of how Glaciers erode rock

 

Weathering and Erosion are two very different processes that tend to act sequentially.

Weathering is the result of the physical and chemical changes of rock and mineral material; the resulting products might or might not be transported.

 

Deposition

  • Deposition occurs where the agents (forces) of erosion lay sediment down.
  • Weathering and Erosion wear down, and deposition fills in the Earth’s surface.

Deposition by Water

  • As water moves through a river, it loses some of its energy and it can no longer carry some of its sediment. As a result, it drops, or is deposited, to the bottom of the stream. Sediments being deposited by Classzone
  • Rivers and streams erode and deposit water along their path. 
  • Water also loses energy and deposits sediment when it empties into an ocean or lake.
  • Sediment that is deposited as water empties into an ocean or lake forms a triangular shaped deposit (delta). 
  • The Mississippi River flowing into the Gulf of Mexico forms the Mississippi River delta.
  • Currents, wind, and storms carry and deposit sand along beaches.
  • Sandbar
  • Barrier Island

Deposition by Wind

  • Sediments blown away by wind eventually are deposited. Over time, these deposits develop into landforms.
  • Sand Dune

Deposition by Ice

  • When glaciers begin to melt, they deposit sediment on the land.

END