Weathering and Erosion

weathering

Physical or chemical disaggregation of rocks into smaller particles

• physical weathering accounts for roughly \(5.6 \times 10^{15}\) g/yr; more frequent in cold, arid environments
• chemical weathering accounts roughly for \(4.0 \times 10^{15}\) g/yr; more frequent in warm-tropical environments

type of weathering

• physical weathering

  pounding a rock disaggregates it into smaller pieces. breakdown the rock into sediment without changing chemical composition.

  • water limited environments (“stuff is dry”)
  • sites of significant relief

  • fire and freeze-thaw

    as you heat up the rock, it expands, and then once it cools it shrinks it cracks and then weather!

  • freeze-thaw

    frozen water density is larger. freezing + thawing results in cracked rocks. glacier + freeze/thaw results in half dome

  • biogenic

    “a tree went through it”

  • various weathering

    • bathliths are great chemical weathering

• chemical weathering

  Msotly happens in soil Water etc., weathers. this changes their composition

  • chemistry
  • mineralogy

  principle agent of chemical weather is water: ion exchange is catalyzed by water.

  Olivine most susceptible to weathering => Pyroxene => …. => feldsphar, quartz, etc. Similar order as Bowen’s Reaction Series.

  This means Mafic mineral most susepctableto weathering, and stable felsic quartz etc. least susepctable

  • hydrolysis

    Hydrolysis is the process of using ionic bonds by water. Unusually:

    igneous rocks + acid volatiles -> sedimentary rocks + salt. For instance, \(CO_{2} + H_{2}O = H_{2}CO_{3}\) (carbonic acid!). The water in our rain plus carbon dioxide, we get weakly acidic byproduct. “CO2 + water => lower pH”

    water in solution will disassociate into OH -> H (which makes pH 7, so OH and H should be balanced).

    generally hydrolysis reaction is:

    • water + co2 + maffic thing => clay mineral + sodium

    • dissolution

      Soluable minerals “congruent hydrolysis” react with water and can go into solution full.

  • oxydation

    Oxydation is the removal of electrons from something and then add oxygen. For instance, \(4 Fe^{2} + O_{2} + 10H_2O = 4 Fe\qty(OH)_{3} + 8H^{+}\); that is, we can crash rust out from the water. (iron hydroxide.)

weathering by-products

• mechanical: sediment
• secondary: chemical weathering, clay (hydroxl in the chemical bonds)
• leftover ions

erosion

After you are done weathering, erosion is the process of the resulted sand going somewhere (i.e., “move it.”)