STUDY GUIDE 2 - Midterm 2 Study guide Geog 1011 Landscapes...

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Midterm 2 Study guide Geog 1011 Landscapes and Water Fall 2007 1. What is the critical zone, and what layers comprise the critical zone? – The weathering processes that are responsible for creating an environment at the Earth’s surface thought of as a porous membrane where water and life interact. a. Layers include: Atmosphere, biosphere, hydrosphere, lithosphere, and the pedosphere (includes unweathered rock to the top of the vegetation canopy) 2. What does chemical weathering do; what does physical weathering do? a. Chemical Weathering- chemical alterations of minerals and rocks at Earth surface conditions from unstable minerals at Earth’s surface i. Releases nutrients- Ca, K, P ii. Weakens rocks iii. Delivers salt to oceans iv. Produces clays v. Consumes CO2 from atmosphere b. Physical Weathering- breaks rocks down by fracturing them. i. Makes rocks transportable ii. Creates avenues for water to infiltrate and move through rock iii. Produces surface area 3. Why is the amount of surface area produced important? – Enhances the surface for chemical weathering and provides habitats for a variety of bacteria, fungi, and other small living things 4. Physical weathering processes- a. Tectonic Crushing- crust is deformed by tectonic processes and fractured by earthquakes at depths below the surface—preconditioned for weathering b. Exfoliation Jointing- fractures that form parallel to the surface, forming layers of rock (not already cut by vertical joints) i. Unloading- removal of rock mass from surface by erosion, reduces pressure, allows expansion c. Frost Cracking- rocks cracked by growth of thin layers of ice in microfractures. 9% volume expansion, thin layer of water over ice below freezing point that migrates d. Thermal Expansion Cracking- rocks subjected to diurnal swings in temperature, intense/brief heating (fires), thermal expansion of minerals produces high stress that flake off rock e. Hydration Cracking- minerals expand when combined w/ H20 (biotite expands 40%), leads to crack formation f. Salt Cracking- arid climates, salt crystals grow in microcracks. Salt derived from dissolution of minerals in rock by rare rainstorms water evaporated, salt crystals precipitate, exerting stress g. Biophysical Processes (root wedging)- fractures widened by growth of roots over time
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5. Chemical Weathering Processes- a. Congruent Dissolution- products dissolved mineral breaks apart into constituent ions/molecules into water solution, no solid material left, H20 carries dissolved salts. i. Reaction 1: NaCl + H2O = Na + + Cl - + H2O ( Halite= mineral name for table salt, increases electrical conductivity of H20) ii. Reaction 2: CaCO3 + H2CO3 = Ca2 + + 2HCO3 - ( Calcite + carbonic acid—CO2 dissolved in H2O--= calcium ions + bicarbonate ion) b. Incongruent Dissolution- products include new solid mineral w/ dissolved species (silicate minerals weather this way, dominate crust) i. Reaction: Mineral A + carbonic acid = Mineral B + Ions + Dissolved Silica ii. Newly formed minerals- secondary minerals (clay minerals)— formed from weathering decay of primary minerals c. Oxidation- reaction with oxygen transfer of electron between atoms, give red-yellow-brown hues to soils i. Reaction: 2Fe2 + + O2 = Fe2O3 (iron + oxygen gas = hematite/iron oxide)
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