---

Environmental Science I: Geology - ENV 601
Lecture Topics - Brief Notes

Overview of Minerals and Rocks

The most important part of minerals and rocks is an understanding of the basic material, what it is made of, how silicate minerals are put together (metal cations holding together covalently bonded silicate structures), how readily the various silicate minerals and calcite are chemically weathered, and the basic rock textures and resultant porosities.

Kinds of Rocks (how they formed)
Igneous: cool and crystallize from a melt (magma or lava). Intergrown crystal texture.
      little or no porosity except for vesicular (gas bubble holes) volcanic rocks or where fractured
      (e.g., granite, diorite, basalt)
Metamorphic: recrystallize at depth under high pressure and temperature yielding intergrown crystal texture.
      little or no porosity except where fractured
      (e.g., slate, schist, gneiss, marble, quartzite)
Sedimentary: deposited, compacted, and cemented sediments (products of weathering); void spaces remain
      most are porous and permeable
      (e.g., sandstone, shale, limestone)     
Rock Composition
- the 8 most abundant elements in the crust (O, Si, then Al, Fe, Ca, Na, K, Mg)
- bonds: covalent & ionic
      bonds between Si & O are more covalent
      bonds with remaining metals are more ionic
- result in compounds, including minerals (which make up rocks)
- the most abundant minerals are silicates (based on the most abundant O & Si)
- silicate mineral (and rock) compositions range from felsic to mafic
      felsic: silica (Si & O) rich, metal cation (Fe, Ca, Na, K, Mg) poor
            more covalent, less ionic - less susceptible to chemical weathering
      mafic: Mg & Fe rich, silica poor
            more ionic, less covalent - more susceptible to chemical weathering
- carbonate minerals (esp. CaCO₃) only important in limestone and marble- susceptible to chemical weathering

Durability of Rocks: mineralogy, texture (grain size, foliation), and structure (tilted strata or foliation)

Minerals & Rocks and Environmental Health
asbestos
dissolved minerals in drinking water and cardiovascular health
radon risk from trace amounts of radioactive uranium or potassium in some rock and sediment types

Weathering

- mechanical weathering: frost wedging, stream abrasion, sand blasting, unloading, salt crystal growth
- chemical weathering: acidification of water, hydrolisis, dissolution, oxidation
- rock composition and chemical weathering rates
- the products of weathering the common minerals: clays, +/- quartz, soluble silica, metal cations (iron, calcium, etc.)
- sedimentary particle sizes: gravel, sand, silt, clay
durability of rock
- tendency to split into sheets
- porosity
- susceptibility to chemical weathering

Soils

importance of soil
      natural resource: soil erosion -> USDA Universal Soil Loss Equation
      sediment source to streams
      water filter
      contaminant sink -> (e.g., soil remediation)
      load-bearing material -> engineering properties
formation of soil
- soil-forming processes: weathering of bedrock, incorporation of organic matter, downward leaching of fines and solubles
- 6 factors determining characteristics of the soil profile:
      climate, vegetation cover, soil organisms, parent material, topography (slope of the land), time
- typical soil profile: characteristics of the O, A, B, and C horizons
- special horizons: E, Bk or K
- different definitions of "soil" used by geologists/soil scientists vs. engineers
soil classification
- climate classification
      general differences in soil by climate belt: equatorial, desert, temperate midlatitude, high latitude/polar
      USDA Soil Classification System soil orders,etc. (know they exist)
- textural classification based on relative proportion of sand, silt, and clay
- particle size distribution of soils, soil gradation and the uniformity coefficient
engineering properties of soils
- soil moisture: water content, void ratio, porosity
- conditions of dry, moist, and saturated soil/sediments
- cohesion of soil particles due to water's surface tension
- Atterberg Limits: liquid limit (LL), plastic limit (PL), plasticity index (PI)
- strength, compressibility, sesitivity, liquefaction
- properties of clays
      shrink-swell potential of kaolinite and montmorillonite (PI as an indicator)
      shearing in clays, house of cards structure and quick clays
- erodibility

- angle of repose
- effects of grain size, grain shape, and water content on angle of repose
- difference between force and stress
- angle of repose: quantitative relationship between weight (gravitational stress), shear stress, normal stress, slope angle, and cohesion
      (see homework and online notes on angle of repose)
- factor of safety (slope stability factor)
- effects of water in unconsolidated hillslopes:
      unsaturated soil: cohesion
      saturated soil: increases weight, decreases friction (pore pressure reduces normal stress); enhances mass wasting
- processes that increase driving forces
- processes that decrease frictional resisting forces
- landslide hazard and risk, Specific Risk
- strategies for reducing mass wasting risk
- types of mass wasting and examples of creep, flows, slides
     examples: lahars (Mt St. Helens, Armero Columbia, Vaiont Dam Italy)

groundwater
- relative sizes of global reservoirs of H₂0: oceans, glaciers, streams and lakes, groundwater, atmosphere, biosphere
- the hydrologic cycle: Precipitation = Runoff + Iniltration + Evapotranspiration
- aquifers, aquicludes, water table, zone of saturation, zone of aeration
- porosity, permeability
- typical porous and permeable materials that make good aquifers
- typical impermeable materials that make aquicludes
- water table aquifers
- confined aquifers, potentiometric surface, artesian and flowing artesian conditions
- groundwater flow: from areas of higher water tables to areas with lower water tables
- recharge and discharge
- relationship between groundwater and surface water
      gaining and losing streams, perennial, intermittent, and ephemeral streams
- water supply
     well drilling, water towers, cone of depression, drawdown
- overuse of groundwater (e.g., high plains aquifer, aquifers in Israel)
- groundwater pollution:
- groundwater pollution:
      non-point sources: lawn and agricultural chemicals
      point sources: landfills, leachate, proper design of sanitary landfills
- flow nets: mapping the top of the water table via well levels and lake levels
      contours of water table elevation
      flow lines: water flows from high to low contours perpendicular to the contours
      flow nets, recharge, discharge, cone of depression on flownets
- dispersion of a plume of pollution
- saltwater intrusion in coastal areas (e.g., Savannah)