Basic geologic processes important
to environmental science:
naturally occuring, inorganic, fixed or limited range of chemical
composition, crystalline (regular atomic arrangement of constituent
Major groups of minerals:
the most common type of mineral, relatively low solubility, quartz
and feldspars the most common terrestrial minerals, feldspars
weather to clays.
these are mostly silicates, but very fine-grained, with a sheet
geometry and some with distinctive shrink-swell propertites.
typically consists of a metal linked to oxygen, solubility is
sensitive to conditions.
typically consists of a metal linked to sulfur, solubility is
sensitive to conditions, unstable in oxygenated surface environments
producing acidity as a product.
(evaporites): soluble, and important to biologic activity.
has a carbonate radical (carbon linked to three oxygens), relatively
soluble, produces hard water.
- we will introduce minerals in specific contexts
as lecture goes along.
hard rock, a basic distinction.
How can sediment be described?
- size distribution of particles.
- shapes of particles.
- mineral make-up of particles.
- alignment and geometry of particles (e.g.
- average chemical composition.
- organic content.
- for each of this you can think on how it
might be described/measured, and how that information might be
Description on the basis of grains size: mud
-> silt -> sand (fine to medium to coarse) -> gravel
If you think of surface sediment the particles
come in different sizes. How would knowing the size distribution
of surface sediment be of potential interest environmentally?
Lithification = process whereby sediment ->
rock, sand -> sandstone.
How can rocks be described and classified?
- color, density, mineral make-up, isotropic
vs. anisotropic, chemical composition.
- different classifications for different purposes.
- three fold basic genetic classification:
- + hydrothermal.
From an environmental perspective what are
important rock and/or sediment properties?
What would you want to know more specifically about a given rock
or sediment type from an environmental perspective? Why is this
- strength (e.g. compactability or elasticity).
- specific chemical consitutents such as;
- heavy metals such as lead (Pb), mercury (Hg).
- sulfides and/or oxides.
- seismic properties.
What near surface processes alter geologic
- physical breakdown.
- chemical alteration (silicates to clays,
production of oxides).
- cementation and precipitation.
- bioturbation, bioerosion.
What earth processes create natural hazards:
- volcanic eruptions.
- mass wasting.
- soil erosion.
- coastal erosion.
- subsidence, collapse.
- radon, asbestos, other geologic toxins.
- meteorite impacts.
- we will, once again learn more about each
of these and other concerns in specific contexts as the course
important in understanding geologic resources:
- hydrologic cycling, including groundwater
- geothermal processes (heat flow, hydrothermal
- soil forming processes.
- fossil fuel forming processes.
- ore forming processes.
We will focus a bit more on groundwater flow
for several reasons:
- it is becoming a more and more important
- much environmental industry is related to
the cleanup and management of groundwater.
- since it is hidden from sight, most are less
familiar with it.
How does the water get into the ground?
An answer may be found in considering part
of the hydrologic cycle. The diagram below attempts to show some
of the reservoirs linked to groundwater, and the processes that
transfer water between these reservoirs.
This leads to a second question. What determines
how much seeps into the ground?
- soil porosity/ permeability (what in turn
- rainfall or seepage flux (rate of supply
of the water).
- captured in the concept of recharge
rate. For a partly depleted groundwater reservoir how
long will it take for water to refill it.
How much water can the ground hold (what
is its porosity)?
- definition: percentage of void space within
rock body under consideration.
- two types:
space between grains, porosity typical of sediment.
- fracture: space
provided by fractures, typical of hard rock.
- what attributes of the fracture system control
- determining factors on intergrain porosity
-> sorting, packing, and grain shape.
- The above diagrams illustrate in 2-D how sorting and packing
- how can porosity be measured?
- representative values for various geologic
media: conglomerates and sandstones - 20-40%, muds - 60%, shales
(lithified muds) up to 10%.
What determines in what pattern and how
fast water flows in the ground?
- intergrain permeability: influencing factors
-> porosity, geometry of pore spaces, grain size.
- fracture permeability: common in crystalline
rocks, anistropy of permeability.
How can we map groundwater surfaces (given
they are hidden from view)?
- surface manifestations and connections.
- monitoring vs. extraction wells.
- geophysical techniques.
- contoured surfaces and shallow flow nets.
Aquifer is a groundwater reservoir. What are
local aquifers (for Omaha area)?
Dr. Schimmrich has collected links to hydrology