Scientific method involves:
· “experimental design”
· data collection
· objective reasoning and analysis
--results testable and may be predictive (contrast with “pseudoscience”)
Method--
1. observation
2. hypothesis
3. “educated guess”--predict likely outcomes
4. design study to test hypothesis and collect data
5. compare results with predictions
6. accept/reject/modify hypothesis
--if good, hypothesis becomes theory
--if really good, theory becomes a universal law or a “unifying theory”
Technology--application of scientific knowledge for practical purposes
(basic vs. applied)
Why is basic knowledge useful?
Example--why do we care about fossils?
1. fossil fuels
2. Earth history--global change
Science and technology rely upon cumulative knowledge;
in a sense, both advance by accident
Technology “feeds” science
Ways of applying the scientific method--
1. empirical (observation of environment)
2. experimental
3. modeling (advanced by technology)
Applying the scientific method (continued)--
scientific predictions: good for weather, not so good for earthquakes
or for effects of population growth
(distinguish between prediction and forecast [longer-term])
Science can provide information, but cannot answer moral/ethical questions
History of (Earth) science--four general periods
1. antiquity (particularly ancient Greeks and Romans)--mostly astronomy,
math, philosophy of science (e.g., inductive/deductive reasoning)
2. Scientific Revolution (c. 1500-1700)--astronomy (e.g., Galileo),
physics/calculus (Newton et al.)--”natural philosophers”
3. “Age of Earth and evolution”--19th century--(geology developed relatively
late as a formal discipline)--
fundamentals:
(1) Earth is very old
(2) “the present is the key to the past” (Earth processes ongoing throughout
much of Earth’s history)
--supported by non-geologists (e.g., Darwin, M. Curie)
4. 20th century--
(1) plate tectonics--outgrowth of theory of continental drift
(2) Earth system science (planet exists, in a sense, as a number of
overlapping spheres) (lithosphere, atmosphere, hydrosphere, pedosphere,
biosphere)
Evolution and environment (brief intro.)--
· Earth is ~ 4.6 billion years old; single-celled bacteria originated
~ 3.6 billion years ago; multicelled terrestrial organisms originated ~
3 billion years ago
· There have been five major extinctions during Earth’s history
(humans are causing the sixth)--
the number of families (taxonomically speaking) has increased over
geologic time, but the number of species crashes during major extinctions
(Linnean taxonomy: kingdom; phylum; class; order; family; genus; species)
· biodiversity rules--evolutionary niches are filled
· evolution and extinctions may be tied to plate tectonics (realignment
of positions of continents) as well as impacts
· human effects on the environment:
prehistoric “wipeout” of large animals in North America and Australia
(and elsewhere)?
ancient civilizations of the Middle East--irrigation;
deforestation (e.g., the Sahel [sub-Saharan Africa] [present-day],
eastern North America [beginning in colonial time], Great Britain, Greece
[classical])
Critical issues--
1. human population growth (currently exponential [doubling every 40-46
years])
limits of growth?--consequences include not just extinctions, but habitat
degradation, drought, famine, war, pollution
READ “Our Real China Problem”, Atlantic Monthly, November 1997
(http://www.theatlantic.com/atlantic/issues/97nov/china.htm)
Critical issues (continued)--
2. resources and sustainable development--
resource: anything we get from the environment that meets our needs/wants;
can be divided into:
(a) potentially renewable (e.g., soil, water(?), trees)
(b) nonrenewable (coal, oil, other fossil fuels, mineral resources)
(in part, availability = function of economics)
(c) perpetual (e.g., solar)
(see Fig. 1-12, production rate of resources vs. time)
3. pollution--contamination of one substance by another, undesirable
one
waste--unwanted byproducts (but may be reused);
as population (and population density) grows, and technology advances,
waste becomes more of a problem
Problems thus far:
(1) too many people (overpopulation)
(2) consumption overpopulation
(3) pollution overpopulation
Can minimize problems by:
(1) reducing population growth--
educate and raise standard of living in developing countries, especially
for women
(2) reducing resource consumption (reduce, reuse, recycle [in decreasing
order of efficiency])
(3) reduce pollution and waste generation by more efficient technologies
Critical issues (continued)--
4. natural disasters--sudden, destructive changes resulting from long-term
geologic processes
geologic hazard--natural phenomenon or process with potential for disaster
Are natural disasters increasing?
--some are (e.g., floods, because of increasing human alteration of
watersheds)
--others may be (incidence of severe storms as a result of climate
change?)
--others aren’t, but seem to be, because populations expand into risky
areas and damage therefore increases (e.g., earthquakes)
risk--magnitude of death, injury, or property loss due to a particular
hazard (based on statistical calculations)
Chapter 2
Systems--
reservoir = container
stock = content of reservoir (term not commonly used)
flux = movement of mass/energy in/out of reservoir
open system = mass/energy can move in/out
closed system = energy can move in/out
isolated system (artificial) = nothing moves in/out
Systems (continued)--
dynamic system = active (work being done, like on Earth)
static system = no work done (“dead”, like moon)
steady state--inflows = outflows (approximately the case for mass fluxes
on Earth)
Earth’s planetary evolution (quick overview)--
BIG BANG--
(1) 10-20 billion years ago, gamma rays filled universe
(2) gamma rays decayed to form subatomic particles
(3) subatomic particles combined to form hydrogen and helium
(4) H and He condensed into gas clouds (nebulae)
(5) gas clouds formed stars
(6) stars formed heavier elements
(7) planets created as byproduct of stars (which continue to form)
Earth formed by collision, compression of matter around young Sun;
radioactive decay made early Earth molten (iron melted);
differentiation (layering by weight) resulted
(Note: Mercury, Venus, Earth, Mars are “rocky” planets)
Earth’s layers viewed by composition:
(1) crust (around surface)
(2) mantle (with oxygen, silicon, iron, magnesium-rich rocks)
(3) nickel/iron core
Earth’s layers viewed by physical properties:
(1) lithosphere (rigid; to about 70 km depth)
(2) asthenosphere (ductile, or plastic [deforms without breaking];
70-200 km depth)
(3) mesosphere (mantle [relatively rigid]; 200-2891 km depth)
(4) outer core (liquid; 2891-5150 km depth)
(5) inner core (solid metal; >5150 km depth)
Composition and properties inferred from earthquakes and rocks at surface
Quick chemistry review:
element = composed of only 1 type of atom
atom = smallest particle of an element (that retains its fundamental
characteristics)
compound = substance composed of 1 type of molecule
molecule = smallest particle of a compound (chemical combination of
atoms)
Fundamental particles of an atom:
nucleus comprised of protons (positively charged) and neutrons (uncharged);
electrons (negatively charged, much lighter) orbit nucleus
Elements are classified by atomic number (number of protons);
atomic mass = number of neutrons + number of protons
Actual atomic size = 0.0000001 mm
Ion forms when atom gains or loses an electron (+ ion = cation; - ion
= anion);
oppositely charged ions form ionic bonds (as observed for salts);
electron sharing results in covalent bonds (as observed for metals)
Mineral = any naturally occurring element or compound with a specific
chemical composition or range of compositions
(can have different minerals if there’s more than 1 possible arrangement
of atoms);
properties depend on:
(1) how atoms are arranged
(2) types of elements
(3) kinds of bonds
Spheres revisited:
(1) lithosphere--2 types of crust:
continental (light-weight, light-colored); oceanic (heavy, dark)
(2) pedosphere--soil (weathered rock, organic matter); up to 200 m
thick
(3) hydrosphere--Earth unique because there’s lots of water as gas
(vapor), liquid, ice
(10-20 km thick on surface; 12 km thick in atmosphere)
(4) atmosphere--10,000 km thick (78% nitrogen, 21% oxygen, 0.9% argon,
0.03% CO2)
(5) biosphere (life in/on/above Earth)--carbon-dominated; unique in
our solar system
Energy cycle--99.98% of Earth’s energy from solar radiation; a little
from radioactive decay of rocks; even less from gravitational attraction
Kinetic energy = energy of motion
Potential energy = energy of position
Rock cycle--
magma (molten rock) rises buoyantly from mantle; cools and hardens
as igneous rock
(lava = magma at land surface)
At surface, (1) weathering (rock broken up)
(2) erosion (a.k.a. transport of rock particles [e.g., clay, silt,
sand, pebbles])
(3) sedimentation (grains settle out)
(4) lithification (grains become sedimentary rock)
Metamorphic rocks = “cooked” (buried, heated, pressurized) igneous
or sedimentary rocks
Hydrologic cycle--driven by solar energy;
condensation: formation of water droplets or ice crystals around nuclei
(e.g., dust);
precipitation (rain, snow, sleet, hail);
runoff: overland flow + storm flow through soil zone to surface water
bodies;
infiltration (soaks into ground);
evaporation: loss of water as vapor from land surface;
transpiration: loss of water as vapor from plants (commonly lumped
with evaporation as evapotransipiration);
groundwater: saturated zone in subsurface
Hydrologic budget--
96.54% of water in oceans; 1.74% in glaciers/snow; 1.69% groundwater
(>50% saline)
Residence time = stock/flux;
average = 2650 years for oceans, 403 years on continents, 8 days in
atmosphere
(but water can reside millions of years on continents [e.g., as deep
groundwater])
Chapter 3--Geologic Time
We’ve talked about (1) the Earth being very old (4.6 billion yr), (2)
how “the present is the key to the past”, and (3) how we know absolute
ages (via radiometric dating)
--more detail:
Leonardo da Vinci--
observed marine fossils in Apennine Mountains (central Italy) and live
sea creatures; concluded that fossils hadn’t been transported (i.e., they
died in place) and hadn’t died during Biblical flood;
suggested marine deposition and subsequent uplift
Niels Stensen (Nicolaus Steno)--
conjectured that strata (layers of sedimentary rock) record Earth history;
developed (1) principle of superposition (younger rocks overlie older
ones) and
(2) principle of original horizontality (strata were originally flat
lying, but may have been folded/tilted/faulted after deposition) (useful
but simplistic--why?)
William “Strata” Smith--
mapped units of rocks in England;
developed (1) concept of formations (units with similar appearance,
properties, and relative age [based on fossils]) and (2) principle of faunal/floral
succession
Worldwide geologic time scale--
(1) eons--3 during Earth’s history; span hundreds of millions to billions
of years
(e.g., Phanerozoic [current])
(2) eras--coincide with major boundaries in rock or fossil record;
span tens to hundreds of millions of years (e.g., Mesozoic [“age of dinosaurs”])
(3) periods--span tens of millions of years (e.g., Jurassic)
(4) epochs--span 10,000 years (Holocene [current]) to tens of millions
of years
Evolution--
Darwin’s finches (on Galapagos Islands)--
different species became isolated on different islands and developed
different characteristics; genetic mutations favored adaptation and were
passed on
(natural selection, like breeding)
Hurricanes--
showed storm track and satellite image of Hurricane Floyd (as of this
morning);
category IV (maximum sustained winds 140 mph), moving toward NC coast,
but affecting northeast Florida, Georgia, and SC coasts (>1 million people
evacuated)
Compare with previous hurricanes affecting southeastern USA in past
decade:
Hugo (1989), hit Charleston, SC; 86 deaths, $7 billion in damage
Andrew (1992), hit southeastern Florida and Louisiana; 61 deaths, $26.5
billion
Residence time of water (revisited)--see 9/13 notes
Evolution (continued)--
genetic mutations over relatively long periods can confer competitive
advantages for organisms and are passed on;
some organisms migrate to better habitats;
losers become extinct (sometimes by impacts);
all of this fits with Smith’s principle of floral/faunal succession
Absolute time--
radioactivity = propensity of certain elements to change form and emit
rays of energy (i.e., decay); source of Earth’s internal heat
--unstable atom decays spontaneously, loses particles/energy, becomes
another element (daughter);
decay chain--multiple (sequential) daughters exist, with (ultimately)
a stable end product
--number of atoms decaying in a given period is proportional to the
total number of radioactive atoms in a sample
isotope = form of an element with a specific number of neutrons (different
isotopes have different numbers of neutrons)
--unstable if number of neutrons and number of protons differ greatly
Example:
most common isotope of carbon: 12C (6 protons + 6 neutrons; stable);
less common stable isotope: 13C (6 protons + 7 neutrons);
radioisotope: 14C (6 protons + 8 neutrons)
Mechanisms of decay:
(1) beta decay: 14C – beta particle --> 14N (neutron splits into proton
and energetic electron)
(2) proton --> neutron (by electron capture or positron emission)
(3) alpha decay (2 protons + 2 neutrons lost; more common for heavy
isotopes)
Half-life--time for half of the atoms of a radioisotope to decay;
constant for each radioisotope
Example (relevant to dating water):
3H (tritium)--half-life 12.3 years; decays via beta decay to 3He
Background concentration in rainfall (circa 1950) = about 10 tritium
units
(1 TU = 1 3H atom per 1 quintillion 1H atoms; measured with mass spectrometer)
Assume 3H2O falls in precipitation and infiltrates (is isolated from
atmosphere)--
after 12.3 years, 5 TU remain;
after 24.6 years, 2.5 TU remain;
after 36.9 years, 1.25 TU remain;
after 49.2 years, 0.63 TU remain (close to detection limit).
Therefore, 3H is normally useful for dating waters recharged within
the past 50 years;
however, 3H is also useful for dating waters recharged during the period
1952-1963, when atmospheric nuclear testing increased 3H concentrations
in precipitation
(to a maximum of approximately 2000 TU in North America);
3H testing peak will be detectable for >50 years.
Problem with 3H dating: waters of different ages mix; at best, you
can say that some component of water has been recharged within the past
50 years
(reference: High Plains aquifer case study)
Revisiting absolute dating of water:
if the amount of tritium released (input function) to atmosphere is
not well known, how do we determine the age of young ground water (infiltrated
within the last 50 years)?
(1) look at rates of tritium loss AND daughter (helium-3) accumulation
(2) use chlorofluorocarbons (input function to atmosphere well known)
Hurricanes revisited--injuries, deaths, damage caused by:
(1) high winds (debris flies around; tornadoes can spin off)
(2) flooding (storm surge at beach; flash floods can follow storm farther
inland)
(“silver lining”--Hurricane Floyd helped mitigate drought in mid-Atlantic
states)
(showed U.S. Geological Survey data for Raritan River, New Jersey--
streamflow rate increased from about 20 cubic feet/second [cfs] [below
long-term median] to about 4000 cfs during 9/16/99; record flood stage
[height] resulted)
Chapter 4
Plate tectonics revisited--rigid plates move horizontally (at rates
up to tens of cm/year) due to convective currents in the asthenosphere
(upper mantle);
viewed from above, plates move along cycloidal (spiral) trajectories
Seafloor spreading--”conveyor belt”--either side of ocean basin opens
up as new seafloor is created at mid-ocean ridge (like Mid-Atlantic Ridge);
coastlines on either side are passive margins (like eastern North America);
plate-plate collisions occur at active (convergent) margins (like western
North America)
Subduction--heavy oceanic crust is overridden by lighter continental
crust;
oceanic crust melts (volcanism and some deep earthquakes result)
(example: “Ring of Fire” [Pacific rim])
Rifting--splitting of continental (as opposed to oceanic) crust
(example: Red Sea forms as Africa and Arabia split)
Mineral = naturally formed, inorganic, crystalline solid with a specific
composition or range of compositions
Rock = assemblage of minerals
Which of the following is a mineral? Which is a rock? Why?--
limestone, concrete, coal, diamond, quartz, ice, sandstone
8 elements (Fe, Mg, O, Si, K, Na, Ca, Al) account for about 99% of weight
of crust; range of pressure and temperature in crust is relatively small;
therefore, there are about 12 common rock-forming minerals
Mineral definition revisited--
(1) inorganic--contrast with organic compound (example: methane [CH4]),
which tends to have C-H bonds
(2) crystalline solid--long-range atomic order (lattice)
--atoms bonded in orderly, 3-D solid structures
--not all crystals are minerals (example: rock candy)
Talked about Taiwan earthquake (9/20/99, Richter magnitude 7.6)
Crystallization (continued)—
crystals have regular, planar faces;
crystallization can occur by:
(1) cooling of molten rock
(2) precipitation from an evaporating solution (like salt)
Rock-forming minerals—
98% of Earth’s crust consists of silicate minerals;
silica tetrahedron is fundamental building block of silicates (like
pyramid: 4 oxygen atoms at corners, silicon atom in center);
tetrahedra occur as sheets, chains, and rings at atomic scale
remaining 2%--oxides and hydroxides (e.g., hematite [Fe2O3]), sulfides/sulfates (e.g., pyrite [FeS2]), halides (e.g., halite [table salt] [NaCl]), native elements (e.g., gold [Au])
Mineral properties—examples--
(1) hardness (measure of bonding strength)
(example: diamond [very hard, strongly bonded] and graphite [very soft,
weakly
bonded] are both native carbon)
(2) color and streak (color when mineral is marked on a ceramic tile)
(3) malleability (can it be pounded into sheets? [like copper])
(4) “feel” (soft, slippery minerals are weakly bonded)
(5) taste (distinctive for halite)
(6) odor (pyrite can give off smell of hydrogen sulfide [like rotten
eggs])
(7) melting point
(many of these involve using one’s senses)
Rock groups—classified by mineralogy, texture (size, shape, arrangement
of minerals)
(1) igneous—cooled from molten magma (= lava if on surface)
(2) sedimentary—bits of mineral and organic matter that are (a) deposited,
(b) buried, (c) compacted, and (d) cemented
(3) metamorphic—elevated pressure and temperature causes recrystallization;
minerals transformed without melting (example: limestone goes to marble)
Plate tectonics and the rock cycle—
convection drives plate movement (via thermal cells in asthenosphere);
dense (cool) fluid sinks, light (hot) fluid rises
whether rocks deform elastically (like rubber band), plastically (like
Silly Putty), or brittlely (like glass) depends upon pressure and temperature;
faulting = brittle behavior (rocks break);
faulting and plate boundaries:
(1) convergent (compression) (example: US Pacific Northwest)
(2) divergent (extension) (example: Mid-Atlantic Ridge)
(3) transform (lateral) (example: San Andreas Fault)
Subduction—convergence of continental (light) and oceanic (heavy) crust;
oceanic crust is completely recycled about every 200 million years,
whereas the oldest continental crust is about 4 billion years old
Types of faults:
(1) normal = hanging wall (block of rock overlying fault) moves down
relative to foot wall (block of rock underlying fault)
(2) reverse = hanging wall moves up relative to foot wall
(3) strike-slip = transform
Notes:
(a) if fault is not vertical, hanging wall represents obtuse angle
(> 90 degrees) and foot wall represents acute angle (< 90 degrees)
(b) Turkish earthquake about same magnitude as Taiwanese earthquake,
but types of plate boundaries different (Turkey--transform; Taiwan--convergent
[subduction zone])
General notes—
1. Midterm exam—multiple-choice, 35 questions, taken twice
(1) 30 minutes—closed notes, closed book, no discussion
(2) 20 minutes—open notes, open book, small-group discussion
--scores for two parts will be averaged
2. No recitation this week!
3. Exam review—7:30 PM Monday, 200 Funkhouser (combined with Dr. Howell’s class)
Last of Chapter 3—
Review of plate tectonics—see 9/22 notes (and note that obduction [accretion of crust] is not limited to continent-continent collisions [my mistake in class this morning]!)
Volcanism can occur (volcanoes can form, or magma can upwell) in the
middle of continental or oceanic plates (examples: Yellowstone, Hawaii)—
hot spots are associated with mantle plumes
Brief introduction to folding (ductile deformation of crust)—
anticline = rainbow-shaped (upwarped) fold; following erosion, oldest
rocks are in the middle and youngest are on the edges (like the Inner Bluegrass
in the Cincinnati Arch);
syncline = U-shaped (downwarped) fold;
anticlines and synclines often occur in sequence laterally following
compression
Deformation style (ductile vs. brittle) depends upon temperature, pressure, and rate of deformation
Rock types—
1. igneous—3 types of magma—
(a) at divergent boundaries, mafic magma (Mg-, Fe-rich);
extrusive rock (formed from lava)—basalt (smaller crystals, relatively
quick cooling);
intrusive rock (subsurface, or plutonic)—gabbro
(intrusive and extrusive rocks distinguished by textural differences)
(b) at convergent boundaries, intermediate magma (more Si than mafic
magma);
associated with melting of continental and oceanic crust (like in subduction
zones);
extrusive rock—andesite;
intrusive rock—diorite
(c) in continental interiors, felsic magma (Si rich);
forms, for example, where hot spots melt continental crust;
extrusive rock—rhyolite;
intrusive rock—granite
2. metamorphic rocks—marked by directional texture (banding, or foliation);
particularly seen in metamorphosed mudrocks, like shale
3. sedimentary rocks—
(a) clastic rocks—sandstones, shales (mudstones), conglomerates (made
of gravel)—
tend to be buried and lithified in sedimentary basins (low areas);
clast = particle
(b) biological rocks—limestone (made of shells and other invertebrate skeletons secreted as calcium carbonate (CaCO3)); coal (made of plant fragments)
(c) chemical rocks (evaporites)—precipitated from solution (like salt)
(Showed slides of basalt, limestone, and evaporites, and discussed environmental
significance of mineralogy [example: the asbestos debate].)
Exam results—out of 105 people taking the exam, there were:
10 A’s (90-100)
37 B’s (80-89)
40 C’s (70-79)
11 D’s (60-69)
7 E’s (<60)
(high 96, low 31, mean 77 [based on average of parts 1 and 2])
If you didn’t do well, be concerned, but DON’T PANIC! Remember that
each of the two midterms counts only 10% of the overall grade. Come see
me if you need to talk.
Chapter 5—Lithosphere: Resources, Hazards, and Change
(We’re skipping the resources part; take GLY 120 for more info.)
Volcanoes!—
>1000 active or potentially active volcanoes;
mostly in Japan, Indonesia, and western U.S.;
about 80% around “Ring of Fire” in Pacific;
about 20% are at mid-ocean ridges (but these contribute about 20 cubic
km/yr of lava, while arc volcanoes contribute <2 cubic km/year)
A few volcanoes, like the Hawaiian volcanoes, are at midplate “hotspots”
(showed example of continental hotspot volcano: Capulin, New Mexico
[now extinct])
What do volcanoes erupt?—lava, ash, gas (mostly water vapor)—all can
be deadly
(example: Lake Nyos, Cameroon: volcanic lake “belched” CO2 gas (heavier
than air); gas flowed down slope and suffocated town)
Volcanoes (cont’d.)—
Viscosity of a liquid = measure of resistance to flow;
in magma or lava, linking of Si tetrahedra (polymerization) increases
viscosity;
basaltic magmas are relatively low in Si and thus less viscous (can
flow at rates up to 100 km/hr)
Intermediate (e.g., andesitic) and felsic magmas (higher in Si) are
more viscous and can trap gas more easily, which results in more explosive
eruptions
(kitchen analogy #1: boiling water [less viscous] versus spaghetti
sauce).
Caldera = collapsed magma chamber following explosive eruption (like
Crater Lake)
Violence of eruptions increases with amount of water in the magma;
water produces superheated steam under pressure in magma chamber;
eruption results in explosive decompression
(kitchen analogy #2: like shaking a pop bottle and removing the cap)
Intermediate and felsic magmas also produce more pyroclastic eruptions
(pyro- [fire] + clastos [particle])—ash, volcanic “bombs” (like pumice)
(“igneous on the way up, sedimentary on the way down”).
Ash falls can be used for regional dating of sediments and sedimentary
rocks
Basaltic lavas form shield volcanoes (gently sloping);
andesitic and other higher-Si lavas form stratovolcanoes (like layer
cakes of ash and rock)—cone-shaped, like Mt. Fuji (or Mt. St. Helens before
last eruption)
When is a volcano dead (extinct) versus just sleeping (dormant)?
Extinct = no magma genesis (depends on position of plate)
(example: Hawaiian islands northwest of the island of Hawaii are no
longer volcanically active, because they’ve ridden away from the hotspot
beneath the Pacific plate)
Dormant = magma genesis, but no eruption (like Mt. Rainier);
magma chamber in dormant volcano will slowly refill and reinflate
Recurrence intervals—some volcanoes erupt more frequently than others
Volcanic hazards:
1. lava flows (not widespread, but can set your house on fire if you
build too close)
2. ash clouds (example: jet flying through cloud from Redoubt Volcano
[Alaska] had engines “sandblasted” and lost power; millions of dollars
in repairs)
3. pyroclastic “bombs” (if you’re climbing a volcano)
4. ash flows (lahars)—pyroclastic debris flow; superheated ash can
flow down slope;
if ice and snow are melted, mudflow can result (kitchen analogy #3:
like Slurpee)
(example: eruption of Nevada del Ruiz buried town of Armero, Colombia;
killed >20,000)
Eruption prediction—exact timing is difficult, but we can monitor:
1. earthquakes (increase as magma chamber fills)
2. dome expansion
3. gas emission (is it smoking?)
4. changes in water chemistry (e.g., of hot springs around volcano)
Earthquakes!
Offset along a fault causes shaking and displacement (lateral and/or
vertical, depending on type of fault motion [normal, reverse, strike-slip])
See Fig. 5-24—elastic rebound model
Hypocenter = focus of earthquake within crust;
Epicenter = point above focus on surface (need at least 3 seismic-wave
receiving stations to locate)
Earth hazards in the news:
volcanic eruption in Ecuador; flooding and mudslides in Mexico
Clarification from last lecture:
hot volcanic gas and ash flow = pyroclastic flow (nuée ardentee);
lahar = mudflow containing ash
Earthquakes (cont’d.)—
Seismometer measures seismic waves (direction, amplitude, frequency,
duration)
Types of seismic waves:
1. P (primary) waves: fastest (velocity about 6 km/sec); compression
and expansion of Earth materials PARALLEL to direction of wave propagation
2. S (secondary) waves: velocity about 3.5 km/sec; SHEAR motion perpendicular
to direction of wave propagation
3. surface waves: various types, such as compressional and shear; slow
but devastating
Dr. Howell’s P- (and S- and surface-) wave dance!
—note that seismic velocities are faster in rock than in soil and sediment
Earthquake hazards and energy release—
A. Richter scale (commonly used, but actually obsolete
[designed for a specific type of seismograph in California])
—determined magnitude from amplitude of largest seismic wave (corrected
for distance from source)
—logarithmic scale (magnitude 7 earthquake is 10 times as powerful
as a magnitude 6) (there are >100 magnitude 6 earthquakes worldwide each
year)
B. Modified Mercalli intensity scale (I – XII, with I recorded only
by seismographs and XII representing total destruction) (NOT a logarithmic
scale)
—useful for assessing magnitudes of historical earthquakes, where eyewitness
accounts were recorded, but seismographs weren’t (such as 1811-12 New Madrid
[MO] earthquakes); can be roughly correlated to Richter magnitude
C. Moment magnitude (now preferred)—measures seismic source energy (depends on dimensions of fault plane that broke and the volume of deformed rock)
Question: why did 8/99 Turkish earthquake (magnitude about 7.4) kill
about 20,000 people, while the 9/99 Taiwanese earthquake (magnitude about
7.6) kill about 2,000?
Answer: damage depends upon local conditions (geology, building materials)
Damage in 9/85 Mexican earthquake was worse in Mexico City than at
epicenter, because Mexico City is built on an ancient lake bed (filled
with clay, shook like Jello)
Can’t predict earthquakes, but can forecast them based on probability
of occurrence in a seismically active area over a period of years
In the meantime, what can we do?
—monitor crustal strain along surface faults
—map geology and develop/enforce earthquake-resistant building codes
Recitation HW review—things to recall about Volcano Petula:
(1) steep, 1500-m tall
(2) seismically active—earthquake knocked people out of bed
(3) smoking
(4) volcanic rocks—pumice (light gray, glassy, vesicles [lots of little
holes], lightweight);
rounded, marble-sized rocks, and a few oblong rocks up to 50 cm long—pyroclastic
(5) loose, gray, powdery slope
—hot-spot or island-arc volcano?
For good general info: www.usgs.gov/themes/volcano.html
Response to e-mail question: will California “fall off” around 2011?
(1) San Andreas is a transform fault—lateral, not vertical, movement
(2) Max. rate of movement along fault = 5 cm/yr;
5 cm/yr x 12 yr = 60 cm = 2 ft (fault is 1500 km long)
(3) There’s been movement on the San Andreas fault for about 65 million
yr;
total length of movement is about 600 km (= 60 million cm);
long-term average rate of movement is therefore < 1 cm/yr
Answer: no, California won’t fall off, especially not in 12 years, but there will be earthquakes associated with slow lateral movement along San Andreas fault
Video on Mt. Pinatubo (from “Nova”, PBS) and short-answer questions (DUE IN RECITATION)—note that a typhoon is a hurricane in the western Pacific Ocean
Disasters in the news:
1. Hector Mine earthquake in southern California, 2:46 AM Pacific time
Saturday (10/16);
magnitude 7.0
—4th-strongest in southern CA this century; 4th earthquake > magnitude
7 worldwide in last 2 months
—close to epicenter, ground fissures and rails bent (Amtrak train derailed)—Mercalli
magnitude X-XI
—rupture occurred along 25 mi of a fault that had been considered inactive;
max. lateral displacement = 15 ft
(note: short-term movement along a fault during a quake can exceed
longer-term average, because quakes don’t tend to occur continuously)
—about 20 hr of “preshocks”; aftershocks may continue for 10 yr
2. Hurricane Irene (category I—maximum sustained winds 75-94 mph)
—crossed Florida and skirted North Carolina (3rd hurricane in 2 months
there)
—as much as 7 in of rain in eastern NC—more flooding: showed hydrographs
(stream stage and flow rate) for the Neuse River near Goldsboro
—seas as high as 27 ft along coast—more beach erosion
Chapter 6—Soil and weathering systems
Images of “Dust Bowl”—Chapter 1 of “The Grapes of Wrath”, by John Steinbeck
Pedosphere = layer of disaggregated, decomposed rock debris and organic
matter at the continental surface (max. thickness about 200 m [in tropics])
—geomembrane (like skin): mass and energy move across it from:
(1) lithosphere (e.g., by rock weathering)
(2) hydrosphere (e.g., by rain infiltrating)
(3) biosphere (e.g., by rooting and burrowing)
(4) atmosphere (e.g., by wind erosion)
Weathering = in-place alteration of rocks and minerals by Earth surface
processes—
items (2), (3), and (4) affect (1)
Physical weathering = disintegration (literally, pulling apart)—mechanical
fragmentation of rocks and minerals
Chemical weathering = decomposition (suggests decay of organic matter,
but can also result from inorganic reactions)
Both chemical and physical weathering can be enhanced by biological
processes (e.g., rooting promotes physical weathering; decay of organic
matter promotes chemical weathering [organic acids produced])
Physical weathering enhances chemical weathering by increasing the
surface area of rocks and minerals available for reactions
Weathering occurs when stress (force per area) exceeds the strengths
of chemical bonds holding rocks and minerals together
Erosion = removal and transport of weathered material (by wind, water,
or ice)
Types of physical weathering:
(a) exfoliation jointing (rock sloughs off as a result of decompression
after erosion of overburden)
(b) thermal expansion (after fires)
(c) biological disintegration (rooting, burrowing)
(d) frost weathering (expansion and contraction with freezing and thawing
[like formation of potholes])
Chemical weathering—
primary (rock-forming) minerals + acids + oxygen -->
sediments (rock fragments and secondary minerals) + dissolved ions
(for discussion of acids, see Ch. 6, Table 1)
Main types of weathering reactions:
(1) carbonation (common weathering reaction in Kentucky):
CaCO3 (calcite—makes up limestone) + H2CO3 (carbonic acid—like fizz
in soda pop) --> Ca2+ + 2HCO3-
In atmosphere, CO2 + H2O --> H2CO3
(2) hydrolysis: H2CO3 + silicate minerals (such as feldspars) --> clay minerals
(What is a clay mineral?—
(a) a layer silicate such as kaolinite (used for making pottery)
(b) one with particles < 4 microns in size (1 micron = 1 millionth
of a meter))
(Why do clays seem to be wet?—
in particular, clay minerals that have an octahedral layer “sandwiched”
between layers of Si tetrahedra (like smectite) can hold water in the interlayer
spaces;
depending on the moisture content, they shrink and swell [thus dry
soils can crack])
(3) oxidation—loss of electrons;
element + O2 --> oxide or hydroxide (like Fe2O3 [hematite, an iron
oxide])
(iron oxides make soils red)
(What is dirt?—another term for soil)
Soil = an internally organized, natural body or weathered minerals
and organic constituents (like compost) arranged in horizons (relatively
flat layers)
O (organic) horizon (includes leaf litter)
A horizon—topsoil (contains minerals; rich in organic matter relative
to deeper horizons)
B horizon (relatively mineral-rich compared to O and A)
C horizon (weathered parent material (bedrock or sediments)
(Note: can have buried soils [paleosols])
Soil-forming factors—
(1) nature and types of organisms (including vegetation)
(2) relief (topography)—i.e., how steep is the slope?
(3) time (soils tend to form slowly)
(4) climate (amount of water, temperature, wind, etc.)
(5) nature and composition of parent material
Soils in Inner Bluegrass—residual (form in place from weathering of shaly interbeds as limestone dissolves)
Humus—complex organic molecules forming by decay (weathering) of organic matter
Soil fertility—function of the amount and availability of essential nutrients (e.g., nitrogen, carbon, potassium, phosphorus, calcium) and organic matter
Soil erosion—generally, rates of soil formation and erosion are in balance
unless disturbed
Formation of 1 m thickness of soil takes 10,000-50,000 yr
Loss of topsoil (like in “Dust Bowl” [Plains states in 1930s])—
removes organic matter and clays, which retain nutrients and moisture;
eroded sediment washes into streams and chokes off aquatic life
—associated with poor farming practices and rapid deforestation
—controlled by degree of slope and amount of bare soil
Most soil erosion in temperate regions (like U.S.) due to:
(1) rainsplash—puts dust into air
(2) sheet wash erosion—forms rills and gullies
Desertification—productive land degraded, unable to support plants and
animals—
vicious cycle:
(1) exposure and stress dry out soil
(2) native plants decline
(3) soil hardens
(4) infiltration decreases (so soil hardens more)
(5) runoff into rills and gullies
Soil conservation practices—
(1) crop rotation; let soils lie fallow (and vegetated)
(2) terracing and contour plowing (work with the topography of the
landscape)
(3) shelter belts (windbreaks) and riparian strips (along streams)—involves
planting new vegetation or leaving existing vegetation in place
(4) sediment traps
(Slides:
(1) Owl Cave, KY (karst is an example of carbonation)
(2) slump and rockfall in Mammoth Cave NP (more karst)
(3) SEM of clay minerals forming from feldspars (example of hydrolysis)
(4) calcic paleosols on High Plains, TX
(5) aerial photo of playas and gullies (examples of erosion by wind
and water)
(6) cattle kicking up dust
(7) desiccation cracks on playa floor (example of shrink-swell clays)
(8) desiccation cracks with ballpoint pen inserted)
Mass wasting = erosion
Mass movement = downslope motion; governed by gravity
Recall definitions of pyroclastic flow and lahar—both are examples
of mass movement
Why does mass movement happen?—
force of gravity > strength of material (soil or rock or sediment)
controlled by (1) angle of repose, (2) moisture content
Demonstration—pouring dry vs. wet sand down a slope of about 30 degrees
Observations—
(1) dry sand moves en masse (pours readily down to base of slope)
(2) for wet (water-saturated) sand, a slurry of fine sand in water
moves fastest (keeps moving beyond where dry sand stopped), but smaller
clumps of partially saturated sand remain on slope
(3) wet clumps slowly drain
(4) “seismic” shaking of wet clumps moved them a little farther down
slope
What does this mean?
(1) round grains of sand will roll downhill (duh)
(2) sand will drain fairly easily—bigger particles (like gravel) will
drain even more easily; smaller particles (like mud) will not drain as
easily
(3) over time, as wet sand drains and dries, it will all move downhill
(4) “sand castle effect”—partly-wet sand is more cohesive (because
of surface tension, it sticks together better) than either completely dry
or completely saturated sand
(5) the steeper the slope, the more easily sediment, soil, or (sometimes)
rock moves downhill
Vegetation can anchor a hillslope, but can also break rock apart
Sheer rock faces are cohesive unless weakened by fractures, joints
(as along bedding planes), or faults
Case study—Hickman, KY (SW corner of state, on Mississippi R.)—
landslides occur there because:
(1) slope is steep (bluffs above the river)
(2) geology is a problem:
(a) stratigraphy—loess (windblown glacial silt) above thin, saturated
gravel above smectitic clay (subject to shrinkage and swelling, slides
easily)
—like tilting a pizza—cheese and toppings slide off sauce
(b) earthquakes—right across river from New Madrid
(3) human activity weakens slope (dredging channel, digging, etc.)
Mass movement occurs when the force of gravity > strength of Earth materials
(soil, sediment, rock)
Variables:
(1) angle of repose—critical angle at which failure occurs;
depends on strength of material (32 to 34 degrees for sand);
essentially, material slides more easily down a steep slope
(2) water content—recall that soil or sediment will collapse with either
too much or too little water in pore spaces between grains
(3) nature of solids—lithified? fractured? coarse-grained? fine-grained?
Types of mass movement—
(1) slow movement as a result of freeze/thaw or wet/dry cycles—
heave (if rocks “expelled”, like potholes forming) or creep
(if hillslope moves down)
(2) slide—movement along a failure plane (plane of weakness,
like a bedding plane); compare with a slump (rotational movement
along curved surfaces)
(3) flow—rock, soil, or sediment mixed with a fluid (typically
water, but can be air or another gas—think of pyroclastic flow vs. lahar)
(4) fall—like rocks moving downslope
Causes of mass movement—
(1) driving forces (DF) are increased
—by increase in moisture content, loading (including seismic shock),
steepening slope
(2) resisting forces (RF) are decreased
—by uprooting vegetation or blasting
In order to avoid failure, RF must be > DF;
RF = S + (G x F), where S = strength of material, G = gravitational
force, F = friction
If friction = 0, like on a cliff, you have to depend on S.
How do you avoid damage from mass movement?—
(1) don’t build in susceptible areas!—rely on hazard maps
(2) minimize DF or maximize RF
—can grade slope (make angle less steep), dewater slope (put in wells,
drains, etc.), or reinforce slope (with anchors, rock bolts, fencing, etc.)
Chapter 7!—Surface water
= 0.01% of water on Earth, but it supplies the needs of >90% of people
on Earth;
uneven distribution of surface water causes hardships and conflicts
How is water introduced, and (in particular) how does infiltration occur,
in arid and semi-arid regions (like deserts and grasslands)?
—maybe during cooler, wetter climatic periods (like last glacial period
in North America)
—maybe along adjoining mountain fronts, as in the western U.S.
—maybe in low spots, such as valleys
Perennial streams—flow all the time; ephemeral streams—don’t flow all
the time
Baseflow (ground-water discharge) sustains perennial streams
Surface water and the hydrologic cycle (continued)—
Hydrologic equation: inflow = outflow +/- changes in storage (stock)
Hydrologic budget: precipitation = (evapotranspiration + surface runoff)
+/- (changes in soil moisture and ground-water storage)
Drainage divide—separates runoff between watersheds
(like Continental Divide—precipitation running off E side flows eventually
to Mississippi River; precipitation running off W side flows to streams
feeding Pacific Ocean)
Drainage networks are commonly dendritic (look like tree);
smaller tributaries feed trunk stream of watershed; watersheds are
“nested”
Example: Elkhorn Creek watershed fits within Ky. River;
Ky. River watershed fits within Ohio River watershed;
Ohio River watershed fits within Mississippi River watershed
Base level—lowest point in watershed (Ky. River for central Kentucky);
controls flow of water and sediment out of watershed
Runoff = surface storm flow (overland flow) + subsurface storm flow
(interflow)
(Interflow occurs through soil zone, such as through cracks and burrows)
Overland flow occurs when infiltration capacity is exceeded (function
of slope, saturation [depends on permeability—ability to transmit water])
Total runoff = maybe 35% of precipitation
Overland flow is greater in paved (urban) areas (relatively low permeability)
Flooding involves transition from bankfull flow to overbank flow
Sample test questions—note mistake in question 1!—
in the Richter scale, the amplitude of the largest seismic wave
increases by a factor of ten for each whole number increase in the magnitude
(i.e., a Richter magnitude 5 earthquake has an amplitude 10x that of a
Richter magnitude 4 earthquake);
in the moment magnitude scale, the energy released increases
by a factor of ten for each whole number increase in the magnitude (i.e.,
a moment magnitude 5 earthquake releases 10x the energy of a moment magnitude
4 earthquake)—
I accidentally crossed this up!
Note that there will be 5 true-false questions, 5 matching questions, and 25 multiple-choice questions; < 5 will be from Chapter 7, and the remainder will be divided roughly evenly between Chapters 5 and 6 (with some carryover from previous chapters).
Know italicized terms and bolded terms from book (but don’t worry about
earth resources or the nitrogen cycle), as well as terms and concepts I
stressed in class;
be familiar with case studies (such as Mt. Pinatubo and recent disasters)
Test 2 results—99 people took the test; scores improved from Test 1—
grades (average of parts 1 and 2) ranged from 56 to 96, with a mean
of 83
Breakdown by letter grade:
90 and above (A)—26 people
80-89 (B)—46
70-79 (C)—18
60-69 (D)—8
below 60 (E)—1
Surface water and the hydrologic cycle (continued)—
note that delineating watershed involves drawing divide between drainage
areas of adjoining streams
Tie-in to prerecitation exercise for this week:
Stream discharge (Q) = volume of water (V) flowing past a given point
on the stream channel per unit of time (t)
V = length (L) x width (w) x height (h) of water column (or depth of
stream)
w x h = A (cross-sectional area of stream)
v (velocity) = L/t
Q = v x A = (L/t) x w x h = V/t
Discharge depends on:
(1) the drainage area upstream of the measuring point
(2) the amount of precipitation that falls on the drainage basin upstream
of that point
(3) the loss of water due to evapotranspiration (largely a function
of temperature, wind)
(How else can water be lost (i.e., how else can precipitation not contribute
to runoff)?
—by diversion (such as for irrigation)
—by infiltration (or percolation) to ground water)
Factors (2) and (3) (climatic variables) are more influential than
(1) in determining Q
Stream stage = stream height above some datum (or reference elevation);
commonly recorded automatically by a stream gage
Discharge is measured manually (by wading with a current meter) over
range of stages; discharge is then graphed versus stage and a correlation
is calculated so that Q can be predicted from stage data
Showed slides of stream gages and of measuring discharge with a current meter.
Stream flow (continued)—
More about flooding—
(1) lag between end of a storm and peak discharge—
time for runoff to arrive increases with distance downstream
(depending upon where precipitation fell and how much runoff occurred,
flood height may increase or decrease downstream)
(2) See “Geologist’s Toolbox” (section 7-2)—how often do floods occur?
—depends on magnitude of stage and discharge; small floods are more
common (maybe a 50:50 chance in a given year);
the chance of a relatively large flood may be 1 in 100 per year
Can define recurrence interval—average period of time between events
(earthquakes, volcanic eruption, or, in this case, floods) of a given size
= 1/P, where P = probability (as a decimal)
For a probability of 1% (1 in 100 chance), P = 0.01, so 1/P = 100 (thus
a 100 year recurrence interval, or a 100-year flood)
How do you estimate a recurrence intervals for large (say, >50-year)
floods?
—use historical data or (sometimes) prehistoric data (for example,
carbon-14 dating of logs in ancient flood deposits)
Flood recurrence intervals are based on probability, so a 100-year flood may actually occur more than once every 100 years, but if it happens too often (for example, Houston got 3 100-year floods in 1979), conditions may have changed (probably as a result of human activity)—may need to recalculate probabilities.
Recent 500-year floods: Red River (in North Dakota and Minnesota), spring 1997; eastern North Carolina rivers (as a result of 3 hurricanes in 2 months) this fall.
Like with earthquakes, damage from floods generally increases with the magnitude of the event, but it really depends on where people build.
(3) flood control—
(a) can build flood-control dams
(b) can channelize (straighten) stream (both (a) and (b) can really
harm stream ecology)
(c) can build levees or flood walls (just defers problem to someone
downstream)
(d) don’t build in flood plains (can use flood hazard maps from FEMA)
Stream landforms—terms—
stream competence (ability to carry relatively large particles)—controlled
by velocity and slope;
stream capacity (ability to carry sediment)—controlled by velocity
and stream size;
alluvium—sediment carried or deposited by water;
bar—deposit of relatively coarse sediment laid down by water;
meander—bend in a stream—
occurs where there is a low gradient (slope), low energy per unit area,
small width-to-depth ratio (high capacity, low competence)
Stream velocity highest on outside of bend (erosion forms a relatively
steep cut bank there), lowest on inside of bend (where bar deposited).
On stream bends, pools form; riffles form on relatively straight stretches
in between
Showed slides of stream erosion, deposition, and flooding along Little Bayou and Bayou Creeks in McCracken County
floodplain—nearly level alluvial surface that occurs along a stream
in a valley bottom; becomes bed of channel during flood
lateral (side-to-side) migration—stream channel moves by cutting away
at banks and depositing sediment at bars
Stream flow (continued)—
Unit conversions and dimensional analysis (for recitation assignment)—example:
if water flows in a stream at a rate of 200 ft3/sec (cubic feet per
second, or cfs), and the stream is 100 ft wide and 1 ft deep, what is the
stream velocity in miles per hour (mi/hr)?
Q = 200 ft3/sec
w = 100 ft
d = 1 ft
w x d = A = 100 ft x 1 ft = 100 ft2 (units of L2)
Q is in units of volume per time = L3/t = (length x w x d)/t
v = L/t
Q/A = v = (L3/t)/(L2) = L/t = (200 ft3/sec)/(100 ft2) = 2 ft/sec
(2 ft/sec) x (60 sec/min) x (60 min/hr) x (1 mi/5280 ft) = 1.36 mi/hr
Terms (continued)—
overbank deposition = deposition of relatively fine (small) sediment during flooding (mostly mud, laid down on flood plain)
levee = a low berm (like a bank) of coarser sediment deposited during
flooding
(can have man-made as well as natural levees)
delta = triangular alluvial deposit where stream empties into a sea
or lake;
can have slightly different shapes, depending on wave vs. river energy
(Questions to ponder:
why is the Mississippi delta shaped the way it is [sticking out into
the Gulf]?
Why is it now shrinking?)
wetlands—used to be thought of as pestholes (buggy, swampy places);
defined as poorly-drained (i.e., wet), low-relief (i.e., relatively
flat) areas in which soil is seasonally or perennially saturated or inundated—
waterlogging leads to anaerobic (oxygen-limited) conditions
Wetland = bog if sustained by precipitation, = fen if fed by ground
water
(Showed slides of Metropolis Lake, KY [fen] and playa on TX High Plains
[bog])
Wetlands can be very productive ecosystems, but since independence,
over half of the wetlands in the U.S. have been drained (for agriculture,
development, or sanitation)
Chapter 8!—Ground water
Ground water is 32% of the fresh water on Earth and the largest supply
of liquid water
Focus on the subsurface part of the hydrologic cycle—what happens to
infiltration?
—some moves as storm flow through soil zone to streams;
water that makes it beneath the soil zone recharges the water table
Water table =
(1) boundary between saturated zone (in which all pore space in rock,
soil, or sediment is filled with water) below and unsaturated zone (in
which pores are filled with a mixture of water and air) above
(2) surface below which fluid pressure becomes greater than atmospheric
(3) top of an unconfined aquifer (more later)
Regional base level for surface water also tends to be base level for ground water
Position of water table varies seasonally with wet and dry periods and with climate (tends to be deeper in dry areas)
Showed slides:
in much of Kentucky, ground water flows mainly through bedrock, but
in far western Kentucky (west of the Tennessee River), ground water flows
mainly through sediment;
in central and south-central Kentucky, ground water flows through karst
(conduit networks [like caves] in limestone)—like stream drainage beneath
ground;
in other places, ground water flows through pores in sediment or rock—
recharge tends to be more diffuse (not like through sinkholes), but
can still have discharge through springs, as well as seeps;
in wells, we measure the depth to water with measuring tapes (often
electric)
Ground water (continued)—
How does ground water move?—from high hydraulic head to low hydraulic
head
(i.e., from high potential energy to low potential energy);
therefore, ground water doesn’t just flow from high elevation to low
elevation
(otherwise, why would some springs flow upward?),
but the water table does tend to mimic the shape of the land surface
Ground water flow paths are often curved (downward in the recharge zone, where infiltration occurs, and upward in the discharge zone)
hydraulic head = water level in a well
= elevation (of the well intake) + fluid pressure component (as a result
of the weight of the overlying column of water)
porosity = ratio of void space to total volume of rock, sediment, or
soil
(in other words, what percentage of rock, sediment, or soil consists
of holes?)
primary porosity = original porosity
(example: primary porosity in basalt is vesicular—holes created by
gas bubbles escaping as lava cooled)
secondary porosity = porosity formed as a result of weathering
(example: karstic porosity in limestone)
specific yield (Sy) = ratio of drainable water to total volume of water
specific retention (Sr) = ratio of retained water to total volume of
water
Sy + Sr = porosity in the saturated zone
Demonstration: specific yield and specific retention in (1) coarse,
well-sorted sand vs. (2) poorly sorted silty sand:
(1) For about 300 mL of coarse sand, I poured in about 120 mL of water—
therefore, porosity = about 120/300 = 40%;
I got about 45 mL of water back—therefore, Sy = 37.5% (and Sr = 62.5%).
(2) For about 300 mL of silty sand, I poured in about 100 mL of water—
therefore, porosity = about 100/300 = 33%;
I got about 2 mL of water back—therefore, Sy = 2% (and Sr = 98%);
Sy is lower because lots of fine grains are filling pores between large
grains.
permeability = ability of rock, soil, or sediment to transmit a fluid
(typically water);
increases with amount of interconnected pore space;
high porosity doesn’t always mean high permeability (example: clays
have high porosity but low permeability)
aquifer = rocks or sediments that are porous, permeable, contain water
and can yield water to a well
unconfined aquifer = water-table aquifer
confined aquifer = aquifer that is overlain (or sandwiched) by aquitards
aquitard = poorly-permeable strata; usually consists of fine-grained
sediment, like clay
artesian aquifer = aquifer in which the water level (head) in the well
rises above the top of the aquifer
flowing artesian aquifer = water level in the well rises above land
surface
hydraulic gradient = change in head between wells divided by distance
between wells
(gradient suggests “steepness” or “slope”; refers to a change in a
property in space);
remember that water flows from high head to low head
Ground water (continued)—
Hydraulic head revisited—for a well completed (screened) across the
water table,
hydraulic head = elevation of water table
(recall that pressure is atmospheric [defined as 0] at the water table).
For a well screened below the water table, the weight of the overlying
column of water tends to make the hydraulic head higher than the intake
(screen).
Hydraulic head = pressure head + elevation
Darcy’s law governs the movement of ground water:
think of the hydraulic gradient (Dh/L) as
a driving force;
recall from the Falmouth flood exercise that Q is the discharge rate
(in terms of volume per time) and A is the cross-sectional area.
Q/A = (Dh/L) x K;
hydraulic conductivity (K) is the permeability of rock, soil, or sediment
to water.
Q/A and (Dh/L) x K are in units of velocity
(length/time);
however, unlike surface water, ground water doesn’t flow across the
entire area A;
instead, it just flows through the part of the area occupied by pores.
Therefore, actual ground-water velocity = (Q/(A x n)) = (Dh/L)
x (K/n),
where n is the porosity.
As the number of connected pores decreases, ground-water velocity increases.
Water supply—
As of 1992, U.S. domestic water use per capita was 188 gallons per
day;
about half the world’s population used < 25 gallons per day.
Ground-water supply—
about 40% of all water used in the U.S. is ground water (more in rural
areas)
Ground water is typically considered renewable, but it can be “mined”
if pumpage > recharge (occurs in semi-arid and arid areas).
One possible solution to ground-water mining is artificial recharge
(enhanced infiltration—not just practiced in arid areas)
Ground-water pumping—forms a cone of depression in the ground-water
surface
(such as the water table); pumping differs for water-table vs. confined
aquifers.
Pumping a water-table aquifer is like slurping water through a straw
from a drink with ice —the water table is actually lowered, with residual
water trapped above it.
Pumping a confined aquifer is like squeezing a sponge—
yields water by depressurization and rearrangement of grains (withdrawal
from storage); reduction in pore volume can cause land subsidence.
Land subsidence is gradual, while solution collapse (such as the roof
of a cavern collapsing after dewatering) is dramatic (but localized); both
tend to be irreversible.
Salt-water intrusion can occur in coastal areas—
fresh water, which is less dense, tends to overlie salt water near
the shoreline;
pumping ground water or digging canals can cause the fresh-water/salt-water
interface to migrate inland.
Ground water (continued)—
Darcy’s law revisited—how ground water flows:
Q/A = ((h1-h2)/L) x K,
where hydraulic head in well 1 = h1,
hydraulic head in well 2 = h2,
distance between wells 1 and 2 = L,
and water flows from well 1 to well 2—thus hydraulic gradient = (h1-h2)/L
= Dh/L;
hydraulic conductivity K = (k x r x g)/m,
where k = permeability of rock (or soil or sediment) to any fluid,
r = density of water,
g = acceleration due to gravity (9.81 m/(sec x sec)),
and m = viscosity of water;
r, m, and thus
K depend on temperature.
Consider slicing a pipe packed with sand through which water is flowing
(like Darcy’s original experimental set-up):
the area of the pipe through which water flows is not the entire cross-sectional
area A (unlike a stream), but is the area occupied by pores (holes) = A
x n,
where porosity = n;
therefore, velocity of ground water flow (v) = Q/(A x n).
What controls ground-water chemistry?
(1) evaporation during infiltration (concentrates solutes)
(2) weathering reactions that dissolve minerals (oxidation, carbonation,
hydrolysis)
(3) ion exchange (like a water softener—example: removes Ca2+ and Mg2+
(which cause hardness), adds Na+)
(4) nutrient cycling—bacterial transformations of carbon and nitrogen
(5) contamination—introduction of pollutants
Types of contamination (in both surface water and ground water):
(1) biological—bacteria, viruses, protozoa;
more of a problem in surface water, because most germs are strained
out (i.e., stuck) during flow through pores or they stick to the rock (or
soil or sediment) because of electrical attraction (like static cling)
(2) chemical—
(a) inorganic contaminants (metals, nitrate, sulfate, chloride)
(b) radionuclides (like plutonium)
(c) organic (like hydrocarbons (including chlorinated solvents))
—can cause cancer, liver/nervous system damage, rashes, birth defects
at relatively low concentrations (parts per million or billion)
Point-source pollutants—direct discharge from pipes, leaks, spills
Non-point-source pollutants—diffuse seepage or runoff from mines, urban
areas, farms, holding ponds, etc.—most hazardous during floods
Case study (with slides and overheads): Natural attenuation of contaminants at the Paducah Gaseous Diffusion Plant: a watershed perspective
Ground water (continued)—
Sources of contamination: top 2—
Leaking Underground Storage Tanks (LUST) (typically associated with
hydrocarbons); septic tanks (sewage)
others—landfills, surface impoundments (ponds that collect polluted
effluent), agricultural chemical infiltration (non-point source), spills
How do pollutants move?—if they’re soluble, with the water
Solute dispersion results from:
(1) mechanical mixing at the pore scale due to tortuous (twisty) flow
paths
(2) (less important) solute diffusion (movement along concentration
gradients) at the molecular scale
(3) mixing at the field scale due to the presence of variable-permeability
zones
—smearing along flow path results in a contaminant plume
Non-Aqueous Phase Liquids (NAPLs)—immiscible (poorly soluble) organic
pollutants:
light NAPLs (like gasoline) = floaters; dense NAPLs (like some solvents)
= “sinkers”
Cleanup options:
(1) containment (e.g., put walls in ground, or control ground-water
flow by pumping)—controls spread of contamination, but doesn’t remove it
(2) withdrawal (and above-ground treatment)—commonly used in conjunction
with (1), but “pump & treat” is not very effective—contaminants can
become trapped in low-permeability zones and continue to dissolve and move
into higher-permeability zones
(3) in-situ treatment—examples include:
(a) bioremediation (bacteria that degrade contaminants)
(b) abiotic degradation (example: putting iron filings in path of chlorinated
solvent plume)
(c) steam flooding (injecting steam into ground)
(d) electrical heating (putting electrodes in ground)
(e) surfactants (adding detergent)
(a and b destroy contaminants; c – e mobilize them for easier removal)
(4) natural attenuation—monitoring natural processes that can remove
or destroy contaminants (volatilization, degradation, adsorption, etc.)
Chapter 9!—The Atmospheric System
Atmosphere = envelope of gases surrounding a planet (a.k.a. air);
atmospheric composition has evolved over Earth history because of volcanic
eruptions and the evolution of organisms
Atmospheric composition: 78% N2 (nitrogen), 21% O2
(oxygen), 0.9% argon, 0.04% CO2 (but rising), water vapor (0.3%
in cold, dry air to 4% in hot, humid air), traces of methane (CH4)
and ozone (O3)
Ground-level ozone (bad)—pollutant produced by internal combustion
engines (part of smog);
stratospheric ozone (good)—naturally produced, blocks ultraviolet radiation
CO2, water vapor, and CH4 are greenhouse gases—they
regulate air temperature
Aerosols = suspended liquid or solid particles, like sea spray or volcanic
dust;
they provide nuclei for precipitation
Layers of the atmosphere—
(1) troposphere = weather zone (sea level to 10-18 km altitude)
(2) stratosphere = ozone production and destruction zone (about 10
to 50 km altitude);
horizontal but not much vertical mixing
(note: chlorofluorocarbons, like Freon, react with stratospheric ozone
and destroy it;
this is bad because UV radiation can cause cancer and genetic damage)
(3) upper layers—mesosphere (50 to 85 km), thermosphere (85 to 160
km)
Weather = daily fluctuations in temperature, wind speed, and precipitation
Climate = long-term average weather
Greenhouse effect (necessary for life on Earth [warms surface], but
can have too much of a good thing [global warming])—
(1) incoming solar radiation is absorbed by Earth’s surface
(2) heat energy is emitted as infrared radiation
(3) some outgoing radiation is absorbed by greenhouse gases and reradiated
The atmosphere (continued)—
Seasons on Earth depend more on the tilt of the planet than its distance
from the Sun (about 147 million km on Jan. 3 and about 152 million km on
July 3);
Earth is tilted away from Sun in winter (Dec.-Mar. in northern hemisphere,
Jun.-Sept. in southern hemisphere) and toward it in summer; poles are in
darkness during winter.
Incoming solar radiation is spread over a greater area (thus any one
place is colder) at the poles than at the equator.
Tropospheric circulation—
driven by convection—warm air rises, cold (denser) air sinks
Simplest model of circulation:
(1) regions around equator have net annual gain of solar energy
(2) warm equatorial air rises, moves toward poles, cools and sinks
(3) cold air flows from poles toward the equator
Air moves along pressure gradient (from high to low pressure)—thus
winds result.
Complication #1—Earth rotates, so convection cells are shifted laterally
(Coriolis effect).
Therefore, next-simplest model—
Hadley (convection) cells—3 sets in each hemisphere (northern and southern):
(1) 0° to 30° N or S—wind blows from E (direction of hurricane
movement across Atlantic)
(2) 60° to 90° N or S—wind blows from E
(3) 30° to 60° N or S—wind blows from W (jet stream)
Complication #2—landmasses affect atmospheric circulation. Examples:
(1) air flow over mountains—warm air loses moisture as it rises; dry
air flows down, warms, and promotes evaporation (thus precipitation focused
on western slopes of Rocky and Cascade Mtns.; rain shadow and Chinook winds
on eastern slopes)
(2) monsoons—reversing seasonal winds (and precipitation) in vicinity
of high plateaus (like Tibet or Colorado Plateau)
STORMS!—formed by upward movement of warm, moist air;
typically associated with colliding air masses (temperature and humidity
are relatively uniform within each air mass but differ between them)
Front = boundary between 2 air masses (in Kentucky, cold fronts move
in from NW)
More detail:
(1) warm, lighter air overrides colder, denser air
(2) condensation results (water vapor becomes droplets or ice crystals)
(3) updraft results (because condensation warms air)
(4) precipitation falling causes a downdraft (negative feedback—slows
and eventually shuts off updraft)
Tornadoes tend to form when cold, dry air moving SE from the Arctic meets warm, moist air moving N from the Gulf of Mexico; interaction of up- and down-drafts (temperature contrast) produces a vortex that rotates vertically—wind speeds can exceed 260 mph.
Hurricanes (revisited; recall we talked about Floyd)—maximum sustained
winds of 75 mph or greater—slower but much larger than tornadoes.
Hurricanes originate as low-pressure zones near equator (Atlantic hurricanes
originate off coast of west Africa); sustained by warm ocean waters (26°
to 27°C).
Most hurricane-related deaths in U.S. are now caused by inland flooding
rather than by coastal storm surges (because of improved forecasts and
willingness to evacuate).
The atmosphere (continued)—major types of air pollution—
(1) smog = O3 (tropospheric) + NOx (NO2,
NO…) + hydrocarbons (from gasoline and combustion products)
—when air temperature cools (at night or in winter), an inversion results—
polluted air is trapped (doesn’t warm, rise, and disperse);
aggravated by other factors, like topography (example: Mexico City—sits
in a “bowl”)
(2) acid rain
(a) organic sulfur in hydrocarbons is combusted and becomes sulfate
(SO42-) in atmosphere: 2SO42-
+ 2H2O --> 2H2SO4 (sulfuric acid) + O2
--> 4H+ (acid) + 2SO42- + O2
(b) NOx + H2O --> HNO3 (nitric acid)
--> H+ + NO3-
Think about weathering reactions, especially carbonation—
H+ + CaCO3 (e.g., limestone) --> Ca2+ +
HCO3-
Acid rain is a problem in industrial areas and (in general) on the ground—
unbuffered acidity kills trees, fish, etc.
Effects of acid rain are controlled by location of industrial and population
centers (polluters) and by geology (via acid-neutralizing capacity of soils
and rocks).
(Note: pH is a measure of H+ concentration; low pH = high
acidity.)
(3) ozone depletion by CFCs—noted previously.
Chapter 10!—excerpted (p. 300-308)—
Seawater properties and ocean circulation—
ions from weathering ultimately wind up in sea water;
salinity of ocean water = 3.38-3.68% by weight (generally 3.5%)—dominated
by NaCl (Na = 1.07% and Cl = 1.90% by weight)
If rivers (which are fresh) deliver solutes to ocean, why is ocean
salty?
—because ions are removed from ocean more slowly than they’re added
(but system is at steady-state)
(Isolated seas (e.g., Caspian, Dead, Aral) in arid regions can be saltier
and can precipitate salts as a result of evaporation.)
Ocean chemistry is relatively uniform because of mixing by currents.
Nutrient = molecule that provides nourishment to an organism (mainly
nitrate (NO3-) and phosphate (PO43-))
Unlike salts, amounts of nutrients vary with location in ocean because
of biochemical cycling.
Carbon cycling—
O2 and CO2 concentrations vary in space and time;
burning of fossil fuels and biomass has added CO2 to atmosphere.
Continuous carbon circulation among seven reservoirs:
rock (mostly limestone), deep ocean (mostly dissolved CO2),
fossil fuel, soil and litter, land biota, atmosphere, and surface ocean
Largest flux of C = photosynthesis (from atmosphere --> plants)—
CO2 + light --> C + O2 (simplified)
Respiration and decomposition send more C to atmosphere than combustion
does (but volcanoes have sent the most C to atmosphere over geologic time).
CO2 is a greenhouse gas—traps infrared radiation (heat)
emitted from Earth.
Human additions of CO2 to atmosphere currently = 7 billion
tons/year;
of this, 3.4 billion tons/year stay in atmosphere, 2 billion tons/year
go to ocean, and (we think) 1.6 billion tons/year go to biosphere (via
enhanced photosynthesis).
Ocean currents—
surface mixed layer—about 200 m deep; composition vertically but not
laterally homogeneous
thermocline—occurs at depth of 0.2 to 1 km; separates surface layer
from deep ocean, which is colder, more saline, and therefore denser
Ocean circulation (continued)—
Ocean currents are very big—example: Gulf Stream flows at up to 150
million m3/sec, vs. 600,000 m3/sec for all rivers
flowing into the Atlantic
Ocean currents don’t necessarily travel in same direction as prevailing
winds—
in surface layer, currents flow at 90° angle to prevailing winds
(Ekman transport)
Upwelling—net direction of water transport is offshore (thus cold water
moves up from deep ocean to surface)
Downwelling—net direction of water transport is onshore (thus warm
water piles up and sinks)
In N Hemisphere, ocean currents tend to flow N along E edges of continents
(like Gulf Stream along coast of N America) and S along W edges—clockwise
gyre;
circulation in opposite direction (counter-clockwise) in S. Hemisphere
Deep-ocean circulation is like a conveyor belt: water warmed at the equator flows north or south, becomes chilled and more evaporated, then sinks and flows back toward equator
Sea-level change—rising about 2 mm/yr over past several decades (probably
because of melting of polar ice, like West Antarctic ice sheet—if it goes,
sea level could rise 5 m); problematic for low-lying (coastal) areas
Other local/regional causes of relative sea-level change:
(1) uplift (tectonic—like Pacific coast of Alaska following 1964 earthquake)
(2) glacial rebound (after ice sheets retreated from eastern Canada
and Scandinavia)
(3) subsidence (opposite of rebound—can result from accumulation of
sediment or withdrawal of fluid [ground water or hydrocarbons], like along
Gulf Coast of TX and LA)
El Niño—upwelling off coast of Peru stops periodically as atmospheric circulation and ocean currents shift; warm water in N Pacific moves E, leading to more storms in Americas
Sea level has fluctuated dozens of times in the past few million years.
(Have covered p. 263-284 in Chapter 9 and p. 300-312 in Chapter 10.)
Chapter 12!—Causes of climate change (p. 368-372):
(1) Plate tectonics—
(a) changing distribution of continents between equator and poles
(b) uplift (such as of Tibet and Colorado Plateau—altered atmospheric
circulation)
(c) seafloor spreading (accelerated seafloor spreading led to more
release of magmatic CO2 during Mesozoic era—greenhouse conditions, no ice
caps)
(d) volcanic eruptions (particles in atmosphere cause short-term cooling)
(2) Oceanic circulation—
conveyor belt can “flip-flop” over alarmingly short periods (less than
a century);
global warming could result in global cooling if melting ice
in Greenland alters N Atlantic salinity and thus shuts off circulation
(3) Earth’s orbit—
(a) eccentricity (deviation from circular orbit) occurs on a 100,000-yr
cycle
(b) tilt of spin axis varies on a 40,000-yr cycle
(c) precession (wobble of spin axis) occurs on a 23,000-yr cycle—halfway
through cycle, summer and winter months are reversed in N and S Hemispheres
—(a) through (c) were combined by M. Milankovitch, who looked at insolation
(amount of incoming solar energy) over the last 600,000 yr;
he calculated that ice ages corresponded to periods of minimum insolation
Chapter 13!—Tracing and predicting environmental change (particularly p. 394-404)
Focus here on p. 394-398—
from 65 to 38 million yr ago, Earth remained quite warm (not sure why);
at about 30-40 million yr ago, Australia and South America broke away
from Antarctica—circumpolar current resulted, and Antarctic ice sheet developed;
about 3.2 million yr ago, northern polar ice sheet developed (due to
uplift of plateaus?).
At last glacial maximum (22,000 to 14,000 yr ago)—
30% of Earth was covered by ice and snow (vs. 10% today), sea level
was 120-160 m lower, and Earth was about 5-7 °C cooler.