Spring 2008
Geology 110: Natural Disasters
Karner's personal lecture notes page.
Disclaimer: These are my personal lecture notes, in all their glory. I provide them to you to augment your own notes, and to help you identify those points that I consider to be essential for this class. You should be coming to class all the time, and reading the book. You should be discussing this material with your classmates.
Each lecture below starts with my typical heading (e.g. first lecture= F07.110.L1). To quickly find a lecture, use the find command and search for the lecture that you need.
Note: In addition to posting the information from my lecture notes, you will also see my post-lecture comments to myself. Generally I KNOW when my lecture is not a good one (e.g. Lecture 2 was a stinker!). I always enjoy (well, most of the time) receiving your feedback on a particular lecture). When I know that my lecture was not clear, I will attempt to clarify the content that I post on the website, so that you have a better learning experience.
Okay, here we go:
S08.110.L1
Introduction of course syllabus, textbook, etc. to students.
Hazards vs. Disasters :
Hazard: Natural Process that poses a threat to human life or property
The Natural process is not the hazard; it becomes one when it threatens human interests.
Disaster: the effect of a hazard on society over a limited span of time or area.
Catastrophe: A massive disaster, usually involving significant loss of time, money and/or life.
S08.110.L2
Bring to class: Fe-Ni meteorite (= core). Mantle chunk (mantle), basalt (= ocean crust), granite (= continental crust)
Chapter 2: Earthquakes
Topics
Earth’s internal layers
Plate tectonics
Faults
Plate boundaries
Introduction
We are starting our discussion of how the escape of Earth’s internal heat leads to natural hazards. This is the first of four lectures on earthquakes. This is an overview of why earthquakes happen, and where they happen. To understand this, we need to learn a little about earth’s interior, and recognize that earth is density-layered.
[[Fig. 1.7b: Earth and its interior]]
Major layers based on
Composition and density
Crust
Continental = 2.7 g/cc (=lighter in color due to less iron, more quartz)
Oceanic = 3.0 g/cc (= darker in color due to more iron than continents, less quartz)
Mantle > 3.3 g/cc (density increases with depth)
Core =11 g/cc
Physical properties
Lithosphere = rocky sphere = crust and uppermost mantle = all solid
Asthenosphere = weak sphere = lower part of upper mantle (solid plus a little liquid)
Mesosphere = lower mantle (solid)
Outer core = liquid metal
Inner core = solid metal
Density of materials in these different layers will change; some materials get less dense and float toward surface and others get denser and sink into the interior from the surface. This leads to a recycling of earth’s crust and replacement with new crust, and the growth of the inner core as the outer core cools and solidifies.
The mantle convects (boils…on a geologic time scale), and this process carries the overlying lithosphere along for the ride.
This is the process that we call plate tectonics
[[Plate tectonic movie of last 200 Myr.]]
It’s been recognized for a century that the continents’ shapes on both sides of the Atlantic looked like they fit together.
Point out Pangaea, and its breakup
Formation of Atlantic Ocean at expense of Pacific Ocean
Note that the rates of motion are different for different continents, and trajectories change too.
Earth’s ocean crust gets recycled; continental crust is too light to sink into the mantle and so stays at the surface.
Fault = fracture in rock along which there is displacement
Terminology
Hanging wall = rock above fault
Footwall = rock below fault
Dip= angle the fault
Strike = direction of horizontal line on the fault
Dip-slip (results in vertical displacement)
Normal= displacement caused by gravity (which is perpendicular to ground)
Reverse (thrust)= displacement caused by stresses within crust…horizontal stresses > normal stresses
Strike-slip= displacement along strike line (displacement horizontal)
Paleomagnetism: The key to acceptance of plate tectonics
Paleomagnetism: As magnetite cools below Curie Temperature (585 C), it locks in the magnetic field orientation of its location on Earth:
This works well for basalts, but magnetization of sediments also occurs- clay minerals often have weak magnetization and grains will rotate to align with magnetic field during deposition.
Polarity = Reverse or Normal
Inclination: Horizontal at equator and vertical at poles
Benefits of paleomag: globally synchronous, which means you can use reversals as a correlation tool, and also you can apply dates from one location to another
Topics
Plate Tectonics
Plate Boundaries
Seismic Waves
Elastic rebound theory
Body waves: P, S
Surface waves
Refraction
Plate Boundaries and their associated faults
Much of the deformation of these tectonic plates is concentrated at their edges. If stresses are applied slowly, the crust can deform in ductile fashion (results in bending or folding). If stresses applied quickly, the crust will fracture along faults.
Three types of plate boundaries exist:
1) Divergent Plate Boundaries= constructive plate margin.
This is the mid ocean ridges and the continental rifts
Ocean ridges constitute 20% of Earth’s area.
Changes in elevation of the spreading ridge could drastically affect sea level.
Average elevation of ridge is 2-3 km higher than nearby ocean crust.
NORMAL FAULTS- principal stress is gravity, minimum stress is confining pressure
Spreading rates average 5 cm/year, but vary from 2-17 cm/year.
Note that Atlantic is centered, but Pacific is NOT.
[[Figure 19.19]]- the development of a rift valley
[[Figure 19.20]- the East Africa Rift separates African and Arabian Plates
East African Rift
[[Picture of the Basin and Range?]]
Basin and Range
2) Convergent Plate Boundaries – destructive margins. Subduction when ocean-continent or ocean-ocean collision, but continent-continent collision doesn’t caused subduction (e.g., the India-Eurasia collision).
REVERSE FAULTS (thrust faults)= principal stress is horizontal and minimum stress is vertical
[[19.21A]
Accretionary wedge develops by scraping sediment off the down-going slab
-In California this is called the Franciscan Complex or Melange (mixture). Consists of sediment and pieces of oceanic crust that got scraped off
Up to 50% of the sediment can be scraped off the downgoing plate.
Ocean-Ocean collision
[[19.21B]]
[[19.17]]
Volcanic Island Arc
[[19.21C]]
[[19.23]] India Collision with Eurasian plate. Note that lithosphere MIGHT continue to go down by separating from crust.
3) Transform fault boundaries (conservative margins). Transform faults accommodate differences in plate velocities.
Strike-slip faults Principal stress is horizontal, minimum stress is also horizontal.
HOWEVER:
San Andreas Fault
[[19.25]]- shows that Juan de Fuca plate’s southern boundary is the Mendocino Fault. This is the northernmost extent of the San Andreas Fault.
San Andreas Fault joins the Juan De Fuca Ridge with the East Pacific Rise in the Gulf of Calofornia.
[[show quicktime movies of East Pacific 80 Ma,
Atwater model of San Andreas Fault]]
Students: you can download these movies yourselves: http://emvc.geol.ucsb.edu/downloads.php
Topics
Tornadoes in the news! (Note that th first midterm will not include this content; we’ll return to it later in the semester.)
Elastic Rebound Theory
Waves
Body waves = P and S waves
Surface waves = Love and Rayleigh waves
Refraction
Seismic Waves
[[Figure 6.11- Distribution of earthquakes with magnitudes > 5 from 1980-1990.]]
Earthquakes are a part of our planet. Earthquakes occur in many regions of the world, but most of the earthquakes are concentrated in narrow regions that are the edges of large pieces of the Earth’s crust. These large pieces of crust move as one and we call them plates.
[[Figure 16.3: Focus and Epicenter]]
An Earthquake is a vibration caused by the rapid release of energy. Usually caused by slippage along a fault.
Focus: The point in the ground where the earthquake occurs.
Epicenter: The point at the surface directly above the focus. This can be hundreds of km from the focus!
Elastic Rebound Theory:
[[Figure 16.5- elastic rebound]]
Rocks can store elastic energy like the bending of a stick. Once the elastic energy overcomes the frictional resistance (“glue”) that holds the rock together, it will rupture. This releases the elastic energy that was held in the rocks.
[[snap a stick demonstration]]
Seismic energy travels out in all directions- can be portrayed as wave fronts or rays. (this works pretty well- as the wave front distorts, the rays bend towards the slower material.)
Body Waves:
Thunder and lightning analogy: People often count the distance to lightning storms by the amount of time between the lightning bolt and the sound of thunder. The lightning flash is instantaneous (at the speed of light = 300,000 km/sec), but the thunder travels at the speed of sound, which is about 0.3 km/sec (= 1 million times slower). So it takes about 5 seconds for the sound of thunder to travel about one mile.
Earthquakes also produce different kinds of waves with different velocities, and these can be used to tell you the distance to the earthquake focus. The two waves used for this are the P and S waves.
[[Figure 17.2 transmission of P and S waves]]
P waves= primary waves (the first to arrive at a seismograph…these are the fastest waves). compressional waves. They change the VOLUME of material that they pass through. waves vibrate in the direction of propagation. transmit through solids and liquids- both return to their initial volume after the p waves pass through.
S waves- secondary waves (these arrive after the primary waves, hence they are slower)
Secondary waves are shear waves. They change the SHAPE of the material that they pass through. waves vibrate perpendicular to the direction of propagation, transmit through solids but not liquids; liquids have no shear strength- you change their shape and they don’t go back…they have no memory.
Surface waves:
While not used to measure the distance to the earthquake, another kind of earthquake wave is concentrated at the Earth’s surface, and is measured by seismographs.
These are the surface waves.
They are the slowest waves
Largest amplitude of displacement on seismograph
These produce the most damage
Actually two kinds of surface waves:
Love waves- create side-to-side shear of ground. This must be the manifestation of the S wave that is traveling parallel to the surface.
Strangely, these move faster than Rayleigh waves
Rayleigh waves- must be a combination of the P and S wave that are traveling perpendicular to the ground surface.
RELATIVE Velocities of seismic waves: P=1.7xS= Surface = 0.9X S waves
Earthquake Intensity Scales
[[16.10. Typical Seismogram. (also 6.7)]]
[[6.12 Richter magnitude from the seismogram.]]
Point out that the distance to the earthquake affects the Richter Magnitude. So without knowing how far away the epicenter is, you cannot gauge the magnitude of the quake. You cannot say, “That felt like a M 4 quake to me,” if you are talking about the Richter scale”
Topics
Intensity scales
Seismic hazards
California Fault Map
California earthquakes
1906
1989
1994
The next big one
Richter Magnitudes: [[Table 6.2]]
= Determined from travel time charts. Greatest deflection of the seismograph and distance to focus enables you to determine Richter Magnitude.
Modified Mercalli Intensity Scale: [[Table 6.1]]
=Intensity of shaking at different locations (meaning there could be different intensities from the same earthquake. This is a qualitative scale, but one which enables emergency response to be sent where greatest damage is most likely.
Moment Magnitude
= An estimate of the total amount of elastic stress produced by an earthquake. It’s measured by the length of fault rupture, the amount of displacement along the fault, and the strength of the rocks found along the fault. The moment magnitude is what you hear reported on the news today (Richter magnitude is more or less retired from use).
[[16.11 Travel-time graph enables you to determine the distance.]]
Note that arrival times enable you to use a chart to determine distances to earthquake.
Amplitude of signal is the displacement of the seismograph drum relative to a stationary mass = the pen
Earthquake hazards
Liquefaction- shaking allows grains to settle in porous material (=densification). Water is forced by pressure to escape upward. If under building foundation…bye to the foundation.
Tsunamis (aka tidal waves). Produced by vertical displacement of sea floor as crustal plates slip.
Note that waves slow as they approach shallow water. Friction causes them to slow, but to conserve energy, waves increase in amplitude
tsunami wavelength = 100-700 km – so can take half an hour to spill up the beach.
[[Active faults in California USGS map]]
[[Restraining bends in fault at Transverse Range and at Loma Prieta]]
Additional friction imposed on fault at these locations, so no slippage- all energy released through earthquakes.
Thrust faults in addition to strike-slip faults. More thrusts because faulting thickens crust and adds weight to older fault segments- so new ones develop
[[releasing bend probably produces SF Bay]]
at the coarsest scale the SAF energy is transferred inland to the Hayward and Calaveras Faults = releasing bend overall
[[Bay Area Faults]]
Topics
California earthquakes
1906
1989
1994
The next big one
How earthquakes on one fault affect stresses on others
Lecture notes are posted in the viewgraphs. With so many pictures, it seemed unnecessary to have separate commentaries!
Chapter 3: Volcanoes
Topics:
Sources of magma
Volcanic rocks
Volcanic edifices
California volcanoes
Materials:
Rocks- basalt, basaltic cinders, andesite, rhyolite breccia
The United States ranks third behind Japan and Indonesia for the county with the most active volcanoes. About 150 volcanoes have erupted in the past 10,000 years, which means that scientists consider them to be active.
Two thirds of all volcanoes in the world are found around the margin of the Pacific Ocean: The Ring of FIRE!!!
Igneous Rocks
Source of igneous rock = molten rock from the mantle= magma. When rock melts, it expands and so is less dense. It then rises toward the surface.
Ways to melt mantle:
1) decrease pressure
2) increase temperature
3) Add water (lowers melting temperature- allows ions to mobilize easier.
Once magma forms it pools in a magma chamber at a depth in the lithosphere where its density matches that of the surrounding rock. Then it begins to cool.
Cooling leads to crystallization. This happens in a predictable way, and depends on the chemical make up of the magma.
Crystal settling- denser crystals can sink to bottom of magma chamber, which causes residual magma to change chemistry (increases in quartz, which forms long thick chains that leads to increase viscosity). Also the volatiles remain in the melt, and so volatiles increase in concentration (explosive potential).
Igneous rocks: Extrusive if erupted onto the surface
Lava = thick fluid with low volatiles
Pyroclastic = erupts as fragmented lava, propelled into the air by the expanding volatiles.
Intrusive if magma chamber solidified below ground.
Granite a typical example- magma has enough time to fully crystallize, so rock has a crystalline texture. Note that intrusive igneous rocks are not hazardous…they cool and crystallize deep below ground. We will not discuss them any further here.
Several places where igneous rocks form
1) Mid Ocean Ridges
Divergent plate Boundary
Rock type = Mid Ocean Ridge Basalt (MORB) lava (dark, dense rock that underwent only a little crystal settling prior to eruption.
Decompression melting – only Pressure decrease involved here- no water!
2) Continental Margins
Convergent plate Boundaries
Rock type = Andesite (lighter in color, less dense than basalt). The crystal settling had to proceed much further before the top of the magma chamber was light enough to move upward through continental crust to reach the surface.
Subduction of oceanic crust with water causes partial melting of mantle wedge
Involves volatiles (dissolved gases, especially water and carbon dioxide)
basaltic magma rises into Continental Crust and ponds when density is matched. Then after further crystal settling the magma can ascend to the surface.
3) Intraplate Volcanism
Increase heat
Unrelated to plate tectonics- Source of HEAT is the core-mantle boundary (but why this happens is poorly understood).
Rock type variable- ranges from flood basalt lava (if mantle plume ascends through ocean crust), to assimilation of continental crust to form explosive pyroclastic eruptions.
[[Hawaiian Hotspot trace across the Pacific Ocean]]
Hawaii hotspot- source of heat has remained stationary while lithosphere has conveyed over it- for 80 Million Years!
Mantle ~ 150 C hotter at hotspots than surrounding mantle.
Pyroclastic materials (bombs, lapilli, ash)
-all materials are fragmented due to the escape of large amounts of gas at the surface- the expansion rips apart lava
-materials often glassy- no time for crystals to form.
Volcanic ash falls- slow rain of very fine ash. Can be distributed to distances of 100s to 1000s of km by wind.
Pyroclastic flows (ignimbrites)- eruption column too dense to be supported by air, and so falls back to earth in a catastrophic eruption column collapse.
material collapses onto air beneath it, and this air gets trapped beneath the pyroclastic material. The materials flows down hill about 100 km/hr.
Lahar (volcanic mudflows) The tops of volcanoes often have water or ice, and when this melts during an eruption, it creates a stream of mud and debris that flows down hill and into stream valleys. If people colonize along the stream valleys, then they are in serious trouble!
Note that it does not take an eruption to melt the ice, and so lahars can occur at any time during an eruption cycle- even when the volcano is dormant.
Pyroclastic eruption example: Mount Saint Helens, Washington
May 18, 1980
Triggered by landslide and decompression
volatiles -> gas, blow side of mountain off= lateral blast.
Led to the full eruption column which settled over several states.
Eruption total about 1 km3
Type of volcano= composite
Cone shaped, composed of explosive dasite and basalt flows
Types of volcanic rock = pyroclastic
[[Figure 8.1]]= Mount Saint Helens before May 18, 1980 eruption
[[Figure 8.1b Mount Saint Helens After 1980 eruption]]
[[Figure 4A. Model of Eruption of Mt. Saint Helens]]
Earthquake preceded the eruption- caused massive landslide
landslide caused sudden decompression
What determines eruptive behavior (i.e. violence of eruption)?
In a word, “viscosity” = stickiness of magma
What affects viscosity?
1) SiO2 content basalt = 50 % rhyolite = 70%
Silica forms long chains in unstructured magma- increases viscosity.
2) Volatiles (dissolved gases)
can be 1-6% of the total weight!
Help to clear a conduit to the surface- erosion
H2O > CO2 > N2 > SO2 > Ar
Volatiles are dissolved until near the surface and then expand to fragment the magma
Volatiles increase in the upper part of the magma chamber
3) Temperature (1100-900)
Higher Temp= lower viscosity
Basalts= high temp Rhyolites = low temp
Volcanic edifices
Shape determines by eruptive behavior.
Shield Volcano = fluid lava
Composite Volcano (mixture of lava and pyroclastic material
Chapter 3: Volcanoes
Topics:
Volcanic hazards
Video: Volcano’s Deadly Warning
1. Measuring volcanic gas output
Fumaroles- gas escapes to the surface through these conduits
Stanley Williams- believed that physical measurements of gas needed to be used to identify immanent eruptions.
CO2 +SO2are gases that come from the magma, not the porewaters of the volcano (i.e. H2O)
Good for monitoring open volcanoes. But if magma seals the gas conduits, then low gas could be a sign of immanent eruption. On Galeras, it was interpreted as no gas to be measured = safe.
Video: Volcano’s Deadly Warning
Hand out supplemental questions for students to address during the video.
A-type earthquakes – caused by rock fracture associate with magma injection into country rock. Te injection is done under pressure, and causes rocks to burst apart and magma to intrude.
Seismologically these appear very similar to tectonic earthquakes, with a sudden rise in seismic amplitude and a gradual decline.
Difference- these occur in clusters, rather than as aftershocks. Magnitudes are relatively small (M3-5).
B-type earthquakes- different pattern. Long period seismic waves that slowly builds up and slowly decreases. This is more like a symmetric sine wave.
Cause: Pressure in magma chamber builds up, and these increase in number.
Successful in predicting several notable eruptions, including:
Popocatepetl, Mexico
Colombia- Novado del Ruis- the signal was detected but people not warned. 1985- 25,000 people died by lahar- a volcanic mud flow
1989- Redoubt, Alaska – successfully predicted, saved oil workers.
Galeras, Colombia, 1991- Formed a lava dome (indication that magma is near surface. So long as gases continue to escape (open dome) from fumaroles, then pressure is not building. When they stop letting out gas (closed dome), then the pressure is building.
Topics:
Volcanic hazards
Pyroclastic eruptions
Gases effects on climate
Lahars
Caldera eruptions
California volcanoes
Long Valley
Shasta
Medicine Lake
Lassen
Midterm 1 Review
Pyroclastic materials (bombs, lapilli, ash)
-all materials are fragmented due to the escape of large amounts of gas at the surface- the expansion rips apart lava
-materials often glassy- no time for crystals to form.
Volcanic ash falls- slow rain of very fine ash. Can be distributed to distances of 100s to 1000s of km by wind.
Pyroclastic flows (ignimbrites)- eruption column too dense to be supported by air, and so falls back to earth in a catastrophic eruption column collapse.
material collapses onto air beneath it, and this air gets trapped beneath the pyroclastic material. The materials flows down hill about 100 km/hr.
Lahar (volcanic mudflows) The tops of volcanoes often have water or ice, and when this melts during an eruption, it creates a stream of mud and debris that flows down hill and into stream valleys. If people colonize along the stream valleys, then they are in serious trouble!
Note that it does not take an eruption to melt the ice, and so lahars can occur at any time during an eruption cycle- even when the volcano is dormant.
Climate Change and volcanoes
Volcanoes put out greenhouse gas such as CO2. CO2 remains in the atmosphere for a century or more, and so its effects are long-felt following an eruption.
Volcanoes also put out SO2 which is a gas that leads to global cooling because SO2 reflects incoming sunlight back into space. However, SO2 has a much shorter residence time in the atmosphere (typically about a year) and so the cooling effects are short-lived.
The 1991 Mt. Pinatubo eruption of about 5 km3 led to global cooling of about 1 degree Fahrenheit for the years 1992-1993. However, following that time it contributed to global warming from its CO2 emissions.
California Volcanoes:
There are more active volcanoes than I’ll talk about, but these are the four that pose significant hazards.
Mount Shasta
Composite volcano (= pyroclastic eruptions followed by minor lava flows and lots of lahars). Last eruption = 1786. Largest Cascade Range composite volcanoes.
Mount Lassen
Volcanic dome. Very viscous magma which leads to significant pyroclastic eruptions. Last eruption 1914-1917, included a large lateral blast akin to Mt. St. Helens.
Medicine Lake volcano
Shield Volcano (basalt lava)
Has erupted 600 km^3 of magma, making it the largest of the Cascade Volcanoes (but because it’s basalt lava it forms a broad shield volcano)
Formed where crust is being pulled apart (decompression melting)
Last eruption about 1,000 years ago (Glass Mountain)
Long Valley
Hotspot volcano (mantle plume source). Origin of hotspot is unclear. Crustal assimilation into basaltic magma has created large pyroclastic eruptions from LVC. The last was ~ 700ka and produced the Bishop Tuff (600 km3) which led to the caldera collapse.
Mammoth Mountain is a composite volcano on the rim of the caldera, and formed over the past 200 kyr.
Inyo Craters- youngest activity from the LVC. These are small volcanic domes that have erupted in past kyr.
S08.110.L10
Topics
Meteorology
Global heat transport
Hadley circulation
[[Figure 16.7- atmosphere cross section]]
4 spheres: (based on temperature)
Troposphere= ~0-12 km= mixed layer- where almost all weather occurs.
Cools upward,
thunderstorms rise to about this level and then stop at the Tropopause.
99% of all water vapor is in the troposphere.
environmental lapse rate = the rate that air cools with altitude in the troposphere.
6.5 degree/km on average (known as the normal lapse rate), but ranges to 9.8o for dry air
[[Figure 16.17: radiation from Sun and Earth]]
Troposphere heated from below by IR radiation
[[Figure 15.15. Wavelengths of light]]
Wavelength related to source temp.
Sun 6000C ~ 0.5 µm
Earth 25 C ~10 µm
[[Figure 16.19- the distribution of sunlight as it enters the atmosphere]]
[[BACK TO 16.7: atmosphere profile]]
Stratosphere= ~10-50 km
At height of stratosphere, UV radiation breaks apart O2 molecules and they recombine to form O3.
A catalyst is needed to bring O and O2 together
Ozone absorbs UV radiation and emits heat.
Ozone layer causes heating. This causes stratification of the atmosphere because air above is lighter. stratopause.
Next two layers are not important for Natural Disasters
Mesosphere: 50-80 km. Ozone not here, so cools again.
Mesopause- the top of the mesosphere. Temperature inversion
Thermosphere: 80-? No well defined boundary
Absorption by O and N of high-energy UV radiation
Molecules very HOT (1000C) but so infrequent that not really hot to the touch.
Incoming radiation = UV radiation
absorbers = O2, O3 and H2O
Outgoing radiation = IR = H2O, CO2, CH4
[[Show Figure 16.19 again- note that 20% radiation absorbed by atmosphere.]]
Water vapor absorbs infrared radiation very well.- IR radiation captured by clouds and re-reflected to Earth.
Accounts for 5X absorption of all other atmospheric gasses combined.
So atmosphere heated from ground up (because that’s where the IR comes from.
Water mostly- water a unique material that changes physical states in Earth’s temperature ranges.
[[Figure 17.2 states of water]]
Note that latent heat = heat required to change physical state
Very high for water
80 cal Solid-Liquid
540 cal Liq-gas
If water evaporates at equator and rains elsewhere, then heat is transferred away from equator.
Ocean circulation
There are two principal ways that ocean water circulates around the World:
1) Surface Currents
2) Deep water currents
1) Surface Currents
Surface currents are driven primarily by wind.
When you are sitting on the beach at the Equator on a windless day, the wind is really moving about 1700 km/hr; it just happens to match the speed that the ground is moving.
When you are sitting near the pole on a windless day, the wind really is not moving velocity = 0 km/hr!
The reason for this is that the wind is tied to the Earth by friction, but that coupling is not perfect…the wind can have different velocities than the ground beneath it.
[[Fig. 18.16 Wind directions of planet]]
[[Fig. 18.15 Generalized Hadley Cell circulation]]
Follow air form equator to pole to explain wind directions,
Bending of air masses= Coriolis forcing.
Air not really bending. It is the position of the ground relative to the air above it that is changing.
[[Draw Earth with equator and 2 longitude lines]]
Wind- generated by heat gradients.
Equator gets most heat. Air rises here and moves away from equator.
Atmospheric pressure = weight of column of air.
If pressure is low, air will rise, expand, cool, form clouds.
If pressure high, air will sink, heat up, and NOT form clouds.
But it doesn’t flow away in a straight line.
Note Earth rotates counterclockwise in Northern Hemisphere (from west to east).
At equator, speed of rotation = ~ 40,000 km/24 hrs =~1700 km/hr.
Near the poles, the speed of rotation is less- virtually 0 km/hr at rotational pole.
[[Draw ground speed versus air speed]]
ground speed = angular speed
air speed = velocity
What this means is that air moving from equator towards poles has higher west-eastvelocity than ground beneath it. So it moves towards the east.
By 30 degrees N or South, the air is moving due east. This air descends and returns to the equator to replace the rising air.
THIS MEANS THAT AT GROUND LEVEL, THERE IS A STRONG EAST TO WEST FLOW OF AIR, AND THIS DRIVES OCEAN CURRENTS.
[[Figure 18.16- general wind pattern over Earth]]
just point out wind flow at equator is to the west
=TRADE WINDS.
We’ll talk about the rest of the air movement later, but for now it is sufficient to know that these winds drive the ocean surface currents.
S08.110.L11
Topics
Atmospheric pressure
Ocean Circulation
Thermohaline Circulation
Atmospheric pressure = weight of column of air.
If pressure is low, air will rise, expand, cool, form clouds.
If pressure high, air will sink, heat up, and NOT form clouds.
We’ll talk about the rest of the air movement later, but for now it is sufficient to know that these winds drive the ocean surface currents.
Ocean circulation
There are two principal ways that ocean water circulates around the World:
1) Surface Currents
2) Deep water currents
1) Surface Currents
Surface currents aredriven primarily by wind, which in turn is driven by heat gradients and coriolis forcing.
[[Figure 15.2- average ocean surface currents]]
Note the GYRES = coriolis forcing
Note this means western sides of continents COLD
From Equator to pole we find the following temperature and salinity effect:
[[Figure 14.3- salinity and temperature by latitude]]
explain that temp is high at equator and low at poles
NOW LET”S LOOK AT THE OCEANS IN CROSS SECTION TO SEE HOW TEMPERATURE AND SALINITY VARY WITH DEPTH
[[Figure 14.4- temperature by depth]]
There is no temperature change at the high latitudes- the water is cold from top to bottom.
Near the equator, there is warm water near the surface, but this drops off rapidly by 1 km depth. This drop is called the thermocline.
Why is there a thermocline at the Equator? Surface waters are hot. This causes surface waters not to descend (hot = less dense).
At poles, the water is cold from top to bottom- no heat-induced density change
Density layering
[[Figure 14.5 pycnocline]]
Density is a combination of temperature and salinity
Salinity control
Oceans are salty
~ 35 ‰ salt
Relatively constant, but local concentrations change by the addition or removal of water
Addition of fresh water = runoff, melting of sea ice, melting of glaciers
Subtraction of fresh water= evaporation, production of sea ice, production of glaciers.
Sea ice affects the high latitudes salinity seasonally.
Ocean density also has the rapid change just like the thermocline. It is called the pycnocline.
[[Figure 14.6. Three layers of the ocean]]
1) surface mixed zone ~ 2% of ocean volume. Doesn’t reach the polar oceans.
2) transitional zone ~18% represents the thermocline and pycnocline region.
3) Deep zone ~ 80% of ocean.
This creates a very stable water column near the equator that doesn’t mix much vertically. However, at the poles, there is no density of thermal layering, and so small changes in density or temperature sends water from the surface to the deep ocean.
Thermohaline Circulation
Thermo = heat
Haline = salt
circulation = movement of the ocean water
[[Figure 15.6: Thermohaline circulation model]]
Formation of sea ice at poles causes density increase and water sinks to the bottom.
Cold water fills the ocean basins.
Warm water moves from equator to pole to replace lost water.
Occasionally this system breaks down.
End of last ice age = fresh water floods N. Atlantic. Sea ice does not increase salinity.
Thermohaline circulation stops.
[pictures of 8200-year event in North Atlantic]
[Picture of Day After Tomorrow]
8200 year ago the last of the North American ice sheet melted and sent a huge pool of fresh water into the North Atlantic Ocean. This eliminated the pycnocline, thereby shutting down the equator-pole heat transfer.
S08.110.L12
Topics
Clouds
Fronts
Middle Latitude Cyclones
Saturation: The maximum amount of water the air can hold
Controls: Temperature
[[Show example- plot of data from Table 16.1]]
This shows that carrying capacity of air increases exponentially.
[[Same plot with example of air cooling]]
Suppose we have air at 30 C at sea level and we raise it in the atmosphere to 4 km altitude. Then the air would cool by 26 C (with a lapse rate of 6.5C/km), and so the air would cross into the region of saturation. So clouds would form and then rain would fall.
The basis for cloud formation is adiabatic cooling
Note as an aside- radiation cooling produces fog- clouds at ground level
Adiabatic cooling- no heat exchanged with surroundings
If gas compressed- heating (molecules closer together- more collisions)
If expanded = cooling
[Fig. 17.9-.13- the four processes that lift air]]
1) Orographic lifting = air forced over mountains
Rain shadow deserts- Leeward side of mountains- as air descends, it heats, and so can hold more water
2) Frontal wedging- cold air mass wedges beneath warm one forcing the warm air upward. Mid latitude cyclones
3) Convergence – two air masses of equal density meet and are forced upward- e.g. Florida. Land heats and air rises. This causes ocean air from Gulf and Atlantic to flow together.
4) Localized convective heating. Some areas with low albedo heat faster and cause localized rising.
Thermals- localized uplift associated with this type of heating.
This basically is what happens at the equator.
Not all clouds produce major storms. Some produce mild weather. Mild weather is produced by stable air- air that doesn’t rise to undergo adiabatic cooling.
stable- air cooler than surroundings so sinks to stable place- the parcel of rising air cools faster than the surrounding air, so it sinks back down to a stable elevation.
unstable- air warmer than surroundings and so rises
what causes instability- adiabatic cooling slower than environmental lapse rate.
Clouds – visible droplets of air
1) Cirrus – high. thin wispy clouds
[Figure 1619A: Cirrus cloud]
2) Stratus – sheets, layers; stable air
[[Figure 16.19 F. Nimbostratus; stable air]]
3) Cumulus – flat bottomed, cauliflower clouds- thick!
[[Figure 16.19 G. cumulus= unstable air]]
4) Cumulonimbus- covers the entire thickness of the troposphere- very unstable air!
[[Figure of cumulonimbus = note flat top = hits stratosphere]]
Fronts
When one air mass moves into area occupied by another air mass.
Warm front- warm air moves into area where cold air exists. since warm air is less dense, it overrides the cold air; it is more difficult for warm air to move cold air than vice versa. Warm fronts low angle, and so produce gradual increasing cloudiness is an area.
Cirrus -> stratus
Cold front- cold air moves into area where warm air was located. The dense, cold air can easily displace the warm air, and so this produces a steep front.
= cumulus and/or cumulonimbus clouds
We often see a pattern to the passage of warm and cold fronts with midlatitude storms.
These travel from west to east, probably due to the prevailing westerly winds.
two air masses converge
polar high = flows east to west
maritime tropical low
[[Figure 18.9. Point out these on opposite sides of the polar front]]
[[Figure 18.9- the development of a midlatitude cyclone.]]
Warm air traveling to east also moves north, and the cold air traveling west and moves south.
This results in counterclockwise rotation
Two fronts develop: first a warm front and then a cold front
Eventually the cold front circulates back until the warm air is pinched off (=occlusion) and then the storm stops.
[[Several satellite pictures of a midlatitude cyclone over Central US.]]
S08.110.L13
Topics
Thunderstorms
Tornadoes
Hurricanes
Ozone Hole
Thunderstorms Tornadoes and Hurricanes (oh my!)
Smaller than middle latitude cyclones, but generally more violent
Note that these are associated with low pressure centers
Thunderstorms are isolated low pressure systems that produce thunder and lightning
Florida example of convergence
Over the central US these form due to frontal wedging- no barrier between polar high and subtropical low through the plains.
Uplift in low pressure is caused by release of latent heat of condensation- this causes the low pressure system to accelerate.
Updrafts can reach speeds of 100 km/hr, which allows droplets and ice to form and stay aloft
Also causes lots of water drops to stay aloft until the updraft speed is lowered, then rain falls by the bucketload.
This allows large hailstones to develop, as their freefall speed is exceeded by the updraft speed, so they stay aloft and water droplet run into them.
[[The Coffeyville Hailstone- 1970- about 2 pounds]]
hailstone show repeated passes through the supercooled portion of the cumulonimbus cloud. Fall velocity about 100 mph, so sustained updraft exceeded this for quite some time.
What causes lightning? (rubbing feet on carpet analogy) The removal of electrons from upward moving clouds by the cold clouds that they run into. This causes the top of the cumulus clouds to have positive charges and the bottoms to have negative charges. The negative charges in the cloud push the ground surface negative charges further into the ground so that only positive charges are at the surface. Then the quick transfer of electrons from cloud to ground re-establishes charge balance.
Tornadoes- form in association with really large thunderstorms called supercells. Within supercells they form beneath really large cumulonimbus clouds- called mesocyclones.
[[Figure 18.18 T&L- occurrence of tornadoes in the US]]
Due to cumulonimbus clouds caused by convergence over FLA and due to frontal wedging in the plains areas of Central US- here there are no geographic barriers between the polar and subtropical air masses.
[[Show T&L 18.17- the wind starts horizontally by faster wind aloft. Then this column gets sucked up into a large cumulus cloud = mesocyclone.]]
Vortex = really low pressure cell causes winds to stream inward very quickly.
Most tornadoes form in the mid-west where warm tropical air from the Gulf of Mexico collides with the polar air from Canada- there is no geographic barrier in the Midwest to separate these two bodies.
Average tornado width = 100-600 meters.
Highest wind speeds in nature- approaching 300 mph
[[opening picture is Hurricane Floyd. Central America 1999. $5 billion in damage]]
Wind speed in excess of 74 mph =119 km/hr
rotary circulation around a low pressure cell
Fueled by the latent heat of condensation
Requires lots of warm (>27C) (>80F) water
This means that hurricanes form in the subtropics (5-20 degrees) and lose energy as they travel over colder water.
[[Hurricane Andrew]]
most damaging US hurricane.
1992
Property damage est. $25 billion
How they die= their energy is choked off by colder water or less water (when they move over land).
Hurricane damage:
1) Storm surge (strongest on north end of hurricane- the part that’s rotating into the shoreline,)
2) Wind damage
3) Inland flooding
Ozone:
O3 = O2 + O (freed from other O2 molecules by UV radiation. They combine on the surface of a catalyst- a particle that does not get consumed in the process.
Why ozone hole at South Pole?
Polar vortex- wind circulates around Antarctica and doesn’t mix with rest of atmosphere.
During winter, little light, and many atmospheric gasses build up in the stratosphere –
polar stratospheric clouds form.
In Spring, light hits these and causes lots of chemical reactions between Cl and O3 and breaks up the ozone for several months.
Then the vortex breaks up and ozone-depleted air dissipates.
Northern Hemisphere doesn’t have a strong polar vortex, so this type of build-up the stratosphere doesn’t happen.
S08.110.L14
DVD: Global Warming: The signs and the Science
Questions to consider during the DVD
S08.110.L15
Topics- ??
I set up this lecture to follow the Global Warming DVD. My discussion for this lecture was scattered, but it was centered on several observations about global warming science. I provide them here for your consideration, not for your adoption.
What does that mean? It means that it’s darned difficult to use statistical arguments to prove the causes of global warming. That’s difficult for an experimental scientist such as myself to accept, since my work has to meet the rigorous statistical proof in order to be accepted. But for global warming discussions, there are far more inputs to the climate system to be able to identify a single component (such as carbon dioxide) as the sole cause of the observed warming.
So, what does THAT mean? It means that carbon dioxide may indeed be the primary cause of global warming (and no one in their right mind denies that 100 ppm of atmospheric carbon dioxide is attributable to human activities). But unless all the other potential influences on the climate system have been quantified very precisely, it will be nearly impossible to prove just how much of global warming is due to carbon dioxide. (in fact, if one were to use a box model of the atmosphere with CO2 as an adjustable input, we’d have predicted twice the global warming that was observed during the 20th Century. Some suggest that the second half of this warming has not yet occurred because ocean circulation brings cool water to the surface, and the oceans will take another century to equilibrate with the atmosphere). But based on statistics, it can be easy to be dismissive of many scientists’ interpretations of their data. That, by my observation (and participation), is where there remains significant disagreements that you read about with regard to human influences on global warming.
So where does this leave us? Anecdotal evidence, such as melting of permafrost is the Arctic), retreat of glaciers, sea level rise, changes in vegetation, increased elevations of the snowline in mountains, and melting of the Northern polar ice cap, all indicate that global warming is real. Carbon dioxide is a greenhouse gas, and we are responsible for about a third of what’s in the atmosphere. We increased its concentration by about 1 ppm per year during the 20th century, but we now are putting about 3 ppm per year up there.
If global warming continues along its recent trajectory, there will be catastrophic consequences for many countries. People as well as the rest of the biosphere will need to adapt and be able to migrate to more habitable areas, or become extinct. Natural resources, particularly fresh water, will need to be stored in greater amounts, and moved to areas that become more arid. In short, people have grown accustomed to climate remaining in a very narrow range of temperature and amounts of precipitation, and global warming will cause the climate system to move out of that narrow range. So be prepared!
What can we do to reduce the build-up of carbon dioxide? I did a back of the envelope calculation in class, assuming that if we reduced the amount of carbon dioxide we put into the atmosphere by the amount that the atmospheric concentrations have been increasing (1 ppm), then every human being could do their part by reducing their emissions by the equivalent of about 1 gallon of gas per day. For us Americans, that should be quite possible by improving gas mileage in our cars, and some simple acts of energy conservation. Gas and electricity have been so cheap for so long that we have become undisciplined and careless about our misuse of them. (As I write this I note that I have left on, unnecessarily, about 2,000 Watts of electric lights. There, now I’m using 150 Watts. That’s a 92.5% reduction in lighting electricity).
I suggest that you do some additional research on your own. A couple of good websites to visit are those of Steve Schneider (Stanford University) and Wally Broecker (Lamont-Doherty Earth Obervatory). Just Google them.
I liked the following Steve Schneider statement, which I stole from his webpage. It provides a cold splash of water in the face of paleoclimatologists, such as myself, who try to use evidence of past climate behavior to anticipate future climate behavior:
The validity of a model depends on how it deals with structural change — evolving functional relationships or parameters. Predictions based on past observations are valid only as long as future conditions replicate past conditions. This is unlikely to be the case for large climate changes, which are expected to arise from unprecedented rapid changes in the composition of atmospheric greenhouse gases, land surface changes, etc.
With that I’ll close this discussion, shut off my computer and save another 100 Watts of electricity.
Topics
Climate causes of excessive rainfall
Streams
Profile of a stream
Baselevel
Mature streams- why they meander
SALT
Salt may not be the first thing that comes to mind when you think about pollution, so let me give you some examples. The Great Salt Lake didn’t used to be salty. Neither did Mono Lake.
[[Figure 6.21- the extent of pluvial lakes in the Basin and Range]]
Let’s look back at the west of 10,000 years ago. Pretty remarkable huh? The west was much wetter back then, for two reasons. One was that the great ice sheets created their own weather and led to wetter conditions throughout the Basin and Range but also there was water draining off the glaciers, particularly as they retreated.
Salt is also a problem for agricultural land, and one way to keep salt from building up is to irrigate fields with lots of water so that the salts run off instead of accumulate in the soil.
Many of you may have noticed when driving by farmland that it seemed like the farmers were wasting a lot of water. While that may be partially true, the farmers are not being totally irresponsible. They are making sure that salt does not build up in their soils.
The unfortunate consequence is that run off has lots of salt, and so if you rely on water sources downstream from agricultural land, your water will be salty; sometimes very salty.
I would like to suggest a book for those of you who are interested in reading more about the water issues affecting the American west. The book is called “Cadillac Desert” by Marc Reisner, This book is a fabulous documentary into the history of water in the US, and all the good and evil that accompanied it.
Why does flooding occur?
A: Increase in rainfall and/or poor land use planning.
Climate events that lead to increased rainfall in USA
Stalled Midlatitude cyclones
1993 Flood: Greatest Flood in US History
What happened? Early snow melt saturates ground
High pressure over East Coast prohibits Midlatitude cyclones from migrating East
Rainfall all occurs in the Mississippi and Missouri River Valleys
At St. Louis, Mississippi River above flood stage for 144 days.
[[Lots of photos about the damage]]
St. Louis – floodwalls create bottleneck, leads to upstream flooding
El Nino events
Normal climate pattern is for the Trade Winds to blow east to west across the Pacific, building up a pool of warm water in the western Pacific. This leads to increase rainfall for Indonesia and Australia. During El Niño events, the Trade Winds die off and the warm water moves eastward across the Pacific, bringing with it the intense rainfall to the North American Southwest. This leaves the west Pacific without its normal rain source, and so drought conditions develop there while we get soaked.
Having produced the unusual rainfall, we now have to follow it across the landscape.
Streams- Transport water at the surface.
1) Gradient- steepness of the stream
2) Channel characteristics- width, shape, roughness
3) Discharge- amount of water
[[Fig. 5.6: Stream profile- concave upward]]
To understand the return path of water requires us to introduce the term:
Baselevel- the level to which streams erode.
Both ultimate and temporary baselevels exist.
[[Figure 5.12- the concept of baselevel- the level to which streams erode.]]
Ultimate baselevel= the ocean
Temporary Baselevel = a lake, etc., that is above sea level. These are all temporary storages, and ultimately erosion will remove them.
Narrow “V” shaped valleys- tend to be young valleys.- energy of the stream goes into eroding the stream channel, so it downcuts rapidly.
Wide “U” shaped Valleys- the downcutting to baselevel has occurred already so the energy of the stream goes into widening the stream course- the stream works laterally to erode the walls of the valley, and produce wide flood plains.
Note that the stream youngens landward- continued downcutting increases size of drainage basin.
They’ve already cut down to baselevel, and then the stream continues to mature inland. This leads to more runoff and finer sediment. These factors increase stream velocity, and so since the steam cannot downcut any further, it adjusts its gradient to compensate.
S08.110.L17
Chapter 4: Flooding
Topics
Water resource issues: Storage capacity
Groundwater usage, subsidence
Good and bad sides to dams
Good: provide water storage and floor control
Bad: capture sediment in dam, and starve downstream sections of sediment (erosion!)
Huge West Coast problem! Beach starvation!
[[Fig. 4.13 areas of US flooded in recent time]]
Flooding is the greatest year-to-year hazard in the US. It is especially bad for our part of California.
1993 Flood: A great Flood in US History
What happened? Early snow melt saturates ground
High pressure over East Coast prohibits Midlatitude cyclones from migrating East
Rainfall all occurs in the Mississippi and Missouri River Valleys
At St. Louis, Mississippi River above flood stage for 144 days.
[[Lots of photos about the damage]]
St. Louis – floodwalls create bottleneck, leads to upstream flooding
The Great Missoula Flood: Channeled Scablands, Washington State.
Considered by some to be the greatest flood in recent geologic history.
~ 15 ka.
Glacial Lake Missoula. Dam = glacial ice. Melts and let loose a 2000 foot-tall wall of water that flows to the Pacific.
[[Figure shows path of Scablands Flood]]
Evidence of enormous water flow:
1) Dry Falls. Evidence that the waterfall was 400 ft. tall and 4 Mi wide.
Lake at bottom were pools where water hit after coming over the dam.
2) Megaripples. Normal ripples ~ 1 inch high.
Scablands ripples = 50 feet high and hundreds of feet long.
In some places the rocks have interconnected pore spaces that allow the water to infiltrate and flow below ground level.
[[Figure 5.25- shows the water table and also porosity and permeability]]
water table: the level of saturation- where all pore spaces are full of water
Porosity: the spaces in the rock
Permeability: the interconnectedness of the pores which allows water to move
e.g. some rocks have lots of pores (like pumice) but these pores are not connected, and so water cannot flow through them.
Perched Aquifer Impermeable layer makes local water table- Good in wet times, but not in dry times- the perched aquifer will be the first to dry out.
Springs- when the water table intersects the surface. Keeps streams flowing year-round.
Removal of groundwater faster than it can be recharged leads to replacement of water in pore spaces with air. Air cannot support the weight of the overlying sediment and collapses.
[[San Joaquin Valley subsidence]]
S08.110.L18
Ch. 8 Coastal Hazards
Topics
Waves
Refraction
Coastal landforms
human intervention
While the processes that we talk about today occur in everything from the oceans to lakes to small puddles of water, we’ll talk about the oceans here.
The shoreline is the location where forces governed by the oceans clash with forces from the land.
The relative strengths of these competing forces dictates the type of shoreline that develops.
For instance, a shoreline that is dominated by river process will look substantially different from one that has no river influence.
It should not be surprising to you that the shoreline should move as a consequence of natural processes.
In order for a shoreline NOT to move, the addition of sediment to the coastal area has to be perfectly balanced with erosion rates. Also, any change in sea level, from compaction, tectonic movements, or global sea level rise, must be perfectly balanced by some opposing movement.
This just isn’t reality. But coastal development depends on the coastline being in the same place through time. Thus, human intervention is required to make this happen.
Coastal property is the most expensive property that exists. Keller suggests not purchasing or developing it; I don’t think that’s very likely. Considering the probability that the coastline is going to migrate through time, this might be a risky investment, particularly is coastal erosion is eating away at your property. On the other hand, if the coastline is building seaward as a consequence of more sediment being supplied than erosion is taking away, and your property line is determined by the position of high tide, then your coastal investment may pay off as your property continues to grow.
So let’s look at shorelines that are dominated by the ocean first
1) Waves
In water, waves transfer energy rather than transferring material; a wave can traverse the ocean in a day (e.g. Tsunami) but water takes several years to circulate.
[[Figure 14.2- waves, oscillations ]]
Label: Crest, trough, wave height, wave length, period
In open ocean, waves are oscillatory waves- a cell of water follows a circular path
You feel this on a boat
the oscillatory motion decays with depth and by 1/2 wavelength the oscillatory motion is gone.
Note that the wave energy dissipates because the force that creates the waves is wind, which is a force at the surface.
Water does move a little bit in the direction of the waves, but most of the motion is in the wave (this is the transfer of energy rather than translation of water)
at shoreline energy changes from wave of oscillation to wave of translation= the energy is transferred from one body to another.
[[Fig. 14.2- wave refraction toward headlands]]
Irregular coastlines cause wave energy to focus and diverge. Focus on headlands
Diverge in bays = dissipation of wave energy causes particles to settle out of water- develops
How waves break on shore.
[[Figure 14.9 ES]]
Note that the waves no longer follow a circular path; they drag due to friction at the bottom. Eventually the crest of the wave advances far enough ahead that it is no longer supported by the wave. It breaks.
[[Fig. 9.4 Plunging Breaker vs. spilling breaker]]
Note that plunging breakers break on the beach- they require a rapid shallowing of the coastline. Spilling breakers dissipate energy over a much larger area, and so don’t transfer so much energy to the beach.
1) Wind speed: increase wind speed, increase wave height
2) Duration of blowing. Longer duration, bigger waves
3) Fetch: distance wind blows across ocean: Longer the fetch, larger the waves
These all work to a point where the wave is fully developed = won’t get any bigger.
Note that the energy stored in a wave is roughly proportional to the square of the wave height.
If 1 m high wave = 1 unit of energy
2 m high = 4 units of energy
10 m wave = 100 units of energy
2) Currents:
[[Figure 14.2 ES Global surface currents]]
Long-shore currents: Waves do not usually approach the shoreline perpendicularly. Usually they approach at an angle and bend (refraction) as the waves feel bottom.
(we already talked about waves bending in the direction of lower velocities, but let’s review it for shorelines.)
Causes: Longshore transport (aka littoral transport by Keller)
[[Figure 14.9- longshore transport]]
Inward trajectory= at a slight angle
Outward trajectory= perpendicular to shoreline= controlled by gravity rather than waves.
[[Fig. 9.7 rip current diagram]]
Outflow of water not uniform. Some areas concentrate on outward flow = rip current.
Longshore transport leads to :
[[hand-drawn figure of spit, baymouth bar, barrier island]]
1. sandspit= extension of beach into a bay.
2. baymouth bar= spit crosses whole bay
1) some isolated sand spits separated from mainland by continued sea level rise
2) Others by erosional scour of sea floor by storm waves that pile up sand offshore
Seawalls- keep wave energy from eroding base of seacliff. Problem- the reflect wave energy outward, and so waves carry beach sediment offshore.
Groins: capture sand. Problems they starve places downcurrent and can cause erosion there.
[[Figure of groins with sediment trapped.]]
Note downcurrent has depleted sediment
Jetties: extend out and block sand from filling a harbor entrance
[[Figure 14.16 = a jettie]]
Breakwater: barriers that cause wave energy to dissipate offshore. Problem that causes sedimentation at shoreline.
Seawall: wall limits erosion of beach.
Beach nourishment: adding sand artificially.
West Coast problems: Damming the rivers eliminated a large portion of the coastal sediment, so beaches are thinning. This leads to less wave energy dissipation so headlands erode faster.
East Coast problems: Development on barrier islands, which naturally move.
S08.110.L19
Video: Tsunami: The wave that shook the world (Shown in class, then on reserve in library)
1) What were the warning signs of an impending tsunami?
2) Might we expect similar events along the California Coast?
3) How does the shape of the coastline affect wave energy (note refraction)?
4) Is there just one tsunami wave?
5) What else causes tsunamis?
S08.110.L20
I used this lecture to tell you about my work in Italy. there I use coastal sediments near Rome to work out the history of sea-level change caused by ice-age cycles (ice age lowers global sea level by several hundred feet).
Volcanic ash layers deposited in these coastal sediments provide a means of assigning ages to those interpreted changes in sea level (I date the ash layers by radioactive decay dating methods).
S08.110.L21
Chapter 5: Mass Wasting
Topics:
slope processes
human interaction
minimizing hazards
Review the different types of mass wasting in Keller and Blodgett, CH. 5.
Physical factors that cause mass wasting
Angle of repose- the angle at which rock strength equals the gravitational force= the steepest slope a material can attain before becoming unstable.
Types of mass wasting:
[[classification in Keller Table 5.1]]
1) FALLS: free fall of material off free face of cliff
2) SLIDES- movement of cohesive block of material
a) slump- soft, cohesive material moving along a curved slip face
3) FLOWS: movement of unconsolidated material
a) slow flow = creep
b) rapid flow= earthflow, mudflow, debris flow
Also discuss earthflows, mudflows, rockfalls, snow or debris avalanches
LAST TWO IMAGES: signs of mass wasting
Prevention tools: change the angle of repose and eliminate water.
Slumps- the most common type of mass wasting around here.
Slump = the downward sliding of a mass of material.
Forms a recognizable topographic feature= a scarp
[[Draw the plan view and cross section through a slump]]
Mass wasting types:
lahars
subsidence
natural and unnatural compaction
sinkholes
Prevention
Crescent-shaped cracks in hillsides
Tongue-shaped area of soil or rock on the hillside
Large boulders or talus at the base of a hill
Linear path of cleared or disturbed vegetation
Exposed bedrock with sedimentary layers parallel to slope
Irregular land surface (hummocky)
bent trees
tilted fenceposts
Pre-existing landslides (subsequent erosion can lead to reactivation of an older landslide)
Case studies: La Conchita (2005), 1995
Problems:
Very steep, high slopes. Uplift of coastal terrances at La Conchita is extreme. 40,000 year-old terraces at 180 m above sea level. That’s 4+ meters of uplift per 1000 years.
Presence of weak rocks. The “rock” at La Conchita is mostly loosely-lithified sediments, ranging from clay to silt to sand. It is typical beach material for California.
Presence of historic and prehistoric landslides. The landslide of 2005 occurred by reactions of the 1995 landslide; they knew it was coming, but they just didn’t want to believe it could happen again. Southern Pacific Railroad wrote reports in the 1800’s that stated they felt the railroad should not be built through this area for fear of slides.
Periodic rainfall. The added weight and wetting of sediment causes them to move.
Remedies
Structural control- build retaining walls
Change land use
Install warning system.
CH. 6: Subsidence
Topics
Karsts
Permafrost
Compaction
Groundwater mining
Groundwater flow
In some places the rocks have interconnected pore spaces that allow the water to infiltrate and flow below ground level.
[[Figure 5.25- shows the water table and also porosity and permeability]]
water table: the level of saturation- where all pore spaces are full of water
Porosity: the spaces in the rock
Permeability: the interconnectedness of the pores which allows water to move
e.g. some rocks have lots of pores (like pumice) but these pores are not connected, and so water cannot flow through them.
Springs- when the water table intersects the surface. Keeps streams flowing year-round.
Removal of groundwater faster than it can be recharged leads to replacement of water in pore spaces with air. Air cannot support the weight of the overlying sediment and collapses.
[[San Joaquin Valley subsidence]]
Underlays about 25% of the United States (though very little in California)
Occurs in areas where the geology is affected by dissolution
Rock types: Carbonates, gypsum,salt
Types of dissolution features
1) Solutional sinkholes: dissolution at the surface where water ponds
2) Collapse sinkholes: Occurs where water table is lowered and so groundwater flows beneath the surface. At the water table flow becomes horizontal, and caves begin to form.
Tend to collapse in the dry season when caves empty of water- air provides less support than water, and so the caves collapse.
Thermokarst- form in areas where permafrost exists. Here, the presence of structures which produce heat will locally melt the permafrost, leading to localized subsidence.
Karst towers: Some areas have such extensive cave systems that subsidence is nearly complete. Occasional pillars of undissolved materials are left to tower above subsided landscape
Importance of Karsts: These underground caves provide 40% of groundwater to the US., and about 25% of World’s water supply.
Areas where this occurs:
River deltas: Rapid deposition of lots of material leads to settling of sediment grains into pore spaces= densification
Natural process: As areas subside, the delta breaches its levee and sedimentation occurs again in these low areas to raise height of the delta plain. People have altered this process by building stronger levees (New Orleans) or reducing sediment load by building dams (Nile River).
Affected areas: New Orleans, Nile Delta
Consequence: Coastline migrating landward. This brings wave activity closer to New Orleans, and so flooding hazards are increased.
Organic soils- high organic content leads to anoxia, which preserves the organic material. Organic material porous, and so it soaks up water like a sponge. If areas are drained, oxygen is reintroduced, and this decomposes the organic materials into water and CO2. Other processes: Burning the organic material, erosion.
Affected areas: Florida Everglades: 0.3-3 meters of subsidence. This has led to marine incursions into system, causing flooding and change in type of vegetation.
Expansive soils: Areas with expansive soils (tend to occur from weathered volcanic rock) and seasonal changes in precipitation cause soil to undergo shrink and swell periods. This occurs throughout the US Southwest.
Consequence: Pavement buckles, Foundations of structures settle unevenly. e.g. Do your doors stick during certain times of the year??
While this damage is slow and relatively mild in most places, the wide extent of damage leads to $Billions in damage annually.
Groundwater removal: California Central Valley. Groundwater pumping faster than aquifer recharge leads to loss of pore space by compaction- irreversible process! Locations where water removed then are lowered relative to the rest of the flood plain. Consequently, these areas are susceptible to flooding.
Chapter 13:Impacts and extinctions
Location= primarily between Mars and Jupiter
Largest = Ceres = 1000 km in diameter
Est. 50,000 over 1 km in diameter
We’ll talk about the consequences of being hit by one next time (tend to hit Earth at 20 km/sec)
Most orbit Solar System at distance of about 3 Astronomical Unit = (AU=Sun-Earth distance)
Asteroid Families (common parent body that broke up):
Themis = 2 degrees from ecliptic
Koronis= 3 degrees from ecliptic
Eos= 5 degrees from ecliptic
Brought into inner solar system through collisions with each other, so some cross earth’s path.
Dirty snowballs
Composition: ice>rock>gas
No gas (= no H + He) because too small = small gravitational force
Where they reside:
1) Kuiper Belt = Beyond Neptune, probably compositionally similar to Pluto
Short period comets = they are closer to Sun and so orbit once per several decades to several 100 years.
These are found in the ecliptic, and so are probably the outward extention of our planetary system.
These have nearly circular orbits.
Example: Halley’s comet = period = 76 years
nucleus = 8x16 km
Brought into inner solar system by gravity or collisions.
2) Oort Cloud objects. Long Period Comets
Distance = 10,000-100,000 AU
Distribution = uniform throughout celestial sphere.
In either case, for a comet to make its way into the inner solar system requires it to have veered way off course, through a collision or gravitational perturbation by a passing star.
The Physics of asteroids and comets (see powerpoint slides with details about speeds)
Kinetic energy = 1/2 x mass x velocity x velocity
So an object traveling 10x as fast as some other object carries 10 x 10 = 100x the kinetic energy
velocity rifle bullet = 1 km/sec
velocity asteroid ~ 30 km/sec = 900x the kinetic energy of the bullet!
velocity comet = ~ 45 km/sec = 1800x the kinetic energy of the bullet!
Gram per gram when compared with TNT
asteroid = 100 x TNT
10 km asteroid = 100,000,000 Megatons of TNT
a large hydrogen bomb = 1 Megaton
Total nuclear arsenal at end of Cold War =10,000 MT
So the asteroid = 10,000 x World’s nuclear arsenal!
(that’s a big bomb!)
Largely missing because of crust recycling (subduction via plate tectonics), erosion, the presence of an atmosphere (which causes many objects to blow up above the ground, rather than on it (recall Tunguska impact of 1908 over remote Siberia), or burial (deep holes fill in with sediment).
Moon has none of these processes, and so has preserved its cratering history since its early history (about 4.5 billion years). The Earth’s surface would look like the Moon’s surface if we had no atmosphere or plate tectonics.
Extinction Events- two primary ones:
separating the Paleozoic-Mesozoic Eras (called the Permian-Triassic Extinction) at 250 Ma; and
separating the Mesozoic-Cenozoic Eras (called the Cretaceous-Tertiary Extinction)
If you look at the lecture slides you will get some sense of the evidence associated with impacts- Iridium, glass droplets (spherules), craters).
The mass extinction events also have large mantle plume volcanic eruptions at about the same time, leading many scientists to consider them to be the cause of some extinctions. In this sense the Cretaceous-Tertiary extinction is atypical, as there is tons of evidence that this extinction was caused by an asteroid impact.
S08.110.L24
Chapter 10: Wildfires
What contributes to California wildfire disasters?
The stages of a wildfire
1) Preignition
Preheating (drives off water and other volatiles)
Pyrolysis (decomposes vegetation into simpler molecules that are easy to burn
(combined, preignition can be thought of as what happens when you burn the toast- first you drive off the water from the bread and then you char the bread, which is basically turning it into simpler chemical compounds (carbon).
Preignition is an endothermic reaction- it takes heat in from the surroundings to cause this to happen.
2) Combustion – burning the products created during preignition. This is an exothermic reaction- it releases heat during burning. This heat then promotes preignition in the nearby vegetation. Thus, combustion promotes the spread of wildfires.
3) Extinction- once the fuel is mostly gone, then the feedback of combustion producing more preignition decreases and then the fire dies out.
Wind brings oxygen into the combustion area, accelerating the burn. The wind will push combustion in a certain direction (downwind) and causes the flames to lean closer to the ground in that direction. This causes heat and radiation to reach the ground, causing preignition in the downwind direction.
Large-scale convection patterns develop in areas where crown fires (see below) occur. Air rises above the combustion and air rushes in from the sides to replace it. This produces very strong winds with this type of wildfire.
1) convection- circulation of gases (hot air away from combustion)
2) conduction – molecular transfer of heat
3) radiation- electromagnetic transfer of heat (think of this like sunlight- no atoms travel through space to bring us the sun’s heat…the sunlight travels here as light, which is a form of electromagnetic radiation)
Types of fires
Related to how the materials burn, and what kinds of materials are available to burn
1) ground- involves burning materials on or in the ground. Low flames and hence no significant convection associated with ground fires. They will move slowly and are difficult to extinguish.
2) surface – low vegetation canopy which also does not set up really significant convection patterns in the air. Consequently they burn somewhat slower.
3) crown fires- Travel high up in the forest canopy (note this pretty much means the fire has to be in a forest to be a crown fire). Crown fires spread from treetop to treetop, and develop very strong convection patterns which bring in oxygen-rich air, which further fuels the fire. Additionally, embers (burning fragments of wood) are entrained in these convection cells and this causes rapid spread of the wildfire.
Consequences of wildfires to the geology?
1) Soil erosion due to loss of vegetation cover (which holds together the soil, and shelters the soil from direct rainfall)
2) Hydrophobic soils- removal of the porous organic material leaves behind the rocky minerals only, and these have less porosity than does the organic material. Consequently, the ground tends to promote runoff of water rather than infiltration.
3) Very similar to 1), but following the soil downslope- tremendous sedimentation in downstream areas. But this tends to be short-term, since the removal of soil upslope leads to greater runoff. As the runoff moves downstream, it picks up the soil again and moves it further downstream. Solution to this is to replant an area quickly or to create catch basins to collect the sediment, rather than allowing the sediment to clog drain systems downstream.
Climate influences on wildfires- El Niño- La Niña cycles control the amount of water delivered to east and west Pacific regions. El Niño years= high rainfall for eastern Pacific (= North America), so more difficult for wildfires to spread (preignition has more water to remove). But El Niño = lower rainfall in the western Pacific Ocean, so Australia and Indonesia have their droughts when North America has its heavy rains. The reverse happens during La Niña- this causes lower than normal rainfall for North America, and consequently drought conditions (which leads to preignition).
S08.110.L25
Oil and natural gas
Middle East
California
CAFÉ = Corporate Average Fuel Economy. Note that the USA is the worst of the industrialized countries when it comes to fuel economy.
US consumption per day
1 barrel oil = 42 gallons
TOTAL = 20.0 mbl/d (million barrels/day)
motor gasoline = 9.0 mbl/d (44% of the total)
distillate fuel oil consumption was 4.1 mbl/d (20%)
jet fuel consumption was 1.6 mbl/d (8%)
residual fuel oil consumption was 0.8 mbl/d (4%)
Profits 2007:
Exxon-Mobil net profit last yr = $41 Billion ($479 B cap)
Google = $4.2 Billion ($186 B cap)
Microsoft= $16.4 (271 B cap)
Chevron = $18.5 (199 B cap)
Fossils fuels are nature’s way of storing energy from the Sun. Our burning these fossil fuels releases this energy. Plants and animals use the Sun’s energy to create complex molecules of H+C+O+N. Normally, these molecules break back down into their constituent parts. But if the organic material is buried quickly, then the molecules can end up in an anoxic environment and the molecules will not decay.
Often the minerals that grow in this environment are the anoxic minerals. Sulfide minerals can accumulate along side oil reservoirs and in coal beds. As a consequence, extraction of fossil fuels also brings out large quantities of metal sulfides, which oxidize as the surface to form metals and sulfuric acid (H2SO4), and burning fossil fuels also releases SO2. which combines with water to form sulfate (SO42-)
Fossils Fuel groups:
Coal
Natural gas (CH4)
crude oil
methane hydrates
20% of all energy consumption in the US.
Plant remains that do not weather (oxidize) because of environment of deposition
Peat
Lignite
subbituminous
bituminous
anthracite
Evaluated based on rank and sulfur content. These combined determine how much pollution will be caused by coal burning
[[13.3: Rank- how much energy is released when the coal is burned]]
[[Tab. 13.1: Sulfur content = high medium low]]
[[Fig., 13.2. Changing peat to coal]]
burial and heat change
peat -> lignite ->bituminous coal -> anthracite
Of these bituminous is the best to burn (most efficient)
But it also has the highest sulfur content of the coals
Sulfur the biggest environmental concern associated with coal burning.
SO2
can go into forming sulfuric acid (H2SO4) = acid rain
or sulfate aerosols= atmospheric cooling due to sunlight reflection (potentially a good side effect)
Sulfate emissions associated with fossil fuel burning = 3 main sources: United States, Eastern Europe, China.
Pattern of global cooling loosely associated downwind from sources of sulfate emissions
Suggested that volcanic eruptions a good analogy for sulfate emissions
Mt. Pinatubo, 1991 eruption: Release of huge quantities of sulfur (15 –30 million tons of SO2) into high atmosphere led to 2-3 years of global cooling of about 0.3 C.
[[13.4: coal reserves by continent]]:
US has about 25% of world’s coal
[[Fig. 13.8 – shows the maturation of oil with depth]]
Temperature ranges for oil formation = 60-120 C
Temperature range for gas formation 120-150 C
Geologic bodies involved in creating a hydrocarbon deposit
1) Source rock- several % carbon Sediments tend to be fine-grained clays
2) Reservoir rock coarse-grained rock with high porosity and permeability to accommodate migrating oil
3) cap rock- impervious surface that works to trap oil…without it the oil would migrate to the surface to form oil seeps (see Labrea Tar pits)
Because oil and natural gas are lighter than water, they migrate toward the earth’s surface until they hit a barrier.
[[Fig. 13.9- oil traps]]
trap = anticline or dome, fault, angular unconformity
- a trap is required to keep oil from floating to the surface; if one doesn’t exist, you end up with tar seeps. such as at La Brea tar pits in Los Angeles.
[[13.11. Location of major oil producing areas of the world]]
[[13.11. Location or major natural gas producing areas of the world]]
RUSSIA HAS MOST
Middle East next
Combined they have 70% of world’s supply
Global reserves: 1 trillion barrels
Present usage: 27 billion barrels / year
US consumption = 20 MBD = 7.3 BBY
= 40 years of supply
US production ~ 4 MBD = 1.5 BBY
We’ll use up the US oil reserves in about 50 years (at about the same rate that the World’s oil will be used up)
peak production expected = 2020 –2050
following this time prices will rise exponentially
= probably the biggest economic crisis the world has ever seen.
Note: Production cannot increase on existing oil fields significantly above present extraction rates; if you remove it faster, you will produce collapse of the oil reservoir and this will slow the migration of oil to the well (same as what happens to water in the California Central Valley (see subsidence lecture)
Perfect Storm of oil geology- lots of source rock, reservoir, caps and anticlines to concentrate it. Additionally, the burial history brought the oil to proper temperatures and pressures for oil to form.
Recall the Plate tectonic movement along the San Andreas Fault. While the restraining bend north of Los Angeles produced convergence and hence mountain ranges (thickening the crust), other places experienced releasing bends, which led to divergence and hence crustal thinning. It is within these thinned areas that basins formed, and within these basins were deposited sediments that were the source rock for oil.
This occurred during Miocene time (~25 Ma-10 Ma); these deep basins opened up and allowed high-productivity regions to develop and fill basins = Monterey Formation.
Found commonly on land throughout Southern and Central California (Note that the San Andreas is in the center of the state in Southern California…those areas to the west were shallow seas. But in Northern California the San Andreas is at the coast or offshore; hence the Monterey Formation is mostly at the coast or offshore here).
Estimate of California Oil reserves = 11 billion barrels = $1,325 Billion
Natural gas reserves ~ 19 Trillion cubic feet ~ $285 Billion
Combined we’re talking a $1.6 Trillion!
By comparison, all the gold taken out of California during the Gold Rush totaled about $100 Billion (= $0.1 Trillion).
S08.110.L26
We watched the first act of Spike Lee's 2006 documentary about New Orleans titled, "When the Levees Broke." You can view this documentary using the copy in the Library, or you can find the whole documentary divided into 14 segments on YouTube (roughly the first 4 = Act 1). There will be several questions on the final that any one who watched the documentary will be able to answer.
S08.110.L27
We're going to do a final exam review and then continue with Act 2 of "When the Levees Broke".There will be several questions on the final that any one who watched the documentary will be able to answer.
S08.110.L28
We will watch the third installment of "When the Levees Broke". There will be several questions on the final that any one who watched the documentary will be able to answer.