Download In-class Video Summaries - CSU

Intelecom (producer). 1992. Down to Earth, episode #1, from The Earth Revealed,
Annenberg Media, with James Sadd (Occidental College), 30 min.
http://www.learner.org/vod/vod_window.html?pid=312
This first episode gives an overview of Geology, and the topics to be covered in greater
detail, both in this class and the Earth Revealed video series.
Earth is unique in the solar system in its ability to support life as we know it:
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size – holds atmosphere (oxygen-rich atmosphere)
distance from Sun – appropriate temperature (liquid water)
Geology – study of the whole Earth
Two heat engines:
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internal – radioactive decay, creates convection
external – solar energy, creates the hydrologic cycle (major source of
erosion, rocks => soil)
Plate Tectonics – outer skin of plates floating on molten layer beneath
geologic (natural) resources –
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fossil fuels (petroleum, natural gas, coal), minerals (precious
metals), groundwater (thirty times as much as surface
waters), soil (lost by wind and water erosion)
reflection seismology – generate shock waves, record reflections
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remote sensing – large areas viewed at once (from space)
geologic hazards –
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earthquakes – little ability to predict
landslides and mud flows – destructive land movements
duel obligation of the geologist:
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to find resources, and to protect and promote their wise use
Knowledge of the Earth's function and history will permit the creation of products and
the understanding of processes that will help prevent damage due to geologic hazards.
Randall, Terri (director). 2010. The Pluto Files, NOVA, Public Broadcasting Service, Neil
deGrasse Tyson (host), WGBH Boston, 52 min.
https://www.youtube.com/watch?v=FvksfIDVGAA
In 2006, the International Astronomical Union (IAU) officially reclassified the planet Pluto, stripping it
from its designation as the ninth planet. This video looks at Pluto’s place in our Solar System, the history
of its discovery, and how subsequent discoveries continue to change our classification of objects that orbit
around our Sun.
Dr. Neil deGrasse Tyson, Director of the Hayden Planetarium (in New York City), is sometimes blamed
for “misfit” Pluto being demoted from planethood (after a boy noticed Pluto was moved - from where the
planets hang to a wall with the objects of the Kuiper Belt - and it was picked up by the press).
A scale model of the relative size (not distance) of the planets shows if the Sun were 8 feet across (a
weather balloon), Mercury would be a bead (2x Pluto’s size = 2x P), Venus a tiny rubber ball (5x P),
Earth a marble (6x P), Mars a half-inch gumball (3x P), Jupiter a kickball (62x P), Saturn a bowling ball
(50x P), Uranus a bocce ball (22x P), Neptune a croquet ball (21x P), and Pluto a ball bearing (1x P).
Drs. Brian Marsden, Mark Sykes and Owen Gingerich discuss the properties of Pluto. Oddities of Pluto
include: 1) Pluto is only 1,500 miles across, so would reach only from California to Kansas. Thus, it is
very small; 2) It also has less mass than the Moon; 3) It’s orbit is tilted 17 degrees, so it dives through the
plane where the other planets orbit; 4) Because the orbit is also elliptical, it crosses Neptune’s orbit, so that
it is sometimes closer to the Sun than Neptune is; 5) One of its moons (Charon) is very large compared to
the size of Pluto; 6) It is very far from the Sun (Pluto is 4 billion miles from the Sun, so no spacecraft has
visited it yet).
But, it is also like other planets: 1) It may have an atmosphere; 2) It has three moons; 3) It is round in shape
(a sphere, rather than potato-shaped like an asteroid); 4) It may have mountains or other world-like
features.
In 1894, Percival Lowell built a personal observatory near Flagstaff, Arizona, to find life on Mars. He
noticed the effect of some force (a gravitational pull) on other planets (i.e., Neptune’s orbit) that he
hypothesized was an undiscovered planet he called Planet X. Clyde Tombaugh was hired to clean up and
change photographic plates. Using a blink comparator he was able to find a dot moving across the sky, or
Planet X!
With the help of her grandfather, an English school girl studying the Roman gods suggested the name
Pluto. The abbreviation (PL) fit with Percival Lowell, who had hypothesized the planet, and even though it
reminded most people in the U.S. of a laxative call Pluto Water, the name was adopted. The image was
helped by Walt Disney and his studios (they not only had an inspirational film series, Man in Space, but
they also introduced a new cartoon character – Pluto the Pup).
Clyde Tombaugh became a local hero in his hometown of Straitor, Illinois. He became part of a small elite
group who have discovered planets (originally called planetes, Greek for wanderers): Polish astronomer
Nicolas Copernicus established that the Sun does not circle the Earth, but the Earth and Moon circle the
Sun. Italian Galileo Galilei discovered Jupiter’s four largest moons, and Dutchman Christiaan Huygens
identified Saturn’s rings and its moon Titan. Italian Giovanni Cassini discovered four more of Saturn’s
moons. Englishman William Herschel discovered Uranus, and German Johann Gottfried Galle found
Neptune, and American Clyde Tombaugh discovered Pluto. Tombaugh also constructed his own
telescopes! Since then, others (Mike Brown, David Jewitt and Jane Luu) have looked for outer solar
system objects in the icy Kuiper Belt (discovered by Jewitt). Brown has found three larger than Pluto,
including one he named Eris, after the Greek god of strife.
In Prague in 2006 the IAU decided that, by definition, a planet “must clear the neighborhood around its
orbit,” meaning that after 76 years Pluto was no longer a planet. However, hundreds of planetary scientists
do not accept this ruling.Alan Stern suggests that this new type of planet (the dwarf planets) are the
dominant class in the Solar System–“planetary embryos” that got blown out to distant reaches where they
cannot join with other material. The New Horizons spacecraft will arrive at Pluto in 2015, where we can
truly explore dwarf planets.
Dobis, John (executive producer). 1996. Atmospheric Circulation Classroom Videos,
Meteorological Bureau, 22 min.
https://www.youtube.com/watch?v=WXuGYSM2D8k
This short video describes how the solar heating varies according to latitude, causing rings of rising and
descending air around the planet. The spin of Earth on its axis creates latitudes where air is going from
faster speeds at the equator to slower speeds towards the poles, causing it to be pushed ahead of the
surface. Conversely, air traveling from the slowly turning poles towards the equator will lag behind the
surface movement. The combination leads to global bands of winds, which move through the seasons with
the Sun.
Heating of the atmosphere of Earth and other planets causes circulation that we experience as winds.
Steady bands of winds occur around the globe, though it is still difficult to forecast weather for an exact
location.
The global heat budget shows that solar energy is uneven, with the Sun directly overhead at the equator,
leading to concentrated sunlight (1 kW/m2) as opposed to the Sun’s angle (low in the sky) at higher
latitudes, which spreads the sunlight making it more diffuse towards the poles (0.5 kW/m2). The Sun’s
angle also increases reflection from the ocean surface and the ice at the poles.
Clouds reflect sunlight, keeping the planet cool (about 30% of sunlight is reflected).
We “bathe in the warm bath” of our atmosphere, with greenhouse gases (water vapor, carbon dioxide,
methane, etc.) absorbing the infrared radiation as it tries to escape back to space. In contrast, the Moon
with its minimal atmosphere has extremely cold nights and hot days.
The ground heats the air right at the surface via conduction, but the hot air rises as convection.
Evaporation carries heat energy up into the atmosphere where it is released by condensation.
Hot air (e.g., in a hot air balloon) causes convection, and leads to a pocket of low pressure, and wind
(advection) rushes in to replace it. Cold air in the evening sinks.
Because of Earth’s rotation, winds do not travel in a straight line. Cold air sinks at the poles, and rises at
the equator. However, as winds flow from the poles towards the equator, their slow rotation (inertia)
causes them to lag behind the spin of the surface, and they are deflected, causing easterly winds. This is
called the Coriolis Effect.
At the equator, hot air rises and moves towards the poles. Since the surface is traveling fastest here, if air
travels towards the more slowly moving poles, it will be pushed ahead. The lag of polar winds, and the
push of equatorial winds creates bands of westerlies (or roaring forties), trade winds (meeting at the
intertropical convergence zone), and the doldrums or horse latitudes.
Rising air creates bands of low pressure, with cloudy skies (as seen from space). Descending air creates
bands of high pressure, with dry cloudless skies, and global bands of deserts at 30 degrees.
Seasons are caused as Earth’s 23.5 degree tilt faces towards (N. Hemispherre summer) or away from (N.
Hemisphere winter) the Sun, or neither (fall and spring). As Sun moves north and south over Earth’s
surface, the bands follow, leading to monsoon weather.
Riddick, Iain (director). 2013. Earth from Space, NOVA, Public Broadcasting Service (PBS),
24 min. (total program time = 1 hour 52 minutes)
http://www.pbs.org/wgbh/nova/earth/earth-from-space.html
Earth-observing satellites reveal hidden information about how the Sun’s energy is transferred to
water and transported around the globe, producing weather and climate. By combining satellite
information with computer models and graphics, we can visualize Earth’s endless changes, in
which its spheres interact, and the local events triggered by these global interactions.
The Suomi satellite detects the massive influence of the Sun’s warmth by detecting the electromagnetic
spectrum beyond the very small portion (visible light) that we can see.
Information from Suomi shows Earth in shades of heat. Heat is reflected from the pole’s ice and clouds,
while the intense sunlight is absorbed at the equator.
Cape Verde Islands (off the west coast of Africa) show the influence of Sun’s energy on ocean water. The
Aqua satellite detects water vapor rising from ocean water that reaches 80 degrees F. These evaporating
invisible H2O molecules carry heat upward.
Heat (absorbed by evaporation) is released as air rises and cools, causing condensation into clouds (liquid
droplets). Clouds of up to 10 miles in height spin into a vortex, as a hurricane is born.
The TRIMM satellite uses microwaves to look at the internal structure of the hurricane, and reveals huge
vertical columns of warm water vapor (known as hot towers) which add water and energy into the heart of
the storm. This runaway reaction takes the storm to a category 5 in just 24 hours.
Hurricane Katrina has winds of 175 mph, and delivers 3 trillion gallons of rainwater, along with waves of
sea water (storm surge) that flood the Gulf Coast, leading to 1 million displaced people.
A diversity of environments across the globe appear to be unrelated, but staellites reveal their connections.
The GOES East satellite, along with other geostationary satellites, orbit around the Earth such that each
always looks down at the same given location on Earth’s surface.
Looking at the total water vapor, we can see how the sunlight energy shining on the equator is transported
towards the poles. The torrential rains in Mumbai are part of the Asian monsoon that is fed by this moist
air traveling away from the equator, and forming rain as it is forced up against high mountains.
Air forced over the Andes Mountains falls instead as snow (on the windward side of the mountains), drying
the air which then continues on to the extremely dry Atacama Desert (on the leeward side).
Moisture from the Gulf of Mexico moves north without any barriers, producing hot humid air in New York
City.
Though each of these local climates are different, they are all produced by the interconnected system of
Earth’s atmospheric movements.
Tibbon, T. and J. Locke (directors). 2012. Inside the Megastorm, NOVA, WGBH Boston,
53 minutes. (https://www.youtube.com/watch?v=sKNpqY1srPI)
The forces behind the formation of Hurricane Sandy, the preparation for the storm, and the devastating
impact it had on the New Jersey Shore and New York City are shown in this play-by-play account of how
the storm unfolded. The importance of heeding evacuation orders is shown. Rising sea level and an
unstable jet stream may mean that this storm is a sign of things to come.
October 22, 2012 a tropical depression turns into a tropical storm 120 miles south of Jamaica. Forming
over 80 F water, warm water leads to water vapor that condenses and releases the latent heat that powers
the storm. Historically, half of such storms become hurricanes, but only 1 in 20 will strike the East Coast.
The European Weather Center’s supercomputer runs a model that predicts the storm will head NW
instead of out to sea, putting the Jersey Shore and New York City in danger.
October 25, 2012 the winds have increased to 110 mph, making the storm a strong category 2 hurricane
that hits Jamaica, Haiti and Cuba, killing more than 70 people. The NOAA model still predicts that the
storm may take one of many paths, including coming ashore. Preparation begins in New York City.
The weather conditions are unusual. There is no (clockwise) Bermuda High to send the storm out into the
Atlantic. The hurricane goes over and feeds off of the Gulf Stream, which is 5 F warmer than usual. A
flight over the storm shows it is expanding (since waters are not cool enough to dampen it), and it is
combining with a n’oreaster, making a hybrid storm that is as powerful as a hurricane, but much larger.
A mandatory evacuation of low-lying areas is ordered, but 2011’s Hurricane Irene hit with little impact,
giving folks a false sense that the city will once again escape damage, and many refuse to leave.
An unusual high pressure area in the N. Atlantic creates a jet stream along the East Coast. This rapidly
flowing air sucks the storm towards it, slamming it into the coast right at high tide. Flights are shut down,
along with the New York Stock Exchange, and the transit system (both busses and subway).
The storm is 260 miles from the coast, but the water level is already 3 - 4 ft above normal, and there are 75
mph winds. 10 - 12 hrs before landfall, there are already record high flood levels. The Queen’s
Boardwalk, and the Far Rockaway evacuation area and the Breezy Point Community Center (both on a
barrier island) are all flooded. Long Island Sound funnels storm surge straight towards Staten Island.
Many people are stuck in these areas, with 20 thousand calls per hour coming into the 911 switchboard.
To prevent fires, the power is cut. When the eye wall of the storm hits Atlantic City, it causes > 40 ft.
waves and has 80 mph winds, tearing buildings apart. The Hudson Rivers floods the Battery Tunnel,
causing a huge explosion when salt water hits the underground electrical substation. Lower Manhattan
goes dark, leaving 3 million people without power. A house in Breezy Point bursts into flame, but fire
fighters are trapped by floodwater. When the water recedes, their fire engines start, but there is not enough
water pressure to fight the fire, and 100 houses are destroyed.
The aftermath of Sandy looks like a war zone. Ships are tossed on land, houses are knocked from their
foundations, the Jersey Shore resort area is wiped out, and 8 million people are without power. Some are
rescued, but others are not as lucky. 130 people are killed. Salt water must be pumped from the tunnels,
but the brine still damages wiring, etc. There are shortages of heat, food and gasoline.
Is this a once in 100 year storm, or does warming cause the wavy jet stream that will pull hurricanes on
shore? Warming does cause sea level to rise, and hurricanes may become fewer but more powerful.
Intelecom (producer). 1992. Birth of a Theory, episode #5, from The Earth Revealed,
Annenberg Media, with James Sadd (Occidental College), 30 min.
http://www.learner.org/vod/vod_window.html?pid=316
In the 1960s, earth scientists developed the theory of plate tectonics. This program traces the development of plate
tectonics, beginning with the contributions and methods of geologist Alfred Wegener. Sea-floor spreading,
continental drift, paleomagnetism, and the primordial supercontinent Pangaea are covered.
Earth is composed dynamic planet composed of an outer skin of rigid plates that slide
on molten layer beneath.
1912 -- Alfred Wegener first proposed the idea of mobile continents (evidence included identical rock
types, fossils, glaciation zones & minerals deposits that occur across ocean basins).
Gondwana was an early "supercontinent" of united current-day Southern Hemisphere continents.
Wegener could not adequately define a process that could account for the observed movement.
Hess ran his fathometer continuously during WWII, leading to his discovery of sea floor spreading, based
on his observation of guyots (submerged flat-topped seamounts) which were eroded away the further you
got from mid-ocean ridges.
Sea floor spreading occurs at mid-ocean ridges, with subduction occurring at deep ocean trenches along
ocean margins where the sea floor meets the continents.
Paleomagnetism reveals mirror images of periods of reversals in the Earth's magnetism on either side of
the mid-ocean ridges (in studies pioneered by oceanographers Vine & Matthews, Wilson & Sykes).
Spreading produces transform faults along the ridges to accommodate plate movement. Their existence
also demonstrates spreading is occurring (as studied aboard the R/V Glomar Challenger).
Robert & Palmer introduced the term "Plate Tectonics" which is considered to be the unifying theory of
Earth Systems Science, although questions remain about the mechanisms & processes underlying plate
movement.
PBS (producer). 1995. Plate Tectonics: The Hawai’ian Archipelago, NOVA, from Hawai’i
- Born of Fire, WGBH, 5 min. http://www.teachersdomain.org/asset/ess05_vid_hawaii/
Most of the phenomena associated with plate tectonics occur along the plate boundaries, including
volcanic eruptions. However, the Hawai’ian eruptions do not fit this pattern. These eruptions are thought
instead to be associated with a phenomenon known as a hotspot. This short video clip shows how the
placement of the volcanic island chain is thought to trace the movement of the Pacific plate over a
stationary plume of magma.
The Hawai’ian islands are not part of those that ring the Pacific.
They are instead formed over a fixed plume of superheated rock (magma) that comes up through the
mantle and reaches the surface as a hotspot. Such plumes rise from the core or an area of high
radioactivity.
Where the magma erupts through the sea floor it creates new land, leading to the world’s largest volcano,
Mauna Loa, and its neighbor, Kilauea.
The Pacific sea floor is slowing drifting NW over the fixed hotspot creating a chain of volcanoes (an
archipelago).
The plate has been moving for 70 million years, leading to a series of submerged extinct volcanoes, and a
new volcano (Loihi) which won’t reach the surface of the ocean as an island for a couple of thousand of
years.
PBS (producer). 2009. Earthquakes in the Midwest, NOVA Science Now, with Neil
DeGrasse Tyson (exec. ed.), WGBH, 13 min.
http://www.pbs.org/wgbh/nova/earth/earthquakes-midwest.html
Another instance of tectonic phenomena not associated with plate boundaries are earthquakes in North
America’s Midwest. Unlike California quakes, which occur where plate margins slip past or under each
other, these large dangerous quakes occur through processes that aren’t well understood. Evidence from
caves show that they have been happening for thousands of years, and a big dangerous quake will
undoubtedly happen again, perhaps in the near future.
When tension along the edges of a tectonic plate gets too great, the plates slip causing an earthquake. But
another mechanism may cause a big dangerous quake in the heartland of America.
Deep in a cave in Illinois, stalagmites may reveal information on the biggest looming quake in the U.S.A..
200 years ago, the region near Memphis, TN (New Madrid, MO) was rocked by 3 huge quakes (18111812), though no big cities existed there at the time. These were some of the biggest quakes in North
America, and were felt from Mexico to Canada.
These quakes show up in the shifts of the rings of layers of crystal that form as the drips from the ceiling of
the cave that deposit them move because of the quake. Chemical analysis of the crystals is used to
determine the date of the layers, showing that there is a pattern of quakes that has been going on in the New
Madrid Seismic Zone (NMSZ) for 15,000 years.
200 small (imperceptible) quakes a year show that the region is very active, as it sits over a “failed” rift
zone. Moreover, sediment in the Mississippi River bed shows deformed layers that are outside the NMSZ,
suggesting that the quake area may jump again. A repeat of these large quakes would be catastrophic,
with 12 million people in the area under- (or un-) prepared and unaware.
Intelecom (producer). 1992. The Sea Floor, episode #4, from The Earth Revealed,
Annenberg Media, with James Sadd (Occidental College), 30 min.
This episode examines major sea-floor features: the mid-oceanic ridge, oceanic trenches, and fracture
zones; evidence of Earth's mobile crust.
The ocean floor is an environment with no light, near freezing temperatures and crushing pressures.
Specialized submersibles and remote techniques must be used to explore “planet ocean.”
Water from volcanic steam and melting comets filled ocean basins (made of relatively thin, but heavy
basaltic rock that sinks below the level of the granitic continents); and runoff weathered the land, adding
salty chemicals.
Gently dipping, shallow continental shelves (2 – 70 km wide) comprise one sixth of Earth’s surface.
These extend out to the continental slope (steep) with submarine canyons (valleys), continental rise
(gradual, with fans of debris), and abyssal plain (flat).
The ocean bottom is continually showered by a gentle “marine snow” of pelagic sediment made of
organisms’ shells, dust, and clay particles.
Volcanic peaks (lava hills and larger seamounts) dot the seascape. A long, connected system (“baseball
seam”) of volcanic mid-ocean ridges have crests with central valleys formed by fissures filled by undersea lava flows, making for a young sea floor (only 200 million years old vs. 4 billion year old continental
crust).
Stromatolites (fossilized microbial colonies of marine algae) and sedimentary rock of marine origin that
have been uplifted on the continents give evidence that oceans existed early in Earth’s history. Where is
the older sea floor?
As new sea floor is added at the mid-ocean ridges (sea floor spreading) the older sea floor moves outward,
with the oldest sea floor back sinking back into the mantle at subduction zones, resulting in underwater
trenches (where the sea floor is pulled down sharply to deep depths).
Oceanographic sampling of the sea floor includes retrieval of sediments with grabs and corers.
Echosounding (used to detect enemy submarines) bounces sound waves off the sea bottom landforms.
This technique provided the first 2-D profile (return time = depth) of sea floor topography.
1983 – “Gloria” sonar technology towed behind the ship, combined with satellite location (Global
Positioning System or GPS) provided a mosaic of images used to determine the composition of the sea
floor for the Atlas of Exclusive Economic Zone of the United States (200 miles from the shoreline,
including rights to oil, gas, and minerals (e.g., manganese nodules)).
Harvest of resources may be difficult (especially in the deep sea), and environmentally damaging.
The oceans host unique forms of life. At the mid-ocean ridges, hot vents on the sea floor (up to 350°C, but
doesn’t boil due to high pressures) have organisms living on chemical energy from hydrogen sulfide
(energy from the interior of the Earth rather than external sunlight energy) at these deep sea hydrothermal
vents.
Understanding the sea floor will helps to determine the influence of oceans on global climate change.
Intelecom (producer). 1992. Sedimentary Rocks: The Key to Past Environments , episode
#17, from The Earth Revealed, Annenberg Media, with James Sadd (Occidental College),
30 min.
The exposed layers of sedimentary rock at the Grand Canyon and elsewhere allow scientists to peer into the geologic past. This
episode explores the movement of sediment and its deposition, along with the processes of lithification, compaction, and
cementation that produce sedimentary rocks. The organic components of rock are also discussed.
Two billion years of Earth’s geologic history is recorded in the sedimentary rock of the Grand Canyon,
Arizona, revealing conditions at the time the sediments were deposited (climate, vegetation, position of
shoreline, etc.).
Sediment is the product of chemical weathering and mechanical/physical weathering (forming clastic
sediments), biological activity, and wind, water and ice erosion.
Size categories include (in decreasing size): boulder (rock), cobble, pebble, sand, silt and clay (the
consistency of flour).
The primary surface of Earth is composed of compacted layers of sediment formed into rock.
Particles become smoothed and rounded during transport by wind, water, gravity, etc.
Deposition occurs where water slows, with coarse grains dropping out first (sand along the beach; with
mud and clay dropped further offshore).
Lithification occurs when compaction rearranges and distorts the particles, and cementation (by
dissolved minerals in the pore space) binding the particles together into rock.
Warm or shallow waters (desert lakes, lagoons) may lead to the precipitation of evaporites that form as
minerals come out of solution (e.g., calcite, gypsum, or salt deposits).
Biological processes form limestone by way of the accumulation of calcium carbonate from the “shells”
of dead plants, algae and animals (e.g., chalk). Diatoms and radiolarians produce glass “shells” that form
chert and diatomite.
Accumulation of vegetation in bayous and swamps leads to deposits of peat, which with time and pressure
are transformed into coal.
The principle of uniformity states that processes today are the same as in the past, thus you can interpret
past environments at the time of sediment deposition; the law of original horizontality states sediments
are laid down/settle in the water column in horizontal layers (with gravity).
Ripple marks, mud cracks and other features record other aspects of the ancient landscape.
The Ridge Basin (between San Andreas & San Gabriel faults) shows evidence of opening and filling with
water (i.e., a spreading zone).
Valuable resources can be derived from sedimentary rock, including limestone for cement, sand, gravel,
iron ore, bauxite for aluminum, and materials needed to manufacture brick, tile, and asphalt.
Intelecom (producer). 1992. Waves, Beaches and Coasts, episode #24, from The Earth
Revealed, Annenberg Media, with James Sadd (Occidental College), 30 min.
This program shows the dynamic interaction of coast and the energy of the ocean. Wave types, parts, movement, and their
impact on the shore are illustrated. The program also covers shoreline characteristics, currents, erosion and deposition, and
discusses how the greenhouse effect could impact sea level and coastal lands.
Winds transfer energy to the water as waves – a surge of energy that is then transferred to the coast by surf.
Water in waves takes a circular motion (lifted up and forward, return down and backward) with diameter at
the surface equal to wave height. The wave base (beyond which no movement occurs) is one half the
wave length.
Waves are slowed by the ocean bottom, steepening the wave until it breaks as surf.
A seismic sea wave, or tsunami, is much more powerful than wind-generated waves, bringing destruction.
A wave front will bend (refraction) due to the local decrease in velocity of wave that hit bottom first, thus
decreasing the angle at which waves come onshore. Waves wrap around headlands (wearing them away)
and disperse into bays (filling them with sediment).
Waves approach the coast at an angle, and return with gravity, leading to a zig-zag motion, with the overall
flow along the coast in a longshore current. Sand is deposited as an extension of the beach (a sand spit)
and behind breakwaters, so that they must be dredged.
Low, gentle summer waves lead to a wide gently sloping beach, while energetic winter waves produce a
narrow steep beach. Streams and rivers, and erosion of the coast add sediment to coastal waters. Dams
trap river sediments and deprive beaches of sand.
People soon forget severe storms that happen every few decades, and build along the shore. Sea walls built
for protection are a threat to beaches (they cut erosion, thus decreasing the sand supply), and are undercut.
Water tank studies show irregular shapes, like natural features, help prevent undercutting by waves.
Transporting sediment around dams or reintroducing sand from inshore sources may help feed beaches.
Tides are the work of the Moon (and to a lesser degree, the Sun). These bulges of water towards and away
from the Moon can cause severe flooding when high tides occur at the same time as storms. Tides ebb and
flow two times per day.
There is a more than 100 m rise in sea level (a eustatic change) since the peak of the last ice age. There is
a small but steady worldwide increase in sea level with the warming of the global climate.
The greenhouse effect occurs because water and carbon dioxide re-radiate infrared radiation back to Earth.
Tremendous quantities of carbon dioxide have entered the atmosphere because of the historic burning of
coal, gasoline and oil. An increase of a few meters in sea level will flood coastal communities.
In general, living along the coast brings with it a risk of change, since this is a dynamic area, making
coastal management very important.
Williams, M. (producer). 2005. Tsunami: The Wave that Shook the World, NOVA,
WGBH Boston, 52 minutes. (http://www.pbs.org/wgbh/nova/tsunami/anatomy.html)
December 26, 2004, a magnitude 9 earthquake off the coast of Sumatra triggered destructive waves of
water that killed over 250,000 people across regions bordering the Indian Ocean. Understanding the
origin and nature of this destructive force is necessary to prevent similar loss of life in future events.
Subduction has been occurring for 40 MY at an oceanic-oceanic convergent boundary 155 miles from
the Indonesian island of Sumatra:
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stick-slip friction built up along 700-mile long boundary between tectonic plates
underwater margin of the plate snapped back, causing a 4 minute shallow earthquake (with a 30 km
focus) that was 30 times more powerful than a magnitude 8 quake
disturbances occurred in all world oceans
The Pacific Tsunami Warning Center established after the 1949 tsunami in Hilo, Hawaii monitors a
network of seismic stations, ocean floor pressure sensors (with relay buoys) and coastal tide gauges in
the Pacific Ocean. No such network exists in the Indian Ocean.
A wave travelling almost 500 mph hit Banda Aceh, Indonesia 15 minutes after the quake.
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amplification – front slows in shallow water, rear catches up => height increases
water recedes – as much as 1 mile exposed as the wave draws water off the land
wall of water – 1 cubic meter of water weighs a ton => massive surge throws debris
water drains back to sea with equal force
Gentle slope of sea bed off of Kamala Beach allows water to travel onshore for kilometers.
Staff at the Pacific Tsunami Warning Center did not know who/how to warn Asia. However, Africa was
warned via diplomatic channels. Kenya’s coast was evacuated - only one death occurred.
Earth’s rotation was influenced by changes caused by rapid subduction of 10 m of oceanic crust:
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mass is out of balance – produces a 2 cm wobble (like an unbalanced tire)
faster spin – shift in the center of gravity reduces day length by 3 millionths of a second
causes of tsunamis –
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earthquakes – tectonic displacement
asteroids – relatively rare, but possible
volcanic eruptions – near or below the surface of the water
landslides – a Cumbre Vieja (Canary Islands) slide could effect entire east coast of U.S.
Pacific NW coast of U.S. has a subduction zone similar to Sumatra where very large earthquakes occur
once per 500 years. The last such large quake occurred 300 years ago.
Oregon State University’s wave tank is devoted to tsunami research. 32 new buoys will be added to the
system, but education is also needed to make warnings effective.
Lee, Spike. 2006. When the Levees Broke: a Requiem in Four Acts, Act #1, HBO
Documentary Films, 55 min. (255 min. series)
https://www.youtube.com/watch?v=12xj1sHvIWA
This documentary film covers the human dimension of Hurricane Katrina. Meant for mature
audiences, the film includes strong language and scenes of human suffering, tragedy and death.
Some of you may have or have had first-hand experience with a hurricane during your lifetime. Others of
you may (now or in the future) be in decision-making capacities during similar life and death
situations. Reflecting on how people responded to this massive storm may assist you in better
understanding, and in dealing with such natural disasters.
After viewing the first 55 minutes of this documentary, you should be able to answer the following
questions about one of the most devastating weather disasters in U.S. history:
When was the City of New Orleans told to evacuate? Who gave the order? Was it voluntary or
mandatory?
What category on the Saffir-Simpson scale was Hurricane Katrina at its maximum? When did it make
landfall?
What happened to parts of the roof of the Superdome?
When Hurricane Betsy hit New Orleans in 1965, what was done to the levees? Why?
How high did the water get in some areas of the city?
Which government agency was most responsive to the emergency? Why do you think they were effective?
What extreme weather conditions affected people after the storm?
The majority of rescues of people stranded by flooding were done by the "Cajun Navy." Explain.
Not only did storm surge (ocean waves) batter the levees from the southeast, but consider how the
northwest movement of water-laden air caused Lake Pontchartrain to flood the various canals, contributing
to the collapse of the levees.
(See http://www.nola.com/hurricane/popup/nolalevees_jpg.html for more detail).