The Hydrosphere ...an overview
A brief overview of the fluid system of our planet.
This page is still under construction - please be patient!
If there is magic anywhere on Planet Earth, it's in the water.
Water is a di-polar molecule. This results from the arrangement of the hydrogen atoms (which meet at a 105° angle across the oxygen) and gives water a slight electrical charge.
Surface tension: Water's polarity results in a slight electrical charge, which causes water molecules to be attracted to other water molecules.
Basically, water carries with it a glue which it uses to gum up the works.
Water and Gravity:
Water is stuff and is therefore subject to the laws of physics - including gravity.
Water contains an immense amount of gravitational potential energy, which is converted to kinetic energy when the water is allowed to move.
This kinetic energy is used to perform all sorts of work: from the transport of sediments to turning electric generators in hydroelectric plants.
Thermal properties: Water has a relatively high specific heat. This means that it changes temperature very slowly.
Because of this, any large body of water (like the ocean) tends to act as a "thermal storage unit" which can be used to store and transfer heat energy, and moderate climates.
All substances can exist in either the solid, liquid, or gaseous (vapor) phase.
Changing from one phase to another requires the addition or removal of heat energy.
Ice + heat ð Water + heat ð Steam
Water is the only known substance which can exist in all three states at normal surface temperatures and pressures.
Water and density: As a substance loses heat energy, molecular motion slows and the atoms come closer together. This results in a higher specific gravity (mass/unit volume). All known substances abide by this rule, except for water.
The density of water does increase as it cools (as it should), but at 4°C the density vs. temperature graph goes the other way and the density actually begins to decrease.
This decrease continues until the solid state is achieved (at 0°C), at which temperature the density vs. temperature graph resumes its normal trace.
This "magic" property of water is no small thing. Think of what would happen if ice was more dense than water.
Humans, as well as the vast majority of life as we understand it, are composed almost entirely of water (approx. 70%).
Without a constant and secure water supply, life as we understand it will not continue.
Water at the cellular level is very important. If our cells dehydrate they die (and so do we).
In addition, water imbalances at the cellular level can occur due to exercise, dehydration, freezing, and other factors. This can result in water/salt concentration problems which can lead to cramping, and ultimately death of the affected cells.
As weird as it sounds, if you want to lose weight drink a large amount of water. If your cells are used to getting an ample supply of fluids, they tend to store less (so you have less "water weight"). If your cells are constantly threatened with dehydration, they will tend to stockpile additional water supplies, increasing your weight. In addition, your body needs water to metabolize fat - if you're dry, the fatty foods that you eat cannot be broken down.
Geologists theorize that liquid water has existed on earth from very early in geologic time.
Some of the oldest known rocks (>4 billion years old) were originally deposited as sediments in water. This means the rivers and oceans had to have existed at that time.
Originally, scientists thought the earth's water came from the earth itself, usually from volcanic eruptions, and it is certain that some water comes from these sources.
Recent work indicates that some (possibly most) of the water on earth may have arrived from extra-terrestrial sources in the form of comets (basically giant snockballs in space).
It is assumed that there were many more cometary impacts early in the earth's history, and that these led to the addition of massive amounts of water during the early stages of the earth's formation.
The overall volume of water on earth, while clearly not static in the long term, can be considered constant at human time scales.
However, the spatial distribution of water can and does change constantly, moving between numerous "temporary storage units."
These include the ocean (obviously the largest), glacial ice, groundwater, streams, lakes, the atmosphere, organic material, Pepsi cans, and many, many others.
The earth's atmosphere is composed almost completely of nitrogen (78%) and oxygen (21%), with trace amounts of several other gasses.
Water also occurs in the atmosphere (commonly in the vapor phase). The amount of water vapor varies greatly, depending on a multitude of factors.
The evaporation of water requires the addition of 80 calories of thermal energy per cubic centimeter. This heat energy is robbed from the local environment, and is stored in the vapor.
This heat energy remains locked up in the vapor until conditions change and the vapor condenses into the liquid phase, releasing the energy back into the environment.
This addition and loss of energy results in a global energy transfer which affects our lives, and the earth processes which make life possible (and pleasant). For example:
Perspiration: When our bodies sweat, the water which evaporates from our skin obtains the heat energy necessary for the phase change from the skin, cooling our bodies.
In comparison, dogs have no sweat glands, so they have no cooling mechanism. That's why they pant so much - all cooling comes from evaporation of water from their tongues.
Global energy transfer and temperature moderation: Far more solar energy is received on earth at the equator than at the poles. Excess heat energy is used at the equator to evaporate seawater, which is then transferred north and south to mid-latitudes, where it condenses, rains, and gives up the heat to areas which need it. This tends to moderate surface temperatures on earth.
If you don't think this is important, try living on Venus or Mars, there temperatures can vary by several hundred degrees from sunlight to shadow, and day to night.
Adiabatic cooling and rain shadow deserts: As warm, moist marine air masses move onshore and rise up over mountains (like the Cascades) they are cooled at a rate of 5.5F°/1000' of vertical lift (called the "dry adiabatic rate").
This cooling continues until the temperature drops to the "dew point" when condensation begins. Above the dew point the temperature drop is reduced to 3.5F°/1000' (the "wet adiabatic rate") due to the additional heat energy released by the vapor as it condenses back into the liquid phase.
As the air mass (which is now dry) descends the far side of the mountain, it heats back up at the dry adiabatic rate, resulting in a warmer and drier air mass on the lee side of the mountain.
Looking at the surface of the earth in simple terms, there are really only 2 topographic levels (elevations) - above and below sea level.
The portion above sea level gets beat on by all kinds of natural (and unnatural) processes, while the portion below the ocean is relatively protected from the ravages of nature (and humans).
Weathering is the process of breaking down rock material under surface conditions.
Water and pH balance: Water has a pH of 7, and is therefore neither (or both) an acid or base.
Because of this, water is considered a "universal solvent" which will, if given enough time, chemically attack any and all substances.
There are three main types of weathering which affect rocks, minerals, and other substances at the surface of the earth. Each type is directly affected by water, and they are interrelated, working together to reduce the mountains to rubble.
Mechanical (physical) weathering: this involves several processes, all of which result in smaller pieces of material which are compositionally identical to the original.
Frost Wedging: Water expands in volume by 10% when it freezes. This expansion results in incredible pressure on any container the water might be in.
If water seeps into cracks in rock and freezes, this expansion literally blows the rock apart.
Obviously, frost wedging doesn't work worth a darn in the tropics. It is also relatively ineffective at the poles, where the water freezes once, and then never melts. It is most effective when daily temperatures ("diurnal temperature fluctuations") vary above and below the freezing point of water.
Abrasion: Moving water carries sediments (small to large pieces of stone) which can act like hammers and sandpaper (depending on the size of the pieces), wearing away the bedrock of the stream (as well as further breaking down the sediments themselves). This is how streams carve the valleys they flow within.
Chemical weathering: This also involves several processes, all of which result in smaller pieces of material which are compositionally different from the original.
Water is considered a universal solvent, and over time will chemically weather anything. This results in the chemical disintegration of rock - the earth's crust is basically being dissolved.
Chemical weathering is also affected by temperature.
Warm and humid conditions increase the efficiency of chemical weathering processes.
Biological weathering: Living organisms (usually plants) can effectively wear away rock in many ways, usually by causing mechanical and/or chemical weathering processes to occur.
Roots can grow into cracks and mechanically weather the rock by prying it apart.
Acids produced by plants can chemically weather the rock. This is especially common in the mosses, etc., which are often the initial weathering agents of exposed stone.
Disintegration of organic remains also can produce acids which will weather rock material.
Erosion: Erosion is the process of moving weathered rock material downslope to a stream or river.
Erosional processes range from the subtle "creep" of the upper soil layer (my personal favorite) to more spectacular events, such as rockfalls and mudslides (also lots of fun).
While the primary erosional force is generally gravity, water acts as both a catalyst and lubricant for most of the processes.
It is important to note that all surface materials are subject to weathering and erosion - nothing will last forever!
Water always moves downslope under the influence of gravity, and collects in the low spots.
Concentrated downslope movement of water in defined channels is called a stream (or river).
Water will continue along the stream channel until it reaches a low spot which has no outlet (called a "base level").
The ocean is the ultimate base level, but there can be temporary base levels along the course of a stream (such as a lake).
Moving water can perform many important tasks due to its kinetic energy.
One important process is the transportation of sediments from areas above sea level to (ultimately) the ocean.
The ability of water to transport sediment is affected by the mass (amount) of water and its velocity, and is expressed by the formula Ek = 1/2mv2.
Note that in the formula velocity is squared, which means than any increase in velocity results in a large increase in the amount of energy.
Water velocity is affected by several factors, and can be expressed by the equation V=Q/A (where V=velocity, Q=discharge, and A=cross-sectional area of the channel).
Basically, sediments are transported when the velocity of the water is increased, and deposition occurs when the velocity drops.
This velocity differential is expressed both locally along a stream or river due to variations in channel geometry, and seasonally due to increased and decreased discharge.
Streams can transport sediments produced by both mechanical and chemical weathering.
Mechanically weathered sediments (called clasts) are transported as small to large pieces of rock in the water.
This material can be seen and separated from the water by several processes (screening, reducing velocity)
Bed load vs. suspended load: Bed load is the big stuff which is too large to be completely picked up by the stream and bounces along the bottom. Suspended load is the smaller stuff which completely loses contact with the bottom of the channel.
It is important to remember that "big" and "small" vary greatly and are completely dependent upon the velocity and discharge of the water. In a major flood, a large boulder which is usually part of the bed load may well become part of the suspended load. This is why it's usually not a real good idea to go swimming when the river is in flood stage.
Chemically weathered material is dissolved in the water and cannot be seen or separated from the water.
In most cases, this "dissolved load" can only be separated when the water is evaporated, leaving the dissolved material behind (ex. salt flats in an arid environment).
Streams evolve (both spatially and temporally) from "youthful" to "mature" to "old age."
Youthful streams have steep gradients and steep, V-shaped valley walls. The tend to occur in the mountains.
Mature streams have lower gradients and less steep valleys. They tend to occur in the foothills.
Old age streams have poorly defined channels, a very low gradient, extensive flood plains, and commonly meander. They tend to occur in the lower reaches of the river, usually near its mouth.
Groundwater is fluid which occurs beneath the surface and occupies open space in the rock of the earth's crust.
Groundwater supplies a vast amount of drinking, industrial, and/or agricultural water for many parts of the world.
In arid lands, often the only secure and constant water source is in the ground.
There are two main factors which affect the storage and movement of groundwater:
Porosity: the percentage of open (pore) space in a rock.
The greater the porosity, the greater the volume of fluid which can be contained in the rock.
Permeability: the size of the pore spaces, and the degree to which the pore spaces are interconnected. If the pores are too small, or are not connected, the movement of the fluid will be restricted.
The greater the permeability, the easier the contained fluids will move through the rock.
Porosity and permeability are especially important when assessing the potential of water, oil, or gas wells. If both are good, the well will be good. If one or the other is poor, the well will be poor.
An "aquifer" is a rock layer which will hold and transmit water, while an "aquiclude" is limited by either porosity or permeability (or both) and will not hold and/or transmit water.
Aquifers occur at varying depths in the crust, but all are relatively near the surface. At greater depths the earth's internal temperature and pressure make the occurrence of water impossible.
Recharge: all aquifers lose water (naturally or through pumping). Recharge is the addition of new water to the aquifer. In a balanced situation, the recharge equals the loss, and the aquifer is maintained at a relatively constant level.
Near-surface aquifers recharge seasonally but are subject to contamination, while deeper "bedrock" aquifers are relatively safe from contamination, but recharge very slowly.
The recharge rate of many deep aquifers is so slow that they are in reality non-renewable resources, and pumping of water from them can be considered "mining" of the water supply.
Unfortunately, in many parts of the world these "water mines" are rapidly depleting water supplies which have taken thousands of years to develop and will not recharge in our lifetimes. This is an excellent example of how short-term gain will lead to long-term disaster.
Glaciers are just ice cubes that form naturally and are so large that they flow internally.
Glacial ice acts like a plastic. It can flow (slowly), at rates measured (usually) in centimeters per day.
Glacial ice forms in areas where winter snowfall exceeds summer snowmelt.
Snowline: the elevation which marks the limit of the year's permanent snowfall. Above this elevation, summer temperatures are so low that snow from the previous winter does not melt.
Zone of Accumulation: above the snowline, where the glacier gains mass.
Zone of Ablation (or Wastage): below the snowline, where the glacier loses mass.
Glaciers can advance or retreat, depending on the climate. This is immediately apparent from yearly observations of the snowline. If it lowers in elevation, the glacier will advance.
There is very little fundamental difference between a glacier and a series of sedimentary layers.
Both represent layered accumulations of material which are laterally extensive, with the younger layers on top and older layers on the bottom (Law of Superposition).
Glacial ice: Every winter's snowfall adds a new layer of "raw material."
Snow converts to granular ice (called "firn" or "Névé") which then converts to glacial ice (a true metamorphic process).
It takes about 30 meters (100 feet) of snow/firn to achieve enough pressure to make the final conversion to true glacial ice and initiate internal plastic flow.
At the upper end of an alpine glacier the ice is confined to the lower portion of the glacier where the pressure is great. Above this is firn, with recent snow covering the surface. As the same material creeps very slowly down the valley it changes more and more to ice. Below the snowline, the greater warmth of the lower valley may destroy the snow cover, so that in late summer many glaciers carry no snow at their lower ends.
There are 2 general types of glaciers: Alpine (valley) glaciers, and Ice Caps (continental ice sheets).
Alpine Glaciers: The most common conception of glaciers, found in mountainous regions like the Alps or Canadian Rockies. Such glaciers occupy mountain valleys, and as such have clearly defined lateral margins, as well as a beginning and end.
Ice Caps: In colder latitudes (polar regions) ice may form a broad sheet covering an area of relatively low relief (or even a rough surface) to such a great depth that all topographic features are obscured.
Such broad expanses of ice differ from alpine glaciers in depth, lateral extent, and the absence of clearly defined margins.
Such ice caps now cover Antarctica and Greenland, and reach depths in excess of 3000 meters (10,000 feet).
General notes concerning glacial erosion: Glaciers and are very efficient agents of weathering, erosion, and transportation. Unlike streams, they are characterized by non-turbulent flow, and can even flow up and over topographic highs.
Debris in the Ice: Glaciers are incredibly efficient erosional agents, and have the capacity to carve deep valleys. The eroded material is carried along by the glacier until it is either deposited along the margins, or dumped off the end.
Material carried at the base acts as sandpaper, scratching the valley floor if the pieces are large (leaving striations), and polishing the bedrock if the pieces are fine grain.
Debris on the Ice: Alpine glaciers derive much of the debris they carry from the steep side slopes of their valleys when rocks roll down onto the ice.
The very nature of a continental glacier limits the amount of this surface material. Only an exceptionally tall mountain (called a "nunatak") may rise above the ice. Continental glaciers, therefore, carry little or nothing on the surface.
General notes concerning glacial deposition: A moraine is a deposit of material (rock/gravel) at the toe or along the margins of the glacier.
Ground Moraine: a wide-spread surface covering of glacial debris dropped by a glacier during rapid retreat.
The thickness of ground moraine can vary from a trace to 100's of feet.
Terminal Moraine: Deposits made at the edge of the ice which cover much less area than that of the ground moraine but are locally much more prominent. When an advancing glacier melts at the edge as fast as it advances, the debris which it carries is deposited at the margins. If the edge of the ice remains on the same line for many years this material accumulates in a ridge called terminal moraine.
Alpine glaciers tend to accentuate the topography. Erosional and depositional features include:
U-shaped valleys: the result of glacial erosion versus V-shaped valleys which are characteristic of stream erosion in alpine regions.
Truncated spurs: lower parts of ridges that have been carved into triangular facets by glacial erosion.
Arête: A glacially carved ridge separating two or more major glacial valleys.
Hanging valleys: tributary glaciers are generally smaller that the trunk glacier they flow into, and have correspondingly less capacity for erosion. When the ice melts, the tributary valley is left higher on the valley wall, and is commonly the site of a waterfall. Yosemite Valley is famous for hanging valley waterfalls.
Cirque: a steep-sided, rounded hollow carved into a mountain at the head of a glacial valley.
Tarn: a small lake filling a cirque.
Paternoster Lakes: chains of down-valley lake filling depressions carved by glacial plucking and other remnants of differential erosion.
Horn: a sharp peak remaining after cirques have cut back into the mountain on several sides. An example is the Matterhorn in the Swiss Alps (or is it at Disneyland?).
Grooved and striated bed rock: rocks carried by the glacier carve tracks into bed rock.
Continental glaciers tend to subdue the topography. Erosional and depositional features include:
Rounded mountains - the Canadian Shield has been flattened by the most recent period of glaciation.
Grooved and striated bed rock: rocks carried by the glacier carve tracks into bed rock.
Till: unsorted and unlayered rock debris carried and deposited by a glacier.
Moraine: a body of till carried within a glacier and left behind after the glacier has receded. New York's Long Island was built up by morainal debris, most of it probably scoured out of New England.
Lateral moraine: a ridge-like pile of till along the sides of a glacier.
End moraine: If the terminus of a glacier remains stationary for a period of time a distinct ridge of till piles up along the front edge of the ice.
Terminal moraine: the end moraine marking the farthest advance of a glacier.
Ground moraine: a fairly thin, extensive layer or blanket of till dragged along by a glacier and deposited as the ice melts.
Drumlin: ground moraine reshaped into streamlined hills formed by an ice sheet overriding and reshaping a deposit of till left by an earlier glacial advance. Numerous drumlins are preserved in areas such as upstate New York.
Outwash: material deposited by the debris-laden meltwater coming from the zone of wastage where large quantities of meltwater usually run over, beneath, and away from the ice.
Esker: a long sinuous ridge of water-deposited sediment. These represent river systems which formed beneath the ice. In this case, the rivers build up into the ice as opposed to normal streams which cut down into the bedrock.
Kettle: a depression formed when an ice block incorporated in outwash finally melts. Kettles commonly fills up with water. These "kettle lakes" dot the landscape in large sections of Minnesota ("Land of 1000 Lakes").
Loess: Continental glaciers tend to erode rock down to the size of flour. Loess deposits are this material, first deposited as outwash, which has been blown away from the glacier by the wind. (Why would continental glacier commonly have winds blowing away from their margins.)
Evidence of past glaciation:
Differences in the atomic weight of isotopes of oxygen allow glaciologists to interpret past climatic conditions from an examination of long-term glacial ice.
Nearly all oxygen in the atmosphere has an atomic weight of 16 (O16). However, approx. 0.2% of oxygen has an atomic weight of 18 (O18)
Both isotopes behave the same chemically and combine with hydrogen to form water. O18, however, is 12.5% heavier than O16.
Therefore, water with O18 does not evaporate as readily as water with O16. In general, the atmosphere must be warmer in order to get water with O18 evaporating.
Glaciologists can measure the O18/O16 ratio of different layers of glacial ice.
A high O18/O16 ratio indicates warmer conditions because O18, being heavier than O16, requires warmer conditions for evaporation from the ocean.
The past 120,000 years has seen several major advances of glacial ice in North America and Europe/Asia.
Glacial ice accumulated to so great a depth that it spread southward, extending well into the United States. To some extent the general slope of the continent was southward, but much of the southward advance was merely spreading out, due to piling up of additional snow/firn/ice in the northern latitudes.
The Great Lakes and the Canadian lakes to the northwest all define limits of glacial ice in the recent geologic past.
In addition, there is geologic evidence for glacial episode in the distant geologic past.
Tillite: Lithified glacial till. Late Paleozoic tillites in the southern continents (South Africa, Australia, Antarctica, South America) have been used as evidence that these land masses were once joined (see the lecture on Plate Tectonics).
Causes of Glacial Ages:
Milankovitch, a Serbian astronomer, observed that variations in the earth's orbit, wobble of its axis, and inclination to the sun affects the amount of heat from solar radiation received by any particular portion of the earth.
Changes in the atmosphere may affect its ability to filter solar radiation. Air bubbles in ancient glacial ice suggests that CO2 and CH4 are much higher in the atmosphere during interglacial periods than during glacial periods.
Changing of the positions of the continents during continental drift may place continental land masses in a position favorable for glaciation.
Changes in circulation of sea water due to plate motions.
There are basically only 2 elevations to the earth - above and below sea level
Composition of seawater
Water is water, and has always (?) been water
But seawater isn't just molecular water (H2O)
Seawater (as well as freshwater) contains other materials
Called "salts" - but not all is NaCl
Little pieces of sediment in the water
Can result from mechanical or chemical weathering
Usually VERY small - mud, silt, and clay size particles
Held in suspension by the energy of the water
Related to velocity - review Q=AV
You can see this stuff
Makes the water cloudy, dirty, etc.
The look of the water reflects composition of material held in suspension
These sediments can settle out to form sedimentary layers
Lead to the formation of sedimentary rocks
Material dissolved in water
You cannot see this stuff - water remains "clear"
Particle size is not relevant in this case
Nor is the energy or velocity of the water
A chemical weathering process
The materials will remain in solution until
Change in chemistry causes fluid to loose its capacity to hold material - usually related to evaporation which results in oversaturation
Some other process extracts the material directly from the water. Ex.: Biological processes - animals extract CaCO3 or SiO2 to use as shells
Once extracted from the water, the minerals can become "sediments"
Water is stuff, has mass, and occupies space
One cubic foot of pure water weighs 62.4 pounds
Would salt water be higher or lower (higher)?
Therefore, pressure rises by approx. 650 pounds for each 100 feet of depth
Results in some pretty interesting aspects to things which live (or work) in ocean
Fish with headlights
Several forces combine to keep the ocean's water in motion
Wind, density differences, thermal differences, and Coriolis effect
The Coriolis effect
Need to cover first - affects all fluids in motion
Result of the rotation of the earth (DESCRIBE in detail)
Affect upper few hundred meters of the water only
Most caused by wind
Have a major climatic effect on the lands they pass by
East vs. west coast of North America
Move due to density differences in the sea water
Causes of density differences
Cold polar waters are denser - Sink and move towards the equator as very deep currents
Warm equatorial waters flow nearer to surface to replace the polar waters
Salinity - also related to latitude
Seawater freezes at the poles - Remaining water has high salinity
These cold, saline waters travel towards the equator at depth
Additional Thermal Effects
Strong surface winds "blow water away" from an area
Deeper, colder waters rise to "fill the hole" - Called upwelling
Bring nutrients to the surface (remains of dead plants and animals)
Make excellent fishing areas
Show film "Tides of the Ocean" (FK850; 17 min.; 6-12)
What is sea level?
Not a constant level around the globe
Actually higher in some places than in others
There are also daily variations in sea level - called "tides"
Actual bulge of sea level
Related to the gravitational attraction of moon and sun
Review Law of Gravity
Moon is smaller, but much closer
Therefore has the greatest affect on the tides
Actually pulls the water closer to the moon (and sun)
There are approx. 2 high and 2 low tides per day
Due to earth's rotation relative to the moon and sun
Diagram on board or overhead
Because the moon is also revolving around earth, each day's tides are 50 min. later than the day before
Spring tides - sun and moon lined up (full and new moon)
Neap tides - sun and moon at right angles (1st & 3rd quarters)
Swells and Waves
Show video "Waves in the Ocean" (VK1404; 23 min.; 11-12)
Morphology of the Seafloor
Liquids conform to the shape of the container
Two main elevations on the earth's surface
Above and below sea level
Correspond (roughly) to continental and oceanic plates
The shoreline does not mark the boundary between the two
Was the cause of some of the initial problems with Continental Drift
Three general levels to the seafloor
Continental Shelf - Portions of continental crust below sea level
Abyssal Plain - Deep ocean basins underlain by oceanic crust
Continental Slope - The transition between the two main levels (crustal types)
The relatively low-relief platform seaward from the shore
Usually fairly shallow water
Surrounds most of the continents
Not uniformly wide - vary quite a bit
Local relief can be somewhat steep
Especially in areas subjected to glaciation
Or to stream erosion at times of lower sea level
Connects the two major levels of the earths surface
The major continental land masses at just above sea level (average!)
And the abyssal depths at 12,000' below sea level
Actually a fairly gentle gradient - average slope 4°
Looks steep on most X-section due to vertical exaggeration
Characteristic features of the continental slopes
The formation of these is difficult to explain
Most now agree that Turbidity Currents are primarily responsible - Density currents of debris-laden water
Can move fast and far
Up to 100 kph for distances of up to 700 km
Can be set off by seismic or other disturbances
Example: Grand Banks - off Newfoundland 1929
Earthquake set off a large turbidity current
Severed Trans-Atlantic phone lines
Many cables over 13 hours
Speed of the current 66 ft/sec. (75 kph)
Anyway, all this debris piles up at the mouth of the canyons
Submarine fans - Like alluvial fans in an arid landscape
Coalesced fans (like a bajada in an arid landscape)
Forms the boundary between the slope and the abyssal plain
The abyss - the basic oceanic depths
Primarily underlain by basalt
Less than 200 m.y. old
Generated at spreading centers - Consumed at subduction zones
Abyssal Plains - Cover large portions of the ocean floor
Generally fairly low-relief
Most have at least a thin veneer of sediments (or oozes) covering them
Topographic mounds on the abyssal plain
Remain well below sea level - Mere "pimples" on the sea floor
Oceanic Ridge systems
Spreading centers for the earth's tectonic plates
The actual rift at the crest of the ridge/rise system
Increased depths below the main level of the abyssal plains
Generally long and narrow features - like the ridges
Associated with island arc chains
Represent zones of oceanic plate subduction
These are the lowest elevations on earth!
Mariana Trench @ -35,785'
Tonga Trench @ -35,326'
Depositional Environments and Sedimentation
Different types of sediments cover most of the ocean floor
Near shore - mostly Terrigenous sediments
Sand and silt predominate on the beaches and Continental Shelf
Claystone and shale farther out
Facies changes with distance from shore reflect energy of environment
Describe in detail
In canyons and at base of continental slope (rise)
Deep ocean sediments - the abyss
Descriptive term which characterizes the majority of deep ocean sediments
Usually microscopic marine organisms
Lack of terrestrial sediments causes them to be concentrated in the deep ocean
Ooze composition varies systematically across the ocean floor
Form in shallow, tropical and temperate seas
Single-celled calcium based creatures
Reproduce by dividing into two individual creatures
The vacated shells sink to the bottom
If too deep, or too cold, the calcium re-dissolves
Single-celled silica based organisms
Deposits form in deeper water where calcium can't remain stable
Also has a depth/pressure limit
Red/Brown clays - occur in the deepest oceanic basins
Most widespread of all sedimentary deposits on the earth
Almost totally inorganic
Accumulates at a very slow rate
Only thing which can survive the pressure of the deepest basins
Plate Tectonics and the ocean floor
Already touched on this quite a bit
Passive continental margin
Both sides of the Atlantic
Trailing edge of Continental plate
Minimal tectonic activity
Wide Continental Shelf
Active continental margin
West coast of North & South America
Leading edge of continental plate
Narrow Continental Shelf
Common where two oceanic plates collide
Japanese Islands, and many others in western Pacific
Similar volcanism occurs at Oceanic/continental margins
A secure supply of good water has always been important and formed the basis for civilization. The rise and fall of civilization ultimately is controlled by water.
As a source of needed bodily fluids, as well as for transportation, communication, irrigation, access into continental interiors, industrial needs.
Miscellaneous Topics - 1 day each
Flooding and the Rogue River Valley
The ocean through time - Banded Iron Formation
Glacial-Interglacial transition - the Bretz Flood
Yukon massive sulphide discovery
Tri-State Mining District
Island Mountain and the Queen of Bronze
Agricultural pollutants in the mid-west
Nuclear waste disposal - Yucca Mountain
Hydroelectric power - Bonneville Power Administration
Geothermal power - a clean source of energy