Exam 3 Flashcards
Invented in 1920s
Primary instrument for measuring depth
Reflects sound from ocean floor
Echo Sounder
Employs an array of sound sources and listening devices
Obtainsa profile or a narrow strip of seafloor
Multibeam Sonar
Found along most coastal areas that surround the atlantic ocean
Not associated with plate boundaries
Experience little volcanism and free earthquakes
Passive Continental Margin
Flooded extension of the continent
Varies greatly in width
Gently sloping
Contains important mineral deposits
Some areas are mantle by extensive glacial deposits
Continental Shelf
Marks the seaward edge of the continental shelf
Relatively steep structure
Boundary between continental crust and oceanic crust
Continental Slope
Found in regions where tranches are absent
Continental slop merges into a more gradual incline - the continental rise
Think accumulation of sediment
At the base of the continental slope turbidity currents deposit sediment that forms deep-sea fans
Continental rise
Primarily in pacific
Trench
Accretionary wedge
Active Margins
Long, relatively narrow features
Deepest parts of the ocean
Most are located in the pacific ocean
Sites where moving lithospheric plates plunge into the mantle
Associated with volcanic activity
Deep Ocean Trench
Likely the most level places on Earth
Sites of thick accumulations of sediment
Found in all oceans, especially atlantic
Abyssal Plains
Isolated volcanic peaks
Many form near oceanic ridges
May emerge as an island
Seamounts
Vast outpourings of basaltic lavas on the ocean floor create extensive volcanic structures
Oceanic Plateaus
Broad, linear, swells along divergent plate boundaries
Oceanic ridges
Axis of some ridge segments exhibit deep down-faulted structures
Rift Valleys
Concept formulated in early 1960s by Harry Hess
Occurs on relatively narrow zones, called rift zones, located at the crest of ocean ridges
Seafloor spreading
Newly created oceanic lithosphere is hot and occupies more volume than cooler rocks
As the basaltic crust travels away from the ridge crest it is cooled by seawater
As the lithosphere moves away it thermally contracts and becomes more dense
Why are oceanic ridges elevated
sequence of unconsolidated sediments
Layer 1 of oceanic crust
consisting of pillow lavas (basalt)
Layer 2 of oceanic crust
numerous interconnected dikes called sheet dikes (basalt)
Layer 3 of oceanic crust
gabbro, in a sequence of rocks called an ophiolite complex
Layer 4 of oceanic crust
Basaltic magma originates from partially melted mantle peridotite
Molten rock injected into fractures above the magma chambers creates the sheeted dike complex
The submarine lava flows chill quickly and the congealed margin is forced upward to provide large tube-shaped protuberances known as pillow basalts
Formation of oceanic crust
Hydrothermal fluids dissolve ions of various metals and precipitate them on the ocean floor as particle filled clouds
Black smokers
- Mantle plumes/ hotspots
- Slab pull/slab suction
Two mechanisms that have been proposed
Concept of floating crust in gravitational balance
If weight is added or removed from the crust, isostatic adjustment will take place as the crust subsides or rebounds
the principle of isostasy
Buoyancy of hot rising mantle material accounts for broad upwarping in the overlying lithosphere
vertical motions and mantle convection
the processes that collectively produce a mountain belt
Including folding, thrust faulting, metamorphism, and igneous activity
Orogenesis
region where subduction g oceanic lithosphere bends and descends into the asthenosphere
Deep ocean trench
built upon overlying plate
Island arc if on ocean floor or
Continental arc if oceanic lithosphere is subducted beneath a continental block
volcanic arc
As the subducting plate sinks in creates a flow in the asthenosphere that pulls the upper plate toward the trench
Extension and back arc spreading
Where two oceanic plates converge and one is subducted beneath the other
Volcanic island arcs result from the steady subduction of oceanic lithosphere
Continued development can result in the formation of mountainous topography consisting of igneous and metamorphic rocks
Island arc mountain building
Mountain building along continental margins
Involves the convergence of oceanic plate and a plate whose leading edge contains continental crust
Andes mountains
Andean arc mountain building
Subduction and particle melting of mantle rock generates primary magmas
Magma is less dense than surrounding rock so it begins to buoyantly rise
Differentiation of magma produces andesitic volcanism dominated by pyroclastics and lavas
Building a volcanic arc
An accretionary wedge is a chaotic accumulation of deformed and thrust-faulted sediments and scraps of oceanic crust
Prolonged subduction may thicken an accretionary wedge enough so it protrudes above sea level
Descending sediments are metamorphosed into a suite of high-pressure, low-temperature minerals
Development of an accretionary wedge
The growing accretionary wedge acts as a barrier to sediment movement from the arc to the trench
This region of relatively undeformed layers of sediment and sedimentary rock is called forearc basin
Forearc basin
a summary of the circulation of Earth’s water supply
hydrologic cycle
Begins as sheetflow
Infiltration capacity is controlled by
Intensity and duration of rainfall
Prior wetted condition of the soil
Soil texture
Slope of the land
Nature of the vegetative state
Running water
Sheetflow develops into tiny channels
Rills
Gradient, or slope
Channel characteristics including shape, size, and roughness
Discharge - the volume of water moving part a given point in a certain amount of time
Factors that determine velocity
Laminar flow
slower flow
turbulent flow
faster flow
Cross-sectional view of a stream
Viewed from the head (headwaters or source) to the mouth of a stream
A smooth curve
Gradient decreases downstream
profile
Velocity
Discharge
Chanel size
increase downstream
Gradient
Channel roughness
decrease downstream
Lifting loosely consolidated particles by
Abrasion
Dissolution
Stronger currents lift particles and move them more effectively
stream erosion
the stream’s load
Types of load
Dissolved load
Suspended load
Bed load
transported material
the maximum load a stream can transport
capacity
Indicates the maximum particle size the stream can transport
Determined by the stream’s velocity
competence
Competence is reduced
Sediment begins to drop out
decrease in velocity
Generally well-sorted
Stream sediments are known as alluvium
stream sediments
Back swamps
Yazoo tributaries
floodplain deposits
Develops where high-gradient stream leaves a narrow valley
Slopes outward in a board arc
alluvial fans
Form when a stream enters an ocean or lake
Consist of three types of beds
Foreset beds
Topset beds
Bottomset beds
deltas
V-shaped
Downcutting toward base level
Features often include rapids and waterfalls
narrow valleys
Steam in a ner base level
Downward erosion is less dominant
Stream energy is directed from side to side forming a floodplain
wide valleys
a this mass of ice that originates on land from the accumulation, compaction, and recrystallization of snow
glacier
Exist in mountainous areas
Flow down a valley from an accumulation center at its head
valley glaciers
Exist on much larger scale than valley glaciers
Two major ice sheets on earth (greenland and antarctica)
ice sheets
Air infiltrates snow
Snowflakes become smaller, thicker, and more spherical
Air is forced out
Snow is recrystallized into a much denser mass of small grains called firn
Ocne the thickness if the ice and snow exceeds 50 meters, firn fuses into a solid mass of interlocking ice crystals
formation of glacial ice
Occurs within the ice
Under pressure, ice behaves as a plastic material
plastic flow
Entire ice mass slipping along the ground
Most glaciers are thought to move this way
Basal slip
the area where a glacier forms
Elevation of the snowline varies greatly
zone of accumulation
the area where there is a net loss to the glacier due to
Melting
Calving - the breaking off of large pieces of ice (icebergs where the glacier has reached the sea)
zone of ablation
lifting of rocks
plucking
Rocks within the ice acting like sandpaper to smooth and polish the surface below
abrasion
Rock flour (pulverized rock)
Glacial striations (grooves in the bedrock)
Landforms
Glacial trough
Arêtes
Horns
Hanging valleys
Cirques
Fjords
Truncated spurs
glacial abrasion products
refers to all sediments of glacial origin
Types of glacial drift
Till - material that is deposited directly by the ice
Stratified drift - sediments laid down by glacial meltwater
glacial drift
Smooth, elongated, parallel hills
Steep side faces the direction from which the ice advanced
Occur in clusters called drumlin fields
Formation not fully understood
drumlins
line that marks the contact between land and sea - moves during the day with tides
shoreline
extends between the lowest tide level and the highest elevation affected by storm waves
shore
area exposed at low tide and submerged at high tide
foreshore
area found landward of the high-tide mark
backshore
lies between the low-tide shoreline and the point where waves break at low tide
nearshore zone
seaward of the nearshore zone
offshore zone
an accumulation of sediment found along the landward margin of an ocean or lake
the beach
extends inland from the shore as far as ocean-related features are found
coast
marks the coast’s seaward edge
coastline
he horizontal distance between two crests
Below a depth of ½ wavelength, water movement is no longer felt
If you are scuba diving in the ocean, you will not feel the effects of a storm passing the surface
wavelength
turbulent water that washes up a beach
Greater on flat beaches
at an angle
swash
is water flowing back into the ocean after swash
straight down
backwash
Currents parallel to shoreline produced in surf zone by waves reaching shore at an angle
longshore current
Wave cut cliffs
Wave cut platform
Marine terraces (old wave cut platforms elevated by changing sea level or local uplift)
Sea arches
Sea stacks
erosional coast features
Composed of sediment that is eroded, transported, and deposited by wave energy
depositional coasts
an elongated ridge of sand that projects into the mouth of an adjacent bay
spit
a sandbar that crosses a bay, cutting it off, from open ocean
bar
Low ridges of land parallel to the coast
Gebrally 3-30 km offshore
1-5 km wide, 15-30 km long
barrier islands
built perpendicular to the shoreline and extend into the ocean near the mouths of rivers and harbors
Usually built in pairs to develop and maintain harbors
Results in deposition and up-current and erosion down-current
jetties
Built perpendicular to the beach and extend into the ocean
Designed to maintain or widen beaches: causes erosion downstream
groins
Creates a region of sand accumulation between the breakwater and the shoreline
Built offshore to protect property from breaking waves
Causes deposition landward of breakwater
breakwater
Built onshore to protect property from breaking waves
Focuses wave energy at seawall, increases backwash
Causes severe erosion seaward of seawall
seawall
Adding large quantities of sand to the beach
Costly and not a permanent solution
nourishment
Develop because of uplift of an area or a drop in sea level
Generally erosional
emergent coasts
Caused by subsidence of land adjacent to the sea or a rise in sea level
Usually depositional
Features:
Estuaries (drowned river mouths)
Highly irregular shorelines
submergent coasts
Atmosphere
Hydrosphere
Geosphere
Biosphere
Cryosphere (ice and snow)
the climate system
Plates tectonics (very long term)
Variations in Earth orbit (long term)
Eccentricity, obliquity, and precision
Volcanic activity (short term)
Changes in the sun’s output associated with sunspots
natural causes of climate change
Humans have been modifying the environment for thousands of years as ground cover has been altered by
Fire
Overgrazing
Modification of climatological factors such as reflectivity, evaporation rates, and surface winds (windmills for power)
anthropogenic climate change
Because the climate system is so complex, predicting specific regional changes to increased levels of CO2 is speculative
However, some possible consequences include
Rise in acidic as well as sea level (virtually certain)
Altering the distribution of the world’s water resources (very likely)
Changes in the extent of Arctic sea ice and permafrost (very likely)
Frequency of heavy precipitation (very likely)
Areas affected by drought (likely)
Loss of glaciers will accelerate (likely)
Greater intensity of tropical cyclones (not sure)
consequences of global warming
Changes that reinforce the initial change are called positive-feedback mechanisms
Warmer surface temperatures cause an increase in evaporation, increases temperatures as water vapor absorbs more radiation, warmer surface temperatures
Warm ocean. Longer melting, decline in ice, reduced reflectivity (albedo), increased absorption of solar energy, warm ocean…
climate feedback mechanisms
Produce results that are opposite of the initial change and tend to offset it
Example - negative effect of increased cloud cover, ash, and haze on the amount of solar energy available to heat the atmosphere
negative feedback mechanisms
