Physical Geography
SECTION 3 REVIEW
TEST,
IMPORTANT
CONCEPT: In all physical science, we try to study,
describe, quantify and predict (then reproduce through experimentation) how a
system will behave. This is true for
geomorphology except three different factors:
1)
length
of geologic time scales
2)
range
of spatial scales is extreme (microscopic to continental)
3)
geomorphic
thresholds are unknowable (don’t know when something will reach a threshold and
that no two systems will react to weathering the same way.)
Endogenic (internal) system
Exogenic (external) system
Organization
of materials from core to lithosphere is due
to gravity- iron towards that center and silica towards the surface. The fluid
outer core generates 90% of Earth’s magnetic field. As it rotates it generates electrical
currents that induce magnetic fields.
Composition of continental
(lighter, made of granite) and ocean
(denser, made of basalt) crust is different. The difference is the key to the concept of
drifting continents (when colliding, the denser ocean crust dives below
continental crust.) The crust is in a
constant state of adjustment (isostasy)
Tectonic cycle
brings heat energy and new material to surface and recycles old. Crust (99%) composed of 8 natural
elements. Oxygen and silicon account for
74.3% of crust.
Earth has 3 areas- Core, mantle and lithosphere
(crust).
Geologic Cycle: Fueled by internal heat and solar
energy with the leveling force of gravity.
3 subsystems (hydrologic, rock and tectonic cycles)
Rock cycle: produces 3 rock types- igneous,
sedimentary and metamorphic.
Sedimentation
driven by solar energy and gravity- water is principal medium
Sea floor
spreading produces new crust. Subduction is the collision of ocean
floor and continental crust (remelts, recycled as magma and rises again.) Both
areas are zones of earthquakes and volcanoes.
14 main plates in present crust.
Tectonic
processes deform, recycle and reshape Earth’s crust.
Principal
seismic and volcanic activity zones occur along plate boundaries.
Endogenic processes result in gradual uplift and
new landforms.
3 types of
convergent plate collisions that cause orogenisis:
Two world
mountain chains: Cordilleran System
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Physical
(mechanical) and chemical weathering processes reduce landscapes and release
minerals from bedrock for soil formation.
Weathering/mass movement provides raw material for erosion.
Slopes (hillslopes): a curved, inclined surface. The angle of a slope combines with gravity
and is resisted by forces of friction, cohesion and inertia. Slope
is an open system seeking and angle of equilibrium.
Controls on
weathering: climatic elements (precipitation, temperature and freeze-thaw
cycles), water table, water movement (hydraulics), geographic orientation of
slope and vegetation. TIME IS A FACTOR
IN ALL MASS MOVEMENT.
Physical weathering: rock is broken and disintegrated with
no chemical alteration. Four processes
include frost action, crystallization, hydration and pressure-release joining.
Chemical weathering: the decomposition
(chemical change) of minerals in rock (reactions between air, water and
minerals.) Three processes include
hydrolysis, oxidation and carbonation and solution. Physical
weathering dominates in drier, cooler climate, chemical weathering in wetter,
warmer climates.
Karst Topography: Created from limestone (lots of
calcium carbonate) and chemical weathering.
Composed of pitted, bumpy surfaces (with sinkholes and towers- where surrounding limestone has been
weathered), with poor surface drainage and well-developed solution channels
(underground conduits such as caverns, cave, etc.)
Most caves are
formed in limestone rock, through carbonation, below the water table. This forms dripstones.
Stalactites:
grow from ceilings
Stalagmites: grow from the floor
Mechanics of Mass Movement: any movement of material propelled and
controlled by gravity. All mass movement
(mass wasting) occurs on slopes under influence of gravitational stress. Balance between driving (gravity) and
resisting forces. The greater the slope,
the more mass wasting. The resisting
fore is the shearing strength of slope material (force working against
gravity.)
Classes of Mass Movement: (gravity pulls on a mass until a
critical shear-failure point is reached- the geomorphic threshold) The four
classes include:
1) fall- faster, drier
2) slide- average
3) flow- faster, wetter
4) creep- slower, drier
Geomorphology: the science of origin, evolution,
form and distribution of landforms
Denudation: any process that wears away or
rearranges landforms
Stream related
processes are called fluvial processes.
Insolation and
gravity power the hydrologic cycle and are the driving forces of fluvial
systems. Fluvial process includes 3
systems, that of erosion, transport and deposition.
Erosion and Drainage Basins: An area will have many drainage
basins (depends upon the scale of observation.)
Each basin is formed by a divide, which are ridges that control the flow
of water. The terms, basin, watershed
and catchment, are basically the same. A
basin is a combination of hillslopes and channel (valleys and streams.) Basins are open systems with inputs
(precipitation and geology) and outputs (water- streamflow and sediment.) Basins work towards equilibrium between
discharge, transported load, channel shape and steepness.
Streamflow-
decreases downstream with increase in drainage area. Upstream hydraulic action is low-volume,
low-velocity and turbulent and downstream
is high-discharge, high velocity and
smooth (laminar) flow. 3 hydrologic
processes:
1. Erosion: through hydraulic (work of flowing water) and abrasive (rock particles grinding together, acting like sandpaper)
forces. Hillslopes
3. Deposition: when a stream deposits alluviam
creating depositional landforms (floodplains, terraces or deltas) Floodplain, Delta or Alluvial terrace
Water is the dominant
agent of landmass denudation.
40% population
live 60 miles of coast (50% in US.) 50%
world’s coastlines are at risk.
Physical and
chemical properties of ocean water makes it different from lakes and
streams. Seawater is a solution
(salinity). Oceans: homogeneous mixture
of chlorine, sodium, sulfur, calcium, potassium and bromine, dissolved gases,
organic matter and sediment. Average salinity is 3.45%. Brine has salinity over 3.5% and brackish
means salinity under 3.5%.
Subtropical oceans = higher salinity (more evaporation) and equatorial
areas have less (more precipitation.)
Components of ocean: ocean floor, deep cold zone,
thermocline and mixing zone. Water in
deep cold zone is 32 and freezes at 28.
Gravity
provides potential energy of position for motion/generates tides. Coastal environment = littoral zone. Includes highest storm watermark and where
water too deep to be affected by storms (200 feet deep). Shoreline is the contact line between land
and sea. Coast is from high tide to the
first major landform change. High tide is the flood tide and low tide is the ebb tide (twice a day.)
Remember: Sea
Level is a relative term. It changes
with ocean currents and waves, tidal variation, air temperature and pressure
differences, ocean temperatures, etc.
Currently, mean sea level (MSL) is rising (8-16 inches per 100 years.)
Tides: Tides are an agent for geomorphic change. Produced by gravitational pull of sun and
moon. When sun and moon line up or are opposite (spring tide) there is a larger
tidal bulge (greater gravitational
pull.) An inertial tidal bulge is on the
other side. Important: The water does
not move to produce a tide. It is the
position of the earth as it rotates into the “fixed” tidal bulges. A neap tide is when the sun and moon are at
angles to each other and not lined up.
Waves: caused by friction between moving air and ocean
surface. A swell is a regular pattern of
smooth, rounded waves. What you see is the wave energy moving, not
the water (water moves in circular patterns.) A breaker is when the height of the wave
exceeds its vertical stability and the wave crashes down. This motion then results in water and energy
moving forward. Crest is the top of the
wave and the trough is the low point between crests. Wave actions straighten coastlines.
A beach is a place along a coastline
where sediment is in motion and deposited by waves and currents (constantly
moving.) Average beach spans 16 feet
above high tide to 33 feet below low tide.
Beaches are dominated by quartz
sands because it resists weathering and remains after other minerals are
removed (remember the constant moving and abrasion and the nature of ocean as a
solute.) Beaches act to stabilize shorelines, by absorbing wave energy.
Coral: is a simple
marine organism, related to jellyfish that secrete calcium carbonate to form an
external skeleton. Coral and algae have
a symbiotic relationship (algae produces 60% of coral’s nutrition.) Live in warm waters and East Coast water is
warmer than West Coast, therefor more coral on east coasts. Need clear sediment free waters. Coral reefs are structures built upon the
skeletons of old coral. Coral bleaching
may be caused by pollution, disease, sedimentation or temperature rise. The world’s coral could all perish by 2010 (linked
to rise in ocean temperature.)
Wetlands and Mangrove Swamps: Areas of great biological
productivity (plants, fish, shellfish, etc.) based upon trapped organic and
sediment and mixture of fresh and salt water.
These areas can out-produce a wheat field in terms of vegetation per
acre. Very fragile and easily threatened
by humans. Wetlands occur on poorly
drained soils and saturated with water.
Salt mashes occur north of 30th parallel and mangrove swamps
south of this- dictated by freezing
temperatures (remember that this works the other way in Southern
Hemisphere.) Salt marshes form estuaries behind barrier beaches in inter-tidal
zones and are populated by halophytic plants (which trap alluvial sediments,
helping the marsh to grow.) Along
tropical coastlines, mangrove swamps
grow. The root zones offer habitat for
many fish and other wildlife. Mangrove
loss is between 40-80%.
Essay Practice:
1) Compare
physical and chemical weathering.
2) The
geologic cycle has 3 sub-cycles. Name and define these, describing their forces
(energy) and processes and whether they are endogenic or exogenic.