Physical Geography (GEOG
1301.01)
Spring 2004 Lecture 9
Chapters 13, 14 & 16
TEST 3:
Note:
This lecture is a quick overview of geomorphology. We will review this from the point of view of
how energy shapes the lithosphere and the lithosphere as an open system. Chapters 11 and 12 looked at endogenic
(internal) processes while these 3 chapters look at exogenic (external)
processes. 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.)
Chapter 13: Weathering,
Karst Landscapes and Mass Movement
Important Concepts
Physical (mechanical) and chemical weathering processes reduce
landscapes and release minerals from bedrock for soil formation. Weathering and mass movement provides raw
material for erosion.
Dynamic Equilibrium: Model that looks at landscape
developing and changing emphasizing a balance between force, form and
process. Uplift creates potential energy
of position, creating disequilibrium between relief and energy. Sun supplies radiant energy (heat.) Hydrologic cycle provides kinetic energy
(motion) and air and reaction in crust provide chemical energy. Look at an average over time. Think about chapters 11 and 12, specifically
the weight of mountains on the crust and the effect of volcanic activity or
earthquakes upon relief.
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
Scarification: human-induced mass movement.
Key Terms
Geomorphology: the science of origin, evolution,
form and distribution of landforms
Denudation: any process that wears away or
rearranges landforms
Regolith:
upper surface of broken-up bedrock
Bedrock: parent rock
Assignment:
Questions: 14
Definitions: Geomorphology, Karst Topography, Stalactites,
Stalagmites
Chapter 14: River Systems
and Landforms
The worked performed by water
flowing in rivers is .003 % of the volume of all fresh water and is the
dominant agent of landmass denudation.
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.
Important Concepts
Base level is the elevation at which a stream can no longer
erode its valley. Sea level is the
ultimate base level.
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.
Density refers to the amount of dissection within a basin.
(Humid regions have a high, density and deserts, low.) It describes an area’s topography. A drainage pattern reflects an area’s
steepness, rock resistance, climate, hydrology, relief and structural
controls. You can deduce some of the
underlying geology and climate (hydrology, etc.) by examining drainage
patterns. Most common pattern is the
dendritic- tree-like pattern.
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.
Erosion: through hydraulic (work of flowing water) and abrasive
(rock particles grinding together, acting like sandpaper) forces.
Transport: Material available
for transport depends upon, relief, local soils and rock, climate, vegetation
and human activity. Three types of
stream load are dissolved (through chemical solution), suspended (fine-gained
particles) and bed (coarser materials, dragged by traction or rolled by
saltation.) Aggradation occurs when load
exceeds streams ability to carry sediments.
This forms braided streams.
Deposition: when a stream deposits alluviam
creating depositional landforms (floodplains, terraces or deltas) Know the definitions for test.
Key Terms
Alluvium
Base Level
Drainage basins (watershed)
Continental Divide
Drainage Density and Pattern
Discharge
Braided Stream/Meandering Stream
Gradient
Floodplain
Alluvial Terrace
Delta
Distributary
Estuary
Assignment
Questions: 12
Definitions: alluvium, watershed, estuary &
hydrograph
Chapter 16: The Oceans,
Coastal Processes and Landforms
Forty percent
of earth’s population lives within 60 miles of coast (50% in US.) Half of the world’s coastlines are at
risk. Given the above, this is an
important chapter,
Important Concepts
Physical and chemical properties of ocean water makes it
different from lakes and streams.
Seawater is a solution (salinity).
The oceans are a homogeneous mixture of chlorine, sodium, sulfur,
calcium, potassium and bromine, as well as dissolved gases, organic matter and
sediment. Average salinity is
34.5%. Brine has salinity over 35% and brackish
means salinity under 35%. Subtropical
oceans have has higher salinity (more evaporation) and equatorial areas have
less (more precipitation.)
Four components of ocean, ocean floor, deep cold zone,
thermocline and mixing zone. Water in
deep cold zone is 32 and freezes at 28.
Coastal system inputs: solar, atmospheric winds (ocean currents
and waves), climate, coatal rock and human activities. Gravity provides potential energy of position
for motions and generates tides. Coastal
environment is known as the littoral zone.
This 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.
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. 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.
Coastal Formations:
Erosional coastlines are rugged, have high relief and tectonically
active- on the leading edge of drifting lithospheric plates. Remember the relationship between erosional
and tectonic activity. Depositional
coastlines are located around land with gentle relief and locally available
sediments. 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 (know what a coral reef is composed
of.) 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. Three kinds of
reef stages, fringing, barrier and atoll.
Descriptive of relationship between reef building and volcanic islands,
which are in equilibrium. 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%. Know the difference.
Key Terms
Salinity
Tides
(flood-rise and ebb-fall)
Beach
Coral
bleaching
Hydrophytic vegetation
Halophytic plants
Assignment
Questions: 9