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 Physical Geology Lecture Outlines # 3

Lectures 20, 21- Running Water
Reading: Chapter 16 of Tarbuck and Lutgets, 8th edition
Topics:
1. Water
2. Hydrologic cycle
Evaporation/Transpiration
Condensation
Precipitation
Infiltration
Runoff
3. Properties of moving water
4. Sediment Transport
5. Types of River Sytems
 
1. Water, water everywhere
 
Liquid Water:
Distinctive feature of Earth, the blue planet
Right temperature range
Global climate-self regulating system
Water is the most powerful erosive agent on earth
Even in deserts
Bryce Canyon
Without active tectonics earth would be worn down to to a smooth sphere.
 
Mars:
Ice caps
Permafrost?
Erosional evidence for episodic flow of water
Valles marineris
Valles marineris detail
Due to asteroid impacts?
Or was the atmosphere thicker and the climate warmer in the past?
 
Venus:
Too hot due to greenhouse effect
No liquid water
Evidence for episodic flow of a fluid.
We don't know what, maybe molten salt?
 
The volume of water on Earth is estimated to be about 1.36 billion cubic kilometers with:
 
97 % in the oceans
2 % in glaciers
l % in streams, lakes, ground water, and the atmosphere
2. The Hydrologic Cycle
 
Continuous exchange of water between the surface, the subsurface and the atmosphere
The Cycle
 
Evaporation:
 
Liquid to vapor
As temperature increases
Radiant energy from the sun heats water, causing the water molecules to become so active that some of them rise into the atmosphere as vapor.
 
Transpiration.
 
Plants absorb water through the roots and release it through the leaves.
 
 
Condensation.
 
As water vapour rises, it cools and eventually condenses to liquid or ice.
 
Why are clouds often fluffy on top, but flat at the bottom?
Clouds from a the shuttle
Clouds from the ground
 
Dew Point: depends on water saturation (humidity) and temperature.
 
 
Precipitation.
Water released from clouds as rain, sleet, snow, or hail.
Begins after water vapor becomes too heavy to remain in atmospheric air currents and falls.
 
Infiltration.
A portion of the precipitation that reaches the Earth's surface seeps into the ground.
Depends on:
Slope
Amount and type of vegetation
soil type and rock type
whether the soil is already saturated by water.
The more openings in the surface (cracks, pores, joints), the more infiltration occurs.
Runoff.
Water that doesn't infiltrate the soil flows on the surface as runoff.
Can also come from melted snow and ice.
When there is a lot of precipitation, soils become saturated with water.
Additional rainfall can no longer enter it.
Runoff will eventually drain into creeks, streams, and rivers, adding a large amount of water to the flow.
Sheet flow
Stream Flow
 
Ground water:
The water that percolates into the ground also flows through the pore spaces in the rocks or soil.
It can be tapped by wells.
It contributes to streams, or draws water from streams depending on the setting.
 
Running Water
Streams modify their channels
 
Gradient - slope over which the stream flows
 
The ULTIMATE BASE LEVEL is sea level - streams will not erode their base below base level
 
 
There may be temporary base levels which control the behavior of segments of a stream - a dam, for example
 
Imagine constructing a dam across a river. Above the dam the river begins to deposit material as it adjusts to the new base level.
Below the dam erosion can occur at the base of the dam.
A lake forms behind the dam - becomes a temporary base level
 
3. Properties of Moving Water
 
Stream Discharge = Width x Depth x Velocity
(cubic feet/second, cfs: or cubic meters per second)
 
Stream Competence= Biggest particle a stream can carry
Depends on velocity
 
Stream Capacity= Volume of material a stream can transport
Depends on discarge
 
Mississippi River near its mouth:
High capacity, low competence
 
Cheat River at flood:
High competence, moderate capacity
Big Boulder tranported by 1Cheat River 985 flood

4. Sediment Transport
 
Streams carry material as:
DISSOLVED LOAD
Ions in solution
SUSPENDED LOAD
Particles of silt or mud suspended by turbulence
BED LOAD
Rocks pushed along the bottom of the channel
 
Laminar flow= smoth flow, no mixing between layers
Turbulent Flow= mixing between layers
 
Rapids
 
In general, the suspended material is finer than the bed load and is transported faster
than the bed load material.
 
As velocity changes, material in the bed load may be suspended and transported with a higher velocity
 
5. Types of River Sytems
 
Depend on changes of gradient along the profile
 
Mt. Streams
High gradient
Rough channels
Narrow valleys
High competence, low capacity
Very coarse sediment
 
Braided Streams
Moderate gradient
Multiple active channels
Wide valley
Channels change rapidly
Moderate capacity, moderate to high gradient
Tok River
 
Meandering Streams
Single channels that makes big loops
Due to vorticity of flow
Low gradient
Cut bank
Point bar
Changes of velocity across channel
Meanders migrate over time
Oxbow lakes
Photo
Kuskokuim river
Lectures 22- Floods and Drainage Patterns
 
Reading: Chapter 16
 
Topics:

1. Test results, Review,
2. Floods
3. Recurrence Interval
4. Flood Damage
5. Controlling Floods
6. Drainage Basins
7. Alluvial Fans and Deltas
Power Point Presentation Floods
 
2. Flooding
Flood Plain Floods

The floodplain is a natural part of the river system
Flooding is takes palce recurrently, sometimes every year
Floodplain sediements are mud and silt: good for agriculture
Cities in the past tended to be locanted nest to rivers for access to transportantion
Many cities have expanded into the floodplain
Meandering rivers from natural levies that keep the river in the channel most of the time
During the flood events the levies break
Large areas go under water sometimes for an extended period of time
 
Flash Floods
Flash floods take place in narrow valleys
After heavy rainfal water is focused through a small area
Very fast moving water, powerfull and destructuve
Lasts only a short time
Flood covers a small area
Common in areas of episodic rainfall (semi-deserts)

3. Recurrence Interval (Flood Frequency)
Average Time Between Events of a Given Size or larger
Like earthquakes:
small events are common
large events are rare but catastrophic
Most urban planning takes into account frequent, common flood events
Extreme events (hundred-year flood) are usually beyond our control

4. Flood Damage
Water Damage-This is the obvious result of a flood
Flood Erosion
Not so obvious
During flood the competency of the stream is much greater than normal
Lots of bank erosion occur
The river can change course dramatically
 
Flood Deposits
As the flood water subsides it looses its ability to carry load
Thick layers of mud, rock, debris are left behing
 
5. Controlling Floods
Dams-
Store some of the run off
Decrease risk of flooding downstrean (up to the reservoir's capacity)
Change the stream gradient
Eventually fill up with sediment
Levies-
Keep the river in its channel
They decrease the storage capacity of the river basin
Increase the chance of catastrophic flooding during extreme events
Shortcuts
Avoid meanders which tend to pond the water.
This increases the velocity of flow
Decrease the storage capacity of the river basin
Increase the chance of flooding down stream
 
Lesson:
Don't mess with the rivers
Don't build on floodplains
Disaster aid may be counterproductive because it encourages people to remain in flood-prone areas
 
6. Drainage Basins
A network of streams that converge into one larger one
Tributaries-order
Usually limited by topographic divides
Stream flow is determined by rainfall over its entire drainage area, not just over the course of the stream
7. Drainage Patterns
The drainage pattern speaks about the relationship between erosion and tectonics
Erosion tends to level the land
Tectonics tends to make highs and lows

Dendritic Pattern- Streams are developiong without much regards to the rocks
Radial Pattern- Flow away from a high topographic area
Rectangular Pattern-
    A network of fractures determines where the streams lie
    The Cheat River is controlled by two fracture sets one NE-SW, one NW-SE
     
Trellis Pattern-
    Resistant ridges of folded rockguide the streams
    The Appalachian Valley and Ridge is a great example
     
Relationship between streams and uplift
Rapid uplift leads to:
Change of base level
Rapid incision
Steep canyon walls
Incised streams are not free to move laterally
If a river already exists when uplift begins it is likely to cut across structure
Example: Appalachian water gaps
 
8. Deltas & Alluvial Fans

Alluvial Fans
Cones of debris that form at the foot of mountians in arid climates
When river goes into the valley it looses velocity, drops much of its load
Cone is usually traversed by braided streams
 
Deltas

How the stream load gets dumped into a basin
Distributary Channels
Progradation vs. Subsidence
Bedding Types

Topset Beds- flat-near sea level
Foreset Beds- steep
Bottomset Beds -flat- in the basin


Lectures 22- Glaciers and Glaciations
Reading: Chapter 18 of Tarbuck and Lutgets, 8th edition
 
Topics:
1. Intro to glaciers
2. Origin of glaciers
3. Movement of glaciers
4. Types of glacier
5. Glacial Landforms
Glacial Erosion
Glacial Deposits
6. Glaciations
7. Evidence from the past
 
Objectives:
1. Define the term glacier, and explain the difference between valley glaciers and ice sheets.
2. Explain how a glacier moves.
3. Describe the features and landforms caused by glacial erosion and glacial deposits.
4. Explain what an ice age is.
5. Identify the indirect effects of glaciers, and list some of the possible causes of glaciation.

GLACIER

Hydrologic Cycle

Glaciers-Where they are

Types of Glaciers

Formation and Growth of Glaciers

Growth

Wastage

Movement of Glaciers

Glacial Erosion

Under glacier

Above glacier

Erosional Landscapes Associated with Continental Glaciation

Glacial Deposition

Erratic-Alberta, Canada

Other Glacial Landforms

Glacial ages

Effects of Past Glaciation

Causes for glaciation

Lectures 24- Deserts

Topics:

Desert

Distribution of Deserts

 

Was this hurricane (or typhoon) in the N or S Hemisphere?

Other Causes for Deserts

Some characteristics of deserts

Desert Features in S.W. United States

Basin and Range Province

Lectures 25- Wind

Topics:

Sandy vs. Rocky Deserts

Wind Action

Wind Transportation

Wind Erosion

Wind Deposition

Types of Dune

Namibian Desert dunes

Entrada Sandstone- Utah- Jurassic Sand Sea

Dune Field near Kaiser Crater- Mars

Source of sand in Mars?

Asteroid impacts

Reading: Chapter 13 of Tarbuck and Lutgets, 8th edition

Ocean Basins

Topics

History
Origin of Ocean
Oceans vs. Continents
Methods of Surveying the Sea Floor
Features of the Seafloor
Passive Continental Margins
Turbidity Currents
Active continetal Margins
Mid Ocean ridges
Black Smokers

History

Seafloor was one of the great mysteries
Inaccessible and unknown until recently
Legend of Atlantis (reported by Plato, 350 BC)
Continent located offshore Gibraltar sinks
This legend persisted until recently
What is wrong with this legend
What is right

Origin of the Ocean

Water
Released during degassing of early Earth
From fragments of comets
From volcanic eruptions
Salt from chemical weathering on land
Rivers continually add salts to the sea
Seas can dry out and leave thick layers of rock salt

Continents vs. Oceans

Fundamental difference
Oceanic crust is dense (2900 kg/m3)
Continental crust is buoyant (2700 kg/m3)
This is why there are ocean basins
What is wrong with the myth of Atlantis:
You can't get rid of a continent so easily
What is right:
The margins of continents do sink sometimes
Due to Earthquakes
Due to Slow subsidence

Methods of Studying the Sea Floor

Depth sounding
Dredging, coring
Sea Floor Drilling
Submersibles (Alvin, Sinkai)
Echo Sounder
Seismic Profiler
Remote Surveys: Magnetic, Gravity, Seismic Refraction
Deep Sea Cameras

Features of the Sea Floor

Depth of the ocean depends on the age of the sea floor
Deepest near the continents (particularly at the trenches)
Shallower along the mid ocean ridges (submarine mountain ranges)
Why?
Young oceanic crust is warm and buoyant
Old oceanic crust is cold and heavy
Continental Margins
Passive
Active
Oceanic trench
Midoceanic ridge
Seamounts

Passive Continental Margins

Continental shelf, slope, rise
The Continental Rise
Types of Sedimentation
Turbidity currents
Abyssal plains

Turbidity currents

Underwater avalanches
Sediment transported by gravity, not by moving water
Discovered only recently (1929)
TransAtlantic cable broken
Turbidites are very common in the rock record
Turbidites move sediment from the continental shelf to the slope and basin

Active Continental Margins

On land earthquakes, young mountain belt, volcanoes
Off shore Continental shelf, continental slope, oceanic trench

Oceanic Trenches

Deepest parts of the Ocean
Up to 12,000 meters deep (Mt. Everest is less than 9000 m high)
Located along subduction zones
Earthquakes of the Benioff seismic Zones
Accretionary Prisms: Piles of sediment scrapped off the subducting plate and paltered onto continental margin

The Mid Oceanic Ridge

Rift Valley
Geologic Activity on the Ridge
Shallow focus Earthquakes
High Heat Flow
Basalt Eruptions
Submarine Hot springs
Biologic Activity on the Ridge
Geomicrobiology

Submarine Hotsprings

Black smokers
Spew out black clouds of metal-sulfur compounds
First observed in 1977 by Alvin submersible
New Ecosystem:
» Independent form the sun
» at 2500 m (8000 ft) depth
» energy from the hydrothermal vents
Very strange fauna
Giant clams
Tube worms
Albino crabs
 
Lectures 28- Shorelines
Reading: Chapter 20 of Tarbuck and Lutgets, 8th edition

Topics:

Shoreline processes-Moving water
Tides
Waves
Long shore Currents
Coastal Features
Beaches
Erosional Features
    Marine Terraces
    Headlands
Depositional Features
    Barrier Islands
Man-Made Features
 
Video on the implication of shoreline erosion for coastal communities

What is a shoreline

Moving Water at the Shore

Tides

Sea Waves

Wind -
Creates Most Ocean Waves

Nearshore Water Circulation

Beaches

Longshore Drift of Sediment

Coasts and Coastal Features

Erosional Coasts

  • Depositional Coasts

  • Drowned Coasts (rising relative sea level)

  • Uplifted Coasts (Emergent)

  • Coasts Shaped by Organisms