Base Level
-the level below which a stream cannot erode
-the ocean (larger streams), river, lake or pond (smaller streams) that a stream flows into
Q: Base level __________________.
is the level below which a stream cannot erode
Drainage Basins- Large & Small ?
NEED TO KNOW? p. 343 & slide 3
Floods are exceeded..
-Largest past event likely to be exceeded at some point
Q: The largest flood known in an area is likely to be exceeded someday by a larger one, even in an area with a long history. True or False? TRUE
Equilibrium Factors
1. Discharge- rate of water flow in volume per unit of time
2. Sediment load- the available clay, sand, and larger rock material waiting to be moved
3. Gradient- stream bottom slope
4. Sinuosity/Channel Pattern- crookedness, (length)/(distance between end
Straight Streams
Q: A stream with very little bed load will result in what type of channel pattern?
-straight
Sinuosity
-the "crookedness" of a stream
-the length of a stream divided by the straight-line distance between its two ends
High Discharge (Too Much Water)
-stream will flow faster, with higher energy
-energy is spent on (a) erosion of stream bottom and banks and (b) increased sediment load
-erosion results in (a) decreased gradient/slope of stream bottom, flatter profile and (b) increased sinuosity- meander
Meandering Stream
Q: If a stream has a meandering section, that section is most likely to be ________________.
-in its downstream section, near its mouth
Q: Q: If a stream experiences more energetic water flow, the stream ___________________.
-responds by increasing the si
High Sediment Load
-stream gets choked with sediment
-the excess sediment builds up on channel bottom, which (a) increases gradient and (b) makes stream flow faster
-faster flow increases load-carrying capacity
-channel straightens to shorten the flow distance and increase
Braided Stream
Q: If a stream is choked with sediment and has insufficient water to carry it away ________________.
-the water will pick its way through as a braided stream
Q: A braided stream has ____________.
-too much sediment to carry
Lake Filling ?
NEED TO KNOW? p. 346, slide 13
Flood Frequency Curves
-larger floods -> longer recurrence times between each
-plot flood discharge volumes vs. recurrence interval
-can be used to estimate return time of given size flood
Recurrence Interval
return period - % chance of occurring any 1 year
2yr-50%, 5yr-20%, 10yr-10%, 20yr-5%, 50yr-2%, 100yr-1%
Q: Assume that we have a 25-year flood here this year. What is the probability that a 25-year flood will occur here next year? 4.0 PERCENT
Q: Statistic
Flood Styles
slide 21
Q: Killer floods are caused by __________________.
A. local thunderstorms
B. abundant rainfall lasting for days
C. the storm surges of tropical cyclones flooding the coasts
D. the break-up of winter ice on rivers
ALSO CAUSED BY: failure of short-
Flash Floods
-intense precipitation over short time span
-commonly by thunderstorms
-50% of flash flood deaths are vehicle related
Q: Most flood-related deaths in the United States are caused by ___________________.
-flash floods from local thunderstorms
Q: About 50%
Big Thompson Canyon, Colorado
-flash flood, 1976
-killed 139
Q: In 1976, a flash flood near Estes Park, Colorado, killed at least 139 people. This flood was on
-the Big Thompson River.
Regional Floods ?
?
Great Midwestern Flood of 1993
Q: At the end of August 1993, the upper Mississippi River basin had endured record high floods yet this flood water mass did not significantly affect the lower Mississippi River basin because -the input from the Ohio River flow was low.
Q: Which of the fo
Levees ?
? p. 359, slide 43
Huang (Yellow) River
-has supposedly killed more people than any other natural feature
-1887 floods killed around 1 million people (famine & flood)
Q: The __________ is reputed to have killed more people than any other natural feature
-Huang (Yellow) River in China
Q: The 188
Red River
-likely to flood each spring because:
-geologically young (about 9000 years old), has not carved a deep valley.
-gradient/slope of the riverbed is very low.
-river flow increases as snow melts, meltwater runs northward into still frozen parts of the river
Societal Responses to Flood Hazard
structural: dams, levees, sandbagging, channelization
Q: Efforts to control rivers include _____________.
A. dams
B. levees
C. channelization
Dams ?
? p. 360, slide 49
Levees ?
? p. 361, slide 50
Hydrographs
Q: A hydrograph is a plot of _________________.
-the volume of water or stream-surface height versus time
Urbanization and Floods
-increased runoff (less water soaks into ground)
-increased discharge
-higher stream levels
-short lived high levels- flash flooding more frequent
Urbanization makes hydrograph curve much steeper
-urban flood might only last 20% as long but be 4x higher
Q
Channelization
-makes channels- clear of debris, deeper, wider, straighter, smoother- results in excess flow/"too much discharge"
-routes water downstream, straightens path, faster flow, intensifies downstream flooding and erosion
Q: With respect to channelization, stra
Ice-Dam Failure Floods
Biggest floods on Earth happened during melting of continental ice sheets- lakes behind ice dams that failed suddenly
Q: The most famous of the ice-dam failure floods is preserved in the "channeled scablands" topography in __________________.
-Washington
US Geological Survey stream-gauging stations
-measures water depth, channel width, water velocity
--allows calculation of discharge/flow volume
-more than 7,000
Q: United States Geological Survey stream-gauging stations measure all but which of the following?
-amount of sediment being carried by the
Chemistry of Fire
-chemical equation for fire is the same as for photosynthesis, except opposite
Q: In the photosynthesis reaction in plants, consumption of ________ is part of the reaction.
-water AND carbon dioxide
Q: In the photosynthesis reaction in plants, OXYGEN is g
Fire-related Deaths
Q: The trend of annual fire-related deaths in the United States over the last 20 years has- decreased, despite population increase.
Q: In terms of human death from fire, the single-most dangerous structure in the U.S. is the- family home
Q: The vast major
The Fire Triangle
-fire requires fuel, oxygen, and heat
Q: What are the components that make up a fire triangle? Fuel, Oxygen, Heat
Fire Dependent Ecosystems
-grasslands, seasonal tropical forests, Mediterranean-climate shrublands (California, Australia, South Africa, Mediterranean region)
-wildfires needed for seed germination (smoke and/or heat), parasite control
Q: In Mediterranean climates such as in the C
Fuels
Q: The organic debris left on the ground after logging or windstorms is called SLASH
Q: Grasses have broad, exposed surfaces resulting in FAST-SPREADING FIRES
Q: The most intense fires occur in SHRUBS CONTAINING HIGH CONTENTS OF NATURAL OILS
Q: Wildfires
Ladder Fuels
Q: The term "ladder fuels" refers to- vegetation of varying heights, which allow fire to quickly climb upward
Q: Fire burns faster UP A SLOPE
Stages of Fire
Preheating- water expelled from fuel
Thermal degradation - pyrolysis
Flaming Combustion- of pyrolized gases
Glowing Combustion - no flames, slower burning (slow oxidation), lower temperature
Pyrolysis
Q: Pyrolysis results in emanation of- flammable hydrocarbon vapors, tar , and water vapor , BUT NOT oxygen
Q: During burning, the chemical structure of solid wood breaks apart and yields- flammable hydrocarbon vapors , water vapor , tar , mineral residues
Flaming Combustion
-flaming combustion of pyrolized gases-oxygen presence
-stage of greatest energy release
-released heat transfer through: convection, radiation, diffusion, conduction
Q: Transfer of heat occurs by- conduction, radiation, convection, diffusion- NOT refusio
Spread of Fire
-depends on four factors: fuel (type of plant/material), weather (esp. wind), topography (shape of the land), and behavior within the fire itself
Q: The spread of fire depends on behavior within the fire itself and on- type of fuel, weather, and topograph
Foehn WInds
-high pressure air mass spilling over mountain range toward low pressure zone; warm dry wind
Q: Fierce winds occur when a high-pressure air mass spills over a mountain range and descends as warm, dry wind toward a low-pressure zone. These winds are called
Local Winds
-sea breezes & land breezes, slope winds & valley winds
Q: Sea breezes reach their maximum on-shore wind speeds- during the hottest part of the day
Santa Ana Winds
-foehn winds in Southern California
-blow southwest from land to over the Pacific Ocean
Q: Which of these drives fires in Southern California? Santa Ana winds
Q: Santa Ana winds blow- from land towards the seashore
Great Lakes Region Fires
-1871
-Chicago, Illinois partially/largely destroyed
Q: Which of the following was partially destroyed by a large fire in 1871? Chicago
Q: Which of the following was largely destroyed by fire in 1871? Chicago
How to burn down your house
1. on slope; 2. made of wood; 3. wooden deck; 4. firewood; 5. flammable shingles; 6. tree limbs over house; 7. shrubs around house; 8. large glass windows facing slope; 9. louvers facing slope; 10. chimney lacks spark arrestors; 11. poor access; 12. woode
Yellowstone
-1988, 1.4 million acres burned- almost half of Yellowstone
Q: In 1988, a U.S. national park had fires that burned over a million acres of forest. That park was- Yellowstone National Park, Wyoming, Montana, and Idaho
Prescribed Fires
Q: Prescribed fires are designed to control- build-up of underbrush that frequently fuels wildfires
Gravity
-gravity vs. inertia & friction
Q: Before a landslide mass begins to move downhill, it must overcome INERTIA AND FRICTION
Creep
-slowest but more widespread form of slope failure
Landslides ?
-typical landslide: mass whose center of gravity has moved downward and outward, with tear-away zone upslope and pile-up zone downslope
Parts of a landslide????
p. 405, slide 123
External Causes of Slope Failure
-adding mass high on slope (sediment deposition)
-steepening slope (fault movements)
-removing support from low on slope (stream/ocean-wave erosion)
Q: External processes that increase the odds of a slope failure include-
A. adding mass high on a slope, a
Internal Causes of Slope Failure
-inherently weak materials (clay)
-water (in different roles)
-decreasing cohesion
-adverse geologic structures
Clays
-material most commonly associated with earth failures
-form primarily by physical weathering
-bulk chemical composition of feldspars and clays are similar, but internal structures are radically different
-chemical composition of clays can change -> alter
Quick-Clay
-most mobile of all deposits; "fine rock flour"
-"house of cards" structure held together by salt
-freshwater passing through uplifted sediments dissolves & removes much of sea salt 'glue'
-leaves quick clay with (a) weak structure, (b) grains mostly less
Roles of Water
Ways that water weakens earth materials:
-WEIGHT- fills pore spaces, heavier than air
-ABSORPTION & ADSORPTION- water is absorbed & adsorbed by clay minerals -> decreases strength
-ABILITY TO DISSOLVE CEMENT- flows through rocks -> dissolves minerals hold
Piping
-formation of conduits? due to erosion by water moving underground
Q: Subsurface erosion by groundwater can cause PIPING
Groundwater & Water Table ?
? p. 409, slide 130
Quicksand
-occurs where sand grains are supersaturated with pressurized water
-pore-water pressure = weight of sands -> no shear strength
Q: Escaping water within a sand body may create quicksand when- the uplifting force of the water EQUALS the weight of the sand
Ancient Slide Surfaces
-weaknesses that tend to be reused over time
-reactivation of ancient slide surfaces: sliding creates smooth, slick layer of ground-up materials that can easily slide over and over again, especially when wet
Q: Many hill-slope masses are weak due to preex
Structures within Rocks
Rock weaknesses that set up slope failure-
-rocks that are not cemented together
-clay layers that provide basal slip surfaces
-soft rock layers sliding off strong materials
-joints splitting & separating rock
-ancient fault acting as slide surface
Q: Roc
Daylighted Bedding ?
Many hill-slope masses are weak due to preexisting geologic conditions such as:
a) ancient slide surfaces
b) ROCK LAYERING DIPPING LESS THAN GEOGRAPHIC SLOPES
c) structures within the rocks, including as fractures, ancient faults, and thin clay seams
Mass Movement Triggers
-most failures have complex causes- underlying causes + immediate cause AKA trigger
-triggers- heavy rains, earthquakes, thawing of frozen ground, the construction projects of humans
Q: The sum of all the underlying causes can push a slope to the brink of
Mass Movement Classification
Downward- falls, subsides
Downward and outward- slides, flows
-speed of movement (extremely slow to extremely rapid) and water content (wet or dry)
Falls
-occur when elevated rock masses separate along joints, bedding (rock layers) or weaknesses -> falls DOWNWARD through air IN FREE FALL -> hits the ground -> bounds (bounces) and rolls
Ex: Yosemite National Park, California
Slides (Landslides)
Translational- along STRAIGHT surface
Rotational- along CURVED surface
Rotational Slides
-move downward and outward on top of curved slip surfaces
-movement is more or less rotational about an axis parallel to the slope
-when a slump occurs- head moves downward and rotates backward, toe moves upward, riding out on top of the landscape
-move s
Translational slides
-move down and out by sliding on planar (straight) slip surface- faults, joints, clay-rich layers (bedding), etc.
-move as long as they sit on downward-inclined surface & driving mass exists
-different behaviors- need to know??
Q: In TRANSITIONAL SLIDES m
Flows
-mass movements that behave like fluids
-internal movements dominate, slip surfaces absent or short-lived
-range of: materials, water contents, velocities
-many names:
Long-Runout Debris Flows
-AKA sturzstroms
-most spectacular, complex mass movement
-massive rock falls that convert into highly fluid, rapid debris flows that travel far
-very large rock falls travel long distances- imply lower coefficients of internal friction
Q: A sturzstrom is
Movement of Highly Fluidized Rock Flows
Most likely hypothesis for fast and far movement-
-blocks in moving mass hit blocks in front of them, imparting kinetic energy -> vibrational or acoustical energy propagates as internal waves, fluidizing rock debris (acoustic fluidization)
Q: The most lik
Snow Avalanches ?
slide 161, p. 424
Mitigation ?
p. 426, slide 168
Subsidence
-ground surface sags gently
--slow compaction of loose, water-saturated sediments or
OR
-drops catastrophically in hours or days as spaces in rocks collapse
--rapid collapse into caves
Nevados Huascar�n
-1970, Peru
-mass movement triggered by 45 second magnitude 7.7 earthquake
Q: A mass movement at Nevados Huascaran in 1970 was triggered by- a very large earthquake.
Catastrophic Subsidence
-limestone forms from the CaCO3 shells of marine organisms
-limestones dissolve in naturally acidic groundwater flowing through them -> forms extensive water-filled caverns
-H2CO3 = carbonic acid (formed from carbon dioxide)- primary variable controlling
Cost of Disasters in Kansas
-never very many killed, but lots of financial difficulty brought on by bad weather
Lawrence Hailstorm
-April 1991-a hailstorm in Lawrence did about $50 million in damage to cars and roofs within a few minutes. Because most of the damage was insured, the storm actually caused a small economic boom in Lawrence. Roofing companies were extremely busy for many
Kansas Hailstorms
-Until a 2003 storm in Nebraska, the largest hailstone on record was found in Coffeyville, Kansas, on September 3, 1970
Freeze Damage
-Late freezes (early May) can cause major financial damage to growing winter wheat crops.
-At the end of the first week of May 1981, for example, more than 100 million bushels of potential wheat yield in Kansas was lost in a freeze. This translates into h
Blizzards
...