Geological Hazards Final Flashcards
Why do people choose to live near rivers?
Fertile soil
Transportation
Food source (fish)
Trade
What are the dangers of rivers?
Susceptible to flash flooding
Fast flowing water
What is the ‘hydrologic cycle’ and how can it be altered?
The natural cycle that circulates water throughout the environment to maintain an overall balance between water in the air, on the surface and in the ground.
Human activities that can alter the hydrologic cycle include:
Agriculture
Industry
Alteration of the chemical composition of the atmosphere
Construction of dams
Deforestation and afforestation
Removal of groundwater from wells
Water abstraction from rivers
Urbanization
What affects stream flow?
Weather
Snow accumulation and melting
Rainfall and snowmelt
Evaporation
Water use by plants
Vegetation
Subsurface water flows
Water withdrawal for irrigation and municipal water needs
Diversion for hydropower generation
Urbanization
What causes streams to either erode or deposite sediment?
Adequate stream flow
How do people mitigate against flooding dangers?
Levees
Dams
Channel straighening
Inundation maps
Transpiration (hydrologic cycle)
Water inside of plants in transferred from the plant to the atmosphere as water vapor.
Condensation (hydrologic cycle)
Vapor to liquid
Forms clouds
Precipitation (hydrologic cycle)
Rain or snow
Evaporation (hydrologic cycle)
Occurs when the physical state of water is changed froma liquid to a gaseous state.
Water comes from lakes or oceans
Run-off (hydrologic cycle)
Rivers or streams
Infiltration (hydrologic cycle)
The physical process involving movement of water through the boundary area where the atmosphere interfaces with the soil. The surface phenomenon is governed by soil surface conditions. Water transfer is related to the porosity of the soil ad the permeability of the soil profile. Water that is infiltrated and stored in the soil can also become the water that later becomes subsurface runoff.
Percolation (hydrologic cycle)
The movement of water through the soil, and its layers, by gravity and capillary forces.
Stream profile: head, mouth, gradient
Discharge
The volume of water flowing through a channel in one second.
Drainage area
Drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody such as a river, lake, reservoir, estuary, wetland, sea, or ocean.
Local base level
Where a stream’s gradient temporarily approaches or reaches zero before increasing again.
Can be a lake or reservoir or a layer of rock that is highly resistant to the stream’s erosive force.
Ultimate base level
All rivers and streams erode toward sea level, which is also known as the “ultimate base level.”
Capacity
The total amount of load that the stream can move.
Controlled largely by discharge.
Competence
Measures the largest particles that the stream can transport.
Controlled largely by velocity.
Hydrosphere
Water
- Oceans
- Lakes
- Rivers
- Groundwater
- Ice
What percentage of the hydrosphere is fresh water?
2.8%
Drainage systems
Defined by topography
Streams and mass wasting influencing topography
Stream processes (x3)
Sediment production
Sediment transport
Sediment deposition
Stream Morphology
Tributary (head)
Trunk
- Anastomosing streams
- Meandering streams
- Straight streams
- Braided streams
Distributary (mouth)
Sinuosity
Is a ratio expressing the amount of curvature along a stream.
Straight Streams
A single straight channel without sediment bars and with low sinuosity.
Braided Streams
Relatively straight channels carrying latge amounts of sediment typically found in mountainous areas.
Anastomosing
A river with several separate channels which divide and join along the river.
Meandering River
Have many bends which change the shape of the river through time by erosion on one bank and deposition on another.
High sinuosity
Meandering river: cut bank and point bar
Floodplain
An area of land between or beyond a stream which receives water when the river is at flood stage.
Terraces
Abandoned floodplains that formed when a river flowed at a higher level than it does today.
Old floodplains that are cut into by the current stream.
Deltas
A discrete shoreline protuberance formed at a point where a river enters an ocean or other body of water.
The distributary portion of a river with no set morphology.
3 Types of Deltas
Stream dominated (Yukon River, Nile River)
Tide dominated (Amazon River)
Wave dominated (Rhone River)
Natural Levees
Deposition of coarse sediment near the river channel when the river is in flood.
3 Types of Sediment Load
Bed load
Suspended load
Dissolved load
Sediment Load: Bed Load
Large material that moves along the bottom of a stream channel (rolling and saltation).
Material size: sand, gravel, and boulders
Sediment Load: Dissolved Load
Dissolved inorganic and organic material present in the water column.
Salts and organic compounds:
- Halite
- Silvite
- Pesticides
- Fertilizers
Flood
When the discharge of a stream becomes so great that it exceeds the capacity of its channel and overflows.
Too much water in the stream channel.
Events are often described as probability floods.
4 Types of Floods
Flash floods
Regional floods
Jokulhlaup
Dam-failure floods
Flood Types: Flash Floods
Occur with little warning, produce rapid rise in water level and may have very high discharge.
Common in mountainous, desert, and urban areas.
Localized devastation.
Flood Types: Regional Floods
Seasonal floods caused by snow melts and spring rain.
Common in relatively flat aras where rivers join.
Regional devastation
Flood Types: Jokulhlaup
Glacial outwash flood
Occur with little warning when a volcano erupts under a large mass of ice or water breaches an ice dam.
Relatively uncommon
Regional devastation
Flood Types: Dam Failure Floods
May occur with little warning process occurs by failure of a dam or levee designed to retain water.
Relatively uncommon
Local devastation
Mitigation Methods for Flooding
Levees
Dams
Channel straightening
Inundation maps
Mitigation Methods: Levees
High mound of sediment placed parallel to a channel to prevent flooding.
Mitigation Methods: Dams
Dam types by use:
- storage,
- diversion,
- detention
Dam types by materials:
- Earthfall
- Rockfill
- Steel
- Wood
- Concrete
Mitigation Methods: Channel Straightening
A process were-by meander bends are removed from a channel in order to increase the discharge.
This leads to increased erosion and increased river gradients.
4 Drawbacks to Flooding
Loss of property
Loss of infrastructure
Loss of life
Toxic waste in water
- Sewage
- Chemicals
- Other waste
Benefits of Flooding
Fertile soil
Healthy wetland ecosystem
- Increased biodiversity
- Increased water quality
Significant Floods (3)
California Flood (1861-1862)
ARkStorm Model
Big Thompson Flood 1976
California Flood of 1891-1862
Started December 24th 1861
Raining lasted 45 days
Creation of inland sea
- Area flooded
- 480km (300mi)long
- 32km (20mi) wide
State government moved to San Francisco and stayed for 18 months
Deaths unknown
Property damage unknown
Big Thompson Flood, Colorado 1976
Peak discharge 3.8 x higher than 100 year flood.
Low probability flood
~12.5 “ of rain in 4 hours
1/3rd of the drainage basin
15 mph
Crest of the flood ~19’
Exceeded previous record by 10’
139 people died
Oxbow lakes
A U-shaped body of water formed when a wide meander from the main stem of a river is cut off to create a lake.
Energy for geohazards
Hurricanes, thunderstorms, tornadoes, etc. driven by the SUN’s energy.
Atmosphere
Made of gas: Nitrogen, Oxygen, Argon, Carbon Dioxide
Gets thinner
Separated into layers:
- Exosphere (gas escapes to space)
- Thermosphere (very small amounts of gas, Aurora)
- Mesosphere (small amounts of gas, slow meteors down)
- Stratosphere (ozone created, NO convection)
- Troposphere (all weather happens here)
Layers are defined by: thermal charactaristics, density, composition, and movement
Redistribution of heat: conveciton cells
Convection of air in the troposphere
Influences where wet and dry areas are
Redistribution of heat: jet stream
Found near temperature gradients
Flow west to east
Follow the sun
Redistribution of heat: Oceans
Surface current driven by wind
Deep ocean currents driven by density
Ocean Circulation
Antarctica is isolated from mid-latitude from mid-latitude heat transfer (Antarctic Circumpolar Current)
Greenland is not insulated from mid-latitude heat transfer (Gulf Stream/ Norwegian)
Temperature
Heat is provided by the sun
Changes with altitude (3-5 degrees F/1,000’)
Land heats and cools quickly
Water heats and cools slowly
Humidity
Measure of how much water vapor the air contains
Warm air holds more water than cool air
Relative humidity
The relationship between how much moisture is in the air versus how much it is capable of holding.
50% relative humidity = air is half full
>100% relative humidity = rain
Dew Point
Is the temperature to which the air must be cooled to reach saturation
High dew points indicate very moist air
Low dew points indicate very dry air
Temperature and humidity
Changes laterally
Control air pressure
Air pressure
Amount of pressure exerted by the atmosphere
High air pressure zones: diverging air
As the air spreads away, cool air from above must sink to replace it and warms
Warm air can hold more water vapor, which means that clouds will tend to evaporate
Why fair weather is often associated with high pressure
Low air pressure zones: converging winds
Air forced to rise and then cool
Cold air holds less water vapor so some condenses, forming clouds and precipitation
Why there is often inclement weather near low pressure areas
Wind
Wind follows pressure gradient
The steeper the gradient the stronger the wind
Acted on by gravity, Coriolis effect, friction, and centrifugal forces
Coriolis Effect as it applies to weather
Leads to deflection of moving air masses
5 Types of Weather Fronts
Cold front
Warm front
Stationary front
Occluded front
Trough
Cold Front
Dense cold air displaces warm moist air
Can form thunderstorms
Warm Front
Warm moist air displaces dense cold air
Stationary Front
A front between warm and cold air mases that is moving very slowly or not at all.
Occluded Front
A composite of two fronts, formed as a cold front overtakes a warm or quasi-stationary front.
Trough
An elongated area of relatively low atmospheric pressure
Where do storms form?
At the boundaries between fronts
Clouds
High-level clouds (12km-5km)
Mid-level clouds (5km-2km)
Low-level clouds (2km-okm)
Warm Problems (x5)
Sever thunderstorms
Lightning
Torrential downpours
Tornadoes
Hurricanes
Cold Problems (x4)
Blizzards
Windchill
Frostbite
Hypothermia
Tornado key points (x4)
Surface geohazards, related to the sun (ultimately)
Largely a US phenomenon (spring and summer)
Sometimes funnel is not visable
These days, much easier to predict and get to safety (Doppler Radar)
Where do tornadoes come from?
Form at trailing end of thunderstorms within warm, moist air in front of eastward moving cold fronts
Can also form in front of hot, dry air flowing from the west
And where air is sweeping up mountains
Tornado factoids
In an average year,
- ~800 tornadoes
- ~80 deaths
- ~1500 injuries
Wind speeds over 250 mph
Can travel up to 219 miles (typically shorter ~50miles)
Damage over 1 mile wide
Average forward speed of 30mph
- Can be stationary
- Top speed 70mph
Fujuta Scale
F-0 (light damage)
F-1 (moderate damage)
F-2 (considerable damage)
F-3 (severe damage)
F-4 (devastating damage)
F-5 (incredible damage)
Not merely based on wind speed
Takes kinto accound damage using set of 28 “damage indicators”
Also looks at “degree of damage”
3 Other words for hurricanes
Typhoons
Cyclones
“Big wind”
What are hurricanes?
Is a large, warm-core, low-pressure storm system over tropical or subtropical waters with water temperatures of at least 25 degrees C
- Counterclockwise in N hemisphere, clockwise in S hemisphere
Wind sppeds of > 120kph, can exceed 260kph
How do hurricanes form?
Begin over warm seawater (at least 25 degrees C), typically b/t 5-20 degrees latitude
Air rises due to localized heating, causes condensation, and formation of towering convective “chimneys”
Warm, moist air spreads out at top “chimney”
Rising warm air expands, cools, and releases latent heat
Rise of air in eye wall pulls more moist air into center of the storm from low elevations
Coriolis forces initiate rotation in rising air with the highest winds and lowest pressures focusing toward the core of the storm
Hurricane rotation
The eye of the storm is generally 20-50km in diameter
- Wind drops from high speeds to low speeds at wind “wall”
Whole storm may be 160 to >800km in diameter
Follows prevailing winds, traveling at ~25kph
Features of hurricanes
Defined as a hurricane when sustained wind speeds reach 74mph (119kph)
Always move toward the west and spin about the eye
Need high humidity, light wind, and warm sea surface temperatures
Hurricane season
The Atlantic: begins June 1st and ends November 25th
The Eastern Pacific: begins May 15th and also ends November 30th
Where do hurricanes come from?
Often begin in warm waters off the west coast of Africa, then move westward across Atlantic with trade winds
Warm, pick up wind speed and energy, and often develop into hurricanes before they reach Americas
Generally track west, northwest, and then north, either off the southeast US or sometimes onto continent
Storm classifications (4)
Tropical depression
Tropical storm
Hurricane
Major hurricane
Tropical depression (storm classification)
A tropical cyclone with maximim sustained winds of 38mph (33 knots) or less.
Tropical storm (storm classification)
A tropical cyclone with maximum sustained winds 39-73mph (34-63 knotts)
Hurricane (storm classification)
A tropical cyclone with maximum sustained winds of 74mph (64 knotts) or higher
Major hurricane (storm classification)
A tropical cyclone with maximum sustained winds of 111mph (96 knotts) or higher, corresponding to a Category 3, 4, or 5 on the Saffir-Simpson Hurricane Wind Scale
Hurricane factoids
80-90 tropical storms each year
45 hurricanes each year
6 named hurricanes per year in Atlantic Ocean and gulf of Mexico
More than 44 million people live in coastal areas in the US susceptible to these storms
- Gulf Coast and southern Atlantic coasts
- ~15% of total population
1900 Galveston Hurricane
September 8th
Category 4 hurricane
Barometric pressure fell to 28.55 in of Hg
Winds estimated at 140mph
Storm surge of 15.7’
Deadliest in US history (estimated minimum death toll of 6,000, likely 8,000-12,000
2005 Hurricane Katrina
Category 3
Barometric pressure of 902 mb
125 mph sustained wind
Though not the strongest, one of the costliest and deadliest (over $100 billion in damages, 1,836 dead)
Category 3 storm hit New Orleans dead on
Most of the damage due to levee failure following storm surge (more than 50 failures) –> 80% city flooded
Showed failures in US protection
Tornado watch
Tornadoes are possible in your area. Remain alert for approaching storms.
Tornado warning
A tornado has been sighted or indicated by weather radar. If a tornado warning is issued for your area and the sky becomes threatening, move to your pre-designated place of safety.
What is the Enhansed Fujita Scale used to measure tornadoes? How is the scale created?
Rate the strength of the tornadoes in the US and Canada based on the damage they cause.
Implemented in place of the Fujita scale
It was revised to reflect better examinations of tornado damage surveys, so as to align wind speeds more closely with associated storm damage. Better standardizing and elucidating what was previously subjective and ambiguous, it also adds more types of structures and vegetation, expands degrees of damage, and better accounts for variables such as differences in construction quality.
3 common myths about tornadoes
It is thought by some people that taking shelter under highway overpasses or in the southwest corner of the building provides extra protection from a tornado, but both of these probably increase the danger of injury or death. Some still believe that opening windows ahead of a tornado will reduce the damage from the storm, but this is not true. Some people also believe that escaping in a vehicle is the safest method of avoiding a tornado, but this could increase the danger in some situations.
What is the highest wind speed ever recorded in a tornado?
318 mph
What is the relationship between thunderstorms and tornadoes?
Thunderstorms produce tornadoes
How long do tornadoes last?
Several seconds to more than an hour.
