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UA / Geology / GEOL 104 / A tsunami was caused by what?

A tsunami was caused by what?

A tsunami was caused by what?

Description

School: University of Alabama - Tuscaloosa
Department: Geology
Course: Hazardous Earth
Professor: Rona donahoe
Term: Fall 2016
Tags: Geology, Natural Hazards, Hazards, Tsunami, Flooding, volcanoes, Exam 2, and Study Guide
Cost: 50
Name: GEO 104-001 Exam 2 Study Guide
Description: Here is my personal study guide that I have created for our second GEO 104-001 exam. This study guide covers (in detail) material from chapters 4, 5, and 6 that may be presented on the exam. This study guide includes a self quiz section made up of multiple choice, true false, and matching questions. Answers to the self quiz section can be found highlighted throughout the study guide and also at the
Uploaded: 10/21/2016
20 Pages 40 Views 5 Unlocks
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GEO 104-001 Exam 2 Study Guide


Tsunami was caused by, what?



Chapter 4: Tsunamis

Tsunami  

• Japanese for “harbor wave”

• Caused by a sudden vertical displacement of ocean water

Earthquake caused tsunami

• Earthquake suddenly uplifts or downshifts the seafloor 

o Need M 7.5 or greater to create enough displacement 

o Rupture uplifts or collapses the sea floor

o Dome forms on the surface of the water above the fault

o Dome collapses and generates the tsunami wave

o Waves radiate outward (pebble in pond)

o More than one wave produced by oscillations/aftershocks

• Tsunami moves rapidly in deep ocean 


What are the three ways that silicate rocks melt?



o Can travel >720 km/hr (~500 mph)

o Spacing (frequency) of crests is large 

o Amplitude of waves is low 

▪ Boats in open ocean don’t notice the tsunami waves

• Tsunami nears land, loses speed, gains weight 

o Depth of ocean decreases, slowing tsunami waves to ~28 mph 

▪ Wave frequency increases 

▪ Amplitude increases 

• Tsunami moves inland 

o destroys everything in path We also discuss several other topics like What is the nature of commitment?

o first wave can be meters to 10s of meters thick


How does magma forms?



o trough may arrive first, exposing seafloor

o often arrives as rapid increase in sea level

o Runup 

▪ Furthest horizontal and vertical distance the largest wave moves inland o Water returns to ocean in strong flow

o Edge Waves 

▪ Generated from when the tsunami waves hit the shore

▪ May be generated parallel to shore Don't forget about the age old question of What are the new techniques in agriculture?

o More waves likely that may be amplified

• offshore earthquakes can cause tsunamis to go toward land and out to sea o uplifted dome of water splits in two waves

• 1. Distance Tsunami 

o travels out to sea and can travel long distances with little loss of energy • 2. Local tsunami Don't forget about the age old question of Cancer is a disease of what?

o travels towards land quickly

o little time to react

Landslide caused tsunamis:

• Submarine landslides

o Occur when landslides occur underneath water- water displaced vertically • On land, rock avalanches from mountains can cause tsunamis

o EX. Lituya Bay, Alaska 1958

Regions at risk:

• All oceans, coastlines, areas near/across from major subduction zones • Highest risk areas:

o Pacific Ocean rim

o Northern Mediterranean

o Northeastern Indian ocean  

Tsunami effects:

• Primary effects (during hazard)

o Flooding, erosion and deposition of sediment

▪ Shortens and reshapes coastline

▪ Debris erodes both landscape and human structures

• Secondary effects:

o Fires

o Contaminated water supplies

o Disease

• Tsunamis can also be triggered by

o Earthquakes, landslides, volcanic eruptions, asteroids If you want to learn more check out Who is alexander hamilton?

▪ Asteroids can produce a “mega-tsunami”

• Ex. Chicxulub impact

o

• Caused by tsunami We also discuss several other topics like What is a predator?

o Coastline erosion, deposition of sediment

Natural service functions

• Nutrients/sediments from ocean needed by soil

• sediment needed to build shoreline

Human interaction

• Cannot prevent or control tsunami 

• Human activity does not affect frequency or magnitude We also discuss several other topics like What are the three things a video needs to go viral?

• Increased use of shoreline increases risks and consequences

• Past tsunamis help minimize destruction

o Buildings which survive

o Buffer zones of trees and green space

Minimizing hazard:

• Detection and warning

o Tsunami warning system

▪ Only 2 in the world

▪ Seismographs to detect earthquakes 

▪ Automated tidal gauges to determine sea level changes

▪ Buoy sensors with tsunameter to detect small water pressure changes in  ocean

o Information relayed by satellite to give arrival time and estimates

o Sirens

• Building codes

• Tsunami runup maps

o Show level to which water traveled inland/ used to help determine future hazard • Land use

o Vegetation/land development monitoring can provide defense

• Probability analysis- Risk = probability x consequences 

o Identify potential earthquake sources

o Specify relationship that increase or decrease tsunami waves

o Apply probabilistic analysis to the tsunami hazard

• Education

o Educate people on warning signs of tsunami  

▪ Tsunami watch 

• Possible trigger has occurred for a tsunami 

▪ Tsunami warning 

• A tsunami has been detected 

• Tsunami ready  

o Establish emergency operation center

o Be able to receive tsunami warnings

o Have ways to alert public

o Develop a preparedness plan with drills

o Promote community awareness programs

Sumatra cave records:

• Cave contained record of tsunamis that had impacted the island between 7,500-3,000 • Deposits are easy to see between layers of bat guano

• Scientists have identified 7-10 tsunami deposits

What to do:

• Feel strong earthquake? Leave coastline immediately

• If ocean recedes, run from beach

• Do not assume that all locations are safe because of an absence of dangerous waves  elsewhere

• Stay out of dangerous areas until “all clear” notice is given

• If you hear a siren, move away from coastline to higher ground

• If aware that tsunami watch or warning has been issued, don’t approach areas of coastline  to watch tsunami

Chapter 5: Volcanoes

Intro to volcanoes:

• Activity is directly related to plate tectonics

o Most volcanoes are near active plate boundaries 

o Some are associated with hot spots

• Magma is created at plate boundaries 

o Magma 

▪ Molten rock below the surface

o Lava 

▪ Molten rock on the earth’s surface  

o Volcanoes form around a vent 

▪ An opening through which lava or other volcanic material is ejected 

• Ring of fire contains 2/3rds of the worlds active volcanoes  

How magma forms 

• Most magmas come from asthenosphere

o Weak, but not molten, layer of rock

• Three ways that silicate rocks melt 

o 1. Decompression melting (dry rock only) 

▪ pressure put on hot rock is decreased the closer it is to the surface

▪ occurs at divergent boundaries, continental rifts, and hot spots

o 2. Addition of Volatiles (how wet rocks melt) 

▪ chemical compounds (usually water) that lower melting temp of rock

o 3. Addition of Heat 

▪ as magma rises, it releases heat to overlying rocks  

▪ Stoping

• Magma makes its way to shallower depths

▪ Assimilation

• Magma breaks pieces of rock off as it rises and if the magma is hot  

enough the rock will melt (assimilate) into the magma  

Magma properties

• Magma viscosity (ability to flow) is determined by

o Silica content (high silica (SiO2) =low viscosity) 

o Amount of dissolved gases (volatiles) 

o Temperature 

▪ Basaltic erupts at a higher temperature than andesitic 

• Three major types of magma based on silica content (low to high)

o Less than 40%= ultra-mafic rocks

o Basaltic (40-55% silica) ocean islands

o Andesitic (55-65% silica) island and volcanic arcs (wherever there’s a subduction  zone)

o Rhyolitic (>65% silica) continental volcanoes

• Viscosity affects the flow of lava- effects shape/ eruption style of volcano • Lavas volatile content determines how explosive the eruption will be 

o High volatile content = explosive eruption 

o As silica content rises, so does volatile content 

▪ Felsic magma (2-5% volatiles)

▪ Mafic magma (<1% volatiles)

o Rapid decompression (lowering of the pressure as the magma rises to the surface)  results in explosive release of volatiles 

• Explosive eruptions produce tephra or pyroclastic debris

o Tephra (all material of volcanic origin) is classified by particle size

▪ Ash (smallest- finer than coarse sand)

▪ Lapilli (medium in size, about the size of a walnut)

▪ Blocks  

• comes out of the vent as a cold particle

▪ Bomb

• lava blob ejected out of the volcano and is shaped into a teardrop  

shape as it fly’s through the air

▪ pyroclastic deposit

• accumulation of tephra

o tuff - pyroclastic rock formed of consolidated ash

Shield Volcanoes:

• largest in world - Hawaiian Islands, Iceland, Indian Ocean

• Basaltic magma - Low viscosity, low volatile content 

o Gently flowing magma, non-explosive eruptions 

• Build from lava flows 

o “warriors shield”

• Can form Lava tubes underground 

Composite Volcanoes:

• More viscous magma, higher volatile content 

o Basaltic to andesitic and rhyolitic lava 

• Produce combination of lava flows + pyroclastic deposits 

o Cone shape – Stratovolcanoes 

• Violent/dangerous explosions 

o Mount St. Helens, Mount Rainer, Mount Fuji

Volcanic Domes:

• highly viscous magma, highly explosive eruptions 

• After eruptions small domes tend to form in the crater 

o Lassen Peak, Mono Craters

Cinder Cone Volcanoes:

• Small volcanoes- form from buildup of tephra 

o Small pieces of black/red lava

o Form when lava meets groundwater 

• Common on larger volcanoes, normal faults, or along cracks and fissures o Also known as scoria cones 

o Parícutin, Mexico

Features:

• Craters: 

o Depressions formed from explosions/collapses of volcano tops 

o Few kilometers in diameter (a mile)

• Calderas: 

o Large craters formed from violent collapse of a cone 

o Can be 20 or more kilometers (12 or more miles) in diameter + contain vents/hot  springs

o Eruptions are very rare but are extremely violent 

▪ produce large amounts of ash + forms calderas

▪ media – “super volcanoes” 

▪ most recent North American caldera eruptions:

• 640 mya Yellowstone National Park

• 700 mya Long Valley, Calif.

• Vents: 

o Any opening for lava and debris 

o Can be circular or thin fissures

o Can produce flood basalts

• Hot springs: 

o Hot rocks heat groundwater that is discharged at the surface 

• Geysers: 

o Groundwater boils, erupting steam at surface 

Origins:

• Mid-Ocean Ridges/ Continental Rifts 

o Basaltic magma comes directly from asthenosphere

o ¾ of all lava extruded on Earth

o if on land, shield volcanoes form

o Iceland at Mid-Atlantic Ridge

• Subduction Zones 

o Composite cones from here

o Most common on Pacific Rim

o Andesitic magma w/ intermediate silica content

o Account for over 80% of eruptions in historic times

▪ Cascade Mountains

• Hot spots beneath oceans 

o Basaltic magma forms shield volcanoes

o Hot spot remains stationary building volcanic islands on seafloor

▪ Hawaiian Island chain

• Hot spots beneath continents 

o rhyolitic magma from mixes of rising magma and continental crust o caldera-forming eruptions

▪ Yellowstone National Park

Geographic regions: 

• Ring of fire – Pacific Ocean Subduction Zones

• Hot spots – Hawaii and Yellowstone

• mid-ocean ridges - Iceland

• rift valley – East Africa

Effects:

• 50-60 volcanoes erupt each year 

o US- 2-3 volcanoes erupt- mostly in Alaska

o Most eruptions are in regions with low populations

o 500 million people live close to volcanoes

Primary effects:

• lava flows 

o when magma reaches surface through crater or vent 

o basaltic, andesitic, rhyolitic

▪ basaltic is most abundant  

• basaltic are most rapid 15-35 km/h

o Pahoehoe lavas = smooth and ropey 

o Aa = blocky flows 

o Slow enough for people to get out of way 

• pyroclastic activity

o ash fall 

▪ vegetation may be destroyed

▪ surface water contaminated with sediment

• fine particles can harm fish life

▪ ash accumulation on roofs can cause structural damage

o lateral blasts 

▪ rock fragments blown horizontally from volcano at high speeds o pyroclastic flows 

▪ avalanches of hot ash, rock, volcanic glass fragments, gas 

• move rapidly down sides of volcano

o ash flows, hot avalanches, nuée ardentes

▪ incinerate everything in path

▪ responsible for more deaths than any other hazard 

▪ flow at 160 km/h, temps over 100 C

• gases 

o suffocation/poisoning

o acid rain produced by sulfur dioxide  

o Vog- volcanic smog 

Secondary effects:

• Lahars 

o Extremely dangerous events produced when loose tephra becomes saturated with  water, becomes unstable, and moves downslope (can be hot and cold events) ▪ Mud Flows 

• Ash sized particles mixed w/ large volumes of water 

▪ Debris Flows 

• Over 50% of particles = larger than ash 

▪ Populous areas of Pacific Northwest are built on old mudflows

▪ Sources of water

• Ice/snow melted by volcano, heavy rainfall

▪ Similar to wet concrete in viscosity

▪ Generally low temperature

▪ Can occur long after an eruption

• Landslides 

o Can be triggered by events other than an eruption 

o Can affect areas far from the source 

o Can cause tsunamis 

o EX. debris from massive landslides off coasts of Hawaii/ Canary Islands lies on  ocean floor

▪ Tenerife, Canary Islands- most recent landslide was over 150,000 years  ago

Mount St. Helens (1980)

o Cascade volcano (stratovolcano/Composite)- dormant over 120 years o example of Cascade volcanic eruption

o March 1980- seismic activity/small explosions

o May 1- bulge begins to grow  

o May 18 M 5.1 earthquake triggers 2.3 km3 landslide/debris avalanche of the bulge  area

o Seconds later, lateral blast from bulge area moves at rate of 480 km/hr (300mph) o 1 hour after blast, vertical cloud of ash extended 4 km into stratosphere o about 1 km3 of ash erupted over 9 hours, w/ ash falls covering areas of  Washington, northern Idaho, western and center Montana 

▪ pyroclastic flows begin to move down the northern slope 

o mudflows begin at speeds of 29 to 55 km/hr (18 to 34 mph)  

o 57 people killed 

o flooding destroyed over 100 homes

o 800 ft. of timber flattened

o damage = over $1 billion

o September 23, 2004- Mt. reawakens 

▪ Lava dome begins to form on crater floor

▪ Continues to form today 

Other Secondary effects:

• Earthquakes 

o Usually accompany/proceed volcanic activity

o Harmonic tremors signal movement of magma 

• Landslides 

o Mudflows, ashflows, and landslides are the most common secondary effects • Fire 

o Hot lava may ignite plants/structures

o Explosions of methane gas

• Climate Change 

o Ash and SO2 help cause global cooling

Natural service functions:

• Volcanic soils 

o Good for growing coffee, grapes, sugar cane, maize, pineapple, etc. • Geothermal Power 

o Can create energy for nearby urban areas

▪ Used in Hawaii, Cali., Japan, Iceland, etc.

• Mineral Resources 

o Metal deposits

o Non-metallic resources- pumice, tuff, etc.

▪ Used for soap, building stone, aggregate for roads, etc.

o Recreation

o Creation of new land

Human interaction with Volcanoes

• Humans do not affect the frequency or severity of eruptions 

• Minimization of loss of life and property damage is best action

o Forecasting v. Prediction- Involves

o Monitoring seismic activity

o Monitoring thermal, magnetic, hydrologic conditions

o Monitoring land surface for tilting, bulging

o Monitoring volcanic gas emissions

o Studying history of volcano or volcanic center

• Difficult to forecast because of infrequency 

• Monitoring seismic activity 

o Shallow earthquakes + swarms can precede eruption 

o May not provide enough time for evacuation

• Thermal, magnetic, and hydrologic monitoring 

o Hot magma changes temps, mag. properties, and groundwater level o Detected by satellite remote-sensing or infrared aerial photography o May also melt snow

• land surface monitoring 

o monitoring growth of bulges or domes

o Kilauea tilts and swells

• Monitoring volcanic gas emissions 

o Changes in CO2 and SO2 emissions correlate with subsurface volcanic  processes 

• Geologic history 

o Mapping and dating of volcanic deposits give idea of types and extents of  effects to be expected 

o Allows preparation of volcanic hazard maps

Minimizing volcanic hazard:

• USGS Alert Notification System 

o 2 components

▪ ground based 

▪ aviation based color code levels 

• four levels for each  

Perception of the volcanic hazard

• reasons for people to live near a volcanic hazard

o place of birth

o fertile land for farming

o people believe eruption is unlikely

o economic limitations

• good education can help produce people understand volcanic hazard

• Volcanic Crisis can develop when scientists predict a volcanic hazard for near future o Improved communications among scientists, emergency managers, educators,  media, and private citizens is key

o Goal is to prevent a disaster or catastrophe 

What can you do?

• Primary adjustment is evacuation

o Warnings may be ignored

o Warnings may be too late

• Psychologic adjustment to losses

Attempts to control lava flows

• Hydraulic Chilling 

o Water is used to chill and control the lava flow 

o Used in Iceland 

• Wall construction 

Chapter 6: Flooding

1973 

• 100-year floodof Mississippi R. + Tributaries

• Damage upward of $1.2 billion

1993:

• Mississippi river floods again 

• rained on and off from April through July – total of 35+ inches of rain • 50 deaths

• $15 billion in damage  

2008:

• Mississippi river floods again 

• 9.5” of rain in 24 hours

• 24 deaths

• a little over $9 billion in damage

2010

• Nashville TN

o Flooding of Cumberland River

Ways to prevent flooding:

• Straighten stream out more so it’s not meandering as much 

• Change shape/length of channel 

• Build levee’s (walls on either side of the stream channel)

o Restricts stream channel between walls

• 60% loss of wetlands along Mississippi river  

Streams:

• part of the Hydrologic cycle

o stream 

▪ any channeled flow of water, regardless of size 

o reservoirs: ocean, ice, atmosphere, groundwater, streams, lakes, etc. 

o processes moving water between reservoirs:

▪ evaporation, transpiration (plants), wind transport, condensation,  

precipitation, runoff, infiltration

o water returns to ocean by underground flow of soil and groundwater or across the  land by streamflow and runoff

o Runoff – surface drainage 

▪ Tributaries merge into larger streams 

Materials transported by streams

• Load: amount of sediment stream carries 

• Capacity: maximum load a stream can carry at any particular time 

• Total load of streams consists of 

o Bed load 

▪ Larger particles that roll/slide/bounce along bottom 

▪ Moves only by being pushed or saltation

• Movement of hard particles (sand) 

o Suspended load 

▪ Silt + clay particles carried by water 

o Dissolved load 

▪ Materials carried in solution as ions (not visible)

Velocity, discharge, erosion, and deposition

• Streams = primary transportation/erosion agent of rock cycle

• Amount of erosion and deposition depends on…

o Velocity (V) speed of water (meters per second) 

o Discharge (Q) volume of water flowing through a cross sectional area of a stream  channel per unit time (m3 per second) 

o Q = V (decreases downstream) x A (increases downstream) = meters per second o Meters per second x (meters)3 = m3 per second

▪ Discharge increases downstream because of the addition of water  from tributary streams to the main channel 

▪ Changes in channel area (A) lead to changes in velocity  

▪ Narrow channels have higher velocity than wide ones 

• Ex: putting your thumb over the tip of a running hose, causing the  

stream to jet out  

• Stream flow widens and slows when moving from high to low gradient o Deposited sediment forms Alluvial fan or delta

o Alluvial fan: can be found where streams are coming out of a steep mountainous  area hit a flat valley (load becomes greater than capacity) 

o Delta: birds foot deltas only form when the velocity of the stream is higher than  the velocity of the ocean the stream is dumping in to 

Channel Patterns and floodplain formation

• Braided channels

o Contains numerous sand + gravel bars that divide and reunite the main channel o Wide and shallow 

• Meandering channels

o Migrate back and forth with a floodplain

o Velocity is greater on the outside curves causing erosion (Cut banks) o Water velocity slows on the inside curves causing sediment deposition (Point  bars) 

o Floodplains built during overbank flows 

▪ When the height of water in the stream exceeds the channel top

o During avulsion, streams shift position rapidly 

▪ Movement of meander loops themselves

o Often contain pools and riffles

▪ Pools: calm water 

▪ Riffles: turbulent areas  

o Oxbow lake

▪ An area where the original stream channel was cut off 

Flooding:

• Overbank flow

• Related to

o Amount/distribution of precipitation in the drainage basin

o Rate at which precipitation soaks into the earth

o How quickly surface runoff reaches the stream

▪ Faster rates can cause flash flooding 

o Amount of moisture in soil

▪ Water-saturated soil cannot hold additional moisture 

▪ Bone try soil cannot hold additional moisture either  

Flood description:

• Stream stage = water level (depth) in channel 

o Measured by stream gauging stations 

o Stream gauge record is used to produce stage-time graphs (stage curve) o Stage discharge graph (rating curve) shows stream discharge at different stream  stage

• Flood discharge 

o Discharge of the stream at the point where water overflows the channel banks • Flood stage 

o Height of water in the stream reaches a level likely to cause property damage ▪ Depends on human use of floodplain

Flood Magnitude and Frequency:

• Hydrograph: 

o Graph of stream discharge over time 

▪ Produced by combining stage-time and stage-discharge graphs

• Peak annual discharge (flow) 

o Highest discharge event for each year 

▪ Shown on the stream hydrograph

• Recurrence Interval (RI) 

o Average time between flood events of a certain size 

• Discharge frequency curve (flood frequency curve) 

o Graph peak annual discharge vs. RI 

▪ Allows size of larger flood events to be estimated 

Flood categories:

• Flash floods  

o Upper portion of drainage basin and in small tributaries of larger streams o Caused by intense rainfall of short duration over a relatively small area or dam  failure

o Common in arid environments with steep slopes or little vegetation and following  breaks of dams, levees, and ice jams (damn formed out of ice)

o Can be severe locally

o Most deaths occur in cars

o EX. May 31, 1889 Johnstown, PA

▪ Book “The Johnstown Flood”

▪ 2,209 deaths

o EX. July 1976- Big Thompson Canyon Flood 

▪ Only killed 143 people

▪ Caused by brief but intense rainfall- nearly 10 inches of rain fell in only 10  hours

o EX. Ohio River food 

▪ One of the 5 greatest floods in the history of the US

• Downstream floods

o Occur on larger streams

o Cover a wide area

o Usually produce by long period of heavy rainfall- saturates the soil + produces  increased runoff

o Can be caused by combined runoff from thousands of tributary basins

▪ Characterized by large rise and fall of discharge at a particular location Who’s at risk?

• Any place that gets precipitation has potential to flood

• Floods were #1 disaster in US during the 20th Century

• All areas of US and Canada are vulnerable to floods

o Single flood can cause billions of dollars of damage and more than 200 deaths

Effects:

• Primary effects: (directly caused by flood)

o Injury/ loss of life

o Property damage

o Erosion and deposition

• Secondary effects: (indirect effects of flood)

o Short-term pollution of streams

o fires

o Hunger and disease

o Displacement and homeless

Factors effecting damage:

• Land use of floodplain

• Depth and velocity of floodwaters

• Rate of rise and duration of flooding

• Season in which flooding occurs

• Quantity and type of sediment transported/deposited

• Effectiveness of forecasting, warning, and evacuation

Natural service functions:

• Fertile lands

o Deposits of minerals enrich soil

• Aquatic ecosystems

o Floods clear streams of debris/bring in nutrients

• Sediment supply

o Flooding can build up land elevation

o Levees can lead to subsidence  

▪ EX. New Orleans

Human Influences:

• Streams maintain dynamic equilibrium 

o Balance between sediment load received and flow velocity needed to transport  load 

▪ Water flow velocity is a function of the stream gradient and the channels  cross-sectional shape, channel smoothness

▪ Stream changes its gradient and/or cross-sectional shape to change the  flow velocity

o Land use changes can affect streams equilibrium

▪ Forest to farming creates more erosion/sediment

▪ Sediment will build up gradient of stream

▪ Stream will flow faster to carry a greater sediment load

▪ Farming to forest has opposite effect

• Stream down-cuts channel- decreases gradient in response to lower  

sediment load

▪ Basically, when land is cleared it becomes much more vulnerable to  

erosion. Because land erodes, sediment begins to build up in streams  

which causes the stream channel to change shape and increases the 

velocity of the water flowing through the stream 

Dam Construction:

• Upstream water slows down, deposits sediment, forms delta

• Downstream water devoid of sediment will erode sediment and transport it o Slope of stream will decrease until equilibrium is reached  

Urbanization:

• Increases magnitude + frequency of floods 

• Urban areas have impervious cover and extensive storm sewers

o Water reaches stream channels more quickly

o Decreases lag time; increases peak discharge 

▪ Causes “flashy” discharge

• Rapid rise/fall of floodwater

• Storage capacity of soil is reduced due to construction of foundations/pools • Reduces stream flow during dry season

o Less groundwater (base flow) available  

• Bridges block debris, creating dams/flash flooding

Minimizing hazard:

• Physical barriers:

o Levees 

o Concrete flood walls 

o Dams (produce reservoirs) 

o Storm water retention ponds 

o Levee breaks cause higher energy flows and bottlenecks in upstream areas o All physical barriers need to be maintained

• Channelization: 

o Straightening, deepening, widening, clearing, or lining existing stream channels ▪ Can improve navigation/decrease flooding

o Drawbacks

▪ Drainage of wetlands adversely affects plants/animals

▪ Cutting trees eliminates shading and cover for fish/wildlife

▪ Cutting hardwood trees eliminates habitats/increases erosion and  

sedimentation

▪ Changing the streambed destroys both diversity of flow patterns +  

feedback/breeding areas for aquatic life

▪ Loses the aesthetic

• Channel restoration 

o Create natural channel by allowing stream to meander/reconstruct variable water  flow conditions by 

▪ Cleaning urban waste to allow channel to flow freely

▪ Protecting existing channel banks by not removing trees

▪ Planting additional trees or vegetation where necessary

o EX. Kissimmee River Restoration in FL

▪ Channelization 1960-1970 $32 mil

▪ River length reduced by half

▪ Water quality decreased-wildlife decreased

▪ Channelization actually increased flooding because of a loss of wetlands

Perception of flood hazard:

• Most people don’t understand the hazard

• Local govt’s create flood maps

• Federal gov’t encourages local gov’t to develop floodplain management plans • Public safety campaigns- help educate public about flash flooding

Flood insurance:

• FEMA manages US National Flood Insurance program 

o Est. 1968

• Maps of 100-year floodplain created to determine risk 

o Areas where there is a 1 percent chance of floods in any given year 

• New property owners are required to purchase flood insurance

• Building codes limit new construction on floodplain

o Cannot build on 20-year floodplain- higher probability of experiencing a flood in  this area 

• 1994 National Flood Insurance Reform Act

“Flood proofing”

• raise foundations above flood hazard

• build flood walls

• use waterproof construction methods

• install drains/pumps

Flood plain regulation

• goal: get the most beneficial use of floodplains but at same time minimize flood  damage/cost of flood prevention 

o structural controls might be needed for floodplains that are heavily used o less physical modification of streams

• flood hazard mapping

o shows location/extent of previous flooding

o helpful in land use planning

• relocation

o gov’t purchasing/removing homes damaged by floods

Self-quiz

Multiple Choice:

_____1. Which of the following is not a tsunami trigger?

A. Earthquakes

B. Volcanic Eruptions

C. Coastline Erosion

D. Landslides

_____2. An earthquake magnitude of ______ or greater is needed to generate a tsunami A. 7.5 M

B. 6.5 M

C. 2.0 M

D. 5.5 M

_____3. Which of the following areas is at high risk of experiencing a tsunami? A. Northeastern Indian Ocean

B. Pacific Ocean Rim

C. Northern Mediterranean

D. All of the above

_____4. Most volcanoes can be found…

A. On the east coast of the United States

B. Near active plate boundaries

C. In the middle of the ocean

D. At hot spots

_____5. Which of the following is not a way in which magma forms? A. Addition of heat

B. Decompression melting

C. Addition of volatiles

D. Viscosity

_____6. If lava has a high volatile content, then the eruption will be… A. Explosive

B. Medium sized

C. Minor

D. Non-explosive

_____7. Which of the following is not a type of magma? A. Basaltic

B. Rhyolitic

C. Silicate

D. Andesitic  

_____8. Mt. St. Helens is what type of volcano?

A. Cinder cone

B. Caldera

C. Shield

D. Cascade

_____9. The total load of a stream consists of…

A. Bed load

B. Suspended load

C. Dissolved load

D. All of the above

True/False:

_____1. Tsunamis move slowly through deep ocean

A. True  

B. False

_____2. There are only two Tsunami warning systems in the world A. True

B. False

_____3. Basaltic lava (40-55% silica) content has a high volatile content and will create  explosive eruptions

A. True

B. False

_____4. Viscosity affects the flow of lava along with the shape and style of the volcano A. True

B. False

_____5. Hydrographs are produced by combining stage-time and stage-discharge graphs A. True  

B. False

Matching:

A. Extremely dangerous events produced  

_____1. Runup

_____2. Distance Tsunami _____3. Decompression Melting _____4. Volatiles

_____5. Tuff

_____6. Shield Volcano

_____7. Volcanic Dome

_____8. Lahar

_____9. Reservoir

_____10. Load

_____11. Capacity

_____12. Avulsion

_____13. Peak Annual Discharge _____14. Recurrence Interval _____15. Discharge Interval

when loose tephra becomes saturated with  water, becomes unstable, and moves  downslope (can be hot and cold events) B. Chemical compounds (usually water) that  lower melting temp of rock

C. Gently flowing magma, non-explosive  eruptions. EX. Hawaiian Islands, Iceland,  Indian Ocean.

D. Ocean, ice, atmosphere, groundwater,  streams, lakes, etc. where water is stored E. The amount of sediment a stream carries F. Highest discharge event for each year G. Graph peak annual discharge vs.  recurrence interval

H. Average time between flood events of a  certain size

I. Maximum load a stream can carry at any  particular time  

J. When a stream shifts position rapidly K. Furthest horizontal and vertical distance  the largest wave moves inland

L. Pressure put on hot rock is decreased the  closer it is to the surface. Occurs at  divergent boundaries, continental rifts, and  hot spots

M. Highly viscous magma, highly explosive  eruptions. EX. Lassen Peak, Mono Craters N. Travels out to sea and can travel long  distances with little loss of energy

O. Pyroclastic rock formed from  

consolidated ash

Multiple Choice: 1. C, 2. A, 3. D, 4. B, 5. D, 6. A, 7. C, 8. D, 9. D

True/False: 1. B, 2. A, 3. B, 4. A, 5. A

Matching: 1. K, 2. N, 3. L, 4. B, 5. O, 6. C, 7. M, 8. A, 9. D, 10. E, 11. I, 12. J, 13. F, 14. G, 15. H

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