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Geology 120 > Test 2 > Flashcards

Test 2 Flashcards

1
Q

What was the 1 in 1000 year flood event and where did it happen

A
  • South Carolina
  • multiple days of torrential rain fall- the long duration of high water put pressure on and weakened the earthen dams
  • resulted in 14 dam failures, monitoring $$$
  • more than 10 deaths
  • AKA Natural Disaster
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2
Q

Historical Precipitation in NC

A

-Oct. 4=record rainfall was 5.19 inches in one day (2015)

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3
Q

Europe predicted Joaquin would

A

remain in the ocean (correct)

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4
Q

What physical evidence do we have to prove past tsunamis and the numerical model of a future event (Cascadia)

A
  • Cascadia (subduction zone) (NOAA)
  • Last time it occurred was in 1700s with Native Americans
  • Deposition of sand attributed to tsunami, followed by tidal muds
  • Geological evidence when it happened
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5
Q

P waves are also known as ___ and are _____ waves that travel fastest through ______

A
  • PRIMARY waves

- compressional waves, travel fastest through all physical states of media (liquids, solids, and gases)

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6
Q

P waves metaphor

A

like a slinky, energy directed towards travel
IIIWWW
——–> (energy)

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7
Q

S wave

A
  • SECONDARY waves
  • known as shear waves
  • travel slower than P waves
  • travel faster than surface waves
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8
Q

S waves can only propagate or travel through

A

solid materials

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9
Q

R waves are commonly known as

A

surface waves

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10
Q

Surface waves

A
  • move along the earth’s surface
  • travels slowest, but causes the most damage
  • much like an ocean wave
  • rolling motion
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11
Q

Surface waves cause most damage to

A

buildings

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12
Q

Frequency is the number of

A

cycles per second

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13
Q

Frequency is measured in

A

Hertz (hz) or cycles per second

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14
Q

High frequency causes

A

low buildings to shake

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15
Q

Low frequency causes

A

tall buildings to vibrate

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16
Q

Location of earthquake is determined by

A

-expanding seismic wave front and multiple seismometers

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17
Q

High Frequency

A
  • a lot of cycles in a short amount of time (fast cycling shakes low buildings)
  • Does not damage tall buildings
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18
Q

Energy is lost much faster with

A

high frequency

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19
Q

Low Frequency

A

-less energy loss, extends further from the point of earthquake

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20
Q

Earth Materials and shaking amplifications

A 
o	Hard Igneous (harder)
o	Sed rock (hard)
o	Alluvium (weak rock)
o	Silt, Mud (weakest rock)
-surface waves
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21
Q

Amplification goes further through___

A

-harder rock (igneous, sedimentary)

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22
Q

Amplification goes slower but shakes with

A

-weaker rock (alluvium, silt)

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23
Q

low amplification in

A

hard rocks

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24
Q

high amplification in

A

weak rocks

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25
Q

1985 Mexico City

A
  • Mexico city located on top of lake beds resulted in serious damage
  • Most densely populated city in the world
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26
Q

EQ in San Francisco

A
  • Bay bridge and cypress highway
  • structural damage indicated they built bridge on soft mud
  • Damage occurs in areas on top of soft mud (amplification much stronger)
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27
Q

Earthquake cycle

A
  • Time 1: no strain, no displacement, material being deposited, no serious activity
  • Time 2: elastic strain begins (rocks begin to bend)
  • Time 3: elastic strain accumulates (rocks bend more)
  • Time 4: (displacement/fault) Rupture occurs and rocks rebound, elastic strain is replaced by horizontal displacement known as fault slip
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28
Q

During what stage of the earthquake cycle do rocks separate

A

-Time 3

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29
Q

Causes of Human Induced EQ

A
  • (much smaller mag)
  • loading: building a dam or heavy structures
  • waste disposal via wells
  • underground explosions (includes nuclear explosions)
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30
Q

Denver, Colorado human induced EQ

A
  • Earthquakes began to increase over time after use of disposal well
  • No direct proof
  • Correlation: no waste injected=little quake activity, as injections increases quake activity increased
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31
Q

Hydraulic fracturing and EQs

A

o Controversial
o Waste water injection may cause ground to move
o Links earthquakes to fracking

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32
Q

Effects of EQs

A
  • Ground shaking, tilting, and ground rupture
  • Loss of life and collapse of infrastructure
  • Fires and liquefaction
  • Landslides
  • Health issues
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33
Q

Alaskan landslide

A

-2002, magnitude 7.9

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34
Q

El Salvador EQ

A
  • Jan, 2001

- 500 dead

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35
Q

1995 Japan Earthquake

A

-Kobe

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36
Q

Long-term EQ prediction

A

-earthquake hazard risk mapping

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37
Q

Short term EQ prediction

A
  • Frequency and distribution pattern of foreshocks
  • Deformation of the ground surface: Tilting, elevation changes
  • Emission of radon gas from rocks
  • Seismic gap along faults
  • Abnormal animal activities
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38
Q

Etho-Geological Forecasting

A

Unusual Animal Behavior & Earthquake Prediction

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39
Q

Response to EQ hazards

A
  • Site selection for critical facilities
  • Structure reinforcement and protection
  • Land-use regulation and planning, structures
  • Emergency planning and management: Insurance and relief measures
  • Warning systems (time, reliability)
  • Education (pre-, during & post event)
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40
Q

What does tsunami mean in japanese

A

large harbor waves

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41
Q

Tsunamis are produced by the

A

sudden vertical displacement of ocean water

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42
Q

Tsunamis are triggered by

A
  • any rapid uplift or subsidence of the seafloor, such as
  • submarine earthquake (most),
  • landslide,
  • volcanism, collapse
  • impact of asteroid or comet (mega-tsunami – low frequency)
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43
Q

Indonesian Tsunami occurred on _____ and within a few hours, close to ________ people were killed

A
  • December 26, 2004
  • within a few hours, close to 250,000 people were killed
  • No warning system in place (30 mins could have saved thousands of lives)
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44
Q

Indonesian Tsunami facts

A
  • Largest earthquake on Earth in the past 40 yrs
  • M 9.1
  • A large amount of displacement along the thrust faults in the subduction zone, classified as “megathrust event”
  • The total length of the rupture over 1500 km (930 mi)
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45
Q

megathrust event

A
  • a large amount of displacement along the thrust faults in the subduction zone
  • ex: Indonesian tsunami
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46
Q

four stage process of the Tsunamigenesis

A

(starts with vertical displacement)

  1. EQ rupture in seafloor pushes water upward
  2. tsunami moves rapidly in deep ocean (over 500 km/hr)
  3. as tsunami nears land it slows to around 45 km/hr but is squeezed upward generating height
  4. tsunami heads inland destroying everything in path
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47
Q

In the fourth stage of the tsunamigenesis

A

the trough of wave may arrive first, exposing the seafloor

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48
Q

Distant tsunami

A

Travels out across the deep ocean at high speed for thousands of kilometers to strike remote shorelines with very little loss of energy

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49
Q

Local tsunami

A

Heads in the opposite direction toward the nearby land and arrives quickly following an earthquake

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50
Q

Each (distant and local) tsunami has a wave height

A

~ ½ of that of the original dome of water

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51
Q

Submarine landslides

A

can generate very large tsunamis

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52
Q

Lituya Bay, Alaska (1958)

A
  • highest known mega-tsunami
  • The landslide set in motion by a M 7.7 earthquake on a nearby fault.
  • Caused waters in the bay to surge upward to an elevation of about 524 m (1700’) above the normal water level
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53
Q

Greatest risk of tsunami (location)

A
  • Coasts close to a major subduction zone or directly across the ocean basin from a major subduction zone are at greatest risk
  • The greatest tsunami hazard with return periods of several hundred years
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54
Q

High risk tsunami regions

A

The Cascadia subduction zone, the Chilean trench, the subduction zones off the coast of Japan, parts of the Mediterranean, as well as the northeastern side of the Indian Ocean

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55
Q

location and risk of tsunami is dependent on

A

topography, reefs, vegetation

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56
Q

Primary impacts of tsunamis

A

-Damage to both the landscape and human structures from resulting flooding and erosion

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57
Q

Secondary impacts of tsunamis

A
  • fires from ruptured natural gas lines or flammable chemicals
  • water pollution and damaged waste water treatment systems
  • disease outbreaks, health impacts, complete environmental contamination
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58
Q

How to minimize the tsunami hazards

A
  • Detection and warning
  • For distant tsunamis: can be detected in the open ocean and accurately estimated their arrival time to within a few minutes
  • Ex: Hawaii has up to 14 hours to evacuate, minimal time to reach safety
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59
Q

Tsunami warning system

A
  • A network of seismographs to measure submarine movement
  • Automated tidal gauges to measure unusual rises and falls of sea level
  • A network of sensors connected to floating buoys
  • Pressure sensors used to measure wave height (bottom of seabed)
  • Waves=1 meter in open ocean, 500 Kl
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60
Q

You can minimize tsunami hazards through structural control and building design

A
  • Build updated and strong homes
  • Japanese home
  • Fukushima nuclear power station; harbor walls break waters and resist tsunami
  • Aceh, Indonesia: nothing left standing but the masque
  • Hilo Hawaii: elevated home allows tsunami to pass underneath
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61
Q

Tsunami run up maps

A
  • minimize tsunami hazard
  • Need information about elevation of city to predict storm surge
  • Determine runup height and level to which water travels inland
  • Huntington beach, CA: U.S. pro surf contest (thousands of ppl)
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62
Q

Land use planning, forests and mangroves

A
  • minimize the tsunami hazard
  • Healthy mangrove forests helped save lives in the Asia tsunami disaster
  • IUCN compared the death toll from two villages in Sri Lanka; two people died in the settlement with dense mangrove and scrub forest, while up to 6,000 died in the village without similar vegetation
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63
Q

healthy ecosystems

A

act as natural barriers against tsunamis

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64
Q

Three main ways to minimize tsunami hazard

A
  1. structural control and building design
  2. tsunami run up maps
  3. land use planning-forests and mangroves
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65
Q

Probability Analysis

A
  • The risk of a particular event occurring times the consequences (damage, cost, lives)
  • Identify and specify the potential earthquake sources
  • Specify relationships that will either attenuate or reduce tsunami waves
  • Similar approach to earthquake hazard analysis
  • Still being developed
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66
Q

Education is critical for tsunamis

A
  • most people don’t know if a tsunami watch or warning is issued
  • In 2005 in Santa Barbara, no mention of size of the possible tsunami, some people drove too far to the top of a nearby mountain pass thousands of feet above sea level
  • No plan for people to directly observe the tsunami
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67
Q

Tsunami watch

A

an earthquake that can cause a tsunami has occurred

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68
Q

Tsunami warning

A

that a tsunami has been detected and is spreading across the ocean toward their area

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69
Q

Chilean EQ

A
  • tsunami advisory issued for California coast following deadly 8.3 magnitude EQ in Chile
  • Sept 17th, 2015
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70
Q

Tsunami warning issued for Hawaii

A
  • after magnitude 7.7 EQ in British Columbia

- October 8, 2012

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71
Q

Typically, all waves in ocean are generated by

A

wind

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72
Q

wind generated waves

A
  • 5-60 miles per hour (8-100 kilometers/hr)
  • wave period: 5-20 seconds apart (low frequency)
  • wavelength=300-600 ft apart (100-200 meters)
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73
Q

Tsunami wave

A
  • 500-600 miles per hour (800-965 kilometers/hr) (100x stronger)
  • wave period: 10 minutes (600 seconds)-2 hours apart (7,200 seconds)
  • wave length=60-300 miles apart (100-500 kilometers apart)
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74
Q

wave period

A

time between waves

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75
Q

large swells

A

20 second waves generated by hurricanes

76
Q

center of hurricane

A

choppy, low frequency

77
Q

During a tsunami

A
  • the second and third waves may be larger than the first one, these may be up to an hour apart between waves
  • Move to higher ground and stay there until instructed otherwise
78
Q

Ways to establish a tsunami ready status

A
  • Establish an emergency operation center with 24 hour capability
  • Have ways to receive tsunami warnings from the national weather service, Canadian meteorological center, coast guard, or other agencies
  • Have workable ways to alert the public
  • Preparedness plan with emergency drills
  • Promote community awareness and education
79
Q

Why do you think that prior to the 2004 Indonesian tsunami there was no warning system in the Indian ocean?

A

-They never had a tsunami of that magnitude

80
Q

Harry Glicken

A
  • ph.d student observation posts at mount st. helen (1980) with dave Johnston
  • Eruption took place, Dave let emergency services know, died at the site
  • Harry Glicken became well known, died monitoring Mt. Unzen in Japan
81
Q

Papua, New Guinea

A

volcano eruption accompanied by shockwave

82
Q

Mt. Unzen

A
  • One of 19 active volcanoes in Japan

- Erupted and killed approx. 15,000 people 200 years ago

83
Q

Violent eruption on June 3, 1991 (Japan)

A
  • 1000s of ash falls by 1993, the king of the ash flow centers’
  • 44 people killed, including Harry Glicken, a U.S. volcanologist who escaped death in the May 18, 1980 eruption of Mount St. Helen
84
Q

The king of the ash flow center

A

Mt. Unzen

85
Q

Mt. Unzen, Japan precautions

A
  • attempts to control mud overflow via constructed channel

- not entirely successful

86
Q

How many volcanic eruptions on earth/yr

A

1,500 active volcanoes on earth, 50 eruptions per year

87
Q

Most active volcano countries

A

Japan, Mexico, Philippines, and Indonesia

88
Q

Where is most volcanic activity concentrated?

A

Most activity concentrated along major plate boundaries

89
Q

U.S. volcanic activity

A
  • Alaska, Hawaii, and pacific NW most active

- 1 to 2 eruptions/year

90
Q

How and where is magma formed

A
  • From asthenosphere associated with subduction zones
  • Forms lava when reaches surface
  • Mid-oceanic ridges
91
Q

Volcanic activity depends on

A
  • Depending on lavas viscosity And amount of dissolved gas content
  • Determined by silica content (lava composition) and lava temperature.
92
Q

Viscosity

A

liquids resistance to flow

93
Q

High Silica means

A

high viscosity

94
Q

Quiet flow v. violent eruptions

A
  • quiet flow: low viscous basalt flow

- violent explosion: high viscous lava eruption

95
Q

Four main volcano types

A
  • shield volcano (flat)
  • composite or stratovolcano
  • volcanic dome
  • cinder dome
96
Q

Two main types of volcanos

A

Shield and composite (or stratovolcano)=two main types

97
Q

Shield volcano is built up almost entirely from

A
  • numerous basaltic lava flows
  • Low silicon content (not explosive)
  • Typically made of basalt
98
Q

The slope of a shield volcano is

A

very gentle

99
Q

Example of shield volcano

A

Mauna Loa, Hawaii

100
Q

Composite or stratovolcanoes are known for their

A

-beautiful cone shape, distinguished by a mixture of explosive activity and lava flows

101
Q

Classic volcano

A

composite or stratovolcanoes

102
Q

Composite or stratovolcanoes are made up of

A
  • rock form: andesite

- intermediate silica content (explosive)

103
Q

Example of composite volcano

A

(stratovolcano) Mt. Fuji, Japan’s tallest peak (3.7 km) and one of the three sacred mountains

104
Q

Volcanic Domes are characterized by

A
  • viscous magma with a relatively high silica content
  • dome shaped and highly explosive
  • High silica/viscosity
105
Q

Rock form of volcanic domes

A

Rhyolite

106
Q

Example of volcanic dome

A

-Mt. Lassen, CA: erupted in 1914

107
Q

Cinder Cones

A
  • relatively small cone-shaped volcanoes formed from tephra (volcanic ash)
  • Cone shaped, often with summit crater
  • steep sides
108
Q

Cinder cones have

A

-low silica/low viscosity

109
Q

Rock type of cinder cone

A

Basalt

110
Q

Cinder cone eruption type

A

tephra (mostly ash) ejection

111
Q

Example of Cinder cone

A
  • Paricutin, Michoacan, Mexico
  • A fast growing cinder cone volcano and the youngest in Mexico
  • also, Springerville, AZ
112
Q

The tectonic origins of different types of volcanoes helps explain

A

the chemical differences in their rock types

113
Q

Volcanism occuring at mid-oceanic ridges

A

produces basaltic rocks (low si-content-low viscosity)

114
Q

Shield volcanoes are formed

A
  • above hot spots located below moving lithospheric plates

- Rock type is mostly basalt

115
Q

Composite volcanoes are formed along

A
  • subduction zones where rising magma mixes with oceanic and continental crust
  • (rocks are mostly andesite-intermediate Si content)
116
Q

Composite volcanoes are common along the

A

pacific belt

117
Q

Caldera-forming eruptions

A
  • may be extremely explosive and violent, usually inland from subduction zones.
  • Penetrate hi Si continental crust
118
Q

main rock type in caldera-forming eruptions

A

Rhyolite

119
Q

Silica increases

A

-Basalt->Andesite->Rhyolite

120
Q

Typical Volcanic Features

A
  • Craters
  • Calderas
  • Volcanic vents
  • Hotsprings & geysers
121
Q

Craters

A
  • Bowl-shaped depressions at the top of volcanoes
  • Formed by explosions or collapse of the upper part of the volcanic cone
  • Few kms in diameter
122
Q

Calderas

A
  • When a large magma chamber is emptied by a volcanic eruption or by subsurface magma movement
  • The unsupported rock that forms the roof of the magma chamber collapses to form a large crater
123
Q

Volcanic Vents

A

Locations from which lava flows and pyroclastic material is erupted

124
Q

Volcanic vent components

A

vent, conduit, and chamber

125
Q

Example of volcanic vent

A

Kilauea, Hawaii

126
Q

Hot springs

A
  • Hydrologic features associated with some volcanic areas

- Groundwater comes into contact with hot rock and discharges at surface as hot or thermal spring

127
Q

Example of hot spring

A

Blue lagoon, Iceland

128
Q

Geysers

A
  • A vent in earth’s surface that periodically ejects a column of hot water and steam
  • Groundwater comes into conduit (vent), water heats, forces accumulation to release steam and water
129
Q

Example of Geyser

A
  • Fly (artificial) geyser, Fly Ranch NV

- Old faithful, Yellowstone National Park

130
Q

Volcanic Hazards

A
  • Lava flows: from the vent of a crater or along a line of fissure
  • Most common and abundant type: basaltic lava low
131
Q

Basaltic Lava types

A
  • Pahoehoe lava and Aa lava
  • both are slow moving
  • able to outrun the lava
132
Q

Pahoehoe lava

A

less viscous, higher temp, with a smooth ropy surface texture

133
Q

Aa lava

A

more viscous and slow moving, lower temp, with a blocky surface texture

134
Q

Lava Flow example

A
  • Hawaiian Island Lava Flows: 1983-2005

- Kalapana & Kilauea Google Earth

135
Q

What 3 records did the U.S. break this year

A

-failure of snow, excess of rain, hottest july, (1 in 1000 floods in SC, excess rain in NC)

136
Q

Hurricane Patricia Recap

A
  • Strongest Landfalling Pacific Hurricane on Record
  • Maximum sustained winds reached an unprecedented 200 mph (320 kph) and its central pressure fell to 879 millibars (along pacific coast of Mexico)
137
Q

Deaths and damage reported in powerful Afghanistan quake

A
  • 7.5 magnitude earthquake hits south Asia
  • Many people in this region live in mud brick buildings prone to collapsing
  • The mountainous region and poor infrastructure make assessing the aftermath difficult
  • Epicenter of EQ is a rural and sparsely populated area
138
Q

Where and how did they attempt to control ash flows

A
  • Mt Helgafell, Iceland (1973)

- Hydraulic chilling of lava flows using water cannons

139
Q

Pyroclastic flow

A

A fluidized mixture of solid (rock) to semi-solid fragments (volcanic glass and ash) and hot, expanding gases that flows rapidly down the flank of a volcanic edifice.

140
Q

Associated with explosive volcanic eruptions

A

Pyroclastic flow

141
Q

Examples of Pyroclastic

A
  • Mt Pinatubo, Phillippines (1991)

- Dome collapse and pyroclastic flow at Unzen Volcano

142
Q

Ash Falls

A
  • Cover large area, 100s or 1,000s of km2
  • Impacts to crops and trees
  • Surface water contamination
  • Harm to human health – poisonous gases, smog
  • Structural damage to buildings (weight)
  • Blocking of solar radiation
  • Hazardous for air traffic – volcanic glass
143
Q

Nuue Ardentes

A
  • (french for Glowing Cloud)
  • Up to 200 degrees C and move up to 800 km/hr
  • Incinerate everything in their path
144
Q

Mt Pelée, Martinique (1902)

A
  • 30,000 dead, 2 survivors
  • ‘Prisoner of St Pierre’ circus show
  • example of Nuee Ardentes
145
Q

Volcanic Impact Risks

A

-Poisonous gases
 Floating in air
 Dissolved in water
 Dangerous for health, plants, and animals
 Producing smog air (vog), acid rain, and toxic soil
 Health effects of vog: breathing problems,
headaches, sore throats, watery eyes
 Can release from a dormant volcano (does not have to be active to release toxic gas)

146
Q

Volcanic gases

A

-H2o, CO2, CO, SO2, H2s (acid rain, toxic soils)

147
Q

Lake Nyos, Cameroon (1986)

A
  • Dormant crater lake volcano
  • CO2 moved 10 km downslope
  • 1700 people dead and 3000 cattle
148
Q

Vog

A
  • poisonous gases that produce smog air

- Vog health warnings are also issued In Hawaii periodically (So2)

149
Q

Debris and Mudflows are also known as

A

-Lahars

150
Q

Debris and mudflows (Lahars)

A
  • Large volumes of volcanic material become saturated with water-destabilize
  • sudden melting of snow caps and glaciers at the top of a volcano
  • Rapid downslope flow at the speed of 50 km/h
  • Long flowing distance: tens of miles from the volcano
151
Q

Lahars may trigger

A

submarine avalanches and tsunamis

152
Q

Example of a mudflow or lahar

A

a hot lahar rushes down a river valley in Guatemala near the Santa Maria volcano, 1989

153
Q

Canary Islands, Atlantic (potential volcanic landslides and tsunamis)

A
  • Six huge landslides and debris avalanches in the past
  • Mt. Teide and Canera Caldera off Tenerife
  • Worries about potential Atlantic mega-tsunami
  • Potentially could affect the east coast
154
Q

How to forecast volcanic activity

A
  • Seismic Activities: Earthquakes as precursors

- Thermal, magnetic, and hydrologic conditions

155
Q

Volcanic monitoring and prediction procedures

A

o Topographic monitoring: tilting and special bulging
o Remote sensing: radar 3-D interferometry
o Geologic history of a volcano

156
Q

Pakistan floods 2010

A
  • Population has grown from 34 m in 1951 to 170 m in 2010
  • Most people live close to the Indus River
  • August of 2010, the greatest monsoon rains in decades, caused catastrophic flooding in Pakistan
  • Killed about 1,600 people and 20 million people were affected
  • 20% of Pakistan was flooded
157
Q

Historical use of rivers

A
  • Soil, water supply, ease of waste disposal, commerce, transportation
  • Need to understand floodplain and its relation to the river
  • The pioneers moved west modifying the land: cutting and burning trees, modifying natural drainage
158
Q

History of Cape Fear River

A
  • Wilmington was a large trading center and getting naval stores which included lumber, tar, and resin was important for early commerce
  • Salt, commodities, and important from NY and the West Indies, and had to travel upstream to the states interior
  • Critical for economic needs
159
Q

Streams

A

small rivers

160
Q

Streams and rivers are part of the

A

hydrologic (water) cycle – water runoff makes its way to rivers & streams

161
Q

River components

A
  • River channel
  • Floodplain (flat area next to river which is periodically inundated)
  • Network of streams
  • Watershed or drainage basin (region drained by single river)
162
Q

Stream total load

A

Total amount of sediments

163
Q

Bed load

A

Coarse particles moving along the bottom of river channel,

164
Q

Suspended load

A
  • Accounts for ~90 % of total load and makes river look muddy
  • stuff in suspension within the water column gets picked up as its relatively light
165
Q

Dissolved load

A

(e.g. Mg, Ca & Na ions)

166
Q

Sediments in river

A
  • stream total load
  • bed load
  • suspended load
  • dissolved load
167
Q

Continuity equation components for river

A
  • Q = discharge (e.g. m3/sec)
  • W = width of flow
  • D = depth of flow
  • V = velocity (e.g. m/sec)
168
Q

Stream velocity

A

Largely dependent on stream gradient, discharge, and channel shape (erosion vs deposition)

169
Q

Velocity is dependent on

A

gradient (slope) of river

170
Q

Stream Competence

A
  • measuring he maximum size of the sediments transported by a river
  • ex: mountains: boulders
171
Q

Stream capacity

A
  • is the maximum amount of solid load (bed and suspended) a stream can carry
  • depends on both the discharge and the velocity
172
Q

Hjulstrom curve

A

deposition, transportation and erosion of different particle sizes based on flow velocity

173
Q

Alluvial plains and deltas

A
  • As rivers enter a coastal plain or water body, they deposit their load due to a reduction in velocity
  • distributary channels
174
Q

Examples of alluvial plains and deltas

A

-Ex: Tenakee Inlet river delta Alaska, Mississippi river delta, Alluvial fan-death valley

175
Q

Distributary channels

A

several channels which distribute sediment

176
Q

Riverbank erosion or deposition is attributed to

A
  • Change in cross-section properties (width, depth, slope)
  • Rock and sediment types and properties (mud, sand, and rock)
  • Vegetation
  • Land-use change (dams)
177
Q

Land-use change examples

A
  • effects stream morphology
  • deforestation, farming, reforestation
  • dams
178
Q

Braided channels

A

wide, shallow, gravelly and associated with steep rivers or glaciers

179
Q

Braided channels require

A

coarse sediments and high flows

180
Q

Examples of braided rivers

A
  • Saskatchewan River

- Granada, Spain

181
Q

Meandering rivers

A 
-Erosion and deposition along meanders formation 
of:
-cut banks
-point bars
-oxbow lakes
182
Q

Example of meandering river

A

-Koyakuk River, Alaska

183
Q

Flooding or overbank flow

A

occurs when discharge is greater than channel’s holding capacity

184
Q

Flooding or overbank flow depends on

A
  • rate & amount of precipitation
  • Soil type (e.g. porosity)
  • Topography
185
Q

Flooding or overbank may occur

A

due to snow melt or dam failure

186
Q

River flooding

A
  • Stage: The height of the water level in a river at a given location at a given time
  • Hydrograph: Graphic representation of a river’s discharge over time
  • Lag time: The amount of time between theoccurrence of peak rainfall and the onset of flooding
187
Q

Upstream, Downstream and Flash Flooding

A
  • Upstream flood: Shorter duration, smaller area
  • Downstream flood: Longer duration, greater magnitude, larger area
  • Flash flood: High volume of flooding over short duration, short lag time, usually upstream

Geology 120 (1 decks)

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