Midterm Flashcards
(134 cards)
1
Q
Internal Structure of Earth
A
Earth is layered and dynamic
Internal structure of earth can be considered in 2 fundamental ways
By composition, state, and density
By strength
2
Q
Structural Layers of Earth
A
Inner Core Outer Core Mantle Crust
3
Q
Inner Core
A
Solid
1300 km thick
high temp
composed of iron (90% by weight), as well as Sulphur, oxygen, nickel
4
Q
Outer Core
A
Liquid
2000 km thick
composition similar to inner core
5
Q
Mantle
A
Solid
3000 km thick
Composed of iron-rich and magnesium-rich silicate rock
6
Q
Crust
A
Outer rock layer of earth
Mohorovicic discontinuity separates lighter crustal rocks from the denser mantle
7
Q
Lithosphere
A
Cool, strong outermost layer of earth
8
Q
Asthenosphere
A
Constitutes all but the uppermost part of the mantle
Hot, slowly flowing layer of relatively weak rock
100 km down from lithosphere
non-brittle, never cracks just slowly deforms
9
Q
Continents and Ocean Basins and Convection
A
Crustal rocks are less dense than the mantle rocks below good bc if not they would sink
Continental crust is less dense than oceanic crust, oceanic crust gets dragged under continental crust when they run into each other
Oceanic crust is relatively thinner oceanic crust is always being made and destroyed
Oceanic crust is 200 myo and continental crust is up to 1 byo
Earth’s internal heat causes magma to heat up and become less dense
The less dense magma rises while the cooler magma falls to side and further downward
10
Q
How do we Know about Earth’s Internal Structure?
A
Most knowledge comes from seismology study of earthquakes
Earthquakes cause seismic energy to move through the earth
Some waves can move through solids, but not liquids
Some waves are refracted (change direction), some are reflected
What we have learned about earth from earthquakes
Where magma is generated in the asthenosphere
The existence of slabs of lithosphere that have sunk deep into the mantle
The variability of lithosphere thickness, reflected differences in its age and history
What is liquid and what is solid
11
Q
Plate Tectonics
A
Tectonic refers to the large –scale geologic processes that deform earths lithosphere
It produces ocean basins (separating), continents (colliding), and mtns (colliding)
Driven by forces deep within the earth
Lithosphere is broken into pieces
Lithospheric plates- all moving in slightly diff speeds and directions
Can cause sudden displacements that are forceful resulting in a natural disaster
Plates move relative to one another
12
Q
Plate Boundaries
A
These are delineated by earthquakes and active volcanos (geologically active areas)
They are defined by areas of seismic activity
Dynamic events on earth surface occur when the plates move
Diverge, converge, or slide past one another (transform)
Sliding causes most damage
13
Q
Seafloor Spreading
A
This is the mechanics for plate tectonics
At mid-ocean ridges, new crust is added to edges of lithospheric plates
Continents are carried along plates
Crust is destroyed along other plate edges
Called subduction zones
The rate of production of new lithosphere at spreading centres is balanced by consumption of lithosphere at subduction zones
The lithosphere grows at the same speed it subducts
14
Q
Types of Plate Boundaries
A
Divergent
Convergent
Transform
15
Q
Divergent Plate Boundaries
A
Where two plates move away from one another
New lithosphere is created at these boundaries
Divergence b/w two ocean plates
Causes mid-ocean ridges
Seafloor spreading
ex. Mid-Atlantic Ridge
16
Q
Convergent Plate Boundaries
A
Where two plates collide head-on
Oceanic-continental collisions results in subduction zones
More dense ocean plates sink and melt cause problems along coast
Melted magma rises to form volcanos
Collisions b/w 2 continental plates results in a continental collision boundary
Neither plate subducts, instead the plates crumple together
Large mtns form such as the Himalayas
These aren’t as common
17
Q
Transform Plate Boundaries
A
Where the edges of two plates slide horizontally past one another
Most common on the ocean floor but some occur within continents
When they come on land they can be extremely powerful lack of water matters
Ex. San Andreas Fault separates the Pacific plate and the North American plate
18
Q
Rates of Plate Motion
A
Plates move a few centimetres per year
Although the central portions of plates move at a steady slow rate, movement may not be steady at plate boundaries
Plates can displace by several metres during great earthquakes through stored up energy
19
Q
Magnetic Stripes
A
Two possible driving mechanisms for plate tectonics
Ridge push and slab pull
Ridge push is a gravitational push away from crests of mid-ocean ridges
Slab pull occurs when cool, dense ocean plates sinks into the hotter, less dense asthenosphere
Weight of the plate pulls the plate along
Evidence suggests that slab pull is more important process
But can’t happen without both ridge push and slab pull
20
Q
Hot Spots
A
Weaknesses in the crust
Concept developed by Canadian geophysicist J. Tuzo Wilson
Volcanic centres away from plate boundaries resulting from hot material from deep in the mantle
Magma moves up through the mantle and overlying plates
Found under both oceanic and continental crust
Plates move over hot spots creating a chain of volcanos ex. Hawaiian Islands
21
Q
Plate Tectonics and Hazards
A
Divergent plate boundaries (mid-Atlantic ridge) exhibit earthquakes and volcanic eruptions
Transform plate boundaries that slide past each other (San Andreas Fault) have appreciable earthquake hazards
Convergent plate boundaries where one plate sinks (subduction zones) contain explosive volcanos and earthquake hazards
Convergent plate boundaries where continents collide (Himalayas) have high topography and earthquakes
22
Q
Earthquake
A
An earthquake is a motion/trembling of the ground caused by the sudden displacement of rock
23
Q
Consequences of Earthquake
A
depend on: Magnitude Depth Distance from populated areas Direction of fault rupture Nature of the local earth materials Engineering and construction practice Population density
24
Q
Earthquake Magnitude
A
Measured by moment magnitude (MW)
The scale is logarithmic and based on powers of ten
Ground motion for a M 3 is 10 times that of a M 2
Amount of energy released for a M 3 is 32 times that of a M 2
Smaller earthquakes are more frequent than larger ones
25
Earthquake Intensity
Measured by the Modified Mercalli Intensity Scale
The scale is qualitative and based on damage to structures and people’s perceptions
Modified Mercalli intensity maps show where the damage and perceived shaking is most severe
Shake maps use seismograph data to show areas of intense shaking
26
Earthquake Processes
Earthquakes commonly occur at or near plate boundaries
Plate boundaries may contain many faults (where movement and friction can occur)
Friction along plate boundaries exerts strain or deformation
When stress on rocks exceeds their strength, the resulting rupture produce seismic waves
27
Dip Slip
Vertical movement
Three types of dip-slip faults based on which way the bounding earth materials move
Walls on an incline are defined as:
Hanging wall block- higher surface going down
Footwall block- lower surface going up
Normal Fault: the hanging wall has moved downward relative to the footwall (usually happens where things are diverging)
Reverse Fault: the hanging wall has moved up relative to the footwall
if the fault plane angle is 45 degrees or less, it is a thrust fault
Blind Faults: do not extend to the surface
28
Strike Slip
horizontal movement: plates don’t move up or down just sideways
29
Fault Activity and Tectonic Creep
Active faults: movement during the past 11 600 years
Potentially active faults: movement during the past 2.6 million years
inactive faults: no movement during the past 2.6 million years
Tectonic creep: occurs when movement along a fault Is so gradual that earthquakes are not felt
Can slowly damage infrastructure
Such slow movement that doesn’t really cause earthquakes but slowly damages infrastructure (ripping away at sewer lines and building layouts)
30
Seismic Waves- Body Waves
```
travel within the body of the earth
2 types:
P-Waves (primary or compressional waves)
Move fast with push/pull motion
Can travel through solid, liquid, and gas
S-Waves (secondary or shear waves)
Second fastest wave
Move slowly with a back-and-forth motion at right angles to the direction the waves are moving
Can travel only through solids
```
31
Seismic Waves- Surface Waves
```
Travel along Earth’s surface horizontally and vertically and can produce rolling motion
Move more slowly than body waves
Are responsible for damage near the epicenter
2 types:
Love waves
Cause horizontally shaking
Rayleigh waves
Rolling waves, elliptical motion
```
32
Earthquake Shaking: Distance to the Epicentre and Focal Depth
Seismographs record arrivals of waves to station sites
P waves and S waves travel at different rates and arrive at each station at different times
Distance to the epicentre can be found by comparing travel times of the waves using triangulation
Focal depth influences amount of shaking due to attenuation
You need 3 stations at least to determine the earthquake epicentre
33
Local Soil and Rock Conditioning
Local geology influences the amount of ground motion
Dense rocks (eg. Bedrock) transmit earthquake energy quickly
dissipates quickly) and slows down in sediment (loose sediment)
Seismic waves slowdown in the heterogeneous rocks, unconsolidated sediment and sediment with high water content
Slowing it down can allow for amplification of the energy
Heterogeneous rocks- rocks that are different
Amplification occurs when energy is transferred from P waves and S waves to surface waves
More damage can occur in areas farther away from the epicentre depending on local ground conditions
Mexico City has the potential for catastrophic earthquakes (bc of the sediment)
34
The Earthquake Cycle
First part is inactive period where stress builds in the fault (some sort of movement occurring but it isn’t showing in the rocks)
Period of small earthquakes where stress begins to release, causing strain
Foreshocks: occurs prior to a major release of stress (this stage does not always occur)
it’s a smaller earthquake before the mainshock (largest earthquake)
Mainshock: when the fault releases the majority of the stress
Aftershock: releases of stress after a major earthquake
35
Geographic Regions at Risk from Earthquakes
Earthquakes are not randomly distributed
Most occur along plate boundaries
“Pacific Ring of Fire”, Japan, Western US/Canada, Indonesia, New Zealand
Himalayan Mountains, Middle East
However, not all areas are at risk near plate boundaries
36
Plate Boundary Earthquakes
Strike-slip earthquake
Occur on transform faults, where plates slide past each other
Ex. San Andreas and Queen Charlotte faults
Thrust earthquakes
Faults separating converging plates
Ex. Cascadia subduction zone
Normal fault earthquakes
Occur on diverging plate boundaries- tend to be a lesser magnitude
Ex. Mid-Atlantic ridge
37
Intraplate Earthquakes
Earthquakes that occur within plates, happens at zones of weakness
Ex. New Madrid seismic zone in Missouri, Southern Quebec and eastern Ontario
Intraplate earthquakes are often smaller than plate boundary earthquakes
However, they can cause considerable damage due to the lack of preparedness and because they can travel greater distances through dense continental bedrock
38
Effects of Earthquakes and Linkages
Shaking
Causes damage to buildings, bridges, dams, tunnels, pipelines, etc.
Measured as ground acceleration
Buildings are damaged due to resonance
Ground rupture
Displacement along the fault causes cracks in the surface and faults scarps (rising of the ground, big problem if it happens under buildings)
Where the ground moves and shakes, destroying highways, railways
Liquefaction
Water-saturated loose sediment turns from solid to liquid, causing buildings and land to subside
Land-level changes
Landslides
Fires
Ground shaking and surface rupture can sever electrical power and gas lines
Disease
A loss of sanitation and housing, contaminated water supplies, and disruption public health service
39
Natural Service Functions of Earthquakes
Water, oil, and natural gas may be rerouted due to faults
Faults can channel groundwater to the surface at springs
New mineral resources may be exposed
Some minerals are preferentially deposited in veins
Scenic landscapes may form ex. Rocky Mountains
40
Human Interaction with Earthquakes
The weight form water reservoirs may create new faults or lubricate old ones
Liquid waste disposals deep in the Earth can create pressure on faults
Pumping of oil and gas and hydraulic fracturing can both cause small earthquakes
Nuclear explosions can cause the release of stress along existing faults
41
Minimizing the Earthquake Hazard
Earthquake Hazard Reduction Programs
Five major goals:
Operate national seismograph networks
Develop and understanding of earthquake sources
Predict effects of earthquakes on buildings and other structures
Communicate research to educate individuals, communities, and governments
42
Short-Term Prediction
Forecast: specific the probability of an earthquake occurring
Prediction: specific when and where an earthquake will occur
Precursors
Pattern and frequency of earthquakes
Land-level change
Seismic gaps along faults
Physical and chemical changes in earth’s crust
Pattern and frequency of earthquakes (foreshocks and microearthquakes)
Land-level change (uplift or subsidence)
Seismic gaps (areas that have not seen recent earthquakes)
Physical and chemical changes (changes in electrical resistivity and groundwater levels)
43
Perceptions of and Adjustment to the Earthquake Hazard
Perception
One community’s experience does not stimulate other communities to improve their preparedness
Community Adjustments
Critical facilities must be located in earthquake safe locations
Requires detailed maps of ground response to seismic shaking
Buildings must be designed to withstand vibrations
Retrofitting old buildings may be necessary
People must be prepared through education
Insurance must be made available
44
Personal Adjustments before, during, and after an Earthquake
Before the shaking starts
Make sure that your home is structurally sound
Secure large objects
Turn off gas, water, and electricity
Make personal plan of how to react to an earthquake
During the shaking
Do not panic
Move away from windows, protect your head and face
When the shaking stops
Leave the building
Check for damage and injuries
*even though you only have 15 seconds to do this*
45
Volcanoes
Most active volcanos are located near plate boundaries
Volcanos happen along plate boundaries just like earthquakes
Mid-ocean ridges and subduction zones are sites where molten rock reaches the surface
Magma is molten rock
Lava is magma on earth’s surface
2/3 of all active volcanos on land are located along the Ring of Fire which surrounds the Pacific Ocean Indonesia around South American plate and up to Japan
It’s impt to understand how volcanos work to predict volcanic hazards and to understand the nature of the earth’s interior
46
Pyroclastic Debris
Lava and rock fragments ejected in an eruption
47
Volcanic Bombs
Large material thrown out and is very viscous
48
Lapilli
Small volcanic bombs
49
Caldera
Depression >1km wide
50
How Magma Forms
Most magmas come from the asthenosphere (weak, but not liquid, layer of rock)
Three main ways in which silicate rocks can melt:
Decompression
Pressure exerted on hot rock is reduced
Occurs at divergent boundaries, continental rifts and hot spots
Addition of volatiles
Chemical compounds that lower the melting temperature of the rock
Addition of heat
As magmas rise, they release heat to overlying rocks
51
Magma Properties
Magma is composed of melted silicate minerals and dissolved gases
Two most abundant elements in magma are silicon (Si) and oxygen (O); when combined they are referred to as silica (SiO2)
Volcanic rocks are named depending on the amount of silica present in the rock
Basalt, andesite, dacite, rhyolite
Affect style of eruption and type of volcano produced
Silica content of magma is critical
The more viscous the magma the higher and thinner your magma will be (silica rich)
52
Silica-rich (felsic) lavas
Very viscous, flow slowly
Gases cannot escape easily
Violent eruptions, explosive
Ex. rhyolite
53
Silica-poor (mafic) lavas
Low viscosity, flow easily
Gases escape easily
Quiet eruptions, lava flows
Ex. basalt
54
Shield volcanos
Largest volcanos in the world
Gentle slopes built almost entirely of lava flow
Resembles a warrior’s shield
Common in Hawaiian Islands, Iceland, and Indian ocean
Associate with basaltic magma (low viscosity, low gas content, no fractionation)
Gentle flowing lava with non-explosive eruptions
Can form lava tubes underground
55
Composite Volcanos/ Stratovolcanos
Explosions are more violent but less frequent
Produce a combination of lava flows and pyroclastic deposits
Conical in shape, many active volcanos on west coast of North America
Eruptions involve andesitic or dacitic magma (high silica and high viscosity)
56
Volcanic Domes
Form around vents form the eruption of high viscous silica-rich magma
Exhibit explosive eruptions
Small domes often form within the crater after an eruption
57
Cinder Cone Volcanos
Small volcanos, not explosive
Built from small peices of red or black basalt
Found on the flanks of larger volcanos, along some normal faults, and along cracks or fissures
Tephra from extinct cinder cones is the “lava rock” used widely in commercial landscaping
58
Maars Volcanos
The violent interaction of magma and groundwater produces maars
Roughly circular volcanic craters commonly filled with water
59
Ice Contact Volcanos
Erupt beneath or against glaciers
Subglacial volcanoes erupt, rapidly melting ice and produce huge floods known as jokulhaups
Ex. Iceland, Mt Garibaldi
60
Volcanic Features
Hot springs: hot rocks heat groundwater and discharges at the surface
Geysers: groundwater boils in an underground chamber, erupting steam at the surface
Resurgent calderas and super eruptions
Very rare but extremely violent eruption from supervolcanos
Produce huge amnts of ash and form calderas
Most recent North American caldera eruptions were 640 mya at Yellowstone National Park and 700 mya at Long Valley, California
61
Geographic Regions with Active Volcanos
Ring of fire
Pacific Ocean subduction zones
Highest risk in Canada is in northwestern and central BC
Hot spots
Hawaii and Yellowstone National Park
The volcano that poses the greatest risk to Canada is Mt Baker in northern Washington State
An eruption could spread ash over Vancouver
62
Effects of Volcanos
50-60 volcanos erupt each year
Most eruptions are in sparsely populated areas
Nearly 100,000 people have been killed by eruptions in the past 100 years
500 million people live in vicinity of volcanos all would be impacted if a volcano went off
Japan, Mexico, Philippines, Indonesia, Western North America
63
Volcano Primary Effects
Lava flows, ash fall, volcanic bombs, pyroclastic flows, pyroclastic surges, lateral blasts, and poisonous gases
64
Volcano Secondary Effects
not happening directly due to the volcano going off but rather it causes something else to happen (chain rxn)
Lahars, debris avalanches, landslides, groundwater and surface contamination, floods, fires, and tsunamis
65
Lava Flows
Occur when magma reach the surface
Can move slowly or rapidly depending on the viscosity and temperature
High viscosity moves more slowly (more silica=more viscous= more explosive
Basaltic lava flows are the most common
Pahoehoe
Harden with a smooth ropy texture
Travel at speeds of up to a few km per hour
Aa
Harden with a rough, blocky texture
More viscous, travels at rates of a few meters per day
66
Pyroclastic flows and surges
Flows: avalanches of hot rock, ash, volcanic rock fragments
Can move at speeds up to 150 km/h
Surges: dense clouds of hot gas and rock debris produced by explosive interaction of water and magma
67
Ash falls
Ash blown high into the atmosphere during a volcanic eruption and then falls over large areas, described as microscopic shards of glass
Vegetation may be destroyed, surface water may be contaminated
Building may be damaged as ash piles up on roofs
Health hazard (respiratory illnesses)
Mechanical and electrical equipment can be damaged disrupting electrical power
Aircraft engines can experience failure
68
Poisonous gases
Killed 142 ppl when C02 was released from volcano, C02 was denser than air and travelled down to village where it killed people by suffocating them
69
Mt. Saint Helens
Prior to erupting in 1980, it was dormant for 120 years, largest volcanic issue in North America
In March 1980, seismic activity and small explosions were observed
May 1, 1980- a bulge began to grow on the northern flank of the mtn at a rate of 1.5 m per day
May 18, 1980- a M 5.1 earthquake triggers a landslide/debris avalanche of the bulge area
Seconds later a lateral blast from the bulge area occurred at a rate of 480 km/h, the lateral blast was unexpected
One hour after the blast a vertical cloud of ash extended into the stratosphere
9hrs of ash fall covers areas of Washington, northern Idaho, and western Montana
Pyroclastic flows came down the northern slope, mudflows occurred at speeds of 55km/h
57 Killed, $1 Billion Damage
70
Linkages b/w Volcanos and Other Natural Hazards
Earthquakes- commonly precede or accompany volcanic eruptions
Landslides- sector collapses can cause tsunamis if it enters water (mass movement of material down slope)
Fire- hot lava may ignite plants and structures
Climate Change- volcanic ash from an eruption can temporarily cool climate
71
Adjustments to Volcanic Hazards
Bombing
block channels to cause lava flows to take a less damaging route
Hydraulic chilling
Water used to chill and control lava flows
Wall construction
Walls are used to redirect lava flows
72
Landslides
```
Landslide/Mass wasting: terms used to describe the downslope movement of rock or sediment due to gravity
Types of landslides are determined by:
Mechanism of movement
Type of material-> rocks, mud, etc
Amnt of water present
Rate of movement
```
73
Types of Landslides
Fall: bounding of rock or blocks of sediment from the face of a cliff
Slide: downslope movement of a coherent block of rock or sediment along a discrete failure plane
Slump: failure plane is curved upward
Flow: Downslope movement of sediment in which particles move semi-independently of one another often with the aid of water
Debris Flow: typically move rapidly, mixtures of mud, debris, and water
Most dangerous, occur in conjunction with flooding events
Creep: very slow flow of rock or sediment
74
Forces on Slopes
Driving forces move rock or sediment down a slope
The weight of slope material is the largest driving force
Can include fill material and buildings
Resisting forces oppose downslope movement
Shear strength of the material
Resistance of material to sliding or flowing along slip planes
Factor of safety (SF) is the ratio of resisting forces to the driving force
Stable when greater than 1; unstable when less than 1
Driving and resisting forces are not static
as local conditions change, these forces may change and the SF can inc or dec
75
Forces on Slope Determined By
```
Type of material
Slope angle and topography
Steeper=more risk for failure
Climate
Rainfall= adds weight=risk for failure
Closer to 0 degrees= more chance for failure
Vegetation
Tress can add weight but also strengthen w the roots
Water
Adds weight for failure
Time
More time goes by=more likely something will fail
```
76
The Role of Material Type
Planes of weakness
Occur in bedding planes, foliation planes in metamorphic rocks, joints, or zones along which Earth has moved before
Degree of consolidation
Slumps are common in unconsolidated materials
Shape of slip surface
Rotational slides or slumps are curved
Translational slides are planar
77
The Role of Slope and Topography
Slope steepness
Steeper the slope, the greater the driving force
Steep slopes are associated with falls
Moderated slopes are associated with flows
Gentle slopes are associated with creep
Topographic relief
Refers to the height of a hill or mtn above the land below
Landslide occur more frequently in areas of high relief
78
The Role of Climate
Climate is the characteristic weather typical of a place or region over years or decades
Influences the amnt and timing of water that infiltrates or erodes a slope
Arid regions are prone to rock falls, debris flow and soil slips; free-face and talus slopes are common
Humid and sub-humid regions are prone to complex landslides, creep, slides, slumps and debris flows
79
The Role of Vegetation
Vegetation provides a protective cover that reduces the impact of falling rain
Plant roots adds strength and cohesion to slope materials
Vegetation adds weight to slopes
Increases the likelihood that the slope will fail
80
The Role of Water
Water saturates soil, causing soil slips and debris flows
Slumps develop months or even years following deep infiltration of water into a slope
Water erodes bases of slopes which decreases stability
Water can cause spontaneous liquefaction or quick clay failure
Fine grained material that loses strength when disturbed and flows like a liquid
Will be tested!
81
The Role of Time
The forces acting on slopes change with time
Driving and resisting forces change seasonally as the water table fluctuates
Chemical weathering of rocks occurs slowly over time
82
Geographic Regions at Risk from Landslides
Landslides occur wherever there are significant slopes
In Canada, landslides are most common in
Western Cordillera region of B.C, Alberta, and Yukon
Appalachian Mtns of Quebec and New Brunswick
Factors expected to increase landslide incidence:
Urbanization and development of landslide- prone areas
Tree cutting in landslide-prone areas
Changing global climate patterns resulting increased precipitation
83
Effects of Landslides
30 ppl are killed each year on avg in NA; damage exceeds 1 billion USD/year
Slides may damage homes, roads, and utilities constructed at the top, base, or a side of a hill
Slides may block roads and railways impeding travel or may block streams causing flooding
84
Linkages with Other Natural Hazards
Earthquake, volcanos, storms, and fires may cause landslides
Landslides may cause flooding or tsunamis ex. Grand Banks, 1929
Wildfires leave debris that becomes landslide prone
85
Natural Service Functions of Landslides
Produce deposits that become mineral resources
Weathering frees mineral grains from rocks, and landslide transport these materials downslope
Gold and diamonds have been mined from landslide deposits
Creation of new habitats in forests and aquatic ecosystems
Increases plant and animal diversity
86
Human interaction with Landslides
Timber Harvesting
Clear-cutting and logging road construction
Increases landslide-related erosion on unstable slopes
Interrupts surface drainage, alters subsurface movement of water, and can change the distribution of materials on a slope
Urbanization- things that will cause problems
removal of anchoring vegetation’s
construction of roads and buildings (adds weight)
installing septic systems, watering lawns and gardens (adds lubrication to system)
cutting the base of slopes
placing fill materials on slopes (more weight added)
87
Minimizing Landslide Hazard and Risk
dentification of Potential landslides:
Crescent-shaped cracks or terraces on a hillside
A scalloped or recessed crest of a valley wall
A tongue-shaped area of bare soil or rock on a hillside
Large boulders or piles of talus at the base of a cliff
Trees that are convex at their base but straight higher up
An area of tilted tress
Exposed bedrock w layering that is parallel to the slope
Tongue-shaped masses of sediment at the base of a slope or at the mouth of a valley
A hummocky, or irregular and undulating, land surface at the base of the slope
88
Prevention of Landslides
Drainage control
Objective is to keep water from infiltrating a slope
Drains can intercept and divert water
Grading can improve slope stability
Material from the upper slope can be moved to the base
Slope supports
Retaining walls constructed of concrete or brick
89
Personal Adjustments
| Landslides
Seek an evaluation of the property by a geologist
Avoid homes at the mouth of a valley or canyon
Consult local agencies and engineering departments
Monitor small landslides on the property
Look for crack in house walls, leavening retaining walls, doors or windows that stick, or uneven floors
Be wary of leaks in swimming pools or septic tanks, trees or fences that tilt, or sagging or taut utility wires
Avoid slopes with small springs
Look for linear or curved crack that might indicate instability
Do not purchase property that is in an area prone to landslides
90
Japan Tsunami
Occurred on March 11, 2011, killing 16,000 people
Sources was a M 9.0 earthquake beneath the seafloor subduction zone east of Honshu Island
The direct damage from the earthquake and tsunami was U.S. $235 billion most expensive natural disaster in history*
Three nuclear reactors were damaged which led to their meltdown thousands of residents were forced to evacuate
The tsunami propagated throughout the Pacific Ocean, causing 2m high waves in Chile
Only 58% of people in highest impacted areas heeded the tsunami warnings and evacuated to higher ground
91
Tsunamis
```
A tsunami is a series if waves caused by the displacement of a large volume of water
Triggered by:
Large earthquakes
Underwater landslides
Volcanoes flank collapse
Submarine volcanic explosion
Asteroids (can produce mega tsunami)
```
92
Earthquake- Triggered Tsunamis
Earthquake rupture in the seafloor pushed water upwards (generally requires> M 7.5 earthquake)
Tsunamis move rapidly in the deep ocean
Can typically travel up to and over
Spacing (frequency) of crests is large and amplitude is small; people on large boats do not notice tsunami waves
Tsunami nears land, loses speed, gains height
Depth of ocean decreases, slowing tsunami waves to 45 km/h
More water piles up, increasing amplitude and frequency
Tsunami moves inland, destroying everything in its path
Can be metres to tens of metres high
Trough may arrive first, exposing the seafloor
Run up– furthest horizontal and vertical distance of the large wave
More waves likely to follow
93
Indonesia Tsunami
Occurred on December 26, 2004, killing 230 000 people
Source was a M 9.1 earthquake off west coast of Sumatra (subduction zone between Burma and Indian and Australian plates)
No tsunami warning system in the Indian ocean at the time
Few people knew tsunami warning signs
94
Landslide – Triggered Tsunamis
Submarine landslides cause water to become displaced in lakes or oceans
Landslides can fall into the ocean from mountains, causing waves to form (e.g. Lituya Bay, Alaska – bay water surged to a level 525m above normal)
Volcano flank collapse may also cause tsunami
Lose energy over distance
95
Volcanic – Triggered Tsunamis
```
Less common than earthquake triggered
The second most deadly tsunami was triggered by the Krakatoa eruption
Between Java and Sumatra
Eruptions on August 26 and 27, 1883
Explosion heard 5000 km away
```
96
Effects of Tsunamis
Primary effects are related to flooding and erosion
Shorten the coastline
Debris erodes the landscape and damages structures
Diminish with distance from the coast
Deaths from both drowning and the force of impact of the water
Secondary effects
Fires
Contaminated water supplies
Disease
97
Minimizing the Tsunami Hazard
Detection and warning
Monitor earthquake zones
Tsunami warning system: seismographs to detect earthquakes, tidal gauges to determine sea level changes, and buoy sensors to detect tsunami in open ocean
Structural Control: building codes for susceptible coastline areas
Tsunami inundation maps (run-up): show the height to which water is likely to rise
Land use: native vegetation may provide defense, development of land must be monitored
Probability analysis: similar to earthquake analysis
Education: educate people on the signs of tsunami, differences between tsunami watch and tsunami warning
Tsunami readiness: establish a 24 hour emergency operation centres, be able to receive tsunami warnings, have ways to alert the public, develop a preparedness plan with emergency drills, promote community awareness programs through education
98
Flooding
Stream and rivers are part of the hydrologic cycle
Surface flow (runoff) finds its ways to streams
Streams are tributaries of rivers
A region drained by a single stream is called a drainage, watershed, river basin, or catchment
The gradient of a river is determined by calculating its drop in elevation over distance
Greatest in its headwaters, decreases downstream, and is lowest at the river mouth, which is its base level
Base level is the lowest elevation that a river will erode down to
The slope of a river is shown on a longitudinal profile
The valley of a river is steeper-sided and narrower in its headwaters
The floodplain is the flat surface adjacent to the channel
99
Earth Material Transported by Rivers
Rivers move a tremendous amount of material
Bed load
Particles of sand and gravel that slide, roll, and bounce along bottom of a channel in rapidly moving water
Suspended load
Silt and clay particles that are carried in the water (accounts for nearly 90% of the total load of most rivers)
Dissolved load
Ions that are carried in solution in the water
100
River Velocity, Discharge, Erosion, and Deposition
Amount of erosion and deposition depends on stream are (A), velocity (V), and discharge (Q)
Discharge is the volume of water flowing through a cross section of a river per unit time (V x A = Q)
Changes in area lead to changes in velocity
Narrow channels have high velocity than wide ones
When a river slows, it deposits sediment creating an alluvial fan on land or a delta in water
101
Channel Patterns and Floodplain Formation
Braided channels: contain a large number of intersecting channels
Anastamosing: two or more channels with stable islands or bars where sediment is temporarily stored
Meandering channels: migrate back and forth within a floodplain, very prone to flooding
Velocity is higher on the outside of curves causing erosion
Cutbanks
Velocity is lower on the inside of curves causing deposition
Pointbar
Floodplains are created during overbank flows
During avulsion, a river abandons a looping section of the old channel, which is left as a meander cutoff
Oxbow lakes are parts of the river that were cutoff from the mainstream
102
The magnitude and duration of a flood are determined by the:
Amount, distribution, and duration of perception in the drainage basin
Extreme rain event that goes on for days= likely a flood will happen
Rate at which perception soaks into the ground ex. Manhattan is mostly concrete=flooding risk increases
Presence or absence of a snowpack
Air temperature
Speed at which surface runoff reaches the river
Amount of moisture in the soil at the time precipitation starts
103
Flash Floods
Occur in the upper parts of watersheds and in small tributary basins of a large river
Caused by intense rainfall of short duration over a relatively small area
Common in steep-sloped arid areas with little vegetation, and following break of dams, levees, and ice jams
Most people who die during flash floods are in automobiles
104
Downstream Floods
Affect larger areas than flash floods and are commonly much more destructive and deadly
Produced by storms of long duration or by rapid melting of snowpacks
Characterised by a large slow rise and fall of discharge at a particular location
Outburst floods: are short-lived and result from the sudden draining of dammed lakes
105
Southern Alberta Floods Geographical Location
Geographical area of 55,000 km2
Total population of 1.6 million
Both urban and rural areas
Federal and provincial jurisdictions
Federal national parks and three First Nations
Local authorities and provincially managed improvement districts
Early forecasts were 80-160 mm over 48 hrs
No significant changes in forecast until the rain started (June 19)
As the rain feel, flood advisories watches and warnings were issued
Up to 300 mm in 24 hours in some locations
Extreme rainfall created by a ‘cold low system’ that was essentially blocked by high pressure systems to the N and E
106
Glacial Lake Outburst Floods (GLOF)
mass wasting event sudden-onset outburst floods that result from the failure of a moraine-dam, ice dam or sudden release of water from englacial or subglacial reservoirs
how it happens:
Trigger
Breach initiation and development
Downstream routing of the outburst flood wave
Peru
107
Geographic Regions at Risk for Flooding
Flooding is the most widespread natural hazard
Developing countries suffer much greater loss of life than developed ones; due to:
Larger numbers of people at risk
Lack of monitoring and warning capabilities
Poor infrastructure and transportation systems
Inadequate resources for effective disaster relief
108
Several factors affect the damage caused by floods:
Land use of the floodplain
Extent, height, and strength of dykes
Depth and velocity of the floodwaters
Rate of rise and duration of flooding
Season of the flooding
Amnt and type of sediment deposited by the floodwaters
Effectiveness of flood forecasting, warning, and evacuation
109
Natural Service Functions
| Floods
Fertile land-> periodic deposits of nutrient rich sediment enriches the soil for agriculture
Aquatic ecosystems-> floods clear rivers of debris and carry nutrients downstream and into estuaries, increasing the food supply of aquatic organisms
Sediment supply-> flooding keep the surface of a delta plain above sea level ex. Mississippi Delta in Lousiana
110
Human Interaction w Flooding
A river generally maintains a dynamic equilibrium
Maintains the gradient and cross-sectional shape that provides the flow velocity it needs to move sediment load
Land-use changes can affect equilibrium
Forest to agriculture increases the amnt of sediment delivered to a stream
This will increase the gradient of the stream
The stream will flow faster until it can carry a greater amount of sediment
Agriculture to forest will result in an opposite effect
Dam construction
Upstream of the dam, the river deposits sediment forming a delta
Downstream water is devoid of sediment and will erode sediment
Slope of the stream will decrease until equilibrium is reached
Urbanization
Increases the magnitude and frequency of floods
Urban areas have impervious cover and are served by storm sewers
Carry water to stream channels quickly
Decrease in lag time bw peak rainfall and the flood crest
A short time is characterized by a rapid rise and fall in discharge
Urbanization reduces stream flow during the dry season
Bridges may block debris, creating dams
111
Minimizing the Flood Hazard- Physical Barriers
Levees are barriers built to keep flood waters contained
Earthen levees, concrete floodwalls, reservoirs, floodways that bypass populated areas, storm-water retention basins
Levee breaks cause higher energy flows and bottlenecks in upstream areas
Physical barriers encourage development on the floodplains they are intended to protect
Better off to not build on floodplains at all
112
Minimizing the Flood Hazard- Channelization
Examples of channelization include straightening, deepening, widening, clearing, and lining existing stream channels
Degrades river and wetland ecosystems
Benefits are greatest in urban areas with a high flood risk
The Red River Floodway in Winnipeg has prevented many major floods
113
Minimizing the Flood Hazard- Channel Restoration
Attempts to return modified streams to a more natural state by:
Removing urban water from stream channels
Planting native trees and other vegetation along channel banks
Re-establishing deeper pools and shallower riffles within channels
114
Adjustments to the Flood Hazard
Floodplain regulation
The objective is to maximise the benefits that floodplains offer while minimizing flood damage and the cost of flood protection
One approach is to disallow new development that would lessen a rivers access to its floodplain
An impt step is to flood-hazard mapping
Useful in regulating development, purchasing land for parks, creating guidelines for future land use on floodplains
Flood Proofing
Several methods are currently available:
Raising foundations of buildings above flood hazard level
Constructing flood walls or earthen mounds around buildings
Using waterproofed doors, basement walls, and windows
Installing drains with pumps to remove water
Installing ground-level windows that open to allows floodwaters to pass through the building without washing it away
115
Canada Water Conservation Assistance Act ,1953
Enabled the federal gov to provide finical assistance to the provinces and territories for construction of works to conserve and control water
116
Canada Water Act, 1970
Comprehensive planning including all water uses
Views of people affect should be sought
Non-structural flood control alternative should be considered
Planning should take place on a watershed scale
117
Flood Damage Reduction Program
Established in 1975
Operates under a series of federal-provincial and federal-territorial cost-sharing agreements
Agree to not build, approve, or finance developments in flood-risk areas
Will not provide flood disaster assistance for developments build after an area is designated to have a flood risk, except for flood-proofed structures
Encourage local authorities to zone on the basis of flood risk
118
Fort McMurry
10,016 residential properties that are partial loses
40 dead, 3 billions dollar in insured damage
Wildfire is no longer an imminent threat to the community
Critical infrastructure is repaired to provide basic service
Implications:
Respiratory infection and long term health effects
Tourism would go down
Insurance premium increase
Psychological issues that come along with living through something like this
119
Wildfires
Wildfire is an ancient phenomenon
Dating back more than 350 million years ago
Before humans, fire would burn until they ran out of fuel naturally
After a fire, colonizing plants become established on the burned landscape
Natural fired allowed humans to harness fired for heat, light and cooking
120
Pre-ignition Phase
Vegetation is brought to a temperature and water content at which it can ignite and burn
Preheating
Vegetation loses water and other chemical compounds
Pyrolysis
Processes that chemically degrade the preheated fuel
Products include volatile gases, mineral ash, tars, and char
Heat radiating from flames causes preheating and pyrolysis in advance of the fire
121
Combustion Phase
Begins with ignition
Involves external reactions that liberate heat and light
Ignition does not necessarily lead to a wildfire
Wildfires only develop when vegetation is dry and has accumulated in quantities to carry the fire across the land
Ignition is not a single process but occurs repeatedly as the wildfire moves
Flaming Comubustion:
Rapid high temperature conversion of fuel to thermal energy
Characterized by flames and large amount of unburned material
Smouldering combustion
Can take place at lower temperature
Does not require rapid pyrolysis
Wildfires transfer heat mainly by convection
Radiation also plays a role
Convective and radiant heating increase the surface temperature of the fuel
As heat is released, air becomes less dense and rises
Rising air removes heat and combustion products from the zone flaming
This process pulls in the fresh air required to sustain combustion
122
Extinction Phase
The point at which combustion, including smoldering, ceases
| A fire is considered extinct when it no longer has sufficient heat and fuel to sustain it
123
Fuel
Consists of leaves, twigs, decaying material, grasses, mosses, ferns, shrubs, trees
Smaller fuels burn most readily and most vigorously
Organic materials can dry and decay during disease or drought, allowing it more easily burn
The density of trees is an important factor
Boreal forests of Canada contain abundant fuel and easily sustain wildfires once they start
124
Topography
Drier fuels are found on:
South facing slopes in the Northern Hemisphere
Slopes exposed to prevailing winds
In mountainous areas, winds tend to move up or down canyons, providing easy paths for wildfires
Wildfires preheat fuel upslope from the flames
This increases the rate of movement and the spreading of a fire moving upslope
125
Fire Environment: Weather
Large wildfires are most common following droughts
Fire spread more rapidly under hot, dry conditions
Winds greatly influence the spread, intensity, and form of a wildfire
Strong winds help preheat adjacent unburned fuel
Winds can carry burning embers that may ignite spot fires far ahead of the flaming front
126
Surface fires:
Move close to the ground
Some may burn the soil just under the ground surface
Differ greatly in their intensity
127
Crown Fires:
Move rapidly though the forest canopy by flaming combustion
Can be fed by surface fires that move up tree limbs or can spread independently of surface fires
Large crown fires are generally driven by strong winds
Intermittent crown fires consume the tops of some trees where continuous crown fires consume tops of all or most trees
128
Effects on the Geological Environment
| Fires
Fires may leave a near surface, water repellant hydrophobic layer
Increases surface runoff and erosion
Soil erosion and debris flows are common following wildfires
Significantly greater likelihood on steep slopes charred by a severe burn
129
Effects on the Atmosphere
| Fire
Increase the concentration of particles in the atmosphere
Can remain for months
Can be observed thousands of km downwind of large fires
130
Impacts of Wildfires on Plants and Animals and Animals
Vegetation
A fire can burn millions of hectares of forest
Some plants use fire to propagate
Animals
Most animals are able to escape advancing fire
Aquatic species may suffer from increased sedimentation
New habitats are produced for grazing animals
Humans
Smoke and haze can cause eye, respiratory and skin problems
Destroys personal property
131
Natural Service Function of Wildfires
Benefits to soil
Increases nutrient content
Reduce populations of micro organisms
Benefits to plants and animals
Reduces competition for sunlight and rainfall among plants
May trigger a release of seed in some species
Removes surface litter for grasses
Recycles nutrients in the ecosystem
Grazing animals find new forage in plants that proliferate following fire
132
Fire Management
Aim is to control wildfires for the benefit of ecosystems while preventing them from harming people and destroying property
Fire management in Canada is a provincial and territorial responsibility, except on federal lands
Scientific research on the role of fire in ecosystems is critical to fire management
Remote sensing is an important tool for fire management
Satellite imagery is used to map vegetation and determine fire potential
133
Fire Suppression
A common practice is to steer the fire into an area with no fuel, called a fire break
Reliance on fire suppression has led to a build up of fuel is forests and an increase in potential for high intensity fires
134
Reducing Wildfire Risk
Fire danger warning
Rating systems to alert land managers, residents, and visitors
Education
Community awareness programs and fire safety presentations in schools
Codes and Regulations
Enact building codes that require fire resistant materials
Fire Insurance
Allows people whose property has been destroyed by a fire to be reimbursed for part or all of their losses
Evacuation
Most common response to wildfires
Ensured personal safety but don’t not protect homes
Structural protection
Actions taken to protect homes from a wildfire
