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Notes on Natural Disasters

Topics: Volcano, Volcanology, Magma, Lava, Basalt / Pages: 12 (2856 words) / Published: Feb 4th, 2013
Energy Source of Natural Hazards
Disasters occur where and when the earth’s natural processes concentrate energy and then release it, killing and causing destruction.

Four energy sources make the earth an active body: 1) the Earth’s internal energy; 2) solar energy; 3)gravity; 4)the impact of extraterrestrial bodies
The interior of the Earth holds a tremendous store of heat released primarily from the ongoing decay of radioactive elements. Earth’s internal energy flows unceasingly toward the surface. * Over short time span: released as eruptions from volcanoes and by earthquakes. * Over long intervals of geological time, the flow of internal energy has produced continents, oceans and atmosphere. * On a planetary scale, this outward flow of internal energy causes continents to drift and collide, constructing mountain ranges and elevated plateaus.
Gravity is an attractive force between bodies. The relatively great mass of the earth has powerful effects on smaller masses such as ice and rock, causing snow avalanches and landslides.
Hydrological Cycle: about a quarter of the sun’s energy that reaches the Earth evaporated and lifts water into the atmosphere, creating the hydrological cycle. At the same time, constant gravity bring atmospheric moisture down as snow and rain. * On short timescales, unequal heating of the oceans and atmosphere at the Earth’s pole vs the equator created density differences in water and air that are acted on by gravity to create weather like storms, strong winds and ocean waves. * On a long timescale, the sun and gravity power the agents of erosion—glaciers, streams, underground waters, winds, ocean waves and currents that wear away the continents and dump their broken pieces and dissolved the remains into the sea.
Asteroids and comets: impact the earth .

* Origin of the Sun and Planets * Solar system formed by growth of the Sun and planets through collisions of matter within a rotating cloud of gas and dust. * * Solar System grew as a rotating spherical cloud of gas, ice, dust and other solid debris known as the solar nebula gravity within the cloud attracted the particles together and grew in size-> resulting in greater gravitational attraction to nearby particles and thus more collisions matter drew inward and size of cloud decreasesspeed of rotation increases and the mass began flattening into a disk greater accumulation of matter at the centre resulted the sun
The two main constituents of the Sun are the lightweight elements H and He
Nuclear fusion began at very high temperature
Solar radiation: H combine to form He with some mass converted to energy.
The inner planets *

Volcanoes Learning Goals 10/11/12 11:51 PM

Lecture 1

1. Identify key properties (density, viscosity, silica content, & temperature) of different types of magma.
Density: water<magma<crust and mantle, so magma sinks in water but rises from crust and mantle.
Viscosity: it controls flow and eruption style, depends on temp, gas and crystal content.
SiO2 content: Felsic —light color, high V, sticky, Granite, Rhyolite. Mafic —dark color, low V, runny, Basalt, Gabbro
Temperature: 600-1200,
Hot magma: low V, low silica
Cool magma: High V, high silica
Gas content: Volities, begins with 10% gas dissolved.
Gas content decreases V and decrease density.
Magma riseslower Pless solubilitybubbles

2. Explain why magma erupts or not
Magma, created by melting pre-existing rock below the Earth’s surface, reached surfaces through fractures and extrudes as lava or explodes as pyroclastic material. (Below the Earth’s surface)
Lava is melted rock exposed at the Earth’s surface.
It goes through source, transport (dikes and sills), storage and eruption region during an eruption.

3. Describe the different types of eruptions and how they are related to magma properties * 4. List the different categories of volcanic rocks and explain the difference between the magmas they cooled from. * * Dark Color | * | * | * Light Color | * Basalt | * Andesite | * Dacite | * Rhyolite | * Mafic, less silica | * Intermediate | * Intermediate | * Felsic, more silica | * Hot 1200-1400 | * | * | * Cool 600-1000 | * Low V | * | * | * High V | * N-explosive, lava | * | * | * Explosive, ash |
Bubbles escape easily from low V mafic, but not high V felsic, making felsic eruptive and ash form.

5. Explain why some magma erupt explosively (as pyroclastic material) and some magmas erupt effusively (as lava).
Explosivity is different:
Mafic magma: low gas content + low V=effusive eruption, lava
Felsic magma: High gas content + high V=explosive eruptions, pyroclastic material

6. Explain the differences between pahoehoe and a’a lavas.
They have the same composition but because of the different viscosity, the flow differently:
Pahoehoe lava: close to the source of volcano, flow smoothly
A’a lava: far from the source, flow slowly

Lecture 2

1. Explain the global distribution of volcanoes.
Plate boundaries—volcano distribution matches the Pacific Ring of Fire
Hot spots 2. List the three types of plate boundaries and the different types of volcanoes that occur at each plate boundary.

3. Describe the type of volcano that occurs at hot spots. * 4. Describe the morphology, dominant rock type and typical eruption style of the different types of volcanoes. * Cinder Cones | * Layers of pyroclastic from fire fountaining | * Mafic(Basalt) | * Explosive | * Erupt for a few years then never * FREQUENT | * Shield Volcanoes | * Lava erupts from fissure, runs down gentle slopes and cools | * Mafic, lava flows of pahoehoe and then a’a | * Non-explosive | * Erupts often * FRE/PERMANENT | * Stratovolcanoes | * Interbedded lava flows, pyroclastic flows, lahars | * Intermeditate, felsic | * Frequently explosive and viscous magma | * May erupt many times and stay active. * FREQUENT | * Calderas | * Created from large, explosive eruptions of felsic pyroclastic materials; * When roof of the magma chamber collapses. | * Felsic | * Explosive * * | * RARE * * Most devastating eruptions! |

5. Describe the tectonic setting of Southern British Columbia (Cascadia) and determine the dominant style of volcano that occurs here. * * * * * *
Lecture 3 1. Explain what lava flows, fire fountains, lava bombs and volcanic ash are and how they form. * Effusive—outpouring of molten magma from the ventlavas * Passive eruption of magma * Lava flows (mafic-int) * Lava domes (felsic-int)) * Gravitational collapse of lava flows/domes—block and ash flows * Explosive—gas driven violent eruptionspyroclastic deposits * Buoyant eruption column of ash * Pyroclastic airfall * Pyroclastic flows (column collapse) * Ballistics proximal to vent * 2. Explain what controls volcanic explosivity. * GAS CONTENT and V determines eruption style (ex or ef) * Gas Content
Bubbles are produced during ascent of magma and expand (lower P)
Foaming resulted, and explosivity depends on: 1) amt of bubble; 2) rate of rise; 3) bubble retention * Melt viscosity * V fights bubble growth * Pressure rises inside bubbles until the strength of the liquid magma is overcome FRAGMENTATION * Gas bubbles expand rapidly and blow up the liquid magmafreeze in mid air to form ash particlesPyroclastic material (tephra) produced.

3. Describe the different types of volcanic eruptions and how they are related to magma properties. * Type | * Hawaiian | * Strombolian | * Vulcanian | * Pelean | * Plinian | * Rock | * Basaltic magma | * Basaltic/Andesitic magma | * Viscous andesitic/rhyolitic magma | * | * Andesitic/ * rhyolitic * ash | * Viscosity | * Low | * | * | * | * High | * Gas cont | * Low | * | * | * | * High | * Safety | * Safe | * | * | * | * Dangerous | * Hazards | * Lava flows; Fire Mountaining | * Bombs, lavas | * Sustained explosions of ash | * Dome collapse; Block-and-ash flows | * Pyroclastic * flows, * sustained column of * ash | Explosive | Low | Mildly | Very | Violent | Violent |

*Phreatomagmatic: contact b/w magma and water, violently explosive
Mafic: Low gas content+fluidquiet (effusive)eruptions ; gas escapes, pressure released=safe
Felsic: High gas content + gooey explosive eruptions; gas kept under increasing pressure=dangerous * 4. Use the VEI to rank the size of explosive eruption.
Key characteristics that define VEI (Logarithmic scale, 0-8):
Volume of ash produced (main)
Height of eruption cloud above the vent
Duration of eruption

Lecture 4

1. Describe the particular hazards associated with pyroclastic flows, lahars, dome collapses, sector collapses, lateral blasts and toxic gases.
Lava Flows:
Slow, usually not dangerous, easy to predict flow path, (usually) mafic + low viscosity
Hazard: to building not to people
Fire Fountaining:
If basaltic lava is gas-rich, small explosive eruptions from fire fountains
Partially liquid drops fall back to ground, coalesce to lava flow
Pyroclastic Falls (Ash Fall)
Hot ash + Gas ejected from volcano
Hazards to people
Breathing in ash – can be deadly
Total darkness
Roofs collapse – most dangerous, most fatalities are people trying to shelter
Hazards to aircraft:
Engines such in ash and stop
Windshields are scratched and break
Turbulence (satellites now watch for ash clouds)
Pyroclastic flows
Avalanche of pyroclastic material, air and gas
Driven by gravity, Velocity=(40-400km/hr)
Origins
Collapse of a volcanic column
Explosive collapse of lava domesilica rich magma, highly viscous, steep-sided domes and glow at night
Usually stay in valleys but if big enough can flow over ridges
Very fast moving, even over water
Lahars (volcanic mud flows)
Flows of water + loose volcanic debris
Prevalent at snow-clad and ice-cad volcanoes
Hazard: very dangerous because can travel far and occur without eruption
Sector Collapse-debris avalanche (Volcanic Landslide)
Debris avalanche occurs when volcanic edifice is weakened
A scalloped scar remains
Eg: Mt St Helens Eruption (1980) landslide triggered an explosive eruption, lateral blast is cool but speed up to 500km/hrdevastating to a very large area.
Volcanic Gases
Highly acidic and toxic: kill pants and animalsasphyxiation, mainly of H2O, CO2, HCL, SO2, HF

2. Explain what a volcanic hazard map is and why they are useful. * 3. Understand the hazard potential of specific volcanic events.
See #1

Lecture 5

1. Learn to interpret a volcanic hazard map.
Map volcanic deposits
Determine deposit type (lava flow, mud flow, pyroclastic flow etc) an distribution
Determine age of deposits and eruption rate

2. Understand how risk is assessed.
Volcanic Hazard: any potentially dangerous volcanic process (eg lahars)
Volcanic risk: any potential loss or damage as a result of the volcanic hazard that might be incurred by person or property.

3. List the different volcano monitoring techniques and the instruments that are used.
Seismology – Earthquakes: seismic stations.
Most important tool, baseline monitoring for long-term
Ideal seismic networks - >=6 stations within 15km of epicenter
Ground Deformation (Volcano changes shape)
GPS (Global Positioning System)—change in position
TM (Tiltmeter)— change in angle of slope
Interferometric Synthetic Aperture Radar (InSAR)—satellites detect changes in elevation
Gas Emission (Fumaroles)
COSPEC & FTIR—look throught the gas by examine light from the sun, CO2 and SO2 have distinctive signals when deflecting light, total amt can thus be calculated
Direct sampling: close to the volcanoe
Disadvantage:
COSPEC and FTIR: not pure gas
Direct Sampling: Must go very close to volcanoe
Satellite Observation—thermal pulse, ash and SO2 tracking
Global coverage, Rapid repeat measurements (15 min)
Ideal for early warning—airline routes, remote areas * 4. Evaluate the hazards to Vancouver associated with an eruption from Mt Baker.
Dominantly intermediate magma: potential for explosive activity
Glacier-covered: Potential for lahars in surrounding valleys (ABBOTSFORD—high risk due to high population)
Lava & Pyroclastic flow hazard close to Mt- Low risk (uninhabited)

Landslides Learning Goals 10/11/12 11:51 PM

Lecture 1
Describe how the impact of landslides depends on: population density, economic infrastructure, and population preparedness

Explain why BC has highest frequency of landslides in Canada and what we should expect as our population expands into the mountains.
Why BC: Mountainous terrain, lots of rain, complex geology (unconsolidated glacial sediments), lots of triggers (EQ).

Distinguish between the 3 main failure modes(falls, flows and slides)and how they are influenced by geology. | Material | Speed | Motion | Fall | Rock | Very fast | On steep slopes, material detach due to weakness and fall due to G | Slide | Soil, rock, debris | Vary, slow or fast | Material moves as a coherent mass along a surface of failure | Rotational Slide (Slump) | Weak material (sediment) | Intermediate speed | Rotation on a curved failure plane, a curved scarp above slide | Trans Slide | Strong material | Slow to fast | Cohesive motion of material along a flat surf | Flow | Soil, mud, wet debris, (rock) | Very slow to Very fast | Water! Fluid or plastic flow of material (chaotic) | Complex Movements: combinations of mass movements, slide becomes fall |

Categorize, Identify and Name a variety of different landslides.
Classified by 1) Type of material; 2) Type of movement 3) Rate of movement. (Name is usually combination of 1 and 2)
Material: Rock, Soil/Earth, Mud, Debris (mixture of rock, earth, trees, water etc)
Rate of movement: if slow, the name is Creep, Soil Flow or Earth Flow

Lecture 2
1. Defines Angle of Repose
Steepest angle a slope can maintain without collapsing (exact angle varies depending on material)
At the angle of Repose, Shear Stress is exactly balanced by shear strength, FoS is equal or just abv 1.0

2. Assess the balance between the strength of the slope and the destabilizing forces acting on it (Factor of Safety)
Driving Force: as Shear Stress (T) (component of force of G // to slope)
Resisting Forces: as Shear Strength (Tf)
Friction-resistance to sliding (% to normal force/stress)
Cohesion-how the material holds together
Stability of SlopeFactor of Safety (Fs)
Ration of Shear Strength to Shear stress Fs=Tf/T
>=1.0: stable slope
<1.0: Fail

3. Compare and contrast landslides causes and landslide triggers.
Causes : Factors (often long term) leading to instability of a given slope
Reduce Tf of a slope but do not initiate movement
Triggers: Factors (usually short events) that translate instability into motion
There can be many causes but only one trigger

4. List and describe several external causes of landslides.
External Causes: Factors outside the slope that affect stability
High Slope Angle: essential for mass movement, the steeper the slope, the more movement
Undercutting: Lower part of slope which acts as support is removed for roads, river, building etc.
Overloading: Adding weight for buildings, roads, landslides, trees etc.
Vegetation: 1)Roots bing loss material, removal can make slopes unstable. 2) Heavy trees instability--overloading
Climate: 1) avg temp is high—more water and weathering of rocksmore fractures and soil. 2) Avg temp is ard 0 degrees internal cause
Lecture 3
1. List and describe 3 internal causes of landslides.
Internal Causes—Factors inside the slope that affect sability
Water Content
In all slopes water:
Adds weight (overloading)
Decrease normal force/normal stress, which decreases friction and thus Tf
Increases weathering
Acts as a medium for flows
In sediment (loose rocks, sand, silt, and clay):
Water can help or hinder cohesion
Depends on the amount of water
No water-low angle of repose
Some water-high angle
Too much-very low angle
In solid rock
Water reduces shear strength along planes of weakness (fratures)
Or causes-Frost Wedging
Colder Climates
Water gets into cracks and fractures in rock
If freezes it expands-forcing the fractures apart.
Inherently Weak Materials
Some materials are very weak, Fail at relatively and/or very low angles of repose, eg Volcanic rock, volcanic layer, quick clay
Quick Clay
Clay is so small that Van Der Waals force has an effect (Electrostatic effects)
When deposited in salt water, clay is attracted to other clay particles (quite rare) with salt: compact and stable without salt: liquid
Salt content s lowered by percolating groundwater-Quick clay slide
Adverse Geologic Structures
Unfortunate bedding or fracture orientation
Structures angled in an instable direction or layered precariously

2. List several landslides trigger.
Trigger-A force or event that disrupts the equilibrium of a slope and initiates mass movement
EG:EQ, Snow melt, Heavy rainfall, rain or snow, loud noises, vehicles, volcanic eruptions, excavation, skiing, jumping up and down

3. Compare and contrast key triggers and causes of landslides and how they affect the force balance equation. (i.e. Factor of Safety)

4. Explain how liquefaction landslides develop in sensitive marine clays (Quick Clay Slides)

5. List and describe the site conditions (Causes and Trigger) that lead to the development of the Rissa quick clay slide in Norway.
Type: Quick Clay complex movement (flow+slide)
Internal Cause: Quick Clay—inherent weak material
Trigger: Excavation

Lecture 4
1. Relate the type of landslide damage expected as a function of its velocity.

2. Identify tell-take signs of an unstable slope.

3. Compare and contrast avoidance, prevention, and protection strategies for dealing with landslide hazards.
Avoidance-move to a different area, avoid problem
Prevention-do something to make sure events don't occur
Protection-armour or strength the area that might be affected

4. List the mitigation techniques commonly used for avoidance, prevention and protection strategies.
Avoidance
Hazard Mapping-may be used to plan the “best”route for a new highway, pipeline or rail line. Eg, one that minimizes the number of major landslide hazard areas encountered.
Modelling
Prevention
Removal of material-remove the part that put on shear stress to the mountain. Very simple, but too expensive for most situations. Eg, Scaling-know down or dynamite rocks
Stabilizing Slopes-increase the resisting forces by applying a resisting force at the toe of the landslide. Eg, add gabions or anchors, cables to increase FoS.
Draninage-control the water amount in and on the mountain
Protection
Barriers and netting-effective of minimizing the hazard of rockfalls, which let falls to occur but control the distance and direction of travel. (use replaceable system, see slide)
Debris Flow Protection separate water and debris by removing debris from the flow(barriers)
Prevent more debris from entered (concrete-lined channel)
Decrease flow’s velocity and erosive capabilities (boulder-embedded channel)
5. Identify the appropriate mitigation strategy for a variety of risk situations.

*

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