Blue & Orange terms Flashcards
What is a Natural Disaster?
An extreme natural event in which a large amount of energy is released in a short time with catastrophic consequences for life and infrastructure in the vicinity
What is the key aspect of natural disasters?
The impact on society
What is a natural hazard?
a source of danger that exists in the environment and that has the potential to cause harm. Hazards are potentially damaging
What is vulnerability?
the likelihood that a community will suffer, both in terms of fatalities and physical damage when exposed to hazards in the environment
Summary of terms: Natural disaster, natural hazard and vulnerability
Natural disaster: the event, past tense
Natural Hazard: the danger source
Vulnerability: the impact on humans/community
What is frequency regarding a metric to describe hazard levels
number of similar events per unit time. For example, on average 4 tropical cyclones affect canada every year.
What is a return period?
length of time between similar events. Severe hurricanes strike the US on average every 6 years. This does not mean that there is a severe hurricane every six years.
What is magnitude?
The amount of energy fuelling a natural event
What is gravity?
Force of attraction between masses m1 and m2 separated by a distance of r. F=Gm1m2/r2. G is the gravitational constant
What is risk?
Risk= Vulnerability x Harm
What is response?
The Immediate actions taken after a natural disaster has occured to put the event under control
What is recovery?
Middle term activities to put the situation back to normal
What is mitigation?
Long term actions taken to minimize the risk associated with natural hazard. Specifically, damage on infrastructure
What is preparedness?
Actions taken in advance to ensure people are ready when a disaster strikes. applied to humans and communitiies
What is adaptation?
new term applicable mainly to climate change and weather events. Long term actions taken to lower risk and gradual adjustments to minimize harm
What is important to remeber about where earthquakes and volcanoes occur?
They do not occur at random locations, most coincide with plate boundaries
What is differentiation?
Process by which gravity causes denser material to gradually migrate to the center of a planet
What are the 3 most important layers of the earth in the theory of plate tectonics (based on strength)?
Rigid lithosphere, soft plastic asthenoshpere, and stiff plastic mesosphere
What are tectonic plates?
lithospheric plates floating on top of the asthenoshpere
What is the depth of the lithosphere- asthenosphere boundary?
boundary is at a depth of about 100km
What is convection?
Heat transfer by liquid circulation. Warm low density water rises, and cool high density water rises.
Where are large convection cells located?
in the asthenosphere and mesophere
What does tectonic mean?
related to the deformation forces acting on the earths surface
What is a tectonic cycle?
it is an episode of large scale deformation of the earths surface. One cycle ~250 million years
According to the theory of plate tectonics, which plates slide over which other plate?
Rigid lithopshere plates slide over the plastic asthenosphere
What is lithosphere?
continental and oceanic crust and rigid upper mantle
What is the athenosphere?
the plastic upper mantle
What sets the plates into motion?
Convection in the asthenosphere and mesosphere sets plates into motion
What is subduction?
process in which a lithospheric plate descends beneath another, pulled down by gravity
In the subduction process, What is the less dense plate called?
The overriding plate
In the subduction process, what is the denser plate called?
the subducting plate
What is the hypocentre?
the point of origin of an earthquake in the subsurface
What is the epicentre?
Point on earths surface directly above the hypocenter. Epicentre locations outline plate boundaries.
What is tension?
force that pulls a body apart
what is compression?
force that shortens a body (pushes together)
what is shear?
force applied parallel to the surface, causing slippage
What is a divergent zone?
The dominant force is tension. It is an elongated region where two plates are being pulled away from each other. New lithosphere is formed as molten asthenosphere is forced upward into the gap
What is a convergent zone?
The dominant force is compression. It is a region where two plates collide.
What is collision style controlled by?
by the density of the plates
What happens where an oceanic plate and a continental plate collide?
The oceanic plate which is always denser subducts beneath the continental plate which is always less dense
(subduction zone)
What happens where 2 oceanic plates collide?
the denser oceanic plate slides under the less dense plate (becomes a subduction zone)
What is a continent to continent collision zone?
Where 2 continental plates collide both plates are too buoyant to subduct so plates compress and crumple which leads to thickening of the crust.
What is a transform fault?
The dominant force is shear. A fault that accomodates horizontal movement of tectonic paltes against each other. No material is created nor consumed
What is a hot spot?
The dominant force is mainly tension and some compression. Plume of slowly rising hot rocks that create volcanism on the earths surface. It originates in the mesophere, passes through the asthenosphere and lithosphere as magma and supplies an active volcano
Where are earthquakes and volcanoes most frequent?
They do not occur at random locations and they are most frequent in tectonic environments
What is the hypocenter depth boundary and why can earthquakes not occur past this depth?
No earthquake below ~700km because the material in the plastic asthenosphere is not rigid enough to break abruptly
What kind of earthquakes occur at convergent zones?
They are infrequent and great (immense amount of energy is stored and then realized suddenly magnitude of 8-8.5+). Shallow, intermediate and deep earthquakes occur.
What happens at subduction zones with depths <30 km?
Crustal earthquakes (shallow) due to compression in both overriding and subducting plates
What happens at subduction zones with depths ~30km?
Megathrust earthquakes due to shear stress at the contact b/w the overriding and subducting plates
What is a megathrust fault?
boundary between the subducting and overriding plates
What happens at subduction zones at depths >100km
Intraslab earthquakes in the subducting plate due to cold rock being consumed into the hot asthenosphere.
What are megathrust earthquakes?
The worlds largest earthquakes
What type of earthquakes have the highest risk in the Cascadia subduction zone?
Crustal earthquakes, average return period ~30 years
What type of earthquake has the most catastrophic risk?
A megathrust earthquake, average return period~600 years
What kind of earthquakes occur at transform faults?
Stress from plates being stuck is released on infrequent, major (M=7-7.9) and shallow earthquakes
What kind of earthquakes occur at hot spots?
Tension and compression forces, result in frequent, strong (M= 6-6.9) and shallow earthquakes
What is a fault?
fracture across which two blocks of rock move realtive to each other
What is a slip?
Displacement between the two rock blocks
What is a rupture area?
Surface area where rocks have moved?
What is a wave?
Oscilliation in space and time travelling away from an initial disturbance
What is a seismic wave?
waves caused by the release of energy in the earth
What is a seismometer?
Sensor that detects ground motions
What is a seismograph?
An instrument that records ground motions
What is a seismogram?
paper record or digital file w/ data describing ground motion
What are body waves?
propagate throught the whole body of the earth, Primary and secondary waves
What are surface waves?
propogate only near the earths surface
What are primary waves?
Compressional energy, small amplitude, travel fastest and first to be recorded. Propagate in liquids solids and gasses
What are secondary waves?
Shear energy, larger amplitude than p waves, Travel 1.7 seconds slower than p waves and propagate in solids only
Which wave motion is potentially more damaging?
The sideways motion from S waves is potentially more damaging to buildings than the up and down motion from p waves
What is arrival time?
Time at which a particular seismic wave is recorded
What 2 measurements is the richter magnitude scale based on?
Difference between P and S arrival times (plot on left column) and Maximum amplitude of Body waves (plot in right column) (read magnitude in center column)
How do you interpret the logarithmic scale used in the richter magnitude scale?
When the amplitude is multiplied by a factor of 10 the magnitude on the scale increases by +1
What is intensity?
Measure of the effects of an earthquake on people and infrastructure
What is the mercalli intesity scale?
Descriptive and subjective scheme based on eye witness accounts and damage to infrastructure. 12 divisions of increasing intensity
What is a shakemap?
intensity map generates automatically in near real time using data from seismograph stations. Inputs include: ground motion data and knowledge of regional geology and outputs include computed intensity
Did you feel an earthquake reports are based on what?
After the fact summaries of intensity data based on input from the public
What are intensity reports?
Maps of georeferenced intensity data. it is the current state of the art. Data is referenced using postal codes
What are isoseismal maps?
intensity contour maps (classic display)
What is the felt area?
Area of pereceptible earthquake ground motion. Corresponds approximately to II-III intensity contours. The shape is influenced by local geology
What is the typical hypocentre depth of megathrust earthquakes?
Hypocentre depths of megathrust earthquakes are typically shallow (~30km)
What is a foreshock?
Small earthquakes that precede the mainshock. Impossible to tell if an isolate EQ is the foreshock of a larger main shock to come
What is an aftershock?
Small earthquakes that follow the largest shock (mainshock) in an earthquake sequence. if the mainshock and aftershock dont have the same hypocenter it is considered a new event
What is soil?
Top layer of the earths surface consisting of rock and mineral particles mixed with organic matter
What is natural frequency?
A mechanical system (e.g., guitar string, building) us characterized by a particular natural frequency. Frequency at which the system oscillates when disturbed
What is the natural frequency of soil and hard rock?
Soil < 1 Hz and Rock is > 1Hz. Ground motion in hard rock are amplified by body waves. Ground motion in soils are amplified by surface waves
What is resonance?
phenomenon by which a system experiences very large oscillations when it is disturbed by a forcing function of frequency equal to its natural frequency. The energy of the forcing function is added to the system so that oscillations are reinforced (they grow larger and larrger until it breaks)
What is liquefaction?
phenomenon in which the strength of soil is reduced by rapid and violent shaking or loading. Occurs in saturated soils in which the space between particles is filled with water, it then behaves like a liquid and does not have the strength to support a load.
What are the 2 scenarios that could occur when buildings go beyond the elastic limit?
Some materials fail immediately: higher hazard and total collapse (brick and stone) and Some materials undergo plastic deformation before failing: Less hazard, potential for partial collapse
What is a tsunami?
Ocean wave most often created by under water disturbances of the seafloor. Mostly triggered by MAJOR earthquakes (M>7.5) with their epicentres under water
What is the motion of the rock blocks on the sea floor in an earthquake caused tsunami?
Vertical motion, it acts as a piston
Where are wind caused waves confined to?
The first 100 metres of water
What is a tsunami wave always interacting with?
the seafloor
Why was the indian ocean tsunami of 2004 so devastating?
M9, 3-4 minutes of ground shaking. No warning system yet, lack of awareness about tsunami and poverty. Vertical slip ~10m
What was good about the Tohoku Earthquake in 2011?
Megathrust M9 took place, but exemplery preparedness: warning issued within ten seconds and tsunami warning in 3 minutes
The grandbanks 1929 earthquake
Underwater epicentre 250 km south of NF M7.2. Minor EQ damahe however earthquake triggered a large submarine landslide which generated a tsunami of 3 waves that struck NF 2.5 hours after. 28 people drowned and 1 child died of injuries later
What can happen after a megathrust EQ?
the plate will rebound by a few meters over a few minutes a tsunami might follow
What two elements account for 75% of the crust?
8 elements form 98% of the crust, Silicon and oxygen account for 75%
What is magma?
(ointment in ancient greek) partially molten rock below the earths surface
What is lava?
Magma that reaches the surface
What are the 3 components of magma?
Liquid: molten rock
Solids: minerals incorporated in the melt
VOLATILES: gases dissolved in the melt
What are igneous rocks?
form by cooling and solidification from hot molten rock material
What are intrusive igneous rocks?
cooling takes place at depth, slow cooling and large grains. Most magmas solidify at depth and are later exposed by erosion
What are extrsive igneous rocks?
(synonym: Volcanic) Cooling at the surface, fast cooling, small grains and contact w/ atmosphere or water
What is viscosity?
Internal resistance of a liquid to flow ( low viscosity consistency is like water and high is like toothpaste)
What is the most important property in controlling magma behaviour?
Viscosity
What controls magma viscosity?
%SiO2, temperature and amount of solids in the melt
What is basaltic magma?
Low viscosity, low, SiO2 content, High temperature. 80% of magma reaching the earth is basaltic
What is andesite and rhyolitic magma?
Medium/high visocsity, Medium to high SiO2 content, medium to low temperature, more solids in the melt
What does low volatile content mean?
Volatiles can escape easily (bc of high temperature)
What does high volatile content mean?
Volatiles are “trapped” in magma and have to burst out to escape
What is ejecta?
Volcaninc material extruded onto the earths surface and into the atmosphere
What is pyroclastic material?
(synonym tephra) material formed by volcanic explosion or aerial explosion from a volcanic vent
What are volaties made up of?
Mainly H2O, CO2, SO2
What is aa?
High %SiO2, viscuous lava, flows slowly and flows with a jagged upper surface
What is pahoehoe?
Low SiO2, fluid lava flows quickly and over large distances, lava flows with smooth upper surfaces and flow wrinkles
Pyroclastic material according to particle size
Ash < 2mm
Lapilli 2-64 mm
Scoria > 64mm
bombs: ejected as incandescent lava fragments which were semi molten when airborne
Blocks: ejected as solid fragments with angular shapes
What is Jokulhlaup?
An outburst flood
In hot spot volcanoes what direction are the chain of volcanoes lined in?
aligned in the direction of plate motion. Age increasing with distance from hot spot.
What are the characteristics of Oceanic hot spots?
Peaceful eruptions-Rising magma (basaltic) does not mix much with thin oceanic crust, Magma derived directly from asthenosphere with low SiO2 content, low viscosity and low volatile content
What the characteristics of continental hot spot volcanoes?
Explosive eruptions, rising magma mixes with thick continental crust. Magma enriched in SiO2, high viscosity, high volatile content
What causes solid rock to melt?
Most important mechanism: Decrease in pressure causes rocks to melt partially decompression melting
what are the 2 eruptive styles?
Peaceful and explosive, Relationship between tectonic environment, magma composition, eruptive style
What is important to remember about eruption types?
Caution: a volcano can change eruptive type through time.
What are the 3 V’s of volcanism?
Factors controlling volcanism and volcanic landforms
1) viscosity
2) volatiles
3) volume of magma
Describe Icelandic type eruptions
Occur in divergent zones and hot spots. Magma composition is Basaltic. Low viscosity (lava flows like water), low volatile content (volatiles escape easily) and small volume. The landform is a lava plateau
What is a lava plateau?
Small areas covered by nearly horizontal layers of solidified lava. Surface rupture is a fissure: linear fractures (
Describe Hawaiian type eruptions
Occur in divergent zones and hot spots. The magma composition is basaltic.
Low viscosity (lava flows like water and travels long distances. Each lava flow cools to form a thin gently dripping layer)
Low volatile content (volatiles escape easily)
Large volume (eruptions commonly preceded by small earthquake)
Land Form: Shield Volcano
What is a shield volcano?
Volcano in the shape of a flattened dome built by numerous flows of very fluid lava over a long time (broad and low) Surface rupture: Central vent
What are the characteristics of strombolian type eruptions?
Peaceful eruptive style in divergent zones. Magma composition: basaltic to andesitic. Medium viscosity, Medium volatile content (Lava pours out oc central vent and eruptions generate pyroclastic material), Small volume (Pressure is released in separate short-duration bursts, daily activity)
Landform: Scoria cone
What is a scoria cone?
Volcano in the shape of a conical hill formed by pyroclastic debris piled up next to a central vent. Destroyed quickly by erosion because pyroclastic debris is weak and unstable. Harder volcanic conduit might remain creating a volcanic neck. Typically a monogenetic volcano (eruptive phase of a few years but doesnt erupt again)
What are vulcanian type eruptions?
Mostly in subudction zones and can be in hot spots. Magma composition is basaltic, andesitic and Rhyolitic. Medium/high viscosity (eruptions alternate b/w medium/high viscous lava and pyroclastic material). Medium volatile content, and Large volume. Vulcanian type often preceding a more violent plinian. Landform: Stratovolcano
What is a stratovolcano?
a large volcanic cone built of alternating layers of viscous lava and pyroclastic debris. Steep sided and symmetrical. Surface rupture is a central vent. Width ~ height
What occurs during the main phase of a plinian type eruption?
Plinian eruptions occur mostly in subudction zones but also hot spots. Magma composition: andesitic to rhyolitic. Medium/high viscosity, high volatile content, large volume. Volatile powered vertical eruption accompanied by pyroclastic flows and lots of pumice. Landform is the continued development of a stratvolcano
What occurs during the final phase of a plinian eruption?
High viscosity (lava behaves like a paste forming a plug in volcanic conduit) low volatile content (few volatiles remain), small volume. Landform is a lava dome
What is a lava dome?
Volcanic cone with a highly viscous blob of lava forming a half ball shape over the vent , lava is too viscous to flow far from the vent
What is an ultra plinian eruption?
A collosal plinian eruption
What is a caldera type eruption?
Mostly in subduction zones but can be in hot spots hese are the largest volcanic eruptions. Magma (andesitic to rhylotic) and very large volume. 2 different phenomena can occur: Volcano collapse OR cataclysmic explosion
What are canadian volcanoes associated with crustal rifting?
Volcanoes in divergent zone, Stikine volcanic belt, northwest BC. Most extensive in Canada with≈ 100 volcanoes. 3 volcanoes erupted in the last few
hundred years. Example: Tseax Cone, Northern BC
Where are Canadian Hot spot volcanoes?
Anahim volcanic belt, central BC: Chain of hot spot volcanoes 14 Ma old. West (oldest): eroded volcanoes
along BC coast, East (youngest): Nazko Cone in central BC
Where are Canadian subduction zone volcanoes?
Northern extension of the Cascades Volcanic Belt in the northwestern United States. Contains the most explosive young volcanoes in Canada, Close to densely populated areas. Example: Mt. Garibaldi
What is the volcanic explosivity index?
Metric established to quantify the hazards posed by volcanoes. Volume of material extruded, height of eruption column and duration of major eruptive blast.
What is pyroclastic flow?
A primary hazard, Synonym is Nuée Ardente. It hot gases, ash and rock fragments moving down the sides of volcanoes. The temperature is ~1000 degrees, velocity of 10-300m/s. High density flows follow valleys and low desnity flows can move up and over ridges
What are the direct and indirect effects of pyroclastic flow?
Responsible for largest number of fatalities related to volcanism. highly destructive due to momentum, High Temp., and great mobility. Indirect effects: fires
What is volcanic gas
A primary hazard of volcanic eruptions. Volcanic gasses that come out of the melt during eruptionm main driving force of explosive eruptions. Most adbundant is H2O, CO2, and SO2
What is a lahar?
A secondary hazard. Mudflow that originates on the slopes of volcanoes when volcanic ash and debris become saturated with water and flow rapidly downslope (speed~40m/s). Almost always occur on stratovolcanoes (tall cones often snow covered). A lahar can be a primary hazard if the triggering mechanism is the melting of snow and ice from a minor eruption. Heavy rainfal is a secondary hazard/
What is an active volcano?
Volcano which has erupted in historical times
What is a dormant volcano?
Volcano that has not erupted in historical time but is capable of erupting in the future.
What is an extinct volcano?
volcano that is not expected to erupt again.
