Lectures 10-20 Flashcards
what do magnetometers measure?
earth’s magnetic field
what do electrodes measure?
telluric currents
magnetotelluric does what
estimates the electrical conductivity in the subsurface
what does electromagnetic surveying achieve?
estimates depth, shape, and electrical conductivity of subsurface
does does electromagnetic surveying work?
artificial varying magnetic field induces currents in subsurface, the magnetic field of these currents are recorded at surface
what does a magetometer at the surface of the earth record?
superposition of signals from “internal geomagnetic field”
external “geomagnetic field”
what causes the internal geomagnetic field?
liquid iron movement:
earth’s rotation
heat transfer by convection
what is meant by slow variations?
magnetic poles wander around geographic poles
few hundred thousand years: magnetic poles flip
what disturbances affect technological systems?
variations of the external geomagnetic field..driven by solar activity
define solar wind, and how long it takes to reach earth.
solar wind is a stream of charged particles that takes 4-5 days to reach earth
what are solar winds caused by?
coronal hole explosions in small localized areas of sun’s surface
coronal mass ejections are?
star-scale events. charged particles are released from sun’s corona in a vicinity of sunspots
solar activity follows a ___ year cycle
11 year cycle for solar activity
how long do magnetic storms last?
temporary (hours to days)
when are magnetic storms most frequent?
peak of solar cycle
declining phase of solar cycle
what is magnetosphere
region around the earth shielded from solar winds by internal geomagnetic field
how do aurora borealis exist?
charged particles are guided by the magnetic field lines towards poles and excite atoms
how are telluric currents produced?
charged particles create currents in ionosphere, these cause variations in external geomagnetic field
how do we predict space weather?
satellite observations from sun
geomagnetic data from international network observatories
knowledge of solar cycles
what are the problems of magnetic storms?
1) bombardment by charged particles
2) ionospheric disturbances
3) electromagnetic induction effects
what problems are associated with particle bombardment?
- pressure from solar winds affects satellite orbit
- charged particles can interfere with circuity
- charge build-up can lead to violent discharge
what problems are associated with ionospheric disturbances?
- GPS signal delayed between ground and satellite
- loss of signal
problems associated with electromagnetic induction
variations in external geomagnetic field induce telluric currents along electrically conducting networks
- pipelines
- telegraphs
- telephones
- power transmission lines
what are the extraterrestrial debris primary source
asteroids: small rocky body orbiting sun
where is the asteroid belt
between terrestrial planets (Mars) and Giant planets (Jupiter)
why do asteroids from the main belt represent a relatively low impact hazard?
collisions between asteroids in the main belt send few fragments off orbit to impact earth
what represents the highest impact hazard
Near-Earth asteroids
what is the secondary source of extraterrestrial debris?
comets (a few meteoroids are fragments from comets)
which comet will eventually collide with earth
swift-tuttle comet
list the meteoroids size classifications
comic dust: a few molecules to 1mm
shooting stars: 1mm
meteorites: 1mm - 100m
asteroids: larger than 100m
how often are frequency of impacts?
smaller the impactor, shorter the return period
list the impacting scenarios for comic dust, and shooting stars
comic dust, passes through the atmosphere and settles on earth’s surface
shooting stars, melt in the atmosphere with a blaze of 1 second
why are there less stony meteorites than iron meteorites?
stony meteoroids break more easily during atmosphere entry.
stony meteorites on the ground are destroyed more rapidly
stony meteorites look like terrestrial rock
why are meteorites important
they contain information about extraterrestrial rock formation
do asteroids always leave a crater?
nope (iron normally make one though)
how old is the oldest rock?
4.1 billion years, (earth is 4.6 billion but rocks were recycled between then)
what is the K:PG boundary event?
65% of all species died in a short period of time
discovery of a world-wide iridium rich layer makes a meteorite the culprit
what diameter of asteroid would generate enough iridium to cause K/PG?
10 km
what is NEOSSat’s role?
track near-earth asteroids
identify space debris
bow big are crater diameters?
nearly 20 x impactor diameter
at what point do craters not contain meteorites?
greater than 5 km
what are the 5 distinctive features of craters?
1) circular feature
2) crater is steep-sided and closed
3) rim rocks are titled away from crater
4) shattered rocks on crater floor
5) large angular blocks of rock scattered around crater
what is the shatter cone?
a conical fragment of host rock fractured by the shock wave generated by impact
what are simple craters, complex craters
diameter < 5KM = simple
diameter > 5KM = complex
impact craters usually correspond to low gravity anomalies
this is because the crater has been filled with material less dense than host rocks
when do mass movements occur
when driving forces > resisting forces
whats least stable to most stable (dry clay, granite on granite, moist clay)
least —–> most stable
moist clay, dry clay, granite on granite
in what way do fractures have to be oriented to make it less stable
in the direction of the slope
when does liquefaction occur?
when there is high pore pressure there is weak binding force
what is congelifraction
change from liquid to ice. causing 9% volume increase and tension being generated
how much of the earths crust do silicon and oxygen account for?
75%
what is the basic building block for silicon and oxygen?
Si-O tetahedron
what is clay and why does it attract water?
clay are sheet silicates, sheet surfaces are negatively charged which attracts water and positively charged ions
difference between flocculated clay structure and dispersed clay structure
flocculated structure: stiff strong and salt binds silt together
dispersed structure: like a fluid
how do sedimentary rocks form?
by erosion and compaction of rock fragments
or
by precipitation
why does mass movement occur most often in sedimentary rocks?
rich in clay
deposition planes are planes of weakness
some sedimentary rocks dissolve in water
how are mass movements classified?
1: type of movement
2: material involved
- rock
- debris (coarse soil particles)
- earth (fine soil particles)
3: speed of movement
list the types of movements
falls
slides
- translational
- rotational
flows
subsidesdescribe falls
rapid free falls
- bouncing, rolling,
- fragments ranging in size from small grains to large blocks
- Develops in material weakened by fractures
describe slides
mass movement involving motion along a failure surface
failure surface is well-defined
material remains as a block
what are the planar surface slides? curved surface slides?
planar surface slides -> transnational slide
curved surface -> rotational slide
what is a transnational slide
slide in which earth material moves parallel to planar failure surfaces
describe lateral spreads
special case of transnational slide in which movement of earth material results for liquefaction of subjacent material
what are lateral spreads (type of translational slide)
marine clays are deposited in glacial regions, glaciers melt and uplift occurs causing clays to move above water level. clays are leached by fresh water which causes them to change to a dispersed structure
lateral spreads failures are often retrogressive, what does this mean?
start on a river bank and proceed inland
define rotational slide
slide in which failure occurs on very steep slope, along concave rupture,
- multiple blocks often fail - due to natural factors
what are the main differences between slides and flows?
slides: little deformation within the moving material.
flows: material thoroughly deformed during movement. (less deeply seated than slides)
what is a slow flow called,
fast flow?
slow = creep
fast = rock, debris or earth flow
what is Creep?
gradual slow movement of earth and debris.
- creep is assited by alternating seasons
what are the best soils for creep?
rich in swelling clays because of expansion and contraction
rock, debris, earth flows are
rock fragments, soil and water flowing.
- confined to pre-existing channels - usually related to high water content
what is Gelifluction linked to?
melting of the top layer of permafrost (cause soil under becomes weak)
which avalanche was more disastrous. which was larger (hope rock or frank)
frank was more disastrous (70 people killed, but miners survived)
hope was larger 40 m3 compared to 30 m3
what are the 2 types of subsidence?
slow: gradual sinking of land
rapid: underground collapse of cavities (sinkholes/ abandoned tunnels)
how do sink holes typically occur ?
sedimentary rocks that dissolve into water.
what are the two types of sink-holes
cover-subsidence sinkhole
cover-collapse sinkhole
list the strategies to “REMOVE the hazard”
- decrease slope angle
- bench slope
- rock scaling
list strategies to “REINFORCE” the hazard
- cylinder piles and rock bolts
- shotcrete (sprayed cement)
- rock berms (prevents erosion)
list the strategies to “SUPPORT” the hazard
-buttress supports
list strategies to “CONTAIN” the hazard
- Block Wall
- catchment basin (channel)
“PROTECT” against the hazard
- catchment net
- containment shed
what is cohesion?
property of particles of a material to stick together.
low-cohesion = fresh snow
cohesive snow = wet snow / compacted snow
new snow is less or more cohesive than old snow
new snow is less cohesive
where are weak layers in a snowpack? how do they form?
weak layers are sandwiched between stronger layers.
form
- when wind is increasing during a storm - when hoar crystals develop
when hoar crystals grow their own layer what happens? what is the layer strength?
hoar crystals grow the density of the snowpack decreases
Hoar remains a weak layer
what is Sluff?
an avalanche too small to bury a person
which travels faster and which is more destructive (wet snow vs dry snow?)
dry snow 65 - 100 km/hr
Wet snow 30 - 65 km/hr
how do we rank avalanche size
logarithmic scale -> the mass of snow
10 = sluff 100 rank 2 1,000 rank 3 10,000 rank 4 100,000 rank 5
why types of avalanches happen in low-cohesion snow? cohesive snow?
low-cohesion snow: point-release avalanche
cohesive snow: slab avalanche
describe point release avalanches?
cone - AOE, triggers additional snow during down slope
rely on superficial layer of snow
describe slab avalanches?
- involve several of cohesive snow layers
- fracture develops on perimeter of slab, starts when fracture hits base layer
which are more dangerous slab or release point
slab . greater force because of cohesive snow
slabs are close to ___
while
release point are close to___
slabs ~ slides
release point ~ flows
how does melt-freeze crust decrease stability?
decreases friction
how does weak material decrease stability?
cannot support weight of overlying layers
what avalanches happen at these slope angles
> 50
25 < ? < 50
<25
> 50 frequent point release
25 < ? < 50 infrequent, large dry slab avalanches , recreational use
<25 slab avalanches
how does uploading of slope decrease stability?
wind mainly loads downwind slope
- additional weight decreases stability - cornices develop on downwind slope
how are fractures in avalanches formed?
gravity causes snow pack to move down slope
-top moves faster than bottom, shear stress introduces fractures
how do weather conditions affect avalanches?
most avalanches occur naturally during or after snow storms.. 24 hours after a heavy snowstorm are the most critical
how often do the victim or group members trigger an avalanche? and when is this most dangerous?
90% of the time and most dangerous after natural avalanches have ceased
what are the top 2 activities that avalanche victims do
backcountry skiiing
snowmobiling
how do most people die?
asphyxia (suffocation), Trauma
what % of victims survive being buried in more than 1.5 m of snow
5-10%
give 4 tips to stay alive in a avalanche
make yourself lighter (drop skies , backpack)
swim to stay near surface
keep a pocket of air in front of your face
remain calm and carry on
what infrastructure are in the start zone for avalanche mitigation?
inclined fences supporting snowpack (expensive & rare)
wind-modifying fences (used to stop wind-deposited snow)
what infrastructure is in the track and runnout zone?
rock berms and avalanche sheds.
what is climate
meteorological elements and phenomena, averaged over a long period of time (30 yrs).
why does most weather activity occur in the troposphere?
- warmer air and higher pressure (at base)
- colder air and lower pressure at top
what is the tropopause?
boundary between troposphere and stratosphere ? 8-18 km
in troposphere air must over come gravity. what does this mean
rising air looses energy and becomes cooler
sinking air gains energy and becomes warmer
what is the Coriolis effect?
masses of air moving across latitudes following curved path
describe cyclone.
- counterclockwise surface winds
forms in low pressure zone
air rises
describe anticyclone
- clockwise surface winds
- forms in high pressure zone
air descends
what is latent heat
energy absorbed or released during a change of state
____ is accompanied by a large release of latent heat
RAIN is accompanied by a large release of latent heat
what are the 3 stages of thunderstorm development?
1) Cumulus stage
2) Mature stage
3) Dissipating stage
when do thunderstorms occur?
when warm AND moist air is lifted up
what are the two types of lifting in the Cumulus stage?
Mechanical lifting -cold dense air undercuts warm less dense air
thermal lifting - warm, less-dense air flows up and over cold, dense air along gentle slope
describe mature stage of thunderstorms
- cloud reaches maximum vertical elevation
- ice crystals and water droplets become too heavy to be supported by the updrafts
describe dissipating stage +
- cloud sinks and shrinks
- light rain
why does lighting occur?
charges seperate during cumulus. positive at top negative at bottom
what are the 4 steps of lightning bolt development?
initiation - charge imbalance
stepped leader - negative charges move downward in intermittent steps
connection - a positive discharge leaps up from ground
return stroke: connected path flashes bright during charge exchange between cloud and ground
where is the danger to people for lighting bolts
when they travel cloud-to-ground or ground-to-cloud
what is thunder?
temperature of lightning bolt causes surrounding air to expand explosively
how fast does hail fall and when does most of their mass get added?
speeds < 100 km, most mass gets added during updrafts
where is hail more frequent in Canada
in Alberta
what are most tornadoes associated with
supercell thunderstorms
what are cumulonimbus clouds?
larger than cumulums cloud , develops a anvil shape, most tornadoes are produced within cumulonimbus clouds during supercell thunderstorms
what dmg is the third level EF2 of fujita scale?
permanent houses off foundations 179-218 km/h
what is a condition for freezing rain?
temperature around 0 & layer of warm air sandwiched between two layers of cold air
a portion flows across the surface into streams is ___
a portion flows across the surface into streams is RUNOFF
a portion soaks into the ground is _____
a portion soaks into the ground is INFILTRATION
what % of water makes up rivers and streams
.0001%
what is a drainage basin and which is the largest in canada
area of land that conveys all runoff into a body of water.. largest is Hudson’s bay in Canada
how do you calculate drainage density?
area of basin
are small stream length segments have higher or lower flooding hazards
small stream segments = lower flooding hazard
long overall stream segment length = higher flooding hazard
describe discharge and the discharge formula
volume of water flowing in a stream
discharge = (width x depth) * flow velocity
list the controlling variables of flow
discharge
load (sediments being transported)
channel gradient (slope = elevation / distance)
sinuosity (path wandering, low path wander = straight)
what happens when stream has excess energy (excess discharge)
stream tries to return to equilibrium by:
decreasing flow velocity
inundating its flood plain
how does a stream decrease its flow velocity
stream erodes its bottom
increases sinuosity
increases amount of load
when does flooding occur most often? less often?
due to weather conditions, discharge temporarily exceeds the capacity of a channel to contain the flow
less often: when there is a objection of flow
what are the two factors that affect hydrometeorological floods?
abundant rains
spring melt
when do storm-rainfall floods occur
amount and duration of precipitation exceeds infiltration of capacity of the ground
what is a flash flood:
flood that rises and falls rapidly(minutes) over a small area
what are ice jam floods?
obstruction of flow due to ice buildup.
what rivers are at risk from ice-jam floods
rivers flowing from south to north
ice in the south melts first and ice at the north acts as a plug
how do natural dam floods
- mass movement
- glaciers advance and retreat
- lava flows
what is a outburst flood?
downstream flooding when dam fails
10x greater then hydrometeorlogical floods
what happened in jokulhlaup?
outburst flood resulting from a volcanic eruption underneath a glacier
what was the vulnerability in YYCFlood
poor planning and risk taking.. the flooding was precedence and predictable
what are levees and flood ways
levees: dikes that confine flood water by increasing height
flood way: artificial channel that opens up to handle excess volume
list red river flood common recipe (5 items)
wet autumn
severe frost before snowfall
heavy snowfall during late part of winter
a late and sudden spring melt
list the fundamental flood recipe (3 items)
low slope = ~7 cm per km slope
shallow river body
flat landscape
list the coping mechanisms for red river flood
sand bag dyke
buildings on pads
dyked towns
what is the primary source of energy for a hurricane? and what is most the energy released as?
primary source = ocean heat
released as = rain
what four forces control the circulation of hurricane surface winds?
1) pressure gradient
2) coriolis effect
3) centrifugal force
4) friction
what does a balance of wind forces cause in a hurricane?
surface winds to spiral inward counter-clockwise
what are the 5 ingredients for a hurricane?
water temperature above 27
warm, humid, air
in north hemisphere surface winds have to rotate counter clockwise
significant Coriolis effect
weak high-altitude winds
what wind speed does a force 1 hurricane start at
119 km/h
describe tropical disturbance
poorly organized cluster of thunderstorms
weak surface winds (<37 km/h)
what is a tropical depression
clearly defined low pressure central area
how are tropical depressions organized?
vertically: strong winds lift warm and moist air upwards in the central area
laterally: counter-clockwise surface winds
what is the difference between a tropical storm
classical hurricane but no eye
(64-118 km/h) counter-clockwise winds
where is the most intense rainfall in a hurricane?
in the Rainbands
where do the strongest winds go in a hurricane?
they go up the eye wall
why do hurricanes decline rapidly after they make landfall?
loss of warm water
winds weakens due to increased friction
where are the strongest winds?
in the same direction of the storm direction
what is the most active month for hurricanes and why
September
- warmest air T in July -August
- warmest seawater T in September due to high heat capacity
what are the two types of hurricanes
cape verde-type:
- thunderstorms form in sahel
- intensity increase above atlantic
- path curves right approaching north america
ITCZ hurricanes
- convergence zone near equator, - storms frequent above Caribbean sea
what type of hurricane was Joaquin?
ITCZ hurricane
what pitch of roof does the most damage
pitch < 30 (terrible roof, creates most suction)
when do hurricanes regain strength
hurricanes experiencing post-tropical transition might merge with existing depression.
