EOS 170 II Flashcards
meaning of ‘tsunami’
tau = harbor nami = wave
tsunami ≠ tidal wave
nothing to do with Earth’s tides
tsunami stages
generation
propagation
inundation
Generation, causes of tsunami
anything that displaces ocean water
- volcanoes
- landslides
- meteorite impact
- earthquake
tsunami generation, volcano
caldera collapse
pyroclastic flow
underwater eruption
examples of volcano-caused tsunami
- Krakatau, 1883, caldera collapse
- Tonga, 2009, underwater eruption
example of landslide-caused tsunami
Lituya Bay, Alaska, 1958
wave up to 524m
example of impact-caused tsunami
Chicxulub, Mexico, 65Ma
earthquake-caused tsunamis
especially megathrust earthquakes at subduction zones
example of earthquake-caused tsunami, Indian ocean
‘boxing day’ tsunami, Dec 26, 2004
- M9.2 megathrust eq
- 3 largest ever recorded
- 1300km rupture, 8 minutes to rupture
- 230,000 deaths including ppl 6000km away in Africa
Tohoku tsunami
March 2011, Japan arc, triple junction, M9.0, thrust faulting, 18,500 deaths, 90% from drowning, ~360billion USD, ongoing costs associated w/ Fukushima
water waves
pulses of energy that move through a water mass causing water molecules to rotate in place
water wave particle motion
- prograde (unlike Rayleigh waves - retrograde)
- motion decreases with depth
- motion stops at 1/2L
water waves less than 1/2L
- orbits flatten into eclipses
- wave slows down
- wavelength decreases
- water, energy concentrated
- wave height increases
- shoaling
wind wave size, frequency, velocity determined by
- wind velocity
- wind duration
- wind consistency
- area of water body
wind wave vs tsunami; period, WL, velocity
period: W (5-20s); T (3600s, 1h)
WL: W(40-600m); T(100s of km)
V: W(8-30m/s); T(200m/s)
real danger of tsunamis
-momentum: tremendous mass of water floods inland for several minutes
depth of tsunami wave that can kill
knee-high
long L and p of tsunami allows
wave to bend around land and hit multiple shores: wrapping/refracting
velocity of tsunami wave in deep water
V = sqr. (gD) g = 9.8m/s2 D = water depth
average tsunami velocity in PO
D = 5500m V = 230m/s average = 83/km/hr
run up
how far the waves go up the beach
shoaling
wave rising up
run up height/ distance
depends on nearshore bathymetry, shape of coastline
tsunami peaks
- up to 10
- separated by 10-60min
- largest often not the first
when the first part of the tsunami wave to arrive is a trough
draw down
Tohoku tsunami run up
- eq much larger than anticipated
- tsunami run up much higher (40m)
- went over tsunami wall
1700AD orphan tsunami
- Jan 1700, 2m high
- Felt in Japan
- didn’t feel shaking from ‘parent eq’
ghost forest
trees killed as lowered into tidal zone (salt) by subsidence
tsunami recurrence in cascadia
400-600years
chance of subduction zone eq in cascadia
15% on 50 yr timescale
what would a cascade mega thrust tsunami look like
- wave heights up to 15m, particularly in inlets (Port Alberni)
- first reach Tofino
- smaller in Vic (1-5m)
Lituya Bay
- 1958 tsunami
- M7.8 eq on Fairweather fault
- huge rockfall at head of bay (30 mill. m3)
- 500m high wave
- 5 deaths
- trees stripped
Greenland tsunami
- Karrat fjord, June 2017
- 11 houses gone, 4 deaths
- M4.2 eq ?
- landslide into water
- large local tsunami
landslide tsunamis
devastating locally, no global effect
greenland tsunami earthquake
- seismograms record waves equivalent to a M4 eq but wave structure diff. than normal eq. seismo (no p, s waves)
- probably from the landslide
Grand Banks tsunami
- Nov 1929, M7.2eq
- triggered continental slope landslide – 200km3
- turbidity current severed transatlantic -telegraph cables
- generated tsunami waves
- 28 deaths
- deadliest recent eq in Canada (Nfdld)
- tsunami 2.5hr after eq
- 4-7m waves, 15-30m run up
expect a Grand Banks type tsunami here?
- evidence of turbidity currents offshore cascadia
- fraser river delta is steepening
- 2m tsunami on Texada island 1946
standing wave, enclosed water, swaying back and forth
seiche
seiche cause
- strong winds
- earthquake
example of wind seiche
trade winds blowing over lake Erie
- winds pile water up
- if winds slow, water sloshes back
Hebhen seiche
1959, Hebgen lake, SW Montana
- M7.5eq - subsidence
- dam foreman saw wall of water, then it disappeared
- 17 min periods for 12hours
- largest waves ca. 20ft
- summer, families camping, 28 deaths
- landslide also blocked river
PTWC
Pacific Tsunami Warning Centre
-1949, circum-pacific nation coordinated effort
what PTWC does
assess:
- epicentre
- depth
- magnitude
- travel time for tsunami waves
- initiate tsunami watch
- upgrade to tsunami warning
PTWC, depth
- was eq shallow enough to generate tsunami
- less than 100km
DART
deep-ocean assessment and reporting of tsunamis
- ocean bottom pressure sensors
- feel tsunami waves pass
- send message through acoustic telemetry, satellites
tsunami mitigation
- early detection
- structural countermeasures
- tsunami hazard maps
tsunami structural countermeasures
- tsunami walls
- breakswaters
- underwater berm
- angled walls/ditches
- evacuation, raised earth park
tsunami hazard maps
- use shape of coastline, bathymetry
- predict wave heights at diff. points along coast
mass movement
- movement of large volume of material downslope
- influenced by gravity
types of mass movement classified according to
- material being moved
2. how it moves
mass movement hazards in canada
- no top ten events since 1970s
- most of worst disasters in eastern Canada, especially Quebec
mass movement fatalities
2004-2010: 32,000 deaths from 2600 landslides
mass movement triggers
- earthquake
- heavy rainfall
- freeze-thaw weathering
- human construction
underlying conditions of slope instability
- adding mass on slope
- removing support
- reducing internal strength of rock
water and mass movements
- externally (rivers, waves)- undercut steep slopes
- mobilize sediment
- clays add to sliding
- porosity, weight
- dissolution
- pore water pressure
- freeze/thaw
clay, mass movement
- platy, sheety minerals
- expand when wet, absorb water
- lubricate layers
clay formation
by-product of ice grinding on bedrock, common in formerly -glaciated regions
sedimentary rock porosity
typically 10-30%
water and porosity
replacing air w/ water increases weight
soil porosity
50%
dissolution
groundwater dissolves cements decreasing rock strength
pore water pressure
- added sediment on top increases weight and P
- increased P packs grains tighter but water is incompressible and stores built-up pressure, weakens rock
freeze-thaw weathering
- water enters crack
- freezes, expands, cracks rock
geology and mass movement
- pre-existing geological conditions
- orientation
pre-existing geological conditions
- poor cementation = crumbly
- bedding planes = weaknesses
geology orientation
- weaknesses angled into slope = stronger
- weaknesses parallel to stope = stronger
- weakness parallel = whole slab break free
tectonics and mass movement
eq’s provide ground acceleration
Mass movement classification
- direction of movement
- speed
- water content
Falls
- individual blocks detach along fractures
- free-fall
Flows
also avalanche
- material deformed as it moves (includes creep)
- move as viscous fluid
- turbulent movement over landscape
MM classification by direction of movement
down: falls, subsidence
down and out: slides, flows/avalanche
slow MM
- earthflow
- soil creep
- rarely kill
- infrastructure damage
catastrophic MM
- debris flow
- snow avalanche
- rock falls
- deadly
intermediate MM
- translational slide
- rotational slide
- sometimes catastrophic
- sometimes slow
rate of movement vs water content, MM
high speed: rockfall, loess flow, snow avalanche, debris flow
low speed, low water: creep
high water, low speed: earth flow, slow subsidence
material collapses into a void
subsidence
slide
well defined failure surface and limited deformation of moving material
- semisolid mass
- some coherence within mass
mechanics of soil creep
- slowest
- most common slope failure
- freeze/thaw, wet/dry, heat/cool cycles of clay minerals
- expands perpendicular to slope
- contracts vertically due to gravity
earth flow
- downslope viscous flow of fine grain saturated material
- btw soil creep and catas. debris flow
earth flow example
Slumgullion, Colorado
- slow enough that trees grow and a road crosses it
- few cm/week
debris flow
- water-laden mass of soil, rock frag.s
- rush down, funnel into streams
- entrain objects in path
- thick muddy deposits
rockfall
- free fall of rock block from free face
- when elevated masses separate along fracture
rock avalanche
- rock fall turned into rock avalanche
- if hit steep scree slope
rock avalanche common
flanks of volcanoes
scree
a mass of small loose stones that form or cover a slope on a mountain
rock slide
- movement of rock above failure surface
- characteristic geomorphology
rock slide type
- rotational (concave failure surface)
- translational (planar failure surface)
- debris slide (rock fragments into debris)
rockslide geomorphology
- crown
- head scarp
- head
- minor scarp
- foot
- cracks, ridges
- toe
rotational landslide movement
-rotational about axis parallel to slope
rotational landslide materials
- driving mass -> head of slide
- resisting mass -> toe of slide
how far rotational slide travel
- short distance typically
- motion decreases driving mass, increases resisting mass
composite landslide
-start as one type and evolve into another
composite landslide example
NZ, 2017
- triggered by cyclone Debbie
- starts as rotational rock slide
- morphs into fluid debris slide
Oso landslide
2014
- 150-200% normal rainfall
- steep ridge
- river erodes soil along bank
- unstable layers of sand, silt, clay
- destabalized cliff from earlier slide, 2006
- rotational landslide –> debris slide
- 43 deaths
how the 2006 slide affected the 2014 slide, Oso
- ‘doorstop shelf’ buttress upper slope
- slide undercuts shelf, removed material supporting upper slope
wasn’t likely a factor in Oso slide
logging
-lidar reveals scars and deposits of landslides far older than logging activity
long runout landslide
Sturzstrom
‘fall’ ‘stream’
-soil, rock w/ horizontal movement»_space; vertical
Sturzstrom example
- Collbran mudflow, colorado
- blackhawk slide, California
- Mt Meager
Mt Meager sturzstrom
August 2010
- 50 mi m3 rockfall high up
- turned into giant debris flow travelling down creeks into Lillooet river
- no deaths
- seismometer signal equiv. to M3 eq
- 13km horizontal., 2km vertically
- 10º angle
Landslide mitigation
- scaling
- benching
- unloading the head
- reinforcing the body (meshing, bolts)
- supporting the toe (add material, breakwater)
- drainage channels
scaling
remove loose rock
what are the main differences between debris flow and rock slide
- debris = rock, mud, tree
- flow = fluid behaviour
Volcano classification
- active
- dormant
- inactive
deaths in the past 50 years from volcanoes, landslides
volcano- 30,000
eq- around 1 million
landslide- around 150,000
Volcano fatalities
- volcano-triggered lahars
- densely-populated areas
densely populated volcano cities
Napoli, Mt Vesuvius, Italy
- 3 million
- 1631 eruption killed 3360
molten rock on earths surface
lava
forms of lava
ash
bombs
flows
lahars
molten rock within Earth
magma
most abundant volatile in magma
H2O
gas solubility increases w/
pressure
decreased T
solidified lava above surface
- volcanic or extrusive rocks
- rhyolite pumice (continental)
- basalt (oceanic)
solidified magma
- plutonic, intrusive rocks
- granite (continental)
- gabbro (oceanic)
- larger crystals due to slow cooling
Magma/lava viscosity depends on
- T
- crystal content
- silica content
Temperature and lava
higher T = lower V
mineral crystal content and lava
higher crystal = higher V
Si content
SiO2 increase V
SiO2 and crust
continental: 60% SiO2
oceanic: 48% SiO2
i. e. continental»_space; viscous
explosiveness depends on
magma visocsity - controls amount and ease of volatile release
low viscosity magma
= easy gas escape
= peaceful eruption
3 magma types
- basalt
- andesite
- rhyolite
last crystallizing minerals
Rhyolite
- lowest melting point
- less SiO2
- increased viscosity
- higher gas content
- more explosive
Andesite
intermediate magma
- mixed basaltic magma and continental crust
- intermediate viscosity, gas content, explosivity
Basalt
first crystallized minerals
- highest melt point
- melted mantle material
- lowest SiO2, viscosity, gas content, explositivity
80% of erupted magma
spreading centres
MOR volcanism
- low SiO2
- decompression melting
- high T, low Visc, low volatile
formation of andesite/rhyolite
- plate subduction of hydrated minerals
- P releases water - promotes melting
- magma rises through 40+km of crust
- magma melts surrounding continental rocks – mixing
10% of all magma erupted
- volcanic arcs above subduction zones (10%)
- hot spots (10%)
eruptive styles of plate tectonic settings
- transform fault: little-no
- spreading centre: peaceful
- subduction zone: explosive
how a volcano erupts
- deep heat rises
- decreased P, decompression melting
- heat transfer melting of surrounding rock
- formation of gas bubbles propels magma up
- bubble volum overwhelms magma, explosion
- plume in air
magma at depth, gas
high P keeps volatiles dissolved in solution
-gases only form as P decreases
types of volcanic eruptions
Non explosive: 1. Icelandic, 2. Hawaiian
Explosive: 3. Strombolian, 4. Vulcanian, 5. Plinian
Volcanic gases (elements)
H, O, C, S, Cl, N
Volcanic gas composition
H20 = 90%
CO2, CO, N2, H2, H2S, SO2, HCl, CH4
SO2, H2S = rotten egg smell
Magma minerals
Si, Mg, Fe
+ leeched minerals: Al, Ca, K, Na
volcanic soils
- from weathering
- excellent fertilizers, amongst the most fertile (especially the K)
basalt eruption underwater
pillow basalt
- glassy from rapid quenching by cold water
- 10cm - several m’s
lava flows
- sub-aerial eruptions
- pahoeohoe
- ‘A’a
pahoehoe
- very low viscosity lava
- smooth, ropy surface
chunks of magma and volcanic rocks
pyroclastic debris
-fine ash, coarse ash, cinders, blocks and bombs (m+)
volcanic material that is solid while airborne
blocks
pyroclastic debris is ejected as
air fall
pyroclastic fall
pyroclastic fall
material too dense to be carried up in plume
-chaotic w/ little-no sorting
‘A’a
‘stony rough lava’
- viscous lava
- rough, jagged surface
- broke blocks and vesicles
volcanic material that is liquid while airborne and solidify after landing
bombs
air fall
pyroclastic debris carried up in volcanic plume
-sorted into size layers
very quickly cooling magma
- glass
- obsidian
- no crystallization
frothy glass
pumice
- 90% air
- can float on water
- mostly rhyolitic or andesitic
volcano type and viscosity
Icelandic: low Hawaiian: low Stombolian: low -med Vulcanian: med-high Plinian: high
volcano type and volatility
Icelandic: low Hawaiian: low Stombolian: med Vulcanian: med-high Plinian: high
volcano type and composition
Icelandic: basalt Hawaiian: basalt Stombolian: basalt- andesite Vulcanian: any type Plinian: andesite- rhyolite
Volcanic landform =
Viscosity + Volatiles + Volume
Shield volcano
Viscosity: low
Volatility: low
Volume: large
Flood basalt
Viscosity: low
Volatility: low
Volume: very large
Viscosity: high
Volatility: high
Volume: very large
Caldera
Viscosity: low- med
Volatility: med-high
Volume: small
Scoria cones
lave dome
Viscosity: high
Volatility: low
Volume: small
Viscosity: med-high
Volatility: med - high
Volume: large
stratovolcano
Hawaiian-type eruption
low viscosity and volatiles, high volume
- basalt lava spills out of fissures as lava fountain, flows down slope as hot lava river
- days - years
long developed Hawaiian type eruption
shield volcano
-width»_space; height
Mauna Loa
shield volcano
- 9km above abyssal plain
- 4km above sea-level
- 2ookm wide
- largest sub-aerial volcano on E
Icelandic-type eruption
- low viscosity and volatility
- most peaceful
- basaltic lava out linear vents/fissures
- create wide volcanic plateaus
the 3 explosive volcano types named after
volcanoes in Italy -Stombolian: Stromboli -Vulcanian: Vulcano -Plinian: Vesuvius subduction of Ionian sea forms Calabrian Arc volcano chain
Strombolian-type volcano
- intermediate viscosity and volatile, small volume
- basalt-andesitic
- mildly explosive
- not very powerful
Stromboli
‘lighthouse of the Mediterranean’
- has erupted almost daily for millennia
- bursts of lava few times/hr
- bombs reach tens-hundreds of m’s
wide volcanic plateau formed by icelandic-type eruption
flood basalt
strombolian-type eruptions associated w/
scoria cones/ cinder cones
-modest conical hills of tephra
cinder cones in BC
Tseax cone, Stikine volcanic belt
Kostal cone, Wells Gray
Tseax cone
- erupted 1700 AD
- Canadas worst natural disaster
- may have been triggered by megathrust
- 2000 First Nations died
deaths from Tseax cone
- asphyxiation from CO2
- CO2 denser than air, displaced O2
vulcanian-type eruptions form what type of volcanoes
stratovolcanoes
- tall, steep-sided, symmetrical peaks
- alternating ash/rock
- viscous magma
- some contain craters on top
stratovolcano examples
- Mt Baker
- Mt Rainier
- Mt Fuji
number vulcanian eruptions
3-5/yr
Plinian-type eruption
- high magma and volatility, very large volume
- most violent
- powerful eruption column of gas, ash, rock > 10km
- andesitic or rhyolitic
- few /yr
Plinian-type volcano eruptions form
- startovocanoes
- calderas
caldera
collapsed cone formed form emptying of magma chamber
eruptive sequence
early phase: Vulcanian-type (clearing the throat)
final phase: Plinian-type (throat is clear)
Ultra-Plinian
- very largest eruptions
- columns >25km high and volumes >10km3
VEI
volcanic explosively index
- 0-8
- calculated based on material erupted, height of column, duration of major eruptive blast
pyroclastic flow
-fast-moving gravity current of hot tephra + gas
pyroclastic flow trigger
- collapse of volcanic dome
- spillover from crater
- direct blast from explosive eruption
- collapse of eruption column
‘flow’ of pyroclastic flow
- fluidized from water, gases in eruption
- overrides cushion of air
pyroclastic flow speeds
small: 20m/s
large: 200m/s (700km/hr)
pyroclastic flow temperatures
1000ºC
lahar
mud/debris flow of pyroclastic material mixed w/ rocky debris + water
- travel down valleys
- 1-40 m/s
- travel 100s of kms
formation of lahars
- volcanic debris avalanche mixes w/ snow/ice
- pyroc. flow diluted w/ river water, meltwater as they travel
- natural failure of a crater lake
- rainfall on loose tephra
lahars that occur after eruption
secondary lahars
factors affecting lahar speed, power
- gradient
- viscosity (water)
- containment (narrow channel restricting water increases flow)
Tephra falls
Mount St Helens
Pyroclastic flows
Mount St Helens
Pomeii/Vesuvius
Lahar
Mount St Helens
Nevado del Ruiz
Mount St Helens
May 1980 57 deaths 1 billion in damage Cascade volcanic arc -M5.1 eq triggered landslide
continuation of cascade volcanic arc into BC
Garibaldi Volcanic Belt
-less active
most active cascade volcano
mt st helens
-activity occurs in burst decades to hundreds of yrs
Mount St Helens height
built up from 4 millennia of strombolian and vulcanian lava flows and pyroclastic flows
destabilization of MS Helens
rhyolitic lava dome and andesitic flows 1800s
MSH earthquake swarms
1980
- acceleration magma movement
- rising caused bulge on N side outward up to 120m
most of MSH deaths
loggers who ignored no go zone exec order
MSH bulge explosion
M5.1 eq triggered landslide – released pressure – lateral blast – pyroclastic flows – melted glaciers – lahars
MSH damage
- downed 550km2 of trees
- damaged 27 bridges, 200 homes
- clogged Columbia river, closed port of Portland
- 57 deaths
- highways closed for weeks
- 1000 flights cancelled
- ash over 60000km2
MSH Vulcanian eruption
lateral blast cleared the throat - released pressure - allow more bibles to form - allow 9hr long Plinian eruption
MSH Plinian eruption
- 9hrs
- 20km high cloud
- 540 million ash
- tephra fall-out hazard for weeks, >400km away
MSH doming
-dome growth fed pyroclastic flows
evidence of the 1700AD orphan tsunami
- oregon, washington ghost forests w/ radiocarbon dating and tree ring studies
- tsunami reports in Japan
do some oceans have more tsunamis than others
yes, Atlantic does not have subduction zones
Atlantic earthquakes
no subduction zone eq’s
- Grand Banks, Nwfld, submarine slide
- Karrot Fjord, Greenland, landslide
