GEOL EXAM 2 TSUNAMIS

Many factors play into total tsunami risk

-Size and depth of fault rupture -Depth of water at fault rupture -Determines energy of tsunami wave and speed -Proximity of epicenter to population centers -Population density near shore -Local near-shore elevation -Local near-shore vegetation -Warning time -Education about tsunami

submarine landslides

-Subsea level collapse of the flank of an oceanic volcano such as in Hawaii or the Canary Islands. - caused by displaced water at the bottom of the sea

how do earthquakes cause tsunamis?

-The rupture of the earthquake causes the seafloor to uplift water. -seafloor can move - seafloor sits on a block of earth crust that shifts up or down during a quake -triggers a landslide

step 3 of 4 stage tsunami process

-as tsunami reaches land, water depth and velocity decrease - decrease in velocity decreases the spacing between wave crests, so the wavelength -height of wave increases bc it is squeezed upwards

Submarine Volcanic eruptions

Most lava eruptions occur under ocean (where tectonic plates move apart) explode and causes waves to go up and down less than 5% of tsunamis

Tsunami Steps

Step 1: As subducting plate descends, zone of friction creates a locked fault zone between overriding plate and subducting oceanic plate Step 2: Stress of continuous subducting motion causes strain-- spatial distortion of overriding plate as strain accumulates over time at locked fault zone -Bending Step 3: Fault rupture as strain exceeds the force of friction holding the edges of the plates together. Step 4: Wall of water pushed up from the sea floor

Tsunami speed

-behave like "shallow water waves" in the deep ocean, and thus their speed is based on the depth of the water -don't lose much energy bc the rate at which a wave loses its energy is related to its wavelength -long-wavelength waves don't lose energy

certain coasts at risk

-heightened risk comes from the geographic location of a coast in relation to potential tsunami sources such as quakes, volcanoes, and landslides - Coasts near a major subduction zone are at the greatest risk.

step 1 of the 4 stage process of tsunami

1. if an earthquake ruptures the seafloor, the water surface above the uplift initially forms an elongated dome parallel to the geologic fault. - collapses and generates a tsunami wave - aftershocks along fault create more waves - waves radiate outward like a pebble

Tsunami waves come in a series

2nd or third may be larger than the first one

where are global subduction zones

Entire pacific ocean and ring of fire

Tsunamis impacts

Flooding and coastal erosion due to earthquake-generated tsunami waves

step 2 of 4 stage tsunami process

- in the deep ocean, tsunami waves move very fast and are spaced long distances apart -reach speeds of 900 km/hr -spacing is ab 100 km -height is less than 3 ft so sailors dont notice them

4th step of 4 stage tsunami process

- wave hits land and is super high destroying everything -runup wave

Tohoku Earthquake and Tsunami

-Mar 11, 2011 -Magnitude 9.0 earthquake in subduction zone off the coast of Japan. -pacific ocean bottom was vertically displaced by 9m bc of quake -generated a large tsunami about 40 m high at shh=ore -Approx 15,000 fatalities. -Massive destruction along Japanese coast. -Ongoing problems from meltdown at Fukishima Nuclear Plant.

land-use planning

a set of policies and activities related to potential uses of land that is put in place before an area is developed principle of uniformitarianism

landslide

a slide of a large mass of dirt and rock down a mountain or cliff

Migitation tsunamis

advanced early warning system, elaborate tsunami seawall defense, informed population,

tsunami energy

affects the entire water column down to sea bed

what states have a high hazard of tsunami

alaska and hawaii

buoys

an anchored float serving as a navigation mark, to show reefs or other hazards, or for mooring.

wave shoaling

as the water gets more shallow, the shape of the wave changes, gets taller -compressed wavelengths - waves behind are speeding in

low hazard of tsunami

atlantic or gulf coasts

structural control

building codes for susceptible coastline areas - high rise hotels engineered to reduce effects of a tsunami

tsunamis create

change coastline through erosion and deposition of sediment

How fast does a tsunami travel?

depends on water depth V = (Dg)½ Where V: velocity D: water depth, g: acceleration due to gravity

tsunameter

detect small changes in the pressure exerted by the increased volume of water as a tsunami passes overhead

greatest runup

directly offshore from the quake

Tsunamis are caused by

displacement of sea water by volcanoes, earthquakes or coastal landslides, maybe even asteroids

tsunami runup map

shows the level to which the water traveled inland

How do landslides cause a tsunami

submarine landslides and large rock avalanches that fall from mountains into the sea

Runup

the furthest horizontal and vertical distance a wave moves inland

Principle of Uniformitarianism

the present is the key to the past

Velocity

the speed of an object in a particular direction

elastic rebound theory

theory that rocks that are strained past a certain point will fracture and spring back to their original shape

edge waves

travel back and forth parallel to the shore

in deep ocean

travel faster, velocity is greastest here Velocity tsunami= square root {(4000 m) x (10 m/s^2)} Velocity tsunami= 200 m/s = 720 km/hr = ~450 mi/hr

distant tsunami

travels out to sea and can travel long distances with little loss of energy

Teletsunami

tsunami that travels across an entire ocean basin

high runup elevation

tsunami waves traveled inland to high(ish) elevations

low runup elevation

tsunami waves traveled inland, but did not reach as high

wave height

vertical distance between crest and trough

rare cause for tsunami

volcanic eruptions

high hazard of tsunami

washington, oregon, cali

which best represents the amplitude of a tsunami wave?

wave height

effect a tsunami will have

wave height, run-up height, and indundation

Ghost Forest

earthquake= tsunami which caused forests to be submerged under water

most common tsunami cause

earthquakes of M 7.5 which creates seafloor displacement

what waves can tsunamis generate

edge waves

Tsunami Warning System

entail a network of sensors to detect earthquake activity and communications network to relay the warning - a network of seismographs to accurately locate and determine the depth and magnitude of submarine and coastal earthquakes, -automated tidal gauges to measure unusual rises and falls of sea level, -and a network of sensors connected to floating buoys

vegetation influences runup

estuary -Absorbs wave energy Tsunamis has to wrestle and expend energy trying to move Plants so it loses energy as it moves further and doesn't cause as much damage -Freshwater fighting tsnuami current as it comes forth

shorter wavelength

higher frequency/ amplitude = killer wave

preparation for tsunami

improved perception of the hazard, development of ways to alert the public, preparation and implementation of a tsunami-readiness plan, promotion of community awareness education concerning the hazard

subduction zone

in tectonic plates, the site at which an oceanic plate is sliding under a continental plate. ruptures create M 9 quake and extend 1000 km along subduction zone and produce uplift of seafloor

Effects of Tsunami

*Primary:* -Flooding -Erosion (landscape and human structures) >> Debris *Secondary:* -Fires (ruptured gas lines) -Contaminated water supplies -Disease -Radioactivity

Locked fault

A fault that is not slipping because frictional resistance on the fault is greater than the shear stress across the fault (it is stuck). Such faults may store strain for extended periods that is eventually released in an earthquake when frictional resistance is overcome.

Fjord

A long narrow inlet from the sea between steep cliffs or hills now recognized as a way to trigger tsunami

tsunami wave train

A tsunami is a series of waves, not just one, they are separated by a variable time period.

seismic waves in tsunamis

A tsunami is series of waves caused by a disturbance on the seafloor that displaces the overlying ocean. The disturbance must be a physical displacement of water, whether by movement along a fault, a landslide, or a volcanic explosion. This means that tsunami are caused by movement through the water column, not by seismic waves moving through water

Which site experienced the lowest wave heights during the 1946 tsunami?

D near waikiki beach 2 or 9 ft

Puerto Rico Trench

Deepest point in Atlantic Ocean

local tsunami

Heads in the opposite direction toward the nearby land and arrives quickly following an earthquake little warning time

wave crest

Highest point of a wave

Wavelength

Horizontal distance between the crests or between the troughs of two adjacent waves

Where are tsunamis most common?

Pacific Ocean or subduction zone earthquakes

Run-up height

Run-up height is the tsunami vertical height above sea level at its furthest point inland. Run-up factor is the deep-water wave amplitude divided by the run-up height. so how far out it goes

megathrust fault

The plate boundary separating a subducting slab of oceanic lithosphere and the overlying plate.

Displacement of ocean water

The upward or downward movement of the seafloor displaces the entire mass of water from the sea bottom to the ocean surface

Period of a wave

Time for one complete waveform to travel

measuring runup

UP: Runup= vertical (elevation) extent of tsunami waters above sea level ACROSS: Inundation= the horizontal (inland) extent of tsunami waters Tidal average water level at shoreline

water column

Vertical Zones of the ocean with changing conditions as depth increases.

water waves transmit energy

Wavelength: 100-300 km in the open ocean Loss of wave energy is inversely proportional to wavelength Short wavelength: pppffflt Long wavelength: Can travel over entire ocean with almost no loss in energy

less common cause of tsunami

landslides

shallow water

less energy waves and less devastating

at sea waves have

long wavelength, low amplitude

tsunami geologic history

look for marine sands and sediments

Tsunami effects exacerbated by subsidence

lpate motion can change elevation on land 1. Uplift raises elevation -Subsidence lowers elevation 2. Earthquake caused forest to drop below sea level -In a salt marsh -Saltwater rushed in, drowning and poisoning trees 3. New, lower elevation terrain became a tidal marsh

Natural Service Function of tsunamis

many chemical from land to ecosystems large volumes of sediment that develop landscape over time

Indundation

max distance inland reached by the tsunami measured from tide or shoreline

deep depth

means they can carry more energy, move faster, longer wavelength

very rare cause for tsunami

meteorite

human interaction with tsunamis

not tied to tsunamis people who live near coasts will be affected

nuclear disaster japan

nuclear reactor meltdown

Tsunami

produced by the sudden vertical displacement of ocean water fault rupture along subduction zones at tectonic boundaries

steep slope

provides protection from tall waves

runup man summarizes

run up elevations from one tsunami

Monte Carlo Simulation

selects a random sample of earthquakes of various magnitudes and determines the tsunamis that would be propagated from these quakes