Week 3 Flashcards
what are tsunamis?
japanese for “harbour wave”
they are produced by sudden displacement of water
what can cause tsunamis?
earthquakes that cause uplift of the seafloor
landslides
volcano flank collapse
underwater volcanic eruptions
meteorites
what caused some historic tsunamis?
lisbon earthquake
krakatoa volcanic eruption
sumatra earthquake
tohaku
how can earthquake cause tsunamis?
by displacement of the seafloor
by triggering a landslide that enters water
describe the development of an earthquake-triggered tsunami
STAGE 1
— displacement/rupture of the seafloor sets waves in motion that transmit energy and water upwards and outwards
— when the waves reach the surface of the water, they spread outwards
STAGE 2
— the waves move rapidly across the open ocean (can reach over 500km/h)
— the spacing of the wave crests is very large (can be more than 100km)
— the height of the waves is often small (less than 1m)
—passengers on ships in the ocean rarely even notice tsunamis passing beneath them
STAGE 3
— as the tsunami approaches land, the water depth decreases
— this results in the water “piling up” and causes a decrease in wave speed and the spacing between waves - as well as an increase in wave amplitude
STAGE 4
— as the tsunami impacts land, waves can reach heights of dozens of metres along the coast
— the wave speed at this time can be up to 50km/h, making them impossible to outrun
— during some tsunamis the water first recedes from the shore and exposes the seafloor (when there’s a fault - or indent in the plates)
— pulses are the waves!
what happens to the waves as a tsunami approaches land?
as the tsunami approaches land, the water depth decreases, this results in the water “piling up”
causing a
— decrease in wave speed and
— decrease in the spacing between waves
— increase in wave amplitude
what is a tsunami event?
consists of a series of large waves reaching shore that can last for several hours
in terms of a tsunami, what is a run-up?
maximum VERTICAL distance that the largest wave of a tsunami reaches as it travels inland
what are the types of tsunamis?
distant, regional, local
distant aka tele-tsunamis
— a tsunami that travels thousands of kilometres across the open ocean
– on remote shorelines across the ocean, reduced energy lessens its impact
regional tsunami
— a tsunami that affects shorelines 100km to 1000km from its source
local tsunami
— a tsunami that affects shorelines within 100km of its source, most dangerous type!
what’s the most dangerous type of tsunami? most harmless?
most dangerous: local tsunamis
most harmless: distant tsunami aka tele-tsunami
what regions are risk for tsunamis? least likely?
coasts located near subduction zones or across oceans from subduction zones are most at risk
areas at greatest risk are the Pacific Ocean (49%), followed by the Mediterranean Sea (25%)
and then the Atlantic Ocean (12%) and Indian Ocean (4%)
what are the types of effects a tsunami has?
primary, secondary
primary
— flooding and erosion destroy beaches, coastal vegetation, and infrastructure
— after the tsunami retreats to the ocean, scattered debris is left behind
— most tsunami deaths are from drowning. injuries result from physical impacts from debris
secondary
— effects that generally occur after the event is over
— fires may develop due to ruptured gas lines or from ignition of flammable chemicals
— water supplies may become contaminated and water-borne diseases (cholera) may spread
describe the Indian Ocean tsunami of 2004. and what caused it? what countries were affected the most?
caused by a M9.1 off the west coast of Sumatra (3rd strongest earthquake in world history)
the earthquake occurred in a subduction zone between the Burma and Indian-Australian plates
the plates has been locked for over 150 years, thus allowing strain to build
— the rupture caused some land areas along the coastline to subside below sea level
the tsunami reached nearby Indonesian islands within minutes of the earthquake
many coastal communities in Indonesia and surrounding countries were heavily damaged during the event
countries bordering the Indian Ocean did not have a tsunami warning system like those bordering the Pacific Ocean
—– people were caught by surprise and over 230,000 died
many were unfamiliar with tsunamis, and were intrigued by the approaching waves
—– most people in the area were ignorant of an early warning sign (the receding sea)
what were the lessons learned from the Indian Ocean tsunami in 2004? what do we need to handle a tsunami?
effective tsunami warning systems are needed around all oceans where tsunamis can occur
in 2006, a new warning system started operating in the Indian Ocean
but, a warning system by itself is not enough
—- emergency officials must have an organized plan for evacuating residents during a warning
—- earthquake and tsunami education is necessary for people who live along or visit coastlines
how does the Pacific Ocean warning system detect tsunamis?
via a network of seismographs to estimate earthquake magnitudes
sensors called tsunameters, electronically connected to buoys verify that a tsunami was produced
they rest on the seafloor and measure changes in water pressure passing over them
what are tsunameters and how do they work?
used to detect tsunamis
sensors called tsunameters, electronically connected to buoys verify that a tsunami was produced
they rest on the seafloor and measure changes in water pressure passing over them
how are tsunamis controlled via structures?
damage can be minimized thru regulations on buildings and structures
some cities in Hawaii require floor proofing measures such as basement window sealing and bolting homes to their foundations
concrete levees (onshore) are other preventative measures but can be very expensive
offshore barriers are only feasible outside cities with very large populations
what are inundation maps
maps showing the geographic area that can be potentially impacted by tsunamis are created to help plan for future events
historical records, geologic data, and aerial photography aid in making the maps
many North American cities on the Pacific Coast such maps and development restrictions may exist there in areas at high risk of tsunamis
how does land use practice affect tsunami damage?
vegetation plays a role in determining tsunami
mangroves (open tree vegetation)
in areas impacted by smaller waves, trees and dense vegetation protect areas father inland
describe the Japan tsunami of 2011. and what caused it?
the catastrophic event occurred on March 11th
caused by M 9.0 earthquake 70km (local) off the east coast of Japan
a tsunami warning was issued nearly an hour before its arrival
over 15,000 people died and damage to Japan’s infrastructure was extensive
what are the different categories of adjustment? examples?
modify the loss burden
— loss sharing
— spread the burden well beyond immediate victims
e.g. insurance, relief aid
modify designs
— loss reduction
— requires a knowledge base of the hazard
e.g. retrofitting building
modify human vulnerability
— adjust the population to possible events
e.g. preparedness programs, land use planning, warning systems
what are the factors affecting adjustment choices for governments following hazards?
hazards are not typically a priority of governments (compared to unemployment, inflation, healthcare, crime, poverty, etc.)
radical vulnerability adjustments are unrealistic (e.g. moving entire communities)
— a cost benefit assessments is typically required
what are the 2 scenarios governments take when dealing with loss?
accepting loss
— this is the ‘free’ choice. it is a no-action response
— people choose to live how they want regardless of the hazard risk, but aid may not be provided after a disaster
e.g. floodplain housing can be attractive because it may be inexpensive
sharing loss
— this is the government-action response
— there may be laws in place preventing people from living in certain areas
— if governments do not intervene after a disaster, there are often political ramifications
— aid can come from external sources (UNICEF), internal sources (government), inter-community sources (local), and insurance
what are the problems with the sharing loss approach to hazards?
a disaster of sudden onset is likely to draw more money than another similarly serious disaster
donor fatigue can set in if there are many disasters
recovery can take a very long time in some countries
aid and enthusiasm to donate eventually wanes
what are the periods of the model of disaster recovery?
emergency
— ceased or damage
restoration
— return and function
reconstruction 1
— return at pre-disaster levels or greater
reconstruction 2
— improved and developed
what is “adjustment choices”?
actions that reduce the risk of extreme events in the environment.
these adjustments can be intentional or unintentional
what are factors affecting individual adjustment choices?
experience, material wealth, personality
experience
— more experience with a hazard result in more likelihood of adjustment
material wealth
— more resource results in more information and more options
personality
— some people are more likely to take risks
what is the prospect theory?
generally, people are more willing to protect against a loss than they are willing to gamble on an equivalent gain
what are the human responses to hazards? give examples
cultural adjustment, purposeful adjustment, incidental adjustment, absorptive capacity
cultural adjustment
— this type of adjustment may result from changes in an environment
e.g. the discovery of oil forced the communities to adjust as the resource was developed
purposeful adjustment
— this is an adjustment that is specifically designed to reduce loss or damage
e.g. designing buildings to withstand earthquakes in high-risk areas
incidental adjustment
— these are not primarily hazard-related, but they have the effect of reducing potential loss
e.g. advances in technology have improved warning systems
absorptive capacity
— this is a measure of the ability of people to sustain impacts from a hazard
— it results from combinations of cultural, purposeful, and incidental adjustments
e.g. in parts of Kenya maize, beans, peas, sorghum and ground nuts are planted all together
—- this encourages deep roots among the plants which results in a more drought resistant crop yield
what is Gambler’s fallacy?
the belief that the occurrence of a chance event influences the probability of future occurrences
