Tsunami Flashcards
What is a tsunami?
A series of larger-than-normal waves, which are usually caused by volcanic eruptions or underwater earthquakes.
What causes tsunami?
Most are caused by large underwater earthquakes along subduction zones.
Energy released during the earthquakes causes the sea floor to uplift - displacing the water column above.
This displaced water forms tsunami waves
How big can tsunami be?
Most waves are no higher than 3m, but the largest waves can reach heights of up to 30m.
How fast can tsunami move?
Up to 805km per hour (speed of a jet aircraft).
What happens as the tsunami gets closer to the shore?
When the waves crest reaches the shore, it first produces a vacuum effect - sucking all the water back out to sea and exposing a large amount of sea floor.
The water then returns rapidly in the form of a series of large waves.
What’s an early sign of a tsunami?
The suddenly retreating water and exposed sea floor is a key early warning sign of an approaching tsunami.
What are less frequent causes of tsunami?
Underwater landslides, or meteor or asteroid strikes which suddenly displace large amounts of seawater.
What is a water column?
The area of seawater from the surface to the sea floor.
What are the impacts of a tsunami?
Large tsunami can travel inland for several miles - sweeping away buildings, trees, bridges and people
They also wash away the soil - undermining the foundations of buildings, bridges and roads, uprooting tress and destroying farmland.
Small islands hit by a tsunami are often usually destroyed.
Contamination of food and water supplies with salt, raw sewage, unburied bodies, which can leads to serious illnesses such as cholera.
What causes most tsunami related deaths?
Drowning
However, many are killed or injured by collapsing buildings or being hit by large debris, such as floating vehicles or trees.
How can you predict tsunami?
Most are caused by underwater earthquakes, so there is no way to predict tsunami before they occur.
Although it is possible to give people some early warning before it reaches the coast.
What does early warning systems use?
Seismic sensors to detect undersea earthquakes.
Also use DART as not all undersea earthquakes cause tsunami
What is DART?
Deep-ocean Assessment and Reporting of Tsunami
What does the DART system use?
Uses seabed sensors and surface buoys to monitor changes in sea level and pressure.
What happens when tsunami waves are detected?
The system sends the info via a satellite to tsunami warning stations.
These stations review the transmitted info and use computer modelling to estimate the size and direction of the tsunami, before informing the areas at risk.
Depending on where the tsunami originates, some people might receive a warning hours in advance of any threat - giving them time to move.
