Tsunamis

Question 1

how are tsunamis caused?

Answer 1

• they are caused by earthquakes at destructive plate boundaries which is where an oceanic plate is subducted into the mantle beneath a continental plate
• the movement causes friction which creates excess energy
• when the plates move back to their original position, the movement thrusts the water above which causes a wave to form

Question 2

how do tsunamis differ from normal waves?

Answer 2

• the wave height is very low (less than 1m), but when they reach the shore they increase to 25m
• the wavelength is very long, can be between 100-1000km
• they travel very quickly between 640-960km/hour
• they usually consist of a series of waves
• there is a long time between wave crests, 10-60 minutes

Question 3

where are most tsunamis located?

Answer 3

up to 90% are associated with the ‘Pacific Ring of Fire’

Question 4

what are the steps in the Tsunami Warning System?

Answer 4

1. a sensor on the ocean floor measures water pressure
2. the measurements are sent by acoustic signal to a buoy on the surface
3. the buoy sends the signal further to a satellite
4. the signal is then send to early-warning stations on land

Question 5

what happened in July 2006?

Answer 5

there was a tsunami of the south Java coast generated by a 7.7 magnitude earthquake 112 miles offshore, it devastated the area around Pangandaran resulting in more than 600 deaths

Question 6

what happened in April 2007?

Answer 6

there was a tsunami in the Solomon Islands which were generated by an 8.0 magnitude earthquake, the tsunami swept across the island killing at least 15 people

Question 7

what happened in March 2011?

Answer 7

a tsunami off the pacific coast of the Tohoku region of Japan, the earthquake occurred 70km offshore and at a magnitude of 9.0
the tsunami generated waves of over 40m in height, it also caused nearly 16,000 deaths, with over 6000 injured and 2500 missing
127,000 buildings destroyed, 277,000 ‘half collapsed’ and 750,000 partially damaged
assessed cost of the damage was over $30 billion, with an estimated economic cost of $235 billion

Question 8

what happened in the Boxing Day Tsunami 2004?

Answer 8

it was generated by a 9.0 magnitude earthquake 25km below the Indian Ocean, it killed an estimated 300,000 people, extensive damage to costal communications, bridges, railway lines and damage to local economies

Question 9

what were the primary impacts of the BDT?

Answer 9

• up to 300,000 people died
• vegetation and top soil were removed up to 800m inland
• infrastructure was destroyed, the Andaman and Nicobar islands were all cut off
• coastal settlements were devastated e.g. Banda Aceh in Sumatra

Question 10

what were the secondary impacts of the BDT?

Answer 10

• widespread homelessness, 500,000 people forced into refugee camps
• economies were devastated including fishing, agriculture and tourism sectors, 44% of people living in Indonesia lost their livelihoods
• water supplies and soils were contaminated by salt water
• the gap between rich and poor increased

Question 11

what were the immediate responses of the BDT?

Answer 11

• massive international relief efforts were established that included more than 160 aid organisations and UN agencies
• foreign military troops provided assistance e.g. Australian Air Force improved air traffic control

Question 12

what were the longer term responses of the BDT?

Answer 12

• large scale programmes of reconstruction were implemented
• existing government prejudices were highlighted
• education on tsunami awareness began in schools
• practice drills and evacuation plans were established
• coastal zones were hazard-mapped to identify areas most at risk