A tsunami is a series of sea waves caused by a sudden event beneath or near the ocean. The following events can create a tsunami:
- an underwater earthquake
- a large underwater landslide
- coastal landslides into the sea
- volcanic eruptions beneath or near the sea
- in rare cases, a tsunami can be created by the impact of a meteor
Like a flood, the effects of a tsunami can vary greatly from one region to another but they pose a threat to property and life in all coastal areas.
The three types of tsunami
There are three distinct types of tsunami. The type you encounter depends on the distance you are from the place where it is generated.
- Distant tsunami are generated from a long way away, such as from across the Pacific in Chile. In this case, we will have more than three hours warning time for New Zealand.
- Regional tsunami are generated between one and three hours travel time away from their destination. An eruption from an underwater volcano in the Kermadec Trench, to the north of New Zealand, could generate a regional tsunami.
- Local tsunami are generated very close to New Zealand. This type of tsunami is very dangerous because we may only have a few minutes warning and damage could be quite significant in specific areas. A landslide in the Hikurangi Trench or a large earthquake from an offshore fault could cause a local tsunami
Tsunami warning
Here are the ways you will know that a tsunami is approaching.
- The Ministry of Civil Defence & Emergency Management will issue a national warning on the television and radio
- You will receive a warning from your local council or Civil Defence Emergency Management Group. Talk to them to find out how you will receive your warning
- If you are at the coast and you feel a strong earthquake, see the sea receding (the waterline moving away from the shore), the sea bubbling or making a roaring sound, move to higher ground immediately.
- Be aware that there may be more than one wave, sometimes as many as seven, and it may not be safe for up to 24 hours. The waves that follow the first one may also be bigger
Before a Tsunami
Getting ready before a tsunami strikes will help reduce damage to your home and business and help you survive.
- If you live in a coastal area, check with your council about the level of risk a tsunami would pose to you and your family
- Check with your local Civil Defence Emergency Management Group to find out what warning procedures you should expect
- Develop a Household Emergency Plan and ensure you have a Getaway Kit should you need to leave in a hurry
- If you are buying land, investing or building in a coastal area, talk to your council about the risks of a tsunami, coastal storm surge and erosion
- Know where the nearest high ground is and how you will reach it. Higher ground should be at least 35m above sea level or at least 1km inland. Plan your escape route now with your household
During a tsunami
- If you haven't done so already, move immediately to the nearest higher ground.
After a tsunami
- Listen to the radio for civil defence advice
- Do not go down to the sea until you have been told it is safe to do so
Checklists
These checklists tell you what you need to do to get ready
Household Emergency Plan
Emergency Survival Kit
First Aid Kit
Getaway Kit