Investigating Cascading Hazards
Earthquakes are not just shaking. They can cause other hazards. Scroll down to learn more about hazards in New Zealand ↓
Action Reaction
Every action has a reaction and the flow on effects can be bigger or more complex than the original action.
For example, earthquakes are not only ground shaking and surface rupture, they can also cause a whole series of other cascading hazards which can have immediate, short term and long term or prolonged impacts. This means that when the shaking stops, we need to be aware of the other cascading hazards it may have generated and be prepared for them too.
Scroll down to learn more ↓
Main earthquake
Earthquakes can cause the ground to shake and the surface to break. They can also cause small and more dramatic landscape changes and a whole series of cascading hazards.
Keep scrolling to see how these hazards can cascade over time ↓
Strong ground motions (earthquake shaking) can move the landscape around us causing landsliding, avalanches and rockfall.
And when the landscape is displaced it can move bodies of water as well causing tsunami in lakes and oceans.
The ground motions and land movement can also cause other shorter term complications like liquefaction and tree fall.
While these types of hazards may not impact us for as long, they do mean the hazard risk that we are exposed to may change over time.
The cascade of hazards and landscape changes they generate can impact us for days, weeks, months and even years.
Aftershocks
And when an aftershock happens, the same cascading processes can start all over again.
Let's look at some of these individual hazards in more detail.
Keep scrolling ↓
Landslides
Earthquake shaking can trigger the mass movement of rock, debris, or earth down a slope, causing a landslide.
Liquefaction
Earthquake shaking can trigger liquefaction in loose silty and sandy areas below the water table.
The earthquake shaking causes the sand and silt to move, pushing the water up to the surface through cracks or weaknesses in the ground.
Source: GNS Science
Fire
Earthquake shaking can cause damage to flammable materials causing fires to break out.
Source: MTG Hawke's Bay Tai Ahuriri
Landslide dams
Earthquake shaking can trigger a landslide that blocks a river, causing a dam to build up behind the landslide.
This, if released, can cause flooding.
Seiching
Earthquake shaking can trigger the backwards and forth movement of water in lakes. This is called seiching.
Tsunami
Earthquakes on the seafloor can cause movement of the seafloor, triggering a tsunami, a series of fast-moving waves. Like we saw in the 2011 Japanese tsunami.
Aftershocks
Aftershocks are the smaller earthquakes that can occur following a main earthquake. They are smaller but depending on where they happen, they can cause significant impacts on their own.
Source: GNS Science
Did you know?
The 2011 Christchurch earthquake (Magnitude 6.3) was actually an aftershock of the 2010 Darfield earthquake (Magnitude 7.1)!
Source: GNS Science
Cascading Hazards
These natural hazards can all be triggered from just one earthquake, and they can all be triggered at the same time.
That's why preparing for earthquakes means preparing for other cascading hazards too.
Hazards Happen
We know earthquakes can cause landslides, liquefication, fires, flooding, seiching and tsunami, because we've seen this happen before in Aotearoa New Zealand.
Can you think of an example of a hazard that has happened here?
Scroll down for examples of when an earthquake has caused one of these hazards to occur ↓
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1
Gisborne tsunami 2021
Three offshore earthquakes triggered tsunami near Gisborne. These tsunami were recorded on tsunami gauges across the Pacific.
2
Lake Taupō seiching 2022
A earthquake near Taupō caused seiching across Lake Taupō, causing damage to boats that were moved off their moorings.
3
Napier Fires 1931
The shaking from the Hawke's Bay earthquake caused flammable materials to break in chemists resulting in fires breaking out across Napier.
4
Kaikōura landslides 2016
The Kaikōura earthquake triggered landslides closing roads across the South Island.
5
Christchurch liquefaction 2011
The Christchurch earthquakes triggered liquefaction across the city, damaging buildings, roads, pipes and tanks.
6
Mount Adams landslide dam 1999
A landslide from Mount Adams on the west coast blocked the river valley, damming the Poerua River, and creating a landslide dam. This posed a risk to those living downstream in Poerua Valley.
Impacting us
These hazards can have ongoing impacts on our landscape and lives for days, weeks or even years, after just one single event. This makes the big picture far more complex.
Click through to understand how landslides could impact the South Island following a large Alpine Fault earthquake ← ••• →
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Take Action
Each of these hazards can be triggered by a single earthquake. There are a whole range of reasons these natural hazards may occur after the main earthquake and we can prepare for the impacts of these hazards as well by making plans before they happen.
Imagine, a large earthquake has occurred. You are at the park near a river with a friend. You both drop, cover and hold. A few tree branches break around you and you start to see some muddy stuff come to the surface. You start walking back home and notice the footpath is cracked and some cars have sunk into the ground. When you get home, no one is there. You phone isn't working to check in on your family and the power is off.
It sounds a bit scary, but one simple thing you can do to ease your mind is talk to your friends and family and make a plan.
Make a plan. Have a Prep Talk
Make a plan together so that you are all prepared. It is as simple as thinking about the things you need everyday and working out what you would do if you didn't have them.
When you're away from home, think about how you’ll communicate with each other and, if you can't, where you will meet. Also think about what you’d do if the power was out.
Test your knowledge!
Now that you've investigated cascading hazards, test your knowledge in our quiz and find out if you are a plate boundary expert!
Interact Quiz
For more information on how you can prepare you can visit: www.eqc.govt.nz or www.getready.govt.nz
