Landslides are New Zealand’s deadliest natural hazard. Tom Robinson asks why we still tolerate the risk

By Tom Robinson*

The recent deaths of eight people in two New Zealand landslides has left the public searching for answers. Some questions will be technical, about what failed and why.

But one should surely sit above the rest: why do we keep accepting the human and financial cost of this risk?

While it might be assumed that earthquakes or volcanic eruptions are Aotearoa’s deadliest natural hazards, landslides have claimed more than twice as many lives – approximately 1,800 – as both combined over the past 200 years.

They remain such an insidious and under-appreciated hazard because they cause deaths relatively frequently, but typically only in small numbers. Being one of the most fatal New Zealand landslides since 1846, last month’s tragedy at Mount Maunganui was a stark exception.

A useful analogy is our tolerance for car crashes versus aeroplane crashes. Road deaths in New Zealand kill hundreds of people each year, one by one, with little national reckoning. The 1979 Mount Erebus air disaster, in which 257 people were killed in one afternoon, forever changed aviation policy and remains part of the country’s collective memory.

In natural hazard terms, landslides are car crashes; earthquakes and volcanic eruptions are aeroplane crashes. Yet, with climate change driving heavier rainfall, it’s worth asking whether this is a danger we should be comfortable to continue living with – and paying for.

Since 2010, central government has incurred about NZ$19 billion in costs associated with natural hazards, but 97% of that has gone on response and recovery, with just 3% on reducing risk and building resilience. In practice, New Zealand keeps paying for disasters after they happen, rather than spending to stop them happening in the first place.

A hazard hiding in plain sight

The risk of landslides, specifically, is managed through a complex mix of laws, led by the Resource Management Act (RMA). It largely falls to territorial authorities, which can restrict new developments but, due to land use rights, are more constrained with existing buildings even if at high risk.

There have been some successful attempts to change land use rules, but they have been few and far between. It remains to be seen what effect the latest reforms to the RMA will have.

Recent disasters have also exposed gaps in how local councils, emergency services, central government agencies and insurers respond to events, with unclear responsibilities and slow information flows. This underscores the need for a more joined-up response to events such as floods and landslides, as a high-level inquiry recommended in 2024.

On top of all this is the need to gain a clearer national picture of the hazard. Past landslides indicate where failures are most likely: steep slopes, weak rock, wet soils and sparse vegetation, particularly where forestry was recently cleared. But outcomes also depend on subtler factors such as slope shape and aspect.

We also know landslides come in different shapes and sizes, which determines how far they travel and how much area they can threaten. In New Zealand, the most common type are shallow slides, typically one to two metres deep and involving only the top layer of soil.

Despite their size, these slides can be highly dangerous, carrying hundreds of tonnes of debris at high speed. Their paths are not always straightforward: wet landslide debris can behave like a liquid, following channels in the landscape and travelling for kilometres.

While scientists’ understanding of landslides has improved markedly over recent decades, important gaps remain. Because landslides are highly localised, they demand detailed local knowledge. But New Zealand’s inventories are still patchy, particularly in Northland and the Bay of Plenty, and existing local studies are often hard to access or compare.

This also makes it harder to understand precisely what climate change means for national landslide risk.

Although a warming climate is already driving more intense and frequent storms, emerging research suggests future landslides will mostly increase in areas already prone to them, rather than spread into entirely new regions. Even so, uncertainty in these projections remains high.

The cost of living with risk

To paraphrase New Zealand’s former prime minister Geoffrey Palmer, if you want natural hazards, you’re in the right place in Aotearoa. Managing the ever-present threat from landslides, earthquakes, volcanoes, flooding, tsunamis, liquefaction and wildfire is a daunting responsibility. But it’s a job we expect our authorities to do, all while running other services and keeping our rates and taxes as low as possible.

With the cost of landslides mounting, we might expect that when local authorities identify actions to reduce risk that could save money in the long run, these efforts would be welcomed by central government. Instead, they are often met with a phrase we have become too familiar with: we are in a “fiscally challenging environment”.

That may be. But it is also true that the costs associated with natural hazards are only likely to increase. The cheapest time to invest in resilience is now.

When it comes to landslides, we need to consider whether repeated fatalities from a known and worsening hazard are something we are prepared to tolerate. Aeroplane crashes have always been unacceptable to us, but the 2019 Ministry of Transport Road to Zero strategy suggested deaths in car crashes were becoming intolerable as well.

Perhaps now is the time to take a similar approach to landslides. With an election looming, political parties have a chance to put forward credible plans to reduce natural hazard risk or, better still, to agree on a non-partisan path that builds resilience for the long term.

*Tom Robinson, Senior Lecturer Above the Bar, University of Canterbury.

This article is republished from The Conversation under a Creative Commons license. Read the original article.