Pick the deadliest: Landslides, earthquakes or tsunamis?

On average, there are three deaths a year from landslides in New Zealand and there are more recorded fatalities – 700 deaths – from slips than earthquakes and tsunami, says GNS Science engineering geologist Chris Massey.

“That number of fatalities is higher than earthquakes and tsunami.

“So landslides are a real problem. It’s not just the deaths, the people that they kill, but it’s also the damage to property, the damage to infrastructure.”

GeoNet said there were about 400 slips on artificial slopes on the Wellington City Council road network each year.

Mr Massey said most slips were triggered by rainfall and the main factors influencing the risk of a landslide are geology, climate, and land use.

”The thing is, though, not many people live on slopes… Many in Wellington do, but in the rest of the country a lot of people don’t live on slopes so the risk isn’t evenly distributed across the whole population. It’s kind of weighted to the people who live on slopes.”

That view you’re paying for?  It’s also increasing the odds that you’ll be a statistic one day.

As rainfall intensifies, a slope saturates and essentially liquefies, reducing the material’s strength.

The higher the rainfall intensity, the more landslides happen.

Wellington was built on steep slopes on greywacke. Slip-prone land tended to sit on top of rock defects filled with weaker material or areas where runout was possible, Massey says.

Whether a slope is susceptible to slipping depends on material type, soil or rock, and the angle.

”Those kinds of slopes will not be stable at the same slope angle as other slopes that say didn’t have those defects in them, or the orientations were more favourable for stability.

”It’s a really complicated issue.

”For different types of soil and rock we have different angles that the slopes are comfortable or stable at and you can calculate a probability of a landslide occurring in different combinations of material type and at different slope angles, different rain or earthquake events.”

I’m just surprised it hasn’t been linked to Climate Change.  I guess the data doesn’t support it.  Yet.



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