18 January 2021
Gravity always wins: in New Zealand landslides are more deadly than earthquakes
Posted by Dave Petley
Gravity always wins: in New Zealand landslides are more deadly than earthquakes
New Zealand is a country with an abundance of natural hazards – earthquakes, volcanoes, floods, tsunami, cyclonic storms and landslides, amongst others. Of the geophysical hazards, it is earthquakes and volcanoes that attract most of the attention, driven by large events such as the Christchurch earthquake sequence, the Kaikoura earthquake and the Whakaari /White Island eruption. Landslides are generally not considered to be such a major issue around the world, and are often dismissed as a secondary hazard.
Interestingly though, my colleagues at GNS Science have been looking the comparative impact of landslides and earthquakes through time in New Zealand. The online news service Stuff has a good article about this work today. The simple conclusion is startling:
Landslides are significantly more dangerous than earthquakes, according to an analysis by GNS Science.
Interestingly the article provides some detail to this through some words from Jo Horrocks, the chief resilience and research officer of the Earthquake Commission (EQC), the national insurer against earthquakes (and landslides). She noted that landslides cost the country an average of NZ$250 to 300 million (about £125-150 million) and that over the last 160 years they have claimed about 1800 lives. This is considerably higher than the toll from earthquakes.
Gravity always wins – the aftermath of landslides in Christchurch, New Zealand
The reasons that they are under appreciated is that landslides tend to happen as frequent events from which the losses accumulate. Huge clusters of landslides do occur – the Kaikoura earthquake was a fine example – but of course these are usually triggered by another event, such as an earthquake or a cyclone. Very often it is the landslides that cause the losses.
I am sure that this effect is seen in many other countries as well. The article in Stuff has a nice quote, taken from an article in the Te Ara Encyclopaedia of NZ :
Gravity always wins
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
Would be interesting to know if the costs (and fatalities) of earthquake-induced landslides are counted to the costs of earthquakes or landslides.
I think there is an important punctation mark in the original article: While death toll of landslides is significantly higher compared to earthquakes, the financial costs are still orders of magnitudes larger for earthqakes. Taking the 2010/11 Christchurch events, you can pay more than 100 years of landslide costs with this 40 billion dollars.
Anyway, without gravity, earthquakes would be pretty harmless, as nothing collapses. Indeed, gravity is the champion.
As evidenced by the photo accompanying this article: common sense often loses.
It is traded by those who sell and buy into the senselessness that such locations are risk-free enough to be worthy of long term investment.