Two people died have after a landslide hit their home in New Zealand, and authorities are searching for several others feared dead in a separate slip at a busy campground.
The two landslides, about 17 kilometres apart on the country's North Island, occurred after heavy rains saturated Te Ika-a-Maui's east coast and caused widespread damage.
Here's how landslides occur, the warning signs and where they are most common.
What is a landslide and how do they happen?
Landslides, as the name suggests, are the downhill movement of rock, soil and vegetation on a slope.
Kevin Trenberth, an expert in climate variability at the University of Auckland, says landslides — also known as "slips" in New Zealand — are driven by gravity when downward forces overcome the slope's resistance.
"Landslides occur in steep topography, mountains and hills and can be exacerbated by removal of trees and vegetation," he told the ABC.
"The latter destabilises the region and I am sure has been in play [in New Zealand]."
Landslides can happen very suddenly, especially during rain and after earthquakes.
Lauren Vinnell, a senior lecturer of emergency management at Massey University's Joint Centre for Disaster Research, says there are warning signs to look out for.
"If there are any rocks falling or small slips, it might be a sign that a larger slip is about to happen," she has told RNZ.
Dr Vinnell says "cracks or bulges in the ground, or doors or windows becoming hard to close or open because the frames have moved" can signal a landslide.
Does climate change increase the risk of landslides?
Dr Trenberth says climate change can increase the number and severity of landslides in various ways, including through heavier rains and prolonged dry periods.
"Landslides become more likely with saturated soils following heavy rain. Ironically a dry spell can set that up by causing cracks," he says.
"Water infiltrates the cracks and makes one slab able to break off either from the extra weight of water, and/or the water flows around and through."
Heavy rains can also cause erosion, Dr Trenberth says, which increases the risk of landslides as well.
Dr Trenberth says landslides are often exacerbated by poor or inadequate land use and building on flood plains.
"If [building] plans were based on historical records then they do not account for the extra heavy rains with climate change," he says.
Parts of New Zealand's North Island have experienced fresh downpours this week on already saturated ground.
Dr Trenberth says while these are individual weather events, they are "unfolding against unusually warm seas that load the atmosphere with extra moisture and energy".
Where are landslides most common?
Experts say regions with steep topography and high levels of rainfall are at greater risk of landslides.
Several South-East Asian countries including Indonesia, Malaysia and Thailand have experienced devastating landslides in recent months, as has Nepal, India and Sudan.
At least 1,189 people were killed in widespread floods and landslides across Indonesia's largest island, Sumatra, late last year.
Local authorities say another 141 remain missing and almost 200,000 were displaced.
Dr Vinnell says landslides can occur on "most of the slopes" in the country.
"Landslides are quite common in New Zealand and can cause considerable damage," she says.
The World Health Organisation (WHO) says landslides are the most frequent geological event and can occur anywhere in the world.
Between 1998 and 2017, landslides affected an estimated 4.8 million people and caused more than 18,000 deaths, according to WHO.
Does Australia get bad landslides?
Australia has fewer landslides compared other countries, according to Geoscience Australia.
However, some regions with coastal cliffs and intense rainfall can experience them.
Areas most impacted include:
- Great Dividing Range
- The Strzelecki and Otway ranges of Victoria
- Mount Lofty Ranges near Adelaide
- Tamar Valley and the north-west coast of Tasmania
More localised areas also include the Illawarra Escarpment near Wollongong, Sydney's Northern Beaches, Lake Macquarie and Newcastle in NSW, and Townsville, Cairns and Mount Tambourine in Queensland.
Just last week a landslide triggered by severe storms and heavy rain impacted three homes at Great Mackerel Beach, north of Sydney.
And people living in 16 homes in Newcastle were evacuated after a landslide caused severe damage in May last year.
Australia's worst landslide in history is the Thredbo disaster, which killed 18 people as it tore through the Snowy Mountains community in 1997.
