Scientists have revealed the reason the Southern Alps turned a red colour in the summer of 2019 and 2020.
Victoria University of Wellington researchers studying the environmental phenomenon found desert dust storms that sent massive amounts of red dust across the Tasman Sea was to blame, and the event was likely to occur more often as the climate warms.
“Media reports in 2020 generally assumed the blanket of red on the mountains was caused by ash swept across the sea from Australia’s devastating New Year bushfires,” said the study’s lead author and environmental scientist Holly Winton.
“But the red dust that led to the dramatic colour change actually arrived well before New Year.”
About 4500 tonnes of red dust
Time-lapse photography of the Southern Alps’ Brewster Glacier, taken by the University’s Associate Professor Brian Anderson, showed the red dust arriving on the mountains in late 2019.
Fuelled by high winds that were also fanning bushfires, these storms dumped an estimated 4500 tonnes of red mineral dust on top of snow and ice in the Southern Alps. Most of it fell during a two-week period in late November 2019.
Using geochemical fingerprinting, the researchers analysed samples of the dust from the Fox, Franz Josef, and Tasman glaciers and pinpointed its origin as south-east Australia where it was stirred up by desert dust storms.
Winton said the dust storm event lasted only a short time but it could have long-term effects.
“The huge amount of dust dumped reduced albedo — that’s the ability of snow to reflect sunlight. The dust particles absorb sunlight. This in turn will raise surface temperatures and increase snow and glacier melt, adding to existing pressures on this environment,” she said.
Will it happen again? It’s likely
The findings published findings in the journal Geophysical Research Letters today also detailed why the Southern Alps may experience more of these massive dust dumps in coming years, said project leader Phil Novis.
“Climate change is expected to result in increased desertification and dry conditions in many areas so these storms — as well as wildfires that can be driven by similar weather patterns — are likely to occur more often.”
Novis said the 2019/2020 event was at least the ninth such event recorded in New Zealand since 1902 and “surely one of the most dramatic”.