Between Monday 21st and Saturday 26th September 2009 two very large dust storms swept across eastern Australia and affected three major cities – Canberra, Sydney and Brisbane. The dust cloud that covered Sydney on the morning of Wednesday 23rd was one of the most severe in recent memory, with visibility dropping below 100 metres in some areas, and thousands of tonnes of dust settling across the Sydney basin.
Dust storms are common over inland areas of NSW and Queensland, but usually they are prevented from reaching Sydney by the massive wall of the Great Dividing Range that acts as a large shield, preventing the dust from moving to the coastal fringe.
However when a strong cold front is involved, the dust can be lifted, up to 3000 metres above the ground, and swept over the mountains and across the coastal fringe.
Cold fronts can lift dust up to 3000 m
above the ground (Click on image to enlarge)
The front also tends to produce an organised line of dust that can extend hundreds of kilometres north and south, a line that rolls steadily eastwards and can be readily identified from satellite photography.
In these cases the dust consists of very fine particles of topsoil that are highly penetrative – even houses that have been carefully closed up will have their interiors carpeted with a fine film of dust.
Dust storm lining up with a cold front, 25th September 2009
On occasion the dust cloud can carry across the Tasman Sea and drop across New Zealand, producing red snow on the New Zealand Alps. Much of the dust also falls into the Tasman Sea and sediments at the bottom of the ocean in this area reveal evidence of many similar events that have taken place in the past.
The dust storm of 23rd September was over 1500 km long and 200 km wide (NASA picture)
Another severe dust storm affected Sydney during the summer of 1944 as the following newspaper article recalls.
DUST STORMS AND FIRES IN NSW
SYDNEY, Sun 10th December 1944 – The Argus
Dense dust storms, accompanied by high temperatures, raged over most of New South Wales at the weekend. Bush fires in the Blue Mountains destroyed seven cottages, a dairy, a store, look- outs, and kiosks. Nineteen houses were destroyed in the Richmond district and four near Gosford.
A man and a woman aged 80 were burned to death in the fires. They were J. H. Barnes, who was burned in a paddock at Kurrajong, and . Miss Irene Cavanagh, who was trapped in a house at Oswald.
Some relief from the heat is forecast for tomorrow.
Sydney was swept by a violent westerly gale. The maximum wind velocity recorded at the Weather Bureau was 63 mph, but one gust at Richmond reached 76 mph.
The maximum temperature in Sydney today was 91deg, compared with 91.5deg yesterday. Clouds of dust carried by the wind from inland districts almost blotted out the sun at times.
Metropolitan fire brigades answered more than 150 calls. The task of extinguishing outbreaks was made more difficult by the gale.
One of the biggest dust storms to ever affect an Australian capital city occurred in February 1983, when a massive wall of dust swept across Melbourne, also carried along by a powerful cold front.