What you see here isn’t a cloud or smoke from a fire , but a haboob: a dust storm of monumental proportions that hit Phoenix, Arizona, in August 2011. Although the dust storms themselves aren’t especially unusual in the region, this was a monster at two kilometres (1.2 miles) high and 100 kilometres (62 miles) across.
Early June marks the beginning of the monsoon season for Arizona and it’s where this massive haboob began its life. Most of the land was still very dry when a large thunderstorm-forming depression settled over the desert, causing winds to move into its centre. When it collapsed, the winds reversed and downdraughts of up to 100 kilometres (62 miles) per hour blew across the arid region, kicking up a huge wall of dust that swept over the city.
Haboobs occur in several desert areas, including the Middle East and Australia. They’re not particularly dangerous, but the dust gets everywhere and they can leave a covering of up to 0.3 metres (one foot) of sand. The Phoenix haboob included additional hazards in the form of heavy metal pollutants, fungi and bacteria that could cause eye infections and lung diseases.