They are known by many names: Haboob, Simum, Black Blizzards. A solid wall of dust almost a mile high, moving whole sand dunes and bringing Biblical darkness to the huge areas of the world. Scorching hot winds (up to 40 degrees Celsius) blowing the sand around with hurricane speeds... What seems extreme to us is actually a common occurrence in Africa and the Middle East. The similar sand-saturated hurricane-speed storms over Mediterranian are called Sirocco, Yugo and Ghibli. The dust (or desert sand) particles become airborne and held in suspension, creating a moving front. The convection of cold air over the heated ground maintains the storm and keeps the dust rolling.
See one such storm coming into the Israeli Negev desert from Sinai (advancing with the speed of appr. 40 mph). According to the photographer Eviathar ben Zedeff (link), the sand wall is over 4,000 ft high:
Sand Storm in Khartoum, Sudan:
Here is an alarming fact: sand storms now happen ten times more frequently than fifty years ago. For example, Mauritania had only two storms per year in the early Sixties, now it's more like EIGHTY a year. Sahara's sand is also being sent into the Atlantic at an accelerated pace (five times growth in one year, since 2006!) - however, this could be a good thing, according to Wikipedia, as it will cool off the ocean enough to slightly ease the ongoing 2007 hurricane season.
Dust covers Astana, the new capital of Kazakhstan:
The next picture may look like an incoming dust storm, but it is just a cloud front.