Above is a video of another massive dust storm consuming south Phoenix, Arizona on July 18, 2011. This one measured 3000 feet high. These storms occur when a strong wind front picks up loose sand and dust from the dry surface. They can often be triggered by major thunderstorms nearby. They are more common in the Arabian peninsula and the Sahara, two of the main terrestrial sources of airborne dust. Photographed below is a dust storm touching down in Al Asad, Iraq on April 27, 2005.