Dust clouds above Christchurch

Gillian Needham took this iconic photo from her home in Cashmere minutes after the 22 February 2011 earthquake struck Christchurch. It shows the city's CBD enveloped in a cloud of dust. A number of contributors to QuakeStories who were in the CBD at the time of the earthquake saw the dust cloud and knew that it meant buildings would be down:

Next came a billowing dust cloud, rushing down Kilmore street, my immediate thought was “what building was that which just collapsed….” I stood up and got out my iPhone and started texting my family. I remember having to brush the dust off my phone which was clouding the screen in my attempt to text.
Scott: http://www.quakestories.govt.nz/112/story/

Reaching Wordsworth Street I saw the dust clouds going up in the sky and I knew that a number buildings in Colombo Street had collapsed. Some of them sustained damage from the September quake and I expected it would be bad.
Paul: http://www.quakestories.govt.nz/242/story/ 

I ran down the driveway to the street and joined scores of shell shocked people. Sirens filled the air, and as we looked down towards the inner city (I live quite close to the centre of town) I was shocked to see a dust cloud rising. “Oh my god! Buildings definitely came down in that one!”
Frances: http://www.quakestories.govt.nz/105/story/