Why was the Beirut blast so massive? Ammonium Nitrate explosion explained...

The Lebanese government has ordered an investigation into the blast and how two thousand seven hundred and fifty tonnes of the explosive chemical Ammonium Nitrate was stored at the site.  We can see just how powerful the blast was by comparing before and after photos of the site. We know the firebrigade was fighting a blaze in a boilding just before the huge explosion. After the explosion the building been completely obliterated, so has the ground underneath it, leaving a water-filled crater and complete destruction around it. Whe talk to a Chemist how Ammonium Nitrate explosions can cause such massive damage.