That Iceberg is not 10 kilometers. It's roughly as long as Marineford is, which would be 1-2 miles at best, and even that is a stretch given the size of the battlefield, and how long it took the Marines and Whitebeard Pirates to engage in combat. We all know Oda's scaling is terrible.
But even if we give it the benefit of the doubt and do say it is 10 KM, it is still nowhere near even a billion tons. Again, an Iceberg the size of Delaware (2,489 sq miles or 6446 sq kilometers) is a trillion tons.
https://www.scientificamerican.com/article/5-things-to-know-about-the-trillion-ton-iceberg/
So how would you get 100 Billion tons out of an Iceberg that would only be around 4 Sq Miles?