No they didn't. The Hiroshima and Nagasaki bombs were relatively low-yield weapons. More importantly, they were set to airburst. Little Boy went off at about 1900 feet and Fat Man at around 1600 feet. If you want to move a significant amount of earth with a nuclear bomb you need to bury it, not set it off high in the air.

If you want an example of what a nuclear bomb can do in terms of altering geography look up the Sedan Crater in Nevada. It was created in the early 1960s when they thought that using nuclear explosives for civil engineering might actually be a good idea. That bomb was roughly 7 times more powerful than Little Boy and was buried 600 feet underground. The resulting crater was up to 320 feet deep and around 1000 feet in diameter.