The Canary Islands scenarios seem a little bit unlikely in my humble opinion. The force of a nuclear bomb cannot be shaped; which at first glance seems to be how he got his figures, that is if he has figures at all. A blast takes the path of least resistance and always tries to form a sphere. It will not "dig" into solid rock when it can go into the air. Yes, it will dig up something of a crater, but, as far as I know, they wouldn't dig deep enough to enact the scenarios proposed.
Also, all nuclear weapons today, with the possible exception of the very small (tons to Kilotons) "Bunker Buster" bombs that I am not even sure are currently extant, are designed to explode in the air. This so-called "air-burst" maximizes ground-level destruction while minimizing radioactive fallout, because the former is a sensible way to wage war and the latter is good for business all around. No need to disrupt the environment unduly any further, and piss of a potentially neutral country with a cloud o' death.
Of course this does not mean that someone who can actually fabricate a nuclear device couldn't build it to dig a crater, but AFAIK you can't make a nuclear shaped charge and even if you could I doubt you could achieve the kind of efficiency needed to punch through the amount of rock in question.