This means blasting one off target that is headed toward the earth wouldn't be easy. Brief descriptions are given. These are really good sites, and there are many more out there. This is just to get you started. A one page article, very interesting.
School textbooks keep promoting the idea that asteroids are usually one big rock.
A direct hit by any weapon would merely divert off some of the rubble, and the bulk would keep right on coming, held together by gravity. Get the details on what it would be like on earth if Earth and an asteroid collide. This has a picture of the Barringer Meteor Crater in Arizona, which is 50,000 years old. It is huge and shows what happens when a meteorite or small asteroid get through our atmosphere. It also has a soil sample showing the asteroid layers in the earth.