An anal orgasm happens through indirect stimulation of a woman’s G-spot, through the wall shared between vagina and rectum. With all this stimulation going on, your chances of having an intense orgasm are good.
In addition to the G-spot, there’s another button of joy: the deep spot. The back of the deep spot can be found in the deepest part of the vagina, all the way in before the cervix, and is responsible for intense orgasms. This is why anal orgasms are known for being so powerful.