Samadhi and Kriya yoga are interchangeable. Samadhi which is the result or goal of performing Kriya is more than a method of yoga.
Samadhi which is the alterations in conscious progression can be described as going through five stages. First there is Savikalpa Samadhi. Continuing on there is Nirvikalpa with form, Nirvikalpa without form, Soruba and Budhi.
Although these may be expressions of alterations of consciousness they are greater than simple movements of consciousness from self and environment to higher self and Cosmos.
Samadhi the breathless state (when the heart stops beating and the lungs stop breathing) is something much more important to spiritual progression than one might imagine.
In Kriya the goal of surrendering consciousness from the five bodies (Spiritual, intellectual, emotional, vital and physical) is something that affords Kriyas the greatest spiritual advancements.
In this way advancements in Samadhi can be likened to surrenders through the five bodies. Nirvikalpa is a surrender of spiritual body (this bringing about enlightement and immortality of spirit). In Soruba Samadhi there is surrender to physical body (with its annihilation of remaining physicality and formation of light body).
Great detail of Kriya, spiritual and conscious progression as well as Nirvikalpa and Soruba Samadhi can be learned through purchasing and reading Dr. Greszczyszyn book The Complete Chakra System