For this section let's define them as plot and subplot. An example of calamity would be a guy coming out of a convenience store to get breath mints for a job interview to find he just locked his keys in his car and only has a half hour to solve this problem to get to this dream job. Climax would be the same guy frustrated smashing his window while an older woman is driving up in the spot next to him. He is caught by surprise turns around the woman has a heart attack and dies.
Plot is past the moment.
Subplot is the defining moment of a character's life that explains the reaction properties, the strong virtue or flaw in their make-up mixed with action, emotion or circumstance. Many people define Calamity as plot but the truth of the matter is that it is part of the journey. It is the cobblestones that you write to define the path of your characters till the audience sees all the blocks turned to smooth concrete in their imagination. I can tell you that there is one blatant difference between the two. Calamity has a choice to be a moment without closure.