Answers (2)
We don't explain, we answer questions. You have not asked a question. When you compose a question, you should remember that you have to say what you are talking about, and include enough information to allow somebody to look up an answer.
I assume you are talking about plate tectonics. Physical processes are unknown. Plate tectonics is a conjecture, not based on observations, so there is no explanation of physical processes; only more conjecture.
What happens at a destructive plate boundary?
"A destructive plate boundary happens where an oceanic and continental plate move towards each other. The heavier, more dense oceanic plate is forced under the continental plate. As it sinks below the continental plate the oceanic plate melts due to friction in the subduction zone. The crust becomes molten called magma."
www.geography.learnontheinternet.co.uk/topics/destructive.html