***** NOT A TEACHER *****
(1) I checked Mr. Michael Swan's reliable Practical English Usage.
He advises us to use "into" when we think of the movement itself:
The children keep jumping into the flowerbeds.
He advises us to use "in" when we think more of the end of the movement:
Go and jump in the river.
(2) Here in the United States of America, we have a phrase that some people say
when they are angry with someone, but they do not want to say anything too
Go jump in the lake! (It is NOT so strong as: Go to H - - -! )
Interested in Language