1)Why do some glaciers have more than one medial moraine?

is it because they are formed by two lateral moraines and has more than one source.

2)where does most of the lateral moraine come from?

is it from the valley sides

3)why is the terminal moraine often the highest and the largest moraine?

because it builds up at the snout and does not move.

thankyou for taking the time to help me.:]

You are asking geology questions.

Labelling the subject correctly may get you some answers faster.

Lateral moraines form at the edges of glaciers.