1) why are tsunami often so much more destructive than even very large storm waves? 2) what is the source of most coastal sediment?

1. Huge waves

Explanation:

1. Tsunami is harbor waves that cause the displacement of a large volume of water generally in oceans and lakes. And large storms are water rising from low-pressure systems mostly causing coastal floodings and occur through seismic events.

2). a. Erosion by rivers  

    b. longshore transport from one side to another.

    c. Erosion of older beaches and foreshore deposits.

    d. Erosion of older deposits on the inner shelf