Possible Clues:

• Canyon-creating process
• Famous London statue with one leg wearing away
• It's caused by water slapping rocks
• Cause of a disappearing coastline
• The wearing away of rocks, e.g
• Wearing
• It may reduce some bank deposits
• Natural process illustrated by the last words of 18-, 24-, 37-, 54- and 61-Across
• The wearing away as by water