Instruction :
How did Niagara Falls form?

Response:
Scientists believe a glacier originally formed the falls toward the end of the Ice Age some 13,000 years ago when tons of ice melted and eroded over time. Erosion caused the river bed to drop like a cliff, and the river continued to flow over what is now known as Niagara Falls. This slow process still occurs today when the water freezes and thaws, wearing away and moving more rock under the river surface, causing the falls to move farther upstream.