Explain how it is possible for weathering to take place far below ...

[hubes95]

Explain how it is possible for weathering to take place far below the surface of bedrock.
 
  What will be an ideal response?

Question 2

Why isn't the Grand Canyon of the Colorado simply a product of the erosion by the river?
 
  What will be an ideal response?

[mirabriestensky]

Answer to Question 1

Answer: Weathering penetrates into rock through various openings into which water and atmospheric gases can move. They are pores, joints, faults, etc.

Answer to Question 2

Answer: As the river has cut downward a mile, the canyon sides have been kept steep by a series of caprock layers. these have worn back at a much greater rate than the river has cut downward so the width of the canyon is over 15 km.