How deeply glaciers could erode and about how deeply glaciers could erode?

Answer 1

This begs the question, "Have you seen the Grand Canyon" Or, "Have you heard of the Grand Canyon?"

Yet, the Grand Canyon isn't the deepest, not even the deepest in the US. The deepest canyon on Earth is Cotahuasi Canyon of Peru. Cotahuasi was cut by the Cotahuasi River (or Rio Cotahuasi) and reaches the depth of 2.08 miles (3354 meters).

Answer 2

This gets a bit tricky, but bear with me.

We know that the Great Lakes were largely gouged out by the advance and retreat of multiple glaciers that existed for eons over the region of North America where they lie. With the exception of Lake Superior (Lake Superior is actually the remains of an ancient rift valley that was flooded by the retreat of the glaciers, and the formation of several hundred--perhaps thousand--rivers, streams, and creeks that empty into it), the Great Lakes owe their current depths to glacial erosion.

So, we need to look at the elevation of the remaining four Great Lakes, and their depths:

• Lake Michigan: elevation - 577 ft. above sea level, maximum depth - 925 ft.
• Lake Huron: elevation - 577 ft. above sea level, maximum depth - 750 ft.
• Lake Erie: elevation - 568 ft. above sea level, maximum depth - 210 ft.
• Lake Ontario: elevation - 802 ft.

Now, the reason elevation of the lakes is important (Lake Superior lies at 601 ft. elevation by the way) is that the glaciers that gouged out the area, scraped the land as well. With this in mind, consider that Mt. Arvon is the highest point in the Great lakes region, and it reaches an elevation of 1,979 feet. So, from 1,979 feet to a depth of 925 feet below the elevation of 577 (a total of 2,327 feet) glaciers have scraped or gouged land.