Page 336 - Laboratory Manual in Physical Geology

A CTIVIT Y 11.5 Mass Wastage at Niagara Falls

Name: ____________________________ Course/Section: ___________________________ Date: __________

A. Geologic evidence indicates that the Niagara River began to cut its gorge (Niagara Gorge) about 11,000 years ago as the
Laurentide Ice Sheet retreated from the area. The ice started at the Niagara Escarpment shown in FIGURE 11.9 and receded

(melted back) north to form the basin of Lake Ontario. The Niagara Gorge started at the Niagara Escarpment and retreated
south to its present location. Based on this geochronology and the length of Niagara Gorge, calculate the average rate of falls
retreat in cm/year. Show your calculations.

B. Name as many factors as you can that could cause the falls to retreat at a faster rate.

C. Name as many factors as you can that could cause the falls to retreat more slowly.

D. Niagara Falls is about 35 km north of Lake Erie, and it is retreating southward. If the falls was to continue its retreat at the
average rate calculated in A, then how many years from now would the falls reach Lake Erie?

E. REFLECT & DISCUSS Look at the cross section of Niagara Falls in FIGURE 11.10 . Describe how the process that formed

the falls could have begun. (Hint: Use your knowledge of stream erosion and the effects of stream gradient.)

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