1. Rates of uplift and erosion. ................................................

Question

1. Rates of uplift and erosion. .........................................................................................................(9 pts)
a. The following questions give you a sense of the rates at which uplift, and erosion take place. We will
assume that uplift and erosion do not occur at the same time – that the mountains are first uplifted and
only then does erosion begin – whereas the two processes actually operate simultaneously.
- If mountains rose by 1 mm/yr., how high would they be (in meters) after
- 1,000 years? _____________,
- 10,000,000 years? ______________
- 50 million years? ________________
b.The Himalayas now reach an elevation of 8.8 km, and radiometric dating suggests that their uplift began
about 45 million years ago. Assuming a constant rate of uplift, how fast did the Himalayas rise?
- km/yr? ____________________________________________
- m/yr? _____________________________________________
- mm/yr? ____________________________________________
c. Evidence shows that there were once Himalayan-scale mountains in northern Canada, an area now eroded
nearly flat. If Earth were only 6,000 years old as was once believed, how fast would the rate of erosion
have had to be for these mountains to be eroded to sea level in 6,000 years?
- m/yr? ___________
- mm/yr? _______________
d. Observations of modern mountain belts suggest that ranges erode at rates of 2 mm per 10 years. At this
rate, how long would it take to erode the Himalayas down to sea level?
- Years? __________________

Explanation / Answer

a.

Rate of uplift is 1mm/year

In 1,000 year upliftment is = 1000 x 1 = 1000 mm = 1 meter (as there are 10 mm in a centimetre and 100 centimetres in am meter)

In 10,000,000 year upliftment is = 10000000 x 1 = 1000 mm = 10000 meter (as there are 10 mm in a centimetre and 100 centimetres in am meter)

In 50 million or 50,000,000 year upliftment is = 50,000,000 x 1 = 50,000 meter (as there are 10 mm in a centimetre and 100 centimetres in am meter)

b.

Himalayas uplift in km/year = 8.8/45,000,000 = 0.0000002 km/year

Himalayas uplift in m/year = 0.00019556 meter/year

Himalayas uplift in mm/year = 0.195566 mm/year

c.

If the same height’s mountains were there then rate of erosion = 8.8 x1000/6000 = 1.4666666meter/year

Or 1466.66 mm/year

d.

If the erosion takes place with modern rate of 2mm/10year

Then 8.8 kilometre = 8.8 x 1000 x 1000 mm = 8,800,000 mm

Time for erosion of 8,800,000 mm = 8,800,000 x10/2 = 44,000,000 year

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