A geology girl told me there is a hard side and a soft side to a river, why?

Question

I checked it out. Where I live, the Tennessee river has a hard side of limestone cliffs and a soft side of muddy bottoms. Why is the Grand Canyon hard on both sides.

Answer 1

No, there is no "soft" side or "hard side" of a river. A river flows due to force of gravitation, always taking the slope which is maximum. So the banks may have same or different country rocks. If the rocks are same, both the banks are of equal hardness. If not, they may have different hardness. But this is really immaterial.

If the river course is curved, the bank that is concave with respect to river channel becomes erosional bank because the flowing water only hits that bank. Hence there is no deposition of sediments along that bank and you get hard rocks exposed there.

Conversely, the opposite bank, which convex in relation to channel is slightly protected from erosional action as it is "shadowed" from the current hitting and deflecting from the other bank. so here we get a deposition of sediment, often forming muddy banks.
This is perhaps what your friend-in-geology tried to express. I am sure if you study the geometry of river course of the particular segment of Tennessee river, you will find that the limestone bank is concave with respect to water course. If you take up a rather straight segment of any river course, you will find it does not have any hard or soft bank.
Try drawing a river course and show its current as straight arrows. You will soon realise why there is a depositing bank / an eroding bank.


A canyon is basically a very deep valley with vertical sides. This is formed due to rapid downcutting action of the river together with upliftment of the country rocks (by a process called Rejuvenation). The rocks must be horizontal or near horizontal and fairly hard. (If the rocks are slopping, they will form an asymmetric valley; if the rocks are soft, they will collapse to form a normal V-shaped valley). Grand canyon is a the classic example of a canyon.
Lastly, never think a limestone a hard rock. Although it is hard to touch with your fingers, it is chemically very weak. A hard rock is one which is resistant to weathering. So it has to be physically and chemically very strong.

Answer 2

What she probably meant, is that is the river is curvy ("meandering"), one side (left or right bank) is the erosional side..meaning that sediments are being carried away (the "soft" side), and the other side is the depositional side.. meaning that sediments are being deposited on that side (the "hard" side). which side is which, depends on the direction that the river is flowing, as well as a few other factors... this is why rivers get to be so "curvy"...
my guess is that she was just simplifying this whole idea, and using rough, simple terms to help you understand more easily how it works.

Answer 3

Sorry but the geology gal is wrong.. there is NO SUCH thing as a soft and hard side of a river