Re: how do cliffs form?

First of all thank you very much for your question.
The answer is the following: There are many reasons for the creation of 
cliffs. One of the major reasons is water. 
  Even though some cliffs are far away from water we should consider also 
the water that comes from rain. It took many years or even centuries for 
the cliffs that we look at today to be created. The rain water plays 
an important role in the creation of cliffs and this is caused by a phenomenon 
named corrosion. In simple words, after it rains, portions of water remain on 
top of the rocks causing them to break into very small-small pieces. As the 
time passes the influnce of corrosion may 
be visible to us.
  Another reason for the creation of cliffs is the wind. Even though it 
sounds strange, everyday rocks are facing the wind, which in many cases 
is very strong, especially in high altitudes, and by the same way like 
water acts helps the formation of cliffs.
  One last thing we shouldn't forget is the cause of seismic phenomena 
which may cause slip downs or cause greater break downs of rocks. 
Although this phenomenon has some affect the results are not the ones we 
got used to the idea of what a cliff is.

  I hope i answered your question, once again thank you for your 
questions and be careful on exploring those cliffs:)..

Vassilis Grigoriadis
Aristotle University of Thessaloniki
Greece

PS: the scientific sector researching the subjects of cliffs,lakes, etc 
is described by the term "Physical Geography". You may also find 
that "Geology" is into this subject.