Erosion
One of the most common ways cliffs are created is through erosion and weathering. When a rock face is subjected to moving water, the water gradually wears the face of the rock, and shapes it to conform to the movements of the water. When rocks line a flowing river or the sea, the flowing water or waves gradually wear away at the rock, cutting into the earth, creating a cliff. Rocky areas which receive heavy rainfall are likely to produce cliffs as the water flows to lower elevation. Water erosion is the often the cause of deep narrow fissures; the Grand Canyon is an example of cliffs created by the erosion of flowing water.
The Iceage
Another way cliffs can form is through the movement of glaciers. During the last ice age, significant portions of the settled world were covered in massive glaciers -- piles of snow and ice which can be many thousands of feet thick. Similar to water, the crushing weight of glaciers can cause them to move down slowly over time. As a glacier moves its weight can grind stone, and carve out cliff faces between areas of higher elevation. When global temperatures increased, causing the glaciers to melt, many areas of the world formerly covered by glaciers were left rough and hilly, with many rocky outcroppings and cliffs.
Geological Events
Geological events can also cause cliffs to form. The tectonic plates of the earth shift gradually over time, and when they come in contact with one another, they can push each other upwards creating mountains and cliffs. Earthquakes and landslides can also cause the sudden formation of cliffs. Hot spots in the Earth's mantle, a layer of molten rock deep under the earths crust, can cause magma to seep up to the surface, creating volcanoes and new land formation, which can lead to the formation of cliffs.
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