(i) This is freeze-thaw action, which is a type of mechanical weathering.

(ii) Freeze thaw action is the breaking up of rocks by frost.
It occurs in upland areas, e.g. Wicklow mountains.
During the day, water collects in cracks in the rocks.
At night the temperature drops and the water freezes and expands.
This causes cracks to develop in the rock.
The process of freezing and thawing continues and eventually pieces of rock break off and fall down the mountain under the influence of gravity.
This loose rock that collects at the foot of the mountain is called scree.