A covalent compound is formed when an element shares its valence electron with another element. This bond is formed between two non metals. Example:
An ionic compound is formed when one element completely transfers its valence electron to another element. The element which donates the electron is known as electropositive element and the element which accepts the electrons is known as electronegative element. This bond is formed between a metal and an non-metal. Example:
Thus an ionic compound is typically made of a metal and a nonmetal.
The pressure from the weight of the glacier generates a layer of water that helps the ice glacier move downslope. This process is called basal sliding. Also, the glacier begins to move under its own weight. The glacier is so heavy and exerts so much pressure that the firn and snow melt without any increase in temperature.