Answer:
Melting and Re-freezing
Step-by-step explanation:
Both ice and snow are basically frozen water however the difference lies in their composition. Snow is regular shaped crystal form while ice is solidified sheet of ice.
When the temperature has fallen below 32 degree Fahrenheit, the vapor in air converts to snow and falls on earth. The different shapes of snowflakes depend on the freezing temperature. For example at temperature below 30 degrees, snowflakes are thin, hexagonal plates while at temperature lower that 25 degrees the snowflakes are needle shaped.
When snow lands on the earth, they remain in their crystal form and starts depositing layer by layer. However, these snowflakes melt partially and then get refrozen due to which space between the crystals is filled with water. This process of deposition continues till ice is forms.