Ice Melting: How Icicles Form

Snowfall during the winter months can create many beautiful wintery scenes, as well as problematic situations and ice melting to form icicles is just one of these. As picturesque as icicles can be, it can also prompt curiosity into how they are formed, but also why they form on in specific locations or on certain structures.


Specific weather conditions are required in order for icicles to form and the main component for this is that snow has settled. This usually occurs when the temperature is at freezing level. Icicles are more likely to form on days where the sun is shining despite the freezing temperature, and on areas that are exposed to sunlight.

As well as mother-nature, human action can also cause icicles to form due to the way we heat out homes. When it is freezing outside, we are more likely to protect ourselves from the cold by heating our homes. Even without a specific heat source in the attic of a house, heat can rise from the rest of the property to melt the snow and ice on the roof to such an extent that water runs away.

You are likely to find that icicles will form on the same structures and in the same places every winter as the heat source and position of the sunlight will remain the same.

Watery Beginnings

Surfaces that are in the direct path of sunlight are likely to be where icicles form as the sun will melt the snow and ice and cause the resulting water to drip down the nearest edge. Water that trickles down is capable of refreezing in the air and, where a significant amount of water trickles down, a column of ice will form and an icicle is born. Further, the position of the icicle will usually fall out of the path of the direct sunlight which will leave it susceptible to the cold air and allow it to refreeze.  

How Icicles Grow  

The icicle will increase in size as more water drips down the sides, freezing in the air and adding to the existing icicle. Despite the freezing temperature required for icicles to form, the water from the melted snow and ice releases a tiny amount of heat as it drips down. This heat acts as an insulator that controls the manner in which the icicle grows and controls its familiar shape. The insulation provided by the dripping water reduces the growth of the top of the icicle while allowing the tip to continue to grow.

Icicles that form on buildings can be isolated and form without support so they will only be able to get to a certain size before they break under their own weight. Allowing icicles to continue to grow can cause damage to the guttering as the water will expand as it refreezes, forcing the surrounding property to accommodate it. The roof can also be damaged as icicles can obstruct the water from running off the roof as it normally would which can cause it to back up and leak into the building.