The highest temperature in a channel of thunder is achieved on the position where electric current enters the metal surface, that is, on the bottom of the channel. Because of that on these places the surface is melted, but that is so small that the diameter of these melted parts of surface isn't greater than 5-20 mm. That's why these holes are hard to find in nature or any other place that isn't specially observed. That is explained by the fact that the major part of the energy that the lightning produces is dispersed through surroundings by radiation or pressure, and only smaller part of that energy is spent on heating and melting of the metal surface. That expense of energy on the surface for middle sized lightning is around 150 Ws, and for larger lightning up to 7000 Ws. You can expect that strong lightning can burn through steel plate 0.5 mm thick and make a hole about 20 mm in diameter.

This thermal effect of lightning (melting of material, surface or conductor) causes high pressures that can be the source of mechanical destruction, especially if these conductors, through which electricity flows, are in the walls of buildings. Eventual fires and explosions can be explained as a consequence of sparks made by metal parts on the places of input or output of electricity, or the overheating on the places where the lightning meets a high transient resistance due to bad contact or other reasons.

Very often the flow of lightning after the hit continues through the earth. Because lightning produces heat, after the contact with the ground we can find burnt sand in a shape of a flower. Those are so called fulurities.