University College, southeast corner

Background
This is a good example of a 'cold corner'. In cold weather, corners of heated buildings are not as warm as the rest of the wall. Generally, for every square metre section of a wall exposed to the indoor warmth, there is a square metre exposed to the exterior cold. At corners, the area for heat gain from inside is much smaller than the area for heat loss. Thus, corners such as these are 'colder' than the rest of the wall.

In the diagrams below, the red line represents area of heat gain (interior wall) and the blue line represents areas of heat loss (exterior wall).

But there is more illustrated here. This corner of massive limestone forms a buttress which is exposed to heat loss or gain from the outside air on three sides. The environmental condition that led to the formation of the frost are the same as the conditions described in the Convocation Hall case.

So now with this information can you explain this pattern of frost formation?