In 1978 Ben and Jerry's Ice cream was founded in a small town in Vermont
called Burlington. Later the ice cream would spread to every major city in the
United States and to other locations throughout the world. What type of
cultural diffusion would this be considered?

nobody can learn anything from that map without seeing it. indeed, we must take your word for it that you even have a map.

sediment layers stop spreading when they reach a barrier or they run out of sedimentary material. lateral spreading is the movement of gently to steeply sloping, saturated soil deposits caused by earthquake-induced liquefaction. i hope this . : )