I am adding a new area to my game (a free-roam RPG): the ashlands. I put a small volcano (only about 15ft wide and long, and about 20ft tall. Really, more of a lava vent) on the western edge and have the wind coming in from the west (so that the ash is being blown all over the actual ashlands. Then I realized it: there was nothing stopping the ash from covering the rest of the island. So, toward the eastern edge, I put some tall hills (about 30ft high, the height of the ash cloud coming out of the volcano).

Question: realistically, would his be enough to catch at least *most* of the ash, or would higher hills be required?

(If an answer needs a man-made approach...)

Note that the society is on medieval tech, some magic, and is on an island that is a mix between cold, forest, and tagia. Caves, mines, and workers are plentiful, but wizards and of the sort are far and few between. Magic is cast from rare crystals found in the mines. Force fields and things can be used.

EDIT: the volcano is of a circular shape with a thin, flat edge on the tip rim, with a steep slope leading to it's. Deep inside (down about 50 ft) is a pool of magma (the volcano is not very active, maybe a small eruption every few hundred years).