Fig. 2

Volcanic field boundary options, solid lines represent buffered boundaries, dashed lines represent minimum fitted shapes (see text for shape definitions), North is up. Harrat Rahat: convex hull (a), ellipse (b), rectangle (c), isocontour (d), anisocontour (e), red shaded area represents the extent of Al-Madinah city (Fig. 6a). Auckland Volcanic field: convex hull (f), ellipse (g), rectangle (h), isocontour (i), anisocontour (j)