High current lightning strikes into earthing systems \ud can result in ionization in the soil surrounding the earthing electrode. Most of the published studies investigating this phenomenon have assumed uniform one-layer soil, but soil ionization propagation in a multilayered soil sample has not \ud been extensively addressed. Practical soils may consist of several layers with different water contents, and hence soil resistivity will vary continuously with depth. This investigation considers several sand samples, consisting of two layers with different \ud water contents subjected to standard lightning impulse voltages. A rod-plane electrode configuration was constructed inside a cylindrical plastic test rig, in order to house both wet and dry soil test samples. In order to quantify the propagation of ionization inside the test sample, voltage probes were installed \ud along the tube at specific positions. Localized changes in the ionization zone potential could, therefore, be monitored in real time.