What causes rolling thunder?
Rolling thunder can be due to the zigzag and often forked shape of a bolt, differences in air density along the mostly vertical lightning channel and soundwaves bouncing off clouds, mountainsides and other obstacles – a combination of sound dulled and distorted by distance as well as echoes.
"Rolling" thunder is the echo of thunder off of other storm cells in your vicinity. Lightning and thunder are more prevalent over land than over the ocean, because the sun heats land surfaces to higher temperatures, which leads to a more unstable airmass, which is the cause of thunderstorms.