Lightning from thunderstorm is normal but lightning from Volcano is quite an unusual natural phenomena. New electromagnetic wave technology now been introduced to understand the fact behind this reason as it helps to peer inside the ash plume.
Mainly lightning happens when positively and negatively charged particles are separated from each other in the atmosphere. When the charge separation is larger enough for overcoming the insulating properties of air between the positively and negatively charged particles then only the electricity will flow as bolts of lightning as it will neutralise the charge.
Thousands of lightning flashes have been observed from volcanic eruption the main reason for these are the charged particles which originate from the ash clouds may be the reason for volcanic lightning moving through the atmosphere. The reasons are much big enough behind these phenomena.
There are two different phase on which volcanic lightning happens first one is eruptive phase represents the intense lightning that forms immediately soon after the eruption near the crater. It happens due to the positively charged particles ejected from the volcano. The second is the plume phase lightning that is caused due to the ash plume which is located at the downwind of the crater.
So the above-mentioned reasons are the sole cause for volcanic lightning or in simple words to say lightning from volcano.