Why do volcanic eruptions cause thunder and lightning?

To put it simply: volcanic ash carries a large amount of charge, which interacts with the charge of cloud bands in the sky. Some specific terms: The cause of lightning is generally considered to be the accumulation of electric charge by various particles in the clouds due to collision and friction. When the amount of electric charge reaches a certain level, it is equivalent to the voltage between the clouds or between the clouds and the earth reaching or exceeding a certain level. At a specific value, discharge will occur because the local electric field strength reaches or exceeds the electrical breakdown strength of air under the prevailing conditions. The electricity in the air rapidly heats and expands the air through discharge. Due to the expansion, it is compressed into plasma, and then thunder (the sound of shock wave), a special component of lightning, is produced.