Why there is lightning when a volcano is erupting?

the charged particles of ash and dust rub into each other charging each other up... eventually enough static electricity charge builds up it releases passes through negatively charged particles... same thing in thunderstorms with air molecules and water vapor

As u know that when volcano erupts, the smoke will rise from volcano and smoke which rises from volcano is very warm and if the atmosphere around the volcano is cold then the smoke will rise rapidly and sometimes this smoke can reach to the upper part of troposphere and thus this will cause lightning