You create a 10-foot-tall, 20-foot-radius cylinder of destructive energy around a point you can see within range. The area is difficult terrain. When you cast the spell and as a bonus action on each of your turns, you can choose one of the following damage types: cold, fire, lightning, necrotic, or radiant. Each creature or object that is inside the cylinder when it’s created or ends its turn inside the cylinder takes 6d6 damage of the chosen type, or half the damage with a successful Constitution saving throw. A creature or object dropped to 0 hit points by the spell is reduced to fine ash. The cylinder’s radius expands by 20 feet at the start of each of your turns after the spell is cast. Any creatures or objects enveloped in the enlarged area are subject to its effects immediately.