Until the spell ends, you control any ice inside an area you choose within range that can be as large as a cube 100 feet on a side. You choose one of the following three effects when you cast this spell. As an action on each of your turns thereafter, you can use the same effect or choose a different one. Any alterations made to the ice remain after the spell ends, but can be altered by other effects (temperature, seismic action, or another application of this spell, for example).
Crack. You cause ice in the area to crack and splinter. On level terrain, this effect turns the ice into difficult terrain, possibly producing other hazards, depending on the terrain and the nature of the ice—ice over a deep chasm might open onto a pit, while ice over water can break into individual floes, for example. Using this effect on cliffs, walls, or ceilings made of ice can cause collapse, dealing 4d10 bludgeoning damage to creatures in the area below the collapse, or half the damage with a successful Dexterity saving throw. After such a collapse, the area where the fallen ice collects becomes difficult terrain.
Reshape. You cause ice in a portion of the area to rapidly melt, move, and re-form into whatever shape you command. You can block holes, open tunnels, form bridges, remove difficult terrain, or otherwise alter the form of the ice in the area. You can cause ice to become slippery, making it difficult terrain, or dry to remove difficult terrain. You can fill a hole up to a 20-foot cube or create 20 feet (up to 20 feet wide) of a bridge across a chasm or raise a 20-foot-tall pillar of ice (up to 20 feet square). You can continue this action on consecutive rounds to increase the size of the affected area while you maintain concentration on the spell.
Thicken / Thin. You cause existing ice to increase or decrease in thickness, up to 1 inch per round over some or all of the total area, either making the surface stronger or creating thin ice that is hazardous to walk on.