Concavity

A bright, cerulean glowing wave of energy shakes the ground briefly,  the earth seeming to open up by your command to swallow your enemies whole. Each creature in a 10-foot-radius square must make a Dexterity saving throw as the ground beneath their feet turns to quicksand. A creature becomes restrained in the sinkhole you've summoned, taking 3d8 slashing damage as the inorganic material swept into the sinkhole grinds against their body as the targets make their descent into the hole. A creature that saves takes half the damage and is not restrained. The ground from then on, for a minute, is difficult terrain. A creature, at the end of their turn, can remake the saving throw to free themselves from the sand. A creature made of inorganic material such as stone, crystal, or metal has disadvantage on this saving throw. If the ground is not flat, then this spell only makes the area difficult terrain and no one is restrained, as the ground cannot cave inward easily.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d8 for each slot level above 2nd.