You cause three parallel lines of thick, flared obsidian spikes to erupt from the ground. They appear within range on a solid surface, last for the duration, and provide three‐quarters cover to creatures behind them. You can make lines (up to 60 feet long, 10 feet high, and 5 feet thick) or form a circle (20 feet in diameter, up to 15 feet high and 5 feet thick). When the lines appear, each creature in their area must make a Dexterity saving throw. Creatures takes 8d8 slashing damage, or half as much damage on a successful save. A creature can move through the lines at the risk of cutting itself on the exposed edges. For every 1 foot a creature moves through the lines, it must spend 4 feet of movement. Furthermore, the first time a creature enters the lines on a turn or ends its turn there, the creature must make a Dexterity saving throw. It takes 8d8 slashing damage on a failure, or half as much damage on a success. When you stop concentrating on the spell, you can cause the obsidian spikes to explode, dealing 5d8 slashing damage to any creature within 15 feet, or half as much damage on a successful Dexterity save.