Field of Everice (4e Hazard)
From D&D Wiki
The area around a portal to the Elemental Chaos can become imbued with magic, sometimes manifesting itself as everice. The place appears normal to all but the most knowledgeable observer.
A field of everice is usually 20 contiguous squares. A successful perception check (DC 33) reveals the faintest shimmer in across the ground, but a successful arcana check (DC 24) is required to identify it as everice. When a living creature enters the area, the hazard is triggered and it attacks, chunks of ice erupting around the creature.