The Clue Glacial cave formation
The Answer ICICLE
An icicle is a formation that occurs when water melts and then freezes again, often seen hanging from roofs or cliffs. These structures can form in glacial areas where temperatures fluctuate. As the ice melts during the day and refreezes at night, icicles can grow longer and more defined. This makes "icicle" a fitting answer for the clue about a glacial cave formation.