The Squirm was located on Ice Henge.
The Squirm consisted of giant pillars of ice. These pillars would move, tilting in a series of thrusts and twists that mimicked the closing of jaws and the grinding of teeth. The pillars would smash into each other with booming explosions, shards of ice splitting off, new cracks forming in the ice. This continual movement would block and unblock the way through the channel.
When they arrived at the island of Ice Henge and found the bay in the cliffs, the Jerle Shannara crew journeyed down the channel and found the Squirm.