A blue ice field has formed within the caldera of Mount Moulton behind the Prahl Crags, and contains ice almost 500,000 years old. It is the oldest dated ice in West Antarctica and much older than ice found elsewhere in West Antarctic ice cores. Such blue ice fields like those found at Mount Moulton form when glaciers run into an obstacle - in this case the Prahl Crags - and part of the ice starts moving vertically as it undergoes ablation processes like sublimation. In the case of Mount Moulton, this outcrop of ice is about long. The ice has been used to reconstruct past climate states in West Antarctica, including the beginning and end of the last interglacial, and shows evidence that the West Antarctic Ice Sheet collapsed during that interglacial.