Final answer:
A terminal moraine marks the outermost limit of glacial advance. This feature is formed from glacial till deposited at the furthest extent of a glacier's reach, as can be observed from past glaciations in places like Glacier National Park.
Step-by-step explanation:
The ridge of till that marks the outermost limit of glacial advance is called a terminal moraine. During the periods of glaciation, such as the most recent one that ended about 12,000 years ago, vast ice sheets covered significant portions of the Earth's surface. As glaciers advance and retreat, they deposit glacial till consisting of soil and rocks at their margins. The accumulated till at the furthest point of glacial advance forms an elongated mound, which is the terminal moraine. Glacier National Park (GNP) is a testament to these processes, as evidenced by its numerous moraines and historically larger glacial sizes, especially during the Little Ice Age (LIA). While glacial activity has greatly reduced since then, these moraines remain, providing scientists with clear indications of past glacial extents.