Final answer:
Glaciers are snow and ice masses that flow due to their own weight when they reach a sizable thickness. They play a significant role in Earth's climate history, growing and shrinking in response to temperature and precipitation patterns.
Step-by-step explanation:
Glaciers are defined as snow/ice that deforms/flows under its own weight. They are dynamic systems that move due to their mass and the influence of gravity. Glaciers form when snowfall exceeds summer melting, creating a body of ice that can move if it reaches a sufficient size. In Glacier National Park, scientists use the guideline that a glacier must cover at least 0.1 km2 to be considered active. This size allows the ice to move, unless it is on a steep slope. Glaciation periods have occurred during different ice ages, shaping the Earth's surface significantly. Notable climatic episodes such as the Little Ice Age have induced growth in glacier size, which can be traced through geological features like moraines.