What causes the snout of a glacier to advance?

The advancement of a glacier's snout is primarily influenced by accumulation. Accumulation refers to the process where snow and ice build up at the glacier's upper parts. When winter snowfall exceeds summer melt, the glacier gains mass, leading to an increase in pressure that forces the glacier to flow downward and outward. This movement is a response to gravity, and as the glacier moves, the snout—the front end of the glacier—advances forward.

In contrast, melting, subduction, and evaporation do not contribute to glacier advancement in the same way. Melting typically occurs when temperatures rise above freezing, resulting in the loss of ice, which can lead to the retreat of the glacier. Subduction is a geological process related to tectonic plate movement, which does not directly affect glacier dynamics. Evaporation involves the transition of water from liquid to vapor, leading to a loss of water rather than contributing to the mass of the glacier. Thus, accumulation is the key process driving the advancement of a glacier's snout.