Answer:
Above the equilibrium line, the glacier is in the accumulation zone where there is a net gain of ice mass. On the other hand, below the equilibrium line, the glacier is in the ablation zone where there is a net loss of ice mass due to melting and calving. As the glacier moves, it erodes the land around it in two ways: by plucking and abrasion. Plucking occurs when rocks get frozen to the base, sides, and back wall of the glacier, and the movement of the glacier pulls these frozen rocks away. Abrasion occurs when rocks trapped in the glacier rub against the valley floor, wearing it away like sandpaper.
Step-by-step explanation:
The glacier equilibrium line is the point of transition between the accumulation zone and the ablation zone. Above the equilibrium line, the rate of snowfall is greater than the rate of melting, so not all of the snow that falls each winter melts during the following summer, and the ice surface is always covered with snow. Therefore, the part of a glacier above the equilibrium line is where there is a net gain of ice mass. As snow gradually accumulates above the equilibrium line, it is compressed and turned into firn within which t,he snowflakes lose their delicate shapes and become granules. With more compression, the granules are pushed together and air is squeezed out. Eventually, the granules are “welded” together to create glacial ice .
Below the equilibrium line, the rate of melting is greater than the rate of snowfall, so there is a net loss of ice mass due to melting and calving. Therefore, the part of a glacier below the equilibrium line is where there is a net loss of ice mass . The position of the equilibrium line changes from year to year as a function of the balance between snow accumulation in the winter and snowmelt during the summer. More winter snow and less summer melting obviously favors the advance of the equilibrium line (and of the glacier’s leading edge), but of these two variables, it is the summer melt that matters most to a glacier’s budget .
The terminus of a glacier advances or retreats based on the location of the equilibrium line. If the rate of forward motion of the glacier is faster than the rate of ablation (melting), the leading edge of the glacier advances (moves forward). If the rate of forward motion is about the same as the rate of ablation, the leading edge remains stationary, and if the rate of forward motion is slower than the rate of ablation, the leading edge retreats (moves backward) .