Final answer:
The equilibrium line altitude of a glacier moves up or down depending on whether the mass balance is positive or negative, with the resulting mass balance change affecting the glacier's volume and ELA. The glacier on land increases lake water level more upon melting, as opposed to the floating iceberg. Increased pressure at the glacier base can also cause melting, affecting glacier movement and the ELA.
Step-by-step explanation:
The position of the equilibrium line altitude (ELA) of a glacier is sensitive to changes in mass balance, which in turn is affected by climate conditions such as temperature and snowfall. As the mass balance becomes more positive, meaning there is more snow accumulation than melting and evaporation (ablation), the ELA moves upward on the glacier because the area where accumulation and ablation are equal increases in altitude. Conversely, if the mass balance becomes negative, with more ablation than accumulation, the ELA will move downward as the altitude at which these two are in balance decreases.
Regarding the question about which ice chunk would cause the greatest increase in the level of the lake water if both melt, the glacier sitting on land would cause a greater increase. This is because the iceberg already displaces water equal to its mass according to Archimedes' principle, making its melting effect on water level less significant compared to the melting glacier that adds new water to the lake.
The previous explanation about pressure affecting the melting point of ice also correlates with the dynamics of glaciers and their movements. Increased pressure at the base of a glacier can cause melting, creating a slippery layer that facilitates the glacier's slide over the ground, moving the ELA in response to changing mass balances.