Melting Giants – Glacier ice and equilibrium lines
Our glaciers are melting. But how do glaciers function, and what constitutes a glacier being out of balance? Read on to find out how long it takes for new glacier ice to form and what a dying glacier looks like.
Glacier ice:
New ice forms when more snow accumulates in one place over several years than melts during the summer months. Over time, the snow becomes increasingly compressed by its own weight. The time it takes for glacial ice to form depends on the climate. This process can take anywhere from five years to several decades. Therefore, the survival of a glacier depends on regions where snow remains for many years over summer. This brings us to the topic of the “equilibrium line”.
Cracks in the ice
Equilibrium line
A (theoretical) line on the glacier at which accumulation and ablation (the loss of ice) are in balance. When the glacier is in balance, the areas of the accumulation and the ablation zones are roughly in a 2:1 ratio. That means that about two thirds of the glacier is still covered with snow, while only one third of the ice giant is snow free. In the upper part, that is still covered with snow, new glacier ice can form (accumulation zone). In the lower part, the ice is melting (ablation zone).
I have marked where the equilibrium line would be located approximately. However, as you can see, almost all the snow on the glacier has disappeared. This glacier is clearly out of balance. It cannot sustain its current size because more ice is melting than new ice can form.
It has now become the norm for most glaciers in the Alps to be almost snow-free by the end of summer. As mentioned above, a glacier is in equilibrium when about two thirds of the ice is covered with snow. That is clearly not the case.
A satellite image of Hintereisferner from summer 2024. It is clearly visible that the glacier is free of snow in many places. Only the uppermost part is still partially covered by snow. This means that new ice can only form there.
Mass balance
This is a year-by-year measure of the health of a glacier, reflecting the balance between accumulation and ablation. If a glacier has a positive mass balance in a given year, it gained more mass through accumulation than was lost through ablation. The reverse is true for a negative mass balance.
A scientist taking measurements for the mass balance of a glacier during summer.
Dead ice
By definition, a glacier is a body of ice that moves downhill. In other words, the ice flows. Once a glacier has melted so much that the ice becomes stagnant and stops moving, it is called dead ice. By the way, glaciers move at speeds ranging from a few metres up to a few kilometres per year. The flow speed is determined by the slope inclination, ice mass and temperature.