K.I.3 The glacier as a system. Dynamic Equilibrium Positive and negative feedback

Inputs Throughputs Outputs Energy Transfers (moving ice) Energy (e.g. low Storage (warmer in summer) temperature) Processes (e.g. abrasion) Matter Matter (e.g. Snowfall, meltwater Avalanches direct evaporation from valley sides

Feedback effects Warming will trigger some processes which speed further warming, and other effects which mitigate it. The balance between these positive and negative feedbacks is a major cause of uncertainty in climate predictions. For example, as the diagram shows, decreasing ice cover will mean exposed land absorbs more heat and speeds warming further. (Positive Feedback 1) In contrast, for example, plants' CO2 intake is likely to increase as higher temperatures increase growth (Negative Feedback) 1 Light coloured ice reflects back the Sun’s energy efficiently. 2 Exposed land is darker coloured and absorbs more energy. 3 As the ice melts, more land is exposed. This absorbs more heat, melting more ice. 4 The altitude of the melting ice is reduced so it becomes harder for new ice to form.

Positive feedback 2 Glacier surge is a common phenomenon in Svalbard. Glacier surge is a sudden advance of the glacier where a large volume of ice is transported from a reservoir area down to the frontal part of the glacier, usually followed by a sudden and rapid advance of the glacier front. The active surge advance period usually lasts a few years, while the quiescent, up-building period is in the order of 100 year.

In a glacial cirque as this is enlarged from an initial hollow the capacity for storing accumulating ice grows and so erosion increases. Causing the rate of cirque growth to accelerate. (small scale, short term, low energy) Positive Feedback 3

If a glacier is in steady state (that is with a stationary snout) is affected by increased snowfall high up in the accumulation zone of the cirque then the ice volume will increase and the glacier will advance and the snout will move forward (perhaps creating a push moraine) Negative Feedback

Negative Feedback This is what happens when a glacier advances into a forest. This is on the eastern margin of the Taku Glacier, Juneau Alaska. As you can see, the trees didn't stand a chance against the power of the glacier. The glacier toppled and overrode these trees in the winter of 1992-93. Summer melting of the ice has exposed the debris. The ice is shown in the lower left.

Negative Feedback However, this will cause more of the glacier to lie in the ablation zone and so the output of meltwater will increase. In time the increased output of meltwater will come to equal the increased input of water via snowfall.

The glacier will return to a new steady state and the snout advance will stop ( leading to the build up of a terminal moraine landform in that position where the snout lies) Terminal and lateral moraine ridges, Kazakhstan. The glacier has retreated since it formed the ridges. Negative Feedback.