GlaciationIce ages

Throughout the last million years, global climate has fluctuated between cold (glacial) and warm (interglacial) periods. Global temperature change between glacial and interglacial periods following a cycle of approximately 100 000 years. These cycles are called Milankovitch cycles.

About every 100 000 years, Jupiter and Saturn line up to pull the Earth into an orbit further away from the sun. Being further from the sun lowers temperatures and more ice develop at the poles. The light color of the ice reflects the sun’s energy away from the Earth, so temperatures lower further, creating more ice, and beginning an interglacial period.

When the planets line up to pull the Earth into an orbit closer to the sun, temperatures rise. This starts to melt the ice. The darker color on the Earth’s surface absorb the sun’s energy, so temperatures rise further, and an interglacial period begins.

Formation of a glacier Snow falls in high land. Temperatures are so cold that the snow doesn’t melt in the summer. The next winter’s snow falls on top, and the process repeats each year. The layer of each new layer of snow compresses previous year’s snow into ice, creating ice sheets. Ice from the ice sheets spills over into valleys forming glaciers, which slowly move downhill due to

gravity. Further down the valley, the temperature rises, and the glacier melts at the snout. In cold years there is more snow than melting(accumulation is greater than ablation), and the glacier

advances down the valley. In warm years, there is less snow falling than melting at the snout (ablation is smaller than

accumulation) and the glacier retreats up the valley.

Glacial erosion and weathering

Glacial landforms

Transportation and deposition

MoraineMoraine is material, which is transported and later deposited by a glacier. It is deposited when there is

a rise in the temperature. As the glacier begins to melt, it cannot carry as much material, and so deposition occurs. There are several types :

Lateral moraine : is derived from freeze thaw weathering of valley sides and which is carried at the side of a glacier.

Medial moraine : is found in the center of the glacier and results from two lateral moraines joining together.

Ground moraine : is material dragged underneath a glacier which, when deposited, form the flat valley floor. Ground moraine is also referred to as till or boulder clay.

Terminal moraine : marks the maximum advance of a glacier. It is deposited at the snout or end of a glacier. If a glacier remains stationary for a lengthy period of time then a sizeable amount of material, extending across the valley can build up.

Recessional moraine : form behind and parallel to the terminal moraine. They mark interruption in the retreat of a glacier when it remained stationary for long enough for further ridges to develop across the valley. Both terminal and recessional moraine can act as natural dams behind which ribbon lakes can form.

ErraticsGlaciers can transport material for many kilometers. Erratics are rocks and boulders carried by the ice

and deposited in an area of totally different rock.