Study Guide Chapter What is a glacier? 2.Distinguish between alpine and continental glaciation. 3.Explain how a glacier moves. Explain how a crevass is formed. 4.Use a longitudinal profile of a glacier to diagram the zone of accumulation, the zone of ablation, the firn line, the bergschrund of a glacier, snout or terminus, firn, snow and glacial ice. 5.Explain the formation of erosional features: glacial striations, a cirque, a horn, a tarn, a "U" shaped glacial valley, hanging valley. 6.Explain the formation of depositional features: terminal moraines, lateral moraines, end moraines, outwash plain, till, loess, braided streams, kettle lakes and glacial erratics. 7.Where is most of the world's glacial ice located? 8.When was the most recent "ice age" and what is it called.

Glacial Systems and Landforms Glaciers are moving masses of ice. Form when more snow occurs during the year than melts over an extended time. Alpine glaciers Continental Ice Sheets

Glaciers Most of the world’s ice (14,000 feet thick) is located in Antarctica It is a remnant of our last ice age or Pleistocene Epoch. Major advances and retreats of ice sheets began 2.4 million years ago to about 9,000 years ago. North America and Eurasia covered in ice.

Glaciers Zone of accumulation- Where snowfall exceeds ablation (melting, evaporation, sublimation). Upper portion of glacier. Zone of ablation- Lower portion of glacier. Ablation exceeds snowfall. Movement is helped by melt water and gravity. Glaciers can move a few inches a day or a hundred feet.

Glaciers Down slope movement is seen in the development of a great crack or crevasse. This crack is known as a bergschrund. It shows the ice mass pulling away from the confining rock walls. Snout/terminus- End of the glacier.

Fig. 19-6, p. 540

crevass

Erosional Features Glacial striations- –Caused by dragging or rock fragments along their undersides of glaciers. –The striations (gouges, grooves, and scratches) are evidence of previous glaciation. –Striations indicate the direction of flow long after the glacier has disappeared.

Erosional Features Cirque- Erode backwards- undercutting of rock walls above ice level. A broad amphitheater hollowed out at the head of a glacial valley. Tarn- If a lake forms in the cirque depression after the ice melts. Horn- Where three or more cirques meet at a mountain summit.

Erosional Features U shaped Valleys. Example is Yosemite Valley Main glacier versus tributary glacier Hanging valley

Fig a, p. 547

Fig b, p. 547

Fig c, p. 547

Depositional Features Till- Unsorted drift (rock) laid down by ice. Glaciers deposit a portion of their load when their capacity is reduced. Glacial deposits called moraines occur along the margins of glaciers.

Moraines Lateral Moraines- Ridgelike deposits laid down along the side margins. End Moraines- Located at the snout of a glacier, all the debris carried forward glacier. Terminal Moraine- End moraines marking the farthest advance of the snout.

Lateral moraine End moraine

Depositional Features Beyond the belts of hills that are the terminal moraines lie the outwash plains. Kettle lakes- Found in outwash plains, till plains, and moraines. Formed when blocks of ice became detached from the glacial terminus and were buried. When ice melted holes remained.

Erosional Features Scattered in and on the surface of glacial drift may be boulders that differ from local bedrock. These rocks are known as erratics. Illinois source region from Canada. Braided stream- Stream channel with multiple subchannels that form a braided pattern flowing through alluvial deposits.

p. 552

Braided stream

C4 H-4 H-5 G-2 IDENTIFY AND DEFINE