Lesson 5 glacial features

Types of glacial erosion and the fundamental elements of landform creation

1. Glacial Processes and Landforms Lower Sixth

2. In this lecture We will investigate the factors that impact upon glacial erosion rates Appreciate the size and scale and variety of different landforms in highland glaciation Examine the landscapes formed by glacial scouring Begin to investigate the landforms and landscapes of glacial deposition

3. The factors affecting the rates of Glacial Erosion Consider these and in pairs try to think why these might affect the rates of glacial erosion

4. From these factors we can make several assumptions Explain why erosion rates tend to be higher in warm based glaciers because (4) Explain why slope gradient and angle can have a large influence on erosion (4) Explain why Alpine glaciers tend to move faster due to rates of ablation (4) Remember: All of the 6 factors can play a role and they work at different rates on different glaciers Can you rank the 6 factors as to which is the most important and be ready to explain why Explain the conditions needed for high rates of glacial erosion (6)

5. Glacier landforms and landscapes Glaciers we know alter landscapes The landforms they create vary in scale

6. The 4 glacial processes

7. Complexity Present day landforms can exist from several glacial periods and not just the last one They are the product of many successive advances during ice-house conditions and retreats during green-house conditions These are known as polycyclic or polygenetic

8. The glacial features! – Macro-scale All the macro features listed here need to be known, explained and identified by picture or map. MACRO FEATURES – All above 1km or greater in size Cirque / Corrie/ cwn Truncated Spur Arête Hanging Valley Pyramidal Peak Trough (U-shaped Valley)

9. Cirque / Corrie/ cwn These words refer to the same thing There are three stages to their creation

10. Description: Is an amphitheatre-like valley formed by glacial erosion Explanation: The process of nivation creates and enlarges a hollow (This is a positive feedback) The headwall is steepened by freeze-thaw and plucking The hollow is deepened by glacial abrasion

11. Using the maps provided

12. Arête Description: Is a sharp knife like ridge that separates two cirques on a mountain. Explanation: They are formed when two corries are created back to back

13. Pyramidal Peak Description: These form when three or more cirques erode a mountain Explanation: They form as a corrie forms but this is when 3 appear back to back On a map you need to find 3 Cirques that meet

14. In Welsh a Cirque is called a ‘cwm’

15. Truncated Spur Description: These were spurs from the pre-glacial meandering of a river. Explanation: The spurs have been gradually cut away (‘truncated’) by the glacier as it moves down the valley because glaciers can not easily move around obstacles like a river and so cut through.

16. Locating on a map First you’ll need to identify a U shaped valley and then ‘scree’ like black markings parallel to the sides of the valley should help indicate truncated spurs

17. U Shaped Valley Description: Deep sided steep valleys that are generally U shaped with a misfit stream found at the bottom Explanation: These occur where the glacier has carved through a mountain valley, straightening, widening and deepening it as it goes Glacial troughs often have ribbon lakes within them such as Windermere in the Lake District

18. Hanging Valleys Description: Where a smaller tributary glacier joins a larger glacier, leaving a steep drop that often contains a waterfall as the valley ‘hangs’ above the other valley Explanation: Occur where the main glacier has eroded a trough deeper and wider than smaller glaciers joining it. Little Langdale off great Langdale is a good example of this

19. Ribbon Lakes Description: Long narrow which can form along the base of glacial troughs Explanation: Glacier erodes softer rock at the bottom of the glacial trough and can be dammed by moraine material at one end then as ice melts it creates a lake that dependant on geology will remain or disappear over time

20. Meso-scale Features Meso features are mainly found within a macro feature good examples of these are found in Yosemite National Park and include Whalebacks Roches Moutonnées Crag and Tail Meso features are between 10m and 1km in length

21. Whalebacks Description: These are streamlined bedrock feature. Explanation: where a glacier moves over resistant bedrock (rocky knoll) and abrading it on all sides causing it to be smoothed and rounded on all sides The shape becomes blunted at the up glacier side and tapers on the down glacier side Whalebacks do not have a steep ‘plucked’ side OFTEN REFERRED TO A STREAMLINED HILLS

22. Roches Moutonnées Description: Smooth shaped rocky knoll with one steeped side which is rough and plucked. Explanation: Formed by plucking and abrasion. The abrasion smooths the up glacier side called the ‘STOSS’ side whilst plucking and freeze thaw has made the ‘LEE’ side more jagged and craggy. They can often form in groups

23. Crag and Tail Description: A landform consisting of a rock hill and tapering ridge which is produced by selective erosion and deposition beneath an ice sheet. Explanation: The hill, or crag, is usually of strong rock that has resisted glacial erosion and forms an obstruction to the ice producing a `pressure shadow´ in its lee. The softer rock on the lee side is eroded more and also subglacial material is deposited helping to form a ‘tail’

24. Knock and Lochan Description: A scoured rugged landscape of rocks (knocks)and lakes (lochan) Explanation: When a glacier expands out of a confined mountain valley they can erode large areas of lower landscape (Areal scouring – area scouring) Higher areas of resistant rock (knocks) are eroded at a slower rate than the softer rock and therefore a relief of rocks and lakes are formed. (named after NW area of Scotland)

25. Micro-Scale Features These are a few metres or less in size Striations Chatter marks Crescentic Gouges Striations are scratches in the bedrock caused by the ice dragging debris across the surface

26. Striations Description: Long thin scratches on the visible rock Explanation: Formed as glacial debris is dragged along the surface by the ice (abrasion). They therefore orientate parallel to the direction of ice flow, usually only a few mm deep but can vary in length

27. Chatter Marks Description: Are irregular chips and fractures in the rock Explanation: Small chips, gouges and fractures appear in hard rock when glacial debris is intermittent rather than continuous

28. Crescentic Gouges Description: More regular patterned gouges and usually concave up glacier Explanation: Crescentic gouges form when blocks are pushed down with great force by ice into the underlying brittle rock surface, creating a conical fracture.

29. The importance of Micro features They help glaciologists understand the directions of movement of ice and where it came from ( Provenance ) But also in determining the maximum altitude of glacial erosion Where there are no meso features we can see the extent of where glacial erosion occurred