Late Pleistocene and Holocene glaciation of the Fish Lake valley
Glaciation in the Nant Ffrancon Valley
description
Transcript of Glaciation in the Nant Ffrancon Valley
![Page 1: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/1.jpg)
13.08.03 R Chambers 1
Features of Glacial Erosion
The Nant Ffrancon Valley, Snowdonia
![Page 2: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/2.jpg)
13.08.03 R Chambers 2
Hanging Valley – a small tributary valley high above the floor of the Nant Ffrancon valley trough.
![Page 3: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/3.jpg)
13.08.03 R Chambers 3
There are a number of hanging valleys on the NE slopes where the Nant Ffrancon valley itself was eroded more deeply
as ice flowed in from a number of sources.
![Page 4: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/4.jpg)
13.08.03 R Chambers 4
Truncated spur – steep/rocky section of the
trough where the pre-glacial interlocking spurs of the
river valley have been eroded by a powerful glacier.
![Page 5: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/5.jpg)
13.08.03 R Chambers 5
Roche Moutonnée – asymmetrical outcrop of resistant rock – smoothed and steepened by glacial erosion.
![Page 6: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/6.jpg)
13.08.03 R Chambers 6
The up-valley side has been smoothed by
abrasion as the increased
pressure causes melting and
basal sliding.
![Page 7: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/7.jpg)
13.08.03 R Chambers 7
The leeward side is a jagged steep slope formed by plucking of pre-weakened
bedrock.
As the ice flowed over it, the pressure was reduced and re-freezing occurred
resulting in plucking along joints and bedding planes.
![Page 8: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/8.jpg)
13.08.03 R Chambers 8
![Page 9: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/9.jpg)
13.08.03 R Chambers 9
Ribbon Lake - Llyn Ogwen, Snowdonia
This occupies an area of the trough
floor that was over deepened by
extending and compressing flow.
![Page 10: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/10.jpg)
13.08.03 R Chambers 10
Striations – these grooves on the exposed rock of the Roche moutonnée were created by abrasion caused by debris
embedded in the base of the glacier.
![Page 11: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/11.jpg)
13.08.03 R Chambers 11
U-shaped valley (trough)
The Nant Ffrancon Valley
The once u-shaped valley has been distorted by moraine deposits and a collection of scree from weathering and mass
movement.
![Page 12: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/12.jpg)
13.08.03 R Chambers 12
This armchair shaped hollow situated on the hillside above the Nant Ffrancon valley is a pre-glacial hollow. It was formed due to
enlargement by plucking and abrasion as ice moved in a rotational manner under gravity. Ice from here then fed the Nant Ffrancon valley
below.
Cwm Idwal - Corrie
![Page 13: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/13.jpg)
13.08.03 R Chambers 13
Steep, frost shattered back walls, subjected to plucking
during glaciation
![Page 14: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/14.jpg)
13.08.03 R Chambers 14
![Page 15: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/15.jpg)
13.08.03 R Chambers 15
Diffluent col – area cut by ice spreading out over a col from its valley into an adjoining one.
Here marks the point where the headwall was breached by ice flowing in from the Llandberis valley to the Nant Ffrancon valley.
![Page 16: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/16.jpg)
13.08.03 R Chambers 16
Arête - a knife shaped ridge between two corries.
![Page 17: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/17.jpg)
13.08.03 R Chambers 17
Arêtes – are formed as two corries are enlarged back to back. As this happens the ridge between them narrows.
![Page 18: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/18.jpg)
13.08.03 R Chambers 18
Mount Snowdon
Pyramidal Peak - formed where three or more corries intersect back to back, forming a sharp, pointed hilltop
between them
![Page 19: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/19.jpg)
13.08.03 R Chambers 19
- small tributary valley above the floor of the main valley (due to differential erosion) (e.g. Cwm Dyli, N Wales)
- steep-sided valley with flat-floor (e.g. Nant Ffrancon, N Wales)
- steep, rocky section of the side of a trough where the tips of pre-glacial interlocking spurs have been removed by glacial erosion (nr trough end in Nant Ffrancon Valley)
- resistant rock outcrop with gentle sloping smooth up-valley side and jagged lee-ward side. (e.g. in Nant Ffrancon Valley, N Wales)
Hanging Valley
U-shaped valley
(trough)
Truncated spur
Roche Moutonnée
![Page 20: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/20.jpg)
13.08.03 R Chambers 20
- grooves on rock created by abrasion due to debris embedded in base of glacier
- Sharp, pointed hilltop between three or more corries (e.g. Snowdon, N Wales)
- large armchair shaped hollow enlarged as ice moves in a rotational movement under gravity (e.g. Cwm Idwal, Glaslyn, North Wales)
- Knife shaped ridge between two corries (e.g. Grib Goch, N Wales)
Striations
Corrie (Cirque)
Arête
Pyramidal Peak
Ribbon Lake- long narrow lake occupying an area of the trough floor which has been overdeepened (e.g. Llyn Ogwen, Snowdonia)
![Page 21: Glaciation in the Nant Ffrancon Valley](https://reader036.fdocuments.in/reader036/viewer/2022062704/555886abd8b42aad358b4df0/html5/thumbnails/21.jpg)
13.08.03 R Chambers 21
Diffluent Col- a low pass at a valley side cut by ice spreading out over a col from its valley into an adjoining one.