case study - Snowdonia

• where is snowdonia?


  - Northwest Wales, Uk

  - a landscape shaped by the action of valley glaciers

  - located in the Eyri National Park
• what are the glacial landforms in Snowdonia a product of?

  glacial events through the Quaternary period

  
  

  series of glacials and interglacials
• where and when was ice at its furthest extent in the British Isles?

  20,000 years ago in the Devensian glacial
• how was Wales affected by the glacier?

  - ice sheet across most of Wales and Midlands

  - north Wales at this time was affected by an ice cap with glaciers flowing out along pre-existing river valleys

  - looked similar to Antarctica with exposed nunataks
• what happened when temps rose?

  - the ice sheet melted and valley glaciers would have been fed by smaller corrie glaciers
• what geology makes up the area?

  - Ordovician age (480-443 million years ago)

  - mixture of volcanic rocks, sediments and intrusive igneous rocks

  - hard rock geology, decreased erosion

  - upland area
• describe how the geology has been changed to make what we see today?

  - origins going back 500mill years where the area experienced volcanic activity, folding & sedimentary deposition

  - similar to Himalayas

  - subsequent submergence and more recent activity have resulted in a much lower landscape

  - remnants of what were once much higher mountains have been eroded into what we see today
• what were the erosional impacts on the landscape?

  - easiest path for snowdonia ice was to follow routes previously cut by rivers

  - the Nant Ffrancon u-shaped valley was outlet valley from the Migneint ice sheet moving NW towards Anglesey

  - classic erosion features associated = Roche mountonnee, drumlins

  - ice entered in 3 directions adding significant amounts of ice cutting a rock step (100m), increasing erosion
• what features can be found on the Nant Ffrancon Glacial Trough?

  classic glacial trough

  - straight, flat bottom, steep sides, parabolic in shape

  - direction of ice movement

  
  

  ribbon lake

  - once filled the floor of the valley

  - over time has filled with sediments leaving a flat valley floor

  - there is a misfit stream in its place
• how were the truncated spurs here formed?

  - as the ice forced a straight efficient path to the Irish Sea through the Nant Ffrancon it created truncated spurs

  
  

  - these are the remnants of the interlocking spurs of the pre-existing river valley which were cut off by the advancing ice.
• why were hanging valleys created?

  - along the western side of the valley, smaller glaciers didn't cut the old upper courses of rivers as deeply as the main glacier creating hanging valleys
• what erosional features are found in the Nant Ffrancon valley?

  roche moutonnée

  corrie

  llyn idwal

  ribbon lake

  pyramidal peaks

  arête
• how were Roche moutonnee formed?

  - on the valley floor is a protrusion of a hard volcanic dyke

  - as the glacier moved over it is smoothed the up-glacier (stoss) side by abrasion

  - plucked the down glacier (lee) side, creating a Roche moutonnee
• how were corrie (cwm idwal) formed?

  - very deep, area above was low enough to allow ice to spill over from the Llanberis Pass - greater ice leading to greater erosion

  - learn in shape
• describe Llyn Idwal?


  - it is 10m at its maximum but has an average depth of 3m

  - its mouth is dammed by a terminal moraine

  - terminal, lateral and hummocky moraines found
• how were ribbon lakes formed?

  - occurred due to softer rock being preferentially eroded and potentially by compression flow, then once the ice melted filled the depression
• examples of aretes of pyramidal peaks?

  crib Gogh (arête)

  Mt Snowdon (pp)
• what was the depositional impact of glaciation on the landscape?

  till & moraines

  - 3 types in cwm idwal

  - formed as material deposited at the end of the glacier which flowed down from this corrie above the u-shaped valley

  - as glaciers which originated in northern snowdonia travelled N and NW they made their way out towards Irish sea

  - deposited large amounts of till across the landscape
• describe drumlins in Snowdonia

  - several drumlins throughout the Conwy valley

  - deposited under a large glacier flowing down from the mountains of North Wales
• describe eskers in Snowdonia

  - lowland feature at Pentir

  - as the channel was contained within the ice tunnel, sediments built up on the floor of the channel and were left as a raised feature when the ice melted

  - at Pentir the esker is about 400m long and 5-10m high
• what are the changes in the landscape over time?

  periglacial processes

  fluvial erosion

  weathering

  sediment
• how have periglacial processes changed the landscape over time?

  - even after the ice melted the temps would have been cold enough for much of the land to remain frozen as permafrost and periglacial processes would have operated (still do)

  - forming for example stone stripes and creating patterned ground
• how has fluvial erosion changed the landscape over time?

  - streams from hanging valleys are actively eroded vertically back into the hanging valleys creating gorges
• how has weathering changed the landscape over time?

  - in the winter, temps regularly fall below freezing at night and rise in the day - resulting in freeze-thaw cycles which have created blockfields on mountain summits and ridges

  
  

  - scree is also actively forming from the frost shattering of boulders from the steep valley slopes
• how has sedimentation changed the landscape over time?

  - the flat floor of the Nant Ffrancon once contained a ribbon lake - over 1000s of years sediments and debris brought down by many streams have infilled the lake that once existed here