Graded Profile + Rejuvenation

Graded Profile + Rejuvenation

1. Graded Profile

   • Always trying to reach dynamic equilibrium
   • Erodes protrusions like waterfalls
   • Deposits in intrusive features such as lakes
   • Base level- lowest point, mouth of river

2. Rejuvenation

   • Definition
     • An increase in the rivers energy caused by either a fall in base level (sea level) or an uplift of land
       • Isostatic change
         • Land rising relative to sea
         • e.g. Sctotland has 'bounced back' since weight of ice cap reomved
         • Earthquakes and plate tectonics
       • Eustatic change
         • Change in sea level due to how much water in sea
         • Growth of ice caps 'locks up' water from being in oceans, melting does opposite

3. Features

   • River Terraces
     • Remains of former flood plain, narrow land that runs parallel to river above flood plain, like steps
     • How?
       • Rejuvenation increases gpe of river, so more vertical erosion takes place
         • Hydraulic action and abrasion will erode bed, cutting down to make new flood plain inside old one
           • Lateral erosion over time makes terraces narrower
             • If rejuvenation happens again, another layer of terraces will form
       • Formed either by isostatic or eustatic change
     • Types
       • Paired
         • River cuts down rapidly, leaving pair of same height terraces, valley-in-valley feature
       • Unpaired
         • River cuts down slowly, allows it to meander, may cause on side of terrace to be smaller or gone
     • Example
       • Taplow and Boyn Hill terraces, built up areas of London situated on these
   • Knick points
     • Sudden break or irregularity along long profile of river
       • Some are water falls
     • How?
       • Eustatic change changes base level
       • New base level works its way up river from coast
         • Where new long profile meets old
           • Tend to move upstream but can be halted by more resistant rock
     • Example Beezley Falls, River Greta, NW Yorkshire

4. Incised Meanders

   • How?
     • Isostatic or Eustatic change
     • Well developed meanders must be present
       • Vertical erosion of several metres below old flood plain
         • More gpe causes more vertical erosion
   • Types
     • Entrenched Meanders
       • River Wear, Durham
       • Symmetrical cross section
         • Formed by rapid incision
           • Due to rapid land uplift
             • Can be due to resistant valley sides
               • Creates uniform meander
     • Ingrown meanders
       • River Wye
       • Uplift of land is slower
         • More time to erode laterally
           • Asymmetrical cross section