Please enable JavaScript.

Coggle requires JavaScript to display documents.

Glaciofluvial (Conduits and drainage (How do you generate glacial…

- - - - Pw – water pressure
      - Pi – ice pressure
      - Needs an equilibrium of pw and pi to keep it open, pw must heighten to widen the conduits.
- - - - Dissolving is controlled by temperature and pressure
      - Ions soluble in water: Ca2+, Na+, K+, M2+, Fe, Al, Si
      - Wet subglacial environments important for dissolution due to abundance of freshly crushed rock material.
      - Finite amount of dissolved material it is the dilution effect as discharge changes – extreme melt during summer is usually supraglacial and will dilute dissolved load which has a high electrical conductivity
  - - - Not a linear relationship between flowrate/discharge and sediment load
      - Rising stage can carry more sediment and the falling stage is ‘exhausted’ and cant carry as much (Hysteresis loop)
      - Measured using an automatic vaccum sampler or turbidity meters
- - - - Winter low flow is followed by spring melt seasons, into a peak melt in summer.
      - Discharge is controlled by glacier size eg. in glacial advances discharge increases but can also increase if there is rapid melting/retreat.
  - - - diurnal variations are controlled by daily temperature changes. Diurnal variations are more marked in alpine than Arctic glacial drainage basins and small glacierized basins display larger diurnal variations than large basins.
      - Diurnal variability occurs within seasonal variability.
- - - - Type 1 - Lots of variability in deposits with diurnal 'flood' cycles, multiple small events so non jokulhlaup event. Have massive gravels, imbricated gravels and cross-bedded sands. Close resemblance to sediments in a braided river system
      - Type 2 - Thicker units of cobble-gravels which coarsen upwards caused by the rising limb of low frequency high magnitude events. Major fining is seen interpreted as the waining stage of the flood.
      - Type 3 - Volcanic GLOF with subglacial release of water and sediment, causing a short pulse of hypersedimented flows, this causes structure-less deposits but shows fining with boulders deposited first.
        
        Type A profiles are interpreted as representing hyperconcentrated grain flow deposits containing varying proportions of volcanically derived granules and locally derived country rock or surficial materials. Type B are multi-stage deposition from a volcanogenic jokulhlaup. Type C profiles are characterized by a wide range of graded sediments, Type D profiles, comprising highly deformed granular sediments, often in association with diamicton (Type E profiles, see below), are interpreted as hyperconcentrated grain flow deposits that have been disturbed during over-riding by or convergence with, subsequent pulses of viscous jokulhlaup flows, or by melting of incorporated ice masses. Such situations would arise where sediment-rich flows come into contact with bed obstacles, such as rock or till protuberances, earlier debris flow lobes or deposits, or ice blocks, leading to deceleration and rapid dewatering. while marked deformation of bedding would have occurred during rapid deposition and settling of the flood deposit.
      - six main lithofacies sequences or assemblages can be identified as character- ising j6kulhlaup deposits in proglacial areas: (1) Large-scale cross-bedding with armour capping especially in Type II outwash;
        
        (2) Boulder beds (Type C), in Types II and III outwash
        
        (3) Inversely graded gravels, granules or boulder beds (Types D3 to D5), in Types II and III outwash;
        
        (4) Massive, structureless, matrix-poor gravels, granules or boulder beds, underlain by basal bedded gravels, and capped by fluid bedforms (Type E4), especially in Type III outwash;
        
        (5) Laminated sands and silts in backwater locations (Types A3/A4), in Types II and III outwash; and
        
        (6) Localised massive, matrix-supported diamicton units and deformed bedding containing rip-up clasts (Types G and H), in Types II and III, and Type III, outwash, respectively.
  - - - Glacier advance or retreat can act to release lower or higher volumes of meltwater, and modify the availability of sediments to the proglacial system