the characteristics of drumlins and explain their formation

Drumlins  are roughly ovoid shaped hills of dominantly glacial debris that typically occur within groups or fields of several thousand.They exhibit very strong Enechelon long axis preferred orientation paralleling the main direction of ice flow.The classical drumlins have steeper stross-end slope  and tapered lee-side.Limited relationships appear between drumlins and topography.the topographic locations within which the drumlins are found are many and varied.Drumlins are composed of vast range of sediment types although previously it was thought to be exclusively formed of subglacial Till.Drumlin shapes vary enormously and may reflect post-depositional sub-aerial mass movement.

At present 3 main drumlin forming hypothesis are present:-

a)Formation by moulding of previously deposited material within a sub-glacial environment,in which a limited amount of sub-glacial melt water activity occurs which influences moulding and deformational processes  produced by acting either as lubricating basal film at upper ice-bed interface or as debris-held pore water thereby reducing subglacial effectiveness stresses.Debris is moulded by direct deformation of previously deposited sediment into drumlinoidal shapes by direct basal ice contact following some type of smearing-on process.

b)Formation resulting from anisotropic differences in the subglacial debris (under the dominant M-bed conditions) owing to:

a)Diletency;

b)Pore water dissipation;

c)Localised freezing;

d)Local helicoidal basal ice flow patterns,or

e)Localised sub-glacial debris.

It is suggested changing stress field and/or stress/strain histories owing to the transient basal glacio-dynamics locally affecting subglacial debris rheology are important parameters in determining whether drumlins begin to form or not.

c)Formation resulting from the influence of active basal melt-water(under H-bed conditions) carving out cavities within ice mass