Glacial Meltwater Flashcards
(15 cards)
Meltwater
-glacial meltwater is cold and loaded with suspended sediment
-depending on the type of sediment, it can be milky, grey or brown in colour
-sub glacial meltwater exits the amount of the glacier under hydrostatic pressure though meltwater tunnels
Processes
-fluvioglacial processes are through erosion and deposition by flowing meltwater
-vast quantities of meltwater are produced which transport large amounts of debris
-processes include: basal sliding, nivation, plucking, abrasion
Fluviooglacial depositors are generally
-smaller than glacial till debris
-carry finer material
-smoother and rounder through fluvial processes of attrition, abrasion and corrosion
-sorted horizontally with course material up valley with progressively finer material being deposited as meltwater moves down valley
-have stratified layers that reflect seasonal and annual depositional variations
Glacial till deposits are typically
-unsorted, angular and non stratified (non layered)
Outwash deposits
proximal zone in front of glacier and emerges from the snout
-meltwater had high velocity and particles are large and regular
-can be intermixed with finer glacier till
-outwash my form alluvial fans
medial zone is where meltwater streams begin to form braided channels
-daily and seasonal changes in meltwater discharge
-velocity is decreasing and particle size is rounder and smaller
-deposition begins in meanders of stream and across the outwash plain
distal zone is the furthest from glacial snout
-drainage is similar to normal fluvial drainage systems
-outwash is well sorted, smaller and rounded
Imbrication
-sediments deposited in fast flowing meltwater channels will show imbrication
-this is where rock fragments are pushed in one direction by the flow, which forces overlapping of each other
Examples of ice contact fluvioglacial landforms
-kames
-eskers
Examples of proglacial fluvioglacial landforms
-outwash plains
-pro glacial lakes
-meltwater channels
-kettle holes
Meltwater channels
-formed from erosion due to the flow of meltwater beneath or close to an ice sheet margin
-typically steep sided, deep and straight
-high discharge rate and turbulent flow
-the larger the meltwater channels, the more significant the levels of meltwater erosion and size of deposition
Types of channels
-subglacial found beneath the glacier
-englacial is here meltwater streams form within the body of glacial ice
-lateral meltwater streams that follow the glacial edge
-surface meltwater flows over the surface of the glacier
-proglacial where meltwater drains from the front of the glacier
Outwash plains
-as meltwater begins to descend, the velocity begins to slow
-this allows for the formation of a network of shallow, sedimented split channels that are separated by gravel bars that eventually make up the outwash plain
-traction, saltation, suspension and solution processes transport the eroded material within the channels
-decreasing velocity reduces the ability of the meltwater to hold the debris, sorted sediment is deposited on the valley floor in layers called varves
Kettle holes
-hollows formed when blocks of ice calved from the main glacier and left on the outwash plain as the glacier retreated
-ice block subsequently melts, leaving a depression in the sediment deposits of the outwash plain
Eskers
-long, winding ridges of sand and gravel running parallel to the glacier
-deposited by subglacial meltwater streams and can stretch for several kilometres and reach heights of 30m
-as the glacier retreats, the stream dries up and the load remains as an esker
-eskers show the position of past glacial tunnels
Kames
-mounds of sand and gravel found on the glacial valley floor
-supraglacual meltwater streams collect in surface depressions and deposit layers of debris
-glacial retreat dumps the sorted debris onto the glacial valley floor
