Lesson 12: Glacial Meltwater Flashcards
What are the 2 main sources of meltwater?
Surface melting and basal melting
What is a glacial outburst?
Huge amount of meltwater becomes trapped, either beneath the ice or as surface lakes. When these eventually burst (called a glacial outburst), the surging meltwater has the power to carve deep channels or gorges
Where does meltwater travel?
Supraglacial
Englacial
Subglacial
Meltwater discharged from where is higher in the summer months?
Supraglacial and subglacial streams
Define moulins
Vertical shafts cut out by the water, where water cascades down these into the ice sheet. Remain open by constant melting by water
How do fluvio-glacial deposits differ from glacial deposits?
1) Generally smaller due to the lesser energy of the meltwater streams in comparison to valley glaciers
2) Generally smoother and rounder through water contact and attrition, as well as being sorted and graded
3) Sorted horizontally, with the largest material found up-valley (nearest snout)
4) Stratified vertically with distinctive layers which reflect either seasonal or annual sediment accumulation. During summer months when discharge is high, heavier material is found further down and deposited
Define imbrication
Shows the direction of flow (specifically the sorting horizontally and vertically)
Describe proximal zone of outwash plains
Immediately in front of the glacier, close to the snout. Meltwater has the greatest power here so particle size may be large
Describe medial zone of outwash plains
Further from the ice margin- meltwater streams tend to anastomose and form braided channels because of high daily and seasonal variation. Particle size is more rounded due to attrition
Describe distal zone of outwash plains
Furthest from ice margin- broad flood plain- well sorted sediment and even smaller and rounded than medial zone
What are the 2 types of fluvio-glacial landforms?
Ice contact
Pro-glacial
Describe kame
Undulating mound of fluvio-glacial sand and gravel deposited on the valley floor near the glacial snout
Process of formation of kame
Meltwater streams emerge onto the outwash plain or proglacial lake at the glacier snout, their velocity falls and sediment is deposited
Example of a kame
Yellowstone NP, Wyoming
Describe kame terrace
Flat, linear deposit of sand and gravel deposited along the valley sides
Process of formation kame terrace
Valley sides radiate heat in the summer, melting the edges of the glacier, forming meltwater streams which deposit sediment. When the glacier retreats the sediment falls to the valley floor, forming a kame terrace
Example of kame terrace
Chilliwack river valley, Canada
Describe esker
Long, narrow, sinuous ridge of fluvio-glacial sand and gravel
Process of formation esker
Subglacial streams carry large amounts of rock debris due to high hydrostatic pressure inside tunnels. Streams often meander beneath glacier. Glacial retreat cause debris to be deposited
Example of esker
Mount Pelly, Nunavut, Canada
Describe sandur (outwash plain)
Flat expense of fluvio-glacial debris in front of glacial snout
Process of formation of sandur
Meltwater streams emerge from glacier and enter lowland areas, they lose energy and deposit debris loads. Coarse gravel deposited first near glacier, then sands, then clay
Example of sandur
In front of Red Glacier, Alaska
Describe kettle hole
Circular depression often forming a lake in an outwash plain
Process of formation kettle hole
Glacier retreats, detached blocks of ice remain on the outwash plain. Meltwater streams flow over the ice covering them in deposits. Ice melts a debris subsides to form a depression which can fill with meltwater
Example of kettle holes
Yama Peninsular, Siberia
Describe proglacial lake
Lake formed in front of glacial snout
Process of formation of proglacial lake
Damming action of a terminal or recessional moraine during retreat of a melting glacier. Or meltwater trapped against an ice sheet from isostatic depression of the crust around the ice
Example of proglacial lake
Lake Michigan - part of an old proglacial lake
Describe meltwater channel
Narrow cut channel into bedrock or deposits, either underneath or along the front of an ice margin
Process of formation of meltwater channel
Meltwater can erode deep channels from high hydrostatic pressure within glaciers, and high sediment load. Able to flow uphill and are larger than post-glacial streams. Braiding is common
Example of meltwater channel
Pentland Hills, Cairngorms, Scotland
