Proglacial and Subglacial lakes, and glaciomarine sedimentation Flashcards
What are glaciolacustrine deposits?
Sediments deposited into lakes that have come from glaciers are called glaciolacustrine deposits.
These lakes include ice margin lakes or other types formed from glacial erosion or deposition.
What are deltas?
Delta- When water first goes into a lake it will produce a delta, coarse sediments are closer to the glacier and it ‘fines’ out as it goes further into the lake.
What position are deltas formed?
Deltas are formed in a proximal position
What is the style of delta determined by?
The difference between the density of input rivers and water body
If river water denser or equal + steep in put river = Gilbert type.
What are varves?
Moving into the lake there is a characteristic sediment within the lakes called varves
Comprised of two layers representative of one year…
Winter layer- dark, clay
Summer layer- light, silt
How is the summer layer of varves formed?
Glacial streams carry sediments out into the lake
Gravels and coarse sands are deposited in the delta
Finer sediments are transported out inot the centre of the lake and are held in suspension
Silts and sands settle out at once to formthe ‘Summer layer’
How is the winter layer of varves formed?
There no inputs into the lake - so clay settles out - ‘Winter layer’
What can be another component of summer flow in varves?
If you have big events in the summer (storms, cavity collapses) / extra water in the lake creates…
turbidity underflows due to high discharge events (storms, cavity collapse, marginal lakes, etc)
Essentially a flood of sediment into the lake creating an extra layer in the summer layer
Able to analyse layers in detail to reconstruct past glaciation
What can be another component of winter flow in varves?
if a non-glacial source to lake, there may be coarse layers within the Winter Layer
Relationship to ice flow
Can work out where the rivers are beneath the glacier, some of these are linked with the onset of rapid flow and thought to be draining from one to the other. Active lakes are filling with water and then draining (so linked to one another).
– Due to the water in the lake
– Warming of the base due to the water
– Periodic drainage
Lake drainage causes
Velocity increases –
Drained and provided water to reduce friction so the glacier slides.
Example of an ‘active’ lake
East Antarctica (Wingham et al., 2006), ice 4km thick (temperate base). Lakes are in a trench 16 months 1.8km2 of water transferred to at least 2 other lakes Discharge between lakes via R- channels (4 m in radius) Alternative model –this movement of basal water in distributed system or sediment flows (Siegert et al, 2014)
Life in the lakes?
Before 2000 it was assumed lakes were closed system, potential refugia
Since then it has been realised that some of these lakes are connected.
Glaciomarine Sedimentation
• Direct Sedimentation – morainal banks • chaotic mixture of till and gravel – Subaqueous outwash • outwash fan that is coarse grained at the proximal end and fine grained at the distal end
What are upwellings?
Streams enter sea from englacial and subglacial conduits
In summer form turbulent jet (high pressure under glacier) at the glacier margin
Brings nutrients from underneath the glacier up to the surface
Attracts wildlife
