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Amundsen Subglacial Lakes (Why Lakes Drain Together ? (Lakes drain…
Amundsen Subglacial Lakes
No Amundsen subglacial lakes detected til 2 yrs ago
Despite region being real hotspot - puzzling (Pig, Thwaites etc = fast)
in Amundsen Sea until ~ 2 years ago with IceSat
Possible
reasons:
Data too sparse ? (IceSat broad lines)
Too much meltwater? moves through system too fast to pond
Drainage too efficient ?
Dynamic signals mask lakes?
No active subglacial lake systems detected
Cryosat 2 Swath Processing
More detailed altimetry
higher resolution elevation msmts
Significant thinning observed in Amundsen Basin
Thinning in upstream parts Thwaites
Thwaites Lake Drainages
Between 2011 - 2013 in Thwaites upper catchment
Observed 4 lakes draining
Four surface depressions form
above subglacial lakes which drain
240 cumecs drain over ~ 6 months
Lake communication = interesting
Hydraulic Potential Maps
Using Amundsen Cryosat DEM
1. Confirmed lake presence = plausible
Locations concur with low hydraulic potential
∴ Likely areas for water to pool
2. Showed many closed basins exist
i.e. subglacial envmt = v complex
Water should accumulate until basins fill
3. Likely flow pathway
From top lake --> lower lakes --> ice shelf
Misses lower lake
∴ Hydraulic connectivity exists btwn most lakes
Lakes all drain at same time
Strange -
since different estimated filling times for each lake
∴ Coincident draining seems unlikely
Proposed explanation:
Cascade of lake drainages triggered
Why Lakes
Drain Together ?
Lakes drain together despite differing filling rates
One lake drains -> triggers cascade of lake drainages
Overpressurised lake drains -
initial trickle of water drains
Conduit enlarged
as
moving water melts ice walls
∴ torrent of water drained
Rapid filling of next lake downstream
when pushed beyond capacity
Velocity in lake draining regions
No noticeable velocity change in regions of lake drainage
Thwaites
Steady velocity increase at grounding line for
past few decades
Upstream ( where lakes drained )*
--> no impact of drainage on velocity
Why no velocity ∆ visible nr lake drainage ?
Ice flow controlled by τb - friction btwn bed & ice
Basal drag located in broad narrow bands across glacier
Friction bands
= broad
∴ Small water channels (10-20m wide) across band
has little effect on friction