Siegert et al 2016 (11) Flashcards
How were antarctic subglacial lakes first detected?
Using radio echo sounding (RES) in the late 1960s from a geophysical survey of the Antarctic Ice sheet.
Why were subglacial lakes easily identifiable using radio echo sounding (RES)?
As the bright, flat specular reflections from an ice-water interface are distinct from the rough, variable power reflections from bedrock or sediment.
Why do subglacial lakes exist?
Ice is a particularly good thermal insulator.
With only background levels of geothermal heating, if the ice is sufficiently thick, the temperature at the bed can reach the pressure melting value.
How can basal water flow uphill?
As ice-surface slopes have an order of magnitude greater influence on water flow than basal slopes a phenomenon can occur in which basal water flows uphill provided basal slopes are less than 10 times (and in the opposite direction to) the ice surface.
Interest in subglacial lakes was renewed in the early 1990s, when high-precision ERS-1 satellite radar altimetry revealed that the 1970s RES data from Lake Vostok coincided with a notably flat ice surface, the flat surface being caused by…
the change in ice dynamics from grounded ice shearing to lateral extension when afloat.
What are active subglacial lakes?
Some subglacial lakes are prone to sudden discharges of water (‘active’ subglacial lakes), which can flow hundreds of kilometres and also connect with other lakes.
A significant proportion of targeted ‘active’ subglacial lakes have found little or no evidence for the presence of significant volumes of subglacial water beneath the observed ice-surface anomalies. This may be for several reasons
(i) the change in ice-surface elevation was not caused by the movement of subglacial water (i.e. the measurements do not represent ‘lakes’);
(ii) the lakes were empty at the time of the RES survey;
(iii) the central coordinates of the mapped surface area of the ‘active’ lakes targeted by the RES surveys are offset from the locality which experienced the greatest range of surface elevation change observed by satellite altimetry
The dynamic behaviour of ‘active’ lakes demonstrates what?
That there are hydrological pathways and connections beneath the ice sheet.
What is likely to be a plausible mechanism behind the nature of the connections between subglacial lakes and for draining water issued from ‘active’ lakes?
An R-channel, incised upwards into the ice
