PIG Flow (Ice Penetrating Radar Surveys (Imaged shape of PIG bed, Drive…
Ice Penetrating Radar Surveys
Imaged shape of PIG bed
Drive radar around selected portions PIG (15 x 10 km transects)
High resolution ~1 km
Data = sequence of
Can interpolate shape of PIG bed from radargrams
= resistance to flow along bed
n.b. doesn't tell us what causes resistance
of other data e.g. velocities
Possible causes basal traction
Friction @ ice bed interface
from small obstacles
Resistance in subglacial sediments
e.g. porosity, grain shape etc
resistance to ice flow as ice deforms around/across basal obstacles
Shape @ PIG bed
Need to know about shape @ PIG bed
Past models - invert velocities
to gauge 'basal traction' ~ proxy for bed topog
Basal traction ~ primary control on ice flow
Difficult to model
Important for predicting ice behaviour
Megascale glacial lineations
evince fast ice flow
Provide very little resistance to ice flow
Long, elongate landforms typically comprising soft sediments
Moulded by ice flow over them
Bed = v lineated
All sites reveal bed = very lineated
→ along ice flow direction
~ Megascale lineations ?
Quite a lot of patches = pretty flat
some exceptions - topog protrusions
PIG Flow mechanism
Must be flow along bed
(to explain high velocities)
Basal sliding ?
controlled by small obstacles
Subglacial sed def ?
controlled by ∆ subglacial sed properties
controlled by large obstables @ bed (km-scale)
Absence of data on bed shape + properties
∴ velocities/elevation= inverted
to model basal traction
~300m into ice above
likely affects ice flow/resistance to ice flow
Lineations run over lump
along ice flow direction
Depositional feats ?
Ridge sticks out
up to 50m into ice in along flow direction
Sign ice = trying to erode rocky bed?
Heightened amplitude lineations
~ immature ?
ice still trying to erode bed smooth ?
more rocky bed?
Key PIG Unkown
= How ice flows over bed
Subglacial sed deformation?