This e-mail is very important consideration for Indianice on the possibilities
of land containment failure and large scale ice slippages from the elevated
grounds (especially in forthcoming post-sea ice environment in the Arctic).
I have forwarded this e-mail to Minik Rosing as he would be in a position to
answer the technical questions raised by Peter Wadhams and others. If not able
to answer in person, he knows who might be the best person to respond to this.
In questions of this nature, I believe Minik is in good position and I believe
happy to try provide you answers.
I also note Tom's point, that recent studies suggest that most of the meltwater
from moulins in Greenland might not penetrate to the base of ice but fill the
fissures and caverns within the ice instead. There are pros and cons to this.
(See my comment to this below Tom's message.)
I have often differentiated between Type 1 (seasonal impact) moulins and Type 2
(accummulative impact) moulins. The former forms near the edge of ice sheet
and the meltwater is rather quickly drained out, by the end of melt season all
water and heat with it has drained out. The latter, Type 2 takes water behind
some obstacle over site where Greenland's subglacial terrain has inward ground
inclination, making it hard, if not impossible for the water find its way out
from under the ice if it once fell in.
I have often used the above 'black-and-white' description to briefly describe
the changes occurring in Greenland's moulin populations which have been sky
rocketing along its periphery. It
I would like to draw in attention that the overall undestanding (statistically)
where the water in moulins and crevasses is taken, is in its infancy.
Date: Fri, 9 Jan 2009 10:27:59 +0000From: [email protected]:
[email protected]: [email protected]; [email protected];
[email protected]; [email protected]: Re: [geo] Re:
hydrological geoengineering - new wiki page I'm very sorry. I am aware of all
the relevant references, but I am in Japan at the moment and can't get at them.
Can anyone else help? Peter On Jan 9 2009, Andrew Lockley wrote: Has anyone
got references for any of the studies mentioned below?A2009/1/9 P. Wadhams
[email protected]:
This is a very interesting question. Once upon a time (up to about 4 years ago)
it was conventional wisdom that the Greenland ice sheet will last at least 3000
years, because even with global warming it will take that long to melt
successive layers off the top each summer until it is all gone. Then, with the
apparent evidence of meltwater going down moulins and warming the deeper parts
of the ice sheet, plus the apparent lubrication of the ice-bedrock interface
causing the spectacular accelerations of outflow glaciers mapped by Eric Rignot
et al, we had a new conventional wisdom that the Greenland ice sheet could
disappear very rapidly, with catastrophic consequences for global sea levels.
Now it seems we are backtracking a bit. Something to remember is that the
Antarctic subglacial lakes were discovered by reanalysing radio echo sounding
data from the 1960s and 1970s collected by the SPRI campaigns using US
aircraft. Gordon Robin, having retired, had the time to look at the ice-bedrock
returns in detail and detected water-like echoes, while ice sheet modelling had
advanced to the point where these locations seemed to allow the presence of a
deep water layer rather than a thin skim. To my knowledge, this hasnt been done
for Greenland. The basic radio echo sounding of the Greenland ice sheet was
done by the Technical University of Denmark in the 1970s using a radio echo
sounder which differed in its characteristics from the SPRI instrument. Could
someone sit down and look at the nature of the echoes to see if there are water
layers or even lakes? Best wishes Peter Wadhams
On Jan 8 2009, John Nissen wrote:Hi Tom,Does most flow out to sea? Does some
stay as lakes under the surface? Have such lakes been detected, as they have in
Antarctica? Would it be possible to detect a lake at the base of a thick ice
sheet? Do you have a reference? I'm sure Albert would be interested, and Profs
Wadhams and Shepherd also.I fear that if the Arctic sea ice disappears, it may
be too late to protect the ice sheet from disintegration, unless we start
protecting it now. Moulins could be key for Greenland and for Antarctica (WAIS)
also, don't you think?Happy New Year,John----- Original Message ----- From:
<[email protected]>To: <[email protected]>Cc: "Geoengineering"
<[email protected]>Sent: Sunday, December 28, 2008 10:11
PMSubject: [geo] Re: hydrological geoengineering - new wiki pageRecent field
work has shown that the flow into most Greenland moulins does not get to the
base of the ice. Wiki page needs correcting.Tom.
>>
FIPC Comment to Tom:
I note Tom's point, that recent studies suggest that most of the meltwater from
moulins in Greenland might not penetrate to the base of ice but fill the
fissures and caverns within the ice instead. There are pros and cons to this.
It has been rather natural to suggest that the moulins take the water to the
bottom of ice as the water is heavier.
However, this can be only true if the crevasse is sufficiently filled-up to
produce a higher water pressure than the ice layer can do in order to prevent
the ice re-sealing occurring. It is rather unsuprising that it has been
discovered that not all (even most of) the moulins occurring on Greenland's ice
sheet reach the bottom of ice: the deeper one goes into ice, the higher is the
pressure and the easier (faster) the re-sealing must occur.
It is important to point out that the occurrence of moulins and crevasses and
melt water penetration are seldom occurring in isolation from the other
dynamical processes within the ice:
When there are large increases in number of moulins near glaciers its seems
that the glaciers do start speeding up.
Sometimes glaciers surge forward in a very rapid pulse and then suddenly stop.
These surges are suggested as a result of melt water mattress penetration
between the ice and its underlaying bedrock that produce sudden reduction on
the friction (hold) of glacier and if friction decreases, the ice's falling
speed rapidly increases.
The above sudden pulses in ice streams have been taken as an evidence that
meltwater penetration contributes to the glacier streams' speed up. There is
also the statistical correlation of increases in the number of moulins pouring
water in and then the speeding of nearby glaciers, apparently linking up the
two escalating processes.
Denial of importance of melt water penetration is misleading, there are few
processes that better explain the fast escalation of Greenland's glacier
streams except the meltwater penetration lubricating their base and helping ice
to float over dentures in subglacial terrain when it becomes water filled. The
more warmed ice is, the more pockets of melt water introduce heat, and this
heat helps and speeds up grinding process within dirty ice layers at the base.
Please note that the layers of dirty ice near base has higher densities and
when it crosses water-filled dentures on bedrock, sliding ice often melts over
water and losens debris to fills water-logged spots with moraine until little
or no water is left to fill the gap, therefore, further easing the ice
movements as potholes are filled with compacted soils.
I also often differentiate between Type 1 (seasonal impact) moulins and Type 2
(accummulative impact) moulins.
Type 1 (seasonal impact): The former forms near the edge of ice sheet and its
meltwater is rather quickly drained out, by the end of melt season all water
and heat with it has drained out. Type 1 moulins are the ones that one can see
pouring meltwater from under ice, in creeks, over the rocks and towards the
ocean somewhere below. The water and heat in it is drained out and these little
rivers and creeks stop soon after the melt season ends.
Type 2 (accummulative impact): The latter takes water behind some obstacle over
site where Greenland's subglacial terrain has inward ground inclination, making
it hard, if not impossible for the water find its way out from under the ice if
it once fell in. All moulins that do not drain water out due to (i) subglacial
terrain obstacle or (ii) dead end fissures, crevasses or caverns within ice are
essentially Type 2 (as long as they exist).
I have often used a simple 'black-and-white' description Type 1 versus Type 2
to very briefly describe changes occurring in Greenland's moulin and crevass
populations (which are sky rocketing). However, to be more accurrate there is
a lead time (from water infall to full discharge) that varies (from an instant
towards the infinity) when the melt water (and heat in it) is drained out of
the ice. The longer warm melt water stays under (or within the ice), the more
heat is taken up by nearby ice (in contact with such a warm water). If drainage
is quick, damage is less.
It is difficult or tedious to show public (who have short attention span) the
grayscale occurrence versus the half tone image when it comes to explaining how
long (and how much heat) the meltwater falling in releases into ice. No one
would say that half tone image is incorrect, while the gray scale one is more
approppriate. Neither it will be relevant for the warming of the ice if the
permanently ice-locked melt water (from accummulative impact Type 2) moulins
are held back by ice, soil or rocky material that prevents its escape from
within the ice.
We could equally well label the moulins and crevasses as seasonal impact,
multi-year impact, decadal impact, cetennial impact, etc., whatsover depending
how long the water fallen within or under the ice stays there to create a
grey-scale definition. But for the simplicity, it is just easy to say some are
seasonal, some accummulative impact.
As the number of moulins has increased and their location has moved much
further away from the coastal periphery of ice, it is only fair to assume that
it will take longer for the water to drain out the further it falls in. It
also must be said that many crevasses exist due to interaction of ice with its
subglacial terrain and many historically-formed crevasses readily exist in
Greenland to store water that now falls therein; this increases heat amount
taken by ice.
The stresses created by moulins, crevasses, fissures, and caverns is plain
simply increasing and these are driving the glaciers in Greenland to run ever
faster (irrespective of whether the water travels laterally through the
interface between the ice sheet and bed rocks, 'bottom of ice', or whether it
finds its way down and comes out through myriad of fissures in the glaciers,
travelling on its way in open spaces to any direction it can do between the
horizontal and vertical extremety.
We are certainly not in any position to state reliably that in this, or that,
area of Greenland we have a statistical averages available of meltwater
penetration to say that the water trapped by the ice is, say 50% or more, while
the rest is drained away that 49% or less is traveling between ice and rock to
get out, at a certain variable speed, at certain dept (or locations) within
ice. As far as I know, not a single subglacial drainage system in has been
mapped.
For our own research constituency and principals the issue how melt water is
drained is relevant:
I would caution here against any dismissal of the link between melt water
falling in and the speeding of glacier over terrains (even if some evidence has
been found that most water might remain nearer the ice surface). We also are in
a rare transitionary phase of cold, sustained Greenland ice sheet turning into
a warm, destabilising ice sheet. This is an event that has not been withnessed
since the ending of the ice age, therefore, the description of detailed ice
dynamics of near past and present may be discontinued and escalated to new
forms of ice dynamics. Therefore, if the melting escalates a possibility
remains that large layer of water may eventually come to fall to the base of
ice.
We at FIPC are investigating a complaint to the United Nations General Assembly
where the complainants (against the western group of countries) stipulate that
tomorrow's warmed and wet ice sheets are fundamentally different from our
recent past, i.e. the fjord system may only represent a good case study for a
healthy, cold ice sheet and is a mere over-spill mechanism where a healthy ice
sheet discharges its excessive ice mass accummulation through the few narrow
gaps, fjords, in its ice containment (rock periphery). They suggest that the
land ice melt has a rapid tipping point, the trigger being a summer-time sea
ice loss in the Arctic Ocean causing extensive surface melting in Greenland.
This switches the warmed and wet ice sheet to a new state where the number of
moulins and melt water lakes is so high that there is an overall detachment of
the ice sheet from its base - due to melt water penetration. Although, at
present, the basal penetration can be small, this does not stay so indefinitely
according to these complainants. The overall effect of this is a switch-over of
ice sheet mass balance management from the fjord system to pelag system where
ice no longer seeks passively an escape through gaps, but weakens the barrier
itself.
We at FIPC plan to monitor the Melville Bay section's coastal rocks for the
suggested effect for the 'pelag' switch over by looking for signs on the
periphery if it remains still, i.e. whether there are any signs of large scale
coastal subsidence, seaward movement on few rocky outcrops that jut out of the
ice sheet, or there is ground tilt stress.
We obviously feel uneasy for all attempts, or perceived ideas, that may lead us
to de-couple of the melt water penetration from any speed-up and lubrication of
glaciers in Greenland. We think that there is not yet enough data reliably
make behavioural assumptions of transitional ice sheets (or to draw statistical
conclusions about moulin systems to differentiate between subglacial drainages
where water dwells within ice or between the rock and ice boundary that 50% or
more are "of type this or that", in fact, both could occur within a same
pressurised subglacial stream on its way down to the ocean. In that case, the
moulin system is neither A, nor B.
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