An Avalanche of Glaciologists

An Avalanche of Glaciologists

The English language has a rich and diverse vocabulary which includes a profusion of collective-nouns for animals.

Geese, for example, are collectively called a gaggle when they are not flying and a skein when they are in flight.

But the English language strangely lacks a collective-noun for Settle Scientists.

However, there are many candidate words for describing a group of Settle Scientists.

One obvious choice would be a Herd of Settle Scientists because, just like a Herd of Elephants, they will trample over anything [like observational evidence and logic] that gets in their way.

Another candidate, which is my personal favourite, is a Flock of Settle Scientists because they behave like sheep [simple flockers] and are easily managed by sheep dogs [peer reviewers].

Within the global Flock of Settle Scientists there are many specialties that deserve special recognition.

Geologists, for example, richly deserve to be collectively called a choir because they religiously sing off the same hymn sheet.

Glaciologists, the subject of this posting, qualify to be collectively called an avalanche because some of their Settled Science is exceptionally flaky and tends to [terminally] bury rational thought under metres worth of snow.

The science of avalanches states that they are triggered by “mechanical failure” in the snowpack.

An avalanche (also called a snowslide or snowslip) is a rapid flow of snow down a sloping surface.

Avalanches are typically triggered in a starting zone from a mechanical failure in the snowpack (slab avalanche) when the forces on the snow exceed its strength but sometimes only with gradually widening (loose snow avalanche).

After initiation, avalanches usually accelerate rapidly and grow in mass and volume as they entrain more snow. If the avalanche moves fast enough some of the snow may mix with the air forming a powder snow avalanche, which is a type of gravity current.

Slides of rocks or debris, behaving in a similar way to snow, are also referred to as avalanches.
http://en.wikipedia.org/wiki/Avalanche

The “mechanical failure” of the snowpack is typically associated with “weakening” or an “increased load due to precipitation”.

The load on the snowpack may be only due to gravity, in which case failure may result either from weakening in the snowpack or increased load due to precipitation.

http://en.wikipedia.org/wiki/Avalanche

In 1955 the Swiss civil engineer Andreas Voellmy developed an avalanche model that conceptually treated an avalanche as a “sliding block of snow”.

The Swiss civil engineer Andreas Voellmy was the first to develop a theoretical model in avalanche dynamics.

This was done upon an event in which major property damages resulted from a catastrophic avalanche in Vorarlberg, Austria in 1954.

Voellmy’s equations are intended to predict both the velocity and run out distance of a given avalanche and are based primarily based on what in physics is known as the force-mass-acceleration method.

Avalanche Runout

Avalanche Dynamics – Michael Bestwick – 2010
http://home2.fvcc.edu/~dhicketh/DiffEqns/spring10projects/MichaelBestwick/avyfinal.pdf

Voellmy used a simple empirical formula, treating an avalanche as a sliding block of snow moving with a drag force that was proportional to the square of the speed of its flow…

http://en.wikipedia.org/wiki/Avalanche

Based upon the 1955 science of avalanches it would seem logical to expect glaciers to experience slow-motion avalanches following a “mechanical failure” of the icepack caused by “weakening” or an “increased load due to precipitation”.

Therefore, it is unsurprising that glacial slow-motion avalanches were discovered in the late 1960s by comparing aerial photographs and [later] satellite imagery.

These glacial slow-motion avalanches are called Surging Glaciers by Glaciologists.

Landsat multispectral scanner images and 1:50,000 scale aerial photographs are used to measure marginal fluctuations in 22 outlet glaciers of the Nordaustlandet ice caps, Svalbard, for all or parts of the period 1969 to 1981.

Little was previously known about the behaviour of these glacier termini.

Surging glaciers have been identified by Schytt (1969) and Liestol (in press) from aerial photographs of Nordaustlandet.

Although aerial photographs provide a data set of relatively high resolution, Landsat imagery has the advantage of monitoring the whole of Nordaustlandet every 18 days (16 days for Landsats 4 and 5), assuming that cloud cover is not present.

Surge of Bodleybreen Vestfonna - animation

Remote sensing of ice cap outlet glacier fluctuations on Nordaustlandet , Svalbard
Julian A. Dowdeswell – 1986 – Scott Polar Research Institute, University of Cambridge
http://www.polarresearch.net/index.php/polar/article/download/6916/7749

Glaciers “undergo cyclical” slow-motion avalanches where the active phase of surging lasts for “a few months to a few years” and the subsequent stagnating phase lasts “tens to a few hundreds of years”.

A systematic review of 1959/60 aerial photography, and 1999/2000 Landsat 7 imagery, has identified 51 surge-type polythermal glaciers in the Canadian High Arctic.

These were identified from the presence of features such as looped medial moraines, intense folding visible at the surface, rapid terminus advance, heavy surface crevassing, and high surface velocities.

These observations suggest that surging glaciers are much more common than previously believed in the Canadian High Arctic, where only six surge-type glaciers have previously been described.

Surge-type glaciers undergo cyclical non-steady flow (e.g. Meier and Post 1969; Raymond 1987).

A relatively short active phase (a few months to a few years), during which glacier velocity increases by at least an order of magnitude and advance of the glacier terminus usually takes place, punctuates much longer intervals of stagnation (tens to a few hundreds of years), during which the lower portion of the glacier thins and mass builds up in an upper, reservoir area.
A further surge transfers this mass down-glacier once more.

Clarence Head South Glacier - animation

The distribution and flow characteristics of surge-type glaciers in the Canadian High Arctic
Luke Copland, Martin J Sharp, Julian A Dowdeswell – Annals of Glaciology 36 – 2003
http://www.cpom.org/research/jad-ag.pdf

But glaciologists appear to be a little confused about the speed of these glacial surges.

A relatively short active phase (a few months to a few years), during which glacier velocity increases by at least an order of magnitude and advance of the glacier terminus usually takes place, punctuates much longer intervals of stagnation (tens to a few hundreds of years), during which the lower portion of the glacier thins and mass builds up in an upper, reservoir area.

The distribution and flow characteristics of surge-type glaciers in the Canadian High Arctic
Luke Copland, Martin J Sharp, Julian A Dowdeswell – Annals of Glaciology 36 – 2003
http://www.cpom.org/research/jad-ag.pdf

Glacial surges are short-lived events where a glacier can advance substantially, moving at velocities up to 100 times faster than normal.

http://en.wikipedia.org/wiki/Surge_%28glacier%29

During the increase in velocity, rates of flow may reach more than 1000 times their normal value.

http://www.svalbardglaciers.org/surging_glaciers.html

Glaciologists also appear to be a little confused about the period of stagnation [quiescence].

The surge phase is intersected by longer quiescent phases of about 30 – 150 years, during which the glacier terminus is retreating.

http://www.svalbardglaciers.org/surging_glaciers.html

A relatively short active phase (a few months to a few years), during which glacier velocity increases by at least an order of magnitude and advance of the glacier terminus usually takes place, punctuates much longer intervals of stagnation (tens to a few hundreds of years), during which the lower portion of the glacier thins and mass builds up in an upper, reservoir area.

The distribution and flow characteristics of surge-type glaciers in the Canadian High Arctic
Luke Copland, Martin J Sharp, Julian A Dowdeswell – Annals of Glaciology 36 – 2003
http://www.cpom.org/research/jad-ag.pdf

In some glaciers, however, the period of stagnation and build-up between two surges typically lasts 10–200 years and is called the quiescent phase.

During this period the velocities of the glacier are significantly lower, and the glaciers can retreat substantially.

http://en.wikipedia.org/wiki/Surge_%28glacier%29

Glaciologists also appear to be a little confused about the period of active surging.

In some glaciers, surges can occur in fairly regular cycles with 15 to 100 or more surge events per year. In other glaciers, surging is unpredictable.

http://en.wikipedia.org/wiki/Surge_%28glacier%29

A relatively short active phase (a few months to a few years), during which glacier velocity increases by at least an order of magnitude and advance of the glacier terminus usually takes place, punctuates much longer intervals of stagnation (tens to a few hundreds of years), during which the lower portion of the glacier thins and mass builds up in an upper, reservoir area.

The distribution and flow characteristics of surge-type glaciers in the Canadian High Arctic
Luke Copland, Martin J Sharp, Julian A Dowdeswell – Annals of Glaciology 36 – 2003
http://www.cpom.org/research/jad-ag.pdf

The surges are short-lived periods of rapid movement and sometimes advancing terminus, usually lasting somewhat more than 10 years.

http://www.svalbardglaciers.org/surging_glaciers.html

The data available suggest that the duration of the active phase of the surge cycle on glaciers in this region is relatively long, perhaps reaching as much as 50 years.

The distribution and flow characteristics of surge-type glaciers in the Canadian High Arctic
Luke Copland, Martin J Sharp, Julian A Dowdeswell – Annals of Glaciology 36 – 2003
http://www.cpom.org/research/jad-ag.pdf

Glaciologists also appear to be a little confused about the causes of glacial surging.

There have been many theories of why glacial surges occur.

Hydrological control
Surges may be caused by the supply of meltwater to the base of a glacier. Meltwater is important in reducing frictional forces to glacial ice flow. The distribution and pressure of water at the bed modulates the glacier’s velocity and therefore mass balance. Meltwater may come from a number of sources, including supraglacial lakes, geothermal heating of the bed, conduction of heat into the glacier and latent heat transfers. There is a positive feedback between velocity and friction at the bed, high velocities will generate more frictional heat and create more meltwater. Crevassing is also enhanced by greater velocity flow which will provide further rapid transmission paths for meltwater flowing towards the bed. However, Humphrey found no precise correlation between ice-slow down and the release of water inside of a glacier.

The evolution of the drainage system under the glacier plays a key role in surge cycles.

Thermal regime
Glaciers that exhibit surges like those in Svalbard; with slower onset phase, and a longer termination phase may be thermally controlled rather than Hydrologically controlled. These surges tend to last for longer periods of time than Hydrologically controlled surges.

Deformable bed hypothesis
In other cases, the geology of the underlying country rock may dictate surge frequency.[citation needed] For example, poorly consolidated sedimentary rocks are more prone to failure under stress; a sub-glacial “landslip” may permit the glacier to slide.
This explains why surging glaciers tend to cluster in certain areas.

Critical mass
Meier and Post suggest that once mass accumulates to a critical point, basal melting begins to occur. This provides a buoyancy force, “lifting” the glacier from the bed and reducing the friction force.

http://en.wikipedia.org/wiki/Surge_%28glacier%29

This confusion regarding the causes of glacial slow-motion avalanches is rather surprising given the established avalanche relationship between “mechanical failure” and “increased load due to precipitation”.

Swiss glacier advance and retreat related to Atlantic Multidecadal Oscillation

Swiss glacier advance/retreat related to Atlantic Multidecadal Oscillation
European climate, Alpine glaciers and Arctic ice in relation to North Atlantic SST record
Juraj Vanovcan – 26 Sept 2010 – Watts Up With That?
http://wattsupwiththat.com/2010/09/26/a-must-read-european-climate-alpine-glaciers-and-arctic-ice-in-relation-to-north-atlantic-sst-record/

The Atlantic multidecadal oscillation (AMO) was identified by Schlesinger and Ramankutty in 1994.

The AMO index is correlated to air temperatures and rainfall over much of the Northern Hemisphere, in particular, North America and Europe

http://en.wikipedia.org/wiki/Atlantic_Multidecadal_Oscillation

However, what is truly bizarre is the mainstream claim that only 4% of glaciers are surge glaciers and that their cyclical nature is “almost completely decoupled from climate”.

Perhaps these Glaciologists don’t associate “mechanical failure” [triggered by “increased load due to precipitation”] with “internal mechanical reasons”.

It is worth noting that surge-type glaciers, which account for about 4% of all glaciers (although Hubbard Glacier is not one of them), actually recede and advance cyclically over decades for internal mechanical reasons that are almost completely decoupled from climate.

One cannot draw climatic inferences from the current state of such glaciers.

Global Temperatures
Glaciers – no nonsense science
Michael Hambrey, Jonathan Bamber, Poul Christoffersen, Neil Glasser, Alun Hubbard, Bryn Hubbard and Rob Larter – Geoscientist Online 1 April 2010
http://www.geolsoc.org.uk/Geoscientist/Archive/June-2010/Glaciers-no-nonsense-science

Perhaps these Glaciologists don’t believe the ice age narrative [and temperature reconstructions based upon ice core data] which requires all glaciers to surge [and retreat] as they respond to natural climate variability.

Vostok ice core data
Graph of CO2, reconstructed temperature and dust from the Vostok ice core.
http://en.wikipedia.org/wiki/Ice_core

Advertisements
Gallery | This entry was posted in Glaciology. Bookmark the permalink.

3 Responses to An Avalanche of Glaciologists

  1. But an Ice Cap is not a glacier, is it? 🙂 Why do I get the feeling that some are singing off key.

  2. Jim Coyle says:

    I agree that an ice cap is not a glacier but a land based cap such as the Laurentian Cap would move because as the snow accumulates and converts to ice it will get to the point that it would start to flow under its own mass, much like a cool tar. The speed of the movement would be somewhat driven by the curvature of the earth itself and the amount of melting on the bottom side of the “glacier”. Another factor might be the base rock under the cap. The hard basalts of the Canadian shield should allow easier movement but the sedimentary limestones and sandstone of the U.S. should provide more drag to slow the movement and allow for more accumulation of ice. Now the Greenland ice is captured in the interior basin of the continent and only flows out at, I believe 2 points. I also would believe that an Ice Cap would flow much slower that an alpine glacier due to the lack of impetus from the land forms, but it still moves eventually.

  3. Steve Garcia says:

    Jim – Greenland’s central ice (in the interior) has more than 2 outlets, but not very many.

    Louis – Correct. An ice cap is not a glacier. A glacier is an ice river, flowing down a mountain valley. Sometimes the valley is small, but it’s still a glacier. I’ve been on one in the Rockies that is only about 20 meters across. An ice sheet is on flat ground, essentially. This was especially true for the Laurentide ice sheet, which – based on today’s elevations – was basically the same elevation at it’s central place east of Hudson Bay as in Michigan, near the southernmost extent. Given the principle of isostasy, the center of the terrain underneath would have been lower than in Michigan, where the ice was not 2 km thick but only a few hundred meters thick.

    Jim – I am pretty sure that even where the Canadian Shield was basalts, overlying those in most places was sedimentary rock.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s