Posts Tagged ‘glaciology’

McCarthy Glaciology Summer School 2010: In Limerick Form

November 29, 2012

These are some limericks I wrote while attending the 2010 Glaciology Summer School in McCarthy, Alaska. I tried to write one about each subject that was covered in lecture, although I think there are a few missing. N.B.: the tidewater-glacier-as-leveraged-bank analogy is from the actual lecture.

Ice dynamics
Though its speed is exceedingly low,
Ice is fluid, as glacier shapes show.
Non-Newtonian viscosity
Determines velocity
According to Glen’s law of flow.

Ice fabric and anisotropy
At the microscale, ice grain migrations
Derive from crystalline dislocations
Anisotropies cause
New constitutive laws
To account for in our simulations.

Subglacial hydrology
Water flows through the glacier like blood
Makes it slide over bedrock and mud
When a tunnel melts through
Or ice dam breaks in two
Out comes pouring a Biblical flood

Tidewater glaciers
When these tidewater glaciers retreat
The destruction’s both fast and complete
It advances again
On a borrowed moraine
Like a leveraged bank on Wall Street

Mass balance
Adding up rain, wind, heat, cloud and sun
To get melt isn’t very much fun
You could try degree-day
It’s an easier way
But a somewhat less accurate one

Glacial thermodynamics
Now the species of glaciers are three
Cold are fully below zero C
Temperate’s always at freezing
Polythermal’s a pleasing
Combination of types A and B

Remote sensing with ICESat
When inspecting the tracks of ICESat
Look for spots that are curiously flat
Or locations that flex
From concave to convex
It’s a subglacial lake doing that!

Gravitational remote sensing
For the weighing of glaciers, a scale
Is inevitably much too frail
But science saves face
By celestial GRACE
Which delivers the mass-balance Grail

Laser Altimetry
To determine an ice-surface height
Send out regular pulses of light
Measure time to bounce back
Then, repeating your track
Demonstrates warming glaciers’ dire plight

Inverse methods
To extrapolate former conditions
Using presently measured positions
Although methods inverse
May inspire you to curse
They’ll reveal past climatic transitions

Debris-covered glaciers
Grand white Kennicott looms above town
But its foot is all filthy and brown
If we clean off the sand
It’ll look mighty grand
Till, uncovered, it melts, and we drown.

The consequences of setting forty glaciologists loose on a small town’s alcohol supply
There’s a flow law for ice strain and shear
What we need is a flow law for beer
Given glacier grads, N,
And a drink rate X, when
Will all booze on the shelves disappear?

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The Story of Glacier Joe

November 28, 2012

Written at the request of the President of the International Glaciological Society, for the 2012 IGS meeting in Fairbanks. In the style of the classic The Cremation of Sam McGee by the great Robert W. Service.

The Story of Glacier Joe

There are strange things done ‘neath the midnight sun
   By the folks who study ice
They’ll spend hours of time on a glacier climb
   Just to check on some strange device.
With their crampons donned they ascend beyond
   The realms where sane folk go
Yes, they’re all bizarre, but the oddest by far
   Was the one called Glacier Joe.

The letters I.D. marked his sole degree–
   “That’s ‘Doctor of Ice’,” he’d say
From a glacial perch he’d perform research
   In his own peculiar way.

He’d carefully take his ablation stake
   Back home at the start of spring
For the sunny glare might cause wear and tear
   If snowmelt exposed the thing.
He hated to dig, so his snowpit rig
   Was a big overclocked hair dryer
He never would change, though his numbers were strange
   And his notebook often caught fire.

I answered an ad for a glacier grad
   That’s how I joined Joe’s lab
He’d heard some stories ’bout inventories
   And wanted to take a stab.
Our first sortie was altimetry
   With a stopwatch and big flashlight
But so blindingly fast those light pulses went past
   That our glaciers had negative height.

So next Joe raves about seismic waves
   And runs out to buy T.N.T.
But it came to pass that each change in mass
   Was just what we’d blown to debris.
He thought he’d shoot for the theory route
   With area-volume scales;
So Joe would divide feet-long by leagues-wide
   And end up with volume in bales.

Said Joe, “I guess the I.G.S.
   Are a bunch of clever sots,
They’re hosting some sym-pos-i-um
   So I’ll go expound my thoughts.”
He showed fifty-six slides dense as bricks
   With text in Comic Sans
And spoke with such flair that the Session Chair
   Dragged him offstage with both hands.

We went for beers with our glacial peers
   And they told us of what they did
And all this news made Joe enthuse
   Like a sweet-shop-dwelling kid.
So back we went to our field tent
   To add to our data stores
Energized anew, we both set to
   The task of drilling cores.

We drilled and cored and dug and bored
   ‘Til our hands were sore and tired
And I strained my eyes to analyze
   The samples we acquired.
Well, day by day went on this way
   And the data rose like the tide
But nary a bit of that data would fit
   No matter how hard Joe tried.

“I’ll never know how the glaciers flow,”
   Joe cried out in despair
“From the top to the bed, it’s all over my head–
   I tell you, it just ain’t fair.”
“I know some folks can use full Stokes
   But my models ain’t even one-D.
From densification to surface ablation
   These glaciers befuddle me.”

And after this spiel, Joe turned on his heel–
   And threw himself down a moulin!
With a rope from the sledge I raced to the edge
   But by then he was long gone.
Unhappy and damp I returned to the camp
   And pondered poor Joe’s fate;
Down the hole he’d been flushed to be frozen or crushed
   It was awful to contemplate.

But later that night in the fading light
   I awoke to a bellow grand
Like a trumpet brass from a deep crevasse
   Saying “NOW I understand!”
“It’s all so clear from way down here!”
   Exclaimed the voice with glee.
“Every wax and wane of stress and strain
   Is an open book to me!”

“I can see each kernel of snow and firn’ll
   Become a crystal grain
And each drop of melt makes its presence felt
   In the branched subglacial drain.”
The ice folks say that to this day
   A student or a seeker
Can strain an ear, and faintly hear
   From beneath the ice: “Eureka!”

There are strange things done ‘neath the midnight sun
   By those studying ice and snow
Yes, they’re all bizarre, but the oddest by far
   Was the one called Glacier Joe.

Firn Chantey

November 27, 2012

This is about the work I’ll be presenting at AGU. Written at the request of the University of Alaska Fairbanks crowd, sung to the tune of The Sailor’s Prayer (not to be confused with the somewhat more serious “Sailor’s Prayer” that’s the first Google result for that song title.) I very much want to record all these and post videos, but I haven’t really worked out a good recording setup.

If we wish to learn
About the firn
Upon the ice sheets polar
We’ll want to know
About the snow-
fall and the input solar

Chorus: Oh, snow is white
And clean, and bright
A tricky thing to model
But easy flowed
The Matlab code
‘Longside a friendly bottle

Some grains of snow
Will slowly grow
While others are a-shrinkin’
Which ones win out
Is still in doubt
And needs a bit of thinkin’

(chorus)

Grains change their state
They sublimate
From many different places
When they commence
To recondense
They prefer partic’lar faces

(chorus)

And so we find
Grains are aligned
C-axes all together
And from this state
We can relate
Ice flow to ancient weather

(chorus)
(chorus again, with FEELING)

The Ballad of AGU

November 27, 2012

The American Geophysical Union Fall Meeting (usually just referred to as AGU) is when something like 15,000 scientists descend on San Francisco’s Financial District for a week. There are talks and posters, of course (so many talks and posters!) but as with any convention the main point is to connect with new colleagues and re-connect with old friends. This is a poem I wrote for the Cryosphere gathering at AGU a couple of years ago. The meter and rhyme scheme are modeled after “The Egyptian Diamond” by Randall Garrett.

I will be at AGU again next week! Monday is Science Open Mic Night at Jillian’s Billiards Club, so I have to decide what to perform, which is going to be tricky.

The Ballad of AGU

Sunday, just a bit past five
And you’re feeling half alive
With your poster on your shoulder as you stumble to your flight
You’ve been staying up too late
Your data won’t cooperate
And you found a whole new error around ten PM last night.

But now you’re at AGU
There’s a million things to do
There are friends from far-off places who you haven’t seen all year
In the morning, though, I’m betting
You will find yourself regretting
That moment you decided “Sure, I’ll have another beer!”

Bright and early, you will fight
The grand excesses of last night
You will struggle bravely out of bed and stagger to Moscone
There’s a talk you must attend
By an early-rising friend
And a cutting-edge announcement you suspect might be baloney

Now you’ve coffee cup in hand,
with which to aid your mental band-
width, for a firehose of data’s aimed directly at your brain
There’s a clever new device
To gauge the temperature of ice
And a host of novel ways to watch a glacier from a plane

There’s a brand-new data set
Barely even processed yet
That details the Greenland ice sheet’s elevation, shape and speed
There’s a fellow at a booth
Who, if his pitch has any truth
Sells an instrumental system that does everything you need

There’s an algorithmic way
To take the data from a day
And extrapolate behavior of the system for a week
There’s a dozen gloomy talks
On how the planet’s on the rocks
And the global warming outlook’s gotten just a bit more bleak

Then, before you’re really read
When your spiel is still unsteady
You’re onstage—your poster’s posted and your work you must explain
Visitors interrogate you
Some to praise, some to deflate you
And your voice is going hoarse from giving out the same refrain

But look! some kind soul brought beer
And the end is getting near
And suddenly it’s over, just as quick as it begun
Battling through the teeming streets
You reach a trove of drinks and treats
And the denizens of Cryosphere are here to have some fun!

Whys and Wherefores

January 4, 2011

This one’s a bit late–sorry about that! I’ve gone for a longer post to make up for the tardiness.

Antarctica, as you may have noticed, is a long way away from almost everything. And even aside from being distant, it’s logistically tricky to get to. The Southern Ocean is stormy and mercurial at the best of times, every iota of fuel and supplies must be shipped in, and the preponderance of ice and snow presents its own special problems. So why have we made the trek back once again?

You may recall that last year we came down seeking types of ice that can’t be found anywhere else on Earth: sea ice so cold that the salts trapped within it can crystallize, and ice whose surface has sublimated away to leave behind a crust of the salt mirabilite. This year we’re once again seeking ice that exists nowhere else. In this case, we’re looking for ice that has formed from the accumulation of snow and eventually become re-exposed to the sun by sublimation without ever experiencing temperatures above freezing.

There are three main layers to the Antarctic ice sheet. At the surface is snow. Over time, as surface snow is buried by the accumulation of later years, it compacts and grows dense and hard. This deep-down, compacted snow is called firn. In the rest of the world “firn” simply means snow that has survived through the summer melt season, but in Antarctica, where there is no summer melt season except at a few places near the coast, firn is sometimes defined as snow that has reached a certain density (550 kilograms per cubic meter, which is the density at which simple rearrangement of ice particles gives way to more complicated densification processes.) The firn continues to grow denser under the weight of the snow and firn above it until the spaces between snow grains close off to become bubbles, and the firn becomes ice.

Blue ice stratigraphy

The ice flows under its own weight. In some places, the ice surface may flow into an area of the ice sheet where sun and wind vaporize (or sublimate, which means to turn directly from solid to vapor) the snow faster than it can accumulate. In this case, the snow on the surface will sublimate away, exposing the firn below and eventually the ice. And that firn and ice—exposed to the sun, yet never melted—is unique to Antarctica. These “blue ice zones” are of interest to meteorite hunters, because meteorites that may have been buried in the snow become exposed, and are easy to spot on the surface. My colleagues already found and collected some meteorites during their first trip out.

We’re interested for a different reason, though–we want to know how much light reflects off of these blue ice zones, because there would have been a lot of them on Snowball Earth. (Here’s a great article in the Antarctic Sun that talks about our research.) Many areas of Snowball Earth, particularly near the equator, would have been so dry that snow sublimated away faster than it could accumulate.

These areas of exposed blue ice, being much darker than snow, would have absorbed a lot of sunlight and had a significant effect on the planet’s balance of energy. So knowing exactly how much sunlight they absorb is important to people trying to model Snowball Earth.

So that’s why we’re here. Mostly, anyway–some of us, including myself, also have a keen interest in snow and want to do some side projects involving the microstructure of snow and bubbly ice. But more on that later!