Archive for the ‘Glaciology’ Category

A good week for defense

January 19, 2015

I successfully defended my dissertation last Thursday! Defense title: “Measured and modeled albedos of sea-ice surfaces on the oceans of Snowball Earth.”

Here’s how I summed up my talk:

A planet orbits round a yellow sun
Light years away or megayears ago
Its seas are dark, its continent is dun
But brilliant sea ice sets its pole aglow

Its CO2 drops dangerously low
Tendrils of ice reach from the polar caps
That sparks a feedback: oceans turn to snow,
Glaciers push in to close off any gaps

The oceans roiled with countless living cells
Who learned to take their energy from light
Now locked beneath the cold of Dante’s hells
They starve; how long must they endure this night?

Why has this happened, and by what device?
To know, we must investigate the ice.

As sea ice freezes, tiny drops of brine
Are trapped between the quickly forming plates
When cold enough, their molecules align
Into sodium chloride dihydrates

The solid crystals catch and scatter light
Reflect it back, refuse its energy
And I myself have quantified how bright
The surface of the sub-eutectic sea

And in our lab we’ve watched salt ice sublime
With instruments ingeniously designed
The secrets of another space and time
Unfold beneath my models and my mind

This is my work; I hope you will agree
That it is worthy of a Ph.D.

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.

Graupeling with Seattle Snow, or, Rime and Reason

January 17, 2012

Seattle is enjoying one of its all-too-rare episodes of snow—well, I’m enjoying it, at least. Upon leaving the house this morning to walk to work, I found the sidewalks lightly dusted with an interesting type of snow we in the biz call graupel.

Most snowflakes, the six-sided ones you probably think of when you think of “snowflake”, grow by the condensation of water vapor. The individual water molecules attach to the snowflake in an orderly fashion, like building a structure out of Legos, and you end up with a regular crystalline shape.

Sometimes, though, the snowflake will pass through a cloud of water droplets as it falls down to the ground. As it hits the snowflake, the whole water droplet will freeze almost instantly, retaining its rounded shape. The snowflake bounces around in the cloud of water droplets, accumulating more and more, and your orderly Lego structure starts to look like someone has been pelting it with spitballs. These frozen water droplets are called rime. When so much rime has accumulated that the underlying shape is no longer visible, the snowflake has become a pellet of graupel.

In the picture below (sorry for the questionable quality, it’s a cell phone camera) you can see quite a few snowflakes; I’ve circled one on the left that retains the crystalline snowflake shape, and one on the right that’s still clearly six-sided, but so covered in rime it looks like it’s wearing a fur coat. (My advisor called this a “textbook” rimed snowflake.) Elsewhere in the picture you can see a few pellets of shapeless graupel.

Rimed and unrimed snowflakes

Circled on the left: a classic snowflake. Circled on the right: a snowflake covered with rime (frozen water droplets.)

Incidentally, this also goes to show that you don’t need a microscope to appreciate snowflakes; your eyes will do just fine. I’ve found that a good method is to go out when the snow is falling and catch snowflakes on a fuzzy hat, either faux fur or knitted with especially fuzzy yarn; the snowflakes will be caught on the fibers, where they can be more easily examined without melting.

One glacier, two glacier, fast glacier, blue glacier

June 20, 2011

Oneof the tricky bits about glaciology is distinguishing between different ice features. There’s the question of terminology, such as figuring out when an icefield (a large mass of glacial ice, often with many glaciers flowing out of it) becomes an ice cap (same thing, but larger and tending to be dome-shaped) becomes an ice sheet (like an ice cap, but over 50,000 square kilometers.) Today my dad (happy Father’s Day!) alerted me to an article in the Anchorage Daily News discussing the difficulties of counting glaciers.

Glaciers, like rivers and streams, often flow into each other or split apart. Exactly when one glacier becomes two glaciers can be a tricky thing to determine, and now that so many glaciers are retreating, these points of merging or splitting may disappear altogether. So what was one glacier with three branches might become three glaciers. For instance, in the photo below you can see how several tributaries merge into a single calving front at Columbia Glacier.

Columbia Glacier in 2004

Columbia Glacier in 2004. Photo by W. Tad Pfeffer.

(I got this photo from Wikimedia Commons.)

And here’s an amazing timelapse video from the Extreme Ice Survey (I’ve seen it shown at a lot of glaciologist meetings and conferences) that shows how the front of Columbia Glacier retreats back until the several “tributaries” start to look like separate glaciers again. It goes so far and so fast they have to move their camera several times so that the front of the glacier stays in the frame.

Of course, for many purposes, the important thing is not how many glaciers there are, but how much ice there is in the glaciers. Although there’s not very much water stored in mountain glaciers like these compared to the water stored in the great ice sheets of Antarctica and Greenland, the mountain glaciers are melting extremely quickly (well, quickly by glacial standards) so a major percentage of current sea level rise is due to meltwater from glaciers like the Columbia. You can’t tell how thick a glacier is just by looking, so determining the volume of the world’s glaciers—and just how fast that volume is changing—is one of the important ongoing problems in glaciology.