Snow as Molasses
The end of winter is upon us and although we will be happy to say goodbye to the cold and welcome warmer weather, this season’s lack of snow sparked a lot of chatter about global warming and the rapidly moving and disappearing glaciers around the world. If you’ve been following the discussions about our rapidly diminishing glaciers, the dynamics involved are hard to imagine. Two years ago, oddly fluctuating weather over a 3 week period gave us a wonderful illustration in miniature of how glaciers behave right next to our house!
After about a 14 inch snowfall in February, a spate of warmer weather fluctuating around freezing, began the slide of the snow-pack on our metal shed roof. This is not unusual. It manages to typically hold together until it is hanging up to 24 inches before breaking off under its own weight. Arctic glaciers do the same thing. As they slide off the land into the sea, they break apart in a process called calving, forming sometimes enormous icebergs that may float hundreds of miles into shipping lanes. It was this process that doomed the Titanic when it struck one that may have been the size of a football stadium in the middle of the night. (Remember, nine tenths of an iceberg lurks invisibly under the surface).
But this time, due to the daily warm and cold breezes circulating under the roof, it held together for 3 weeks, as it slowly slid down over a 4 foot gap until meeting the ground and folding over on itself. It was a truly glacial event.
As the underside of our little glacier came into view from below, its ‘glacial erratics’ (the pine needles and tree litter lying on our roof) were transported slowly away from where they had fallen. Seeing this, it was now easy to understand why we can find house-sized boulders in our region that are not native to our geology.
This 8 foot tall, 4 ton erratic was left behind on a 1400 foot high NY mountain ridge after the mile thick glacier retreated- a mere pebble on the landscape.
They were carried- many hundreds of miles, from the north by the expanding glaciers during the onset of the last ice age, and left behind for us when they again started their retreat.
Polished smooth and grooved by the last advancing glacier, this Manhattan Schist bedrock can be found near the south side of the Sheep Meadow.
t was also easy to now envision the glacial scars (long north- south grooves carved into exposed bedrock) that were made as these enormous boulders were slowly dragged south. If you ever visit New York’s Central Park, you can find many beautiful examples on exposed bedrock of Manhattan Schist in the south area of the Sheep Meadow. The park is also dotted with many glacial erratic boulders. I’m sure that if there had been gravel on my roof before the snowfall, the sliding snow pack would have made similar scores in the finish.
Discussions about our shrinking glaciers also mention that the ‘glacial’ pace of their marches to the sea have begun to speed up in recent years. Scientists say that as warmer temperatures on glaciers’ surfaces cause faster melting, the melt water travels through crevices to the bottom of the glaciers and then lubricates the bedrock and increases the speed of the slide down to the sea. Our little glacier demonstrated this as well. Usually the snow pack would stay on the roof, sliding so slowly that after overhanging 24 inches or so, it would break off of its own weight. But this time, warm breezes playing across the metal underside of the roof, melted the snow pack bottom enough to lubricate the slide downward so fast (a blistering pace of 3 weeks) that the pack managed to hold together long enough to touch the ground 4 feet away. With daily temperatures hovering around freezing, it slowly folded over on itself until finally breaking.
Discussions about our shrinking glaciers also mention that the ‘glacial’ pace of their marches to the sea have begun to speed up in recent years. Scientists say that as warmer temperatures on glaciers’ surfaces cause faster melting, the melt water travels through crevices to the bottom of the glaciers and then lubricates the bedrock and increases the speed of the slide down to the sea. Our little glacier demonstrated this as well. Usually the snow pack would stay on the roof, sliding so slowly that after overhanging 24 inches or so, it would break off of its own weight. But this time, warm breezes playing across the metal underside of the roof, melted the snow pack bottom enough to lubricate the slide downward so fast (a blistering pace of 3 weeks) that the pack managed to hold together long enough to touch the ground 4 feet away. With daily temperatures hovering around freezing, it slowly folded over on itself until finally breaking.
Watching our little glacier fold over slowly during a period of almost 3 weeks brought to mind molasses being poured from a jar and the old English saying ‘slow as molasses’!
If you’d like to see a time-lapse of the process, please click the link below.
If you’d like to see a time-lapse of the process, please click the link below.
If you’d like to see calving in action, please click below
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