Science Metaphors (cont.): Isostatic Rebound

Science, every now and then, interrupts its usual flow of thick, painful jargon to speak in metaphors that reveal the poetry at its soul and lay out a clear path to meaning in life.  I’m serious here.

I twitter-follow an author named Robert Macfarlane, whom our Michelle also likes, and who posted his phrase of the day, “isostatic rebound.” His definition was exemplary: ‘’the rise of land masses after the great weight of glacial ice was lifted at the last Ice Age’s end. Areas of northern Britain are still rebounding by up to 10cm a century; southern England is sinking by 5cm. We live on a restless earth.”  I’m less interested in the restlessness – anyway, I’m skeptical about 10cm a century qualifying as restless – than in the rebound.

Land masses, continents or parts of them, periodically get covered by glaciers, miles deep and unthinkably heavy, and under that weight, the land masses sink.  The land that seems to me to be the whole world, is, as geologists enjoy saying, just a ~35-mile thick, hard scum on the top of ~1,800 miles of viscous mantle which, oddly enough, is denser than the land.  So the land floats and when enough ice gets piled on top of it, the land sinks.

I myself am prone to depression — though having seen friends with real, hospitalizable depression, I’m clear that mine is a sissy sub-type.  It’s still nothing to mess with, this conviction that I am dull and incapable of doing anything worth doing, I can’t do it, it’s not worth even trying.  I think of depression as my great enemy.  It moves in for no good reason, or for reasons that are pretty subterranean.  One day I wake up and there I am, useless, afraid, too inert to move with any intent.  I’m betting that more people have this than don’t.

Isostatic:  it’s Greek, “iso” meaning same or equal + “static” meaning static, as in steady.  The noun is isostasy, accent on the “so,” and is tricky to say. Isostatic describes a thing in equilibrium, the pull of gravity and the push of buoyancy cancelling each other out.  In this case, it means a time with no ice, an interglacial, when the land masses are just sitting there, their impulse to sink perfectly balanced against their impulse to rise. I am in love with isostasy.  I am so in love with isostasy, I go to bed at 8:30 or 9:00 every day and I order the same things at the same restaurants every time. 

But, then, then the ice melts.  Melting miles of ice takes a long time, decades or centuries or millenia, depending.  The burden of gravity lightens, and over more millenia the buoyant mantle lifts the land – isostatic rebound.  North America still rises hallelujah! And 10,000 years from now, it’ll be floating 400 meters higher.

One winter I was in Florence, Italy and a depression had moved in: nothing delighted, not even roast pork, and the art made me sad.  But I walked all around and the cold stone streets were full of women walking with energy and intent, linking arms, heads leaning in toward each other; and small groups of men in black coats, backs to the rest of us, talking with their hands; and little kids bundled up into near-immobility and lurching around like tiny bright wind-up toys.  One night, on one of the bridges, one little bundled-up kid yelled, “Guarda, mama!  Guarda la luna!” and I heard him as though he were speaking English, Look! Mama, look at the moon!  He stood and looked at it, Mama looked at it, I looked at it. So the depression that had, for no good reason, moved in, now and also for no good reason, moved back out.  Isostatic rebound: what falls will rise again.


Photo: 1947 photo, via Wikimedia Commons


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