What Lies Beneath? Exploring the Subterranean Fury of Plate Tectonics
By Tom Greve
As human beings here on planet Earth, we typically marvel at the sky with a certain fascination. After all, the sky implies limitlessness; an infinite distance surpassing the physics of life on the ground. We marvel at the night sky, we imagine the travels of astronauts into outer space or to the moon, and we conjure images of still-imagined life on other planets floating in the great beyond.
But to witness other-worldly power and astronomical forces in action, a person’s gaze is better fixed downward than it is skyward. Because for all the promise of the heavens, for all the secrets of astronomy and space exploration, and for all the overwhelming SIZE of the wild blue yonder above us; it seems the sky may hold far less power, fury, and bombast, than what lies beneath the ground.
As a life-long Midwesterner, I have never felt the ground below me shake, buckle, or spasm. The closest thing to seismic activity most Chicagoans encounter is the dull rumble of a construction crew swinging a wrecking ball into an old building down the street. But in writing “Let’s Explore Science: Plate Tectonics and Disasters” for Rourke Publishing, I found compelling reasons to be at least as awed by the seismic forces known to be lurking below us, than by the mysteries held in the sky above us.
Plate tectonics can build and move mountains, it can also break them apart. It can re-route rivers, and re-draw coastlines. It can push the seafloor apart and spew unimaginably hot lava out of the ground like a tube of toothpaste being squeezed.
In short, plate tectonics amounts to the planet’s majestic and yet tragic recycling of its outer layer in a dynamic that is both gradual and yet sudden, imperceptible and yet spectacular.
The basic premise of Plate Tectonic theory is that Earth’s surface or “crust” is made up of dozens of misshapen plates, kind of like the surface of a cracked hard-boiled egg. Except Earth’s plates-unlike the pieces of the egg- can move.
The nature of these movements and their affect on the planet provides the basis of the study of plate tectonics. Borrowing from other scientific disciplines like geology, archeology, and paleontology, plate tectonics is the observed action of subterranean heat and pressure over time on the earth’s surface. This most commonly and directly affects the areas which sit along the edges of the plates. These edges are known as plate boundaries. Most of the earth’s plate boundaries are under the oceans.
The planet supplies its own source of heat and pressure. In fact, the inside of the earth is a massive reservoir of unimaginable heat. While the innermost part of Earth -known as its “core” – is a solid ball of immensely hot iron, the layer existing between the core and the crust –known as the mantel – is a cauldron of superheated rock. Some of the rock is so hot that it becomes liquefied and moves outward in convection currents through the earth’s mantel toward the crust.
The pressure of liquefied rock moving toward and finally through the earth’s crust is what can – over time – create movement in Earth’s crustal plates. When plates move, the results can be the stuff of both majesty and tragedy.
That’s because the symptoms of Earth’s plate tectonic movement can take millions of years to unfold, or they can bring about cataclysmic change in a matter of just seconds. Heat and pressure can gradually create an entire mountain range because of one plate crumpling up due to the advance of another more dense plate. But those symptoms can also unleash the instant fury of earthquakes, tsunamis, and volcanic blasts that destroy life on a massive and terrible scale.
To wit: It can take millions of years to build a majestic mountain range like the Cascades of the western U.S., but it also takes just seconds for the same forces to blow the top of a single mountain apart in a tragic volcanic blast like Washington’s Mount St. Helens in 1980.
It might take millions years for two converging plates to form what’s called a subduction trench under the ocean. Yet it might take just seconds for the buckled top plate to snap back to its former shape. This action is the basis of so-called mega-thrust earthquakes like the one that decimated coastal Japan – along with an accompanying tsunami – in March of 2011.
Or, it can take millions of years for two plates to snag and grind along each other’s edges, until they lurch free of each other in a massive transform fault earthquake like Haiti’s in 2010, or San Francisco’s in 1906 and again in 1989.
Whether sudden or gradual, spectacular or nearly imperceptible, change is constantly happening along the Earth’s surface. These changes are the work of plate tectonics.
Rourke Publishing’s “Let’s Explore Science: Plate Tectonics and Disasters” tries to lay out the various kinds of plate boundary movements. It gives historic examples of each, and provides illustrations of both the majesties as well as the tragedies brought about by plate tectonics.
Save the date! June 23, 2012 Nonfiction Book Blast 1:30 to 3:30 p.m.