Sit on a continent, go for a ride.

My continent moves at a nail's pace. This is what it did since 2009.

My continent moves at a nail’s pace.
This is what it did since 2009.

Of course you know about plate tectonics. Sit on a continent, go for a ride. You were probably told in grade school that continents move with as much speed (and unstoppable determination) as your fingernails are supposed to grow. That’s more-or-less true, unless we use the East Pacific Rise Plate as our model – it moves much faster and that would imply that you have wicked claws. The average speed  for continental motion is two centimetres per year, but you could get dizzy riding the East Pacific Rise –  every two years it moves the width of a charter airplane seat.

These motions are not all smooth sailing. On some parts of the planet, sudden jerks result in horrendous earthquakes. The mid-sized Nazca Plate is grinding itself under South America at a rate over 8 centimetres a year. Its movements are not steady. These are not the progressions of plodding oxen, but rather the leaps of a kangaroo. Sometimes the abrupt jumps are astonishing. I narrowly missed experiencing a violent three-metre crustal leap during the 2010 Chilean earthquake. Near the epicentre, the town of Concepción moved the length of a car in a single lurch as one tectonic plate climbed over another. Now that it has jerked ten feet, it will probably not move again for 50 years. Elsewhere (Iceland, for example) the ground is fairly steadily ripping apart. The place has volcanoes (Eyjafjallajökull kept me in central Europe for a week in 2010 when all flights home were grounded.), but Iceland has few serious earthquakes. However, the island nation is simply  slowly ripping apart.

Plate Motion Table  I thought it would be interesting to see how my part of the world is creeping along under the power of plate tectonics. I found a plate-motion-calculator on this UNAVCO site.

UNAVCO describes itself as a non-profit, university-run “consortium that facilitates geoscience research and education”. Until today, I had not heard of them. They seem to provide massive quantities of GPS-measured plate motion data. You can download huge files collected from around the world and use them to make your own discoveries.

On the page at the end of this link, you will find a rather complicated-looking form that lets you type in your latitude, longitude, elevation and much, much more. There are actually 25 fields in which you may enter data, but I ignored almost all of them. You can see in the image above that I simply input my Calgary latitude and longitude (51 N and 114 W, which needs entered as minus 114 to designate the western hemisphere). The database returned the drift of my house. Calgary seems to be averaging 1.940 cm/year, in a southwestern direction. This is slower than most places on the planet, which surely explains why Calgary is famous for its lack of vertigo epidemics. The velocity from UNAVCO’s website is shown to you in a table, or in a download file, if you prefer. You can see my results here:

Calgary Plate MotionI ran the program again, using Vancouver’s location. Vancouver, about 700 kilometres west of us, had an almost identical result: heading southwest at 1.993 cm/year. Vancouver is apparently outrunning Calgary at a rate of half a millimetre per year. Not much chance of western North America ripping apart somewhere along the TransCanada Highway within my lifetime. However, I did a third measurement, 200 kilometres west of Vancouver and found quite different values. The ocean floor beneath the Pacific (the Juan de Fuca Plate), just off Vancouver Island, is approaching Vancouver at 2 cm/year, heading precisely northeast. This, of course, is already well known and amply documented and it explains earthquakes along the famous west coast subduction zone. Yesterday, in fact, a 6.1 magnitude quake shook the Haida Gwaii region, just north of Vancouver Island.

I hope you have time to enter your hometown’s location and some of your favourite cities. I input a few more: New York City, northwest at 1.52 cm/year; London northeast at 2.47 cm; Tokyo northeast at 2.92; Kolkata northeast at 5.52; Beijing east-southeast at 2.96 cm/year. By the way, if you enter locations on the African plate (say, Cape Town, for example), you get zero motion. Not that Africa is exempt from plate tectonics – it is moving, of course. But all the preceding motions are with respect to Africa – geophysicists general choose to use that continent as the reference. Hope you take a few minutes to discover your own continental motion.

Arrows indicate plate movement with respect to the African Plate.

Arrows indicate plate movement with respect to the African Plate.

About Ron Miksha

Ron Miksha is a bee ecologist working at the University of Calgary. He is also a geophysicist and does a bit of science writing and blogging. Ron has worked as a radio broadcaster, a beekeeper, and Earth scientist. (Ask him about seismic waves.) He's based in Calgary, Alberta, Canada.
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1 Response to Sit on a continent, go for a ride.

  1. Pingback: Created Last Thursday | The Mountain Mystery

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