Okay, now that you’ve gotten the “drift” of plate tectonics…
95% of all volcanoes tend to crop up at plate boundaries. Okay, so where are the other 5% hiding out? Sometimes right in plain sight, and not the most obvious of places.
When we were on our tour of the Earth’s interior, I mentioned that there are hot spots in the mantle called mantle plumes. These areas of superheated rock shoot upward through the mantle like a blow torch. As they reach the lithosphere, they burn a hole right through it. And when the crust is finally pierced, the magma down beneath comes jetting right through. These places where the mantle plume successfully burns through the crust is called a hot spot. And no, it’s not usually the best place to sync your WIFI.
One of my favorite examples of this hot spot action is Hawaii. The island chain is smack dab in the middle of the Pacific Plate. There isn’t a plate boundary in sight. Yet some of the most active volcanoes on the planet are right here. This is because of the hot spot that’s punching a hole right through the bottom of the Pacific plate and letting all that fantastic magma bubble right on up.
Okay, now take a look at Hawaii on a map.
You can distinctly see the 8 main islands on any map. However, there is a long archipeligo that trails across the Pacific Ocean, ending near Russia. Some of the islands dot the surface of the ocean as tiny islands; others are invisible under the waves. But each and every one of them are old volcanoes that have eroded over time. The ones near Russia are the oldest, and as you move southeast, they become larger and younger. Big Island of Hawaii is the youngest visible island, and three of its five volcanoes are considered active. There is even a new island growing off the eastern coast of Big Island called Loihi. If you’re looking for a new bit of land for a vacation home, you can start buying real estate here now, but it’s going to be a few thousand years before you (or your great-great grandkids) will get to lie out on the beach.
How was this massive chain of volcanoes created? It goes back to plate tectonics. The convective currents in the mantle below the Pacific Plate are rotating in a northwesterly direction, and the current moves the plate as it rotates. Here’s my favorite experiment to show how this happens:
DO NOT TRY THIS AT HOME. Seriously. The fire department will not be amused.
I take a candle and set it up so that the flame is vertical, like a mantle plume. Next, I hold a thick piece of card stock over the torch. It burns a hole in the card stock after a few seconds. But then I move the cardboard to the left, like a plate would move over the hot spot. The candle hasn’t gone out, and it starts burning a hole an inch over to the right. I move the card stock again, and the same thing happens. When I blow out the candle and pull the card stock away, I can see a “chain” of burned holes that look strikingly reminiscent of the Hawaiian archipeligo.
Hawaii isn’t the only hot spot on the planet, but it may be the most noticable one. Yellowstone is another fabulous example of a volcano that is fueled by a hot spot. Hop back on Google Earth and take a peek. If you look closely, you can clearly see a very large (and very eroded) trail of craters that has left a path through the mountains in its wake. The hot spot hasn’t moved, but the plate on top of it has.
There are plenty of other hot spots around the world, and off of it. Take Mars, our neighboring planet. It is home to some of the most massive volcanoes in our solar system. Seriously. Badass. The largest, named Olympus Mons, is three times bigger than Mt. Everest, and it was built entirely from the hot spot under it. (Mars does not have plate tectonics like we do, and since it doesn’t move away from the hot spot, the volcanoes there just kept on growing.)
Now that you have your hot spots and your plate boundaries settled, we have a good idea of where to find volcanoes. But the type of volcano that we will encounter won’t be the same cookie-cutter model everywhere we travel. Each volcano has its own distinct personality, which will be determined largely by what creates the volcano (plate boundary or hot spot) and the type of rock that composes the nearby crust.
Take me back to back to Volcanoes 101!