A Tale of Two Continents

Alas, the whirlwind month of April is drawing to a close, meaning that I will soon be working 5 days a week again. That will be a bit of an adjustment. The final bit of April travel was to Iceland, the glorious geological wonderland literally split between North America and Europe.

There are two types of the Earth's crust - continental crust and oceanic crust. You can probably guess where one might find each type. Oceanic crust is generally heavier, so when it reaches the edge of a continent, it sinks beneath the continental crust and ultimately dives down toward the center of the Earth to be melted and recycled. New oceanic crust is made at oceanic ridges, where hot magma is pushed up and onto the ocean floor, where it cools to become crust. So the whole cycle is a conveyor belt of sorts, moving at the blistering speed of roughly 2 cm per year. This whole process is nicely shown here:


Iceland is part of the oceanic ridge - the only place on Earth where oceanic crust is made above sea level. The western part of the island is part of the North American plate; the east is part of the Eurasian plate. Below is a photo of Thingvellir, one of the more dramatic locations where you can really see the distinction between the plates. The big cliff is the North American plate; a couple of kilometers to the east across a flat valley is the Eurasian plate.



It's pretty rare for geology to be so explicit. It's even more rare to overlay geological history and political history: Thingvellir is also the site of the world's oldest Parliament, where, as far back as 930, clan leaders would gather to announce the laws, their voices amplified by the cliffs.