Livin' on the Wedge

Our journey has carried us out onto the Olympic Penninsula. This part of the trip was Summer’s pick, mostly I think because it is the home of F orks, Port Angeles, and the forest battlegrounds of vampires and werewolves of Twilight fame. I think that was fair enough reasoning, as I was so graciously given the opportunity to see the newest movie, Eclipse, on our first night in Port Angeles (pretty exciting stuff man). Thank you Summer, for now my night hiking in this region may be a bit more anxious, and I will always keep ice axe in one hand and bear mace in the other, as if that would do any good (for those unaware, apparently vampires and werewolves are quite fast; oh and the only way to tell them apart is that vampires wear clothes and werewolves do not actually own shirts but have a large selection of jean shorts). Prior to this, my only exposure to werewolves was Michael J. Fox in Teenwolf, which I feel is instantly more classic than Twilight. Oh well, although I clearly don’t have the same respect for the Volturi (spelled correctly?) as my tiny friend/wife, this place is very special to me in possibly an even geekier way…………

Ladies and gentleman, this region is an accretionary wedge!

Some of you already knew this, but you likely represent the minority, so perhaps a little background is needed. Sorry if these last few blogs are turning into repeating science episodes of Mr. Magorium’s Wonder Emporium. So where to start?

In a number of places around the world, oceanic crust is being subducted or basically pushed under an overriding tectonic plate where it heads for the mantle and is destroyed. This is the “recycling” process of plate tectonics where in crust is made at mid-ocean ridges and destroyed at subduction zones (see diagram). At the boundary between the subducting plate and the overriding plate, material is scraped off and piled up to create a zone of convergence and uplift, which often leads to formation of a mountain belt in active accretionary settings.

The Olympic Mountains, in all their vampire rampant glory, actually resulted from processes such as these. In this region, the Juan de Fuca plate is actively being subducted beneath smaller microplates that compose eastern North America, and in doing so forms that Olympic Mountains. This process also generates the famous Cascade volcanoes, such as Mt. Saint Helens and Mount Rainier, although that is a story for another time.

What makes the accretionary wedge so interesting for geologists is that it is often a veritable smorgasbord of rocks. This is because this scraping off process results in extreme mixing of seafloor sediments, metamorphic rocks with lots of cool minerals, as well as basalt and other oceanic crust igneous rocks. We call this amalgamation a mélange, which I believe is a French word that means “lots of random shit.” A mélange could also represent an assortment of cookies found on sale at Big Lots.

Thus, the people of the Olympic region (including vampires, werewolves, and dramatically morose humans that hang out with both) are in fact ‘Livin on the Wedge.’