Those of us who live on the Pacific Northwest know that it is a geologically dynamic place. It's not something we are generally aware of, but earthquakes periodically shake us into remembering just who - or what - is in charge. The volcanoes that dot the landscape up and down the coast, from Alaska to northern California are perhaps more gentle reminders in that they erupt into our consciousness much less frequently.
Fewer people however are aware of what happens offshore. As we stare out over an idyllic Pacific sunset, there is nothing to suggest that beneath the waves lies a geological battle taking place, one that is responsible for the earthquakes and volcanoes on land, as well as yet more earthquakes and volcanoes on the ocean floor. This is an area of real interest to scientists - partly to help better understand our earth systems, and partly to better understand a geological feature that causes the biggest threat to the the population of the area.
Juan de Fuca's Legacy
Juan de Fuca was a Greek explorer working for Spain in the 1500s. He wasn't the first to sail the waves of the Pacific Northwest, but his legacy lived on with name of the Juan de Fuca Srait between Vancouver Island and mainland Canada. The Strait gave name to the tectonic plate that lies beneath the waves that he sailed on.
The Juan de Fuca plate is a section of the Earth's crust. Like the other tectonic plates, it is the hard, rocky crust of the planet that sits atop the hot mantle below. Technically the Juan de Fuca plate is a microplate (i.e. smaller than regular tectonic plates). Granted it used to be bigger, part of the older Farallon plate, but despite its current diminutive size, it still packs a punch when it comes to its ability to face off against its neighbours, the giant Pacific and North American plates.
In this satellite image, we can see the plate clearly. The zig-zag line on the plate's western edge marks the Juan de Fuca Ridge - a ridge of volcanoes that periodically pumps out molten rock to create new ocean floor. On the Juan de Fuca side of the ridge, the new floor moves towards the North American continent. On the eastern edge of the plate, the old ocean floor sinks beneath the North American plate in the process known as subduction. Check out a good animation of this process here.
Ocean Floor Landscape
We're all familiar with Google maps Satellite view, but have you ever gone exploring over the oceans and zoomed in to see what you can see? When we zoom over the likes of the Juan de Fuca ridge we can quite clearly see the plate tectonics at work. We can see the main ridge, with volcanoes pockmarking the ocean floor. The parallel lines are the new ridges of rock that form. The lines on the outside are the oldest, those at the centre of the ridge are the youngest.
Volcanoes & Earthquakes
It is these offshore volcanoes that are ultimately responsible for the dynamic nature of the Pacific Northwest. These are the volcanoes that create the new rock that sends the Juan de Fuca plate eastwards to collide with the North American plate. The collision is the cause of many of the earthquakes that rattle the region - from the build up of pressure along the 'subduction zone' between the Juan de Fuca and North American plates.
The Juan de Fuca Ridge, like other similar ridges around the globe, are home to hydrothermal vents - also known as Black Smokers. Like underwater hot springs, these grow as chimneys off the ocean floor and are extreme environments that are of huge interest to scientists. From their deposits of metal rich minerals, to the sulphur-loving organisms that thrive in the hot waters, they are fascinating places. The Juan de Fuca's vents are well studied. Over the years, samples of hydrothermal vent material has been brought on land to assist in their study. Last year we were very fortunate to acquire a donation of vent material from the Axial Seamount (volcano) offshore of Oregon, making this one of the most important donations to our collections.
Header image: underwater eruption taken on Submarine ROF 2006, NOAA Vents Program, via Creative Commons
Black smoker image: smoker with tube worm community from the Endeavour Ridge, University of Washington; NOAA/OAR/OER, via Creative Commons
The following article was originally published in the Spring 2019 edition of What's Insight magazine.
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