Some of us might remember that day on March 20, 1980, when a series of earthquakes began that caused Mount St. Helens to violently erupt just two months later. It was likened to the eruption of Mount Vesuvius in 79 A.D. which destroyed the city of Pompeii, and the remnants of this major event can still be seen and felt today.
Nearly all the major mountains in Washington are volcanoes, and the five largest ones are still active today. But why are there so many here and not in, say, our Idaho neighbor?
It turns out that our Cascade Range was a couple million years in the making (more like 40 million years!) and that our handful of volcanoes are part of a much larger assortment of seismic regions all around the Pacific Ocean!
Why does Washington have volcanoes?
Washington State is home to five volcanoes that are classified as not only active, but also as a high threat. These, of course, are the mountains we know as Mount Rainier, Mount Adams, Mount Baker, Glacier Peak and Mount St. Helens.
These volcanoes are monitored by the Pacific Northwest Seismic Network and the Cascade Volcano Observatory, both of which monitor for earthquake activity, volcanic activity, potential hazard zones, high-risk areas, evacuation plans and environmental impacts. This website, for example, shows how many earthquakes these volcanoes have experienced in the past month! Spoiler alert: it’s a lot more than one might think.
These volcanoes must be monitored because while they are still fairly safe to hike, bike and camp around, it’s only been four decades since the last eruption happened at Mount St. Helens in 1980. A mountain losing its upper half is no mere walk in the park, and Washington’s other volcanoes are just as likely to cause as much damage, if not much more, if they should explode.
Washington’s five major volcanoes make up just one section of the larger Cascade Volcanic Arc that runs from southwestern British Columbia to Northern California, covering a length of around 700 miles. This range itself is part of an even larger range of volcanoes that wraps itself halfway around the Pacific Ocean; an area so formidably explosive that it’s been given the name Ring of Fire.
To better understand why Washington has so many active volcanoes, we need to understand their place in the larger Ring of Fire that has been active for a whopping 115 million years.
The Ring of Fire
Also known as the Circum-Pacific Belt, the Ring of Fire runs for nearly 25,000 miles around the Pacific Ocean’s eastern, northern and western rim.
The ring, which is 300 miles wide in some places, is dotted with volcanoes and seismic activity that characterizes the boundaries of the unofficial geological area. These features include underwater volcanoes, dormant craters, active volcanoes, earthquake regions, seismic hotspots, mountain ranges and much more that all fall under the result of heavy and repeated seismic activity.
Anywhere from 850-1,000 volcanoes exist in the Ring of Fire, accounting for around 75% of the entire planet’s volcanoes. Around 90% of all the Earth’s earthquakes occur here, as well, which also accounts for higher-than-average tsunami occurrences.
The ring, which doesn’t actually connect in the South, runs from New Zealand up to the Equator, west to Java, north through the Philippines to Japan and Russia, east along Alaska’s coast and down the Americas to southern Chile. These regions coincide with the overlap of tectonic plates on the Earth’s crust, and it is precisely because of them that the Ring of Fire experiences such seismic activity.
As tectonic plates move, one plate will usually pass underneath another at a boundary called a subduction zone. The plate underneath will heat up due to the pressure and heat from the Earth’s core, and the rock that makes up that plate will start to melt into magma. The magma makes its way up as the plates continue to grind together, and eventually that pressurized magma explodes to the surface as a volcanic eruption. The earthquakes that usually occur along with eruptions (but not always) are the release of tension between pieces of the crust.
Eruptions tend to happen in the same place as the magma follows the path of least resistance, and the slow buildup of debris is what forms the mountains and mountain ranges we have today.
This type of activity has been going on in the Ring of Fire for at least 35 million years — and possibly for as long as 115 million years — as the tectonic plates arranged themselves into their present-day configuration.
Not all of these volcanoes are active today, but the ones that geologists do keep track of are the ones that have been active in the past 11,700 years, a mere blink in the eyes of Earth’s history. And, as it turns out, the Cascade Volcanoes are some of them!
Cascade Volcanic Arc
Like we said, the Cascade Volcanic Arc runs for about 700 miles from southwestern British Columbia to Northern California. The Cascade Range as a whole was created as the Juan de Fuca, Explorer and Gorda Plates pushed below the North American Plate around 40-35 million years ago. The many volcanic eruptions slowly built the mountains we hike, climb and camp in today.
There are 14 active volcanoes in this range, which have been active in the recent past, including our five in Washington. All of Washington’s active volcanoes have erupted within the past two hundred years or so, while some of Oregon and British Columbia’s volcanoes last saw activity 100,000 years ago.
There is great variety in this volcanic arc. Dormant and extinct volcanoes include Mount Mazama in Oregon, which collapsed around itself and formed Crater Lake within its caldera. There’s also Tumtum Mountain in southwest Washington, which is a near-perfect volcanic cone. Ring Mountain, just north of Vancouver, Canada, erupted within a glacier and formed a flat-topped volcano called a tuya. Lassen Peak, which is a plug dome volcano in Northern California, was the only other Cascade Volcano to erupt in the 20th century, aside from Mount St. Helens.
In fact, there are 88 peaks in the Cascade Range that were formed as a result of volcanic activity, and 14 of them are here in Washington!
With so many volcanoes in our area, and so many more along the Pacific rim, it’s no wonder that humans have been drawn to these areas of rugged beauty and powerful displays of nature to settle down and call home. Besides, what’s one teensy little volcanic eruption when we get to live in our amazing luxury Seattle apartments the rest of our time here? It’s definitely worth the risk!
Featured photo courtesy Pixabay/bones64