The Cascade Mountains run in an imposing spine from Lytton Mountain in British Colombia down the west coast of the United States to Lassen Peak in California.
They are notable as the range is made up of many large and distinct mountains, such as Mount Rainier, which tower over their relatively low-lying surroundings, often rising more than one and a half kilometres from the surrounding land.
Many of the Northern Cascade mountains (running between Mount Rainier into the Canadian Cascades) are also very rugged with steep and heavily glaciated peaks.
It may then come as a surprise to the casual observer that the Cascades are home to a range of ancient and active volcanoes.
The Cascades make up part of the Pacific Ring of Fire, a circle of volcanic activity stretching across the boundaries of the Pacific Ocean.
More specifically, the Cascade Mountains lie on a subduction
zone, where one of the tectonic plates making up the Earth’s surface is dragged beneath the surface.
As this surface material is drawn down beneath the Earth’s crust, the pressure and high temperatures cause it to melt, releasing the minerals and water vapour which had been held in the rock.
These rise and create molten magma, which is more buoyant than the surrounding crust, and works its way up to the surface creating surface fissures which become the volcanoes of the Cascades chain.
These are the most active volcanoes in North America; all of the known historic eruptions occurring in the contiguous United States have been from Cascade volcanoes.
The Columbia River Gorge, just south of Mount St. Helens, is the only major break in the American part of the Cascades.
When the Cascades began to rise seven million years ago, the Colombia River was already large and fast-flowing enough to keep pace with their growth, continuing to erode through the rising landscape as the mountains grew and cutting the deep valley we see today.