How the Cascade Mountains were Created

The Cascade Mountain range of North America is part of the Pacific Northwest section of what is often called the “Pacific Ring of Fire” that circles around the Pacific Ocean. The range first began forming millions of years ago through movement of the earth’s plate and volcanic action with erosion also playing a part. 

The Pacific Ring of Fire

From south to north the Ring runs around the Pacific Rim including the west coast of South and North America, the Aleutian Islands, and then south to north including Japan, Southeast Asia and New Zealand. This circle a volcanically active area that is also prone to earthquakes

This Ring of Fire contains 75% of the planets active and dormant volcanoes found on land. Volcanoes are also found in the seas as island chains or submerged under the water and along the edges of continents.

The Pleistocene Period

It was around 36 million years ago that the first peaks began to rise above the ground. It was in the Pleistocene Period around 1.6 million yeas ago that the major peaks of today began to form. During volcanic activity around 5 million years ago more than 3,000 vents erupted.   

The Cascade Range

The Cascade Mountain Range is sometimes called the Cascades or Cascade Mountains. The mountain range is made up of different regions that all have their own geological characteristic. The North Cascades has many peaks that are of non-volcanic origin though it does have some significant volcanoes. The High Cascades is of volcanic origin and has many prominent volcanoes. In the state of Oregon there is a volcanic region that is known as the Western Cascades. The Canadian region is known as the Canadian Cascades or the Cascade Mountains. Other names may be used in other regions.

The Cascade Range forms a curve that runs around 100 – 150 miles inland parallel with the Pacific Ocean shoreline stretching over 700 mile from British Columbia, Canada, south to Northern California. Within the range is a string of 13 main volcanic centers and thousands of small transitory volcanoes that have produced raised areas of volcanic debris and lava. Larger volcanoes such as Mount St. Helens rise above these dominating the area.  

However, not all the peaks in the Cascade are of volcanic origin. The region known as the North Cascades has many mountains that are not of volcanic origin, where as the region known as the High Cascades has the most volcanoes and is largely of volcanic origin.

The North Cascades

The geology of the region of the North Cascades  is a build up from a  diverse mixture including ocean sediments, submarine fans, basaltic ocean floor, portions of old continents, and parts of the sub crustal mantle from deep within the Earth. Some of these rocks are evidence of 400 million years or more of the history of the planet.   

Although the different parts have different origins they were brought together by the movement of the tectonic plates. Some of the component parts of this montage were subject to water and wind erosion. In some cases they were covered by their own fragments. Some were lifted above the Earth, while other parts were forced underground where enormous heat and pressure transformed them before forcing them back to the surface. All of these diverse actions contributed to creating the North Cascades region of today.

The High Cascades

Underneath the Pacific Ocean off the coast of Northern California the Juan de Fuca Plate is moving away fro the Pacific Plate and being forced underneath the North American Plate. This action is termed ‘subduction’ and as the Juan de Fuca Plate moves underneath the North American Plate it is forced deeper into the Earth. This causes enormous pressures and high temperatures to build which causes the release of water molecules in the rocks to be released.

As the vapor rises it passes through flexible layer covering the subducting plate with the result that some of the covering melts forming magma. The magma then is forced upwards erupting on the surface of the Earth and creating a string of volcanoes over the subduction zone.

The future

The process of creating mountains is still in action. On May 22, 1915, Lassen Peak erupted and on May 18, 1980, Mount St. Helens erupted, devastating an area of 230 square miles of forested land. Mount St. Helens has also had a number of minor eruptions such as the one in 2006. While the subduction continues underground then more volcanoes will continue to be created and the Cascades will continue to grow.