The Cascade Range is a prominent North American mountain chain that stretches over 700 miles through the Pacific Northwest. It is renowned for its towering, snow-capped volcanic peaks. The question of how many volcanoes exist within this range is more complex than a simple number, as the answer depends heavily on how a volcano is scientifically defined. Understanding the scale of the Cascades requires looking beyond the famous high peaks to the multitude of smaller eruptive centers. The total count can vary dramatically, ranging from a dozen to thousands, based on the classification criteria used by geologists.
Defining the Cascade Range and its Volcanoes
The Cascade Volcanic Arc is a geologic feature extending from southern British Columbia down through Washington, Oregon, and into Northern California. This chain of volcanoes is a direct result of the Cascadia Subduction Zone located off the Pacific coast. The underlying geological engine is the slow, steady subduction of the oceanic Juan de Fuca plate beneath the edge of the North American plate.
As the Juan de Fuca plate descends and heats up, it releases water into the overlying mantle rock, causing it to melt and generate magma. This magma then rises to the surface, fueling the volcanoes of the Cascade Arc. The volcanoes created by this process range from massive, steep-sided stratovolcanoes to smaller, simpler features.
Geologists categorize these structures by their size, shape, and eruptive history. The largest and most visible are the major composite volcanoes, sometimes called stratovolcanoes, which are built up over thousands of years by layers of hardened lava and ash. Smaller features include cinder cones, which are simple piles of volcanic fragments, as well as lava domes and isolated volcanic vents.
The Official Count and Different Classifications
The number of volcanoes cited for the Cascade Range varies widely, depending on whether one counts only the largest, most visually dominant peaks or every single eruptive center. The most commonly cited low number, often used to refer to the “High Cascades,” is approximately 13 to 20 major volcanic centers. These are the towering, composite volcanoes that define the landscape and have erupted repeatedly throughout the Holocene epoch (the last 11,700 years).
This small group includes all the famous, high-threat peaks in the range, such as Mount Rainier and Mount Hood. A broader, intermediate count used by some geological surveys places the number of distinct volcanic centers, including smaller, named features in each state, around 84.
However, when geologists consider all features that have erupted to form a distinct vent, the number dramatically increases. The Cascade Volcanic Arc is estimated to contain over 4,000 separate volcanic vents, including all the small cinder cones, lava domes, and isolated eruptive centers. This vast number represents the total number of places where magma has reached the surface in the entire 700-mile-long arc.
The Major Peaks of the High Cascades
The High Cascades comprise the largest and most recognizable stratovolcanoes, each representing a significant potential hazard and geologic landmark.
Major Peaks
- Mount Rainier: In Washington, it is the highest peak in the range, rising to 14,411 feet. It is covered by the largest single-mountain glacier system in the contiguous United States, which increases the hazard risk from potential mudflows, known as lahars.
- Mount St. Helens: Infamous for its catastrophic 1980 eruption which dramatically altered its shape and profile.
- Mount Adams: The second-highest peak in Washington, it is a broad, massive shield-like stratovolcano with significant glaciers.
- Mount Hood: Oregon’s highest peak, a classic, symmetrical volcano near the city of Portland.
- Mount Mazama: Now recognized as the enormous caldera holding Crater Lake. This volcano collapsed in a massive eruption approximately 7,700 years ago.
- Mount Shasta: A massive, iconic stratovolcano in Northern California and the second-highest peak in the entire range.
- Lassen Peak: Active between 1914 and 1917, marking the most recent period of eruption in the contiguous United States prior to Mount St. Helens in 1980.
Current Activity and Monitoring
The majority of the Cascade volcanoes are currently classified as dormant, meaning they are quiet but not extinct. Since the 1980 eruption of Mount St. Helens, the level of monitoring has been significantly increased across the range. The U.S. Geological Survey (USGS) Cascades Volcano Observatory (CVO) in Vancouver, Washington, is tasked with constant surveillance of these peaks.
Scientists employ a variety of tools to detect changes that might signal renewed activity. These monitoring systems include networks of seismometers, which listen for small earthquakes that can indicate magma movement beneath the surface. Ground deformation is tracked using Global Positioning System (GPS) receivers and tiltmeters, which measure the slightest swelling or deflation of the volcano’s flanks.
Volcanic gas emissions are also sampled to detect changes in the chemical composition of gases escaping from the vents. While the volcanoes are currently at a “NORMAL” background alert level, small earthquakes are routinely detected at various centers like Mount St. Helens. This constant monitoring is necessary because a renewed eruption could trigger hazards such as fast-moving pyroclastic flows or destructive lahars, which pose a threat to nearby population centers.