Cascade Volcanoes

The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a continental volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern California, a distance of well over 700 miles (1,100 km). These volcanoes formed because of the movement of Earth's plates along the Cascadia subduction zone. Even though they share their name with the Cascade Range, they are a group based on geology, not just geography, and they stretch north into the Coast Mountains, past the Fraser River.

Important cities such as Portland, Seattle, and Vancouver lie near these volcanoes, and the area is home to more than 10 million people. Because the population in the Pacific Northwest is growing quickly, these volcanoes are considered very dangerous. They have erupted many times before and could erupt again. The rocks under them can weaken and break easily, which makes eruptions even more risky. This is why Mount Rainier is one of the Decade Volcanoes chosen for special study by scientists.

The Cascade Volcanoes are part of the Pacific Ring of Fire, a circle of volcanoes around the Pacific Ocean. They have erupted several times in history that people have recorded. The two most recent big eruptions were at Lassen Peak from 1914 to 1921 and a major eruption of Mount St. Helens in 1980. The Cascade Volcanoes were also the site of Canada's most recent major eruption, which happened around 410 BCE at the Mount Meager massif.

Geology

The Cascade Arc has almost 20 major volcanoes, with over 4,000 volcanic vents. These include many types of volcanoes such as stratovolcanoes, shield volcanoes, lava domes, and cinder cones. Volcanism in this area began about 37 million years ago, but most of today's Cascade Volcanoes are younger than 2 million years. The two tallest volcanoes, Mount Rainier and Mount Shasta, both rise over 14,000 feet.

The history of these volcanoes can be split into three main parts. The West Cascades period lasted from 37 to 17 million years ago when volcanoes were very active. The Widespread dormancy period from 17 to 9 million years ago saw less activity and erosion. The High Cascades period began 9 million years ago when volcanoes became active again and have continued to the present day.

The volcanoes in the Cascade Arc each have their own unique features. Lassen Peak in California last erupted in 1917, and the Mount Meager massif in British Columbia erupted about 2,350 years ago. The Garibaldi Volcanic Belt is the northern extension of the Cascade Arc and includes various types of volcanoes.

Largest eruptions

The table below lists some of the biggest eruptions that have happened in the Cascade chain.

Human history

Native Americans have lived near the Cascade volcanoes for thousands of years. They created stories and legends about these mountains. Some tales say that mountains like Baker, Jefferson, Shasta, and Garibaldi were places of safety during a big flood. Other stories tell of battles between powerful chiefs, with mountains like Hood and Adams throwing fire and stone at each other. Mount St. Helens was often described as a beautiful maiden. There are many different names for these mountains from the Native American tribes who lived there.

Hot springs on the Canadian side of the volcanoes were important to the First Nations people. These springs were used for special purposes and were considered powerful places. In spring 1792, British explorer George Vancouver began naming the mountains. He named Mount Baker, Mount St. Helens, Mount Hood, and Mount Rainier after people he knew. The quiet period of the volcanoes ended in 1980 when Mount St. Helens erupted, drawing worldwide attention. Since then, scientists watch the volcanoes closely to keep people safe.

Cascadia subduction zone

Main article: Cascadia subduction zone

The Cascade Volcanoes formed because of the Juan de Fuca, Explorer, and Gorda Plate moving under the North American Plate along the Cascadia subduction zone. This is a long fault running far off the coast of the Pacific Northwest, from northern California up to Vancouver Island, British Columbia.

Because this fault is so large, it can create very powerful earthquakes. Over time, energy builds up until it is released in a big earthquake. Even though there isn’t a deep ocean trench here like in other places, the land is slowly being pushed together. When the fault finally moves, it can cause huge earthquakes, like the one that happened in the year 1700.

Famous eruptions

1980 eruption of Mount St. Helens

Main article: 1980 eruption of Mount St. Helens

The 1980 eruption of Mount St. Helens was one of the most studied eruptions in the Cascade Volcanoes and is among the best studied ever. It was a powerful eruption that happened in the western United States. An earthquake caused part of the mountain to collapse, and a huge cloud of ash rose high into the sky, spreading over many states. This eruption changed the landscape and taught scientists a lot about volcanoes.

1914–1917 eruptions of Lassen Peak

Main article: Lassen Peak

In 1915, Lassen Peak had a big eruption that created a tall column of ash and gas. The eruption caused damage nearby and was part of a series of eruptions between 1914 and 1917. The ash could be seen from far away, showing how strong the eruption was.

2350 BP (400 BC) eruption of the Mount Meager massif

Main article: Mount Meager massif

The Mount Meager massif had a major eruption in what is now Canada, sending ash far into nearby regions. This eruption created many different types of volcanic rocks and deposits, which scientists can still see today along rivers.

7700 BP (5783 BC) eruption of Mount Mazama

Main article: Mount Mazama

A very big eruption about 7,700 years ago at Mount Mazama in Oregon caused the mountain to collapse, forming a large crater called a caldera. This created Crater Lake, and ash from the eruption spread across much of the Pacific Northwest and into Canada.

13100 BP (11,150 BC) eruptions of Glacier Peak

About 13,000 years ago, Glacier Peak had several very large eruptions, some even bigger than the 1980 eruption of Mount St. Helens. These eruptions spread ash as far away as Wyoming.

Other eruptions

Silverthrone Caldera

Most eruptions of the Silverthrone Caldera happened during ancient times, with the last one occurring about 1,000 years ago. The volcano’s lava once flowed and was stopped by ice, creating interesting landforms.

Mount Garibaldi

Mount Garibaldi was last active around 10,700 to 9,300 years ago. It produced a long flow of thick lava that formed ridges and other features we can still see.

Mount Baker

Mount Baker woke up again in the mid-1800s after many quiet years. Today, there are still signs of heat and gas near its summit, but scientists don’t expect an eruption soon.

Glacier Peak

Glacier Peak erupted about 200–300 years ago and has had several eruptions in the past few thousand years.

Mount Rainier

Mount Rainier last erupted in the mid-1800s, though people reported activity in later years. It has had many eruptions and mudflows in the past few thousand years.

Mount Adams

Mount Adams was last active around 1,000 years ago. It has had fewer eruptions than other Cascade volcanoes but created several lava flows.

Mount Hood

Mount Hood last erupted about 200 years ago, producing lava flows and a well-known rock formation near its peak called Crater Rock.

Newberry Volcano

Newberry Volcano has been very active over time, with many different types of volcanic features formed over the years.

Medicine Lake Volcano

Medicine Lake Volcano erupted several times in the past 4,000 years, with the most recent activity about 1,000 years ago.

Mount Shasta

Mount Shasta last erupted around the year 1250 and has been one of California’s most active volcanoes for thousands of years.

Eruptions in the Cascade Range

Eleven of the thirteen volcanoes in the Cascade Range have erupted in the past 4,000 years, with seven doing so in just the last 200 years. These volcanoes have had many powerful eruptions over time. Between eruptions, they can stay quiet for hundreds or even thousands of years.

When these volcanoes erupt, they can send fast-moving flows of hot rock and gas, along with mud and ash, far from the mountain. Ash from eruptions can also cause problems for airplanes and affect areas far downwind. The most recent big eruptions were at Lassen Peak from 1914 to 1921, a major eruption of Mount St. Helens in 1980, and a smaller eruption of Mount St. Helens from 2004 to 2008.

List of volcanoes

Main article: List of Cascade volcanoes

Washington has most of the very tallest volcanoes, with 4 of the top 6 overall. But Oregon has most of the next tallest peaks. Even though Mount Rainier is the highest, Medicine Lake Volcano in California is the biggest by how much space it takes up. It is followed by Oregon's Newberry Volcano. This is a list of the twelve tallest Cascade volcanoes, plus the tallest in British Columbia (Silverthrone Caldera) and the one that last erupted the most recently (Mount St. Helens):