Some of the major cities along the length of the arc include Portland, Seattle, and Vancouver, and the population in the region exceeds 10 million.

Consequently, Mount Rainier is one of the Decade Volcanoes identified by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) as being worthy of particular study, due to the danger it poses to Seattle and Tacoma.

This contact metamorphism produced a fine mesh of interlocking crystals in the old rocks, generally strengthening them and making them more resistant to erosion.

The West Cascades period came to an end 17 million years ago when the Columbia River flood basalts began erupting in eastern Washington and Oregon.

[2] For a reason unknown to scientists the initiation of the flood basalts seemingly caused a significant dip in volcanic activity in the cascade chain lasting for over 8 million years.

As production of the Columbia River flood basalts slowed 9 million years ago the Cascade volcanoes became active again.

When the Columbia basalts stopped entirely 6 million years ago the Cascades of central Oregon spectacularly flared up.

[4] It has been hypothesized that a heightened flux of basalt, possibly induced by tectonic slab-rollback, was focused beneath the volcanic arc and into the shallow crust by minor amounts of crustal extension.

This extension allowed for the high flux of basalt to be stored at shallow levels beneath a new arc locus within fertile crust, resulting in the silica-rich volcanism we see in the Deschutes Formation.

Around half a million years ago a generation of older volcanoes died and many of the stratovolcanoes that we see today began their growth such as Glacier Peak and Mt.

A few isolated volcanic centers northwest of the Mount Meager massif such as the Silverthrone Caldera, which is a circular 20 km (12 mi) wide, deeply dissected caldera complex, may also be the product of Cascadia subduction because the igneous rocks andesite, basaltic andesite, dacite and rhyolite can also be found at these volcanoes as they are elsewhere along the subduction zone.

Volcanoes within the volcanic belt are mostly stratovolcanoes along with the rest of the arc, but also include calderas, cinder cones, and small isolated lava masses.

Due to repeated continental and alpine glaciations, many of the volcanic deposits in the belt reflect complex interactions between magma composition, topography, and changing ice configurations.

Recent drilling into the Pemberton Valley bed encountered remnants of a debris flow that had traveled 50 km (31 mi) from the volcano shortly before it last erupted 2,350 years ago.

The possibility of the Mount Meager massif covering stable sections of the Pemberton Valley in a debris flow is estimated at one in 2,400 years.

Around 5,000 years ago, a large chunk of the volcano slid away and that debris avalanche helped to produce the massive Osceola Mudflow, which went all the way to the site of present-day Tacoma and south Seattle.

Native Americans have inhabited the area for thousands of years and developed their own myths and legends concerning the Cascade volcanoes.

Other stories, such as the Bridge of the Gods tale, had various High Cascades such as Hood and Adams, act as god-like chiefs who made war by throwing fire and stone at each other.

The spirit-beings/wizards known as "the Transformers" reached them during their journey into the Lillooet Country, and were a "training" place for young First Nations men to acquire power and knowledge.

Legends associated with the great volcanoes are many, as well as with other peaks and geographical features of the arc, including its many hot springs and waterfalls and rock towers and other formations.

In the spring of 1792 British navigator George Vancouver entered Puget Sound and started to give English names to the high mountains he saw.

As marine trade in the Strait of Georgia and Puget Sound proceeded in the 1790s and beyond, the summits of Rainier and Baker became familiar to captains and crews (mostly British and American).

On May 22, 1915, an explosive eruption at Lassen Peak devastated nearby areas and rained volcanic ash as far away as 200 miles (320 km) to the east.

[18] A huge column of volcanic ash and gas rose more than 30,000 feet (9,100 m) into the air and was visible from as far away as Eureka, California, 150 miles (240 km) to the west.

[19] This activity produced a diverse sequence of volcanic deposits, well exposed in the bluffs along the Lillooet River, which is defined as the Pebble Creek Formation.

About 13,000 years ago, Glacier Peak generated an unusually strong sequence of eruptions depositing volcanic ash as far away as Wyoming.

Thermal anomalies (hot spots) and gas emissions (including hydrogen sulfide) have occurred especially on the summit plateau since the Great Slide of 1921.

[21] Mount Hood was last active about 200 years ago, creating pyroclastic flows, lahars, and a well-known lava dome close to its peak called Crater Rock.

[21] However, certain Cascade volcanoes can be dormant for hundreds or thousands of years between eruptions, and therefore the great risk caused by volcanic activity in the regions is not always readily apparent.

A vast piece on the north side of Mount St. Helens dropped and formed a jumbled landslide environment several kilometers away from the volcano.