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The Cascade Volcanoes (also known as the '''Cascade Volcanic Arc''' or the '''Cascade Arc''') are a and is part of the Pacific Ring Of Fire . Although taking its name from the Cascade Range , this term is a geologic grouping rather than a geographic one, and the Cascade Volcanoes extend north into the Coast Mountains , past the Fraser River which is the northward limit of the Cascade Range proper. Some of the major Cities along the length of the arc include Portland , Seattle , and Vancouver , and the population in the region exceeds 10,000,000. All could be potentially affected by volcanic activity and great subduction-zone Earthquakes along the arc. , including Cascade volcanoes (red triangles) ]] The Cascade Arc includes nearly 20 major volcanoes, among a total of over 4,000 separate volcanic vents including numerous and Newberry Volcano , which are about 145 mi³ (600 km³) and 108 mi³ (450 km³) respectively. Mount Garibaldi and Glacier Peak are the only two Cascade volcanoes that are made exclusively of Dacite . Several of the volcanoes in the arc are frequently Active . The volcanoes of the Cascade Arc share some general characteristics, but each has its own unique geological traits and history. Lassen Peak in California, which last erupted in 1917 , is the southernmost historically active volcano in the arc, while Mount Meager in British Columbia, which erupted about 2,350 years ago, is generally considered the northernmost member of the arc. A few isolated volcanic centers northwest of Mount Meager such as Mount Silverthrone , which is a circular 20km wide, deeply dissected Caldera Complex , may also be the product of Cascadia subduction, but geologic investigations have been very limited in this remote region. About 5-7 million years ago, the northern end of the Juan De Fuca Plate broke off along the Nootka Fault to form the Explorer Plate , and there is no definitive consensus among geologists on the relation of the volcanoes north of that fault to the rest of the Cascade Arc. When the Cascade Volcanic Arc continued 4-5 million years ago after restructuring of the Explorer Plate, there were a number of obvious changes along the northern section of the arc. Where the northern section of the arc originally continued directly north from the present-day location of Glacier Peak - into the Chilliwack Batholith and the Pemberton Volcanic Belt , it now started to move northwest into the Mount Baker - Garibaldi Volcanic Belt . The , Mount Garibaldi and Mount Cayley . The Pemberton Volcanic Belt is an eroded Volcanic Belt north of the Garibaldi Volcanic Belt, which appears to have formed during the Miocene before fracturing of the northern end of the Juan de Fuca Plate. Mount Silverthrone is the only volcano within the belt that appears related to seismic activity since 1975. While the Cascade Volcanoes (a Geological term) includes volcanoes such as Mount Meager and Mount Garibaldi , which lie north of the Fraser River , the Cascade Range (a Geographic term) is considered to have its northern boundary at the Fraser. However this terminology is not universally adhered to; in particular the phrase "the volcanoes of the High Cascades" is sometimes understood to include the peaks north of the Fraser, and sometimes not. CASCADIA SUBDUCTION ZONE See Also: Cascadia subduction zone The Cascade Volcanoes were formed by the from Northern California to Vancouver Island , British Columbia . The plates move at a relative rate of over 0.4 inches (10 mm) per year at a somewhat oblique angle to the subduction zone. Unlike most subduction zones worldwide, there is no Oceanic Trench present along the Continental Margin in Cascadia . Instead, Terrane s and the accretionary wedge have been uplifted to form a series of coast ranges and exotic mountains. A high rate of sedimentation from the outflow of the three major rivers ( Fraser River , Columbia River , and Klamath River ) which cross the Cascade Range contributes to further obscuring the presence of a trench. However, in common with most other subduction zones, the outer margin is slowly being compressed, similar to a giant Spring . When the stored energy is suddenly released by slippage across the fault at irregular intervals, the Cascadia subduction zone can create very large Earthquake s such as the Magnitude 9 Cascadia Earthquake Of 1700 . ERUPTIONS OF THE CASCADES The Cascade volcanoes have had more than 100 eruptions over the past few thousand years, many of them Explosive Eruption s. 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. When Cascade volcanoes do erupt, Pyroclastic Flow s, Lava flows, and Landslide s can devastate areas 10 or more miles away; and huge Mudflow s of Volcanic Ash and Debris , called Lahar s, can inundate Valley s more than 50 miles downstream. Falling ash from Explosive Eruption s can disrupt Human activities hundreds of miles downwind, and drifting clouds of fine ash can cause severe damage to Jet Aircraft even thousands of miles away. Historical eruptions have occurred in , Glacier Peak , Mount Baker , Mount Hood , Lassen Peak , and Mount Shasta . Renewed volcanic activity in the Cascade Arc, such as the 1980 Eruption Of Mount St. Helens , has offered a great deal of evidence about the structure of the Cascades. One effect of the 1980 eruption was a greater knowledge of the influence of landslides and volcanic development in the evolution of volcanic terrain. A vast piece on the north side of Mount St. Helens dropped and formed a jumbled landslide environment several kilometers away from the volcano. Pyroclastic Flow s and Lahar s moved across the countryside. Parallel episodes have also happened at Mount Shasta and other Cascade volcanoes in prehistoric times. Major catastrophic eruptions ; 1980 Eruption of Mount St. Helens See Also: 1980 eruption of Mount St. Helens The , 1980 , caused the entire weakened north face to slide away. An ash column rose high into the Atmosphere and deposited ash in 11 U.S. states. The eruption killed 57 people and thousands of Animal s and caused more than a billion U.S. Dollar s in damage. ; 1914–17 Eruptions of Lassen Peak See Also: Lassen Peak On , 150 miles (240 km) to the west. A Pyroclastic Flow swept down the side of the volcano, devastating a 3-square-mile area. This explosion was the most powerful in a 1914–17 series of eruptions at Lassen Peak. ; 2350 BP Eruption of Mount Meager See Also: 2350 BP eruption of Mount Meager ; 7700 BP Eruption of Mount Mazama See Also: Mount Mazama The 7700 BP eruption of Mount Mazama was a large catastrophic eruption in U.S. state of Oregon . It is estimated to have been 42 times larger than the 1980 Eruption Of Mount St. Helens . It began with a large Eruption Column with Pumice and Ash that erupted from a single vent. The eruption was so great that most of Mount Mazama collapsed to form a Caldera and subsequent smaller eruptions occurred as water began to fill in the caldera to form Crater Lake . Volcanic ash from the eruption was carried across most of the Pacific Northwest as well as parts of southern Canada. ; 13,100 BP Eruption of Glacier Peak About 13,000 years ago, Glacier Peak generated an unusually strong sequence of eruptions depositing Volcanic Ash as far away as Wyoming . Other eruptions ; Mount Silverthrone Most of Mount Silverthrone 's eruptions occurred during the last Ice Age and was episodically Active during both Pemberton and Garibaldi Volcanic Belt stages of Volcanism . The last eruption from Mount Silverthrone ran up against ice in Chernaud Creek . The lava was Dam med by the ice and made a Cliff with a Waterfall up against it. ; Mount Cayley Mount Cayley last erupted about 20,000 years ago. It contains several complex features which probably represent multiple eruptions under different conditions and are difficult to classify. ; Mount Garibaldi Mount Garibaldi was last active about 10,700 to 9,300 years ago from a Cinder Cone called Opal Cone . It produced a 15 km long broad Dacite Lava Flow with prominent wrinkled ridges. The lava flow is unusually long for a silicic lava flow. ; Mount Baker During the mid- 1880s , Mount Baker had volcanic activity for the first time in several thousand years. Fumarole activity remains in Sherman Crater , close to the volcano's main peak, became more intense in 1975 and is still energetic. However there is still no proof that an eruption is about to happen at the volcano. ; Glacier Peak Glacier Peak last erupted about 200-300 years ago and has erupted about six times in the past 4,000 years. ; Mount Rainier Mount Rainier last erupted between 1824 and 1854, but many eyewitnesses reported eruptive activity in 1858 , 1870 , 1879 , 1882 and in 1894 as well. Mount Rainier has created at least four eruptions and many Lahar s in the past 4,000 years. ; Mount Adams Mount Adams was last active about 1,000 years ago and has created few eruptions during the past several thousand years. ; Mount Hood Mount Hood was last active about 200 years ago, creating Pyroclastic Flow s, Lahar s, and a well-known Lava Dome close to its peak called Crater Rock. Between 1856 and 1865 , a sequence of steam explosions took place at Mount Hood. ; Newberry Volcano A great deal of volcanic activity has occurred at Newberry Volcano , which was last active about 1,300 years ago. It has one of the largest collections of Cinder Cone s, Lava Dome s, Lava Flow s and Fissure s in the world. ; Medicine Lake Volcano Medicine Lake Volcano has erupted about 8 times in the past 4,000 years and was last active about 1,000 years ago when Rhyolite and Dacite erupted at Glass Mountain and associated vents near the Caldera 's eastern rim. ; Mount Shasta Mount Shasta last erupted in 1786 and has been the most active volcano in California for about 4,000 years, erupting once every 300 years. The 1786 eruption created a Pyroclastic Flow , a Lahar and three cold lahars, which streamed 7.5 miles (12 km) down Shasta's east flank via Ash Creek. A separate hot lahar went 12 miles (19 km) down Mud Creek. LIST OF CASCADE VOLCANOES British Columbia Washington Oregon California NOTES SEE ALSO
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