USGS/Cascades Volcano Observatory, Vancouver, Washington

Cascade Range Volcanoes Summary

Begin in the North and head South ... highlights about the Cascade Range Volcanoes ... from Meager Mountain (British Columbia) to Lassen Peak (California) ... also includes photos, maps, and links to current activities and latest reports. Some volcanoes have "Alternative Text Pages", which are more "508 friendly".

British Columbia, Canada
- Meager Mountain
- Mount Garibaldi
Washington State
Oregon
California

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British Columbia, Canada

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Meager Mountain, British Columbia

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Meager Mountain

2,679 meters
(8,790 feet)
Stratovolcano

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Meager Mountain Complex The Meager Mountain volcanic complex is the northernmost volcano in the Garibaldi Volcanic Belt, an extension of the Cascade volcanic belt into Canada. It is a Tertiary to Quaternary edifice exhibiting at least eight vents which produced mafic to felsic rocks. Numerous feeder dikes to older units are exposed by deep erosion. The volcano is dominated by porphyritic andesite to rhyodacite lava and pyroclastic breccias, although several Quaternary basalt flows and breccias occur on the periphery. Plagioclase porphyritic andesite lava flows and breccia (0.5 to 1.0 million years ago) are the most voluminous rocks, with a maximum of 1,200 meters of total flow thickness. The most recent volcanic activity occurred 2,350 years ago and produced three distinct units known as the Bridge River Assemblage. ... Meager Mountain lies 150 kilometers north of Vancouver, British Columbia. -- Stasiuk, 1990, IN: Wood and Kienle

The northern segment of the Garibaldi Belt includes the Meager Mountain complex and several remnants of basaltic and andesitic piles which extend north of Meager Mountain almost to the Interior Plateau. Meager Mountain (Read, 1978; Lewis and Souther, 1978) is a complex of at least four overlapping composite dacite to rhyodacite volcanoes that become progressively younger from south to north, ranging in age from approximately 2 million years to around 2,490 years old. -- Souther, 1990, IN: Wood and Kienle

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Mount Garibaldi, British Columbia

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Mount Garibaldi

2,678 meters
(8,787 feet)
Stratovolcano

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Mount Garibaldi Mount Garibaldi is one of the larger volcanoes (6.5 cubic kilometers) in a chain of small Quaternary volcanic piles -- the Garibaldi Belt -- which trend N25degrees W within the southern Coast Mountains of British Columbia. Mount Garibaldi is noteworthy both for the excellent exposures of its internal structure and for its striking topographic anomalies, which can be attributed to the growth of the volcano onto a major glacial stream, part of the Cordilleran Ice Sheet, and the subsequent collapse of the flanks of the volcano with the melting of the ice. ... Mount Garibaldi is located 80 kilometers north of Vancouver, British Columbia, in the Garibaldi Provincial Park. -- Mathews, 1990, IN: Wood and Kienle

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Washington State

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Mount Baker, Washington

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Mount Baker

3,285 meters
(10,778 feet)
Stratovolcano

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Geographic Setting Mount Baker (3,285 meters; 10,778 feet) is an ice-clad volcano in the North Cascades of Washington State about 50 kilometers (31 miles) due east of the city of Bellingham. After Mount Rainier, it is the most heavily glaciated of the Cascade volcanoes: the volume of snow and ice on Mount Baker (about 1.8 cubic kilometers; 0.43 cubic miles) is greater than that of all the other Cascades volcanoes (except Rainier) combined. Isolated ridges of lava and hydrothermally altered rock, especially in the area of Sherman Crater, are exposed between glaciers on the upper flanks of the volcano: the lower flanks are steep and heavily vegetated. The volcano rests on a foundation of non-volcanic rocks in a region that is largely non-volcanic in origin. -- Gardner, et.al., 1995

Historical Activity Historical activity at Mount Baker includes several explosions during the mid-19th century, which were witnessed from the Bellingham area, and since the late 1950s, numerous small- volume debris avalanches. In 1975, increased fumarolic activity in the Sherman Crater area caused concern that an eruption might be imminent. Additional monitoring equipment was installed and several geophysical surveys were conducted to try to detect the movement of magma. The level of Baker Lake was lowered and people were restricted from the area due to concerns that an eruption- induced debris avalanche or debris flow might enter Baker Lake and displace enough water to either cause a wave to overtop the Upper Baker Dam or cause complete failure of the dam. However, few anomalies other than the increased heat flow were recorded during the geophysical surveys nor were any other precursory activities observed to indicate that magma was moving up into the volcano. An increased level of fumarolic activity has continued at Mount Baker from 1975 to the present, but there are no other changes that suggest that magma movement is involved. -- Gardner, et.al., 1995

Cascade Range Current Activity Update -- Monthly (or sooner) Updates

1995 Hazards Assessment Report -- Gardner, et.al., 1995, OFR95-498

Mount Baker -- Living With An Active Volcano -- Scott, et.al., 2000, USGS FS-059-00

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Glacier Peak, Washington

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Glacier Peak

3,213 meters
(10,541 feet)
Stratovolcano

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Glacier Peak Glacier Peak is the most remote of the five active volcanoes in Washington State. It is not prominently visible from any major population center, and so its attractions, as well as its hazards, tend to be over-looked. Yet since the end of the last ice age, Glacier Peak has produced some of the largest and most explosive eruptions in the state. During this time period, Glacier Peak has erupted multiple times during at least six separate episodes, most recently about 300 years ago. -- Mastin and Waitt, 2000

Eruptive History Glacier Peak is a small Cascade Range stratovolcano. Although its summit reaches greater then 3,000 meters above the surrounding valleys, the main cone of Glacier Peak is perched on a high ridge, and the volcanic pile is no more than 500-1,000 meters thick. More than a dozen glaciers occur on the flanks of the volcano, and unconsolidated pyroclastic deposits over 12,000 years old have been largely removed by glaciation. Lava flows locally cap ridges to the northeast of the volcano. While small basaltic flows and cones are found at several points around the flanks of Glacier Peak, the main edifice is largely dacite and andesite. Lava flows extend no more than a few kilometers from the summit. Glacier Peak is probably best known as the source of voluminous tephra eruptions dated to 11,250 years BP. Two tephra layers produced at this time have been identified as far as 800-1,000 kilometers to the east, and are widely used by geologists, anthropologists, and paleoecologists to date late Pleistocene sediments. Also at this time, an extensive valley fill of pumiceous lahars and alluvium was deposited downriver to the west, blocking valleys and affecting drainages as far as 80 kilometers from the volcano. After these major eruptions, Glacier Peak apparently was dormant for 6,000 years. The volcano rewoke 5,500-5,100 years B.P. and intermittent eruptions of pyroclastic flows and tephra have occurred since that time. perhaps the most dramatic geologic features at Glacier Peak are enormous and relatively undissected late Pleistocene and Holocene pyroclastic fans which almost completely fill valleys on the eastern and western flanks of the volcano. -- Beget, 1994, IN: Wood and Kienle

18th Century Indian legends and a thin tephra fall preserved east of the volcano may record a recent eruption in the 18th century, although no eruptive activity has occurred during at least the last 150 years. -- Beget, 1994, IN: Wood and Kienle

Hot Springs and Dacite Domes Three hot springs surround the volcano, and warm ground and snow-free areas occur near fresh-appearing dacite domes which form subsidiary summits both north and south of the ice-covered main summit. -- Beget, 1994, IN: Wood and Kienle

Cascade Range Current Activity Update -- Monthly (or sooner) Updates

1995 Hazards Assessment Report -- Waitt, et.al., 1995, OFR95-499

Glacier Peak -- History and Hazards of a Cascade Volcano -- Mastin and Waitt, 2000, USGS FS-058-00

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. [Mount Rainier Alternative Text]

Mount Rainier, Washington

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Mount Rainier

4,392 meters
(14,410 feet)
Stratovolcano

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"The Mountain" Mount Rainier, highest (4,392 meters - 14,410 feet) and third-most voluminous volcano in the Cascades after Mounts Shasta and Adams, dominates the Seattle-Tacoma area, where more than 1.5 million know it fondly as The Mountain. The Mountain is, however, the most dangerous volcano in the range, owing to the large population and to the huge area and volume of ice and snow on its flanks that could theoretically melt to generate debris flows during cataclysmic eruptions. -- Swanson, et.al., 1989

Mount Rainier Dominates the Landscape Mount Rainier volcano dominates the landscape of a large part of western Washington. It stands nearly 3 miles higher than the lowlands to the west and 1.5 miles higher than the surrounding mountains. The base of the volcano spreads over an area of about 100 square miles, and lava flows that radiate from the base of the cone extend to distances of as much as 9 miles. The flanks of Mount Rainier are drained by five major rivers and their tributaries. Clockwise from the northwest the major rivers are the Carbon, White, Cowlitz, Nisqually, and Puyallup. Each river flows westerly through the Cascade Range and, with the exception of the Cowlitz, empties into Puget Sound near Tacoma, Washington. The Cowlitz joins the Columbia River in the southwestern part of the State to flow to the Pacific Ocean. -- Crandell, 1971

Eruptive Background Mount Rainier is an active volcano that first erupted about half a million years ago. Because of Rainier's great height (14,410 feet above sea level) and northerly location, glaciers have cut deeply into its lavas, making it appear deceptively older than it actually is. Mount Rainier is known to have erupted as recently as in the 1840s, and large eruptions took place as recently as about 1,000 and 2,300 years ago. Mount Rainier and other similar volcanoes in the Cascade Range, such as Mount Adams and Mount Baker, erupt much less frequently than the more familiar Hawaiian volcanoes, but their eruptions are vastly more destructive. Hot lava and rock debris from Rainier's eruptions have melted snow and glacier ice and triggered debris flows (mudflows) - with a consistency of churning wet concrete - that have swept down all of the river valleys that head on the volcano. Debris flows have also formed by collapse of unstable parts of the volcano without accompanying eruptions. Some debris flows have traveled as far as the present margin of Puget Sound, and much of the lowland to the east of Tacoma and the south of Seattle is formed of pre-historic debris from Mount Rainier -- Sisson, 1995

Cascade Range Current Activity Update -- Monthly (or sooner) Updates

Revised 1998 Hazards Assessment Report -- Hoblitt, et.al., 1998, OFR98-428

History and Hazards of Mount Rainier, Washington -- Sisson, 1995, USGS OFR95-642

Mount Rainier -- Living With Perilous Beauty -- Scott, et.al., 1998, USGS FS-065-97

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. [Mount Adams Alternative Text]

Mount Adams, Washington

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Mount Adams

3,742 meters
(12,276 feet)
Compound Stratovolcano

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Mount Adams Volcano Mount Adams, one of the largest volcanoes in the Cascade Range, dominates the Mount Adams volcanic field in Skamania, Yakima, Klickitat, and Lewis counties and the Yakima Indian Reservation of south-central Washington. The nearby Indian Heaven and Simcoe Mountains volcanic fields lie west and southeast, respectively, of the 1250 square kilometers (500 square miles) Adams field. Even though Mount Adams has been less active during the past few thousand years than neighboring Mounts St. Helens, Rainier, and Hood, it assuredly will erupt again. Future eruptions will probably occur more frequently from vents on the summit and upper flanks of Mount Adams than from vents scattered in the volcanic fields beyond. Large landslides and lahars that need not be related to eruptions probably pose the most destructive, far-reaching hazard of Mount Adams. -- Scott, et.al., 1995

Eruptive History Mount Adams stands astride the Cascade Crest some 50 kilometers due east of Mount St. Helens. The towering stratovolcano is marked by a dozen glaciers, most of which are fed radially from its summit icecap. In the High Cascades, Mount Adams is second in eruptive volume only to Mount Shasta, and it far surpasses its loftier neighbor Mount Rainier (which is perched on a pedestal of Miocene granodiorite). Adams's main cone exceeds 200 cubic kilometers, and at least half as much more was eroded during late Pleistocene time form earlier high-standing components of the compound edifice: peripheral basalt adds another 70 cubic kilometers or so. Nearly all the high cone above 2,300 meters in elevation was constructed during latest Pleistocene time, probably between 20 and 10 thousand years ago, explaining the abundance of late-glacial till and the scarcity of older till. -- Hildreth, 1990, IN: Wood and Kienle

Recent Volcanic Activity Approximately 1,000 years ago: four tephra falls and perhaps small lava flows from two vents on upper flanks. -- Scott, et.al., 1995

Debris Avalanches and Lahars During the past 10,000 years, the steep upper slopes of Mount Adams have produced several notable debris avalanches. In 1921, about 4 million cubic meters (5 million cubic yards) of altered rock fell from the head of Avalanche Glacier on the southwest flank of the volcano and traveled almost 6 kilometers (4 miles) down Salt Creek valley. The debris avalanche contained or acquired sufficient water to partly transform into small lahars. Ancient debris avalanches of much larger size have also occurred at Mount Adams, and these formed lahars that traveled far down the White Salmon and other valleys. An avalanche of roughly 70 million cubic meters (90 million cubic yards) of debris initiated the largest of these lahars about 6000 years ago. This lahar inundated the Trout Lake lowland and continued down the valley of the White Salmon River at least as far as Husum, more than 55 kilometers (35 miles) from Mount Adams. The lahar deposit left in the lowland varies from 1 to 20 meters (3 to 65 feet) thick; it is clearly visible today as a sediment layer in the banks of the White Salmon River and as isolated blocks (some more than 5 meters (16 feet) in diameter) that protrude from fields and meadows. -- Scott, et.al., 1995

Cascade Range Current Activity Update -- Monthly (or sooner) Updates

1995 Hazards Assessment Report -- Scott, et.al., 1995, OFR95-492

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Indian Heaven Volcanic Field, Washington

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Indian Heaven
Volcanic Field

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Volcanic Fields During the past one million years, numerous volcanic vents were active throughout south-central Washington, from Vancouver to Goldendale. Most were probably active for relatively short times ranging from days to tens of years. Unlike Mount Adams, which has erupted repeatedly for hundreds of thousands of years, these vents typically did not erupt more than once. Rather, each erupting vent built a separate, small volcano, and over time a field of numerous overlapping volcanoes was created. Clusters of these vents define the Mount Adams, Indian Heaven, and Simcoe Mountains volcanic fields. In addition, the Goat Rocks volcanic center lies 30 kilometers (18 miles) north of Mount Adams. The Mount Adams and Indian Heaven fields have been the most active recently; the Simcoe field and the Goat Rocks center have not erupted for hundreds of thousands of years. -- Scott, et.al., 1995

About 60 Eruptive Centers The Indian Heaven volcanic field, midway between Mount St. Helens and Mount Adams, is a Quaternary center, chiefly of basalt. About 60 eruptive centers lie on the 30-kilometer-long, N10degreesEast-trending, Indian Heaven fissure zone. The 600 square kilometer field has a volume of about 100 cubic kilometers and forms the western part of a 2000-square-kilometer Quaternary basalt field in the southern Washington Cascades, including the King Mountain fissure zone along which Mount Adams was built. -- Swanson, et.al., 1989

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[Mount St. Helens Alternative Text]

Mount St. Helens, Washington

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Mount St. Helens

2,549 meter
(8,364 feet)
(9,677 feet before May 18, 1980)
Stratovolcano

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Mount St. Helens Volcano Mount St. Helens, located in southwestern Washington about 50 miles northeast of Portland, Oregon, is one of several lofty volcanic peaks that dominate the Cascade Range of the Pacific Northwest. Geologists call Mount St. Helens a composite volcano (or stratovolcano), a term for steep-sided, often symmetrical cones constructed of alternating layers of lava flows, ash, and other volcanic debris. Composite volcanoes tend to erupt explosively and pose considerable danger to nearby life and property. In contrast, the gently sloping shield volcanoes, such as those in Hawaii, typically erupt nonexplosively, producing fluid lavas that can flow great distances from the active vents. Although Hawaiian-type eruptions may destroy property, they rarely cause death or injury. Before 1980, snow-capped, gracefully symmetrical Mount St. Helens was known as the "Fujiyama of America." Mount St. Helens, other active Cascade volcanoes, and those of Alaska comprise the North American segment of the circum-Pacific "Ring of Fire," a notorious zone that produces frequent, often destructive, earthquake and volcanic activity. -- Tilling, et.al., 1990

Baron St. Helens Some Indians of the Pacific Northwest variously called Mount St. Helens "Louwala-Clough," or "smoking mountain." The modern name, Mount St. Helens, was given to the volcanic peak in 1792 by Captain George Vancouver of the British Royal Navy, a seafarer and explorer. He named it in honor of a fellow countryman, Alleyne Fitzherbert, who held the title Baron St. Helens and who was at the time the British Ambassador to Spain. Vancouver also named three other volcanoes in the Cascades - Mounts Baker, Hood, and Rainier - for British naval officers. -- Tilling, et.al., 1990

Background Ancestral Mount St. Helens began to grow before the last major glaciation of the Ice Age had ended about 10,000 years ago. The oldest ash deposits were erupted at least 40,000 years ago onto an eroded surface of still older volcanic and sedimentary rocks. Intermittent volcanism continued after the glaciers disappeared, and nine main pulses of pre-1980 volcanic activity have been recognized. These pulses lasted from about 5,000 years to less than 100 years each and were separated by dormant intervals of about 15,000 years to only 200 years. A forerunner of Spirit Lake was born about 3,500 years ago, or possibly earlier, when eruption debris formed a natural dam across the valley of the North Fork of the Toutle River. The most recent of the pre-1980 eruptive activity began in A.D. 1800 with an explosive eruption, followed by several additional minor explosions and extrusions of lava, and ended with the formation of the Goat Rocks lava dome by 1857. Mount St. Helens is the youngest of the major Cascade volcanoes, in the sense that its visible cone was entirely formed during the past 2,200 years, well after the melting of the last of the Ice Age glaciers about 10,000 years ago. Mount St. Helens' smooth, symmetrical slopes are little affected by erosion as compared with its older, more glacially scarred neighbors - Mount Rainier and Mount Adams in Washington, and Mount Hood in Oregon. The local Indians and early settlers in the then sparsely populated region witnessed the occasional violent outbursts of Mount St. Helens. The volcano was particularly restless in the mid-19th century, when it was intermittently active for at least a 26-year span from 1831 to 1857. Some scientists suspect that Mount St. Helens also was active sporadically during the three decades before 1831, including a major explosive eruption in 1800. Although minor steam explosions may have occurred in 1898, 1903, and 1921, the mountain gave little or no evidence of being a volcanic hazard for more than a century after 1857. Consequently, the majority of 20th-century residents and visitors thought of Mount St. Helens not as a menace, but as a serene, beautiful mountain playground teeming with wildlife and available for leisure activities throughout the year. At the base of the volcano's northern flank, Spirit Lake, with its clear, refreshing water and wooded shores, was especially popular as a recreational area for hiking, camping, fishing, swimming and boating. The tranquility of the Mount St. Helens region was shattered in the spring of 1980, however, when the volcano stirred from its long repose, shook, swelled, and exploded back to life. -- Tilling, et.al., 1990

Mount St. Helens Awakens The 1980 eruptions of Mount St. Helens in southwestern Washington marked the re-awakening of a relatively young (40,000 years) volcano that had been dormant since 1857. Frequent dacitic eruptions during the previous 2,500 years had produced pyroclastic flows, ash falls, debris flows, lava domes, and lava flows of andesite and basalt. Pyroclastic flows and lahars accompanied most eruptive periods and were largely responsible for forming fans around the base of the volcano, some of which dammed the North Fork Toutle River to form Spirit Lake between 3,300 and 4,000 years ago. The magnitudes of the 1980 eruptions were not exceptional by worldwide historical standards; however, they were the first volcanic eruptions in the conterminous United States since 1914 (Lassen Peak) and focused national attention on events leading up to the climactic eruption of May 18, 1980. That eruption led to exceptional opportunities for scientific observations, data collection, and the study of infrequent and often inaccessible geologic events and processes. -- Simon, 1999

May 18, 1980 The catastrophic eruption on May 18, 1980, was preceded by 2 months of intense activity that included more than 10,000 earthquakes, hundreds of small phreatic (steam-blast) explosions, and the outward growth of the volcano's entire north flank by more than 80 meters. A magnitude 5.1 earthquake struck beneath the volcano at 8:32 a.m. on May 18, setting in motion the devastating eruption. Within seconds of the earthquake, the volcano's bulging north flank slid away in the largest landslide in recorded history, triggering a destructive, lethal lateral blast of hot gas, steam, and rock debris that swept across the landscape as fast as 1,100 kilometers per hour. Temperatures within the blast reached as high as 300 degrees Celsius. Snow and ice on the volcano melted, forming torrents of water and rock debris that swept down river valleys leading from the volcano. Within minutes, a massive plume of ash thrust 19 kilometers into the sky, where the prevailing wind carried about 490 tons of ash across 57,000 square kilometers of the Western United States. -- Brantley, 1994

Following May 18, 1980 Following the most recent major eruption, on May 18, 1980, there were 5 smaller explosive eruptions over a period of 5 months. Thereafter, a series of 16 dome-building eruptions through October 1986 constructed the new, 270-meter- (-880- feet) high, lava dome in the crater formed by the May 18, 1980 eruption. -- Wolfe and Pierson, 1995

Cascade Range Current Activity Update -- Monthly (or sooner) Updates

Current Volcanic Activity -- Monthly Updates

1995 Hazards Assessment Report -- Wolfe and Pierson, 1995, OFR95-497

Mount St. Helens -- From the 1980 Eruption to 2000 -- Brantley and Myers, 2000, USGS Fact Sheet 036-00

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Oregon

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[Mount Hood Alternative Text]

Mount Hood, Oregon

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Mount Hood

3,426 meters
(11,239 feet)
Stratovolcano

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Mount Hood Volcano For the general public, Mount Hood is perhaps the most accessible and preeminent of Oregon's volcanoes, located only 75 kilometers east-southeast of Portland, Oregon. It is the highest peak in the state (3,426 meters - 11,239 feet) and one of the most often climbed peaks in the Pacific Northwest. In summer, Mount Hood's timberline wilderness is a pastoral garden for backpackers. In winter and spring the volcano's slopes host several downhill ski runs and cross-country tracks. -- Sherrod, 1990, IN: Wood and Kienle

Eruptive History Mount Hood is also one of the major volcanoes of the Cascade Range, having erupted repeatedly for hundreds of thousands of years, most recently during two episodes in the past 1,500 years. The last episode ended shortly before the arrival of Lewis and Clark in 1805. When Mount Hood erupts again, it will severely affect areas on its flanks and far downstream in the major river valleys that head on the volcano. Volcanic ash may fall on areas up to several hundred kilometers downwind. -- Scott, et.al., 1997

Collapse of Lava Domes Eruptive activity at Mount Hood during the past 30,000 years has been dominated by growth and collapse of lava domes. The last two episodes of eruptive activity occurred 1,500 and 200 years ago. Repeated collapse of lava domes extruded near the site of Crater Rock, Mount Hood's youngest lava dome, generated pyroclastic flows and lahars and built much of the broad smooth fan on the south and southwest flank of the volcano. -- Scott, et.al., 1997

Quicksand River In 1805, Meriwether Lewis and William Clark named a river on the south side of the Columbia River gorge the "Quicksand River." Their description of a wide, shallow river with a bed "formed entirely of quicksand," bears little resemblance to the narrow, moderately deep river we call today the Sandy River. What happened? The answer lay 50 miles away at Mount Hood. An eruption in the 1790's caused a tremendous amount of volcanic rock and sand to enter the Sandy River drainage. That sediment was still being flushed downstream when Lewis and Clark saw and named the river. Since 1806, the river has removed the excess sediment from its channel. The Toutle River in southwest Washington was similarly affected by the 1980 eruptions of Mount St. Helens. -- Gardner, et.al., 2000

Cascade Range Current Activity Update -- Monthly (or sooner) Updates

1997 Hazards Assessment Report -- Scott, et.al., 1997, OFR97-89

Geological History and Field Trip Guidebook -- Scott, et.al., 1997, OFR97-263

Mount Hood -- History and Hazards of Oregon's Most Recently Active Volcano -- Gardner, et.al., 2000, FS060-00

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. [Mount Jefferson Alternative Text]

Mount Jefferson, Oregon

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Mount Jefferson

3,199 meters
(10,495 feet)
Stratovolcano

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Mount Jefferson Volcano Mount Jefferson is a prominent feature of the landscape seen from highways east and west of the Cascades. Mount Jefferson (one of thirteen major volcanic centers in the Cascade Range) has erupted repeatedly for hundreds of thousands of years, with its last eruptive episode during the last major glaciation which culminated about 15,000 years ago. Geologic evidence shows that Mount Jefferson is capable of large explosive eruptions. The largest such eruption occurred between 35,000 and 100,000 years ago, and caused ash to fall as far away as the present-day town of Arco in southeast Idaho. Although there has not been an eruption at Mount Jefferson for some time, experience at explosive volcanoes elsewhere suggests that Mount Jefferson cannot be regarded as extinct. If Mount Jefferson erupts again, areas close to the eruptive vent will be severely affected, and even areas tens of kilometers (tens of miles) downstream along river valleys or hundreds of kilometers (hundreds of miles) downwind may be at risk. -- Walder, et.al., 1999

Upper Cone Most of the cone (upper 1,000 meters) of Mount Jefferson is less than 100,000 years old, with much of it younger than the explosive event described above. The upper cone is composed largely of dacite lava flows and domes, many of which appear to have been emplaced when glaciers on the volcano were much large than at present. It is likely that during growth of the domes, material was shed off to form pyroclastic flows and lahars, but if so, that record has been largely removed by glacial erosion. -- Walder, et.al., 1999

Youngest Lava Flows The youngest lava flows in the Mount Jefferson area are basaltic lava flows from Forked Butte and an unnamed butte south of Bear Butte. Both of these flows postdate the large eruption of Mount Mazama (Crater Lake) of about 7,600 years. -- Walder, et.al., 1999

Localized Floods and Lahars During the last few centuries, several small lakes were formed on the flanks of Mount Jefferson when small tributary valleys became dammed by glacial moraines (ridges of sediment left behind by glaciers). Several of these moraines have breached during the 20th century, producing local floods and small lahars. -- Walder, et.al., 1999

Cascade Range Current Activity Update -- Monthly (or sooner) Updates

1999 Hazards Assessment Report -- Walder, et.al., 1999, OFR99-24

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Three-Fingered Jack, Oregon

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Three-Fingered Jack

2,390 meters
(7,841 feet)
Shield Volcano

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Three-Fingered Jack Volcano Three Fingered Jack (2,390 meters) is the most distinctive volcano in this part of the range -- (Central Oregon High Cascades south of Mount Jefferson to Santiam Pass). This deeply glaciated basaltic andesite shield volcano has around 800 meters of relief and is centered on a pyroclastic cone that underlies the summit of the mountain. The cone lacks a high-level conduit-filling plug, however, unlike other shield volcanoes such as nearby Mount Washington south of Santiam Pass. Three Fingered Jack is undated by radiometric methods, but its age probably lies between 0.50 and 0.25 million years ago (500,000 and 250,000 years ago), as inferred from its erosional state compared to other shield volcanoes in the High Cascades. -- Sherrod, 1990, IN: Wood and Kienle

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Mount Washington, Oregon

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Mount Washington

2,376 meters
(7,796 feet)
Shield Volcano

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Mount Washington Volcano Eruptions of relatively uniform basaltic andesite lavas produced a shield volcano, 5 kilometers in diameter, surmounted by a summit cone that probably reached an elevation of 2,600 meters, around 1,200 meters above the pre-existing basalt field. Mafic ash accumulated on the flanks of the shield and has been preserved as thick sections of palagonitic tuff on the southwest and northeast sides of the summit cone. The volcano was intruded by a micronorite plug which now forms the central pinnacle, 0.4 kilometers in diameter. Although no isotopic ages are available, all of the Mount Washington lavas and the underlying basalt appear to be of normal paleomagnetic polarity; the age of Mount Washington is probably no more than a few 100,000 years, similar to that of other central High Cascade stratovolcanoes. During the late Pleistocene, cirques were excavated into the flanks of the summit cone by valley glaciers which extended more than 12 kilometers east and west. -- Taylor, 1990, IN: Wood and Kienle

Recent Spatter Cones The is no evidence of recent reactivation of Mount Washington volcanism, but a series of aligned small basaltic andesite spatter cones erupted on the northeast flank approximately 1,330 years ago (carbon-14). -- Taylor, 1990, IN: Wood and Kienle

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Belknap Shield Volcano, Oregon

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Belknap Shield Volcano

2,095 meters
(6,874 feet)
Shield Volcano

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Youngest Cascade Shield Volcano Another type of (Cascade) basaltic activity is characterized by the concentration of many tephra and lava-flow eruptions at a central vent and several flank vents. This type of activity has built shield volcanoes typically 5-15 kilometers in diameter and several hundred meters to more than 1000 meters high. Many have summit cinder cones. Belknap in central Oregon is the youngest such shield volcano in the Cascades and has lava flows as young as 1,400 years. -- Hoblitt, et.al., 1987

Eruptive History The Belknap shield volcano and its distal lava tongues cover 98 square kilometers of the crest of the central High Cascades in Oregon. Prior to 2,900 years before present, the first eruptive phase distributed basaltic cinders and ash over a broad area to the northeast and southeast, while basaltic lavas moved 10 kilometers eastward from a growing shield. A second phase, 2,883 years before present (carbon-14), produced an adventive shield of basaltic andesite on the east flank, known as "Little Belknap". The third phase was responsible for the bulk of modern Belknap volcano. It was constructed by effusion of basaltic andesite lavas from the central vent (Belknap Crater), 1,495 years before present (carbon-14), and from a vent 2 kilometers to the south (South Belknap cone), 1,775 years before present (carbon-14). The final eruptions from the northeast base of Belknap Crater sent lavas 15 kilometers westward into the valley of the McKenzie River. -- Taylor, 1990, IN: Wood and Kienle

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Three Sisters, Oregon

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Three Sisters

Stratovolcano Cluster

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North Sister

3,074 meters
(10,085 feet)
Stratovolcano atop Shield Volcano

Middle Sister

3,062 meters
(10,047 feet)
Stratovolcano

South Sister

3,157 meters
(10,358 feet)
Stratovolcano

Two Types of Volcanoes in the Region Two types of volcanoes exist in the Three Sisters region and each poses distinct hazards to people and property. South Sister, Middle Sister, and Broken Top, major composite volcanoes clustered near the center of the region, have erupted repeatedly over tens of thousands of years and may erupt explosively in the future. In contrast, mafic volcanoes, which range from small cinder cones to large shield volcanoes like North Sister and Belknap Crater, are typically short-lived (weeks to centuries) and erupt less explosively than do composite volcanoes. Hundreds of mafic volcanoes scattered through the Three Sisters region are part of a much longer zone along the High Cascades of Oregon in which birth of new mafic volcanoes is possible. -- Scott, et.al., 2001

The Three Sisters Volcanoes The Three Sisters area contains 5 large cones of Quaternary age-- North Sister, Middle Sister, South Sister, Broken Top, and Mount Bachelor. North Sister and Broken Top are deeply dissected and probably have been inactive for at least 100,000 years. Middle Sister is younger than North Sister, and was active in late Pleistocene but not postglacial time. South Sister is the least dissected; its basaltic andesite summit cone has a well preserved crater. Most of South Sister predates late Wisconsin glaciation and is therefore older than 25,000 years; however, eruptions of rhyolite from flank vents have occurred as recently as 2,000 years ago. -- Hoblitt, et.al., 1987

Latest South Sister Activity The latest eruptions on South Sister, which occurred in two closely spaced episodes about 2,000 years ago, illustrate a relatively modest scale of eruptive activity. Initial explosive eruptions produced small pyroclastic flows and tephra fallout from several aligned vents low on the south flank. Tephra fallout deposits more than 2 meters (7 feet) thick, composed of pumice, rock fragments, and ash, blanketed areas within 2 kilometers (1 mile) downwind of vents; at 13 kilometers (8 miles) about 10 centimeters (4 inches) fell. Less than one centimeter (0.5 inch) of ash fell at least as far as 40 kilometers (25 miles) south of the vents (at Cultus Lake) and east of the vents (at Bend). Following tephra eruptions, lava emerged from two vent areas, forming a large lava flow, Rock Mesa, and several small lava domes. Decades to a few centuries later, a similar eruptive sequence occurred along a zone of vents that extended from just north of Sparks Lake to high on the southeast flank of South Sister, as well as along a shorter zone on the north flank near Carver Lake. -- Scott, et.al., 2001

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Ground Uplift Near South Sister Volcano, Central Oregon Cascade Range

West Uplift - InSAR Monitoring

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Broken Top, Oregon

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Broken Top

2,789 meters
(9,152 feet)
Stratovolcano

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Broken Top - Complex Stratovolcano Broken Top is a complex stratovolcano magnificently exposed by glacial erosion. Pleistocene eruptions of basaltic andesite lava produced a broad shield with a core of oxidized agglomerate invaded by dikes and sills. Subordinate silicic magmas were erupted intermittently; andesite, dacite, and rhyodacite lavas, intrusives, and pyroclastic flow deposits are associated with the predominant mafic lavas from the lower flanks to the summit of the volcano. The central crater of Broken Top was enlarged to a diameter of 0.8 kilometers, probably by subsidence. The resulting depression was filled by thick flows of basaltic andesite and eventually the summit cone was buried beneath a shroud of thin, vesicular lavas. After the central conduit had congealed to a plug of micronorite, the core of the volcano was subjected to hydrothermal alteration. Glacial cirques have been carved into three sides of the mountain, revealing internal structure. Holocene eruptive activity on the flanks has produced basaltic cones, flows, and ash deposits interbedded with Neoglacial moraines and outwash. -- Taylor, 1990, IN: Wood and Kienle

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Mount Bachelor, Oregon

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Mount Bachelor

2,763 meters
(9,065 feet)
Stratovolcano atop Shield Volcano

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Mount Bachelor Volcanic Chain The Mount Bachelor volcanic chain provides one example of the type and scale of eruptive activity that has produced most of the High Cascades platform, which consists chiefly of scoria cones and lava flows, shield volcanoes, and a few steep-sided cones of basalt and basaltic andesite. The chain is 25 kilometers long; its lava flows cover 250 square kilometers and constitute a total volume of 30-50 cubic kilometers. -- Scott and Gardner, 1990

Mount Bachelor Volcano The Three Sisters area contains 5 large cones of Quaternary age-- North Sister, Middle Sister, South Sister, Broken Top, and Mount Bachelor. ... Mount Bachelor, which is between 11,000 and 15,000 years old is the youngest of these volcanoes in the Cascades. -- Hoblitt, et.al., 1987

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Newberry Caldera, Oregon

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Newberry Caldera

2,434 meters
(7,985 feet -
Paulina Peak)
Shield Volcano, Caldera

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Newberry Volcano Newberry volcano is a broad shield volcano located in central Oregon. It has been built by thousands of eruptions, beginning about 600,000 years ago. At least 25 vents on the flanks and summit have been active during several eruptive episodes of the past 10,000 years. The most recent eruption 1,300 years ago produced the Big Obsidian Flow. Thus, the volcano's long history and recent activity indicate that Newberry will erupt in the future. -- Sherrod, et.al., 1997

Newberry Caldera, Paulina Peak, Paulina and East Lakes Newberry Volcano, centered about 20 miles southeast of Bend, Oregon, is among the largest Quaternary volcanoes in thee conterminous United States. It covers and area in excess of 500 square miles, and lavas from it extend northward many tens of miles beyond the volcano. The highest point on the volcano, Paulina Peak with an elevation of 7,984 feet, is about 4,000 feet higher than the terrain surrounding the volcano. The gently sloping flanks, embellished by more than 400 cinder cones, consist of basalt and basaltic andesite flows, andesitic to rhyolitic ash-flow and air-fall tuffs and other types of pyroclastic deposits, dacite to rhyolite domes and flows, and alluvial sediments produced during periods of erosion of the volcano. At Newberry's summit is a 4- to 5-mile-wide caldera that contains scenic Paulina and East Lakes. The caldera has been the site of numerous Holocene eruptions, mostly of rhyolitic composition, that occurred as recently as 1,400 years ago. ... Newberry lies 40 miles east of the crest of the Cascade Range ... -- MacLeod, 1981

Newberry Basaltic Eruptions Basaltic eruptions are well known from observations elsewhere, such as at Hawaii, where spectacular fountains of spatter and cinders are associated with lava flows. At Newberry, basaltic eruptions have occurred repeatedly on the volcano's flanks and in the caldera. Typical products of a basaltic eruption are the 7,000-yr-old cinder cone of Lava Butte and its surrounding lava flows, located 10 kilometers (6 miles) south of Bend. Basaltic eruptions commonly begin with lava fountains that hurl cinders or spatter as far as 1 kilometers (0.6 miles) from the vent. Ejecta are thrown aloft for hundreds to a few thousand meters. Large fragments are expelled from the vent along ballistic trajectories, like artillery shells. Smaller particles are carried by wind and convective updrafts. The resulting deposits may be many meters thick near the vent and build a steep-sided cinder cone, but they generally thin to a few millimeters within 10 kilometers (6 miles) distance downwind. The chief hazard from ballistic ejection is direct impact. Some spatter will be hot upon impact and likely will start forest fires. -- Sherrod, et.al., 1997

Big Obsidian Flow The eruptive sequence that culminated in the Big Obsidian Flow 1,300 years ago exemplifies several aspects of a typical rhyolitic eruptive sequence at Newberry volcano. The eruptions began with tephra showers that deposited pumice lumps and dense lava blocks as large as 1 meter (3 feet) within the caldera. ... As the eruption progressed, pyroclastic flows swept downslope from the Big Obsidian vent to Paulina Lake. The boat ramp at Little Crater Campground is excavated in these pyroclastic-flow deposits, as is the caldera road upslope from Paulina Lake. The flows entered Paulina Lake, perhaps causing secondary steam explosions and displacing water from the lake into Paulina Creek. The final stage of eruption produced the Big Obsidian Flow itself, a lava flow that moved slowly, probably advancing only a few meters or tens of meters per day as it oozed down an inner caldera wall and ponded on the caldera floor. The Big Obsidian Flow is about 1.8 kilometers (6,000 feet) long and locally thicker than 20 meters (65 feet). -- Sherrod, et.al., 1997

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Lava Butte and Pilot Butte, Oregon

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Lava Butte

Lava Butte
1,544 meters
(4,970 feet)
Cinder Cone

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Lava Butte This cinder cone rises 500 feet from the surrounding forest floor offering breathtaking views of the Cascades. At the 5000-foot summit is a fire lookout and visitor rest area with interpretive displays. Turn left from Lava Lands Visitor Center parking and follow signs to Lava Butte. The Butte is closed to trailers due to inadequate parking. -- U.S. Forest Service Pamphlet, 1994

The basaltic andesite flow derived from Lava Butte extends northward more than 5 miles and westward 3 miles to the Deschutes River. ... It is one of many basaltic andesite flows on Newberry that have carbon-14 ages of about 6,100 years. ... The lava flow emerges from the south side of the butte. -- Hoblitt, et.al., 1987

Pilot Butte A cinder cone at the east city limits at Bend. Visible from its easily accessible top are the snow peaks of the Cascade Range (listed from the north): Mount Hood, 11,235 feet; Mount Jefferson, 10,495 feet; Three-Fingered Jack, 7,848 feet; Mount Washington, 7,802 feet; North Sister, 10,094 feet; Middle Sister, 10,053 feet; South Sister, 10,354 feet; Broken Top, 9, 165 feet; and Mount Bachelor Ski Resort Area, 9,600 feet. -- Bend Chamber of Commerce, 1984

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Diamond Peak, Oregon

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Diamond Peak

2,667 meters
(8,750 feet)
Shield Volcano

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Diamond Peak Volcano Diamond Peak, the dominant landform in the Willamette Pass area, is a basaltic andesite shield approximately 15 cubic kilometers in volume. Like other shields in the area, it has a central pyroclastic cone that is surrounded and surmounted by lava flows. Volcaniclastic rocks such as lahars and pyroclastic flows are unknown. Diamond Peak began erupting from a vent near its northern summit. A second vent later opened near the southern summit, piggy-backing its lava and tephra over the previously erupted volcanic rocks. This vent migration likely involved only a small interval of time. Diamond Peak is probably less than 100,000 years old, but is certainly older than the last glaciation, which ended approximately 11,000 years ago. -- Sherrod, 1990, IN: Wood and Kienle

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Mount Bailey, Oregon

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Mount Bailey

2,549 meters
(8,363 feet)
Shield Volcano

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Mount Bailey Volcano Mount Bailey is the southernmost volcano in a north-south-trending volcanic chain 10 kilometers long that rises west of Diamond Lake. Bailey is about the same age as Diamond Peak, 43 kilometers north: less than 100,000 years but greater than 11,000 years old, on the basis of glacial evidence and morphologic comparisons with dated volcanoes. Like Diamond Peak, Bailey consists of a tephra cone surrounded by basaltic andesite lava. Bailey is slightly smaller (8-9 cubic kilometers) than Diamond Peak, and minor andesite erupted from the summit cone in its late stages, whereas Diamond Peak eruptions were never more siliceous than basaltic andesite. -- Sherrod, 1990, IN: Wood and Kienle

Mount Bailey Volcanic Chain The Mount Bailey chain includes Rodley Butte and other cinder cones to the north, all of which are similar in age (based on morphology) and magmatically related (on the basis of mineralogy, chemistry, and close spatial association of the vents). Volcanism along the Bailey chain migrated spatially from north to south while it evolved chemically. -- Sherrod, 1990, IN: Wood and Kienle

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Mount Thielsen, Oregon

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Mount Thielsen

2,799 meters
(9,182 feet)
Shield Volcano

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Mount Thielsen Volcano Mount Thielsen is a normally polarized shield volcano comprising approximately 8 cubic kilometers of basaltic andesite built atop a broad pedestal (24 cubic kilometers) of older lava. Thielsen is remarkable even at a distance for its colorfully interbedded pyroclastic rocks that dip away from the jagged spire of the central plug, often called the "lightning rod of the Cascades". The most spectacular views are on the north and east sides (accessible only by foot or horseback) where now-vanished glaciers have carved precipitous cirque walls that reveal the construction. Thielsen's age is approximately 290,000 years (whole-rock K-Ar), and its geomorphology is a reference point for assigning Cascade Range volcanoes to the age division 0-0.25 million years (younger than Thielsen) or 0.25-0.73 million years (older than Thielsen). Very little of Thielsen's underpinnings are exposed because Holocene Mazama ash, which erupted from vents at Crater Lake National Park (20 kilometers south), forms a shroud 4-20 meters thick in the Thielsen area. -- Sherrod, 1990, IN: Wood and Kienle

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Crater Lake, Oregon

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Crater Lake

2,487 meters
(8,156 feet -
Hillman Peak)
Stratovolcano -
Caldera
Lake Depth -
1,932 feet

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Crater Lake Caldera The caldera now filled by Oregon's Crater Lake was produced by an eruption that destroyed a volcano the size of Mount St. Helens and sent volcanic ash as far east as Nebraska. -- Wright and Pierson, 1992

Crater Lake caldera formed by collapse during the catastrophic eruption of approximately 50 cubic kilometers of magma, 6,845 carbon-14 years B.P. (before present). The 8x10 kilometer caldera lies in the remains of Mount Mazama, a Pleistocene stratovolcano cluster covering 400 square kilometers in the southern Oregon Cascades. Prior to its climactic eruption, Mount Mazama's summit had an elevation between 3,300 meters and 3,700 meters (10,800 - 12,000 feet). Its southern and southeastern flanks were deeply incised by glacial valleys, now beheaded, that form U-shaped notches in the caldera wall. -- Bacon, 1990, IN: Wood and Kienle

Wizard Island Post-caldera volcanic landforms are present beneath the lake surface and poke through to form Wizard Island. The central platform, Merriam Cone, and Wizard Island are all andesite evidently erupted within a few hundred years of caldera collapse. The small rhyodacite dome 30 meters below lake level one kilometer east of Wizard Island is the youngest feature. -- Bacon, 1990, IN: Wood and Kienle

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1997 Hazards Assessment Report -- Bacon, et.al., 1997, OFR97-487

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Mount McLoughlin, Oregon

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Mount McLoughlin

2,894 meters
(9,496 feet)
Shield Volcano

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Mount McLoughlin Volcano Mount McLoughlin (Mount Pit or Pitt) rises 1,200 meters as a steep-sided, dominantly basaltic andesite lava cone above the low Pliocene and Pleistocene basaltic andesite shields on which it is built. McLoughlin is easily recognized from as far away as Medicine Lake in California, along I-5 between Yreka, California, and Medford, Oregon, or around the rim of Crater Lake. Although it is the tallest volcano between Shasta and Crater Lake, McLoughlin, with a volume of only 13 cubic kilometers, is dwarfed by the bulk of Shasta (350 cubic kilometers) and Mazama (130 cubic kilometers [Crater Lake]). -- Smith, 1990, IN: Wood and Kienle

Part of the Mountain is Missing When viewed from the south or southeast it appears a seemingly perfectly symmetrical Fuji-like volcano. However, when seen from the east, along the shores of Klamath Lake, or from the north along Crater Lake's rim, it is apparent that a major part of the mountain is missing. Late Pleistocene glaciers have carved away the entire northeast side of the mountain, lowering the summit about a hundred meters, excavated the large bowl-like cirque, and exposed the congealed lava that fills two small central conduits. Steeply dipping layers of pyroclastic breccia and tuff and numerous interlayered lava flows are exposed in the walls of the cirque. An explosive origin is sometimes ascribed to this cirque; however, there is no evidence of deposits that would have resulted from such an explosion. Glacial striae and other glacial features are common in the cirque, and glacial deposits such as moraines and till are present at the mouth of the cirque and around the north base of the mountain. Finally, the composition of McLoughlin's lava is much more mafic than that of other volcanoes at which explosive events of the required size have occurred. -- Smith, 1990, IN: Wood and Kienle

A Young Volcano Mount McLoughlin is a young volcano. A pronounced magnetic high centered just east of McLoughlin's main vent is interpreted as indicating that most of the main cone is normally polarized and thus less than approximately 700,000 years old. The well preserved shape of the mountain's west and south flanks, the lack of soil development on many flows, and preservation of primary flow features suggests that the bulk of the main cone is no older than 200,000 years, with much of it probably younger. The main cone was essentially complete before the last major Pleistocene glaciation. Many flank flows are younger than the main cone; some may be as young as 20,000 - 30,000 years. -- Smith, 1990, IN: Wood and Kienle

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California

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Medicine Lake, California

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Medicine Lake

2,412 meters
(7,762 feet)
Shield Volcano -
Caldera

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Medicine Lake Shield Volcano Medicine Lake volcano is a large Pleistocene and Holocene shield volcano in northeastern California about 50 kilometers northeast of Mount Shasta. The volcano is located in a zone of east-west crustal extension east of the main axis of the Cascade Range. The 1-kilometer-thick shield is 35 kilometers from east to west and 45-50 kilometers from north to south, and covers more than 2000 square kilometers. The volcano is composed primarily of basalt and basaltic andesite lava flows, and has a 7 x 12 kilometer caldera at the center. Eruptive activity during Holocene time has included numerous rhyolite and dacite lava flows erupted at high elevations inside and outside the caldera; cinder cones and associated lava flows of basalt and basaltic andesite have resulted from eruptions at vents on the flanks of the shield. Most vents are aligned along zones of crustal weakness that trend NNE to NNW. -- Hoblitt, et.al., 1987

The Medicine Lake shield rises about 1200 meters above the Modoc Plateau to an elevation of 2,376 meters. Lavas from Medicine Lake volcano cover nearly 2000 square kilometers, and their volume is estimated to be at least 600 cubic kilometers, making it the largest volcano by volume in the Cascade Range. -- Dzurisin, et.al., 1991

Eruptive History Medicine Lake volcano began to grow about one million years ago, following eruption of a large volume of tholeiitic high-alumina basalt. Similar high-alumina basalt has continued to erupt around the volcano throughout its history. Although mafic lavas predominate on the volcano's flanks, all lava compositions from basalt to rhyolite have erupted during Pleistocene time. The lower flanks consist of mostly basaltic and some andesitic lavas. Basalt is mostly absent at higher elevation, where andesite dominates and rhyolite and small volumes of dacite are present. During the past 11,000 years, eruptive activity at Medicine Lake volcano has been episodic. Eight eruptions produced about 5.3 cubic kilometers of basaltic lava during a time interval of a few hundred years about 10,500 years ago. That eruptive episode was followed by a hiatus that ended with a small andesitic eruption about 4,300 years ago. During the most recent eruptive episode between 3000 and 900 years ago, eight eruptions produced approximately 2.5 cubic kilometers of lava ranging in composition from basalt to rhyolite. Late Holocene lava compositions include basalt and andesite, but silicic lavas dominate. -- Dzurisin, et.al., 1991

The Caldera Medicine Lake caldera is a 7 x 12 kilometer depression in the summit area of the volcano. Anderson (1941) suggested that the caldera formed by collapse after a large volume of andesite was erupted from vents along the caldera rim. However, the distribution of late Pleistocene vents, mostly concentrated along the rim, suggests that ring faults already existed when most of the andesite erupted (Donnelly-Nolan, 1988). No single large eruption has been related to caldera formation. The only eruption recognized to have produced ash flow tuff occurred in late Pleistocene time, and this eruption was too small to account for formation of the caldera. Donnelly-Nolan (1988) concluded that Medicine Lake caldera formed by collapse in response to repeated extrusions of mostly mafic lava beginning early in the history of the volcano (perhaps in a manner similar to the formation of Kilauea caldera, Hawaii). She hypothesized several small differentiated magma bodies fed by and interspersed among a plexus of dikes and sills. In her model, late Holocene andesitic to rhyolitic lavas were derived by fractionation, assimilation, and mixing from high alumina basalt parental magma. -- Dzurisin, et.al., 1991

The Lake The small lake from which Medicine Lake volcano derives its name lies within the 7x12-kilometer central caldera. -- Donnelly-Nolan, 1990, IN: Wood and Kienle

Glass Mountain Obsidian Flow The most recent eruption occurred around 1,000 years ago when rhyolite and dacite erupted at Glass Mountain and associated vents near the caldera's eastern rim. No field evidence has been found to substantiate a report of an eruption in 1910. -- Donnelly-Nolan, 1990, IN: Wood and Kienle

Glass Mountain consists of a spectacular, nearly treeless, steep-sided rhyolite and dacite obsidian flow that erupted just outside the eastern caldera rim and flowed down the steep eastern flank of Medicine Lake volcano. Ten additional small domes of Glass Mountain rhyolite and rhyodacite lava lie on a N25degreesW trend to the north and one to the south. The age of Glass Mountain and its preceding pumice deposits has been a matter of discussion for some time. A radiocarbon age of 885+/-40 years B.P. was obtained on a dead cedar tree without limbs or bark that is preserved in the edge of one of the distal tongues of the flow. The dated material consisted of a piece of exterior wood containing about 30 annual growth rings. This age may be too old, because some of the outside of the tree is missing. The tephra deposits that precede the flow and domes may be somewhat older but are constrained to be less than about 1050 years B.P. by the Little Glass Mountain and Lassen data. -- Donnelly-Nolan, 1990

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Black Butte, California

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Black Butte

Volcanic Domes

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Black Butte Two of the main eruptive centers at Mount Shasta, the Shastina and Hotlum cones were constructed during Holocene time, which includes about the last 10,000 years. Holocene eruptions also occurred at Black Butte, a group of overlapping dacite domes about 13 kilometers (8 miles) west of Mount Shasta. -- Miller, 1980

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Mount Shasta, California

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Mount Shasta

4,317 meters
(14,161 feet)
Stratovolcano

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Mount Shasta Volcano Mount Shasta is located in the Cascade Range in northern California about 65 kilometers (40 miles) south of the Oregon-California border and about midway between the Pacific Coast and the Nevada border. One of the largest and highest of the Cascade volcanoes, snowclad Mount Shasta is near the southern end of the range that terminates near Lassen Peak. -- Miller, 1980

Mount Shasta, a compound stratovolcano rising 3,500 meters above its base to an elevation of 4,317 meters, dominates the landscape of northern California. ... Mount Shasta hosts five glaciers, including the Whitney Glacier, the largest in California. Shastina is a large subsidiary cone that rises to 3,758 meters on the west flank of the compound volcano. ... -- Christiansen, 1990, IN: Wood and Kienle

Early Volcanic History Mount Shasta is a massive compound stratovolcano composed of overlapping cones centered at four or more main vents; it was constructed during a period of more than 100,000 years. Each of the cone-building periods produced pyroxene-andesite lava flows, block-and-ash flows, and mudflows originating mainly at the central vents. ... Construction of each cone was followed by eruption of domes and pyroclastic flows of more silicic rock at central vents, and of domes, cinder cones, and lava flows at vents on the flanks of the cones. Two of the main eruptive centers at Mount Shasta, the Shastina and Hotlum cones were constructed during Holocene time, which includes about the last 10,000 years. Holocene eruptions also occurred at Black Butte, a group of overlapping dacite domes about 13 kilometers (8 miles) west of Mount Shasta. -- Miller, 1980

Historical Activity Shastina, west of the cluster of other central vents, was formed mainly between 9,700 and 9,400 years; the Hotlum cone, which forms the summit and the north and northwest slopes of Shasta, may overlap Shastina in age, but most of the Hotlum cone is probably younger. Mount Shasta has continued to erupt at least once every 600-800 years for the past 10,000 years. Its most recent eruption probably was in 1786. Evidence for this eruption, recorded from sea by the explorer La Perouse, is somewhat ambiguous, but his description could only have referred to Mount Shasta. A small craterlike depression in the summit dome, containing several small groups of fumaroles and an acidic hot spring, might have formed during that eruption; lithic ash preserved on the slopes of the volcano and widely to the east yields charcoal dates of about 200 years. -- Christiansen, 1990, IN: Wood and Kienle

Debris Avalanche Deposit For more than a century, hundreds of mounds, hills, and ridges of volcanic rocks in Shasta valley, north-central California, had puzzled geologists. ... Comparison with the Mount St. Helens debris-avalanche deposit, however, clearly establishes that the hills are part of a giant debris-avalanche deposit derived from a volcano ancestral to Mount Shasta. ... The Mount Shasta debris-avalanche deposit covers and area of at least 450 square kilometers with about 26 cubic kilometers of debris -- roughly 10 times the volume of the 1980 Mount St. Helens avalanche deposit. Radiometric ages of rocks in the deposit and of a post-avalanche basalt flow indicate that the avalanche occurred between about 300,000 and 360,000 years ago. -- Brantley and Glicken, 1986

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1980 Hazards Report -- Miller, 1980, USGS Bulletin 1503

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Lassen Peak, California

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Lassen Peak

3,187 meters
(10,457 feet)
Stratovolcano -
Volcanic Dome

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Lassen Volcanic Center The Lassen region has been volcanically active for more than 3 million years. The Lassen "volcanic center" began to erupt about 600,000 years ago. From 600,000 to 400,000 years ago, eruptions built a large volcano, often referred to as "Brokeoff Volcano" or "Mount Tehama". Later, this volcano became inactive and was mostly eroded away, leaving remnants that include Brokeoff Mountain, Mount Conard, Mount Diller, and Diamond Peak. Subsequent eruptions in the Lassen volcanic center have formed more than 30 steep-sided lava domes (the Lassen dome field). The most recently active parts of the volcanic center are Lassen Peak and other young domes formed in the past 50,000 years. Clynne, et.al., 2000

Lassen Peak Volcanic Dome Lassen Peak is the largest of a group of more than 30 volcanic domes erupted over the past 300,000 years in Lassen Volcanic National Park in northern California. These mound-shaped accumulations of volcanic rock, called lava domes, were created by eruptions of lava too viscous to readily flow away from its source. Eruptions about 27,000 years ago formed Lassen Peak, probably within only a few years. With a height of 2,000 feet and a volume of half a cubic mile, it is one of the largest lava domes on Earth. When Lassen Peak formed, it looked much like the nearby 1,100-year-old Chaos Crags Domes, with steep sides covered with angular rock talus. However, from 25,000 to 18,000 years ago, during the last ice age, Lassen's shape was significantly altered by glacial erosion. For example, the bowl-shaped depression on the volcano's northeastern flank, called a cirque, was eroded by a glacier that extended out 7 miles from the dome. -- Clynne, 1998

Eruptive Activity During the Past 1,100 Years Three episodes of volcanism have occurred at the Lassen volcanic center in the past 1,100 years. These are the complex eruption at Chaos Crags, the eruptions at Cinder Cone, and the summit eruptions of Lassen Peak in 1914-1917. -- Clynne, 1990, IN: Wood and Kienle

Eruptive Activity 1914-1917 The most recent eruptive activity occurred at Lassen Peak in 1914-1917 A.D.. This eruptive episode began on May 30, 1914, when a small phreatic eruption occurred at a new vent near the summit of the peak. More than 150 explosions of various sizes occurred during the following year. By mid-May 1915, the eruption changed in character; lava appeared in the summit crater and subsequently flowed about 100 meters over the west and probably over the east crater walls. Disruption of the sticky lava on the upper east side of Lassen Peak on May 19 resulted in an avalanche of hot rock onto a snowfield. A lahar was generated that reached more than 18 kilometers down Lost Creek. On May 22, an explosive eruption produced a pyroclastic flow that devastated an area as far as 6 kilometers northeast of the summit. The eruption also generated lahars that traveled more than 20 kilometers down Lost Creek and floods that went down Hat Creek. A vertical eruption column resulting from the pyroclastic eruption rose to an altitude of more than 9 kilometers above the vent and deposited a lobe of pumiceous tephra that can be traced as far as 30 kilometers to the east-northeast The fall of fine ash was reported as far away as Elko Nevada, more than 500 kilometers east of Lassen Peak. Intermittent eruptions of variable intensity continued until about the middle of 1917. -- Hoblitt, et.al., 1987

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Eruptions of Lassen Peak, California, 1914 to 1917 -- Clynne, et.al., 1998, USGS FS-173-98

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References
Table originally compiled in 1997, redesigned in 2000, and continuously modified when needed. Lyn Topinka, April 1997, August 2000
Compiled from:

Bend Chamber of Commerce Pamphlet, 1984, Points of Interest - Bend, Oregon: Bend Chamber of Commerce, Bend, Oregon
Brantley, 1994, Volcanoes of the United States: USGS General Interest Publication
Brantley and Glicken, 1986, Volcanic Debris Avalanches: Earthquakes & Volcanoes, v.18, n.6, p.197-198
Crandell, 1971, Postglacial Lahars From Mount Rainier Volcano, Washington: USGS Professional Paper 677
Donnelly-Nolan, et.al., 1990, Post-11,000-Year Volcanism at Medicine Lake Volcano, Cascade Range, Northern California: IN: Journal of Geophysical Research, v.95., no.B12, p.19,699.
Dzurisin, et.al., 1991, Crustal Subsidence, Seismicity, and Structure Near Medicine Lake Volcano, California: Journal of Geophysical Research, v.96, no.B10.
Foxworthy and Hill, 1982, Volcanic Eruptions of 1980 at Mount St. Helens, The First 100 Days: USGS Professional Paper 1249
Hazards Reports and Maps -- Washington, Oregon, and California
Hoblitt, Miller, and Scott, 1987, Volcanic Hazards with Regard to Siting Nuclear-Power Plants in the Pacific Northwest: USGS Open-File Report 87-297
MacLeod, et.al., 1981, Newberry Volcano, Oregon: IN: Guides to Some Volcanic Terranes in Washington, Idaho, Oregon, and Northern California: USGS Circular 838.
Scott and Gardner, 1990, Field trip guide to the central Oregon High Cascades, Part 1: Mount Bachelor-South Sister area: Oregon Geology, v.52, n.5, September 1990, p.99-101
Simon, 1999, Channel and Drainage-Basin Response of the Toutle River System in the Aftermath of the 1980 Eruption of Mount St. Helens, Washington: USGS Open-File Report 96-633
Sisson, 1995, History and Hazards of Mount Rainier, Washington: USGS Open-File Report 95-642
Smithsonian Institution - Global Volcanism Program,
Swanson, Cameron, Evarts, Pringle, and Vance, 1989, IGC Field Trip T106: Cenozoic Volcanism in the Cascade Range and Columbia Plateau, Southern Washington and Northernmost Oregon: American Geophysical Union Field Trip Guidebook T106
Taylor, 1981, Central High Cascade Roadside Geology: Bend, Sisters, McKenzie Pass, and Santiam Pass, Oregon: IN: Guides to Some Volcanic Terranes in Washington, Idaho, Oregon, and Northern California: USGS Circular 838
U. S. Forest Service Pamphlet, 1984, Lava Lands, Deschutes National Forest: GPO-1984-795-615
Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press
Wright and Pierson, 1992, Living with Volcanoes, The U.S. Geological Survey's Volcano Hazards Program: USGS Circular 1073

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06/25/04, Lyn Topinka