Geology Of Washington (state)
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The geology of the Pacific Northwest includes the composition (including
rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wale ...
,
minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): M ...
, and
soils Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by restri ...
), structure, physical properties and the processes that shape the
Pacific Northwest The Pacific Northwest (PNW; ) is a geographic region in Western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though no official boundary exists, the most common ...
region of
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
. The region is part of the
Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a tectonic belt of volcanoes and earthquakes. It is about long and up to about wide, and surrounds most of the Pa ...
: the
subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...
of the
Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...
and Farallon Plates under the North American Plate is responsible for many of the area's scenic features as well as some of its hazards, such as
volcano A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most oft ...
es,
earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...
s, and
landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...
s. The geology of the Pacific Northwest is vast and complex. Most of the region began forming about 200 million years ago as the North American Plate started to drift westward during the rifting of
Pangaea Pangaea or Pangea ( ) was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous period approximately 335 mi ...
. Since that date, the western edge of North America has grown westward as a succession of
island arc Island arcs are long archipelago, chains of active volcanoes with intense earthquake, seismic activity found along convergent boundary, convergent plate tectonics, tectonic plate boundaries. Most island arcs originate on oceanic crust and have re ...
s and assorted ocean-floor rocks have been added along the
continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...
. There are at least five
geologic province A geologic province or geological province is a spatial entity with common geologic attributes. A province may include a single dominant structural element such as a basin or a fold belt, or a number of contiguous related elements. Adjoining ...
s in the area: the
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 No ...
, the
Columbia Plateau The Columbia Plateau is an important geology, geologic and geography, geographic region that lies across parts of the U.S. states of Washington (state), Washington, Oregon, and Idaho. It is a wide flood basalt plateau between the Cascade Range a ...
, the
North Cascades The North Cascades are a section of the Cascade Range of western North America. They span the border between the Provinces and territories of Canada, Canadian province of British Columbia and the U.S. state of Washington (state), Washington and ...
, the
Coast Mountains The Coast Mountains () are a major mountain range in the Pacific Coast Ranges of western North America, extending from southwestern Yukon through the Alaska Panhandle and virtually all of the British Columbia Coast, Coast of British Columbia sout ...
, and the
Insular Mountains The Insular Mountains are a range of mountains in the Pacific Coast Ranges on the Coast of British Columbia, Canada, comprising the Vancouver Island Ranges and Queen Charlotte Mountains. The Insular Mountains are rugged, particularly on Vanco ...
. The Cascade Volcanoes are an active volcanic region along the western side of the Pacific Northwest. The Columbia Plateau is a region of subdued geography that is inland of the Cascade Volcanoes, and the North Cascades are a mountainous region in the northwest corner of the United States, extending into British Columbia. The Coast Mountains and Insular Mountains are a strip of mountains along the coast of British Columbia, each with its own geological history.


Volcanoes


The Cascade Volcanoes

The Cascades Province forms an arc-shaped band extending from southwestern
British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
to
Northern California Northern California (commonly shortened to NorCal) is a geocultural region that comprises the northern portion of the U.S. state of California, spanning the northernmost 48 of the state's List of counties in California, 58 counties. Northern Ca ...
, roughly parallel to the Pacific coastline. Within this region, nearly 20 major volcanic centers lie in sequence. Although the largest volcanoes like Mount St. Helens get the most attention, the Cascade Volcanic Arc includes a band of thousands of very small, short-lived volcanoes that have built a platform of lava and volcanic debris. Rising above this volcanic platform are a few strikingly large volcanoes that dominate the landscape. The Cascade volcanoes define the Pacific Northwest section of the
Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a tectonic belt of volcanoes and earthquakes. It is about long and up to about wide, and surrounds most of the Pa ...
, an array of volcanoes that rim the Pacific Ocean. The Ring of Fire is also known for its frequent earthquakes. The volcanoes and earthquakes arise from a common source:
subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...
. Beneath the Cascade Volcanic Arc, a dense oceanic plate sinks beneath the North American Plate; a process known as subduction. As the oceanic slab sinks deep into the Earth's interior beneath the continental plate, high temperatures and pressures allow water molecules locked in the minerals of solid rock to escape. The supercritical water rises into the pliable mantle above the subducting plate, causing some of the mantle to melt. This newly formed magma ascends upward through the crust along a path of least resistance, both by way of fractures and faults as well as by melting wall rocks. The addition of melted crust changes the geochemical composition. Some of the melt rises toward the Earth's surface to erupt, forming a chain of volcanoes (the Cascade Volcanic Arc) above the subduction zone. The addition of crustal melt to the original mantle melt results in volcanic and plutonic rocks that differ in mineralogy from the mantle source. A close-up look at the Cascades reveals a more complicated picture than a simple subduction zone. Not far off the coast of the
North Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the contine ...
lies a spreading ridge; a divergent plate boundary made up of a series of breaks in the oceanic crust where melted mantle rises and solidifies, creating new ocean crust. On one side of the spreading ridge new Pacific Plate crust is made, then moves away from the ridge. On the other side of the spreading ridge the Juan de Fuca and Gorda plates move eastward. There are some unusual features at the Cascade subduction zone. Where the Juan de Fuca Plate sinks beneath the North American Plate there is no deep trench, seismicity (earthquakes) is less than expected, and there is evidence of a decline in volcanic activity over the past few million years. The probable explanation lies in the rate of convergence between the Juan de Fuca and North American Plates. These two plates converge at per year at present. This is only about half the rate of convergence of 7 million years ago. The small Juan de Fuca Plate and two platelets, the
Explorer Plate The Explorer plate is an oceanic tectonic plate beneath the Pacific Ocean off the west coast of Vancouver Island, Canada, which is partially subducted under the North American plate. Along with the Juan de Fuca plate and Gorda plate, the Expl ...
and Gorda Plate are the meager remnants of the much larger Farallon oceanic plate. The Explorer Plate broke away from the Juan de Fuca about 4 million years ago and shows no evidence that it is still being subducted. The
Gorda plate The Gorda plate, located beneath the Pacific Ocean off the coast of northern California, is one of the northern remnants of the Farallon plate. It is sometimes referred to (by, for example, publications from the USGS Earthquake Hazards Program) ...
let split away between 18 and 5 million years ago and continues to sink beneath North America. The Cascade Volcanic Arc made its first appearance 36 million years ago, but the major peaks that rise up from today's volcanic centers were born within the last 1.6 million years. More than 3,000 vents erupted during the most recent volcanic episode that began 5 million years ago. As long as subduction continues, new Cascade volcanoes will continue to rise.


Volcanism outside the Cascades

The
Garibaldi Volcanic Belt The Garibaldi Volcanic Belt is a northwest–southeast trending volcanic chain in the Pacific Ranges of the Coast Mountains that extends from Watts Point in the south to the Ha-Iltzuk Icefield in the north. This chain of volcanoes is located in s ...
in southwestern British Columbia is the northern extension of the Cascade Volcanic Arc in the United States and contains the most explosive young volcanoes in Canada. Like the rest of the arc, it has its origins in the Cascadia subduction zone. Volcanoes of the Garibaldi Volcanic Belt have been sporadically active over a time span of several millions of years. The northernmost member, the
Mount Meager massif The Mount Meager massif is a group of volcanic peaks in the of the Coast Mountains in southwestern British Columbia, Canada. Part of the Cascade Volcanic Arc of western North America, it is located north of Vancouver at the northern end of the P ...
, was responsible for a major catastrophic eruption that occurred about 2,350 years ago. This eruption may have been close in size to that of the
1980 eruption of Mount St. Helens In March 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of Phreatic eruption, phreatic blasts occurred from the summit and escalated until a major ...
. Ash from this eruption can be traced eastward to western
Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...
. It is also the most unstable volcanic
massif A massif () is a principal mountain mass, such as a compact portion of a mountain range, containing one or more summits (e.g. France's Massif Central). In mountaineering literature, ''massif'' is frequently used to denote the main mass of an ...
in Canada, which has dumped
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
and rock several meters (yards) deep into the
Pemberton Valley The Pemberton Valley is a valley flanking the Lillooet River upstream from Lillooet Lake, including the communities of Mount Currie, Pemberton, British Columbia and the agricultural district surrounding them and flanking the river as far upstre ...
at least three times during the past 7,300 years. Hot springs near the Mount Cayley and Mount Meager massifs suggest that magmatic heat is still present. The long history of volcanism in the region, coupled with continued
subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...
off the coast, suggests that volcanism has not yet ended in the Garibaldi Volcanic Belt. A few isolated volcanic centers northwest of the Mount Meager massif such as the Franklin Glacier Complex and the
Silverthrone Caldera The Silverthrone Caldera is a potentially active caldera complex in southwestern British Columbia, Canada, located over northwest of the city of Vancouver and about west of Mount Waddington in the Pacific Ranges of the Coast Mountains. The cal ...
, which lie in the
Pemberton Volcanic Belt The Pemberton Volcanic Belt is an eroded Oligocene-Miocene volcanic belt at a low angle near the Mount Meager massif, British Columbia, Canada. The Garibaldi and Pemberton volcanic belts appear to merge into a single belt, although the Pemberto ...
, 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 The Nootka Fault is an active transform fault running southwest from Nootka Island, near Vancouver Island, British Columbia, Canada. Geology The Nootka Fault lies between the Explorer plate in the north and Juan de Fuca plate in south. These a ...
to form the
Explorer Plate The Explorer plate is an oceanic tectonic plate beneath the Pacific Ocean off the west coast of Vancouver Island, Canada, which is partially subducted under the North American plate. Along with the Juan de Fuca plate and Gorda plate, the Expl ...
, and there is no definitive consensus among
geologist A geologist is a scientist who studies the structure, composition, and History of Earth, history of Earth. Geologists incorporate techniques from physics, chemistry, biology, mathematics, and geography to perform research in the Field research, ...
s on the relation of the volcanoes north of that fault to the rest of the Cascade Arc. However, the Pemberton Volcanic Belt is usually merged with the Garibaldi Volcanic Belt, making Mount Silverthrone the northernmost, but an uncertain Cascadia subduction-related volcano. The most active volcanic region of the northern Pacific Northwest is called the
Northern Cordilleran Volcanic Province The Northern Cordilleran Volcanic Province (NCVP), formerly known as the Stikine Volcanic Belt, is a geologic province defined by the occurrence of Miocene to Holocene volcanoes in the Pacific Northwest of North America. This belt of volcanoes ex ...
(sometimes called the Stikine Volcanic Belt). It contains more than 100 young volcanoes and several eruptions known to have occurred within the last 400 years. The last eruptions within the
volcanic belt A volcanic belt is a large volcanically active region. Other terms are used for smaller areas of activity, such as volcanic fields or volcanic systems. Volcanic belts are found above zones of unusually high temperature () where magma is created ...
was about 150 years ago at The Volcano in the Iskut-Unuk River Cones volcanic field. The most voluminous and most persistent eruptive center within the belt and in Canada is
Level Mountain Level Mountain is a large volcanic complex in the British Columbia Interior, Northern Interior of British Columbia, Canada. It is located north-northwest of Telegraph Creek and west of Dease Lake on the Nahlin Plateau. With a maximum elevatio ...
. It is a large
shield volcano A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava ...
that covers an area of southwest of
Dease Lake Dease Lake is a small community in the Cassiar Country of the Northern Interior of British Columbia, Canada. It is 230 km south of the Yukon border on Stewart–Cassiar Highway (Highway 37) at the south end of the lake of the same na ...
and north of
Telegraph Creek Telegraph Creek is a small community located off Highway 37 in northern British Columbia at the confluence of the Stikine River and Telegraph Creek. The only permanent settlement on the Stikine River, it is home to approximately 250 members of ...
. The broad dissected summit region consists of trachytic and rhyolitic
lava dome In volcanology, a lava dome is a circular, mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions ...
s and was considered to be dotted with several minor
basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
ic vents of postglacial age, although considered
Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
activity to be uncertain. The
Mount Edziza volcanic complex The Mount Edziza volcanic complex ( ; abbreviated MEVC) is a group of volcanoes and associated lava flows in northwestern British Columbia, Canada. Located on the Tahltan Highland, it is southeast of Telegraph Creek and southwest of Dease Lak ...
is perhaps the most spectacular volcanic edifice in
British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
. It is the second largest persistent eruptive center within the Northern Cordilleran Volcanic Province and is flanked with numerous young
satellite cone A parasitic cone (also adventive cone, satellite cone, satellitic cone or lateral cone) is the cone-shaped accumulation of volcanic material not part of the central vent of a volcano. It forms from eruptions from fractures on the flank of the ...
s, including the young, well-preserved
Eve Cone Eve Cone, sometimes referred to as Eve's Cone, is a cinder cone in Cassiar Land District of northwestern British Columbia, Canada. It has an elevation of and is one of several volcanic cones in the Desolation Lava Field at the northern end of t ...
. There are some indications that Level Mountain and Mount Edziza volcanic complex may be between 11 and 9 million years old. The Anahim Volcanic Belt is a volcanic belt that stretches from just north of
Vancouver Island Vancouver Island is an island in the northeastern Pacific Ocean and part of the Canadian province of British Columbia. The island is in length, in width at its widest point, and in total area, while are of land. The island is the largest ...
to near Quesnel. It is thought to have formed as a result of the North American Plate moving over a stationary hotspot, similar to the hotspot feeding the
Hawaiian Islands The Hawaiian Islands () are an archipelago of eight major volcanic islands, several atolls, and numerous smaller islets in the Pacific Ocean, North Pacific Ocean, extending some from the Hawaii (island), island of Hawaii in the south to nort ...
, called the
Anahim hotspot The Anahim hotspot is a hypothesized hotspot in the Central Interior of British Columbia, Canada. It has been proposed as the candidate source for volcanism in the Anahim Volcanic Belt, a long chain of volcanoes and other magmatic features th ...
. The youngest
volcano A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most oft ...
within the
volcanic belt A volcanic belt is a large volcanically active region. Other terms are used for smaller areas of activity, such as volcanic fields or volcanic systems. Volcanic belts are found above zones of unusually high temperature () where magma is created ...
is Nazko Cone. It last erupted about 7,000 years ago, producing two small
lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...
s that traveled to the west, along with a blanket of
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to r ...
that extends several km to the north and east of the cone. The volcanic belt also contains three large shield volcanoes that were formed between 8 and 1 million years ago, called the
Ilgachuz Range The Ilgachuz Range is a name given to an extinct volcano, extinct shield volcano in British Columbia, Canada. It is not a mountain range in the normal sense, because it was formed as a single volcano that has been erosion, eroded for the past 5 mi ...
, Rainbow Range and the
Itcha Range The Itcha Range, also known as the Itchas, is a small isolated mountain range in the British Columbia Interior, West-Central Interior of British Columbia, Canada. It is located northeast of the community of Anahim Lake. With a maximum elevation ...
. The
Chilcotin Group The Chilcotin Group, also called the Chilcotin Plateau Basalts, is a large area of basaltic lava that forms a volcanic plateau running parallel with the Garibaldi Volcanic Belt in south-central British Columbia, Canada. Predominantly, during Mioc ...
in southern British Columbia is a north–south range of volcanoes, thought to have formed as a result of back-arc extension behind the
Cascadia subduction zone The Cascadia subduction zone is a convergent plate boundary, about off the Pacific coast of North America, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ m ...
. The majority of the eruptions in this belt happened either 6 to 10 million years ago (
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
) or 2–3 million years ago (
Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
. The
Wells Gray-Clearwater volcanic field The Wells Gray-Clearwater volcanic field, also called the Clearwater Cone Group, is a potentially active monogenetic volcanic field in east-central British Columbia, Canada, located approximately north of Kamloops, British Columbia, Kamloops. It ...
in south-eastern
British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
consists of several small
basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
ic volcanoes and extensive
lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...
flows that have been active for the past 3 million years. It is within the
Wells Gray Provincial Park Wells Gray Provincial Park is a large wilderness park located in east-central British Columbia, Canada. The park protects most of the southern, and highest, regions of the Cariboo Mountains and covers 5,415 square kilometres (541,516 hectares or ...
, which also includes the -high
Helmcken Falls Helmcken Falls is a waterfall on the Murtle River within Wells Gray Provincial Park in British Columbia, Canada. The protection of Helmcken Falls was one of the reasons for the creation of Wells Gray Provincial Park in 1939. There are six other ...
. The origin of the volcanism is unknown, but is probably related to crustal thinning. Some of the lava flows in the field are similar to those that erupted at Volcano Mountain in the
Yukon Yukon () is a Provinces and territories of Canada, territory of Canada, bordering British Columbia to the south, the Northwest Territories to the east, the Beaufort Sea to the north, and the U.S. state of Alaska to the west. It is Canada’s we ...
, where olivine nephelinite occurs. The last eruption in the field was about 400 years ago at Kostal Cone. Numerous
seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...
s lie off British Columbia's coast and are related to hotspot volcanism. The Bowie Seamount located west of
Haida Gwaii Haida Gwaii (; / , literally "Islands of the Haida people"), previously known as the Queen Charlotte Islands, is an archipelago located between off the British Columbia Coast, northern Pacific coast in the Canadian province of British Columbia ...
is perhaps the shallowest seamount in Canada's Pacific waters. Because of its shallow depth,
scientist A scientist is a person who Scientific method, researches to advance knowledge in an Branches of science, area of the natural sciences. In classical antiquity, there was no real ancient analog of a modern scientist. Instead, philosophers engag ...
s believe it was an active volcanic island throughout the last ice age. The Bowie Seamount is also the youngest seamount in the Kodiak-Bowie Seamount chain.


Volcanic disasters

The last eruption of the
Tseax Cone Tseax Cone ( ) is a small volcano in the Nass Ranges of the Hazelton Mountains in northwestern British Columbia, Canada. It has an elevation of and lies within an east–west valley through which a tributary of the Tseax River flows. The ...
around the years 1750 or 1775 is Canada's worst known geophysical disaster. The eruption produced a long lava flow, destroying the
Nisga'a The Nisga’a (; ), formerly spelled Nishga or Niska, are an Indigenous people in British Columbia, Canada. They reside in the Nass River valley of northwestern British Columbia. The origin of the term ''Niska'' is uncertain. The spelling ' ...
village A village is a human settlement or community, larger than a hamlet but smaller than a town with a population typically ranging from a few hundred to a few thousand. Although villages are often located in rural areas, the term urban v ...
s and the death of at least 2000 Nisga'a people by
volcanic gas Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities (Vesicular texture, vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from ...
es and poisonous smoke. The
Nass River The Nass River is a river in northern British Columbia, Canada. It flows from the Coast Mountains southwest to Nass Bay, a sidewater of Portland Inlet, which connects to the North Pacific Ocean via the Dixon Entrance. Nass Bay joins Portland I ...
valley was inundated by the lava flows and contain abundant tree molds and
lava tube A lava tube, more rarely called a pyroduct, is a 'roofed conduit through which molten lava travels away from its vent'. If lava in the tube drains out, it will leave an empty cave. Lava tubes are common in low-viscosity volcanic systems. La ...
s. The event coincided with the arrival of the first
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
an explorers to penetrate the uncharted coastal waters of northern
British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
. Today, the basaltic lava deposits are a draw to tourists and are part of the
Nisga'a Memorial Lava Bed Provincial Park Nisga'a Memorial Lava Bed Provincial Park (Nisga'a: ) is a provincial park in the Crater Creek, Tseax River and Nass River valleys of northwestern British Columbia, Canada, about 80 kilometres north of Terrace, and near the Nisga'a Villages of ...
.


Recent volcanic activity

The Pacific Northwest volcanoes continue to be a geologically active area. The most geologically recent
volcanic eruption A volcanic eruption occurs when material is expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior h ...
s include: *
Level Mountain Level Mountain is a large volcanic complex in the British Columbia Interior, Northern Interior of British Columbia, Canada. It is located north-northwest of Telegraph Creek and west of Dease Lake on the Nahlin Plateau. With a maximum elevatio ...
, Canada's most voluminous and most persistent eruptive center, might have erupted in the
Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
. * Nazko Cone, the youngest volcano in the Anahim Volcanic Belt, erupted 7200  BP. * Hoodoo Mountain erupted 7050  BP. *
Lava Butte Lava Butte is a cinder cone in central Oregon, United States, just west of U.S. Route 97 between the towns of Bend, and Sunriver in Deschutes County. It is part of a system of small cinder cones on the northwest flank of Newberry Volcano, a ...
,
Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...
erupted about 7,000 years ago. *
Mount Mazama Mount Mazama ( Klamath: ''Tum-sum-ne'') is a complex volcano in the western U.S. state of Oregon, in a segment of the Cascade Volcanic Arc and Cascade Range. The volcano is in Klamath County, in the southern Cascades, north of the Oregon– ...
, which erupted catastrophically in 5670 BCE to form
Crater Lake Crater Lake ( Klamath: ) is a volcanic crater lake in south-central Oregon in the Western United States. It is the main feature of Crater Lake National Park and is a tourist attraction for its deep blue color and water clarity. T ...
. *
Mount Meager massif The Mount Meager massif is a group of volcanic peaks in the of the Coast Mountains in southwestern British Columbia, Canada. Part of the Cascade Volcanic Arc of western North America, it is located north of Vancouver at the northern end of the P ...
erupted about 2350  BP, sending an
ash column An eruption column or eruption plume is a cloud of super-heated ash and tephra suspended in gases emitted during an explosive volcanic eruption. The volcanic materials form a vertical column or plume that may rise many kilometers into the air ...
high into the
stratosphere The stratosphere () is the second-lowest layer of the atmosphere of Earth, located above the troposphere and below the mesosphere. The stratosphere is composed of stratified temperature zones, with the warmer layers of air located higher ...
. *
Mount Edziza volcanic complex The Mount Edziza volcanic complex ( ; abbreviated MEVC) is a group of volcanoes and associated lava flows in northwestern British Columbia, Canada. Located on the Tahltan Highland, it is southeast of Telegraph Creek and southwest of Dease Lak ...
, Canada's second largest eruptive center, erupted about 1340 BP. * Medicine Lake Volcano erupted about 1000  BP. *
Silverthrone Caldera The Silverthrone Caldera is a potentially active caldera complex in southwestern British Columbia, Canada, located over northwest of the city of Vancouver and about west of Mount Waddington in the Pacific Ranges of the Coast Mountains. The cal ...
might have eruptions younger than 1000  BP. * Kostal Cone in the
Wells Gray-Clearwater volcanic field The Wells Gray-Clearwater volcanic field, also called the Clearwater Cone Group, is a potentially active monogenetic volcanic field in east-central British Columbia, Canada, located approximately north of Kamloops, British Columbia, Kamloops. It ...
might have erupted and formed in 1500 based on tree-ring dating. *
Glacier Peak Glacier Peak or Dakobed (known in the Sauk-Suiattle dialect of the Lushootseed language as "Tda-ko-buh-ba" or "Takobia") is the most isolated of the five major stratovolcanoes (composite volcanoes) of the Cascade Volcanoes, Cascade Volcanic Arc ...
erupted in the 17th or 18th century. *
Tseax Cone Tseax Cone ( ) is a small volcano in the Nass Ranges of the Hazelton Mountains in northwestern British Columbia, Canada. It has an elevation of and lies within an east–west valley through which a tributary of the Tseax River flows. The ...
erupted in the 18th century. *
Mount Hood Mount Hood, also known as Wy'east, is an active stratovolcano in the Cascade Range and is a member of the Cascade Volcanic Arc. It was formed by a subduction zone on the West Coast of the United States, Pacific Coast and rests in the Pacific N ...
erupted in 1781–82;
fumarole A fumarole (or fumerole) is a vent in the surface of the Earth or another rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...
s on the summit still spew
sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
ous gas. *
Mount Shasta Mount Shasta ( ; Shasta people, Shasta: ''Waka-nunee-Tuki-wuki''; Karuk language, Karuk: ''Úytaahkoo'') is a Volcano#Volcanic activity, potentially active stratovolcano at the southern end of the Cascade Range in Siskiyou County, California. A ...
erupted in 1786. * The Volcano erupted about 150 BP, producing a long lava flow. *
Mount Rainier Mount Rainier ( ), also known as Tahoma, is a large active stratovolcano in the Cascade Range of the Pacific Northwest in the United States. The mountain is located in Mount Rainier National Park about south-southeast of Seattle. With an off ...
erupted 1854. *
Mount Baker Mount Baker (; ), also known as Koma Kulshan or simply Kulshan, is a active glacier-covered andesitic stratovolcano in the Cascade Volcanic Arc and the North Cascades of Washington State in the United States. Mount Baker has the second-most ...
erupted in 1880; fumaroles still occur at its summit. * Ruby Mountain might have erupted in 1898. *
Lassen Peak Lassen Peak ( ), commonly referred to as Mount Lassen, is a lava dome volcano in Lassen Volcanic National Park in Northern California. Located in the Shasta Cascade region above the northern Sacramento Valley, it is the southernmost active vo ...
erupted in 1914–5. * Mount St. Helens erupted in 1980, killing 57 people. (see
1980 eruption of Mount St. Helens In March 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of Phreatic eruption, phreatic blasts occurred from the summit and escalated until a major ...
).


Seismic activity

The Pacific Northwest is seismically active. The Juan de Fuca Plate is capable of producing
megathrust earthquake Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthq ...
s of
moment magnitude The moment magnitude scale (MMS; denoted explicitly with or Mwg, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. was defined in a 1979 paper ...
9: the last such earthquake was the
1700 Cascadia earthquake The 1700 Cascadia earthquake occurred along the Cascadia subduction zone on January 26, 1700, with an estimated moment magnitude of 8.7–9.2. The megathrust earthquake involved the Juan de Fuca plate from mid-Vancouver Island, south along the P ...
, which produced a
tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...
in Japan, and may have temporarily blocked the
Columbia River The Columbia River (Upper Chinook language, Upper Chinook: ' or '; Sahaptin language, Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river headwater ...
with the Bonneville Slide. More recently, in 2001, the Nisqually earthquake (magnitude 6.8) struck northeast of
Olympia, Washington Olympia is the capital city of the U.S. state of Washington. It had a population of 55,605 at the 2020 census, making it the state of Washington's 23rd-most populous city. Olympia is the county seat of Thurston County, and the central city ...
, causing some structural damage and panic. In addition, eleven volcanoes in Canada have had seismic activity since 1975, including: the
Silverthrone Caldera The Silverthrone Caldera is a potentially active caldera complex in southwestern British Columbia, Canada, located over northwest of the city of Vancouver and about west of Mount Waddington in the Pacific Ranges of the Coast Mountains. The cal ...
,
Mount Meager massif The Mount Meager massif is a group of volcanic peaks in the of the Coast Mountains in southwestern British Columbia, Canada. Part of the Cascade Volcanic Arc of western North America, it is located north of Vancouver at the northern end of the P ...
,
Wells Gray-Clearwater volcanic field The Wells Gray-Clearwater volcanic field, also called the Clearwater Cone Group, is a potentially active monogenetic volcanic field in east-central British Columbia, Canada, located approximately north of Kamloops, British Columbia, Kamloops. It ...
,
Mount Garibaldi Mount Garibaldi (, ) is a dormant stratovolcano in the Garibaldi Ranges of the Pacific Ranges in southwestern British Columbia, Canada. It has a maximum elevation of and rises above the surrounding landscape on the east side of the Cheakamus Ri ...
, Mount Cayley, Castle Rock, The Volcano,
Mount Edziza volcanic complex The Mount Edziza volcanic complex ( ; abbreviated MEVC) is a group of volcanoes and associated lava flows in northwestern British Columbia, Canada. Located on the Tahltan Highland, it is southeast of Telegraph Creek and southwest of Dease Lak ...
, Hoodoo Mountain, Crow Lagoon and Nazko Cone.


Columbia Plateau

The Columbia Plateau province is enveloped by one of the world's largest accumulations of basalt. Over of the Earth's surface is covered by it. The topography here is dominated by geologically young lava flows that inundated the countryside with amazing speed, all within the last 17 million years. Over of basaltic lava, known as the
Columbia River Basalt Group The Columbia River Basalt Group (CRBG) is the youngest, smallest and one of the best-preserved continental flood basalt provinces on Earth, covering over mainly eastern Oregon and Washington, western Idaho, and part of northern Nevada. The b ...
, covers the western part of the province. These tremendous flows erupted between 17–6 million years ago. Most of the lava flooded out in the first 1.5 million years: an extraordinarily short time for such an outpouring of molten rock. The
Snake River Plain The Snake River cutting through the plain leaves many canyons and Canyon#List of gorges, gorges, such as this one near Twin Falls, Idaho The Snake River Plain is a geology, geologic feature located primarily within the U.S. state of Idaho. ...
stretches across Oregon, through northern Nevada, southern Idaho, and ends at the Yellowstone Plateau in Wyoming. Looking like a great spoon scooped out the Earth surface, the smooth topography of this province forms a striking contrast with the strong mountainous fabric around it. The Snake River Plain lies in a distinct depression. At the western end, the base has dropped down along
normal fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
s, forming a
graben In geology, a graben () is a depression (geology), depressed block of the Crust (geology), crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German language, German, meaning 'ditch' or 't ...
structure. Although there is extensive faulting at the eastern end, the structure is not as clear. Like the Columbia River region, volcanic eruptions dominate the story of the Snake River Plain in the eastern part of the Columbia Plateau Province. The earliest Snake River Plain eruptions began about 15 million years ago, just as the tremendous early eruptions of Columbia River Basalt were ending. But most of the Snake River Plain volcanic rock is less than a few million years old,
Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58 In the west, the Columbia River Basalts are just that: almost exclusively black
basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
. Not so in the Snake River Plain, where relatively quiet eruptions of soupy black basalt lava flows alternated with tremendous explosive eruptions of
rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...
, a light-colored volcanic rock.
Cinder cones A cinder cone or scoria cone is a steep, conical landform of loose pyroclastic fragments, such as volcanic ash, clinkers, or scoria that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions or lav ...
dot the landscape of the Snake River Plain. Some are aligned along
vent Vent or vents may refer to: Science and technology Biology *Vent, the cloaca region of an animal *Vent DNA polymerase, a thermostable DNA polymerase Geology *Hydrothermal vent, a fissure in a planet's surface from which geothermally heated water ...
s, the fissures that fed flows and cone-building eruptions. Calderas, great pits formed by explosive volcanism, and low shield volcanoes, and rhyolite hills are also part of the landscape here, but many are obscured by later lava flows. Evidence suggests that some concentrated heat source is melting rock beneath the Columbia Plateau Province. At the base of the lithosphere (the layer of crust and
upper mantle The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (geology), crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle (Earth), lower man ...
that forms Earth's moving tectonic plates). In an effort to figure out why this area, far from a plate boundary, had such an enormous outpouring of lava, scientists established hardening dates for many of the individual lava flows. They found that the youngest volcanic rocks were clustered near the Yellowstone Plateau, and that the farther west they went, the older the lavas. Although scientists are still gathering evidence, a probable explanation is that a hot spot, an extremely hot plume of deep mantle material, is rising to the surface beneath the Columbia Plateau Province. Geologists know that beneath
Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...
and
Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...
, a temperature instability develops (for reasons not yet well understood) at the boundary between the core and mantle. The concentrated heat triggers a plume hundreds of kilometers in diameter that ascends directly through to the surface of the Earth. When the hot plume arrives at the base of the
lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...
, some of the lighter rock of the lithosphere rapidly melts. It is this molten lithosphere that becomes the basalt lavas that gush onto the surface to form the Columbia River and Snake River Plain basalts. The track of this hot spot starts in the west and sweeps up to
Yellowstone National Park Yellowstone National Park is a List of national parks of the United States, national park of the United States located in the northwest corner of Wyoming, with small portions extending into Montana and Idaho. It was established by the 42nd U ...
. The steaming fumaroles and explosive
geyser A geyser (, ) is a spring with an intermittent water discharge ejected turbulently and accompanied by steam. The formation of geysers is fairly rare and is caused by particular hydrogeological conditions that exist only in a few places on Ea ...
s are ample evidence of a concentration of heat beneath the surface. The hotspot is probably quite stationary, but the North American plate is moving over it, creating a superb record of the rate and direction of plate motion.


The Ice Age floods

With the beginning of the
Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
time (about one million years ago), cooling temperatures provided conditions favorable for the creation of continental
glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
s. Over the centuries, as snowfall exceeded melting and evaporation, a great accumulation of snow covered part of the continent, forming extensive ice fields. This vast continental ice sheet reached a thickness of about in some areas. Sufficient pressure on the ice caused it to flow outward as a glacier. The glacier moved south out of
Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
, damming rivers and creating lakes in Washington, Idaho and Montana. The ice blocked the
Clark Fork River The Clark Fork, or the Clark Fork of the Columbia River, is a river in the U.S. states of Montana and Idaho, approximately long. It is named after William Clark of the 1806 Lewis and Clark Expedition. The largest river by volume in Montana, it ...
, forming the huge
Glacial Lake Missoula Lake Missoula was a prehistoric proglacial lake in western Montana that existed periodically at the end of the last ice age between 15,000 and 13,000 years ago. The lake measured about and contained about of water, half the volume of Lake Mi ...
. The lake measured about and contained about , half the volume of
Lake Michigan Lake Michigan ( ) is one of the five Great Lakes of North America. It is the second-largest of the Great Lakes by volume () and depth () after Lake Superior and the third-largest by surface area (), after Lake Superior and Lake Huron. To the ...
. Glacial Lake Missoula broke through the ice dam many times, allowing a tremendous volume of water to rush across northern Idaho and into eastern Washington. Such catastrophic floods raced across the southward-dipping plateau a number of times, etching the coulees which characterize this region, now known as the
channeled scablands The Channeled Scablands are a relatively barren and soil-free region of interconnected relict and dry flood channels, coulees and cataracts eroded into Palouse loess and the typically flat-lying basalt flows that remain after cataclysmic floods ...
. As the floods in this vicinity raced southward, two major cascades formed along their course. The larger cataract was that of the upper
Grand Coulee Grand Coulee is an ancient river bed in the U.S. state of Washington. This National Natural Landmark stretches for about southwest from Grand Coulee Dam to Soap Lake, being bisected by Dry Falls into the Upper and Lower Grand Coulee. Geo ...
, where the river roared over an waterfall. The eroding power of the water plucked pieces of basalt from the precipice, causing the falls to retreat and self-destruct by cutting through to the Columbia River valley near what is now the
Grand Coulee Dam Grand Coulee Dam is a concrete gravity dam on the Columbia River in the U.S. state of Washington, built to produce hydroelectric power and provide irrigation water. Constructed between 1933 and 1942, Grand Coulee originally had two powerhous ...
. The other major cataract is now known as
Dry Falls Dry Falls is a scalloped precipice with four major alcoves, in central Washington scablands. This cataract complex is on the opposite side of the Upper Grand Coulee from the Columbia River, and at the head of the Lower Grand Coulee, northe ...
. It started near Soap Lake in Washington State, where less resistant basalt layers gave way before the great erosive power of this tremendous torrent and waterfalls developed. As in the upper Grand Coulee, the raging river yanked chunks of rock from the face of the falls and the falls eventually retreated to their present location. Dry Falls is wide, with a drop of more than . By way of comparison,
Niagara Falls Niagara Falls is a group of three waterfalls at the southern end of Niagara Gorge, spanning the Canada–United States border, border between the Provinces and territories of Canada, province of Ontario in Canada and the state of New York (s ...
, wide with a drop of only , would be dwarfed by Dry Falls.


The North Cascades

The North Cascade Range in
Washington Washington most commonly refers to: * George Washington (1732–1799), the first president of the United States * Washington (state), a state in the Pacific Northwest of the United States * Washington, D.C., the capital of the United States ** A ...
is part of the
American cordillera The American Cordillera ( ) is a chain of mountain ranges (cordilleras), consisting of an almost continuous sequence of mountain ranges that form the western "backbone" of the Americas. Aconcagua is the highest peak of the chain. It is also the ...
, a mountain chain stretching more than from
Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South America, South American mainland, across the Strait of Magellan. The archipelago consists of the main is ...
to the
Alaska Peninsula The Alaska Peninsula (also called Aleut Peninsula or Aleutian Peninsula, ; Sugpiaq language, Sugpiaq: ''Aluuwiq'', ''Al'uwiq'') is a peninsula extending about to the southwest from the mainland of Alaska and ending in the Aleutian Islands. T ...
, and second only to the Alpine-Himalayan chain in height. Although only a small part of the Cordillera, mile for mile, the North Cascade Range is steeper and wetter than most other ranges in the contiguous United States. In geology, the range has more in common with the Coast Ranges of British Columbia and Alaska than it does with its Cordilleran cousins in the Rocky Mountains or Sierra Nevada. Although the peaks of the North Cascades do not reach great elevations (high peaks are generally in the range, their overall relief, the relatively uninterrupted vertical distance from valley bottom to mountain top, is commonly . Rocks of the North Cascades record at least 400 million years of history. The record of this long history can be read in the many rock layers deposited over time through the forces of erosion, volcanic activity and plate subduction. These different forces have made a geologic mosaic made up of volcanic
island arc Island arcs are long archipelago, chains of active volcanoes with intense earthquake, seismic activity found along convergent boundary, convergent plate tectonics, tectonic plate boundaries. Most island arcs originate on oceanic crust and have re ...
s, deep ocean sediments, basaltic
ocean floor The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
, parts of old continents,
submarine fan Abyssal fans, also known as deep-sea fans, underwater deltas, and submarine fans, are underwater geological structures associated with large-scale sediment deposition and formed by turbidity currents. They can be thought of as an underwater ve ...
s, and even pieces of the deep subcrustal mantle of the earth. The disparate pieces of the North Cascade mosaic were born far from one another but subsequently drifted together, carried along by the tectonic plates that make up the Earth's outer shell or were uplifted,
eroded Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust and then transports it to another location where it is deposited. Erosion is disti ...
by
stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a strea ...
s, and then locally buried in their own eroded debris; other pieces were forced deep into the Earth to be heated and squeezed, almost beyond recognition, and then raised again to view. Over time, the moving plates eventually accreted the various pieces of the mosaic onto the western side of North America. About 35 million years ago, a volcanic arc grew across this complex mosaic of old
terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its d ...
s. Volcanoes erupted to cover the older rocks with lava and ash. Large masses of molten rock invaded the older rocks from below. The volcanic arc is still active today, decorating the skyline with the cones of
Mount Baker Mount Baker (; ), also known as Koma Kulshan or simply Kulshan, is a active glacier-covered andesitic stratovolcano in the Cascade Volcanic Arc and the North Cascades of Washington State in the United States. Mount Baker has the second-most ...
and
Glacier Peak Glacier Peak or Dakobed (known in the Sauk-Suiattle dialect of the Lushootseed language as "Tda-ko-buh-ba" or "Takobia") is the most isolated of the five major stratovolcanoes (composite volcanoes) of the Cascade Volcanoes, Cascade Volcanic Arc ...
. The deep canyons and sharp peaks of today's North Cascades scene are products of profound erosion. Running water has etched out the grain of the range, landslides have softened the abrupt edges, homegrown glaciers have scoured the peaks and high valleys and, during the
Ice Age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...
, the Cordilleran Ice Sheet overrode almost all the range and rearranged courses of streams. Erosion has written and still writes its own history in the mountains, but it has also revealed the complex mosaic of the bedrock.


Coast Mountains

The
Coast Mountains The Coast Mountains () are a major mountain range in the Pacific Coast Ranges of western North America, extending from southwestern Yukon through the Alaska Panhandle and virtually all of the British Columbia Coast, Coast of British Columbia sout ...
are the western range of the North American mainland cordillera, covering the
Alaska Panhandle Southeast Alaska, often abbreviated to southeast or southeastern, and sometimes called the Alaska(n) panhandle, is the southeastern portion of the U.S. state of Alaska, bordered to the east and north by the northern half of the Canadian provi ...
and most of coastal British Columbia. The range is approximately long and wide. Most of the Coast Mountains are composed of
granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...
, which is part of the
Coast Plutonic Complex The Coast Range Arc was a large volcanic arc system, extending from northern Washington through British Columbia and the Alaska Panhandle to southwestern Yukon. The Coast Range Arc lies along the western margin of the North American Plate in the ...
. This is the single largest contiguous granite outcropping in the world, which extends approximately in length. It is a large
batholith A batholith () is a large mass of intrusive rock, intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in the Earth's crust. Batholiths are almost always made mostly of felsic or intermediate ...
complex. Its formation is related to
subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...
of the Kula and Farallon tectonic plates along the
continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...
during the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
-to-
Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
periods. The plutonic complex is built on unusual
island arc Island arcs are long archipelago, chains of active volcanoes with intense earthquake, seismic activity found along convergent boundary, convergent plate tectonics, tectonic plate boundaries. Most island arcs originate on oceanic crust and have re ...
fragments,
oceanic plateau An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. There are 184 oceanic plateaus in the world, covering an area of or about 5.11% of the o ...
s and continental margin assemblages accreted between the
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
and the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
periods. In addition, the
Garibaldi Giuseppe Maria Garibaldi ( , ;In his native Ligurian language, he is known as (). In his particular Niçard dialect of Ligurian, he was known as () or (). 4 July 1807 – 2 June 1882) was an Italian general, revolutionary and republican. H ...
, Meager, Cayley and Silverthrone areas are of recent volcanic origin. The Coast Mountains consist of a single uplifted mass. During the
Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
period. Rivers such as the Klinaklini River and Homathko River predate this uplift and due to
erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...
occurring faster than uplift, have continued to flow right up to the present day, directly across the axis of the range. The mountains flanking the Homathko River are the highest in the Coast Mountains, and include
Mount Waddington Mount Waddington, once known as Mystery Mountain, is the highest peak in the Coast Mountains of British Columbia, Canada. Although it is lower than Mount Fairweather and Mount Quincy Adams, which straddle the United States border between Alaska ...
west of the river in the
Waddington Range The Waddington Range is a subrange of the Pacific Ranges of the Coast Mountains in southwestern British Columbia, Canada. It is only about in area, relatively small in area within the expanse of the range, but it is the highest area of the Pacif ...
and
Mount Queen Bess Mount Queen Bess is one of the principal summits of the Pacific Ranges of the Coast Mountains of southern British Columbia. It stands west of Chilko Lake and to the south of Tatlayoko Lake, and crowns a peak-studded ridge to the north of the ...
east of the river, adjacent to the Homathko Icefield. The
Pacific Ranges The Pacific Ranges are the southernmost subdivision of the Coast Mountains portion of the Pacific Cordillera. Located entirely within British Columbia, British Columbia, Canada, they run northwest from the lower stretches of the Fraser River to B ...
in southwestern British Columbia are the southernmost subdivision of the Coast Mountains. It has been characterized by rapid rates of uplift over the past 4 million years unlike the North Cascades and has led to relatively high rates of erosion.


Insular Mountains

The
Insular Mountains The Insular Mountains are a range of mountains in the Pacific Coast Ranges on the Coast of British Columbia, Canada, comprising the Vancouver Island Ranges and Queen Charlotte Mountains. The Insular Mountains are rugged, particularly on Vanco ...
on the coast of British Columbia have not yet fully emerged above
sea level Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...
, and
Vancouver Island Vancouver Island is an island in the northeastern Pacific Ocean and part of the Canadian province of British Columbia. The island is in length, in width at its widest point, and in total area, while are of land. The island is the largest ...
and
Haida Gwaii Haida Gwaii (; / , literally "Islands of the Haida people"), previously known as the Queen Charlotte Islands, is an archipelago located between off the British Columbia Coast, northern Pacific coast in the Canadian province of British Columbia ...
are just the higher elevations of the range, which was in fact fully exposed during the last ice age when the
continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...
in this area was a broad
coastal plain A coastal plain (also coastal plains, coastal lowland, coastal lowlands) is an area of flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and an upland area. Formation Coastal plains can f ...
. Although the
Coast Mountains The Coast Mountains () are a major mountain range in the Pacific Coast Ranges of western North America, extending from southwestern Yukon through the Alaska Panhandle and virtually all of the British Columbia Coast, Coast of British Columbia sout ...
are commonly considered to be the westernmost range of the
American cordillera The American Cordillera ( ) is a chain of mountain ranges (cordilleras), consisting of an almost continuous sequence of mountain ranges that form the western "backbone" of the Americas. Aconcagua is the highest peak of the chain. It is also the ...
, the Insular Mountains are the true westernmost range.Coast Mountains
in the Canadian Mountain Encyclopedia. Retrieved on 2007-12-02
Through the most recent
ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...
about 18,000 years ago,
ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...
enclosed nearly all of the
mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher t ...
s.
Glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
s that ran down to the
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...
sharpened the
valley A valley is an elongated low area often running between hills or mountains and typically containing a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams over ...
faces and
eroded Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust and then transports it to another location where it is deposited. Erosion is disti ...
their bottoms. The Insular Mountains were formed when a large
island arc Island arcs are long archipelago, chains of active volcanoes with intense earthquake, seismic activity found along convergent boundary, convergent plate tectonics, tectonic plate boundaries. Most island arcs originate on oceanic crust and have re ...
, called the Insular Islands, collided against North America during the Mid-
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
period. The mountains are made of
turbidite A turbidite is the geologic Deposition (geology), deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing ...
and
pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or ''subaqueous extrusion''. Pillow lavas in volcanic rock are characterized by thick sequences of discontinu ...
s unlike the plutons of the
Coast Plutonic Complex The Coast Range Arc was a large volcanic arc system, extending from northern Washington through British Columbia and the Alaska Panhandle to southwestern Yukon. The Coast Range Arc lies along the western margin of the North American Plate in the ...
that make the Coast Mountains. The Insular Mountains have much
seismic activity An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...
, with the Juan de Fuca Plate subducting at the
Cascadia subduction zone The Cascadia subduction zone is a convergent plate boundary, about off the Pacific coast of North America, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ m ...
and the Pacific Plate sliding along the
Queen Charlotte Fault The Queen Charlotte Fault is an active transform fault on the boundary between the North American plate and Pacific plates. It is Canada's right-lateral strike-slip equivalent to the San Andreas Fault to the south in California. The Queen Charlott ...
. Large earthquakes have led to collapsing mountains,
landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...
s, and the development of
fissure A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes. Ground fissure A ...
s.Insular Mountains
in the Canadian Mountain Encyclopedia. Retrieved on 2007-12-02
Flood basalt A flood basalt (or plateau basalt) is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Many flood basalts have been attributed to the onset of a hotspot (geolo ...
s on Vancouver Island form a
geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...
called the Karmutsen Formation, which is perhaps the thickest accreted section of an
oceanic plateau An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. There are 184 oceanic plateaus in the world, covering an area of or about 5.11% of the o ...
worldwide, exposing up to of basal sediment- sill complexes,
basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
ic to picritic pillow lavas, pillow
breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...
, and thick, massive basalt flows.


See also

* Beaverhead impact structure,
Idaho Idaho ( ) is a landlocked U.S. state, state in the Pacific Northwest and Mountain states, Mountain West subregions of the Western United States. It borders Montana and Wyoming to the east, Nevada and Utah to the south, and Washington (state), ...
*
Cascade Range The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington (state), Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as m ...
*
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 No ...
*
Cascadia subduction zone The Cascadia subduction zone is a convergent plate boundary, about off the Pacific coast of North America, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ m ...
* Challis Arc *
Columbia River Basalt Group The Columbia River Basalt Group (CRBG) is the youngest, smallest and one of the best-preserved continental flood basalt provinces on Earth, covering over mainly eastern Oregon and Washington, western Idaho, and part of northern Nevada. The b ...
*
Fort Rock Fort Rock is a tuff ring located on an ice age lake bed in north Lake County, Oregon, Lake County, Oregon, United States. The ring is about in diameter and stands about high above the surrounding plain. Its name is derived from the tall, stra ...
*
Garibaldi Volcanic Belt The Garibaldi Volcanic Belt is a northwest–southeast trending volcanic chain in the Pacific Ranges of the Coast Mountains that extends from Watts Point in the south to the Ha-Iltzuk Icefield in the north. This chain of volcanoes is located in s ...
*
Geology of British Columbia The geology of British Columbia is a function of its location on the leading edge of the North American continent. The mountainous physiography and the diversity of the different types and ages of rock hint at the complex geology, which is st ...
*
Geology of North America The geology of North America is a subject of regional geology and covers the North American continent, the third-largest in the world. Geologic units and processes are investigated on a large scale to reach a synthesized picture of the g ...
* Geology of the Lassen volcanic area *
Hole-in-the-Ground Hole-in-the-Ground is a large maar (volcanic explosion crater) in the Fort Rock–Christmas Lake Valley basin of Lake County, central Oregon, northeast of Crater Lake, near Oregon Route 31. It is about across, a little longer N-S than E-W. ...
*
List of volcanoes in Canada List of volcanoes in Canada is an incomplete list of volcanoes found in Geography of Canada, mainland Canada, in the Islands of Canada, Canadian islands and in Canadian waters. All but two Provinces of Canada, provinces, Prince Edward Island and ...
* Olympic–Wallowa Lineament *
Puget Sound faults File:Puget Sound faults.png, upright=1.34, The principal Puget Sound faults (approximate location of known extents) and other selected peripheral and minor faults. Southern tip of Vancouver Island and San Juan Islands at top left (faults not show ...
* Siletzia * Volcanology of Canada


References


External links


Burke Museum web site
Geologic history of Washington.
Evolution of the Pacific Northwest
Good text on the geology of Cascadia.
One link on Northwest geologyReducing Earthquake Losses Throughout the United States: Averting Surprises in the Pacific Northwest (USGS)USGS site on earthquakesOn the eruption of Mt. Meager
{{Webarchive, url=https://web.archive.org/web/20070417163234/http://www.eos.ubc.ca/~krussell/epapers/bv_hrs99.pdf , date=2007-04-17
Geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...
Geology of Oregon Geology of Idaho Geology of Washington (state) Geology of British Columbia
Pacific Northwest The Pacific Northwest (PNW; ) is a geographic region in Western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though no official boundary exists, the most common ...
Geology of the Pacific Northwest