Columbia River Basalt Group
   HOME

TheInfoList



OR:

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 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 ...
and Washington, western
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), ...
, and part of northern
Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...
. The
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 ...
group includes the Steens and Picture Gorge basalt formations.


Introduction

During the middle to late
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 ...
epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...
, the Columbia River
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 engulfed about of 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 ...
, forming a
large igneous province A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive ( sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The format ...
with an estimated volume of . Eruptions were most vigorous 17–14 million years ago, when over 99 percent of the basalt was released. Less extensive eruptions continued 14–6 million years ago. Erosion resulting from the Missoula Floods has extensively exposed these lava flows, laying bare many layers of the basalt flows at Wallula Gap, the lower
Palouse River The Palouse River is a tributary of the Snake River in Washington and Idaho, in the northwest United States. It flows for U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed May 3, 2011 south ...
, the
Columbia River Gorge The Columbia River Gorge is a canyon of the Columbia River in the Pacific Northwest of the United States. Up to deep, the canyon stretches for over as the river winds westward through the Cascade Range, forming the boundary between the state ...
and throughout 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 ...
. The Columbia River Basalt Group is thought to be a potential link to the Chilcotin Group in south-central
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 ...
,
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 ...
. The Latah Formation sediments of Washington and Idaho are interbedded with a number of the Columbia River Basalt Group flows, and outcrop across the region. Absolute dates, subject to a statistical uncertainty, are determined through
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to Chronological dating, date materials such as Rock (geology), rocks or carbon, in which trace radioactive impurity, impurities were selectively incorporat ...
using isotope ratios such as 40Ar/39Ar dating, which can be used to identify the date of solidifying basalt. In the CRBG deposits 40Ar, which is produced by 40K decay, only accumulates after the melt solidifies. Other flood basalts include the
Deccan Traps The Deccan Traps are a large igneous province of west-central India (17–24°N, 73–74°E). They are one of the largest volcanic features on Earth, taking the form of a large shield volcano. They consist of many layers of solidified flood ...
(late
Cretaceous period The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 77.1 million years, it is the ninth and longest geologi ...
), that cover an area of in west-central
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
; the Emeishan Traps (
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...
), which cover more than 250,000 square kilometers in southwestern
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
; and
Siberian Traps The Siberian Traps () are a large region of volcanic rock, known as a large igneous province, in Siberia, Russia. The massive eruptive event that formed the trap rock, traps is one of the largest known Volcano, volcanic events in the last years ...
(late
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...
) that cover (800,000 sq mi) in
Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
.


Formation

Some time during a 10–15 million-year period, lava flow after lava flow poured out of multiple dikes which trace along an old fault line running from south-eastern Oregon through to western British Columbia. The many layers of lava eventually reached a thickness of more than . As the molten rock came to the surface, the Earth's crust gradually sank into the space left by the rising lava. This subsidence of the crust produced a large, slightly depressed lava plain now known as the Columbia Basin or
Columbia River Plateau The Columbia Plateau is an important geologic and geographic region that lies across parts of the U.S. states of Washington, Oregon, and Idaho. It is a wide flood basalt plateau between the Cascade Range and the Rocky Mountains, cut through by ...
. The northwesterly advancing lava forced the ancient
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 ...
into its present course. The lava, as it flowed over the area, first filled the stream valleys, forming dams that in turn caused impoundments or lakes. In these ancient lake beds are found
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
leaf impressions,
petrified wood Petrified wood (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of ''fossilized wood'', the fossilized remains of terrestrial plant, terrestrial vegetation. ''Petrifaction ...
, fossil insects, and bones of vertebrate animals. In the middle Miocene, 17 to 15 Ma, the Columbia Plateau and the Oregon Basin and Range of the Pacific Northwest were flooded with lava flows. Both flows are similar in composition and age, and have been attributed to a common source, the Yellowstone hotspot. The ultimate cause of the volcanism is still up for debate, but the most widely accepted idea is that the
mantle plume A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic ho ...
or upwelling (similar to that associated with present-day Hawaii) initiated the widespread and voluminous basaltic volcanism about 17 million years ago. As hot mantle plume materials rise and reach lower pressures, the hot materials melt and interact with the materials in the
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 ...
, creating
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...
. Once that magma breaches the surface, it flows as lava and then solidifies into basalt.


Transition to flood volcanism

Prior to 17.5 million years ago, the Western
Cascade Cascade, or Cascading may refer to: Science and technology Science * Air shower (physics), a cascade (particle shower) of subatomic particles and ionized nuclei ** Particle shower, a cascade of secondary particles produced as the result of a high ...
stratovolcano A stratovolcano, also known as a composite volcano, is a typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with ...
es erupted with periodic regularity for over 20 million years, even as they do today. An abrupt transition to shield volcanic flooding took place in the mid-Miocene. The flows can be divided into four major categories: The Steens Basalt, Grande Ronde Basalt, the
Wanapum The Wanapum (also Wanapam) tribe of Native Americans in the United States, Native Americans formerly lived along the Columbia River from above Priest Rapids down to the mouth of the Snake River in what is now the US state of Washington (state), Was ...
Basalt, and the Saddle Mountains Basalt. The various lava flows have been dated by radiometric dating—particularly through measurement of the ratios of isotopes of
potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...
to
argon Argon is a chemical element; it has symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
. The Columbia River flood basalt province comprises more than 300 individual basalt lava flows that have an average volume of . The transition to flood volcanism in the Columbia River Basalt Group (CRBG), similar to other
large igneous province A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive ( sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The format ...
s, was also marked by atmospheric loading through the mass exsolution and emission of volatiles, via the process of volcanic degassing. Comparative analysis of volatile concentrations in source feeder dikes to associated extruded flow units have been quantitatively measured to determine the magnitude of degassing exhibited in CRBG eruptions. Of the more than 300 individual flows associated with the CRBG, the Roza flow contains some of the most chemically well preserved basalts for volatile analysis. Contained within the Wanapum formation, Roza is one of the most extensive members of the CRBG with an area of 40,300 square kilometres and a volume of 1,300 cubic kilometres. With magmatic volatile values assumed at 1 - 1.5 percent by weight concentration for source feeder dikes, the emission of
sulphur Sulfur (American spelling and the preferred IUPAC name) or sulphur (English in the Commonwealth of Nations, Commonwealth spelling) is a chemical element; it has Symbol (chemistry), symbol S and atomic number 16. It is abundance of the chemical ...
for the Roza flow is calculated to be on the order of 12Gt (12,000 million tonnes) at a rate of 1.2Gt (1,200 million tonnes) annually, in the form of
sulphur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...
(SO2). However, other research through
petrologic Petrology () is the branch of geology that studies rock (geology), rocks, their mineralogy, composition, texture, structure and the conditions under which they form. Petrology has three subdivisions: igneous petrology, igneous, metamorphic rock, ...
analysis has yielded SO2 mass degassing values at 0.12% - 0.28% of the total erupted mass of the magma, translating to lower emission estimates in the range of 9.2Gt of sulfur dioxide for the Roza flow.
Sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
, a by-product of emitted
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...
and atmospheric interactions, has been calculated to be 1.7Gt annually for the Roza flow and 17Gt in total. Analysis of glass inclusions within
phenocryst image:montblanc granite phenocrysts.JPG, 300px, Granites often have large feldspar, feldspathic phenocrysts. This granite, from the Switzerland, Swiss side of the Mont Blanc massif, has large white phenocrysts of plagioclase (that have trapezoid sh ...
s of the basaltic deposits have yielded emission volumes on the magnitude of 310 Mt of
hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
, and 1.78 Gt of
hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colorless, acidic and highly corrosive. A common concentration is 49% (48–52%) but there are also stronger solutions (e.g. 70%) and pure HF has a boiling p ...
, additionally.


Cause of volcanism

Major
hotspots Hotspot, Hot Spot or Hot spot may refer to: Places * Hot Spot, Kentucky, a community in the United States Arts, entertainment, and media Fictional entities * Hot Spot (comics), a name for the DC Comics character Isaiah Crockett * Hot Spot (Tr ...
have often been tracked back to flood-basalt events. In this case the Yellowstone hotspot's initial flood-basalt event occurred near Steens Mountain when the Imnaha and Steens eruptions began. As the North American Plate moved several centimeters per year westward, the eruptions progressed through the Snake River Plain across
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), ...
and into
Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...
. Consistent with the hot spot hypothesis, the lava flows are progressively younger as one proceeds east along this path. Previous to this eruptive period, it is believed the Yellowstone Hotspot created features like Smith Rock in Central Oregon and perhaps another flood basalt event known as Siletzia which underlies much of the Pacific Northwest coast with exposures in the
Oregon Coast Range The Oregon Coast Range, often called simply the Coast Range and sometimes the Pacific Coast Range, is a mountain range, in the Pacific Coast Ranges Physiographic regions of the world, physiographic region, in the United States, U.S. state of Or ...
. There is additional confirmation that Yellowstone is associated with a deep hot spot. Using tomographic images based on seismic waves, relatively narrow, deeply seated, active
convective Convection is single or multiphase fluid flow that occurs spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
plumes have been detected under Yellowstone and several other hot spots. These plumes are much more focused than the upwelling observed with large-scale plate-tectonics circulation. The hot spot hypothesis is not universally accepted as it has not resolved several questions. The Yellowstone hot spot volcanism track shows a large apparent bow in the hot-spot track that does not correspond to changes in plate motion if the northern CRBG floods are considered. Further, the Yellowstone images show necking of the plume at , which may correspond to phase changes or may reflect still-to-be-understood viscosity effects. Additional data collection and further modeling will be required to achieve a consensus on the actual mechanism.


Speed of flood basalt emplacement

The Columbia River Basalt Group flows exhibit essentially uniform chemical properties through the bulk of individual flows, suggesting rapid placement. Ho and Cashman (1997) characterized the -long Ginkgo flow of the Frenchman Springs Member, determining that it had been formed in roughly a week, based on the measured melting temperature along the flow from the origin to the most distant point of the flow, combined with hydraulics considerations. The Ginkgo basalt was examined over its flow path from a Ginkgo flow feeder dike near Kahlotus, Washington to the flow terminus in the Pacific Ocean at Yaquina Head,
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 ...
. The basalt had an upper melting temperature of and a lower temperature to this indicates that the maximum temperature drop along the Ginkgo flow was 20 °C. The lava must have spread quickly to achieve this uniformity. Analyses indicate that the flow must remain laminar, as turbulent flow would cool more quickly. This could be accomplished by sheet flow, which can travel at velocities of without turbulence and minimal cooling, suggesting that the Ginkgo flow occurred in less than a week. The cooling/hydraulics analyses are supported by an independent indicator; if longer periods were required, external water from temporarily dammed rivers would intrude, resulting in both more dramatic cooling rates and increased volumes of
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 ...
. Ho's analysis is consistent with the analysis by Reidel, Tolan, & Beeson (1994), who proposed a maximum Pomona flow emplacement duration of several months based on the time required for rivers to be reestablished in their canyons following a basalt flow interruption.


Dating of the flood basalt flows

Three major tools are used to date the CRBG flows: Stratigraphy, radiometric dating, and magnetostratigraphy. These techniques have been key to correlating data from disparate basalt exposures and boring samples over five states. Major eruptive pulses of flood basalt lavas are laid down stratigraphically. The layers can be distinguished by physical characteristics and chemical composition. Each distinct layer is typically assigned a name usually based on area (valley, mountain, or region) where that formation is exposed and available for study. Stratigraphy provides a relative ordering (ordinal ranking) of the CRBG layers. Absolute dates, subject to a statistical uncertainty, are determined through
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to Chronological dating, date materials such as Rock (geology), rocks or carbon, in which trace radioactive impurity, impurities were selectively incorporat ...
using isotope ratios such as 40Ar/39Ar dating, which can be used to identify the date of solidifying basalt. In the CRBG deposits 40Ar, which is produced by 40K decay, only accumulates after the melt solidifies.
Magnetostratigraphy Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their ' ...
is also used to determine age. This technique uses the pattern of magnetic polarity zones of CRBG layers by comparison to the magnetic polarity timescale. The samples are analyzed to determine their characteristic remanent magnetization from the Earth's magnetic field at the time a stratum was deposited. This is possible because, as magnetic minerals precipitate in the melt (crystallize), they align themselves with Earth's current magnetic field. The Steens Basalt captured a highly detailed record of the Earth's magnetic reversal that occurred roughly 15 million years ago. Over a 10,000-year period, more than 130 flows solidified – roughly one flow every 75 years. As each flow cooled below about , it captured the magnetic field's orientation-normal, reversed, or in one of several intermediate positions. Most of the flows froze with a single magnetic orientation. However, several of the flows, which freeze from both the upper and lower surfaces, progressively toward the center, captured substantial variations in magnetic field direction as they froze. The observed change in direction was reported as 50⁰ over 15 days.


Major flows


Steens Basalt

The Steens Basalt flows covered about of the Oregon Plateau in sections up to thick. It contains the earliest identified eruption of the CRBG large igneous province. The type locality for the Steens basalt, which covers a large portion of the Oregon Plateau, is an approximately face of Steens Mountain showing multiple layers of basalt. The oldest of the flows considered part of the Columbia River Basalt Group, the Steens basalt, includes flows geographically separated but roughly concurrent with the Imnaha flows. Older Imnaha basalt north of Steens Mountain overlies the chemically distinct lowermost flows of Steens basalt; hence some flows of the Imnaha are stratigraphically younger than the lowermost Steens basalt. One geomagnetic field reversal occurred during the Steens Basalt eruptions at approximately 16.7 Ma, as dated using 40Ar/39Ar ages and the geomagnetic polarity timescale. Steens Mountain and related sections of Oregon Plateau flood basalts at Catlow Peak and Poker Jim Ridge to the southeast and west of Steens Mountain, provide the most detailed magnetic field reversal data (reversed-to-normal polarity transition) yet reported in volcanic rocks. The observed trend in feeder dike swarms associated with the Steens Basalt flow are considered to be atypical of other dike swarm trends associated with the CRBG. These swarms, characterized by a maintained trend of N20°E, trace the northward continuation of the Nevada shear zone and have been attributed to magmatic rise through this zone on a regional scale.


Imnaha Basalt

Virtually coeval with the oldest of the flows, the Imnaha basalt flows welled up across northeastern Oregon. There were 26 major flows over the period, one roughly every 15,000 years. Although estimates are that this amounts to about 10% of the total flows, they have been buried under more recent flows, and are visible in few locations. They can be seen along the lower benches of the Imnaha River and
Snake River The Snake River is a major river in the interior Pacific Northwest region of the United States. About long, it is the largest tributary of the Columbia River, which is the largest North American river that empties into the Pacific Ocean. Begin ...
in Wallowa County. The Imnaha lavas have been dated using the K–Ar technique, and show a broad range of dates. The oldest is 17.67±0.32 Ma with younger lava flows ranging to 15.50±0.40 Ma. Although the Imnaha Basalt overlies Lower Steens Basalt, it has been suggested that it is interfingered with Upper Steens Basalt.


Grande Ronde Basalt

The next oldest of the flows, from 17 million to 15.6 million years ago, make up the Grande Ronde Basalt. Units (flow zones) within the Grande Ronde Basalt include the Meyer Ridge and the Sentinel Bluffs units. Geologists estimate that the Grande Ronde Basalt comprises about 85 percent of the total flow volume. It is characterized by a number of dikes called the Chief Joseph Dike Swarm near
Joseph Joseph is a common male name, derived from the Hebrew (). "Joseph" is used, along with " Josef", mostly in English, French and partially German languages. This spelling is also found as a variant in the languages of the modern-day Nordic count ...
,
Enterprise Enterprise (or the archaic spelling Enterprize) may refer to: Business and economics Brands and enterprises * Enterprise GP Holdings, an energy holding company * Enterprise plc, a UK civil engineering and maintenance company * Enterpris ...
,
Troy Troy (/; ; ) or Ilion (; ) was an ancient city located in present-day Hisarlik, Turkey. It is best known as the setting for the Greek mythology, Greek myth of the Trojan War. The archaeological site is open to the public as a tourist destina ...
and Walla Walla through which the lava upwelling occurred (estimates range to up to 20,000 such dikes). Many of the dikes were fissures wide and up to in length, allowing for huge quantities of magma upwelling. Much of the lava flowed north into Washington as well as down the Columbia River channel 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 ...
; the tremendous flows created the
Columbia River Plateau The Columbia Plateau is an important geologic and geographic region that lies across parts of the U.S. states of Washington, Oregon, and Idaho. It is a wide flood basalt plateau between the Cascade Range and the Rocky Mountains, cut through by ...
. The weight of this flow (and the emptying of the underlying magma chamber) caused central Washington to sink, creating the broad Columbia Basin in Washington. The type locality for the formation is the canyon of the Grande Ronde River. Grande Ronde basalt flows and dikes can also be seen in the exposed walls of Joseph Canyon along Oregon Route 3. The Grande Ronde basalt flows flooded down the ancestral Columbia River channel to the west of the
Cascade Mountains The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as many of those in the ...
. It can be found exposed along the Clackamas River and at
Silver Falls State Park Silver Falls State Park is a state park in the U.S. state of Oregon, located near Silverton, Oregon, Silverton, about east-southeast of Salem, Oregon, Salem. It is the largest state park in Oregon with an area of more than , and it includes mo ...
where the falls plunge over multiple layers of the Grande Ronde basalt. Evidence of eight flows can be found in the Tualatin Mountains on the west side of Portland. Individual flows included large quantities of basalt. The McCoy Canyon flow of the Sentinel Bluffs Member released of basalt in layers of in thickness. The Umtanum flow has been estimated at in layers deep. The Pruitt Draw flow of the Teepee Butte Member released about with layers of basalt up to thick.


Wanapum Basalt

The Wanapum Basalt is made up of the Eckler Mountain Member (15.6 million years ago), the Frenchman Springs Member (15.5 million years ago), the Roza Member (14.9 million years ago) and the Priest Rapids Member (14.5 million years ago). They originated from vents between
Pendleton, Oregon Pendleton is a city in and the county seat of Umatilla County, Oregon, Umatilla County, Oregon, United States. The population was 17,107 at the time of the 2020 United States census, 2020 census, which includes approximately 1,600 people who are ...
and Hanford, Washington. The Frenchman Springs Member flowed along similar paths as the Grande Ronde basalts, but can be identified by different chemical characteristics. It flowed west to the Pacific, and can be found in the Columbia Gorge, along the upper Clackamas River, the hills south of Oregon City, and as far west as Yaquina Head near
Newport, Oregon Newport is a city in Lincoln County, Oregon, Lincoln County, Oregon, United States. It was incorporated in 1882, though the name dates back to the establishment of a post office in 1868. Newport was named for Newport, Rhode Island. As of the 2010 ...
– a distance of .


Saddle Mountains Basalt

The Saddle Mountains Basalt, seen prominently at the Saddle Mountains, is made up of the Umatilla Member flows, the Wilbur Creek Member flows, the Asotin Member flows (13 million years ago), the Weissenfels Ridge Member flows, the Esquatzel Member flows, the Elephant Mountain Member flows (10.5 million years ago), the Bujford Member flows, the Ice Harbor Member flows (8.5 million years ago) and the Lower Monumental Member flows (6 million years ago).


Related geologic structures


Oregon High Lava Plains

observed that the Oregon High Lava Plains is a complementary system of propagating rhyolite eruptions, with the same point of origin. The two phenomena occurred concurrently, with the High Lava Plains propagating westward since ~10 Ma, while the Snake River Plains propagated eastward.


See also

* Grand Coulee *
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 ...
* Wallula Gap *
Interior Plateau The Interior Plateau comprises a large region of the Interior of British Columbia, and lies between the Cariboo and Monashee Mountains on the east, and the Hazelton Mountains, Coast Mountains and Cascade Range on the west.''Landforms of Bri ...
*
Basin and Range Province The Basin and Range Province is a vast United States physiographic region, physiographic region covering much of the inland Western United States and Northern Mexico, northwestern Mexico. It is defined by unique basin and range topography, charac ...


References


Sources

* * Not WP:RS. * * * * * * * * * * * * * * * *


External links


USGS - Page on Columbia Plateau
- ''(source of much of this page)''

* ttps://web.archive.org/web/20080514031955/http://volcano.und.edu/vwdocs/volc_images/north_america/crb.html Volcano World: page on Columbia River Flood Basalt Province {{Volcanoes of Oregon Large igneous provinces Miocene volcanism Pliocene volcanism Plateaus of the United States Volcanism of Idaho Volcanism of Oregon Volcanism of Washington (state) Columbia River Yellowstone hotspot Miocene geology Pliocene geology Paleogene United States Geologic provinces of the United States Volcanoes of Oregon Volcanoes of Washington (state) Volcanoes of Idaho Volcanoes of Nevada