The Big Raven Formation is a

stratigraphic unit A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize ...

of Quaternary age in northwestern

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost Provinces and territories of Canada, province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include ...

, Canada. It is the youngest and least voluminous

geological 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 expo ...

of the

Mount Edziza volcanic complex The Mount Edziza volcanic complex is a large and potentially active north-south trending complex volcano in Stikine Country, northwestern British Columbia, Canada, located southeast of the small community of Telegraph Creek. It occupies the sout ...

(MEVC); it overlies at least six older formations of this volcanic complex. The main

volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcan ...

s of the Big Raven Formation are

alkali basalt Alkali basalt or alkali olivine basalt is a dark-colored, porphyritic volcanic rock usually found in oceanic and continental areas associated with volcanic activity, such as oceanic islands, continental rifts and volcanic fields. Alkali basalt ...

s and

hawaiite Hawaiite is an olivine basalt with a composition between alkali basalt and mugearite. It was first used as a name for some lavas found on the island of Hawaii. It occurs during the later stages of volcanic activity on oceanic islands such as Haw ...

s, although a small volume of

trachyte Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava enriched with silica and ...

comprises the

Sheep Track Member The Sheep Track Member is a stratigraphic unit of the Big Raven Formation, part of the Mount Edziza volcanic complex in northwestern British Columbia, Canada. It consists of pumice from an explosive eruption that fell over an area about . The pum ...

. These rocks were deposited by volcanic eruptions in the last 20,000 years during the latest magmatic cycle of the MEVC. Alkali basalt and hawaiite are in the form of

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 moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...

flows and small

volcanic cone Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature ...

s while trachyte of the Sheep Track Member is mainly in the form of volcanic

ejecta Ejecta (from the Latin: "things thrown out", singular ejectum) are particles ejected from an area. In volcanology, in particular, the term refers to particles including pyroclastic materials ( tephra) that came out of a volcanic explosion and magm ...

which covers an area of about . The Big Raven Formation is widespread throughout the MEVC, occurring on or adjacent to the

Arctic Lake Arctic Lake is a man-made lake located by North Sanford, New York. Fish species present in the lake include pumpkinseed sunfish, black bullhead, rainbow trout, and black bass Black is a color which results from the absence or complete abso ...

, Big Raven and Kitsu plateaus. Two

lava field Lava fields are large, mostly flat areas of surface or subaquatic lava flows. Such features are generally composed of highly fluid basalt lava, and can extend for tens or hundreds of miles across the underlying terrain. Morphology and str ...

s of the Big Raven Formation occur on the Big Raven Plateau which in total contain at least 22 separate vents that issued lava flows. At least four isolated Big Raven vents occur on the eastern flank of

Mount Edziza Mount Edziza is a stratovolcano in the Stikine Country of northwestern British Columbia, Canada. The volcano and the surrounding area are protected within Mount Edziza Provincial Park and Recreation Area, Mount Edziza Provincial Park. It consist ...

and on the extreme northern slope of the Big Raven Plateau. The Kitsu Plateau contains a much smaller Big Raven lava field near the edge of an

escarpment An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations. The terms ''scarp'' and ''scarp face'' are often used interchangeably with ''esca ...

; at least three separate vents are in this lava field. Two isolated Big Raven vents on and adjacent to the Arctic Lake Plateau produced lava flows, as did two isolated Big Raven vents in Walkout Creek valley. Most Big Raven vents are marked by a cone of

pyroclastic rock Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...

Stratigraphy

Stratigraphically Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostrati ...

, the Big Raven Formation is the youngest unit of the late

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...

Mount Edziza volcanic complex in northwestern British Columbia, Canada. It contains one sub-unit called the Sheep Track Member which is lithologically distinct from the rest of the Big Raven Formation. Initially, the Big Raven Formation and the Sheep Track Member were recognized as two separate geological formations by

Jack Souther Jack Gordon Souther (April 25, 1924 – June 1, 2014) was an American-born Canadian geologist, volcanologist, professor and engineer. He contributed significantly to the early understanding of recent volcanic activity in the Canadian Cordillera ...

Richard Lee Armstrong Richard Lee Armstrong (August 4, 1937 – August 9, 1991) was an American/Canadian scientist who was an expert in the fields of radiogenic isotope geochemistry and geochronology, geochemical evolution of the earth, geology of the American C ...

and J. Harakal in 1984; both formations were grouped together in their descriptions and mapping. By 1988, the Sheep Track Formation had been reassigned as a

member Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

of the Big Raven Formation; its recognition as a geological formation has since been abandoned. The Big Raven Formation is the least voluminous geological formation of the MEVC, consisting of of volcanic material. The Big Raven Formation overlies the Klastline, Edziza, Ice Peak, Spectrum, Nido,

Armadillo Armadillos (meaning "little armored ones" in Spanish) are New World placental mammals in the order Cingulata. The Chlamyphoridae and Dasypodidae are the only surviving families in the order, which is part of the superorder Xenarthra, al ...

and

Raspberry The raspberry is the edible fruit of a multitude of plant species in the genus ''Rubus'' of the rose family, most of which are in the subgenus '' Idaeobatus''. The name also applies to these plants themselves. Raspberries are perennial with ...

formations, all of which are older units of the MEVC. It is separated from the Klastline Formation by a layer of

moraine A moraine is any accumulation of unconsolidated debris ( regolith and rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice sh ...

that was deposited by retreating glaciers at the end of the last glacial period. The Big Raven Formation overlies the Ice Peak Formation north and south of Mount Edziza. An

outlier In statistics, an outlier is a data point that differs significantly from other observations. An outlier may be due to a variability in the measurement, an indication of novel data, or it may be the result of experimental error; the latter are ...

of the Big Raven Formation is separated from the Spectrum Formation by a thick layer of unconsolidated

felsenmeer A blockfieldWhittow, John (1984). ''Dictionary of Physical Geography''. London: Penguin, 1984, pp. 66 and 190. . (also spelt block fieldLeser, Hartmut, ed. (2005). ''Wörterbuch Allgemeine Geographie'', 13th ed., dtv, Munich, pp. 107 and 221. ...

and talus. Another outlier of the Big Raven Formation overlies the Nido Formation east of Mount Edziza. Big Raven

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of d ...

on the plateau surface east of

Mess Lake The mess (also called a mess deck aboard ships) is a designated area where military personnel socialize, eat and (in some cases) live. The term is also used to indicate the groups of military personnel who belong to separate messes, such as the ...

directly overlies trachyte of the Armadillo Formation.

Age and lithology

The exact age of the Big Raven Formation is unknown but its oldest rocks were probably deposited during the

Last Glacial Maximum The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Ice sheets covered much of Northern North America, Northern Eu ...

at least 20,000 years ago which corresponds with the beginning of the latest magmatic cycle of the MEVC. A Holocene age for its younger rocks has not been wholly determined from geologic dating but rather from the lack of evidence suggesting that they were overridden by the Cordilleran Ice Sheet which retreated from the area about 11,000 years ago. Tephrochronological,

radiocarbon Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and co ...

and

fission track Ion tracks are damage-trails created by swift heavy ions penetrating through solids, which may be sufficiently-contiguous for chemical etching in a variety of crystalline, glassy, and/or polymeric solids. They are associated with cylindrical d ...

dating has yielded ages of 6520 BCE ± 200 years, 750 BCE ± 100 years, 610 CE ± 150 years and 950 CE ± 6000 years for some Big Raven volcanic rocks at Mount Edziza. Alkali basalt and hawaiite are the main volcanic rocks comprising the Big Raven Formation, having erupted from at least 30 vents along the entire north–south trending axis of the MEVC. They are in the form of lava flows and pyroclastic cones which largely comprise two lava fields on the northern and western flanks of Mount Edziza and

Ice Peak Ice Peak is a stratovolcano, located west of Tatogga and south of Mount Edziza, British Columbia, Canada. It overlaps the 7.5-million-year-old Armadillo Peak. It lies on a large volcanic plateau, which is made of basaltic lava flows from the ...

, respectively. Isolated pyroclastic cones and lava flows occur at the northern and southern extremities of the Big Raven Formation, as well as on the eastern flank of Mount Edziza and along Walkout Creek. Trachyte represents a small volume of the Big Raven Formation and mainly comprises air-fall

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...

of the Sheep Track Member.

Locations

The Big Raven Formation is widespread throughout the MEVC, occurring on or adjacent to the Kitsu, Arctic Lake and Big Raven plateaus. The Big Raven Plateau is the main

physiographic Physical geography (also known as physiography) is one of the three main branches of geography. Physical geography is the branch of natural science which deals with the processes and patterns in the natural environment such as the atmosphere, ...

feature at the northern end of the MEVC; its dominant feature is Mount Edziza which rises from the middle of the plateau. Further south near the middle of the MEVC is the Kitsu Plateau which is bounded on the north by

Raspberry Pass Raspberry Pass is a mountain pass in the Tahltan Highland of northwestern British Columbia, Canada. It is located southeast of Telegraph Creek between the heads of Raspberry Creek and Bourgeaux Creek in Mount Edziza Provincial Park. Raspberry ...

, on the west by the

Mess Creek Escarpment The Mess Creek Escarpment is an escarpment in northwestern British Columbia, Canada, located on the east side of Mess Creek below Mess Lake and southeast of Telegraph Creek. It forms the central-western flank of the Mount Edziza volcanic complex, ex ...

and on the south by the

Spectrum Range The Spectrum Range, formerly called the Spectrum Mountains and the Rainbow Mountains, is a subrange of the Tahltan Highland in the Stikine Country of northwestern British Columbia, 20 km west of the Stewart-Cassiar Highway, south of Moun ...

. The Arctic Lake Plateau is a nearly flat

upland Upland or Uplands may refer to: Geography *Hill, an area of higher land, generally *Highland, an area of higher land divided into low and high points *Upland and lowland, conditional descriptions of a plain based on elevation above sea level *I ...

at the southern end of the MEVC between the Spectrum Range to the east and Mess Creek valley to the west.

Big Raven Plateau

The Big Raven Plateau contains the

Desolation Lava Field The Desolation Lava Field is a volcanic field associated with the Mount Edziza volcanic complex in British Columbia, Canada. It covers on the northern end of the Mount Edziza volcanic complex and is the largest area of the youngest lava flows. The ...

on the northern flank of Mount Edziza which consists of several lava flows that issued from at least 10 separate Big Raven vents. Another area of Big Raven lava flows called the Snowshoe Lava Field occurs on the western flank of Ice Peak; it issued from at least 12 separate vents. The Sheep Track Member overlies much of the southern end of the Big Raven Plateau, including the Snowshoe Lava Field. At least three Big Raven vents occur on the eastern flank of Mount Edziza and comprise another volcanic zone called the east slope centres. An isolated Big Raven vent called

Kana Cone Kana Cone is a red nested cinder cone in northern British Columbia, Canada, located northeast of Eve Cone in Mount Edziza Provincial Park. Adopted 2 January 1980 on 104G/12, as submitted by Geological Survey of Canada.https://apps.gov.bc.ca/pub/b ...

occurs on the extreme northern slope of the plateau while two

cinder cone A cinder cone (or scoria cone) is a steep conical hill A conical hill (also cone or conical mountain) is a landform with a distinctly conical shape. It is usually isolated or rises above other surrounding foothills, and is often of volcanic ...

s occur on the southern slope of the plateau in Walkout Creek valley.

Desolation Lava Field

Blocky

basalt Basalt (; ) is an 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 surface of a rocky planet or moon. More than 90% of a ...

flows, wind-sculptured

ash Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non- gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...

beds A bed is an item of furniture that is used as a place to sleep, rest, and relax. Most modern beds consist of a soft, cushioned mattress on a bed frame. The mattress rests either on a solid base, often wood slats, or a sprung base. Many be ...

and cinder cones comprise the more than Desolation Lava Field. This is the largest lava field of the Big Raven Formation, as well as one of the youngest volcanic features on Mount Edziza.

Sleet Cone Sleet Cone is a cinder cone in northern British Columbia, Canada. It lies in the Desolation Lava Field and is thought to have last erupted in the Holocene period and is part of the Mount Edziza volcanic complex.Storm Cone Storm Cone is a cinder cone in northern British Columbia, Canada. It is thought to have last erupted in the Holocene period and lies on the Desolation lava field which is part of the Mount Edziza volcanic complex.glacial till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

. The Triplex Cones issued lava that flowed to near the south shore of Buckley Lake more than to the northwest.

Sidas Cone Sidas Cone is a cinder cone on the Big Raven Plateau at the northern end of Mount Edziza Provincial Park in British Columbia, Canada. Its name, meaning "cut oneself with a knife" in the Tahltan language, is descriptive of the breach that has cut ...

and Twin Cone are complex volcanic piles resulting from simultaneous, multi-vent

lava fountain Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

ing. Both cones issued relatively thin clinkery-surfaced basalt flows that are sparsely

porphyritic Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning a ...

Moraine Cone Moraine Cone is a cinder cone in northern British Columbia, Canada. It is thought to have last erupted in the Holocene period and is part of the Mount Edziza volcanic complex.Kakiddi Valley near its junction with the

Klastline River Klastline can refer to: * Klastline Cone, a volcanic cone in British Columbia, Canada * Klastline Plateau, a plateau in British Columbia, Canada {{geodis ...

. The two youngest cinder cones in the Desolation Lava Field,

Eve Cone Eve Cone is a well-preserved black cinder cone on the Big Raven Plateau, British Columbia, Canada. It is one of the 30 cinder cones on the flanks of the massive shield volcano of Mount Edziza that formed in the year 700, making it one of the most ...

and

Williams Cone Williams Cone is a satellite cone of Mount Edziza, located east of Telegraph Creek. It lies just off the northern edge of the Tencho Icefield and is one of the many postglacial cinder cones that lie on the Mount Edziza volcanic complex. William ...

, produced basaltic lava that flowed to Buckley Lake and the Klastline River, respectively. A radiocarbon date of 610 CE ± 150 years has been obtained from

willow Willows, also called sallows and osiers, from the genus ''Salix'', comprise around 400 speciesMabberley, D.J. 1997. The Plant Book, Cambridge University Press #2: Cambridge. of typically deciduous trees and shrubs, found primarily on moist ...

twigs preserved in ejecta from Williams Cone. MEVC panorama

Some of the lava flows comprising the Desolation Lava Field issued from vents adjacent to the northern

trim line A trim line, also written as trimline, is a clear line on the side of a valley formed by a glacier. The line marks the most recent highest extent of the glacier. The line may be visible due to changes in color to the rock or to changes in vege ...

of Mount Edziza's summit

ice cap In glaciology, an ice cap is a mass of ice that covers less than of land area (usually covering a highland area). Larger ice masses covering more than are termed ice sheets. Description Ice caps are not constrained by topographical featu ...

where meltwater interacted with the erupting lava to form

tuff ring Phreatomagmatic eruptions are volcanic eruptions resulting from interaction between magma and water. They differ from exclusively magmatic eruptions and phreatic eruptions. Unlike phreatic eruptions, the products of phreatomagmatic eruptions cont ...

s. These tuff rings composed of quenched breccia later transitioned into normal subaerial cinder cones as the progressing eruptions displaced ice and meltwater. The more than lava flow from Williams Cone formed a temporary dam across the Klastline River at its distal end. Lava from Moraine Cone temporarily

dammed ''Dammed: The Politics of Loss and Survival in Anishinaabe Territory'' is a 2020 book by Brittany Luby, Associate Professor of History at the University of Guelph. The book charts the impacts of the damming of the Winnipeg River in the Lake of ...

Kakiddi Creek and the Klastline River, both of which have since etched new

channels Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * Channel Country, region of outback Austral ...

around or through the lava flow. The presence of

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel wh ...

in small terraces upstream from the lava flow suggests that both streams were dammed long enough to form temporary lakes.

Snowshoe Lava Field

The Snowshoe Lava Field is a group of volcanic cones and blocky basalt flows similar in age to the Desolation Lava Field. It covers an area of about and is mostly covered over by air-fall pumice of the Sheep Track Member. As a result, the surface details of most of the upper lava flows in this lava field remain obscured and the cones are mantled with Sheep Track pumice. The Snowshoe Lava Field contains three subglacial cones,

Tennena Cone Tennena Cone is a subglacial mound in northern British Columbia, Canada, located just southwest of Mount Edziza in Mount Edziza Provincial Park. See also *List of volcanoes in Canada * List of Northern Cordilleran volcanoes * Volcanism of Canad ...

being the only one named. Tennena Cone consists of a pile of

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

breccia and

pillow basalt Basalt (; ) is an 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 surface of a rocky planet or moon. More than 90% of a ...

and is one of the oldest cones in the Snowshoe Lava Field. A smaller unnamed subglacial cone to the south also consists of a pile of pillow basalt and tuff breccia. Further south at the southern terminus of

Tencho Glacier Tencho Glacier is a mountain glacier in northwestern British Columbia, Canada. It is located inside Mount Edziza Provincial Park on the Tahltan Highland, an upland area of the Stikine Plateau. Tencho Glacier is the source of several small streams ...

is another unnamed pile of tuff breccia and pillow basalt. It may be the remains of a tuff ring that has been glacially modified after having formed in a meltwater lake when Tencho Glacier existed at lower elevations. Tennena Cone

The Snowshoe Lava Field contains five transitional cones, one of which is named. Two unnamed transitional cones are on the southwestern edge of Mount Edziza's summit ice cap inside the alpine trim lines, both of which have been reduced to low,

drumlin A drumlin, from the Irish word ''droimnín'' ("littlest ridge"), first recorded in 1833, in the classical sense is an elongated hill in the shape of an inverted spoon or half-buried egg formed by glacial ice acting on underlying unconsolidate ...

-like

ridge A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...

s as a result of glacial ice overridding them. The three other transitional cones are unglaciated, having formed at lower elevations just below the terminal alpine moraine. Their inner structures have been exposed by sufficient erosion but they still retain their central craters and original conical form. One of these cones, Coffee Crater, was the source of a lava flow that extended to the southwest; the northern edge of the terminal lobe of this lava flow forms a prominent, escarpment. Three subaerial cones exist in the Snowshoe Lava Field, two of which are named. The largest subaerial cone,

Cocoa Crater Cocoa Crater is a cinder cone in the Stikine Country of northwestern British Columbia, Canada. It is located 38 km southeast of Telegraph Creek and southwest of Mount Edziza. Cocoa Crater is one of the 30 cinder cones around the Mount Edziz ...

, produced a lava flow that travelled into upper

Sezill Creek Sezill Creek is a tributary of Taweh Creek, which in turn is a tributary of Mess Creek, part of the Stikine River watershed in northwest part of the province of British Columbia, Canada. It flows generally northwest for roughly to join Taweh Cree ...

canyon. Keda Cone and an unnamed subaerial cone to the northeast issued the most voluminous lava in the Snowshoe Lava Field, having flowed westward where it engulfed an area more than wide and long. This lava then continued to flow westward into upper Taweh Valley where it transformed into a relatively narrow flow that formerly extended to near Mess Creek. A subaerial vent referred to as

The Saucer The Saucer is a cinder cone in northern British Columbia, Canada. It is thought to have last erupted in the Holocene epoch.

produced the youngest lava flow in the Snowshoe Lava Field from near the southern edge of Mount Edziza's summit ice cap. Unlike the other three subaerial centres, The Saucer flow appears to have issued without any accompanying lava fountaining, resulting in no cinder cone development.

Sheep Track Member

The southwestern flank of Ice Peak and the surrounding Big Raven Plateau are blanketed with loose, air-fall

tephra Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they re ...

of the Sheep Track Member. It covers an area of about and consists of pumice fragments that range in size from snowball-sized chunks to pea-sized debris. The largest fragments occur along the western margin of Tencho Glacier while the smallest fragments form a circular area at least in diameter. Erosion has largely removed the Sheep Track pumice from drainage channels of small intermittent streams on the upper Big Raven Plateau but deposits as much as thick occur in interfluvial areas. Although the Sheep Track pumice was deposited on nearly all of the Snowshoe Lava Field flows and cinder cones, The Saucer is covered by only thin drifts of wind-blown pumice and may postdate the Sheep Track eruption. The source of the Sheep Track pumice remains unknown but it probably originated from a vent hidden under Tencho Glacier. Fission track dating of Sheep Track pumice on the southwestern flank of Ice Peak has yielded an age of 950 CE ± 6000 years.

Walkout Creek valley

Two small Big Raven cones called the Walkout Creek centres occur on the northern and western sides of Walkout Creek valley, both of which are largely buried and deeply eroded. The larger cone on the northern side of the valley is of geological interest because it was constructed on top of an active, slow moving

landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environments, ...

. Although both cones produced lava flows, lava from the larger cone was controlled by the underlying landslide which is characterized by

hummocky In geology, a hummock is a small knoll or mound above ground.Bates, Robert L. and Julia A. Jackson, ed. (1984). “hummock.” Dictionary of Geological Terms, 3rd Ed. New York: Anchor Books. p. 241. They are typically less than in height and ...

, ridge and trough topography. As a result, some of this lava was forced to flow into depressions paralleling minor landslide scarps.

East slope centres

The heavily eroded eastern flank of Mount Edziza contains at least three satellitic centres of the Big Raven Formation.

Cinder Cliff Cinder Cliff is a cinder cone in northern British Columbia, Canada. It is thought to have last erupted during the Holocene period and is part of the Mount Edziza volcanic complex. See also * List of volcanoes in Canada *List of Northern Cordilleran ...

consists of thin, slaggy basalt flows that ponded against an ice dam in the upper part of Tenchen Valley. Tuff breccia and ash, as well as glacial and

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluv ...

gravel, form mixed deposits at the base of Clinder Cliff.

Icefall Cone Icefall Cone is a cinder cone in northern British Columbia, Canada. It is thought to have last erupted during the Holocene period and forms part of the Mount Edziza volcanic complex.Ridge Cone Ridge Cone is a cinder cone in northern British Columbia, Canada. It is thought to have last erupted in the Holocene period and is part of the Mount Edziza volcanic complex.mass wasting Mass wasting, also known as mass movement, is a general term for the movement of rock or soil down slopes under the force of gravity. It differs from other processes of erosion in that the debris transported by mass wasting is not entrained in ...

and alpine glaciation. They both consist of agglutinated spatter,

bombs A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanic ...

, cinders and slaggy basalt flows; the lava flows are almost completely buried under talus, moraine, fluvial gravel and glacial ice. An intermittently exposed basalt flow extending to near Kakiddi Lake may have issued from Icefall Cone, Ridge Cone or an undiscovered vent inside a narrow, wedge-shaped notch on the eastern flank of Mount Edziza.

Kana Cone

The northernmost Big Raven vent and the northernmost vent of the entire MEVC is marked by the nested Kana Cone which rises about above the surrounding

terrain Terrain or relief (also topographical relief) involves the vertical and horizontal dimensions of land surface. The term bathymetry is used to describe underwater relief, while hypsometry studies terrain relative to sea level. The Latin w ...

. Its summit contains a roughly crater that is breached to the north, exposing oxidated bombs and spatter. Lava from the crater breach extends downslope into Klastline Valley where it temporarily dammed the Klastline River; the river has since etched a new channel along the northern valley wall. The lava continued to flow downstream through Klastline Valley and possibly reached the

Stikine River The Stikine River is a major river in northern British Columbia (BC), Canada and southeastern Alaska in the United States. It drains a large, remote upland area known as the Stikine Country east of the Coast Mountains. Flowing west and south ...

where Big Raven lava flows overlie about of sediment at the mouths of the Klastline and

Tahltan The Tahltan or Nahani are a First Nations people of the Athabaskan-speaking ethnolinguistic group who live in northern British Columbia around Telegraph Creek, Dease Lake, and Iskut. The Tahltan constitute the fourth division of the ''Nahane ...

rivers.

Arctic Lake Plateau

Two isolated occurrences of the Big Raven Formation occur on the Arctic Lake Plateau, Nahta Cone near its northern edge being the southernmost vent of Big Raven age. This cone overlies a glacially-scoured

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

hill and contains a crater that is breached to the east. At least five small conelets comprise Nahta Cone, the largest of which has a

topographic Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sci ...

relief of approximately . The breach in the eastern crater rim served as a passageway for at least two highly fluid lava flows that travelled north along a drainage system. Extending north and west of Nahta Cone are two tephra deposits, suggesting it was active twice during different wind directions. Northeast of Nahta Cone on the south flank of Kuno Peak in the Spectrum Range are the remains of a Big Raven pyroclastic cone. The remains consist of steeply dipping beds of coarse agglutinated pyroclastic rocks and basaltic lava flows that overlie thick felsenmeer and talus deposits. Much of this cone has been destroyed by repeated landslides and

solifluction Solifluction is a collective name for gradual processes in which a mass moves down a slope (" mass wasting") related to freeze-thaw activity. This is the standard modern meaning of solifluction, which differs from the original meaning given to ...

on Kuno Peak, the former of which also buried lava flows on the Arctic Lake Plateau that originated from this cone.

Kitsu Plateau

The

Mess Lake Lava Field The Mess Lake Lava Field is a volcanic field associated with the Mount Edziza volcanic complex of the Northern Cordilleran Volcanic Province in northwestern British Columbia, Canada. It lies northwest of the Spectrum Range on the Kitsu Platea ...

is an area of lava flows and tephra deposits between Raspberry Creek in the north,

Nagha Creek Nagha Creek is a tributary of Kitsu Creek and part of the Stikine River watershed in northwest part of the province of British Columbia, Canada. It flows generally northwest and north for roughly Lengths and distances measured using BCGNIS coordin ...

in the south and Mess Lake in the east. It covers an area of about and contains three separate vents of Big Raven age. The two oldest vents are marked by slightly eroded pyroclastic cones whose craters and cone-shaped structures are still apparent despite being somewhat rounded. Lava flows from both cones travelled to the west towards the Mess Creek Escarpment where they most likely cascaded into Mess Creek valley. However, any remnants of this lava on the escarpment or in Mess Creek valley have been removed by erosion. At the southern end of the Mess Lake Lava Field on the steep, south-facing side of Nagha Creek is the third separate vent called

The Ash Pit The Ash Pit is an inactive volcanic crater, located in the Spectrum Range in British Columbia, Canada. It is Holocene in age and is considered the youngest feature in the Spectrum Range volcanic complex. It is within the Northern Cordilleran Volc ...

. This and conical depression is the youngest vent of the Mess Lake Lava Field; it may also be the youngest vent of the entire MEVC. The Ash Pit was the source of a and tephra deposit on the Kitsu Plateau that extends to the northeast. It was also the source of a lava flow that travelled down Nagha Creek valley towards the eastern side of Mess Lake, portions of which are buried under stream gravel, outwash and

braided channel A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, '' aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment ...

deposits.