The Itcha Range, also known as the Itchas, is a small isolated
mountain range
A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arise ...
in the
West-Central Interior of
British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
, Canada. It is located northeast of the community of
Anahim Lake
:''The subject of this article should not be confused with Anaham, which is a different community located nine kilometres east of Alexis Creek, British Columbia, which is in the same area.''
Anahim Lake is a small community in British Columbia. ...
. With a maximum elevation of , it is the lowest of three mountain ranges on the
Chilcotin Plateau
The Chilcotin Plateau is part of the Fraser Plateau, a major subdivision of the Interior Plateau of British Columbia. The Chilcotin Plateau is physically near-identical with the region of the same name, i.e. "the Chilcotin", which lies between t ...
extending east from the
Coast Mountains
The Coast Mountains (french: La chaîne Côtière) 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 Coast of British Columbia ...
. Two mountains are named in the Itcha Range;
Mount Downton
Mount Downton is the highest summit of the diameter Itcha Range, located northeast of Anahim Lake and east of Far Mountain in the Chilcotin District of the Central Interior of British Columbia, Canada. It lies within Itcha Ilgachuz Provincial ...
and
Itcha Mountain. A large
provincial park
Ischigualasto Provincial Park
A provincial park (or territorial park) is a park administered by one of the provinces of a country, as opposed to a national park. They are similar to state parks in other countries. They are typically open to the ...
surrounds the Itcha Range and other features in its vicinity. More than 15 animal species are known to exist in the Itcha Range area, as well as a
grassland
A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur natur ...
community that is limited only to this location of British Columbia. The Itcha Range is within territory which has been occupied by
aboriginal peoples
Indigenous peoples are culturally distinct ethnic groups whose members are directly descended from the earliest known inhabitants of a particular geographic region and, to some extent, maintain the language and culture of those original people ...
for millennia. This area has a relatively dry environment compared to the Coast Mountains in the west.
In contrast to most mountain ranges in British Columbia, the Itcha Range represents an inactive
shield volcano
A shield volcano is a type of volcano named for its low profile, resembling a warrior's 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 v ...
. This highly dissected volcanic edifice consists of a variety of rock types, including
basanite
Basanite () is an igneous, volcanic (extrusive) rock with aphanitic to porphyritic texture. It is composed mostly of feldspathoids, pyroxenes, olivine, and plagioclase and forms from magma low in silica and enriched in alkali metal oxides that s ...
,
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 ...
,
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 al ...
,
rhyolite
Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...
,
phonolite
Phonolite is an uncommon extrusive rock, of intermediate chemical composition between felsic and mafic, with texture ranging from aphanitic (fine-grained) to porphyritic (mixed fine- and coarse-grained). Phonolite is a variation of the igneous ...
and
alkali olivine 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 ...
. They were deposited by different
types of volcanic eruptions
Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are oft ...
characterized by
passive lava flows and
explosivity. Two
stages
Stage or stages may refer to:
Acting
* Stage (theatre), a space for the performance of theatrical productions
* Theatre, a branch of the performing arts, often referred to as "the stage"
* ''The Stage'', a weekly British theatre newspaper
* S ...
of eruptive activity have been identified at the volcano along with three sub-phases that are limited only to the first stage of development. The main body of the Itcha Range is between 3.8 and 3.0 million years old and thus over two million years ago it passed the most active shield stage of life. A period of dormancy lasting for almost a million years followed, which was interrupted by the post-shield stage of volcanism 2.2 to 0.8 million years ago. More recent volcanic activity in and around the Itcha Range might have occurred in the last 340,000 years to produce
cinder cone
A cinder cone (or scoria cone) is a steep conical hill of loose pyroclastic fragments, such as volcanic clinkers, volcanic ash, or scoria that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions o ...
s.
The Itcha Range is part of an east–west trending volcanic zone called the
Anahim Volcanic Belt
The Anahim Volcanic Belt (AVB) is a west–east trending chain of volcanoes and related magmatic features in British Columbia, Canada. It extends from Athlone Island on the Central Coast, running eastward through the strongly uplifted and deeply ...
. This consists of large shield volcanoes, small cinder cones,
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 on ...
s and lava flows that become progressively younger from west to east. Several explanations have been made regarding the creation of this feature, each citing a different geologic process. If volcanic activity were to resume at the Itcha Range, Canada's
Interagency Volcanic Event Notification Plan
The Interagency Volcanic Event Notification Plan (IVENP) is a program in Canada established to outline the notification procedure of some of the main agencies that would be involved in response to a volcanic eruption in Canada, an eruption close to ...
(IVENP) is prepared to notify people threatened by eruptions.
Geography
Location and terrain
The Itcha Range is situated on the northern Chilcotin Plateau, a subdivision of the
Fraser Plateau
The Fraser Plateau is an intermontane plateau. It is one of the main subdivisions of the Interior Plateau located in the Central Interior of British Columbia.
Geography
The region includes the Cariboo Plateau and Chilcotin Plateau, and the adjoi ...
which in turn is one of the main subdivisions of the large
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 British C ...
.
It is bordered on the west by the
Ilgachuz Range
The Ilgachuz Range is a name given to an 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 eroded for the past 5 million years. It lies on ...
, another mountain range on the Chilcotin Plateau.
The Itcha Range is located within one of British Columbia's many territorial divisions known as the
Range 3 Coast Land District
Range 3 Coast Land District is one of the 59 land districts of British Columbia, Canada, which are part of the cadastral divisions of British Columbia.
Islands
* Campbell Island
* Lady Douglas Island
*Lake Island
* Price Island
*Swindle Island
M ...
.
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 stream ...
erosion
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 distin ...
has played a significant role in dissecting the mountain range, and many of its peaks are dotted with
glacier
A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciology, ablation over many years, often Century, centuries. It acquires dis ...
s.
This dissection has resulted in a variety of
landform
A landform is a natural or anthropogenic land feature on the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Landforms include hills, ...
s, such as
valley
A valley is an elongated low area often running between Hill, hills or Mountain, mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers ...
s,
crags and domes. Small graveled creeks flow from alpine mountains out onto the regional
prairies
Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the ...
where there are pale blue rock-bottomed
lake
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 large ...
s, including the so-named
Itcha Lake.
Three streams drain the Itcha Range, namely Corkscrew Creek,
Downton Creek and Shag Creek.
Although the Itcha Range has been dissected by stream erosion and subsequently glaciated, its original shape has been largely preserved.
Rocks in the Itcha Range are a variety of colours, including red, white and yellow.
Climate
The climate of the Itcha Range is influenced by the presence of the
Coast Mountains
The Coast Mountains (french: La chaîne Côtière) 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 Coast of British Columbia ...
to the west, which disrupt the flow of the
prevailing westerly winds and causes them to drop most of their moisture on the western slopes of the Coast Mountains before reaching the Interior Plateau, casting a
rain shadow
A rain shadow is an area of significantly reduced rainfall behind a mountainous region, on the side facing away from prevailing winds, known as its leeward side.
Evaporated moisture from water bodies (such as oceans and large lakes) is carrie ...
over the Itcha Range.
In contrast to the Coast Mountains, the Interior Plateau experiences a precipitation peak in the summer months, reflecting the influence of summer convective storms, and most of winter precipitation falls as snow. The mean annual precipitation for the area ranges from about while the mean annual temperature is approximately , with a summer mean of and a winter mean of .
Flora and fauna
The Itcha Range area is home to a grassland
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
that has not been found elsewhere in southern or central British Columbia. It is dominated by communities of Altai
fescue
''Festuca'' (fescue) is a genus of flowering plants belonging to the grass family Poaceae (subfamily Pooideae). They are evergreen or herbaceous perennial tufted grasses with a height range of and a cosmopolitan distribution, occurring on every ...
and
lichen
A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.[alpine
Alpine may refer to any mountainous region. It may also refer to:
Places Europe
* Alps, a European mountain range
** Alpine states, which overlap with the European range
Australia
* Alpine, New South Wales, a Northern Village
* Alpine National Pa ...]
and
subalpine
Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial f ...
vegetation is also present in the area, some species of which are at the northernmost or southernmost of their range.
Several animal species inhabit around the Itcha Range. Among them are cougars, wolves, grizzly bears, black bears, moose, mule deers, mountain goats, beavers, coyotes, red foxes, muskrats, martens, river otters, lynx and wolverines. Also present is the largest herd of
woodland caribou
Woodland caribou may refer to two North American reindeer (''Rangifer tarandus'') populations:
* Boreal woodland caribou
The boreal woodland caribou (''Rangifer tarandus caribou''; but subject to a recent taxonomic revision. See Reindeer: taxo ...
in southern British Columbia, as well as the most northerly population of
California bighorn sheep in North America.
Geology
Background
A number of mechanisms have been proposed to interpret the origin of
volcanism
Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called ...
in the Anahim Volcanic Belt. This includes
rift
In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics.
Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...
propagation and melting of
mantle associated with
lithospheric
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 portion of the upper mantle that behaves elastically on time scales of up to thousands of years or ...
fracturing due to flexuring of the
crust along the northern edge of the
subducting
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
Juan de Fuca Plate.
However, insignificant evidence exists to support these hypotheses.
The most common and best mechanism used to explain Anahim Belt volcanic activity is a stationary
hotspot. This is supported by a well-defined progression in age of volcanism from west to east along the belt that compares well with the age trend of the
Yellowstone hotspot
The Yellowstone hotspot is a volcanic hotspot in the United States responsible for large scale volcanism in Idaho, Montana, Nevada, Oregon, and Wyoming, formed as the North American tectonic plate moved over it. It formed the eastern Snake Ri ...
track. The
North American Plate
The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Pacific ...
moves westward over the hotspot at a rate of between per year.
Nazko Cone
Nazko Cone is a small potentially active basaltic cinder cone in central British Columbia, Canada, located 75 km west of Quesnel and 150 kilometers southwest of Prince George. It is considered the easternmost volcano in the Anahim Volcanic ...
, a
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 and ...
east of the Itcha Range, is centred near 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 tha ...
.
![Anahim Volcanic Belt-en](https://upload.wikimedia.org/wikipedia/commons/f/f4/Anahim_Volcanic_Belt-en.svg)
The Anahim hotspot is underlain by a
low-velocity anomaly that extends approximately into the mantle north of the Juan de Fuca
slab
Slab or SLAB may refer to:
Physical materials
* Concrete slab, a flat concrete plate used in construction
* Stone slab, a flat stone used in construction
* Slab (casting), a length of metal
* Slab (geology), that portion of a tectonic plate tha ...
. However, this low-velocity anomaly may extend deeper southward beneath the Juan de Fuca slab. Coupled with the well documented temporal progression of surface volcanism, this has led to the conclusion that the Anahim hotspot is supplied by a
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 hot ...
over slab edge flow. A small high-velocity anomaly east of Nazko Cone marks the eastern extent of the Anahim hotspot track.
Magmatism
Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of ...
in the Anahim Volcanic Belt can be traced as far back as 10–14 million years ago with the emplacement of
dike swarm
A dike swarm (American spelling) or dyke swarm (British spelling) is a large geological structure consisting of a major group of parallel, linear, or radially oriented magmatic dikes intruded within continental crust or central volcanoes ...
s and
pluton
In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...
s as well as the eruption of rhyolite flows and breccias on the
British Columbia Coast
, settlement_type = Region of British Columbia
, image_skyline =
, nickname = "The Coast"
, subdivision_type = Country
, subdivision_name = Canada
, subdivision_type1 = Province
, subdivision_name1 = British ...
. The slow continuous westward motion of the North American Plate during the late
Neogene
The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...
positioned the Anahim hotspot further east at the Chilcotin Plateau where volcanic activity built the
Rainbow Range shield volcano 8.7 to 6.7 million years ago. Volcanism then shifted eastwards, in displacement contrary with the North American Plate's movement, 6.1 million years ago to construct the Ilgachuz Range shield volcano. Renewed volcanic activity southeast of the Ilgachuz Range starting 3.5 million years ago led to the creation of the Itcha Range, the youngest of the three Anahim shield volcanoes. The Itcha Range continued to be an area of Anahim hotspot volcanism well into the
Quaternary
The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...
period
Period may refer to:
Common uses
* Era, a length or span of time
* Full stop (or period), a punctuation mark
Arts, entertainment, and media
* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
(2.58 million years ago to present).
Structure
The Itcha Range is the smallest shield volcano in the Anahim Volcanic Belt in terms of area covered. Unlike the Rainbow and Ilgachuz ranges, the Itcha Range is composed of small coalescing volcanic
units
Unit may refer to:
Arts and entertainment
* UNIT, a fictional military organization in the science fiction television series ''Doctor Who''
* Unit of action, a discrete piece of action (or beat) in a theatrical presentation
Music
* Unit (album), ...
rather than a stratiform volcanic pile. It is, in many respects, similar to the small
alkaline
In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...
shields found in
Kenya
)
, national_anthem = "Ee Mungu Nguvu Yetu"()
, image_map =
, map_caption =
, image_map2 =
, capital = Nairobi
, coordinates =
, largest_city = Nairobi
, ...
and
Ethiopia
Ethiopia, , om, Itiyoophiyaa, so, Itoobiya, ti, ኢትዮጵያ, Ítiyop'iya, aa, Itiyoppiya officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea to the ...
along the
East African Rift
The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of a ...
. About 60% of the shield is exposed while roughly 40% of it remains buried under
glacial drift
In geology, drift is a name for all sediment (clay, silt, sand, gravel, boulders) transported by a glacier and deposited directly by or from the ice, or by glacial meltwater. Drift is often subdivided into (unsorted and) unstratified drift (glaci ...
deposits. This suggests that the Itcha Range was glaciated repeatedly during the
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
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 by ...
.
Glacial striae on polished surfaces of some of the oldest volcanic rocks in the eastern part of the shield and the local presence of drift deposits throughout the
stratigraphy
Stratigraphy is a branch of geology concerned with the study of rock (geology), rock layers (Stratum, strata) and layering (stratification). It is primarily used in the study of sedimentary rock, sedimentary and layered volcanic rocks.
Stratigrap ...
indicate that
glaciation
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
and volcanism were contemporaneous through much of the volcanic history of the Itcha Range.
With a maximum elevation of , the Itcha Range is the lowest of the three Anahim shield volcanoes. Its highest point is Mount Downton, which is situated in the middle of the shield. Just to the northeast is Itcha Mountain, the second highest peak with an elevation of . These peaks are situated on top of the shield, which has a
topographic prominence
In topography, prominence (also referred to as autonomous height, relative height, and shoulder drop in US English, and drop or relative height in British English) measures the height of a mountain or hill's summit relative to the lowest contou ...
of about .
The Itcha Range has a broad, gently sloping structure typical of shield volcanoes. It is mainly composed of thick
felsic
In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, whi ...
lava flows that were erupted from a central vent. These are overlain by thick
mafic
A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...
alkaline lava flows and at least 30 small cinder cones. Hawaiite is the dominant rock type, but
alkali
In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...
olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
basalt and
spinel
Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals.
Properties
S ...
lherzolite
Lherzolite is a type of ultramafic igneous rock. It is a coarse-grained rock consisting of 40 to 90% olivine along with significant orthopyroxene and lesser amounts of calcic chromium-rich clinopyroxene. Minor minerals include chromium and alu ...
-bearing basanite is also present. They merge laterally with lavas of the much older
Chilcotin Group, which surrounds the Anahim Volcanic Belt. However, the exact nature of the relationship between the Anahim Volcanic Belt and the Chilcotin Group is unknown.
Exposed in the middle of the mountain range is an assemblage of deformed
andesite
Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomi ...
to
dacite
Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. ...
lava flows and volcanoclastic sediments. These
basement
A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, ...
rocks were created during the late
Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
era
An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth.
Comp ...
, long before the Itcha Range formed. They are similar to rocks found in the
Hazelton Group, situated north of the Itcha Range, and the
Ootsa Lake Group of the
Intermontane Belt
The Intermontane Belt is a physiogeological region in the Pacific Northwest of North America, stretching from northern Washington into British Columbia, Yukon, and Alaska. It comprises rolling hills, high plateaus and deeply cut valleys. The roc ...
.
Volcanic history
Two stages of volcanic activity constructed the Itcha Range. The first stage, referred to as the felsic shield-building stage, occurred between 3.8 and 3.0 million years ago. Three phases comprise this stage; a pre-explosive phase, an explosive phase and a post-explosive phase. Analysis of the first trachyte
magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
s to erupt during the pre-explosive phase suggest they were relatively fluid as shown by their areal extent. Eruptions became more viscous during the explosive phase, followed by more viscosity during the post-explosive phase. As a result, the volume of erupted material became smaller over time. The increasing viscousness of felsic lava during the shield-building stage suggests a maturing plumbing system underneath the Itcha Range, which may have consisted of multiple, isolated,
cupola
In architecture, a cupola () is a relatively small, most often dome-like, tall structure on top of a building. Often used to provide a lookout or to admit light and air, it usually crowns a larger roof or dome.
The word derives, via Italian, from ...
-type
magma chamber
A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it upw ...
s.
![Itcha Range geology](https://upload.wikimedia.org/wikipedia/commons/a/a4/Itcha_Range_geology.png)
A 900,000‑year‑long period of quiescence followed after the felsic shield-building stage, during which time erosion ate away at the shield's gentle slopes. This quiescence was followed by a mafic capping stage between 2.2 and 0.8 million years ago, but renewed activity might have occurred in the last 340,000 years. Alkali olivine basalts of the mafic capping stage were derived from the
fractionation
Fractionation is a separation process in which a certain quantity of a mixture (of gases, solids, liquids, enzymes, or isotopes, or a suspension) is divided during a phase transition, into a number of smaller quantities (fractions) in which the ...
of a
clinopyroxene
The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...
, olivine and
oxide
An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...
assemblage. However, the associated hawaiite lavas may have derived from an alkali olivine basalt parent by the fractionation of a clinopyroxene-dominated assemblage at higher pressures. As volcanic activity waned during the mafic capping stage, lava flows became more viscous and decreased in volume. This suggests that parental magmas may have been derived by increasingly smaller degrees of
partial melting
Partial melting occurs when only a portion of a solid is melted. For mixed substances, such as a rock containing several different minerals or a mineral that displays solid solution, this melt can be different from the bulk composition of the soli ...
with time. If volcanic activity of the Itcha Range is related to a hotspot, this temporal and spatial evolution would suggest a waning heat source.
The main body of the shield erupted over an area of about . Volcanic activity associated with the Itcha Range extended south to the
Satah Mountain area where lavas erupted along a north-northwest trending
fault system and covered an additional area of .
Although the
Satah Mountain volcanic field is not part of the Itcha Range, it is linked to the range by a volcanic ridge.
Felsic shield-building stage
The felsic shield-building stage began with the eruption of phonolite, trachyte, phonolitic trachyte,
quartz
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
-trachyte and rhyolite lava.
Subsequent volcanism of the pre-explosive phase produced a basal sequence of aphyric trachyte lava flows and domes with minor altered flow-banded rhyolite,
sulfide
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...
-bearing rhyolitic
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 cont ...
s and a few thin hawaiite lava flows. This activity was concentrated at the summit of the volcano as shown by the increasing thickness of volcanic material towards the summit. A hydrothermally altered aphyric trachyte
dike
Dyke (UK) or dike (US) may refer to:
General uses
* Dyke (slang), a slang word meaning "lesbian"
* Dike (geology), a subvertical sheet-like intrusion of magma or sediment
* Dike (mythology), ''Dikē'', the Greek goddess of moral justice
* Dikes ...
, which forms a narrow
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 ...
linking Mount Downton and Itcha Mountain, might have been the source for these eruptions.
After the basal trachytes were erupted, the explosive phase produced alkali-
feldspar
Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldsp ...
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 all ...
trachytes, which erupted as pyroclastic deposits with minor, small lava flows and domes. The explosive eruptions produced
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 vol ...
flows, bedded tuffs,
debris flow
Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally ...
s, reworked polymict debris flows and lava flows less than thick. The porphyritic trachytes erupted at the summit of the shield and flowed towards the northeast and east. Because the porphyritic pyroclastic deposits are buried by younger volcanic rocks and glacial drift deposits, the maximum thickness of them is unknown.
The felsic shield-building stage ended with the post-explosive phase. This phase of activity created small
volcanic plug
A volcanic plug, also called a volcanic neck or lava neck, is a volcanic object created when magma hardens within a vent on an active volcano. When present, a plug can cause an extreme build-up of high gas pressure if rising volatile-charged mag ...
s, lava flows, minor
pyroclastic flow
A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of bu ...
s, channelized debris flows and a few glassy dikes at the summit of the shield volcano. These consist of alkali-feldspar porphyritic quartz-trachyte and trachyte. Alkali-feldspar quartz-trachyte plugs formed in rhyolites and trachytes of the pre-explosive phase, as well as pyroclastic deposits and feldspar trachyte lava flows of the explosive phase. Later activity produced trachyte and phonolite plugs and lava flows. This volcanism occurred mainly at the shield's summit and on its western flank. Massive lava flows from this volcanic activity have a thickness of about while three successive lava flows at the summit have a combined thickness of more than . Lava from the western flank flowed over basement rocks and trachytes of the pre-explosive phase. In contrast, lava from the summit flowed over
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 pyrocl ...
s and lava flows of the explosive phase. Mount Downton and Itcha Mountain were formed during this eruptive period. The final volcanic event of the post-explosive phase produced thick trachyte lava flows on the western flank.
Mafic capping stage
![Itcha Range](https://upload.wikimedia.org/wikipedia/commons/0/0c/Itcha_Range_.jpg)
During the mafic capping stage, basanite, alkali olivine basalt and hawaiite erupted mainly from small
parasitic cone
A parasitic cone (also adventive cone or satellite 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 volcano. These fractures occur ...
s,
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 and
fissures
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
...
in the eastern half of the shield.
Eruptions occurred
subglacially,
subaqueously and/or
subaerially as shown by a wide range in the degree of
vesicularity, freshness and
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
content of the lavas. In most cases, each parasitic cone produced three or four lava flows from breaches in the cone walls. These were erupted as
pāhoehoe
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 ...
and
ʻaʻā
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 und ...
, but the tops of the lava flows are commonly missing due to erosion. Hawaiite was the most extensively erupted lava of the mafic capping stage, occurring mostly at the southern end of the Itcha Range but also in its interior.
Volcanism of the mafic capping stage began with the eruption of aphyric hawaiite lava flows. These were
extruded
Extrusion is a process used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex c ...
from dikes and dissected cinder cones in the central and southeastern parts of the Itcha Range. Alkali olivine basalts were erupted contemporaneously from younger better preserved cinder cones and form lava flows reaching thick. Once the alkali olivine basalt flows cooled, they formed well-developed
columnar joints
Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as Joint (geology), joints, result in the formation of a regular array of polygonal Prism (geometry), prisms, or columns. Columnar joint ...
. Feldspar-
phyric
300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...
, highly vesiculated hawaiites and
benmoreite
Benmoreite is a silica-undersaturated volcanic rock of intermediate composition. It is a sodium-rich variety of trachyandesite and belongs to the alkalic suite of igneous rocks.
Nepheline benmoreite
An origin by fractionation from basanite t ...
s were later erupted from several vents on the summit of Itcha Mountain.
In the northwestern and northeastern parts of the shield volcano, basanite lava flows were erupted and are volumetrically
subordinate
A hierarchy (from Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) that are represented as being "above", "below", or "at the same level as" one another. Hierarchy is an important ...
. These represent the youngest known lavas of the Itcha Range. However, a cinder cone in the middle of the shield could be much younger, perhaps as young as the basanites at Nazko Cone to the east, which were erupted 340,000 to 7,100 years ago. The older basanites in the Itcha Range may have been erupted contemporaneously with the late feldspar hawaiites.
Parasitic cones
Parasitic cones of the Itcha Range shield were formed mainly during the
Early Pleistocene
The Early Pleistocene is an unofficial sub-epoch in the international geologic timescale in chronostratigraphy, being the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently estimated to span the time ...
mafic capping stage between 2.2 and 0.8 million years ago.
These secondary vents are monogenetic in nature, meaning each cone was only active for a single eruption sequence before becoming
extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
.
The duration of volcanic activity at these cones can last from hours to years.
Parasitic cones of the Itcha Range are small cinder cones situated at the summit and flanks of the shield volcano.
Human history
Naming
The Itcha Range has had at least two forms of names throughout its history. It was originally named the ''Itcha Mountains'' as identified in the 1930 BC Gazetteer.
This form of name remained official until March 13, 1947, when it was changed to its current form, ''Itcha Range'', as part of an official government policy.
Larger mountain ranges throughout British Columbia, such as the Coast Mountains, retained their gazetted names whereas smaller ones, especially ranges of larger groupings, were subjected to renaming.
In more casual speech, the Itcha Range is referred to as ''the Itchas''.
The name ''Itcha'' is
indigenous
Indigenous may refer to:
*Indigenous peoples
*Indigenous (ecology), presence in a region as the result of only natural processes, with no human intervention
*Indigenous (band), an American blues-rock band
*Indigenous (horse), a Hong Kong racehorse ...
in origin, coming from the local
Tsilhqot'in people.
Mount Downton was named by D. M. MacKay, a member of the British Columbia Land Surveyors (BCLS) who conducted
topographical
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 ...
surveys in the area.
He named it after Geoffrey M. Downton, another BCLS member who is credited for first noting the hydroelectric potential inherent in the elevation differential between the
Bridge River
The Bridge River is an approximately long river in southern British Columbia. It flows south-east from the Coast Mountains. Until 1961, it was a major tributary of the Fraser River, entering that stream about six miles upstream from the town of ...
and
Seton Lake
Seton Lake is a freshwater fjord draining east via the Seton River into the Fraser River at the town of Lillooet, about long, in area and lies at an elevation of . Its depth is .
The lake is natural in origin but was raised slightly as part of ...
on opposing sides of
Mission Ridge above
Shalalth
Shalalth and South Shalalth are unincorporated communities on the northern shore near the western end of Seton Lake in the Squamish-Lillooet region of southwestern British Columbia. The localities are by road about northwest of Lillooet, but o ...
in December 1912.
This name for the mountain was adopted on February 7, 1947.
The name ''Itcha Mountain'' was adopted on March 4, 1954, for the range's second highest peak.
Occupation
![RainbowIlgachuzItcha](https://upload.wikimedia.org/wikipedia/commons/4/45/RainbowIlgachuzItcha.jpg)
Indigenous people of the
Dakelh
The Dakelh (pronounced ) or Carrier are the indigenous people of a large portion of the Central Interior of British Columbia, Canada.
The "Carrier" name was derived from an English translation of ''Aghele'', the name from the neighbouring Sekani ...
and Tsilhqot'in tribes have inhabited the area for hundreds of years. In
pre-contact
In the history of the Americas, the pre-Columbian era spans from the original settlement of North and South America in the Upper Paleolithic period through European colonization, which began with Christopher Columbus's voyage of 1492. Usually, th ...
times, these people lived a
nomad
A nomad is a member of a community without fixed habitation who regularly moves to and from the same areas. Such groups include hunter-gatherers, pastoral nomads (owning livestock), tinkers and trader nomads. In the twentieth century, the popu ...
ic lifestyle. They did not build permanent structures in which to live, as they moved from region to region to find food and resources. Animals such as martin, moose and caribou were hunted and trapped by the Dakelh and Tsilhqot'in tribes. In summer, these people gathered roots, plants and a volcanic glass called
obsidian
Obsidian () is a naturally occurring volcanic glass formed when lava extrusive rock, extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock.
Obsidian is produced from felsic lava, rich in the lighter elements s ...
.
Anahim obsidian was traded widely throughout the Interior and up and down the Coast from the community of
Bella Coola. Arrowheads and knives were made from obsidian because when it breaks with a characteristic
conchoidal fracture
Conchoidal fracture describes the way that brittle materials break or fracture when they do not follow any natural planes of separation. Mindat.org defines conchoidal fracture as follows: "a fracture with smooth, curved surfaces, typically slig ...
, it creates very sharp edges.
A modified form of this lifestyle is practiced by some indigenous people to this day.
Settlers arrived in the area from Bella Coola in the early 1900s to establish
ranch
A ranch (from es, rancho/Mexican Spanish) is an area of land, including various structures, given primarily to ranching, the practice of raising grazing livestock such as cattle and sheep. It is a subtype of a farm. These terms are most often ...
es. One particular ranch, the Home Ranch, used the
Blackwater Trail
''Blackwater Trail'' is a 1995 Australian TV movie directed by Ian Barry and starring Judd Nelson. It was shot in Queensland.Ed. Scott Murray, ''Australia on the Small Screen 1970-1995'', Oxford Uni Press, 1996 p16
Cast
* Judd Nelson as Matt ...
between the Ilgachuz and Itcha ranges to carry supplies and cattle to be sold at cattle sales in the small city of
Quesnel Quesnel or Quesnell means "little oak" in the Picard dialect of French. It is used as a proper name and may refer to:
Places
* Le Quesnel, a commune the Somme department in France
* Quesnel, British Columbia, a city in British Columbia, Canada ...
. Remains of this ranch are still present, as well as many trails that were used as supply routes.
The Itcha Range and the surrounding area were designated as a Class A provincial park in 1995 to protect the alpine grasslands,
wetland
A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...
s and wildlife habitats. This protected area was named
Itcha Ilgachuz Provincial Park after the Itcha and Ilgachuz ranges, the latter of which is also in the park.
Monitoring and volcanic hazards
Like other volcanoes in the Anahim Volcanic Belt, the Itcha Range is not
monitored closely enough by the
Geological Survey of Canada
The Geological Survey of Canada (GSC; french: Commission géologique du Canada (CGC)) is a Canadian federal government agency responsible for performing geological surveys of the country, developing Canada's natural resources and protecting the en ...
to ascertain how active its magma system is. The
Canadian National Seismograph Network The Canadian National Seismograph Network is a network of seismographs to detect earthquakes across Canada. It is operated by the Geological Survey of Canada
The Geological Survey of Canada (GSC; french: Commission géologique du Canada (CGC)) is ...
has been established to monitor earthquakes throughout Canada, but it is too far away to provide an accurate indication of activity under the range. It may sense an increase in seismic activity if the Itcha Range becomes highly restless, but this may only provide a warning for a large eruption; the system might detect activity only once the volcano has started erupting. If the Itcha Range were to erupt, mechanisms exist to orchestrate relief efforts. The Interagency Volcanic Event Notification Plan (IVENP) was created to outline the notification procedure of some of the main agencies that would respond to an erupting volcano in Canada, an eruption close to the
Canada–United States border
The border between Canada and the United States is the longest international border in the world. The terrestrial boundary (including boundaries in the Great Lakes, Atlantic, and Pacific coasts) is long. The land border has two sections: Can ...
or any eruption that would affect Canada.
Because of the remote location of the Itcha Range, future eruptions are not a major hazard. Future volcanism is most likely in the form of basaltic cinder cones, but eruptions of felsic magma can not be ruled out. The most immediate hazard relating to future eruptions is of local concern only and includes the possibility of forest fires by lava flows and the disruption of local air traffic if an
eruption 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 a ...
is produced.
Volcanic ash
Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used t ...
reduces visibility and can cause jet engine failure, as well as damage to other aircraft systems.
See also
*
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 rock types and ages hint at the complex geology, which is still undergoing revis ...
*
Volcanism of Western Canada
Volcanism of Western Canada has produced lava flows, lava plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, greenstone belts, submarine volcanoes, calderas, diatremes and maars, along with examples of more less common volcanic ...
*
List of volcanoes in Canada
List of volcanoes in Canada is an incomplete list of volcanoes found in Mainland Canada, in the Canadian islands and in Canadian waters. All but one province, Prince Edward Island, have at least one volcano.
Alberta
British Columbia
Ne ...
References
External links
*
*
*
*
*
{{Anahim Volcanic Belt
Landforms of the Chilcotin
Hotspot volcanoes
Inactive volcanoes
Pliocene shield volcanoes
Pleistocene shield volcanoes
Polygenetic shield volcanoes
Range 3 Coast Land District
Shield volcanoes of Canada
Tsilhqot'in
Mountain ranges of the Interior Plateau