The Milbanke Sound Group, also called the Milbanke Sound Cones, is an enigmatic group of five small

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

ic volcanoes in the

Kitimat Ranges , photo = Lax Kw'alaams.jpg , photo_size = 280px , photo_caption = Lax Kw'alaams backdropped by Mount McNeil , map = , map_image = BC-relief_Kitimatranges.png , map_caption = Kitimat Ranges ...

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 ...

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 Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

. Named for

Milbanke Sound Milbanke Sound is a sound on the coast of the Canadian province of British Columbia. Geography Milbanke Sound extends east from Queen Charlotte Sound, with Price Island on the west, Swindle Island on the north, and the Bardswell Group of island ...

, this

volcanic group A volcanic group is a stratigraphic group consisting of volcanic strata. They can be in the form of volcanic fields, volcanic complexes and cone A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (freque ...

straddles on at least four small islands (three of which are uninhabited), including

Swindle A swindle is a kind of fraud or confidence trick. Swindle may also refer to: People * Swindle (surname) Places * Swindle Island, British Columbia, Canada * 8690 Swindle, an asteroid Films * ''Il bidone'' (English titles ''The Swindle'' or ' ...

Price A price is the (usually not negative) quantity of payment or compensation given by one party to another in return for goods or services. In some situations, the price of production has a different name. If the product is a "good" in the c ...

, Lady Douglas and

Lake Island A lake island is any landmass within a lake. It is a type of inland island. Lake islands may form a lake archipelago. Formation Lake islands may form in numerous ways. They may occur through a build-up of sedimentation as shoals, and become ...

. Not much is known about this group of volcanoes and they remain undated. However, they all likely formed in the past 10,000 years after the last glacial period as evidenced by a small amount of erosion. The age of the most recent volcanic activity is also unknown. Most of the Milbanke Sound Cones are covered by mature

forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

. Kitasu Hill and Helmet Peak are the only two cones that are officially named. This group of volcanoes is unlike many other volcanic groups in Canada as it resides on islands instead of on the

mainland Mainland is defined as "relating to or forming the main part of a country or continent, not including the islands around it egardless of status under territorial jurisdiction by an entity" The term is often politically, economically and/or dem ...

. The volcanoes form a northwest-southeast trend along the British Columbia Coast. To the west the Milbanke Sound Group is bounded by the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

and elsewhere it is surrounded by adjacent islands that form an

archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster, or collection of islands, or sometimes a sea containing a small number of scattered islands. Examples of archipelagos include: the Indonesian Archi ...

. Although not related, the Milbanke Sound Group is close to the remains of a much older magmatic feature that was formed during the

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

period.

Geology

Volcanoes

Just south of Kitasu Bay on the southwestern shore of Swindle Island, Kitasu Hill rises with an elevation of and 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 . This is a small symmetrical monogenetic

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 ...

and the best preserved volcano associated with the Milbanke Sound Group. It is the northernmost and most prominent volcano of the Milbanke Sound Cones with a circular

volcanic crater A volcanic crater is an approximately circular depression in the ground caused by Volcano, volcanic activity. It is typically a bowl-shaped feature containing one or more vents. During Types of volcanic eruptions, volcanic eruptions, molten magm ...

at its summit. The volcano produced basaltic lava flows that extend to the north. Subaerial

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 rem ...

and

volcanic bomb A volcanic bomb or lava bomb is a mass of partially molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. Because volcanic bombs cool after they l ...

s are the main volcanics comprising the volcano. These volcanics surround eroded remains of the basalt lava flows and are composed of the mineral

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 ...

. Kitasu Hill rests on till that overlies glacially scoured bedrock.

Near the northeastern shore of Price Island, a small eroded monogenetic cinder cone composed of basalt is covered by mature forest. It has an elevation of and is the source of a basaltic lava flow. This lava flow extends down to the northeastern shoreline of Price Island where it covers beach gravel. Helmet Peak on the northern end of Lake Island just off the southwestern side of the

Don Peninsula The Don Peninsula is a peninsula in British Columbia, Canada. It extends southwest between the Mathieson and Spiller Channels in the Milbanke Sound Milbanke Sound is a sound on the coast of the Canadian province of British Columbia. Geography ...

is a steep-sided monogenetic cinder cone. It is composed of welded

volcanic block A volcanic block is a fragment of rock that measures more than in diameter and is erupted in a solid condition. Blocks are formed from material from previous eruptions or from country rock and are therefore mostly accessory or accidental in or ...

s and basaltic feeder

dikes 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 ...

. With an elevation of , Helmet Peak is the highest volcano in the Milbanke Sound Group. During its eruption, basaltic

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 ...

breccia was sent throughout the surrounding landscape that deposited on glaciated granitic rock and unconsolidated beach gravel near the volcano. This basaltic tuff breccia covers parts of Lake Island and nearby Lady Douglas Island. Blocks of basement

granodiorite Granodiorite () is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gra ...

, some up to wide, are randomly suspended within the breccia. Basalt on Lake Island is characterized by abundant to

labradorite Labradorite (( Ca, Na)( Al, Si)4 O8) is a calcium-enriched feldspar mineral first identified in Labrador, Canada, which can display an iridescent effect ( schiller). Labradorite is an intermediate to calcic member of the plagioclase series. It ...

and

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) ...

phenocryst 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 ...

s. At the southern end of the Milbanke Sound Group, a small monogenetic cinder cone with an elevation of resides on Dufferin Island. It sent basaltic lava flows to the north where they reached the island's shoreline to cover beach gravel. Since its formation, the cinder cone has been eroded and covered by forest. Finngal Island, south of Dufferin Island, contains one or more basaltic lava flows that form well-preserved columnar jointing. Like other volcanic deposits in the Milbanke Sound Group, little is known about these lava flows.

Origins

The relationship of the Milbanke Sound Cones and to other volcanoes throughout British Columbia is not clear. In some classifications, they are grouped with 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 ...

because they are parallel with its east-west trend. However, this grouping is not widely accepted because the volcanoes are much younger than other magmatic features at the western end of the Anahim Volcanic Belt. The cause of this significant age change is because the Anahim Volcanic Belt has its origins from 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 ...

moving over the hypothesized

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 ...

. This is 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 ...

that is likely responsible for

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 ...

throughout the Anahim Volcanic Belt. Individual Anahim volcanoes generally become older west of

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 ...

, indicating that the North American Plate is moving in a westerly direction with respect to the hotspot, carrying the volcanoes along with it at a rate of to per year. Thus the hotspot model can not be used to explain the formation of the Milbanke Sound Group. However, the volcanic group is near the remnants of a 14 to 12 million year old magmatic feature that is interpreted to define the westernmost end of the Anahim hotspot track. A possible explanation for the origin of the Milbanke Sound Group is that it reflects a northern extension of the north-west trending

subduction 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 ...

-related

Garibaldi Volcanic Belt The Garibaldi Volcanic Belt is a northwest–southeast trending volcanic chain in the Pacific Ranges of the Coast Mountains that extends from Watts Point in the south to the Ha-Iltzuk Icefield in the north. This chain of volcanoes is located in ...

further south. This in turn is a segment of the

Cascade Volcanic Arc The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern Calif ...

in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

, which includes

Mount Baker Mount Baker (Lummi: '; nok, Kw’eq Smaenit or '), also known as Koma Kulshan or simply Kulshan, is a active glacier-covered andesitic stratovolcano in the Cascade Volcanic Arc and the North Cascades of Washington in the United States. Mount ...

and

Mount St. Helens Mount St. Helens (known as Lawetlat'la to the indigenous Cowlitz people, and Loowit or Louwala-Clough to the Klickitat) is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United St ...

. However, there is currently not enough data to support this suggestion. Its origins might also result from other tectonic processes that are currently not understood.

Monitoring

Currently, the Milbanke Sound Cones are 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 their magma chambers are. An existing network of

seismographs A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The outpu ...

has been established to monitor earthquakes, but is too far away to provide a good indication of what is happening beneath the cones. It may sense an increase in activity if a volcano becomes very restless, but this may only provide a warning for a large eruption. It might detect activity only once a volcano has started erupting. The

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 ...

, Canada's volcanic emergency notification program, was 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 Canada's borders, or an eruption significant enough to have an effect on Canada and its people. It focuses primarily on aviation safety because jet aircraft can quickly enter areas of volcanic ash. The program notifies all impacted agencies that have to deal with volcanic events. Aircraft are rerouted away from hazardous ash and people on the ground are notified of potential ash fall.

References

External links