Volcanology of Canada

Volcanic activity is a major part of the geology of Canada and is characterized by many types of volcanic landform, including lava flows, volcanic plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, submarine volcanoes, calderas, diatremes, and maars, along with less common volcanic forms such as tuyas and subglacial mounds.

Though Canada's volcanic history dates back to the Precambrian eon, at least 3.11 billion years ago, when its part of the North American continent began to form, volcanism continues to occur in Western and Northern Canada in modern times, where it forms part of an encircling chain of volcanoes and frequent earthquakes around the Pacific Ocean called the Pacific Ring of Fire. Because volcanoes in Western and Northern Canada are in relatively remote and sparsely populated areas and their activity is less frequent than with other volcanoes around the Pacific Ocean, Canada is commonly thought to occupy a gap in the Ring of Fire between the volcanoes of the western United States to the south and the Aleutian volcanoes of Alaska to the north. Even so, the mountainous landscapes of the Canadian provinces of Alberta, British Columbia, Yukon Territory, and the Northwest Territories include more than 100 volcanoes that have been active during the past two million years and whose eruptions have claimed many lives.

Volcanic activity is responsible for many of Canada's geological and geographical features and mineralization, including the nucleus of the North American continent, known as the Canadian Shield. Volcanism has led to the formation of hundreds of volcanic areas and extensive lava formations across Canada. The country's different volcano and lava types originate from different tectonic settings and types of volcanic eruptions, ranging from passive lava eruptions to violent explosive eruptions. Canada has a rich record of very large volumes of magmatic rock called large igneous provinces, represented by deep-level plumbing systems consisting of giant dike swarms, sill provinces and layered intrusions. The most capable large igneous provinces in Canada are Archean greenstone belts estimated at 3.8 to 2.5 billion years old, containing a rare volcanic rock called komatiite.

Eruption styles and volcano formations

Eastern Canada

The 2,677‑million-year-old Abitibi greenstone belt in Ontario and Quebec is one of the largest Archean greenstone belts on Earth and one of the youngest parts of the Superior craton which sequentially forms part of the Canadian Shield.
Komatiite lavas in the Abitibi greenstone belt (pictured) occur in four lithotectonic assemblages known as Pacaud, Stoughton-Roquemaure, Kidd-Munro and Tisdale. The Swayze greenstone belt further south is interpreted to be a southwestern extension of the Abitibi greenstone belt.

The Archean Red Lake greenstone belt in western Ontario consists of basaltic and komatiitic volcanics ranging in age from 2,925 to 2,940 million years old and younger rhyolite-andesite volcanics ranging in age from 2,730 to 2,750 million years old. It is situated in the western portion of the Uchi Subprovince, a volcanic sequence comprising a number of greenstone belts.

The 1884- to 1870‑million-year-old Circum-Superior Belt constitutes a large igneous province extending for more than from the Labrador Trough in Labrador and northeastern Quebec though the Cape Smith Belt in northern Quebec, the Belcher Islands in southern Nunavut, the Fox River and Thompson belts in northern Manitoba, the Winnipegosis komatiite belt in central Manitoba, and on the southern side of the Superior craton in the Animikie Basin of northwestern Ontario. Two volcano-sedimentary sequences exist in the Labrador Trough with ages of 2,170–2,140 million years and 1,883–1,870 million years. In the Cape Smith Belt, two volcanic groups range in age from 2,040 to 1,870 million years old called the Povungnituk volcano-sedimentary Group and the Chukotat Group. The Belcher Islands in eastern Hudson Bay contain two volcanic sequences known as the Flaherty and Eskimo volcanics. The Fox River Belt consists of volcanics, sills and sediments some 1,883 million years old while magmatism of the Thompson Belt is dated to 1,880 million years old. To the south lies the 1,864‑million-year-old Winnipegosis komatiites. In the Animikie Basin near Lake Superior, volcanism is dated 1,880 million years old.

During the Mesoproterozoic era of the Precambrian eon 1,109 million years ago, northwestern Ontario began to split apart to form the Midcontinent Rift System, also called the Keweenawan Rift. Lava flows created by the rift in the Lake Superior area were formed from basaltic magma. The upwelling of this magma was the result of a hotspot which produced a triple junction in the vicinity of Lake Superior. The hotspot made a dome that covered the Lake Superior area. Voluminous basaltic lava flows erupted from the central axis of the rift, similar to the rifting that formed the Atlantic Ocean. A '' failed arm'' extends north into mainland Ontario where it forms a geological formation known as the Nipigon Embayment. This failed arm includes Lake Nipigon, the largest lake entirely within the boundaries of Ontario.

Periods of volcanic activity occurred throughout central Canada during the Jurassic and Cretaceous periods. The source for this volcanism was a long-lived and stationary area of molten rock called the New England or Great Meteor hotspot. The first event erupted kimberlite magma in the James Bay lowlands region of northern Ontario 180 million years ago, creating the Attawapiskat kimberlite field. Another kimberlite event spanned a period of 13 million years 165 to 152 million years ago, creating the Kirkland Lake kimberlite field in northeastern Ontario. Another period of kimberlite volcanism occurred in northeastern Ontario 154 to 134 million years ago, creating the Lake Timiskaming kimberlite field. As the North American Plate moved westward over the New England hotspot, the New England hotspot created the magma intrusions of the Monteregian Hills in Montreal in southern Quebec. These intrusive stocks have been variously interpreted as the feeder intrusions of long extinct volcanoes that would have been active 125 million years ago, or as intrusions that never breached the surface in volcanic activity. The lack of a noticeable hotspot track west of the Monteregian Hills might be due either to failure of the New England mantle plume to pass through massive strong rock of the Canadian Shield, the lack of noticeable intrusions, or to strengthening of the New England mantle plume when it approached the Monteregian Hills region.

About 250 million years ago during the early Triassic period, Atlantic Canada lay roughly in the middle of a giant continent called Pangaea. This supercontinent began to fracture 220 million years ago when the Earth's lithosphere was being pulled apart from extensional stress, creating a divergent plate boundary known as the Fundy Basin. The focus of the rifting began somewhere between where present-day eastern North America and northwestern Africa were joined. During the formation of the Fundy Basin, volcanic activity never stopped as shown by the going eruption of lava along the Mid-Atlantic Ridge; an underwater volcanic mountain range in the Atlantic Ocean formed as a result of continuous seafloor spreading between eastern North America and northwestern Africa. As the Fundy Basin continued to form 201 million years ago, a series of basaltic lava flows were erupted, forming a volcanic mountain range on the mainland portion of southwestern Nova Scotia known as North Mountain, stretching from Brier Island in the south to Cape Split in the north. This series of lava flows cover most of the Fundy Basin and extend under the Bay of Fundy where parts of it are exposed on the shore at the rural community of Five Islands, east of Parrsboro on the north side of the bay. Large dikes wide exist throughout southernmost New Brunswick with ages and compositions similar to the North Mountain basalt, indicating these dikes were the source for North Mountain lava flows. However, North Mountain is the remnants of a larger volcanic feature that has now been largely eroded based on the existence of basin border faults and erosion. The hard basaltic ridge of North Mountain resisted the grinding of ice sheets that flowed over this region during the past ice ages, and now forms one side of the Annapolis Valley in the western part of the Nova Scotia peninsula. The layering of a North Mountain lava flow less than thick at McKay Head, closely resemble that of some Hawaiian lava lakes, indicating Hawaiian eruptions occurred during the formation of North Mountain.

The Fogo Seamounts, located offshore of Newfoundland to the southwest of the Grand Banks, consists of submarine volcanoes with dates extending back to the Early Cretaceous period at least 143 million years ago. They may have one or two origins. The Fogo Seamounts could have formed along fracture zones in the Atlantic seafloor because of the large number of seamounts on the North American continental shelf. The other explanation for their origin is they formed above a mantle plume associated with the Canary or Azores hotspots in the Atlantic Ocean, based on the existence of older seamounts to the northwest and younger seamounts to the southeast. The existence of flat-topped seamounts throughout the Fogo Seamount chain indicate some of these seamounts would once have stood above sea level as islands that would have been volcanically active. Their flatness is due to coastal erosion, such as waves and winds. Other submarine volcanoes offshore of Eastern Canada include the poorly studied Newfoundland Seamounts.

Western Canada

The Flin Flon greenstone belt in central Manitoba and east-central Saskatchewan is a collage of deformed volcanic arc rocks ranging in age from 1,904 to 1,864 million years old during the Paleoproterozoic sub-division of the Precambrian eon. Volcanic activity between 1,890 and 1,864 million years ago produced calc-alkaline andesite-rhyolite magmas and rare shoshonite and trachyandesite magmas while the 1,904‑million-year-old arc volcanism occurred in one or more separate volcanic arcs that were possibly characterized by rapid subduction of thin oceanic crust and large back-arc basins. In contrast, the younger 1,890‑million-year-old volcanics indicate evidence of crustal thickening. This was due to long-term growth of the volcanic arcs by continuous volcanic activity and tectonic thickening associated with arc collisions and successive arc deformation. This in turn followed a massive mountain building event called the Trans-Hudson orogeny.

The Cretaceous period 145-66 million years ago was a period for active kimberlite volcanism in the Western Canadian Sedimentary Basin of Alberta and Saskatchewan. The Fort à la Corne kimberlite field in central Saskatchewan formed 104 to 95 million years ago during the Early Cretaceous. Unlike most kimberlite fields on Earth, the Fort à la Corne kimberlite field formed during more than one eruptive event. Its kimberlites are among the most complete examples on Earth, preserving kimberlite pipes and maar volcanoes. The Northern Alberta kimberlite province consists of three kimberlite fields known as the Birch Mountains, Buffalo Head Hills and the Mountain Lake cluster. The Birch Mountains kimberlite field consists of eight kimberlite pipes known as Phoenix, Dragon, Xena, Legend and Valkyrie, dating approximately 75 million years old. The Buffalo Head Hills kimberlite field was dominated by explosive kimberlite volcanism from 88 million years ago to 81 million years ago, forming maars. Kimberlites of the Buffalo Head Hills field are similar to those associated with the Fort à la Corne kimberlite field in central Saskatchewan. The kimberlite pipes of the Mountain Lake cluster were formed during a similar timespan with the Birch Mountains field 77 million years ago.

Formation of the Pacific Northwest

The Canadian portion of the Pacific Northwest began forming during the early Jurassic period when a group of active volcanic islands collided against a pre-existing continental margin and coastline of Western Canada. These volcanic islands, known as the Intermontane Islands by geoscientists, were formed on a pre-existing tectonic plate called the Intermontane Plate about 245 million years ago by subduction of the former Insular Plate to its west during the Triassic period. This subduction zone records another subduction zone called the Intermontane Trench under an ancient ocean between the Intermontane Islands and the former continental margin of Western Canada called the Slide Mountain Ocean. This arrangement of two parallel subduction zones is unusual in that very few twin subduction zones exist on Earth; the Philippine Mobile Belt off the eastern coast of Asia is an example of a modern twin subduction zone. As the Intermontane Plate drew closer to the pre-existing continental margin by ongoing subduction under the Slide Mountain Ocean, the Intermontane Islands drew closer to the former continental margin and coastline of Western Canada, supporting a volcanic arc on the former continental margin of Western Canada. As the North American Plate drifted west and the Intermontane Plate continued to drift east to the ancient continental margin of Western Canada, the Slide Mountain Ocean began to close by ongoing subduction under the Slide Mountain Ocean. This subduction zone eventually jammed and shut down completely about 180 million years ago, ending the arc volcanism on the ancient continental margin of Western Canada and the Intermontane Islands collided, forming a long chain of deformed volcanic and sedimentary rock called the Intermontane Belt, which consists of deeply cut valleys, high plateaus, and rolling uplands. This collision also crushed and folded sedimentary and igneous rocks, creating a mountain range called the Kootenay Fold Belt which existed in far eastern British Columbia.

After the sedimentary and igneous rocks were folded and crushed, it resulted in the creation of a new continental shelf and coastline. The Insular Plate continued to subduct under the new continental shelf and coastline about 130 million years ago during the mid Cretaceous period after the formation of the Intermontane Belt, supporting a new continental volcanic arc called the Omineca Arc. Magma rising from the Omineca Arc successfully connected the Intermontane Belt to the mainland of Western Canada, forming a chain of volcanoes in British Columbia that existed discontinuously for about 60 million years. The ocean lying offshore during this period is called the Bridge River Ocean. It was also during this period when another group of active volcanic islands existed along the newly built continental shelf and coastline. These volcanic islands, known as the Insular Islands, were formed on the Insular Plate by subduction of the former Farallon Plate to its west during the early Paleozoic era. As the North American Plate drifted west and the Insular Plate drifted east to the continental margin of Western Canada, the Bridge River Ocean began to close by ongoing subduction under the Bridge River Ocean. This subduction zone eventually jammed and shut down completely 115 million years ago, ending the Omineca Arc volcanism and the Insular Islands collided, forming the Insular Belt. Compression resulting from this collision crushed, fractured and folded rocks along the continental margin. The Insular Belt then welded onto the continental margin by magma that eventually cooled to create a large mass of igneous rock, creating a new continental margin. This large mass of igneous rock is the largest granite outcropping in North America.

The Farallon Plate continued to subduct under the new continental margin of Western Canada after the Insular Plate and Insular Islands collided with the former continental margin, supporting a new chain of volcanoes on the mainland of Western Canada called the Coast Range Arc about 100 million years ago during the Late Cretaceous epoch. Magma ascending from the Farallon Plate under the new continental margin burned their way upward through the newly accreted Insular Belt, injecting huge quantities of granite into older igneous rocks of the Insular Belt. At the surface, new volcanoes were built along the continental margin. The basement of this arc was likely Early Cretaceous and Late Jurassic age intrusions from the Insular Islands.

One of the major aspects that changed early during the Coast Range Arc was the status of the northern end of the Farallon Plate, a portion now known as the Kula Plate. About 85 million years ago, the Kula Plate broke off from the Farallon Plate to form an area of seafloor spreading called the Kula-Farallon Ridge. This change apparently had some important ramifications for regional geologic evolution. When this change was completed, Coast Range Arc volcanism returned and sections of the arc were uplifted considerably in latest Cretaceous time. This started a period of mountain building that affected much of western North America called the Laramide orogeny. In particular a large area of dextral transpression and southwest-directed thrust faulting was active from 75 to 66 million years ago. Much of the record of this deformation has been overridden by Tertiary age structures and the zone of Cretaceous dextral thrust faulting appears to have been widespread. It was also during this period when massive amounts of molten granite intruded highly deformed ocean rocks and assorted fragments from pre-existing island arcs, largely remnants of the Bridge River Ocean. This molten granite burned the old oceanic sediments into a glittering medium-grade metamorphic rock called schist. The older intrusions of the Coast Range Arc were then deformed under the heat and pressure of later intrusions, turning them into layered metamorphic rock known as gneiss. In some places, mixtures of older intrusive rocks and the original oceanic rocks have been distorted and warped under intense heat, weight and stress to create unusual swirled patterns known as migmatite, appearing to have been nearly melted in the procedure.

Volcanism began to decline along the length of the arc about 60 million years ago during the Albian and Aptian faunal stages of the Cretaceous period. This resulted from the changing geometry of the Kula Plate, which progressively developed a more northerly movement along the mainland of Western Canada. Instead of subducting beneath Western Canada, the Kula Plate began subducting underneath southwestern Yukon and Alaska during the early Eocene period. Volcanism along the entire length of the Coast Range Arc shut down about 50 million years ago and many of the volcanoes have disappeared from erosion. What remains of the Coast Range Arc to this day are outcrops of granite when magma intruded and cooled at depth beneath the volcanoes, forming the Coast Mountains. During construction of intrusions 70 and 57 million years ago, the northern motion of the Kula Plate might have been between and per year. However, other geologic studies determined the Kula Plate moved at a rate as fast as per year.

Cascadia subduction zone complexes

As the last of the Kula Plate decayed and the Farallon Plate advanced back into this area from the south, it once again started to subduct under the continental margin of Western Canada 37 million years ago, supporting a chain of volcanoes called the Cascade Volcanic Arc. At least four volcanic formations along the British Columbia Coast are associated with Cascadia subduction zone volcanism. The oldest is the eroded 18-million-year-old Pemberton Volcanic Belt which extends west-northwest from south-central British Columbia to Haida Gwaii in the northeast where it lies west of mainland British Columbia. In the south it is defined by a group of epizonal intrusions and a few erosional remnants of eruptive rock. Farther north in the large Ha-Iltzuk and Waddington icefields, it includes two large dissected calderas called Silverthrone Caldera and Franklin Glacier Complex while Haida Gwaii to the northeast contains a volcanic formation ranging in age from Miocene to Pliocene