This is a good article. Follow the link for more information.

Level Mountain

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search

Level Mountain
A satellite view of two large mountains near the crest of a mountain range to the southwest.
Satellite image of Level Mountain (middle) and Heart Peaks (upper-left corner). This image is approximately 80 km (50 mi) E-W.
Highest point
Peak Meszah Peak
Elevation 2,166 m (7,106 ft)
Coordinates 58°28′43″N 131°26′14″W / 58.47861°N 131.43722°W / 58.47861; -131.43722
Dimensions
Length 70 km (43 mi)
Width 45 km (28 mi)
Area 1,800 km2 (690 sq mi)
Volume 860 km3 (210 cu mi)
Geography
Level Mountain is located in British Columbia
Level Mountain
Location map of Level Mountain
Country Canada
Province British Columbia
District Cassiar Land District
Range coordinates 58°23′26″N 131°24′06″W / 58.39056°N 131.40167°W / 58.39056; -131.40167Coordinates: 58°23′26″N 131°24′06″W / 58.39056°N 131.40167°W / 58.39056; -131.40167
Topo map NTS 104J/06
Geology
Formed by Shield volcano, stratovolcano, lava domes, spatter cones, subglacial volcanoes
Age of rock Neogene-to-Quaternary
Type of rock Igneous
Volcanic arc/belt Northern Cordilleran Volcanic Province
Last eruption Unknown[1]

Level Mountain is a massive complex volcano in the Northern Interior of British Columbia, Canada. It is located 50 km (31 mi) north-northwest of Telegraph Creek and 60 km (37 mi) west of Dease Lake on the Nahlin Plateau. With a maximum elevation of 2,166 m (7,106 ft), it is the third highest of five large complexes in an extensive north-south trending volcanic zone. Much of the mountain is gently-sloping; when measured from its base, Level Mountain is about 1,100 m (3,600 ft) tall, slightly taller than its neighbour to the northwest, Heart Peaks. The lower broader half of Level Mountain consists of a shield-like edifice while its upper half has a more steep, jagged profile. Its large summit is dominated by the Level Mountain Range, a small mountain range with prominent peaks cut by deep valleys. These valleys serve as a radial drainage for several small streams that flow from the volcano. Meszah Peak is the only named peak in the Level Mountain Range.

The mountain began forming about 15 million years ago, with volcanism continuing up until geologically recent times. There have been four stages of activity throughout the long volcanic history of Level Mountain. The first stage commenced 14.9 million years ago with the eruption of voluminous lava flows; these lavas created a large shield volcano. The second stage began 7.1 million years ago to form a structurally complicated stratovolcano located centrally atop the shield. A series of lava domes were established during the third stage, which began 4.5 million years ago. This was followed by the fourth and final stage with the eruption of lava flows and small volcanic cones in the last 2.5 million years. A wide range of rock types were produced throughout these stages, of which alkali basalts and ankaramites are the most voluminous. They were deposited by different types of volcanic eruptions characterized by fluid lava flows and explosivity.

Level Mountain can be ecologically divided into three sections: an alpine climate at its summit, an Abies lasiocarpa forest on its flanks and a Picea glauca forest at its base. An extensive wild animal community once thrived in the area of Level Mountain. This included a wide range of animal species with caribou being the most abundant. Humans had arrived at Level Mountain by the early 1900s, followed by geological studies of the mountain in the 1920s. This remote area of Cassiar Land District has a relatively dry environment compared to the Coast Mountains in the west.

Geology[edit]

Background[edit]

Level Mountain is part of the Northern Cordilleran Volcanic Province (NCVP), a broad area of volcanoes extending from northwestern British Columbia northwards through Yukon into easternmost Alaska. Volcanism in this geologic province can be traced as far back as 20 million years ago with the emplacement of alkali basalt in western Yukon. Several types of volcanic eruptions have since created different landforms across the NCVP, including shield volcanoes, lava domes, stratovolcanoes and cinder cones. Other volcanic formations, notably subglacial volcanoes, take their shape from the environment they formed, regardless of the type of magma they produced.[2] The NCVP contains over 100 volcanoes and is the most volcanically active area in Canada, with eruptions expected to occur roughly every 100 years.[3][4]

A geologic diagram of Earth's crust and lithosphere being stretched apart.
Cross section of a general rift

The NCVP is underlain by four large crustal fragments, namely Stikinia, Yukon-Tanana, Cassiar and Cache Creek. Stikinia comprises volcanic, plutonic and sedimentary rocks that were created in an island arc environment during the Paleozoic and Mesozoic eras. Mélange and abyssal peridotites, formed largely in an ancient oceanic basin, are the primary rocks of the Cache Creek Terrane. These are also Paleozoic to Mesozoic in age and are intersected by younger granitic intrusions. Yukon-Tanana and Cassiar consist of sedimentary and metamorphic rocks derived from the North American continent. The rocks of these two terranes are displaced and autochthonous in nature.[2]

A number of mechanisms have been proposed to interpret the origin of volcanism in the NCVP. This includes slab windows, mantle plumes, crustal extension and deglaciation. The most common and best mechanism used to explain NCVP volcanic activity is incipient rifting of the North American Plate caused by crustal extension. As the continental crust stretches, the near surface rocks fracture along steeply dipping cracks parallel to the rift known as faults. Mafic magma rises along these fractures to create fluid lava flows, although more viscous felsic magma also makes its way to the surface and can produce explosive eruptions. Two major structural features, the Tintina and Denali-Coast fault systems, run parallel with the NCVP. Both structures have had strike-slip motions since the Cretaceous period, which has resulted in several hundred kilometres of crustal displacement.[2]

Structure[edit]

The mountain comprises two principal components: a voluminous basal shield volcano and an eroded stratovolcano cap.[5] The lower but more extensive basal shield volcano rises from an elevation of 900 to 1,400 m (3,000 to 4,600 ft) above the surrounding forested lowlands much like an inverted dishware plate.[5][6] It consists of four distinctive stratigraphic units comprising thin mafic lava flows.[5] Individual flows have an average thickness of 2 to 3 m (6.6 to 9.8 ft) but can range from less than 1 m (3.3 ft) to more than 10 m (33 ft) thick.[6] They are separated by thin discontinuous breccias, sporadic tuff horizons and local lenses of fluvial, lacustrine and glacial sediment.[5] This volcanic edifice forms a broad, oval-shaped, north-south trending lava plateau that local streams flow on.[2][6] It measures 70 km (43 mi) long and 45 km (28 mi) wide with a net altitudinal reach of only 750 m (2,460 ft). The south and west sides of the plateau are marked by a well-defined but dissected escarpment. In contrast, the north and east plateau boundaries are less clear. From an elevation of 1,400 m (4,600 ft) onwards the overlying stratovolcano is dominant. Ridges and peaks prevail at an elevation of 1,520 m (4,990 ft) and comprise the Level Mountain Range. These rise more steeply to 1,980 m (6,500 ft), eventually reaching the highest point of 2,166 m (7,106 ft) at Meszah Peak.[6] Therefore, when viewed from a distance, Level Mountain appears remarkably flat except for a number of black peaks on its summit which have the appearance of enormous volcanic cones.[7]

Level Mountain is the largest volcano in the NCVP with respect to both volume and area covered.[5] It has a volume of approximately 860 km3 (210 cu mi) and an area of about 1,800 km2 (690 sq mi), although some estimates of its areal extent are as much as 3,000 km2 (1,200 sq mi).[5][6] Smaller but related volcanoes include Hoodoo Mountain, Heart Peaks, Maitland Volcano and the Mount Edziza volcanic complex. Because of Level Mountain's great extent it can be seen from outer space. This, coupled with elevation and snow, helps define the geology of the region.[5] Level Mountain lies on the Nahlin Plateau, a subdivision of the larger Stikine Plateau that is dominated by the volcano.[6][8] The basement of the shield consists largely of felsic igneous rocks comprising northern Stikinia, but sedimentary rocks are also present below the lava plateau escarpment.[2][6] Two major northwest trending faults straddle Level Mountain, both of which were active during the Mesozoic and Cenozoic eras.[5] The King Salmon Fault forms a geological boundary between island arc rocks of Stikinia and seafloor rocks of the Cache Creek Terrane.[9] Paleozoic to Mesozoic rocks are exposed in the hanging wall of this thrust fault and are intensely cleaved, particularly near the sole of the thrust.[10] The other planar fracture, Nahlin, is an east-dipping thrust fault extending several hundred kilometres from northern British Columbia into southern Yukon.[11]

A map explaining the geologic structure of a large volcano.
Geologic map of Level Mountain showing the basal shield volcano and the stratovolcano cap

Several rock types with varying chemical compositions make up Level Mountain. Ankaramites and alkali basalts are the primary volcanic rocks comprising the basal shield. Alkali basalts form columnar jointed lava flows, vesicular lava flows, dikes and scoria while ankaramites are present as dark-coloured lava flows with several columnar cooling units. Trachybasalts, phonolites, trachytes, peralkaline trachytes, pantellerites, comendites and rhyolites form the overlying stratovolcano and domes. They comprise dikes, welded tuffs, pitchstones, volcanic plugs, laccoliths and flows. Trachybasalts are in the form of two textural types: phenocryst-rich lava flows and fragmental flow agglomerates. Phonolites are vesicular and pumiceous in nature, although phonolites with trachytic texture are also present. Trachytes and peralkaline trachytes are the primary volcanic rocks in the Level Mountain Range. Comendites appear to have erupted fluidly, forming lava tubes. Rhyolites are in the form of stubby lava flows and domes.[12]

Intense glaciation has taken place at Level Mountain in the last 5.33 million years, as shown by the presence of strongly developed glacial grooves reaching elevations over 1,675 m (5,495 ft). This evidence indicates that much of the mountain was covered by ice during past glacial periods, with the latest glacial period ending approximately 12,000 years ago.[13] A series of U-shaped valleys have been carved into the volcano by radially directed alpine glaciers.[5] These serve as a radial drainage for at least six small streams: Dudidontu, Kakuchuya, Beatty, Lost, Kaha and Little Tahltan. Those that flow from the Level Mountain Range drain across the lava plateau in a pinwheel-like fashion; Kakuchuya and Dudidontu contain a series of small lakes. The Kakuchuya and Beatty creek valleys have been eroded to a level below that of the plateau surface.[6] Also dissecting Level Mountain are V-shaped stream canyons along the lava plateau margin, exposing a section of Tertiary basalts along the Grand Canyon of the Stikine.[5] Periglacial processes, such as cryoturbation and stone stripping, occur on the mountain at elevations greater than 1,250 m (4,100 ft). Cryoturbation takes place mainly on flat and gently sloping areas while stone stripping happens primarily on gently sloping areas adjacent to peaks of the Level Mountain Range. Some of the steeper slopes of the Level Mountain Range are confined to nivation and solifluction. Snow avalanches are limited only to the Level Mountain Range and the steepest slopes.[6]

Extensive tectonic uplift occurred at Level Mountain and elsewhere on the Stikine Plateau during the Neogene period (23.03–2.58 million years ago).[5][8] This resulted in dissection of the plateau surface by stream erosion which varies greatly across the region.[8] The youthful V-shaped gorges along the lava plateau margin are signs of continuing uplift at Level Mountain, which may in part be caused by doming of the volcano during volcanism.[5][13] Several outcrops of alkali basalt are present south of Kennicott Lake and the Tahltan River. These are comparable in age to the Level Mountain shield volcano and may represent erosional remnants of this structure.[13]

Volcanic history[edit]

Level Mountain has experienced volcanic eruptions sporadically for the last 15 million years, making it the most persistent volcano of the NCVP. More than 20 eruptive centres are present on the summit and flanks of the complex. These have produced mainly felsic and mafic lavas, a chemical composition range typical of bimodal volcanism. Such volcanism commonly occurs at hotspots, continental rifts and leaky transform faults. The existence of olivine, orthopyroxene and spinel xenocrysts in Level Mountain basalt suggest that volcanism at the complex originated from the upper mantle.[5] Hiatuses of up to a million years or more can be expected between periods of volcanic activity at Level Mountain.[14]

A map explaining the geology of a large volcano
Geologic map of Level Mountain showing eruptive products and eruptive centres

Like several other volcanoes in northern British Columbia, Level Mountain was volcanically active during past glacial periods. Its involvement with glaciation resulted in several interactions between magma and ice, affording multiple examples of glaciovolcanic processes. Evidence for contemporaneous volcanism and glaciation is widespread throughout the mountain. This includes interlayered unconsolidated fluvioglacial and tuffaceous deposits, tills and glacial erratics at the base of tuffs and lava flows, lahars composed of till and agglomerate, tuyas on the uppermost surface of the shield and as outliers, till cemented by siliceous sinter and the presence of freshwater pillow basalts and volcano-glacial tuff breccias.[5] It is possible that geothermal outputs at Level Mountain had an influence on dynamics of past ice sheets much like the modern Grímsvötn caldera is an important heat source beneath Vatnajökull in Iceland.[13] However, like other large NCVP volcanoes, much of Level Mountain was formed prior to glaciation.[6]

Initial volcanism of the NCVP 20 million years ago was sporadic, producing small volumes of material.[2] The eruption rate increased markedly to around 0.0001 km3 (2.4×10−5 cu mi) per year when volcanism began at Level Mountain 14.9 million years ago as part of the shield-building stage.[2][5] This stage of volcanism ended 6.9 million years ago with completion of the basal shield volcano. A second stage of volcanism occurred at Level Mountain between 7.1 and 5.3 million years ago to create the stratovolcano cap.[5] The rate of volcanism in the NCVP during this stage of activity increased again to 0.0003 km3 (7.2×10−5 cu mi) per year.[2] Dome-forming eruptions were dominant during the third eruptive stage 4.5 to 2.5 million years ago during which a magmatic lull appears to have been present throughout the NCVP.[5][2] A fourth and final stage of volcanism at Level Mountain commenced in the last 2.5 million years with the formation of minor volcanic cones and lava flows.[1][13] The NCVP volcanism rate has since remained relatively constant at 0.0001 km3 (2.4×10−5 cu mi) per year with volcanism of the final stage having continued possibly in the last 10,000 years.[1][2] Modern NCVP volcanism rates are much less than those estimated for Hawaii or the Cascade Volcanic Arc of western North America.[2]

Mafic shield-building stage[edit]

The mafic shield-building stage began with the eruption of thin mafic lava flows over an erosion surface.[5] Successive eruptions sent lava pouring in all directions from central vents, forming a broad, gently sloping volcano of flat, domical shape, with a profile much like that of a warrior's shield.[5][13] Alkali basalts and ankaramites were the primary lavas produced during this stage of activity which, due to their low silica content, were able to travel great distances away from their source.[13] These lavas also erupted from vents on the flanks of the volcano. Blocky 'a'a and ropy pāhoehoe flows characterized the fluid and effusive nature of volcanism at Level Mountain during the mafic shield-building stage.[5]

Lava flows of the mafic shield-building stage comprise four sub-horizontal units. Initial volcanism produced a 53 m (174 ft) thick sequence of columnar jointed alkali basalt flows and altered grey-green vesicular basalts which form the lowest unit. Subsequent activity deposited the overlying second 107 m (351 ft) thick unit. This comprises up to seven 7.6 m (25 ft) thick columnar cooling units of alkali basalt separated by buff-weathered vesicular lava flows. Renewed volcanism sent a series of massive ankaramite lava flows over the second unit and have a total thickness of 76 m (249 ft). These lava flows, comprising the third unit, are spheroidally weathered. The mafic shield-building stage culminated with emplacement of the fourth and highest unit. Eight to ten sequences of columnar jointed alkali basalt comprise this unit and have a total thickness of 122 m (400 ft).[12] All four sub-horizontal units of the mafic shield-building stage were deposited over a timespan of six million years.[5]

Bimodal stratovolcano stage[edit]

A broad gently sloping mountain cut by a U-shaped valley rising over a vegetated plain
A U-shaped valley of Level Mountain with extensive elevated plateau in the foreground

After the basal shield volcano was constructed, several vents produced oversaturated, undersaturated, peralkaline and metaluminous lavas.[5] This tremendous variation in the erupted magmas and influence of adjacent vents gave rise to a high and volumnous complex bimodal stratovolcano centrally located atop the shield. Mapping indicates that the headwaters of Kakuchuya Creek were the site of this large stratovolcano cap and that it grew over 2,500 m (8,200 ft) in elevation.[5][12] Volcanic rocks of felsic composition, notably peralkaline trachyte and comendite, were the primary products comprising this edifice, forming more than 80% of its volume.[5] Explosive eruptions during this stage of activity deposited basalt agglomerates, ash fall and ash flow tuffs.[12] Peralkaline felsic lava flows reached 7 km (4.3 mi) long and 3 to 8 m (9.8 to 26.2 ft) thick.[5] The eruptive products of the bimodal stratovolcano stage cover an area roughly 20 km (12 mi) long and 20 km (12 mi) wide.[12]

Peralkalinity had remarkable effects on lava morphology and mineralogy during the bimodal stratovolcano stage. A unique characteristic of the peralkaline felsic lava flows produced during this stage of activity is that although they were high in silica content, the flows were overly fluid in nature. This is because the peralkaline content decreased the viscosity of the flows a minimum of 10–30 times over that of calc-alkaline felsic flows. As a result of this fludity, the peralkaline felsic lava flows were able to form small-scale folds and 1 to 2 m (3.3 to 6.6 ft) diameter lava tubes. The liquidus temperatures of these flows were in excess of 1,200 °C (2,190 °F) with viscosities as low as 100,000 poise. Glaciation and volcanism were contemporaneous during the bimodal stratovolcano stage as shown by the existence of volcano-glacial deposits in the volcanic edifice.[5]

Felsic dome-forming stage[edit]

By the Pliocene epoch, radially directed alpine glaciers had eroded away much of the bimodal stratovolcano cap, leaving behind a series of U-shaped valleys with intervening ridges that comprise the Level Mountain Range.[5][12] This dissection of the bimodal stratovolcano was followed by the felsic dome-forming stage. Eruptions of felsic magma were predominantly viscous during this stage of activity, resulting in the magma piling up thick around volcanic vents to create a series of lava domes. Individual domes grew up to 94,000,000 m3 (3.3×109 cu ft) in the glacially eroded core of the bimodal stratovolcano.[5]

Quaternary stage[edit]

Following the emplacement of late Pliocene lava domes, lesser activity continued into the Quaternary period (2.58 million years ago to present).[1] Initial volcanism began on the summit of the volcano, depositing lava in and adjacent to the Level Mountain Range. This activity is indirectly dated as Pleistocene age (2.58–0.0117 million years old), on the bases of the presence of subglacial and/or intraglacial deposits.[2] Meszah Peak, the highest point of both Level Mountain and the Level Mountain Range, was volcanically active during this eruptive period.[15][16]

More recent volcanic eruptions have been a topic of debate among scientists. Several small basaltic vents on the broad summit of Level Mountain were considered by T. S. Hamilton and C. M. Scafe (1977) to have formed during the Holocene epoch (0.0117 million years ago to present), although Holocene activity has been regarded as uncertain by B. R. Edwards and J. K. Russell (2000).[1] These younger eruptions produced spatter cones, agglomerate and volcanic bombs, as well as trachybasalt, mugearite and hawaiite lava flows. This activity was concentrated on and near Meszah Peak and on ridges 14 km (8.7 mi) southeast and 10 km (6.2 mi) south-southwest of Meszah.[13] Exposed on the south side of Level Mountain near Hatchau Lake is a rock outcrop consisting of boulders cemented by calcareous sinter. This suggests an area of hot spring activity that may be related to volcanism at the volcano.[17]

Two 5 to 10 mm (0.20 to 0.39 in) thick tephra deposits, collectively known as the Finlay tephras, are situated between sand, silt, mud and gravel in the Dease Lake and Finlay River areas. They both range in composition from phonolitic to trachytic and are high in iron(II) oxide, indicating that the tephras were likely extruded from a single volcano. Radiocarbon dating of terrestrial plant macrofossils directly overlying the youngest tephra deposit suggest an early Holocene age for this volcanic material. Because Level Mountain has received little scientific study and it is debated on whether or not Holocene volcanic rocks are present, the volcano is a possible source for these tephra deposits along with Hoodoo Mountain, Heart Peaks and the Mount Edziza complex.[18]

Geography[edit]

Plants and animals[edit]

A group of small green-leaved, brown-stemmed trees.
A pair of bog birch (Betula pumila) trees

Level Mountain is characterized by three biophysical zones. The first zone, below an elevation of 1,200 m (3,900 ft), is predominated by vegetation of the Pinaceae and Betulaceae families. Lodgepole pine is associated with communities of kinnikinnick, bog birch, Altai fescue and moss. Mature white spruce and lodgepole pine forests predominate north of Level Mountain, with bog birch occurring in river valley bottoms. Between elevations of 1,200 and 1,540 m (3,940 and 5,050 ft) lies the second biophysical zone. It is characterized by a harsh climate with wind, cold temperatures, snow and short growing seasons. Bog birch is the dominant vegetation, forming extremely large areas of continuous cover. Mature alpine fir forests have been extensively burned by large wildfires and are now limited only to the northern flank of Level Mountain. The third biophysical zone consists largely of an alpine tundra above an elevation of 1,540 m (5,050 ft) on the upper lava plateau. As a result, this region lacks trees because of its high altitude. The most common vegetation is Arctic bluegrass, dwarf willows, louseworts, Altai fescue, boreal mugwort and alpine lichens and mosses. Bog birch less than 1 m (3.3 ft) in height form at lower elevations of this biophysical zone. Common plants on the sparsely vegetated slopes of the Level Mountain Range are sedges, prickly and alpine brook saxifrages, dwarf willows, moss campion, Arctic bluegrass and alpine lichens and mosses.[6]

Several animal species inhabit Level Mountain, notably brown bears, wolves, long-tailed jaegers, caribou, mountain goats, ptarmigans, moose, long-tailed ducks and Stone sheep. Wolves occupy valleys and use the alpine areas for hunting and denning. Brown bears are common in the alpine and are potential predators of newborn caribou calves. The caribou at Level Mountain form a herd that is part of a larger population ranging west of the Dease River and north of the Stikine River into Yukon. More than 400 caribou were identified at Level Mountain in 1978, although the Ministry of Environment and Parks considered the herd to be declining due to poor recruitment. By 1980, the caribou population was estimated to have been roughly 350.[6]

Soils[edit]

A variety of soil types with differing physical properties are found at Level Mountain. Shallow, coarse, textured and steep to strongly sloping soils dominate peaks of the Level Mountain Range and owe their origin to weathering of volcanic rocks. These well drained soils are strongly acidic and xeric in nature and show little or no horizon development. The gently undulating alpine portions of Level Mountain have been affected by cryoturbation, resulting in patterned ground in which coarse material has been separated from each other as patches or stripes. Surface horizons are strongly to very strongly acidic, becoming medium to slightly acidic approximately 50 cm (20 in) in depth. At lower elevations, soils develop on fluvio-glacial deposits. Many of these fluvio-glacial materials contain a high percentage of fine materials while the soils which have developed from them contain a subsurface horizon enriched by clay accumulation. Very poorly drained organic soils are extensive on the southern portion of the lava plateau.[6]

Climate[edit]

Satellite view of a gently sloping mountain with large valleys carved into its flanks.
Level Mountain as seen looking to the north. This satellite image shows the gently sloping surface of the mountain.

The climate of Level Mountain is influenced by the presence of the Coast Mountains 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 Nahlin Plateau, casting a rain shadow over Level Mountain. Because the volcano has a gently sloping and flat profile, it has subtle differences in climate, particularly at the low to upper-mid elevations. Therefore a relatively homogeneous climate extends over Level Mountain, with only gradual temperatures and precipitation gradients occurring altitudinally. As a result, large mammals do not have a wide diversity of local climates from which to choose.[6]

Travel from high to low elevations below 1,700 m (5,600 ft) in the winter can be difficult for some mammals due to the accumulation of snow. Above 1,700 m (5,600 ft), exposure to local winds is improved and ridges of snow are cleared on steeper slopes. Wind speeds increase with elevation but the distribution of wind over the area is fairly uniform.[6] Level Mountain experiences relatively light snowfall unlike the Coast Mountains.[5]

During the late May and early June calving season, winds predominate from a southerly quadrant. Calm conditions are infrequent and average monthly wind speeds are on the order of 3 to 4 m (9.8 to 13.1 ft) per second. At an elevation of 1,370 m (4,490 ft), there is a 15–20% chance that precipitation will occur as snow; that probability increases with altitude. Mixed rain and snow are common at that time of the year. Reduced air drainage, coupled with clear, calm nights, lowers minimum temperatures in the summer, reducing the frost-free period.[6]

Human history[edit]

Occupation[edit]

In 1891–1892, the Hudson's Bay Company constructed a trail from the junction of the Sheslay and Hackett rivers to the southwestern slope of Level Mountain.[19] Here, the company had built a trading post by 1898 named Egnell after its operator Albert Egnell.[19][20] After spending one winter at the post, Egnell found that there was no trade to be done in the area and the post was subsequently abandoned. Egnell died on June 22, 1900 from an accidental gun shot to his leg by his son, McDonald, five days earlier and was buried at the Liard Post near the mouth of the Dease River.[21] In the early 1900s, the Egnell Post served as a repair station for the 3,100 km (1,900 mi) long Yukon Telegraph Line, which extended from Ashcroft, British Columbia to Dawson City, Yukon.[20][22] A small settlement consisting of a mission house and a number of other buildings had been established on the site by 1944. This settlement, named Sheslay, has since been abandoned.[20] Although there is no human population within 30 km (19 mi) of Level Mountain, more than 630 live within 100 km (62 mi) of the volcano.[1]

Geological studies[edit]

Level Mountain basalt and andesite flows were presented in the 1926 Canada Department of Mines Summary Report, 1925, Part A. The andesites were described as porphyritic rocks with phenocrysts of feldspar of various size in a greyish or greenish matrix. Both hornblende and augite andesites were noted to have been represented under a microscope. The basalts were described as black rocks with basic plagioclase with or without olivine and were noted in many cases to contain a considerable percentage of brownish glass. Although there was not sufficient time available to study these flows in detail it was revealed at several points that the andesites formed the older and the basalts the younger flows. G. M. Dawson of the Geological Survey of Canada was able to demonstrate that on the Stikine River there were at least four flows of basalt. The basalts and andesites were considered to be younger than all the rocks they were observed in contact with, namely granitic intrusives, porphyries and greenstones. More definite evidence as to their age was obtained by W. A. Johnston and F. A. Kerr of the Geological Survey of Canada who placed them in the Tertiary with some of the most recent flows of the Stikine valley probably belonging to the Pleistocene.[7]

3D depiction of a low broad vastly deforested mountain
A 3D model of Level Mountain

Level Mountain was demonstrated in the 1920s as a possible source for the extensive lavas in the neighbouring Tuya volcanic field.[7] This field, consisting of flat-topped summits or benches, was considered to have formed as a result of block faulting or by erosion of a formerly much more extensive surface underlain by horizontally bedded volcanic rocks.[23] The possibility of Level Mountain being a source for the Tuya field lavas would deteriorate in the 1940s when Canadian volcanologist Bill Mathews revealed that the flat-topped, steep-sided summits were not products of faulting or erosion but were rather individual volcanoes formed by eruptions of lava into lakes thawed through an ice sheet. Mathews coined the term "tuya" for these subglacial volcanoes after Tuya Butte which is located in the Tuya volcanic field. The recognition of Level Mountain as a long-lived volcano in contrast to the small Tuya field volcanoes has given it status as a separate volcanic centre.[24]

The mountain was identified by the crash mapping program of Operation Stikine in 1956.[25] This program, masterminded by Canadian volcanologist Jack Souther, was carried out over the Stikine River area using a Bell helicopter.[25][26] Reconnaissance mapping in 1962 by Jack Souther and Hu Gabrielse identified a sequence of lavas of late Tertiary to Quaternary age.[14] Level Mountain was then studied by T. S. Hamilton in the 1970s who produced a detailed map and the first petrochemical study of the lavas.[27] The andesites described in the 1920s were mapped as early Tertiary age, long before Level Mountain formed.[12] Hamilton recognized the four sequences of alkali basalt flows and tuffs in the lava plateau as well as the overlying bimodal package of alkali basalt and peralkaline lavas and tuffs.[27]

Naming[edit]

The name Level Mountain is a reference to the gently sloping plateau surface of this large volcano.[6] It was adopted on December 21, 1944 as identified in the Canada Department of Mines Summary Report, 1925, Part A. This name appeared on the National Topographic System (NTS) map 104/NE but was replaced with the name Level Mountain Range on August 14, 1952 upon production of NTS map 104J.[28] The reason for this name change was that cartographers were uncertain as to what the name Level Mountain referred to. They cited H. S. Bostock's 1948 report Physiography of the Canadian Cordillera, With Special Reference to the Area North of the Fifty-Fifth Parallel in which Bostock stated that Level Mountain was a small prominent mountain range on the Nahlin Plateau. Despite this misinterpretation, Level Mountain is still the local name for the entire volcanic edifice and the name Level Mountain Range for a group of steep peaks centered on the volcano's summit.[6]

Accessibility[edit]

Level Mountain resides in a remote location with no established road access.[6] The closest route to this major volcano is a graded road from Dease Lake to Telegraph Creek, which approaches within 50 km (31 mi) of the volcanic edifice.[5][6] From Telegraph Creek or Days Ranch the volcano may be reached by a 30 km (19 mi) hike.[5] Level Mountain is surrounded by several small low-lying lakes that provide float plane access, including Ketchum, Hatin and Granite lakes.[5][6] The Yukon Telegraph Trail of 1890s fame is still passable through Hatin Lake and provides an overland route to the shield volcano.[6] Alternatively, fixed-wing aircraft landings can be made on a runway at Sheslay. Charter helicopter service in the small community of Dease Lake provides direct access to the Level Mountain Range.[5] The alpine lava plateau of Level Mountain is easily travelled by horse or on foot during the snow free period from June to September. Much of the area south of Level Mountain is impassable due to poorly-drained fens.[6]

Monitoring and volcanic hazards[edit]

Like other volcanoes in the NCVP, Level Mountain is not monitored closely enough by the Geological Survey of Canada to ascertain how active its magma system is. The Canadian National Seismograph Network has been established to monitor earthquakes throughout Canada, but it is too far away to provide an accurate indication of activity under the mountain. It may sense an increase in seismic activity if Level Mountain 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.[29] If Level Mountain were to erupt, mechanisms exist to orchestrate relief efforts. The Interagency Volcanic Event Notification Plan 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 or any eruption that would affect Canada.[30]

The lava plateau margins of Level Mountain are vulnerable to landslides. This is particularly true around the steep south and west boundaries where relatively clay-rich, incompetent layers of agglomerates and tuffs are present between more competent basaltic lava flows. Remains of a 60,000 m3 (2,100,000 cu ft) mudflow are present on the eastern slope of the Little Tahltan canyon. Similar older scars, including those in Beatty Creek, are visible around much of the lava plateau parameter.[6]

See also[edit]

References[edit]

  1. ^ a b c d e f "Level Mountain". Global Volcanism Program. Smithsonian Institution. Retrieved 2015-01-30.
  2. ^ a b c d e f g h i j k l Edwards, Benjamin R.; Russell, James K. (2000). "Distribution, nature, and origin of Neogene–Quaternary magmatism in the northern Cordilleran volcanic province, Canada". Geological Society of America Bulletin. Geological Society of America. 112 (8): 1280, 1281, 1283, 1284, 1286, 1291. doi:10.1130/0016-7606(2000)112<1280:dnaoon>2.0.co;2. ISSN 0016-7606.
  3. ^ "Map of Canadian volcanoes". Volcanoes of Canada. Natural Resources Canada. 2008-02-13. Archived from the original on 2008-06-02. Retrieved 2015-01-11.
  4. ^ "Volcanoes". Atlas of Canada. Natural Resources Canada. 2009-02-25. Archived from the original on 2013-01-22. Retrieved 2015-01-11.
  5. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag Wood, Charles A.; Kienle, Jürgen (2001). Volcanoes of North America: United States and Canada. Cambridge, England: Cambridge University Press. pp. 121, 122, 123, 124, 126, 127, 132. ISBN 0-521-43811-X.
  6. ^ a b c d e f g h i j k l m n o p q r s t u v w x Fenger, M.A.; Eastman, D.S.; Clement, C.J.; Page, R.E. (1986). "Caribou habitat use on the Level Mountain and Horseranch Ranges, British Columbia". Ministry of Environment and Parks: 2, 11, 12, 13, 14, 19, 20. ISSN 0831-4330.
  7. ^ a b c Acland, F. A. (1926). Summary Report, 1925, Part A (Report). Ottawa: Canada Department of Mines. pp. 30, 31, 94.
  8. ^ a b c S. Holland, Stuart (1976). "Landforms of British Columbia: A Physiographic Outline". Government of British Columbia: 52, 55.
  9. ^ Cannings, Sydney; Cannings, Richard (2013). The New B.C. Roadside Naturalist: A Guide to Nature along B.C. Highways. Greystone Books Ltd. p. 180. ISBN 978-1-77100-054-3.
  10. ^ Gabrielse, H.; Taylor, G. C. (1982). "Geological maps and cross sections of the northern Canadian Cordillera from southwest of Fort Nelson, British Columbia to Gravina Island, Southeastern Alaska". Natural Resources Canada: 4.
  11. ^ T. Johnston, Stephen; G. Mlhalynuk, Mitch (1994). "NUNA Conference: The Northern Intermontane Superterrane". Geoscience Canada. Geological Association of Canada. 21 (1): 2. ISSN 1911-4850.
  12. ^ a b c d e f g Hamilton, T. S.; Scarfe, C. M. (1977). Report of Activities, Part A. Preliminary Report on the Petrology of the Level Mountain volcanic centre, northwest British Columbia (Report). Geological Survey of Canada. pp. 429, 430, 431, 432, 433.
  13. ^ a b c d e f g h Gabrielse, H. (1998). Geology of Cry Lake and Dease Lake map areas, north-central British Columbia. Geological Survey of Canada. pp. 11, 12, 79. ISBN 0-660-17610-6.
  14. ^ a b Hamilton, T. S.; Evens, M. E. (1983). "A magnetostratigraphic and secular variation study of Level Mountain, northern British Columbia". Geophysical Journal International. Oxford Journals. 73 (1): 39, 40. doi:10.1111/j.1365-246x.1983.tb03805.x. ISSN 0956-540X.
  15. ^ "Meszah Peak". Catalogue of Canadian volcanoes. Natural Resources Canada. 2009-03-10. Archived from the original on 2011-06-04. Retrieved 2015-02-14.
  16. ^ "Meszah Peak". BC Geographical Names. Retrieved 2017-01-15.
  17. ^ Mark, David G. (1987). Geophysical report on airborne magnetic and VLF-EM surveys over the Moon Claim Group, Hatchau Lake, Dease Lake Area, Atlin Mining Division, British Columbia (Report). Geotronics Surveys Ltd. p. 6.
  18. ^ Ryan Lakeman, Thomas (2006). "Late-glacial alpine glacier advance and early Holocene tephras, northern British Columbia". Early Holocene tephras in northwest British Columbia. Simon Fraser University: 41, 45, 49. ISBN 0-494-29462-0.
  19. ^ a b Bilsland, W. W. (1952). "Atlin, 1898–1910: The Story of a Gold Boom". The British Columbia Historical Quarterly. Victoria, British Columbia: Archives of British Columbia: 124.
  20. ^ a b c "Sheslay". BC Geographical Names. Retrieved 2015-11-06.
  21. ^ "Egnell, Albert" (PDF). Hudson's Bay Company Archives. 2002.
  22. ^ Lawerance, Guy (1976). "Memories of the Cariboo & Central B.C. ~1908~1914". Pioneer Days in British Columbia. 4. Surrey, British Columbia: Heritage House Publishing Company. p. 6. ISBN 0-9690546-8-8.
  23. ^ Mathews, W. H. (1947). ""Tuyas," flat-topped volcanoes in northern British Columbia". American Journal of Science. American Journal of Science: 560.
  24. ^ Simpson, K.; Edwards, B.; Wetherell, K. (2006). Documentation of a Holocene volcanic cone in the Tuya-Teslin volcanic field, northern British Columbia. Geological Survey of Canada. pp. 2, 4. ISBN 0-662-42326-7.
  25. ^ a b "Newsletter of the Volcanology and Igneous Petrology Division". Ash Fall. Geological Association of Canada. 1996. p. 3.
  26. ^ Brown, Derek A.; Gunning, Michael H.; Greig, Charles J. (1996). "The Stikine Project: geology of western Telegraph Creek map area, northwestern British Columbia". British Columbia Geological Survey: 4. ISBN 0-7726-2502-6.
  27. ^ a b Abraham, Anne-Claude (2002). The nature of mantle sources for Recent alkaline basalts across the northern Canadian Cordillera. National Library of Canada. p. 38. ISBN 0-612-78635-8.
  28. ^ "Level Mountain Range". BC Geographical Names. Retrieved 2015-11-17.
  29. ^ "Monitoring volcanoes". Volcanoes of Canada. Natural Resources Canada. 2009-02-26. Archived from the original on 2011-02-15. Retrieved 2015-01-31.
  30. ^ "Interagency Volcanic Event Notification Plan (IVENP)". Volcanoes of Canada. Natural Resources Canada. 2008-06-04. Archived from the original on 2010-02-21. Retrieved 2015-01-31.

Further reading[edit]

  • Hamilton, T. S. (1981). Late Cenozoic Alkaline Volcanics of the Level Mountain Range, Northwestern British Columbia: Geology, Petrology and Paleomagnetism (PhD). University of Alberta.

External links[edit]