The Level Mountain Range, also known as Level Mountain, is a mountain range in Cassiar Country, northwestern British Columbia, Canada, located just northeast of Callison Ranch, southwest of Dease Lake and about 50 km (31 mi) north of Mount Edziza. It consists of a massive shield volcano and lies on the Nahlin Plateau, comprising a series of buttes and ridges.
The range is lightly glaciated, as compared to the Coast Mountains just to the west. The only named mountain in the Level Mountain Range is Meszah Peak on the north side of the range with an elevation of 2,190 m (7,185 ft), making it the highest point of the Level Mountain Range. Immediately to the west, however, are the Heart Peaks, a related volcanic range just east of the Sheslay River, which is the edge of the Nahlin Plateau. The Level Mountain Range rises above adjacent forested lowlands and undulating alpine areas surround the steeper central peaks. Streams that originate from these peaks drain across the Nahlin Plateau.
The Level Mountain Range began forming about 14.9 million years ago and has grown steadily since then. Like other volcanoes in northwestern British Columbia, the Level Mountain Range has its origins in continental rifting—a long divergent plate boundary where the lithosphere is being pulled apart. Here, the continental crust of the North American Plate is being stretched at a rate of about 2 cm (1 in) per year.
This incipient rifting has formed as a result of the Pacific Plate sliding northward along the Queen Charlotte
Fault, on its way to the Aleutian Trench, which extends along the southern coastline of Alaska and the adjacent waters of northeastern Siberia off the coast of Kamchatka Peninsula. As the continental crust stretches, the near-surface rocks fracture along steeply dipping cracks parallel to the rift known as faults. Hot basaltic magma rises along these fractures to create passive lava eruptions, known as effusive eruptions.
The Level Mountain Range is the most voluminous and most persistent volcano of the Northern Cordilleran Volcanic Province with an area of 1800 km2 and is the earliest locus of volcanism within the volcanic province. More than 20 Tertiary-to-Holocene volcanic vents have been identified in the central portion of the Level Mountain Range and on its flanks, although Holocene activity (10,000 years ago to present) remains uncertain. It is straddled by two major northwest trending planer rock fractures called the King Salmon Fault and the Nahlin Fault, which were active during the Mesozoic/Cenozoic eras.
The history of the Level Mountain Range records glaciation extending back to the Pliocene period which extends from 5.332 million to 1.806 million years ago", affording numerous examples of the interaction of volcanic and glacial processes. Even though the Level Mountain Range is adjacent to the broad Tuya Volcanic Field
, it is not considered part of the same volcanic formation because the Level Mountain Range is a long-lived volcano whereas the Tuya Volcanic Field consists of small volcanoes noted for having only one short eruptive event.
Eruptive history :
The Level Mountain Range was formed during three phases of volcanic activity. From trace elements and isotope systematics, the origin of the lavas that form the Level Mountain Range requires an upper mantle source for both the basaltic and the salic lavas. Refractory xenocrysts (olivine, orthopyroxene, spinel) from Level Mountain basalt and spinel lherzolites from nearby vents in the Stikine Canyon and at Castle Rock support this contention. The bimodal sodic alkalic lava suite at Level Mountain is typical of hotspot and continental rift volcanism with leaky transform settings.
- Shield volcano eruptive period
- Stratovolcano eruptive period
- Lava dome eruptive period