Big Raven Plateau
The Big Raven Plateau is an intermontane plateau in Cassiar Land District of northwestern British Columbia, Canada. It lies on the Tahltan Highland and is surrounded by several valleys, including those of Mess Creek, Kakiddi Creek, Chakima Creek, Walkout Creek and the Klastline River. The plateau is drained by many small streams that flow into these neighbouring valleys and, unlike the neighbouring valleys, it is relatively barren of vegetation. Stream erosion has resulted in the creation of canyons with intervening ridges on the eastern and western sides of the Big Raven Plateau. The plateau is in Mount Edziza Provincial Park, which is one of the largest provincial parks in British Columbia. Access to the Big Raven Plateau is mainly by aircraft or by a network of horse trails from surrounding roads.
The Big Raven Plateau is volcanic in origin, consisting mostly of basaltic lava flows of the Mount Edziza volcanic complex that were erupted in the last 7.5 million years. These lava flows are interbedded with rhyolite and trachyte which are in the form of rock fragments produced and ejected by explosive eruptions. The dominant feature on the Big Raven Plateau is Mount Edziza, an ice-covered stratovolcano reaching an elevation of. Its composition is more diverse, consisting of alkali basalt, hawaiite, trachybasalt, tristanite, mugearite, benmoreite, trachyte and rhyolite which are in the form of lava flows, lava domes and breccia. The Big Raven Plateau is subdivided into at least 10 geological formations, each being the product of a distinct period of volcanic activity.
Geography and geomorphology
Location
The Big Raven Plateau is located on the Tahltan Highland east of the Zagoddetchino massif and west of the mountainous Klastline Plateau in Cassiar Land District. Between the Zagoddetchino massif and the Big Raven Plateau is Mess Creek valley, which extends more than to the south where it separates the Boundary Ranges of the Coast Mountains in the west from the Spectrum Range and Arctic Lake Plateau in the east. Between the Big Raven and Klastline plateaus is the north–south trending Kakiddi Creek valley, which includes a number small lakes such as Nuttlude Lake, Kakiddi Lake, Mowchilla Lake and Mowdade Lake. The northern end of the Big Raven Plateau is bounded by the Klastline River valley whereas the southern end is bounded by two relatively small east–west trending valleys; a mountain ridge extends south of the Big Raven Plateau between these valleys.This intermontane plateau lies at the northern end of the Mount Edziza volcanic complex, which consists of a group of overlapping shield volcanoes, stratovolcanoes, lava domes and cinder cones that have formed over the last 7.5 million years. Four central volcanoes occur along the north–south trending axis of the volcanic complex; the two youngest central volcanoes, Mount Edziza and Ice Peak, are on the Big Raven Plateau. In addition to the Big Raven Plateau, the volcanic complex also includes the Arctic Lake and Kitsu plateaus, as well as the Spectrum Range to the south. All of these landforms are in Mount Edziza Provincial Park, one of the largest provincial parks in British Columbia established in 1972 to preserve the volcanic landscape.
Drainage
As a part of the Mount Edziza volcanic complex, the Big Raven Plateau is drained entirely by streams within the Stikine River watershed. The northeastern portion of the Big Raven Plateau is drained by Tsecha Creek, which flows to the northeast. Draining the eastern side of the plateau are a series of east-flowing streams choked with glacial and landslide debris from rapidly eroding headwalls; from north to south these are Pyramid Creek, Tenchen Creek, Nido Creek, Tennaya Creek, Sorcery Creek and Shaman Creek. Transportation of the glacial and landslide debris into Kakiddi Creek valley has resulted in the formation of several large alluvial fans behind which Nuttlude Lake, Kakiddi Lake, Mowdade Lake and Mowchilla Lake have ponded. Nido Creek and Tennaya Creek flow into Nuttlude Lake whereas Sorcery Creek and Shaman Creek flow into Kakiddi Lake. Both lakes are expansions of Kakiddi Creek which flows north into the Klastline River, a tributary of the Stikine River.Elwyn Creek and its tributary, Kadeya Creek, drain the northwestern portion of the plateau; Elwyn Creek flows westward whereas Kadeya Creek flows to the northwest. Northwest-flowing Taweh Creek and its tributary, the westward-flowing Sezill Creek, drain the southwestern and western portions of the plateau, respectively. Elwyn Creek and Taweh Creek are tributaries of Mess Creek, which flows northwestward into the Stikine River. The northern end of the Big Raven Plateau is drained by small, unnamed streams which flow north into the Klastline River; these streams are shallowly incised into the plateau. At the southern end of the Big Raven Plateau is a drainage divide between Chakima Creek, flowing east into the Kakiddi drainage, and Walkout Creek flowing west via Raspberry Creek into Mess Creek.
Structure
The Big Raven Plateau is about long, wide and more than in elevation. It is roughly oval in structure, largely covered with colluvium and relatively barren of vegetation, which contrasts with the surrounding valleys. Colluvium on the plateau consists of felsenmeer, till, glacial and fluvial outwash, as well as solifluction deposits. In contrast to the northern end of the Big Raven Plateau which is relatively smooth and uneroded, the eastern side has undergone extensive erosion, which has resulted in the creation of steep spurs with intervening valleys. A handful of these spurs are named on the southeastern side of the plateau; from north to south they are Idiji Ridge, Sorcery Ridge and Cartoona Ridge. Idiji Ridge extends east from the northern end of Tencho Glacier and is the namesake of Idiji Glacier, which exists to the northwest. Sorcery Ridge, which shares its name with adjacent Sorcery Creek, extends east from the southern end of Tencho Glacier. Cartoona Ridge lies between Chakima and Shaman creek valleys and shares its name with Cartoona Peak at the westernmost end of the ridge.The western side of the Big Raven Plateau has been moderately dissected by stream erosion which has resulted in the formation of steep-sided canyons; Elwyn, Sezill and Taweh creek canyons are the most extensive. Elwyn and Sezill creek canyons contain hot springs with recorded water temperatures of and, respectively. Discharge at these hot springs may be linked to shallow hydrothermal systems driven by residual magmatic heat as they are adjacent to recently active volcanic centres on the plateau. Forming the southwestern edge of the Big Raven Plateau is the Mess Creek Escarpment, which extends at least to the south where it forms the western edge of the Kitsu Plateau.
Landforms
The Big Raven Plateau is dominated by the ice-covered stratovolcano of Mount Edziza, which rises to an elevation of in the middle of the plateau. Immediately north of Mount Edziza is the Desolation Lava Field, which covers an area of more than and mostly issued from cinder cones near the northern trim line of Mount Edziza's ice cap. The Snowshoe Lava Field immediately southwest of Mount Edziza covers an area of about and mostly issued from cones on the southwestern flank of Ice Peak.Smaller features on the Big Raven Plateau include Hoia Bluff at the southwestern end of the plateau along Taweh Creek, Kaia Bluff and Cartoona Peak at the southeastern end of the plateau, Camp Hill near the southwestern edge of the plateau, Kana Cone on the extreme northern side of the plateau, Klastline Cone on the eastern side of the plateau near the head of Pyramid Creek and Tsekone Ridge at the northwestern end of the plateau near the head of Elwyn Creek canyon, as well as Ornostay and Koosick bluffs near the middle of the plateau adjacent to the head of Sezill Creek canyon.
Mount Edziza
Mount Edziza is a nearly symmetrical volcanic cone containing a nearly flat summit with an ice-filled, in diameter crater. The symmetry of the volcano is broken by several steep-sided lava domes, including Sphinx Dome, Glacier Dome, Triangle Dome and The Pyramid. Surrounding the summit crater is a circular ridge breached to the east by active cirques where the remains of several lava lakes are exposed inside the crater. The ridge is partially exposed above the ice cap as a discontinuous series of spires and serrated nunataks; spires forming the southern end of the ridge are the highest. Although the eastern side of Mount Edziza has been deeply dissected by glacial erosion, less dissection has taken place on the southern and northwestern flanks of the volcano. Extending northwest from the northwestern flank of Mount Edziza is Pillow Ridge, which is named after its exposures of pillow lava.About south of the summit is Ice Peak, the southern peak of Mount Edziza. This prominent pyramid-shaped horn has an elevation of and is the glacially eroded remains of an older stratovolcano whose northern flank is buried under the younger edifice of Mount Edziza. The southern and western flanks of Ice Peak are approximal to those of the original stratovolcano whereas the eastern flank has been almost completely destroyed by headward erosion of glacial valleys. At its climax, the stratovolcano had a symmetrical profile and contained a small crater at its summit; the current summit is an erosional remnant etched from the eastern crater rim.
Snowshoe Lava Field
The Snowshoe Lava Field at the southern end of the Big Raven Plateau consists of blocky basaltic lava flows that issued from at least 12 separate vents, most of which are associated with a cinder cone. Nearly all of these vents are adjacent to the lower edges of broad glaciers projecting from Mount Edziza's ice cap and occur at elevations greater than. Although most of the lava in the Snowshoe Lava Field ponded as thick flows on the gently sloping surface of the Big Raven Plateau, some of it flowed into the upper canyon of Sezill Creek and into the head of Taweh Creek, as well as into the narrow tributary valleys of Walkout and Shaman creeks.Tennena Cone, Cocoa Crater, Coffee Crater, Keda Cone and The Saucer are the only named volcanic features in the Snowshoe Lava Field, which are in elevation. The oldest named feature, Tennena Cone, is a subglacial volcano that formed on the upper western flank of Ice Peak during the Last Glacial Maximum between 23,000 and 18,000 years ago, under an expansion of Mount Edziza's ice cap during the Younger Dryas between 12,900 and 11,600 years ago or during a more recent glacial advance. Cocoa Crater, Coffee Crater and Keda Cone are subaerial cinder cones whereas The Saucer is a low, nearly circular mound of lava roughly in diameter.