The Big Raven Plateau is an intermontane plateau of volcanic origin in northwestern British Columbia, Canada. It lies on the Tahltan Highland in Cassiar Land District and is roughly oval in shape. The eastern side of the plateau is heavily eroded whereas the western and northern sides are moderately and slightly eroded, respectively. Unlike the surrounding valleys, the Big Raven Plateau is relatively barren of vegetation due to its alpine climate. The lower slopes of the plateau contain a mixture of white spruce, trembling aspen, lodgepole pine and balsam poplar. Draining the Big Raven Plateau are several small streams that flow into the surrounding valleys; these valleys contain the Klastline River and the Mess, Kakiddi, Chakime and Walkout creeks.
The Big Raven Plateau measures about . Its dominant feature is Mount Edziza, an ice-covered volcanic massif reaching an elevation of in the middle of the plateau. The Desolation Lava Field at the northern end of the plateau contains several small cinder cones, 10 of which are named. At the southern end of the plateau is the Snowshoe Lava Field; it contains only five named volcanic features. Surrounding the plateau is Mount Edziza Provincial Park, one of the largest provincial parks in British Columbia. Access is mainly by aircraft or by a network of horse trails from surrounding roads.
At least 10 geological formations make up the Big Raven Plateau, each representing a distinct period of volcanic activity. They were deposited by successive eruptions of lava and pyroclastic rocks in the last 7.5 million years; the latest eruptions occurred less than 2,000 years ago. The formations are part of the Mount Edziza volcanic complex, which also includes the Kitsu Plateau and the Spectrum Range to the south. Renewed volcanism on the Big Raven Plateau could dam local streams with lava or threaten air traffic if ash columns were to be produced.
A wide range of volcanic rocks characterizes the Big Raven Plateau, the most common of which is basalt; it occurs in most of the geological formations comprising the plateau. More evolved volcanic rocks such as trachybasalt, tristanite, mugearite, benmoreite, trachyte and rhyolite largely occur at Mount Edziza. Most of the volcanic eruptions on the plateau in the last 20,000 years have issued mainly basaltic lava from vents in the Desolation and Snowshoe lava fields. The volcanic rocks characterizing the plateau are in the form of lava flows, lava domes and breccias.
Geography Location The Big Raven Plateau is in Cassiar Land District of northwestern British Columbia, Canada. It lies on the Tahltan Highland east of the Zagoddetchino massif and west of the mountainous Klastline Plateau. Between the Zagoddetchino massif and the Big Raven Plateau is Mess Creek valley, which extends more than to the south. The north–south trending Kakiddi Creek valley lies between the Big Raven and Klastline plateaus; it includes the Nuttlude, Kakiddi, Mowchilla and Mowdade lakes. Bounding the northern end of the Big Raven Plateau is the Klastline River valley. The southern end is bounded by two relatively small east–west trending valleys, between which a mountain ridge extends south of the plateau. Southeast of the plateau are the Skeena Mountains whereas the Boundary Ranges of the Coast Mountains occur to the southwest.
The Big Raven Plateau is the northernmost and largest of three intermontane plateaus associated with the Mount Edziza volcanic complex. This north–south trending volcanic complex 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 its axis; the two youngest, Mount Edziza and Ice Peak, are on 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 lie within Mount Edziza Provincial Park, one of the largest provincial parks in British Columbia. The park was 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 plateau is drained by Tsecha Creek, which flows northeast into Kakiddi Creek. Draining the eastern side of the plateau are several east-flowing streams choked with glacial and landslide debris from rapidly eroding headwalls; from north to south these are the Pyramid, Tenchen, Nido, Tennaya, Sorcery and Shaman creeks. Transportation of the debris into Kakiddi Valley has resulted in the formation of several large alluvial fans, behind which the Nuttlude, Kakiddi, Mowdade and Mowchilla lakes have formed. The Nido and Tennaya creeks flow into Nuttlude Lake whereas the Sorcery and Shaman creeks flow into Kakiddi Lake. Both of these 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 Big Raven 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. The Elwyn and Taweh creeks are tributaries of Mess Creek, which flows northwestward into the Stikine River. Small, unnamed streams drain the northern end of the plateau and flow north into the Klastline River; these streams are shallowly incised into the plateau. At the southern end of the 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 and wide. It is roughly oval in shape, largely covered with colluvium and relatively barren of vegetation, which contrasts with the surrounding valleys. Colluvium on the plateau consists of felsenmeer, till and glacial and fluvial outwash, as well as solifluction deposits. The western side of the plateau has been moderately dissected by stream erosion, which has resulted in the formation of steep-sided canyons; the Elwyn, Sezill and Taweh canyons are the largest. Forming the southwestern edge of the plateau is the Mess Creek Escarpment, which extends at least to the south. The plateau surface reaches an elevation of at least whereas the slopes descend to an elevation of around .
In contrast to the northern end of the plateau which is relatively smooth and uneroded, the eastern side has undergone extensive erosion. This 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 the Idiji, Sorcery and Cartoona ridges. 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 the Chakima and Shaman valleys; it shares its name with Cartoona Peak at the westernmost end of the ridge.
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 . Most of the lava forming this feature 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 ; it mostly issued from cones on the southwestern flank of Ice Peak. Smaller features on the plateau include the Hoia, Kaia, Ornostay and Koosick bluffs, the Kana and Klastline cones, Cartoona Peak, Tsekone Ridge and Camp Hill. The Hoia and Kaia bluffs are at the southwestern and southeastern ends of the plateau, respectively, the former of which is along Taweh Creek. Cartoona Peak at the southeastern end of the plateau is a prominent spire and an erosional remnant of a larger volcano.
Camp Hill between the Raspberry and Taweh creeks reaches an elevation of near the southwestern edge of the plateau. Kana Cone on the extreme northern side of the plateau has an elevation of and is covered with vegetation. It is high and contains a deep summit crater whose northern rim has been breached. Klastline Cone on the eastern side of the plateau near the head of Pyramid Creek has an elevation of ; its summit is below the level of the plateau. Tsekone Ridge attains an elevation of near the head of Elwyn Canyon at the northwestern end of the plateau. This isolated, elliptical mound rises above the plateau surface; its north–south axis has a length of nearly . The Ornostay and Koosick bluffs are near the middle of the plateau adjacent to the head of Sezill Canyon. Both bluffs are similar in geomorphology, but Koosick is larger; it has a length of nearly and a width of more than .
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 The Pyramid and the Sphinx, Glacier and Triangle domes. 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, so-named for 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. The northern flank of this volcano is overlain by the younger edifice of Mount Edziza. In contrast, the eastern flank has been almost completely destroyed by headward erosion of glacial valleys. The southern and western flanks are nearly identical to those of the original stratovolcano. At its climax, the Ice Peak volcano 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. It 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 above . Most of the lava ponded as thick flows on the gently sloping surface of the plateau. However, some of it also flowed into upper Sezill Canyon, the head of Taweh Creek and the narrow tributary valleys of Walkout and Shaman creeks.
Tennena Cone, Cocoa Crater, Keda Cone, Coffee Crater 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. Its formation may have occurred during the Last Glacial Maximum, the Younger Dryas or a more recent glacial advance. Cocoa Crater, Keda Cone and Coffee Crater are subaerial cinder cones whereas The Saucer is a low, nearly circular mound of lava roughly in diameter.
Desolation Lava Field