Big Raven Plateau

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 35 by 20 kilometres (22 by 12 miles). Its dominant feature is Mount Edziza, an ice-covered volcanic massif reaching an elevation of 2,786 metres (9,140 feet) 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.