page_title: Wells Gray-Clearwater volcanic field
section_title: Pleistocene epoch
hierarchical_section_title: Wells Gray-Clearwater volcanic field / Geology / Pleistocene epoch
caption_attribution_description: English: Photo by Roland Neave, contributor to White Horse Bluff article. From personal Wells Gray Park collection.
context_page_description: The Wells Gray-Clearwater volcanic field, also called the Clearwater Cone Group, is a potentially active monogenetic volcanic field in east-central British Columbia, Canada, located approximately 130 km north of Kamloops. It is situated in the Cariboo Mountains of the Columbia Mountains and on the Quesnel and Shuswap Highlands. As a monogenetic volcanic field, it is a place with numerous small basaltic volcanoes and extensive lava flows.
  Most of the Wells Gray-Clearwater volcanic field is encompassed within a large wilderness park called Wells Gray Provincial Park. This 5,405 km² park was established in 1939 to protect Helmcken Falls and the unique features of the Clearwater River drainage basin, including this volcanic field. Five roads enter the park and provide views of some of the field's volcanic features. Short hikes lead to several other volcanic features, but some areas are accessible only by aircraft.
context_section_description: Based on radiocarbon and potassium-argon dating, volcanic activity in the Wells Gray-Clearwater volcanic field began in the early Pleistocene epoch, creating valley-filling and plateau-capping lava flows that have a total volume of approximately  25 km³ (6 cu mi). The emplacement of these lava flows spanned at least three periods of glaciation, evidence for which is preserved in the form of tuyas, ice-ponded valley deposits, and subglacial mounds. The few tuyas in the region, such as Gage Hill, Hyalo Ridge, McLeod Hill and Mosquito Mound, were formed when magma intruded into and melted a vertical pipe in the overlying glacial ice. The partially molten mass cooled as a large block, with gravity flattening its upper surface. The glacial erosion of the tuyas suggests they erupted during the early Pleistocene epoch.
  At least one explosive subaqueous volcano formed during the Pleistocene epoch. This subaqueous volcano, known as White Horse Bluff, is thought to have formed in three phases. Its first phase of activity was involved with water, possibly dammed by glacial ice which filled the Clearwater River valley. The volcano heated glacial water then flooded down the volcano's vent, creating violent steam explosions and broken lava fragments. Once the steam explosions had subsided, the broken lava fragments settled back into the glacial water, creating the unvolcano-like form of White Horse Bluff which is mostly made of fragmental volcanic glass called hyaloclastite. The volcano ceased erupting soon after breaching the surface of the glacial water.
  Other volcanic events elsewhere interacted with groundwater and magma creating numerous pit craters. Many of these pit craters have been filled with water creating several crater lakes. In some places glacial till and fluvial sands and gravels are maintained under the several lava flows that form the volcanic field. Paleosols are found, but are rare. Glaciation has left a thick blanket of till over nearly all of the volcanic deposits and therefore outcrop is largely limited to cliffforming exposures in several valleys.
caption: Rock Roses formation on south side of White Horse Bluff
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