The Mount Cayley volcanic field (MCVF) is located in the central Garibaldi Volcanic Belt, northwest of the Mount Garibaldi region. It consists of at least twenty volcanic centres, including Mount Cayley itself. A large (but shrinking) glacier covers the high terrain in the centre of the field, to the north of Mount Cayley, and most of the volcanic centres show evidence for glaciovolcanism (eruption in contact with ice). Volcanic deposits within the MCVF range in age from about 2.7 million years (Green et al., 1988) to less than 10,000 years.

Mount Cayley

Mount Cayley is a precipitous stratovolcano in the south central MCVF comprising a complex pile of overlapping lava flows and pyroclastic deposits formed during at least three stages of volcanic activity (Souther, 1980) probably ranging in age from at least 2.7 million years to 0.3 million years (Green et al., 1988). Unlike the many smaller satellite vents around it, Mount Cayley shows no evidence for volcano-ice interaction. It is substantially eroded and, like many other volcanoes in the Garibaldi Volcanic Belt, it has a history of large landslides, especially on its nearly vertical 500 m high southwest flank. At least five hot springs are present in valleys adjacent to the volcano, and the region has been a geothermal exploration target. Seismic studies, shallow earthquakes in the vicinity of Mount Cayley, and the presence of hotsprings suggest that magmatic activity is still present at Mount Cayley. The most detailed study of Mount Cayley was conducted by Souther (1980).

The oldest volcanic rocks at Mount Cayley represent the Mount Cayley stage of eruption, and consist of a complex pile of porphyritic dacite flows, tephra, and breccia. These are overlain by units from the Vulcan’s Thumb stage which consist of lava flows, blocky agglutinated dacite breccia, and bedded and unbedded fine tephra. Some of these rocks have been potassium-argon dated at 2.7 ± 0.7 million years. Since older rocks underlie those dated, the oldest deposits must be older than 2.7 million years. The youngest volcanic rocks at Mount Cayley are those of the Shovelnose stage, and consist of a thick sequence of dacite flows extending down the Shovelnose and Turbid Creek valleys almost as far as the Squamish River.

Other volcanoes within the Mount Cayley volcanic field:

Little Ring Mountain
Ring Mountain(Crucible Dome)
Slag Hill
Slag Hill tuya
Cauldron Dome
Pali Dome East
Pali Dome West
Ember Ridge Northeast
Ember Ridge North
Ember Ridge Northwest
Ember Ridge West
Ember Ridge Southwest
Ember Ridge Southeast
Mount Brew
Tricouni Southwest
Tricouni Southeast flows
Tricouni Southeast knob

Ember Ridge Northwest, a subglacial dome

Ember Ridge Northwest, a subglacial dome, is one of eight discrete andesite lava masses arranged in a crescent between Mount Fee and Tricouni Peak in the south central Mount Cayley volcanic field (MCVF). These volcanoes consist of jagged to bulbous, steep-sided lava piles whose cooling joint orientations and minimal erosion indicate that their modern shapes approximate their original morphologies. All eight masses represent eruption from isolated point sources beneath ice, and likely involved eruption into well-drained glacial ice cavities without significant penetration of the ice surface. All eight erupted during the Fraser Glaciation (25,000-10,000 years ago), probably during its late stages. Ember Ridge Northwest is the most notably dome-shaped of the Ember Ridge volcanoes. It consists of one or more lava flows that drape the western side of a topographical high.

Little Ring Mountain, a flow-dominated tuya

Little Ring Mountain, a flow-dominated tuya (a type of volcano erupted through glacier ice), is located at the north end of the Mount Cayley volcanic field (MCVF), north of Ring Mountain. It is a cylindrical, flat-topped volcano with near-vertical sides at least 240 m high, and comprises at least three stacked andesite lava flows sitting atop a topographical high. Little Ring Mountain formed from successive pulses of lava melting a hole through a glacier and then repeatedly flooding this hole, impounding against ice on all flanks. Based on its summit elevation, Little Ring Mountain’s final eruptions probably took place during the Fraser Glaciation (25,000-10,000 years ago), probably at or near the time of greatest ice coverage.

Pali Dome East, a site for ice-marginal lava flows

Pali Dome East is located in the central Mount Cayley volcanic field (MCVF), north and northeast of Mount Cayley. It is a long-lived volcano, consisting of a pile of andesite lava flows and minor fragmental rocks cropping out on the east side of the glacier that sits in the centre of the MCVF. Most lava flows have gentle profiles at high elevations but terminate in finely-jointed vertical cliffs at low elevations. The youngest flows show evidence for subaerial eruption at high elevations (meaning their vent areas were probably not covered by ice) and eruption against ice at low elevations, suggesting that they erupted near the end of the Fraser Glaciation (about 10,000 years ago), when the continental glacier was receding but stagnant ice still filled some valleys.