Mount Cayley - Geology - Related Features

Related Features

Mount Cayley is surrounded by smaller volcanic features and volcanoes called satellite cones, also known as parasitic cones. These formed due to Cayley's volcanic vent being heavily blocked by cooled and solidified lava, causing magma to force out of the lines of weakness at the side of the volcano, forming a satellite cone. They commonly derive material from the same source as the initial volcano, although it may have its own magma chamber system. Similar volcanic formations are found elsewhere in the Cascade Volcanic Arc, including Mount Shasta in Northern California, which consists of four overlapping volcanic cones and several satellite cones, including Black Butte and Shastina. The small satellite cones at Mount Cayley become progressively younger from south to north, ranging in age from Pliocene-to-Pleistocene which forms a volcanic field. Because these features are related to the stratovolcano of Mount Cayley, the volcanic field is commonly referred to as the Mount Cayley volcanic field. The high elevations of the volcanic field, coupled with its cluster of mostly high altitude, non-overlapping vents, have resulted in several eruptions under the Powder Mountain Icefield, creating many ice-contact features. Due to the volcanic field's remoteness, it has not been studied or mapped in detail. As a result, the number and age of eruptions remains unknown.

Ember Ridge, the oldest and southern known parasitic vent, is a subglacial volcano that formed and last erupted during the Pliocene period. It comprises a chain of steep-sided lava domes with glassy, tortuously jointed lava, such as hornblende-phyric basalt.

Mount Fee, about 1 kilometre (0.62 mi) north of Ember Ridge, is a parasitic volcanic plug comprising a narrow summit ridge about a kilometre (⅔ mi) long. It contains several spines reaching heights of 100 to 150 metres (330–490 ft). Several pyroclastic deposits are found at the volcano, indicating it might have been covered by layers of pyroclastic rocks that have now been mostly worn away by erosion. The complete denudation of the central spine as well as the absence of till under lava and pyroclastics indicate it is preglacial or Pleistocene age.

North of Mount Cayley lies the parasitic Pali Dome subglacial volcano which is partly covered by glacial ice. It formed and last erupted during the Pleistocene period, producing coarsely lava flows, such as plagioclase-hypersthene-hornblende-phyric andesite. Proximal sections of lava flows contain vertical, well developed, large-diameter columnar joints, and lie beneath scoriaeous oxidized flow breccia, suggesting a possible subaerial origin. Distal sections of lava flows are glassy and contain minor diameter columnar joints with horizontal or nearby radiating orientations. Lava flow terminations appear as subvertical cliffs up to 200 metres (660 ft) in height, which are structures constant with eruptions against glacial ice.

Northwest of Pail Dome lies a parasitic subglacial volcano called Cauldron Dome which also formed and last erupted during the Pleistocene period. It consists of coarsely lava flows, such as plagioclase-orthophyroxene-phyric andesite. Its total geomorphology is comparable to that of a tuya. However, any precise record of volcanic glass or fine-scale jointing has probably been worn away by erosion. Two compositionally identical lava flows spread to the southwest from the base of the volcano. It is likely that Cauldron Dome was formed subglacially and the associated lava flows were erupted within a meltwater conduit.

Slag Hill, another parasitic subglacial volcano located just north of Mount Cayley, was erupted during the Pleistocene period, producing glassy lava flows, such as augite-phyric basaltic andesite. These lava flows were cooled to form steep-sided, glassy, finely jointed lava domes comparable to those found at Ember Ridge, and one minor, flat-topped bluff.

Ring Mountain, just north of Slag Hill, is a parasitic tuya composed of plagioclase-hypersthene-phyric andesite. The highest elevation of the volcano comprises bomb-like fragments of vesicular, oxidized lava, suggesting that the higher elevation lava flows were most likely subaerial. However, as is the case at volcanoes of comparable morphology elsewhere, lower elevations might have erupted subglacially.

Little Ring Mountain, also known as Little Ring Peak, is an almost circular, flat-topped, steep-sided volcanic feature about 270 metres (890 ft) in height and 120 metres (390 ft) wide on its top surface. It is known to be the northernmost parasitic cone and is similar in structure to a flat-topped, steep-sided tuya, although its inner stratigraphy is not yet known because the area has not been studied in detail due to its remoteness.

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