Mount Cayley volcanic field

Mount Cayley volcanic field
A view of the MCVF, with Mount Cayley obscured by clouds on the left. Mount Fee is the relatively small jagged peak to the far right.
Highest point
Peak	Mount Cayley
Elevation	2,375 m (7,792 ft)[1]
Coordinates	50°07′13″N 123°17′27″W / 50.12028°N 123.29083°W / 50.12028; -123.29083[2]
Geography
Mount Cayley volcanic field Location of the MCVF
Country	Canada
Province	British Columbia
District	New Westminster Land District[2]
Topo map	NTS 92J3 Brandywine Falls[2]
Geology
Age of rock	Pliocene-to-Holocene[1]
Volcanic belt	Garibaldi Volcanic Belt[1]
Last eruption	Unknown[1]

The Mount Cayley volcanic field (MCVF) is a remote volcanic zone on the South Coast of British Columbia, Canada, stretching 31 km (19 mi) from the Pemberton Icefield to the Squamish River. It forms a segment of the Garibaldi Volcanic Belt, the Canadian portion of the Cascade Volcanic Arc, which extends from Northern California to southwestern British Columbia. Most of the MCVF volcanoes were formed during periods of volcanism under sheets of glacial ice throughout the last glacial period. These subglacial eruptions formed steep, flat-topped volcanoes and subglacial lava domes, most of which have been entirely exposed by deglaciation. However, at least two volcanoes predate the last glacial period and both are highly eroded. The field gets its name from Mount Cayley, a volcanic peak located at the southern end of the Powder Mountain Icefield. This icefield covers much of the central portion of the volcanic field and is one of the several glacial fields in the Pacific Ranges of the Coast Mountains.

Eruptions along the length of the MCVF began between 1.6 and 5.3 million years ago. At least 23 eruptions have occurred throughout its eruptive history. This volcanic activity ranged from effusive to explosive, with magma compositions ranging from basaltic to rhyolitic. Because the MCVF has a high elevation and consists of a cluster of mostly high altitude, non-overlapping volcanoes, subglacial activity is likely to have occurred under less than 800 m (2,600 ft) of glacial ice. The style of this glaciation promoted meltwater escape during eruptions. The steep profile of the volcanic field and its subglacial landforms support this hypothesis. As a result, volcanic features in the MCVF that interacted with glacial ice lack rocks that display evidence of abundant water during eruption, such as hyaloclastite and pillow lava.

Of the entire volcanic field, the southern portion has the most known volcanoes. Here, at least 11 of them are situated on top of a long narrow mountain ridge and in adjacent river valleys. The central portion contains at least five volcanoes situated at the Powder Mountain Icefield. To the north, two volcanoes form a sparse area of volcanism. Many of these volcanoes were formed between 0.01 and 1.6 million years ago, some of which show evidence of volcanic activity in the last 10,000 years.