Mount Fee is a volcanic peak in the Pacific Ranges of the Coast Mountains in southwestern British Columbia, Canada. It is located south of Callaghan Lake and west of the resort town of Whistler. With a summit elevation of and a topographic prominence of , it rises above the surrounding rugged landscape on an alpine mountain ridge. This mountain ridge represents the base of a north-south trending volcanic field which Mount Fee occupies.
The mountain consists of a narrow north-south trending ridge of fine-grained volcanic rock and small amounts of fragmental material. It is long and wide with nearly vertical flanks. Mount Fee has two main summits, the southern tower of which is the highest. The summits are separated by a U-shaped crevice that gives them a prominent appearance.
Geology
Mount Fee is one of the southernmost volcanoes in the Mount Cayley volcanic field. This volcanic zone forms the central portion of the larger Garibaldi Volcanic Belt, which extends from the Silverthrone Caldera in the north to the Watts Point volcano in the south. The volcanic belt has formed as a result of ongoing subduction of the Juan de Fuca Plate under the North American Plate at the Cascadia subduction zone along the British Columbia Coast. This is a north-south trending fault zone about long, extending off the Pacific Northwest from Northern California to southwestern British Columbia. The plates move at a relative rate of over per year at an oblique angle to the subduction zone.
The edifice of Mount Fee is the remains of a volcanic feature that has been significantly eroded by glacial ice. It likely represents a dissected stratovolcano (also known as a composite volcano) that was larger in area and higher in elevation than its current form. Stratovolcanoes can reach heights of and consist of alternating layers of lava flows, volcanic ash, cinders, blocks and bombs. During the glacial periods, much of the volcano's original outer cone of pyroclastic material was eroded away by moving layers of ice and rock. The removal of the ejected volcanic material has exposed the dacite lava that forms the narrow north-south trending ridge of Mount Fee. The Black Tusk, a pinnacle of dark volcanic rock to the southeast, is also interpreted to be the remains of a deeply eroded volcano that was once covered with pyroclastic material. The present day edifice of Mount Fee contains several lava spines that reach heights of to above the main ridge.
Eruptive history
Volcanic activity at Mount Fee is among the oldest in the Mount Cayley volcanic field. Its volcanic rocks remain undated, but the large amount of dissection and evidence of glacial ice overriding the volcano indicates that it formed more than 75,000 years ago before the Wisconsinan Glaciation. As a result, the rocks comprising Mount Fee do not display evidence of interaction with glacial ice; the duration of volcanic events is unknown, and the exact timing of eruptive events is unknown. However, a large variety of volcanoes formed subglacially between 25,000 and 10,000 years ago in the vicinity of Mount Fee, including the lava domes of Ember Ridge to the south.
At least three phases of eruptive activity have been recognized at Mount Fee. The only exposed remnant of Fee's earliest volcanic activity is a minor outcrop of pyroclastic rock. This is evidence of explosive eruptions during Fee's eruptive history, as well as its first volcanic event. The second volcanic event produced a sequence of volcanic rocks on Fee's eastern flank. This volcanic material was likely deposited when a sequence of lava flows and broken lava fragments erupted from a volcanic vent and moved down the flanks during the construction of the ancestral Mount Fee. Following extensive dissection, renewed volcanism produced a viscous series of lavas on its northern flank. The U-shaped crevice separating the two main summits of Mount Fee separates this lava flow from the main volcanic ridge. The conduit from which these lava flows originated was likely vertical in structure and intruded through older rocks deposited during Fee's earlier volcanic events. This volcanic event was also followed by a period of erosion, and likely one or more glacial periods. Extensive erosion following the last volcanic event at Mount Fee has created the rugged north-south trending ridge that currently forms a prominent landmark.