Landforms of British Columbia 1976 - Department of Geography

A small volcanic cone with associated ash and pyroclastic rocks occurs in the
Nazko Valley west of Quesnel.* The cone is extinct and the fragmental rocks rest
on glacial till-proof of its post-Pleistocene age.
A volcanic cinder cone forms Kitasu Hill (860 feet), which lies on the Mil-
banke Strandflat on the southwest peninsula of Swindle Island (Plate VIA). The
perfect cone has a small summit crater and a lava flow extending eastward from it
to Higgins Passage. It is quite unaffected by glaciation and evidently is post-
Pleistocene. Twenty miles to the southeast, on Lake Island at the entrance to
Mathieson Channel, a conical peak about 1,000 feet high is composed of brown
volcanic tuffs which rest on glaciated surfaces of quartz diorite. It and thin flows
on nearby Lady IsIand are also post-PIeistocene in age.
A period of volcanism that extended from about Middle Tertiary to Recent
time is represented in the Hogem Ranges by necks, dykes, and lavas of basalt and
basaltic glass along a line lying east of Bear Lake. The youngest phases of activity
are represented by deposits of pumice, ash, cinders, and other pyroclastic material,
quite obviously post-Pleistocene in age, that form cone-like peaks 1% miles north-
east and 6% miles southeast of The Thumb.
South of the Nass River, lava from a small cone near the head of Tseax River
flowed westward for several miles to block the main valley of Tseax River and
create Lava Lake; it then flowed northward into the Nass Valley, expanding into
a lava plain 7 miles long and 3 miles wide (see Plate XLVIIB) The lava is thought
to be not older than 300 years. It is so recent that it is very largely devoid of
vegetation, and the original surface features of the several flows, such as ropy lava
and scoriaceous breccia, are clearly visible. Colonization of the lava, first by
lichens and later by mosses, ferns, and larger plants, is proceeding slowly.
Farther to the northwest, in the Boundary Ranges between the Iskut and Unuk
Rivers, there are several small centres from which lava flowed southward into the
Unuk River valley, constricting it and forming the second and third canyons on
the Unuk River and the canyon on the Iskut River downstream from Forrest Kerr
Creek.
Hoodoo Mountain on the north side of the lower Iskut River “ is one of the
most magnificent and interesting mountains in northern British Columbia. It does
not possess the rugged outline of its neighbours, but largely retains the shape char-
acteristic of volcanoes. In general, it rises with gentle slopes of 10 to 20 degrees to
a crater, now ice-filled, at an elevation of more than 6,500 feet. Except for minor
irregularities caused by erosion, any contour Iine is practicaIly a circle. About the
middle of the south side two great vertical cliffs each ri,se for several hundred feet;
over them streams drop in magnificent falls. The west side presents an irregular
series of vertical cliffs of which the lower are as much as 700 feet in height. HOW
does, needle-like pyramids up to 500 feet in height, and other odd monumental
forms, give the mountain a weird appearance.
“ The volcano erupted in the centre of an old,valley that must have drained to
the Iskut about 3 miles above the present Hoodoo River. Successive outflows
from the volcano repeatedly disrupted the drainage, so that the flanking streams and
glaciers have had a difficult struggle to maintain their channels.“S
It is believed by Kerr that some of the very thick flows were the product of
damming brought about by chilling of the lava in contact with glacial ice. The
oldest lavas flowed out onto a glaciated surface and were thought to have been
extruded when ice surrounded the mountains to at least an elevation of 3,500 feet.
Later flows were probably extruded during an interglacial period because they
l Tipper, H. w., Gd. sum. Conocfa, Map 12,959.
+ Kerr, I? A., Gtd. surv., Cono&, Mml. 246, ,948, p. 41.
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