Landforms of British Columbia 1976 - Department of Geography
Landforms of British Columbia 1976 - Department of Geography
Landforms of British Columbia 1976 - Department of Geography
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INSULAR MOUNTAINS<br />
The Insular Mountains comprise the Queen Charlotte Mountains on the<br />
Queen Charlotte Islands and the Vancouver Island Mountains on Vancouver<br />
Island.<br />
Queen Charlotte Mountains<br />
The Queen Charlotte Mountains consist <strong>of</strong> two units-the Queen Charlotte<br />
Ranges, which form the mountainous backbone <strong>of</strong> the Islands and lie mostly along<br />
their western side, and the Skidegate Plateau, an elongated belt <strong>of</strong> plateau-like<br />
country flanking them on the east.<br />
The Queen Charlotte Mountains lie to the southwest <strong>of</strong> a more or less direct<br />
line drawn from Copper Bay at the northeast end <strong>of</strong> Moresby Island, south <strong>of</strong><br />
Dead Tree Point, thence through Juskatla Inlet and past the south end <strong>of</strong> Naden<br />
Harbour to Beresford Bay. This boundary separates the low-lying northeastern<br />
corner <strong>of</strong> Graham Island, the Queen Charlotte Lowland, from the section <strong>of</strong> greater<br />
relief which includes the rest <strong>of</strong> the Islands.<br />
The Queen CharZotte Ranges (see Plate IIB), <strong>of</strong> which only the San Cristoval<br />
Range is named, extend southeastward from RemelI Sound to Cape St. James.<br />
The eastern margin <strong>of</strong> the ranges, between Vertical Point on Louise Island and<br />
Rennell Sound, closely follows a zone <strong>of</strong> faulting. Only the Slatechuck Mountain<br />
mass, part <strong>of</strong> the main ranges, lies east <strong>of</strong> the fault zone.<br />
The highest peaks on the Islands are Mount Needham (3,500+ feet) in the<br />
southwestern part <strong>of</strong> Graham Island, Mount Kermode (3,500+ feet) on the west<br />
side <strong>of</strong> Louise Island, Mount de la Touche (3,600+ feet) just south <strong>of</strong> Tasu<br />
Sound, and an unnamed peak (3,700+ feet) just south <strong>of</strong> Mosquito Lake. The<br />
general summit elevation diminishes southward as the ranges plunge into the sea<br />
at Cape St. James. The core <strong>of</strong> the ranges between Tasu Sound and Nagas Point<br />
and <strong>of</strong> the high range between Skidegate Charmel and Rennell Sound is granitic.<br />
Much nf the rest <strong>of</strong> the ranges is underlain by Triassic and Jurassic volcanic rocks.<br />
Despite the fact that their maximum relief is only about 3,700 feet, the Queen<br />
Charlotte Ranges are extremely rugged, tbeir serrate peaks having been sculptured<br />
by cirque glaciers long since melted away. The cirque erosion has produced topo-<br />
graphic forms at all elevations down to and below sea-level.<br />
The Skidegate Plateau, some 10 miles wide and 100 miles long, is a dissected<br />
plateau whose eastward sloping surface reaches 2,500 feet elevation (see Plate 11~).<br />
It is bounded by the Queen Charlotte Ranges on the west and the Queen Charlotte<br />
Lowland on the east. It extends between Louise Island on the southeast and Beres-<br />
ford Bay at the northwestern tip <strong>of</strong> Graham Island. From Louise Island northward<br />
to Yakoun Lake the surface <strong>of</strong> the plateau cuts across Mesozoic rocks; farther<br />
north tilted Paleocene lavas underlie the plateau surface.*<br />
The Islands show signs <strong>of</strong> intense glaciation. An ice-sheet with a local centre<br />
<strong>of</strong> accumulation, rather than one <strong>of</strong> mainland derivation, sculptured the terrain<br />
below 3,000 feet. Only matterhorn peaks above that height may have projected<br />
through the ice-sheet as nunataks. In a late stage, glaciers moved westward and<br />
eastward from an ice divide lengthwise <strong>of</strong> the Islands. Eastward-moving ice modi-<br />
fied the topography north <strong>of</strong> Cumshewa Inlet and coalesced with other glaciers to<br />
move northward and northwestward across the Queen Charlotte Lowland and<br />
finally westward out to sea across the Lowland past the northern end <strong>of</strong> the<br />
Skidegate Plateau (see Fig. 10).<br />
* Personal communication, A. Sutherland Brown.<br />
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