Landforms of British Columbia 1976 - Department of Geography
Landforms of British Columbia 1976 - Department of Geography Landforms of British Columbia 1976 - Department of Geography
The plateau is a late Tertiary erosion surface of low relief extending across Paleozoic and Mesozoic sedimentary and volcanic rocks intruded by granites. The surface has been elevated, and has been dissected by the major streams, Within the plateau large areas of flat to gently sloping upland lie at and below 5,000 feet. This level serves to differentiate the plateau from the highlands to the west, in which the amount of undissected upland becomes progressively less as it rises to higher elevations. The Taku Plateau is very largely drained by the Taku River and its tributaries flowing westward into the Pacific Ocean. The gradients of these rivers are very much steeper than those of streams tributary to the Yukon River that drain the Teslin Plateau on the north. As a consequence, the Nakina River has been able to capture streams that formerly flowed northward across the Teslin Plateau into Atlin or Teslin Lake.* The Nakina River has effected a considerable reversal of drainage by incising steep-walled canyons in the bottoms of widely flaring valleys. The Taku Plateau was covered by glacial ice, which smoothed the profiles of upland surfaces and valleys. Cirque erosion at a late stage of glaciation sculptured the northern slopes of high points projecting above the general upland surface in the Menatatuline Range. [References: Kerr F. A., “ Taku River Area,” GeoZ. Surv., Canada, Mem. 248, 1948; Souther, J. G., “ Geology, Tulsequah,” Geol. Surv., Canada, Map 6-1960.1 [Photographs: B.C. 899:74,91; B.C. 952:13,55,65,105.] Kawdy PZateau The Kawdy Plateau (see Plate. XVIB) lies on the west side of the headwaters of the Tuya River between the Taku Plateau and the Cassiar Mountains. The upland surface of the plateau is largely unwooded and, for the most part, is at about 5,000 feet elevation. The surface is largely an undissected late Tertiary erosion surface which, between Jennings River and Kedahda River, was locally upwarped to 7,000 feet, and subsequently dissected to form the Atsutla Range. “ The surface of the Kawdy Plateau, 600 to 700 square miles in area, is a gently rolling upland of low relief developed by erosion, mainly on highly folded Pakeozoic rocks. A large area lying near the south-western flank of the Atsutla Range has broad, flat summits. These extensive flat areas are the surface of a peneplain and the gently sloping summit surfaces of the mountains in the south- western part of the Atsutla Range may be relics of a peneplain.” Presumably the peneplain was uplifted differentially and was subsequently eroded in places to give rise to the larger-scale features of the present topography. The southwestern front of the plateau may be situated along a fault or a sharp monoclinal fold. “ On the Kawdy Plateau conical or flat-topped mountains of agglomerate, tuff, and lava, of the Tuya formation built by central eruptions, rest on the pene- plain. . . . Some of the volcanics of the Tuya formation are associated with glacial deposits and at least a part of the volcanism is evidently of Pleistocene age.“? A conspicuous feature of the Kawdy Plateau west and southwest of Tuya Lake are the flat-toppecl, steep-sided volcanoes, called tuyas, which are built up on the plateau surface. There are seven or more in the area, and the highest of them, Kawdy Mountain (6,372 feet) (fee Plate XVIB), rises almost 2,000 feet above the local plateau level. * Gtd. SLWV., Canada, Mem. 307, 1959, pp. S-6. t Watson, IL Dep., and Mathews, W. H., B.C. Dept. of Mines, Bull. No. 19,1944, p. 34. 51
The tuyas consist of nearly horizontal beds of basaltic lava capping outward- dipping beds of fragmental volcanic rocks; they have a most interesting origin. It is thought that they were formed by volcanic eruptions in lakes which had been thawed through the Pleistocene ice-sheet by underlying volcanic heat. The lavas capping the mountains were extruded after the volcanoes were built above lake- level, and the outward-dipping beds were formed by the chilling of the lava when it reached the water’s edge. In the Pleistocene the area was covered by several thousand feet of ice, which moved westward across the plateau to the head of the Nahlin River and then swung northwest and north to escape down the Teslin Valley. In its wake it left a wide- spread mantle of drift, which is modelled into numerous drumlin-like hills and into depressions occupied by the numerous small lakes between Tachilta Lakes and Teslin Lake. [References: Watson, K. Dep., and Mathews, W, H., “ Tuya-Teslin Area, Northern British Columbia,” B.C. Dept. of Mines, Bull. No. 19, 1944; Mathews, W. H., “ Tuyas, Flat Topped Volcanoes in Northern British Columbia,” Am. Jour. Sci., Vol. 245, 1947, pp. 560~570.1 [Photographs: B.C. 692:l10; B.C. 695:22, 44, 56; B.C. 699:92.] The A~sL& Runge (,see Plate XVIIA) is 40 miles long by 15 miles wide between the Jennings River and the Teslin River. It lies within the Kawdy Plateau and rises above the general plateau level of 5,900 feet to a maximum elevation of 7,056 feet. The range has an unroofed core of granitic rocks intrusive into older, closely folded Paheozoic and Mesozoic Formations. The sharp peaks are glacially sculp- tured, but many gently sloping upland surfaces are remnants of the uplifted and dissected Tertiary erosion surface of the Kawdy Plateau. “ Extensive modification of the land forms of the Tuya-Teslin Area by the ice-sheet is not evident. The mountain valleys of the area appear to have been widened and deepened, but it is believed that much of this erosion was accomplished by Inca1 glaciers which existed before and after the ice-sheet. The numerous cirques and small hanging valleys on the northern and eastern slopes of many of the mountains are likewise attributable to local glaciers. The ridges which appar- ently were not buried by these glaciers show little or no rounding, although the presence of erratics testifies that they were covered by the ice-sheet.“* [Photographs: B.C. 692:96; B.C. 695:2.] Nahlin Plateau The Nahlin Plateau (see Plate XVIIB) lies between the Sheslay River on the west and Tuya River on the east. It adjoins the Tahltan Highland on the southwest, and on the northeast is arbitrarily separated from the Kawdy Plateau along a line running from Nahlin Crossing up the Nahlin River and across to the Tuya River just south of the Tachilta Lakes. The area is drained by the Nahlin and Sheslay Rivers flowing into the Taku River, and by the Tuya and Tahltan Rivers flowing into the Stikine River, The area is dominated by the great shield volcano of Level Mountain, whose unwooded, low dome-shaped mass, almost circular and 20 miles in diameter, culminates in Meszah Peak, elevation 7,101 feet (see Plate XVIIB) . The gentle slopes of the mountains parallel the gently outward-dipping thin basaltic lava flows. There has been some dissection of the dome by stream erosion, and late-stage cirque glaciers have scalloped some of the valley headwalls. * Watson, K. Dep., and Mathews, W. H., B.C. Dept. of Mines, Bull. No. 19, 1944, p. 37. 52
- Page 1 and 2: Bulletin 48 Landforms of British Co
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- Page 9 and 10: PLATE PAOE XVIII. (33) Stikine Plat
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- Page 13 and 14: traveller. If he SO wishes, his enj
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- Page 29 and 30: INSULAR MOUNTAINS The Insular Mount
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The tuyas consist <strong>of</strong> nearly horizontal beds <strong>of</strong> basaltic lava capping outward-<br />
dipping beds <strong>of</strong> fragmental volcanic rocks; they have a most interesting origin.<br />
It is thought that they were formed by volcanic eruptions in lakes which had been<br />
thawed through the Pleistocene ice-sheet by underlying volcanic heat. The lavas<br />
capping the mountains were extruded after the volcanoes were built above lake-<br />
level, and the outward-dipping beds were formed by the chilling <strong>of</strong> the lava when<br />
it reached the water’s edge.<br />
In the Pleistocene the area was covered by several thousand feet <strong>of</strong> ice, which<br />
moved westward across the plateau to the head <strong>of</strong> the Nahlin River and then swung<br />
northwest and north to escape down the Teslin Valley. In its wake it left a wide-<br />
spread mantle <strong>of</strong> drift, which is modelled into numerous drumlin-like hills and into<br />
depressions occupied by the numerous small lakes between Tachilta Lakes and<br />
Teslin Lake.<br />
[References: Watson, K. Dep., and Mathews, W, H., “ Tuya-Teslin Area,<br />
Northern <strong>British</strong> <strong>Columbia</strong>,” B.C. Dept. <strong>of</strong> Mines, Bull. No. 19, 1944; Mathews,<br />
W. H., “ Tuyas, Flat Topped Volcanoes in Northern <strong>British</strong> <strong>Columbia</strong>,” Am. Jour.<br />
Sci., Vol. 245, 1947, pp. 560~570.1<br />
[Photographs: B.C. 692:l10; B.C. 695:22, 44, 56; B.C. 699:92.]<br />
The A~sL& Runge (,see Plate XVIIA) is 40 miles long by 15 miles wide<br />
between the Jennings River and the Teslin River. It lies within the Kawdy Plateau<br />
and rises above the general plateau level <strong>of</strong> 5,900 feet to a maximum elevation <strong>of</strong><br />
7,056 feet.<br />
The range has an unro<strong>of</strong>ed core <strong>of</strong> granitic rocks intrusive into older, closely<br />
folded Paheozoic and Mesozoic Formations. The sharp peaks are glacially sculp-<br />
tured, but many gently sloping upland surfaces are remnants <strong>of</strong> the uplifted and<br />
dissected Tertiary erosion surface <strong>of</strong> the Kawdy Plateau.<br />
“ Extensive modification <strong>of</strong> the land forms <strong>of</strong> the Tuya-Teslin Area by the<br />
ice-sheet is not evident. The mountain valleys <strong>of</strong> the area appear to have been<br />
widened and deepened, but it is believed that much <strong>of</strong> this erosion was accomplished<br />
by Inca1 glaciers which existed before and after the ice-sheet. The numerous<br />
cirques and small hanging valleys on the northern and eastern slopes <strong>of</strong> many <strong>of</strong><br />
the mountains are likewise attributable to local glaciers. The ridges which appar-<br />
ently were not buried by these glaciers show little or no rounding, although the<br />
presence <strong>of</strong> erratics testifies that they were covered by the ice-sheet.“*<br />
[Photographs: B.C. 692:96; B.C. 695:2.]<br />
Nahlin Plateau<br />
The Nahlin Plateau (see Plate XVIIB) lies between the Sheslay River on the<br />
west and Tuya River on the east. It adjoins the Tahltan Highland on the southwest,<br />
and on the northeast is arbitrarily separated from the Kawdy Plateau along a line<br />
running from Nahlin Crossing up the Nahlin River and across to the Tuya River<br />
just south <strong>of</strong> the Tachilta Lakes.<br />
The area is drained by the Nahlin and Sheslay Rivers flowing into the Taku<br />
River, and by the Tuya and Tahltan Rivers flowing into the Stikine River,<br />
The area is dominated by the great shield volcano <strong>of</strong> Level Mountain, whose<br />
unwooded, low dome-shaped mass, almost circular and 20 miles in diameter,<br />
culminates in Meszah Peak, elevation 7,101 feet (see Plate XVIIB) . The gentle<br />
slopes <strong>of</strong> the mountains parallel the gently outward-dipping thin basaltic lava flows.<br />
There has been some dissection <strong>of</strong> the dome by stream erosion, and late-stage cirque<br />
glaciers have scalloped some <strong>of</strong> the valley headwalls.<br />
* Watson, K. Dep., and Mathews, W. H., B.C. Dept. <strong>of</strong> Mines, Bull. No. 19, 1944, p. 37.<br />
52